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I. Sh. Abdullin, R. G. Ibragimov, O. V. Zaitseva,

V. V. Paroshin

MODERN METHODS FOR MANUFACTURING COMPOSITE MEMBRANES

Keywords: composite membranes, low-temperature plasma, modification, track etching, powder sintering, phase inversion, coating.

The article describes various methods for obtaining polymer composite membranes and considers some aspects of the physicochemical processes that occur during the formation of membranes.

Keywords: composite membranes, low-temperature plasma, modification, etching tracks, baking powder, phase inversion, coating.

This article describes the different methods of preparation of polymeric composite membranes and some aspects of physical and chemical processes occurring in forming membranes.

Polymer membranes are widely used in industry and a number of methods have been developed for their production.

For the wide use of membrane methods, technologies for the manufacture of membranes are being developed that satisfy a number of requirements imposed in specific cases: high separating power with high permeability, as well as high strength and stability of characteristics during operation, etc.

The separating ability of membranes, their productivity and stability of characteristics depend not only on the chemical nature of the polymer, but also on the subtleties of the technology for their production.

All types of polymeric materials can be used to obtain membranes. The basic principle of creating these materials is to obtain the required membrane structure corresponding to a given separation process. Depending on the purpose of the membrane, a system of pores is formed or not formed in it.

The main methods for producing porous polymeric membranes include the following:

1 - phase inversion (molding from a solution or polymer melt);

2 - leaching (washing out) of the filler;

3 - etching of nuclear tracks

4 - extract in active media;

5 - powder sintering

6 - coating.

Phase inversion is a phase separation process by which a polymer is transferred from a solution or melt to a solid state in a controlled manner. The process of solid phase formation is often initiated by a transition from one liquid phase to two (so-called liquid-liquid breakup). At a certain stage of this decomposition in one of the phases (the phase with a high polymer concentration) a solid phase of the polymer is formed.

The concept of phase inversion includes a wide range of different techniques. Phase separation in the original solution can be initiated in the following ways:

Solvent removal (dry molding, evaporation induced phase inversion (EIPS));

Addition of a precipitant (wet molding, diffusion induced phase inversion (DIPS));

Temperature change (spontaneous gelation method, temperature induced phase inversion (TIPS)).

There are also combined methods, for example, dry-wet molding. In this case, the solvent is partially evaporated (preforming step), and then precipitation is carried out by adding a precipitant. This method produces asymmetric membranes for reverse osmosis. When using high-boiling solvents, it takes a long time for their complete evaporation at room temperature, so the process is accelerated by heating the system. This method is called TAEPS (Thermally assisted evaporative phase-separation process).

Mixed membranes based on polysulfone and polymer A are made by the process of phase inversion from a casting solution containing polysulfone, polymer A, dimethylacetamide and polyethylene glycol. The membranes prepared with varying molecular weights of the polyethylene glycol additives were characterized by scanning electron microscopy, measuring water performance and trypsin retention. Water performance tests show that they do not have any non-linear dependence on the molecular weight of polyethylene glycol. The water performance of the membrane obtained from the casting solution containing polysulfone, polymer A, polysulfone-4000 and dimethylacetamide was 115.2 ml/cm2*h, which is 6 times greater than that of the membrane without polyethylene glycol. Polyethylene glycol as a non-solvent changed the thermodynamic properties in the polymer solution, promoting the phase separation of the casting solution; in other words, the polyethylene glycol increased the viscosity of the solution, slowing down the phase separation. Two different effects work simultaneously, affecting the structure and characteristics of the membranes.

Polyurethane (as ether) and sulfonated polysulfone (as sodium salt) in the presence of polyethylene glycol 600 were mixed in various ratios using N,N-

dimethylformamide as a solvent and the resulting mixtures were used to obtain ultrafiltration membranes by the phase reversal method

The paper presents the results on the synthesis and study of the properties of ultrafiltration membranes based on polysulfone. Membrane synthesis was carried out using the phase reversal method, by changing the concentrations of the polymer and additives, taking into account the wetting thickness of the layer to determine the effect of these parameters on the selective permeability of the membrane. Data are presented on the permeability of each of the obtained membranes based on measurements of water and gas flows, taking into account the pressure used; the determination of selectivity was carried out in the separation of aqueous solutions of polysaccharides. It has been established that an increase in the polymer concentration causes a simultaneous decrease in membrane permeability and an increase in the molecular fraction. An increase in the concentration of additives is manifested in an increase in permeability and a decrease in the molecular fraction. An increase in wetting thickness causes a decrease in permeability and a decrease in the molecular fraction.

Asymmetric ultrafiltration membranes are obtained from solutions of polysulfone and polyethersulfone in an aprotic solvent, for example, M-methylpyrrolidone, with the addition of organic substances [polyethylene glycol (PET) and polyethyleneimine (PEI) (with primary, secondary and tertiary amino groups) by the phase inversion method. The membranes are characterized by the permeability of pure water and the separation of cations depending on the concentration of the solution, pressure, pH and contamination. PEG is injected with a molecular weight of 6000 as a blowing agent, PEI with a molecular weight of 50000 in the form of a 50% aqueous solution. PEG and PEI are also introduced to form ligands with metal ions deposited on the surface of ultrafiltration membranes, which improve the separation of Ca and M^ salts. It has been established that ultrafiltration membranes made of polysulfone show a lower permeability of pure water compared to poly-ethersulfone-ultrafiltration membranes under the same conditions, but with the addition of additives, water purification is also accelerated through polysulfone-new ultrafiltration membranes. Polysulfone membranes are more prone to clogging. Separation of Ca and Mg is less at low pH and Mg2+ is separated less than Ca2 at both membranes. As the ligand-metal ion ratio increases, metal separation improves. PEI forms a high ionic strength and solution pH, which results in separation efficiency and membrane fouling.

The simplest technique for preparing membranes using phase inversion is solvent evaporation precipitation. In this technique, the polymer is dissolved and the polymer solution is deposited on a suitable substrate, such as a glass plate. The solvent can be evaporated in an inert atmosphere

sphere, in order to exclude contact with water vapor, which makes it possible to obtain a dense homogeneous membrane. To obtain porous structures, film formation must go through a stage of phase separation. Therefore, to obtain porous membranes, molding solutions include three or more components: a polymer, a volatile solvent, and one or more pore formers belonging to the group of non-solvents according to the nature of the polymer-solvent interaction. The non-solvent must be less volatile than the solvent. In practice, the difference between the boiling points of the solvent and non-solvent should be at least 30-40 °C. Since the solvent is more volatile than the non-solvent, their ratio changes during evaporation so that a high non-solvent content is reached and the polymer precipitates to form a porous membrane structure.

Hollow fibers with both porous and non-porous walls are also obtained by dry spinning. In this case, the same regularities apply as in the production of polymer flat membranes.

The formation of flat membranes in a dry way is carried out on machines of drum or belt types. On fig. 1 shows a drum machine.

Rice. 1 - Scheme of a drum-type machine for producing membranes by dry molding 1 - casing; 2 - branch pipe for suction of the gas-air mixture; 3 - drum; 4 - die; 5 - membrane; 6 - gas-air mixture heater

The watering drum of the machine is a steel cylinder, the surface of which is polished or coated with a thin mirror layer of another material that provides the necessary smoothness, adhesion and corrosion resistance. Heat carrier for temperature control is fed into the inner part of the drum. Air is supplied to the casing around the drum through the heater 6 to maintain the specified temperature, humidity and solvent vapor pressure above the membrane. Air and polymer tape move countercurrently. Air can be circulated through the solvent vapor trap system. The tape is wound into a roll.

The belt type machine (Fig. 2) consists of two drums, on which an endless belt of stainless steel, copper or nickel is stretched.

0.7-1.4m wide and 28-86m long. To tension the tape, the rear drum is made movable. The drums are thermostatically controlled. The entire movable part is enclosed in a casing that forms a channel for the circulation of the gas-air mixture.

Rice. 2 - Scheme of a belt-type machine for producing membranes by dry molding: 1 - spinneret; 2 - system for circulating the gas-air mixture; 3 - guide drum; 4 - device for additional drying; 5 - winding device

If necessary, the final drying of the membranes is carried out outside the machines on dryers of any type. Other stages (washing, impregnation, etc.) can also be included in the technological scheme of the line.

Ultrafiltration membranes were formed from mixtures of cellulose acetate-polyethersulfone (95/5; 85/15; 75/25) using the phase inversion precipitation method with and without the addition of 2.5-10% to the mixture of PEG 600 polymers. The membranes were used to separate protein solutions and isolate pepsin, trypsin, and albumin, as well as to isolate Cu2+, Na2+, and C^+ cations from aqueous solutions. The performance and selectivity of membranes significantly depend on their composition and the amount of PEG added and varies from 25 to 182 l/m2 "h, protein retention is within 68-93%, and heavy metal cations from 83 to 94%. The performance of membranes from a mixture of polymers was higher than cellulose acetate membranes, and the selectivity is lower.

The effect of shear rate during the formation of cellulose acetate hollow fibers from 25-27% acetate-formamide solutions (1:1 and 1:5) on the morphology and performance of fiber membranes was studied. When forming the membrane, the shear rate at the outer wall of the spinneret was changed from 11233 to 22465 s-1, which was achieved by changing the supply rate of the forming solution (2.5-5 ml/min). A clear correlation has been established between the shear rate and the selectivity of the membrane during the purification of the NaCl solution: with an increase in the shear rate, the selectivity increases, reaches a maximum of 96% at a shear rate of 17972 s–1, after which it begins to decrease to 86–87%. Membrane performance increases with increasing shear rate.

The preparation of membranes for ultrafiltration in the form of hollow fibers by spinning from a solution containing polyethersulfone and polyvinylpyrrolidone (PVP) and N-methyl-2-pyrrolidone at 40 K is considered. The membranes are used to remove humic acids from solutions. The membranes have a permeability of 20*10-5 l/(m2 hour Pa).

The membrane structure was studied by electron microscopy.

The preparation of polysulfone membranes involves the preparation by mixing a homogeneous composition of a polysulfone compound, a solvent such as sulfolane, antipyrine, -

valerolactam, diethyl phthalate and mixtures thereof, and a non-solvent such as poly(ethylene glycol),

di(ethylene glycol), tri(ethylene glycol), glycerol and mixtures thereof. Melt the composition and subject it to molding from the melt. The resulting membranes have high physicochemical properties, biological compatibility,

inert to bleaches, disinfectants and salt solutions.

The processes of casting membranes from crystalline copolymers (CEB) of ethylene and vinyl alcohol, polyvinylidene fluoride (PVDF) and polyamide 66 (PA) are studied in this work. The morphology of the resulting membranes strongly depends on the evaporation temperature of the solvent. At low evaporation temperatures, the particle morphology determines the mechanism of polymer crystallization. With an increase in the evaporation temperature, the structure of CMEA membranes changes due to the transition from the morphology of particles to the morphology of seals. For PVDF and PA membranes, as the evaporation temperature increases, the particle morphology is preserved. The structure of the obtained membranes is discussed with consideration of the theoretical. crystallization from solutions.

Most of the membranes produced in the industry are produced by the wet molding process. The spinning solution is cast onto a suitable substrate or forced through a spinneret and immersed in a coagulation bath containing a precipitant. The precipitation of the polymer occurs due to the exchange of solvent and precipitant. The use of the wet method has, in our opinion, a number of advantages compared to the dry or dry-wet method. Thus, the structure and filtration characteristics of membranes are determined mainly by the composition of the molding solutions and the coagulation bath, so there is no need to create and maintain strictly deterministic conditions for the process, such as the temperature and composition of the gas phase in the preforming zone, the duration of preforming, etc. d. The wet process generally results in a higher throughput of the film forming process. This makes it possible to significantly simplify the technology for obtaining membranes, as well as to achieve higher reproducibility of results due to the dependence of membrane characteristics on a small number of easily controllable parameters.

In the wet method, a preforming stage is sometimes introduced - partial evaporation of the solvent in air or vapor phase (dry-wet method). As a result of partial evaporation of the solvent, the polymer concentration on the solution film surface increases. After the film is immersed in the coagulation bath, an anisotropic membrane is formed. By this method one obtains

reverse osmosis membranes, and when using high-boiling solvents, the preforming step is carried out at elevated temperatures. If the solvent is miscible with water, and the preforming is carried out with the participation of the vapor phase, then already at this stage, the deposition of the polymer in the upper layers of the film will begin.

Polymeric membranes were obtained from homogeneous solutions of 2 different mixtures: polysulfone/dimethylformamide and polysulfone

background/polyvinylpyrrolidone (polyvinylpyrroli-

don)/dimethylformamide. Polysulfone solutions with a concentration of 15%, after casting on a glass plate, were cured either by direct immersion in distilled water or exposure for 5 hours in an environment with 72.5% relative humidity, followed by immersion in a water bath. The resulting membranes were compared with each other in terms of morphological and functional characteristics. In the case of exposure to an atmosphere of water vapor, the rate of delamination of the film from the casting solution increased when a polymer additive (polyvinylpyrrolidone) was added to the casting solution. However, an increase in the rate of separation did not lead to an increase in water permeability or a significant morphological change in the resulting membranes. Conversely, when the cast film was coagulated by direct immersion in an aqueous bath, the polyvinylpyrrolidone in the solution cast film acted as an agent to greatly enhance the membrane performance. It is concluded that at a given polymer concentration, the addition of 15% polyvinylpyrrolidone induces an increase in the rate of delamination of the cast solution, resulting in an increase in the permeability of the obtained membranes, if only the coagulation of the cast film is carried out in a non-equilibrium state.

A known method for producing polysulfone membranes in the form of capillary tubes by dissolving polysulfone in methylpyrrolidone with the addition of polyvinylpyrrolidone at the following ratio of mass fractions (%) of the components in the working solution: polysulfone 9-18, polyvinylpyrrolidone 15-20, methylpyrrolidone - the rest, by casting the resulting solution into a precipitation bath containing (wt.%) methylpyrrolidone 60, water 20, isopropyl alcohol 20. It is noted that instead of polyvinylpyrrolidone, the working solution can contain up to 20% polyethylene glycol with a molecular weight of about 30,000.

A new observation is reported - the appearance of macrovoids in the cellulose acetate/acetone/water ternary system forming the membrane. The membranes were obtained by pouring from a solution of polymer and acetone, followed by phase separation using a coagulant - pure water. It was found that the formation of macrovoids at a concentration of 12.5 wt.% irrigation solution strongly depends on the thickness of the cast solution layer: macrovoids are formed at a layer thickness of 500 μm and do not form at a layer thickness of 150 and 300 μm.

The spontaneous gelation method is used for polymer systems with an upper critical mixing temperature (UCTC). A solution of polymer in a mixture or individual solvent, prepared at a temperature above the UCST, is cooled until phase separation occurs. Technologically, this method does not differ from the formation of film or fiber materials from a polymer melt and is used to prepare microfiltration membranes.

Using the leaching process, porous polymeric membranes can be prepared. The polymer solution or melt containing the appropriate filler is extruded into a film or fiber. Then the filler is extracted. A variation of leaching is the etching of tracks formed in the film by high-energy particles.

This method is used to obtain membranes from polytetrafluoroethylene (Teflon), for example, by sintering a mixture of PTFE powder and a filler, which is calcium carbonate or colloidal aluminum. The filler after sintering is removed by leaching, thus forming a membrane with a pore size determined by the particle size of the filler.

The paper considers the use of co-extrusion of solutions of two different polymers to obtain hollow fibers used as semi-permeable membranes for separating gas mixtures. The hollow fiber consists of a layer of hydrophobic material such as polysulfones and a hydrophilic coating of sulfonated polyethersulfones. The influence of the ratio of these components on the characteristics of capillaries and on the adhesion between layers was studied. It is shown that the content of sulfonated polyester sulfonate in the fiber is optimized.

The application of co-extrusion of solutions of two different polymers to obtain hollow fibers used as semi-permeable membranes for the separation of gas mixtures is considered. The hollow fiber consists of a layer of hydrophobic material such as polysulfones and a hydrophilic coating of sulfonated polyethersulfones. The influence of the ratio of these components on the characteristics of capillaries and on the adhesion between layers was studied. It is shown that the optimal content of sulfonated polyestersulfonate in the fiber is ~30%.

The processes of reduction of nickel ions in porous polyethylene membranes formed in the process of melt extrusion followed by annealing, uniaxial stretching, and thermal fixation have been studied. They contain through pores 100–200 nm in size. It has been shown that when porous polyethylene preliminarily aged in a solution of nickel salts is introduced into a solution of a reducing agent (sodium borohydride), the following processes occur: diffusion of the reducing agent into pores, diffusion of nickel ions towards the reaction front, nickel reduction reaction, nucleation, growth, and

adsorption of nickel nanoparticles on the membrane surface, hydrolysis of borohydride in solution and in pores, nucleation, growth, and release of hydrogen bubbles. It has been established that the nucleation of nickel nanoparticles in the pores of a hydrophobic polyethylene membrane proceeds according to a homogeneous mechanism. Subsequently, the particles are either adsorbed on the pore walls or carried to the membrane surface by a flow of hydrogen released during the hydrolysis of the reducing agent.

Obtaining tubular ceramic. A membrane consisting of two layers coaxial along the X axis - a layer of the substrate material and a layer of active material is characterized by the fact that it includes the following steps: a) simultaneous coextrusion of the coaxial paste of the substrate material at a speed along the X axis X-axis Um at Uє=Um; b) drying the shaped coextrudate; c) removing the binder from the dry coextrudate; d) firing. A device for carrying out this process is also proposed.

The effect of calcination time and temperature on the flux density and porosity of extruded microfiltration membranes (MBMs) was studied. For the complete formation of the mullite phase, a-A1203 was added to kaolin. Na2CO3 was used to increase the porosity and flux density. To reduce the number of experiments to a minimum, we used the Ta^cCl method. The resulting MBMs contained (%): 30 Al203, 3 Na2CO3, and 67 kaolin. After drying, MBM was calcined at 1000°C, after which it was examined by X-ray diffractometry and scanning electron microscopy. It has been established that mullite is the main phase of membranes. The maximum pore size is 5.5 µm. The water permeability and porosity of the membranes were 21.5 kg/m2*h and 33.92%, respectively.

The simplest pore geometry in a membrane is an ensemble of parallel cylindrical pores of the same size. Such a structure can be obtained by etching tracks.

In this method, a film (often polycarbonate or polyethylene terephthalate) is irradiated with a stream of high-energy particles directed perpendicular to the film. The particles damage the polymer matrix and form tracks. The film is then immersed in an acid (or alkali) bath and the polymer matrix is ​​etched along these tracks, resulting in the formation of pores with a narrow size distribution. The pore size is in the range from 0.02 to 10 µm, but the surface porosity is low (not higher than 10%). The scheme of the method is shown in Fig. 1. 3 . The membranes obtained in this way are called track or nuclear filters.

The paper presents a method for manufacturing a track membrane, including irradiation of a polymer film with accelerated charged particles, its sensitization by radiation in the ultraviolet range, treatment of the irradiated film with an etching alkaline reagent, sequential treatment with a solution of polyethyleneimine, and

a solution of a polymer that reduces the sorption capacity of the film with respect to proteins and enzymes, characterized in that, before sequential processing, a neutral electrolyte at a concentration of

0.1-3 mol/l.

The source of the "teaching

Meme4) aka s

capillary

Rice. 3 - Scheme of track etching to obtain nuclear filters

The authors show a method for manufacturing asymmetric polymeric membranes with a thin selective layer containing pores in the micro- and nanometer range. EFFECT: increased productivity of the process for obtaining asymmetric track membranes by creating a continuous technological process. A method for manufacturing an asymmetric track membrane includes irradiating a polymer film with heavy charged particles and subsequent chemical etching, in which additional processing is carried out on one side of the film by exposing the film in an oxygen-containing atmosphere to ultraviolet radiation, or plasma, or a beam of charged particles, and chemical etching is carried out in solution containing at least two dissolved components, of which one is an etching agent, and the second is a surfactant.

A method for manufacturing a track membrane is presented in the work, which includes irradiating a film from the material from which the track membrane is made with a heavy ion flow from an accelerator to create one population of heavy ion tracks in the film, having a uniform angular distribution within specified angles in planes perpendicular to the film surface, subsequent sensitization of the material in the volume of the track and chemical etching of through holes in the film at the site of the tracks, characterized in that several layers of the film are irradiated simultaneously in such a way that at each intersection of one layer of the film, the angle of the planes in which the ion flux crosses the film surface is changed and thus Thus, several populations of tracks with their own given angular distribution are created in the film.

By drawing, an extruded film from an amorphous-crystalline polymer material

rial, stretched in a direction perpendicular to the direction of extrusion (Kelgard process). During extrusion, the crystalline regions are oriented parallel to the direction of extrusion. When mechanical stress is applied, cracks form and a porous structure is obtained. Only amorphous-crystalline polymeric materials can be used for this technique. The porosity of these membranes is higher than that of sintered membranes and reaches 90%.

This method is used to obtain PTFE membranes. The polymer is first subjected to deformation (up to 100-150%), while it is dispersed into the smallest asymmetric aggregates of oriented macromolecules - fibrils with a diameter of 5-50 nm. Such aggregates are separated in space, and the distance between them is from a few to tens of nanometers. Further deformation leads to the collapse of the resulting porous structure. The advantage of this method of creating a porous structure is the possibility of creating matrices with different bulk porosity (from 30 to 67%), morphology and pore size (from 2 to 15 nm).

A variation of this method is the extrusion of a composition of dispersed and fine-fiber PET containing a lubricant (15–20% kerosene), followed by removal of the lubricant by heating, uniaxial or biaxial drawing, and sintering the resulting material. This method is used to obtain Gour-Tex PET membranes.

The principle of the sintering method is to form a film from a bulk material, followed by particle sintering. The porosity of the membranes is due to the gaps between the connected particles, and the pore size is due to the particle sizes.

Often, solid or liquid organic and mineral components are added to the polymer powder, which facilitate the binding of particles during sintering and increase the overall porosity.

As the temperature rises before reaching the glass transition or melting temperature, the interaction between particles is initially of a superficial nature (of the adsorption type), i.e. without interpenetration of molecules or their segments into neighboring particles. The contact zone can be considered as a defective structure in comparison with the structure of the polymer in the volume of particles. The higher the temperature and the longer the contact of the particles, the greater the bonding strength of the particles.

In the contact zone, both intermolecular bonds and chemical interactions arise. To increase the contact zone, it is useful to compress the powder.

The shape of the contacting particles is very important. The best is spherical in terms of contact, porosity, and pore size distribution. Therefore, sometimes the shape of the particles is normalized, for example, in a stream of hot gas in a state of pseudo-boiling at temperatures above the melting point.

Low-molecular additives (plasticizers and solvents) affect the rheological properties of powder compositions (the system acquires plasticity, it can be molded by extrusion and rolling or calendering, and also stretched after molding).

In addition, these additives convert the polymer into a highly elastic state, and in the surface layers - even into a viscous flow, which facilitates the binding of particles.

To increase the strength of the membrane, inert fillers can be introduced into the initial mixture, which are sometimes washed out after heat treatment to increase porosity.

This method is quite simple; it allows one to obtain porous membranes from both organic and inorganic materials. The method involves pressing a powder containing particles of a certain size and heating at elevated temperatures. The required temperature depends on the material used. During sintering, the surface between the contacting particles disappears.

Materials for the sintering process must have high chemical, thermal and mechanical resistance. With the help of sintering, only large-pore microfiltration membranes can be obtained. The porosity of such membranes is usually low - from 10 to 20% or slightly higher, while for porous metal filters it can reach 80%. Basically, sintering is used for the processing of polymeric materials that are poorly or insoluble in common solvents or whose degradation temperature lies below the melting point, which does not allow them to be processed through the melt. This method is most widely used to obtain porous materials from polytetrafluoroethylene (Teflon)

A powder with a structure of the fluorite type U202/2r02 (U82) with an average particle size of 1.74 μm was synthesized by combustion using citric acid. U82 powders were used to obtain gas-tight hollow fibrous membranes by drawing the fiber followed by sintering at 1400°C for 4 h. 500 nm.

New mineral membranes for microfiltration deposited on apatite macroporous substrates have been developed and investigated. The choice of material is justified by its low cost, as well as its thermal. and chem. tenacity. Active layers were obtained from synthesized hydroxyapatite (HA) and natural apatite (AB). Membranes deposited on tubular substrates based on AB were obtained by slip casting.

Heat treatment for membranes with hydroxyapatite included 24 h drying at room temperature followed by sintering at 600°C and at 750°C for membranes with natural apatite. The morphology of the surface and cross section, examined by scanning electron microscopy, was homogeneous and did not contain any

or macrodefects (cracks, etc.). The average pore diameter of the active layer was 0.25 µm and 0.2 µm for membranes with hydroxyapatite and membranes with natural apatite, respectively.

Dense membranes in which transport occurs by molecular diffusion generally show low fluxes. The increase in fluxes through these membranes can be achieved by reducing the effective thickness of the membrane as much as possible. This can be achieved by preparing composite membranes. Such composite membranes consist of two different materials, the selective membrane material being deposited as a thin layer on a more or less porous substrate.

The results of the development of hybrid membrane-catalytic systems by modifying porous ceramic membranes with metal oxide coatings are presented. A bilayer ceramic-metal membrane was used, consisting of a flexible layer of porous stainless steel, on the surface of which a Ti02 ceramic porous layer was formed, and a ceramic membrane made of titanium carbide. The membrane surface was modified using the alkox method based on colloidal organic solutions of metal complex precursors.

The polysulfone/polyethylene oxide (PEO)/silicone rubber (SAR) multilayer membrane is made by double coating the polysulfone substrate PEO and SLA.

Experiments on the gas permeability of hydrogen and nitrogen were carried out at 30°. The membranes showed high and stable performance in relation to the U2/N"2 system, the permeability of H2 and N was 49.51 and 0.601 vRI, respectively, and the separation factor of 82.3 for U2/M2 was optimal. It is believed that the PEO interfacial layer acts as the selective permeability medium is responsible for the high I2/N2 separation factor, which was superior to the specific selective permeability for the three polymers studied.

Membrane membranes based on zeolite 28M-5 were synthesized to release CO2 by hydrothermal treatment of various porous tubes of a-aluminum oxide in the reaction mixture of templates. The effect of each solid support acting as a source of Al in a solution with high pH during hydrothermal treatment and the molar ratio 8/02 in reaction mixtures on the formation of 28M-5 crystalline layers was studied. The synthesized membranes were also surface-modified by coating using a polymeric silica sol that filled the intergranular cavities to improve the separation efficiency with respect to CO2. Membranes based on zeolite 28M-5 were evaluated by CO2/N"2 separation and permeability measurements as a function of fraction cut-off, helium flow rate, feed pressure, and permeation temperature. Maximum separation for a mixture of gases

CO2/M2 (50% CO2) was about 54.3 at 25°C and 14.9 at 100°C, respectively, and the permeability was 3.6*10-8 mol/m2*s*Pa.

Immersion deposition is often used to produce composite membranes with a very thin but dense surface layer for reverse osmosis, gas separation and pervaporation processes. The principle of this technique is shown schematically in Fig. four .

membrane coatings

Rice. 4 - Scheme of application by immersion

In this case, asymmetric membranes are immersed in a special solution containing a polymer, oligomer or monomer, and the concentration of the solute in the solution is very low. The impregnated membrane is then placed in an oven where the solvent evaporates and a layer of modifying polymer is formed. In some cases, to fix the deposited layer to the porous substrate, chemical crosslinking is performed. Such cross-linking is often necessary because the deposited layer does not have mechanical and chemical stability or its structure does not provide the necessary separating characteristics. A variation of this method is coating in filtration mode. In this case, the membrane or membrane element is treated with a solution of a modifying agent (usually a polymer) followed by fixation of the coating by treatment with cross-linking agents or y-radiation.

New heterogeneous cation-exchange membranes using polyethersulfone as a binder and sulfonated polyphenylene sulfide (SPPS) powder as a polyelectrolyte were obtained by the solution-dip method. Compared with the conventional method for producing heterogeneous membranes, the steps of grinding resin into fine powders and pressing at a high temperature are eliminated, and thus a simple technology for producing a membrane is provided. The effect of particle size and SPPS resin loading on membrane properties, such as ion-exchange capacity, water content, electrical resistance, transport number, electrolyte diffusion coefficient, etc., was studied. It was shown that the fundamental properties of membranes strongly depend on both the resin loading and and on the particle size of the SPPS resin. By adjusting these two important parameters, it is possible to obtain heterogeneous membranes with good conductivity, selectivity and proper water content for

various industrial applications such as electrodialysis, diffusion dialysis, etc.

Two systems are obtained in the form of flat ceramic sheets designed for the deposition of mesoporous membranes with a high pore volume. The systems consist of a substrate and a different number of intermediate layers deposited on it. The substrates were obtained by pressing, the intermediate layers were deposited by the immersion method. Studies of rheological properties were carried out in order to control the viscosity of suspensions. To assess the quality of the intermediate layers and the resulting membranes, permeability measurements, studies using mercury porosimetry and microscopy were carried out.

A membrane based on MaL zeolite on the outer surface of a porous aluminum oxide ceramic tube was obtained using the hydrothermal method and the microwave method under hermetic conditions. Four different molar ratios and four different immersion methods have been investigated. The crystal structure of the membrane was studied by X-ray diffraction and scanning electron microscopy. The separating properties of the membrane were evaluated by pervaporating a mixture (95:5) ethanol/water. It has been established that the membrane synthesized by the hermetic microwave method at the molar ratio

No. 20:A1203:8Y2:H20=1:1:3.6:100 immersed in a clean seed solution has the best properties. A mixture passed through this membrane, consisting of 79 wt.% water and 21 wt.% ethanol, had a degree of separation of 63.8, indicating that the MaL zeolite membrane is water selective.

Interfacial condensation is one of the methods for depositing a thin layer on a substrate. In this case, a polycondensation reaction occurs at the interface between two immiscible solvents.

The support layer, which is usually an ultrafiltration or microfiltration membrane, is immersed in an aqueous solution containing an active monomer or oligomer, typically of the amine type. The aqueous solution fills the pores of the membrane and its excess is removed. The film (or fiber) is then immersed in a secondary bath containing a water-immiscible solvent in which another active monomer is dissolved, often a diacid or tribasic acid chloride. These two active ingredients react to form a dense polymer layer. Heat treatment is often used to more fully react at the interfacial surface. The advantage of interfacial polymerization is that the reaction is self-inhibiting as a result of the limited flow of reactants through the already formed layer, thus forming a very thin film with a thickness of less than 50 nm.

During interfacial polymerization to obtain a polymer composition. With nanofiltration polyamide membranes, both high permeate performance and high salt retention can be achieved. Synthesis conditions such as

the concentration of the monomer, the reaction time and the type of swelling agent, significantly influence the partition. ability of composite membranes. The composite polyamide membrane had a permeability of >3.2-8 l/m2^h and a scaling rate of 94-99% when an aqueous salt solution (2000 ppm) was supplied at 1379 kPa and 25°C. In addition, a nanofiltration membrane with increased productivity could be obtained by properly swelling the support matrix during the polymerization period. The results at various feed concentrations showed that permeate productivity decreased with increasing salt concentration in the feed solution. This result may be due to the concentration polarization of the surface of polyamide membranes. The separation performance of polyamide membranes showed almost complete independence from the operating pressure up to 1379 kPa.

Composite membranes in the form of thin films are obtained by polymerization at the phase boundary of trimesoyl chloride (I) and m-phenylenediamine (II). The permeability and selectivity of polyamide membranes and the mechanical properties of the obtained films after delamination from the base were studied depending on the concentration of reagents in the reaction mixture. It has been shown that, at a high content of I, films with an increased thickness and hydrophilicity of the surface are obtained, while at a high content of II, the film thickness and hydrophilicity decrease. The permeability of water through membranes depends on the thickness of the films and their hydrophilicity and decreases with an increase in the content of m-phenylenediamine.

Abstract—The nanoscale structure of composite polyamide membranes for reverse osmosis and nanofiltration has been studied by transmission electron microscopy and atomic force microscopy. It has been established that the polymer density and charge are distributed across the active polymer layer extremely non-uniformly. Polyamide films appear to be constructed from a negatively charged outer layer on top of an inner layer that has a small positive charge. This structure seems to be common for all types of composite membranes. The sharp boundary between the layers refers to the region of the highest density of the polymer, i.e., to the actual selective barrier.

A technology for obtaining thin cation-exchange membranes with sulfonic acid groups is presented. Film membranes were fabricated by plasma polymerization followed by hydrolysis of halosulfone groups. Benzenesulfonyl fluoride and benzenesulfonyl chloride were used as the starting material. In sulfonyl chloride, in the plasma polymerization mode, the 8-C1 bonds are easily cleaved to form the C1 radical; the 8-B bond of benzenesulfonylfluoride is more stable under these conditions. The plasma polymer formed using benzenesulfonyl fluoride has a cation exchange

variable capacity comparable to commercial polymeric cation exchange membranes.

Polypropylene membranes are plasma etched with 802, 802-02 or 802-H20 followed by plasma polymerization coating with 802 and acetylene. 802 plasma etch conditions are optimized by measuring the ion exchange capacity (IEC) as a function of plasma etch power (10-30 W), gas pressure (40-60 mm) and treatment time (15-120 s). For plasma etching of 802-02 and 802-H20, only the pressure ratio (802 and 02/H20) is optimized under optimal conditions determined from 802-plasma etching. Plasma etching was then combined with plasma polymerization coating of 802 and acetylene, for which conditions were again optimized by measuring IOE as a function of plasma power (10-40 W), chamber pressure (50200 µm), 802/acetylene ratio (15:135- 60:90) and treatment time (0-10 min.). After that, the electrical resistance and water absorption were evaluated. The modified membranes were also analyzed by scanning electron microscopy, while the plasma polymerization coating was characterized by Fourier transform attenuated total internal reflection IR spectroscopy.

The preparation of sulfocationite membranes based on glycidyl methacrylate SPLs grafted onto porous polypropylene substrates is described. The data of IR and emission electron spectroscopy, as well as electron microanalysis, describing the structural features of the obtained SPLs, are presented. The main electrochemical properties of the membrane have been studied and it has been shown that their capacitance is 2.53-3.30 mmol/g and the electrical resistance is 0.349-0.589 Ohm*cm2.

The paper considers a tubular membrane filter element containing an open-pore tube, the wall of which is made of layers of fibrous materials impregnated with a thermosetting binder, with the formation of an open-pore adhesive joint over the entire area of ​​their contacts after curing of the binder, and the inner surface is covered with a semi-permeable alkali-resistant polymer membrane, characterized in that that the inner layer of the wall of the open-pore tube is made of a flat tape or sleeve from a mixture of plain weave of polypropylene (warp) and chlorine (weft) threads, and the outer layer is made of a flat tape of plain weave of a mixture of the same threads.

The paper presents a method for manufacturing a tubular membrane module for filtering liquids by impregnating fibrous materials with a thermosetting binder, forming multilayer support open-pore tubes from them, curing the binder in them and applying a semi-permeable membrane to their inner surface, characterized in that the inner part of the wall of each support open-pore tube is formed by placing a plain weave sleeve on a rigid mandrel and winding it in a spiral with a non-woven tape

fibrous material impregnated with a thermosetting binder, in the following ratio, wt.%: Sleeve and non-woven material - 65 - 80; Thermosetting binder - 20 - 35.

The authors present a method that can be used for tangential filtration of liquid mixtures, their concentration, separation and purification of their components. A liquid film is formed on a substrate from a solution containing 20-40 wt.% of a trifluorochloroethylene copolymer with 20-30 wt.% of vinylidene fluoride and 5-16 wt.% of a blowing agent - a lower alcohol, acetone or methylpyrrolidone in dimethylacetamide, tetrahydrofuran or ethyl acetate. The film is then cured. The adhesion of the membrane to the substrate is improved, the formation of blisters is prevented, and the resistance to cracking is increased.

Federal State Budgetary Educational Institution of Higher Professional Education "KNRTU" proposes the introduction of the process of processing with RF plasma into the technological process of manufacturing the frame of the BTU-0.5 / 2 tubular ultrafilter after the operation of purging the frame before assembling them into a block.

The introduction of the process of RF-plasma treatment at the stage of membrane formation makes it possible to abandon the technological operation of annealing the tubular ultrafilter BTU-0.5/2.

The use of RF-plasma treatment reduces the time of technological operations during membrane formation at the stages of membrane preformation, coagulation of the membrane-forming polymer, washing of BTU-05/2, as well as the rejection of the membrane annealing operation.

Thus, the article describes various methods for obtaining polymeric membranes and considers some aspects of the physicochemical processes that occur during the formation of membranes.

The work was performed on the equipment of the Center for Collective Use "Nanomaterials and Nanotechnologies" with the financial support of the Ministry of Education and Science of the Russian Federation within the framework of the federal target program "Research and development in priority areas of development of the scientific and technological complex of Russia for 2007-2013" under state contract 16.552.11.7060.

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© I. Sh. Abdullin - Doctor of Technical Sciences, Prof., Vice-Rector for SR KNRTU; R. G. Ibragimov - Ph.D. Associate Professor of the Department of TOMLP KNRTU, [email protected]; O. V. Zaitseva - Ph.D. cafe PNTVM KNRTU, [email protected]; V. V. Paroshin - Ph.D. the same department [email protected]

The invention relates to the production of porous polymeric membranes and can be used for filtering, analyzing and purifying various media in microbiological, biochemical and other industries. The aliphatic polyamide is dissolved in formic acid containing water. Poly-N-vinylamide with a molecular weight of 2000 to 20000 is added to the solution. The resulting working solution contains 15-20 wt.% aliphatic polyamide, 13-17 wt.% water, 0.02-0.4 wt.% poly-N -vinylamide and the rest of the formic acid. The membrane is then obtained by wet spinning of the working solution. The solution has increased stability, and the membrane has a more uniform porous structure with a rather narrow pore size distribution. 1 tab.

The invention relates to the field of obtaining porous polymer films, and in particular to a method for obtaining microfiltration membranes used for filtering, analyzing and purifying various media in microbiological, pharmaceutical, biochemical, food, fuel and a number of other industries. Known methods for producing membranes from aliphatic polyamides (poly-caproamide), based on phase separation processes occurring in a polymer solution when immersed in a precipitation bath (AS USSR 537100, 704147, 1108737, M. class C 08 L 77/ 02). At the same time, the composition of the molding solution includes polycaproamide (nylon), a solvent (formic acid), and a polymer non-solvent (water). The resulting solution is applied using a die to a plate of polished glass, then the coating is cured in an aqueous solution of ethyl alcohol, acetone or acetic acid. The disadvantage of these methods is the instability of the obtained molding solutions. A known method of obtaining a microporous polyamide membrane (AS USSR N 1503841 MCL C 08 J 5/18) in a mixture of formic acid with water, where in order to increase the service life of the precipitation bath, it contains water and dioxane. A known method for producing a porous membrane by casting a molding composition containing an aliphatic polyamide, an aprotic organic solvent, lithium chloride, and as a modifying additive is phosphoric acid hexamethyltriamide (A.S. USSR 1234405, M. class C 08 J 5/18, B 01 D 13/04). The disadvantage of this method is the complexity of the process - polyamide is dissolved at a temperature of 90-110 o C, followed by cooling, and the low stability of the molding solutions. The closest in technical essence is the known method for producing microfiltration membranes, including the dissolution of aliphatic polyamide in formic acid containing a precipitant - water, molding the resulting working solution into a membrane and drying (EP 0087228 A1, 31.08.1983). The disadvantage of this method is the low stability of the molding solutions. The proposed method differs from the known one in that poly-N-vinylamide with a molecular weight of 2 to 20 thousand is additionally introduced into the working solution with the following content of the solution components: Polyamide - 15 - 20 Water - 13 - 17 Poly-N-vinyl - 0 .02 - 0.4 Formic acid - The rest The present invention is aimed at increasing the stability of spinning solutions and obtaining microfiltration membranes based on them with a narrower pore size distribution, as well as the possibility of precise control of the pore size of the membranes in a wide range. Poly-N-vinylamides are introduced into the ready-made molding solution, which leads to a decrease in viscosity and a sharp increase in the stability of the solution. The stability of the solutions was evaluated visually, fixing the time and viscosity of the solution that elapsed from the moment the solution was prepared until it gelled or crystallized. The viscosity properties of solutions are a convenient measure of the suitability of solutions for membrane formation. Poly-caproamide (PA-6), polyhexamethylene adipamide (PA-6,6) are used as aliphatic polyamides. As water-soluble poly-N-vinylamides, the following are used: poly-N-vinylpyrrolidone (PVP), poly-N-vinylcaprolactam (PVC), poly-N-vinyl-N-methylacetamide, copolymer of N-vinylpyrrolidone and N-vinylcaprolactam. Poly-N-vinylpyrrolidone is a radical polymerization product of N-vinylpyrrolidone (VFS-42-1491-85), poly-N-vinylcaprolactam is a polymerization product of N-vinylcaprolactam, poly-N-vinyl-N-methylacetamide is a polymerization product of N-vinyl- N-methylacetamide, a copolymer of N-vinylpyrrolidone and N-vinylcaprolactam is a copolymerization product of N-vinylpyrrolidone and N-vinylcaprolactam. The invention is illustrated by the following examples, and the properties of the resulting membranes are presented in table 1. Example 1. Prepare a solution containing 20 wt.% polycaproamide (PA-6), 17 wt. % water, 63 wt. % formic acid. To prepare the solution, a specified amount of formic acid and water is poured into the reactor with the equipment turned off. Then, with the stirrer turned on, poly-caproamide (nylon) is loaded. The preparation of the molding solution is carried out under controlled conditions: at the first stage at a temperature of 12-15 o C for 1 hour, at the second stage at a temperature of 20-25 o C for 2-3 hours. In order to remove undissolved polymer particles and mechanical impurities the molding solution is filtered at an excess pressure of 0.5-1.0 atm through a filter with a pore size of 10-20 μm. To remove air bubbles in the molding solution, a deaeration operation is performed for 3-4 hours at room temperature. The resulting solution is applied using a slot die onto a rotating metal drum, which is immersed in a precipitation bath consisting of an aqueous solution of formic acid (40 wt.%, HCOOH, 60 wt.% H 2 O). In the precipitation bath, the molding solution is cured and the membrane is formed. The formed membrane is washed with water in washing baths to remove formic acid residues, then heat-treated and dried on drying drums. The resulting membrane has a water filtration capacity of 18-20 ml/cm 2 min. at a pressure drop of 1 atm and a bubble point of 3.2 atm. The stability of the solution is maintained for 5 hours. Example 2. Polycaproamide with a molecular weight of 30,000 in an amount of 20 wt.% is dissolved in a mixture of formic acid and water (respectively 62.98 wt.% and 17 wt.%) for 3 hours. Then at stirring add poly-N-vinylcaprolactam (PVC) with a molecular weight of 10,000 in the amount of 0.02 wt.%. Next, the preparation of the molding solution, the formation of membranes according to example 1. The characteristics of the resulting membrane are presented in table 1. Example 3. To prepare the molding solution, a mixture of formic acid (69.9 wt.%) and water (13 wt. %). Then turn on the stirrer, add poly-α-caproamide with MM=24000 in the amount of 17 wt. % and stirred for 3 hours Then add poly-N-vinyl-N-methylacetamide (PVMA) with MM=5000 in the amount of 0.1 wt. %. Further preparation of the molding solution and molding of the membrane is carried out as in example 1. The results of testing the membrane are presented in table 1. wt.%) and stirred for 3 hours Then add poly-N-vinylpyrrolidone (PVP) with a molecular weight of 2000 in the amount of 0.2 wt.%. Further according to example 1. The properties of the obtained membrane are presented in table 1. Example 5. Prepare a solution containing 17 wt.% polycaproamide (MM=20000), 14 wt.% water and 68.6 wt.% formic acid. Then, a copolymer of N-vinylcaprolactam with N-vinylpyrrolidone is added to the molding solution at a ratio of 50/50 mol.% with a molecular weight of 20,000 in an amount of 0.4 wt.%. Further, according to example 1. The properties of the obtained membrane are presented in table 1. Example 6. Polyhexamethylene adipamide (PA-6,6) with a molecular weight of 40,000 in an amount of 20 wt.% is dissolved in formic acid (66.98 wt.%), then water is added (13 wt.%). After stirring for 3 hours, a copolymer of N-vinylcaprolactam and N-vinylpyrrolidone is added at a ratio of 70/30 mol.% with a molecular weight of 20,000 in an amount of 0.02 wt.%. Further, according to example 1. The test results are presented in table 1. Example 7. The molding solution is prepared according to example 6. (MM PA-66=24000). Then add poly-N-vinylpyrrolidone with a molecular weight of 2000 in the amount of 0.4 wt. %. The final ratio of components is as follows: 15 wt.% PA-66; 17% H 2 O; 67.6% MK; 0.4% PVP. Further on the example. The test results are shown in Table 1. Example 8 A mixture of formic acid and water according to Example 2 was used to prepare a spinning solution. After stirring for 15-20 minutes, poly-N-vinyl caprolactam with a molecular weight of 10,000 was added in an amount of 0.02 wt.% . Then, polycaproamide (20 wt.%) with a molecular weight of 30,000 is loaded, after which it is stirred for 3 hours. Further, according to example 1. The properties of the membrane are presented in table 1. Thus, the stability of solutions over time is an important indicator in the technology of obtaining membranes, since at In the production of microfilters by the wet method, the molding speed is low, and a rather long time is required for the processing of working solutions. It follows from the table: When poly-N-vinylamides are introduced into the solution of the main polymer (polyamide), a change in the characteristics of the membranes is observed. With an increase in the concentration of injected poly-N-vinylamide, the bubble point increases while maintaining or increasing the performance of the membrane. This fact indicates that the resulting membrane has a more uniform porous structure with a rather narrow pore size distribution. The change in the bubble point with the addition of poly-N-vinylamides indicates the possibility of controlling the pore size of the membranes in a wide range, while significantly increasing the stability of the molding solutions.

Claim

A method for producing microfiltration membranes by dissolving aliphatic polyamide in formic acid containing a precipitant - water, wet forming the resulting working solution into a membrane and drying, characterized in that poly-N-vinylamide with a molecular weight of 2000 to 20000 is additionally added to the working solution with the following content components of the working solution, wt.%: Aliphatic plyamide - 15 - 20 Water - 13 - 17
Poly-N-vinylamide - 0.02 - 0.4
Formic acid - Rest

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The invention relates to the field of membrane technology, namely to semi-permeable membranes, and can be used for wastewater treatment, concentration and isolation of macromolecular substances

The invention relates to membrane technology, in particular to the production of antibacterial polymeric membranes, and can be used to purify water and aqueous solutions in the food, pharmaceutical industries, in medicine

The invention relates to membrane technology and can be widely used for purification and separation of water and aqueous solutions in the food, pharmaceutical and other industries, in seawater desalination, biotechnology, in the creation of highly pure solutions. The composite polymeric membrane contains a non-woven material substrate, an ultrafiltration layer of polysulfone or polyethersulfone deposited on its surface and covering an ultrathin selective layer of polypiperazinamide at a ratio of their thicknesses, respectively (64.3-66.66): (32.36-35.98) :(0.98-1.02). The method for producing a membrane includes applying an ultrafiltration layer of polysulfone or polyethersulfone to the surface of a non-woven substrate by interfacial polycondensation, applying an ultrathin polymer selective layer of polypiperazinamide to the surface of the ultrafiltration layer by treating at 18-25°C first with an aqueous solution of piperazine for 6-10 minutes, then 0, 15-0.6% solution of the acyl chloride agent in an organic solvent for 6-10 minutes and drying at 25-40°C. The acyl chloride agent is a mixture of trimesoyl chloride and isophthaloyl chloride, taken in the ratio (mass parts): 1:1, with a solution concentration of 0.15-0.6%. An aqueous solution of piperazine may additionally contain a surfactant - a mixture of sodium salts of alkylsulfonic acids with a chain length of the alkyl radical C11-C18 in the amount of 3.75-6.0 wt.h. per 100 wt.h. piperazine. 2 n. and 1 z.p. f-ly, 1 tab., 5 pr.

The invention relates to the field of membrane technology. The method for producing a membrane includes applying a polysulfone or polyethersulfone to a substrate, which is a non-woven material, to obtain an ultrafiltration layer and forming an ultra-thin aromatic polyamide selective polymer layer on the surface of the ultrafiltration layer. The selective layer is formed by treatment with an aqueous solution of metaphenylenediamine containing sodium lauryl sulfate, triethylamine, sulphocamphoric acid, tetraethylammonium bromide, followed by treatment with an acyl chloride agent in an organic solvent, and drying. The water used to prepare the metaphenylenediamine solution is deaerated by boiling and then introducing sodium hydrosulfite. As an acyl chloride agent, a mixture of isophthaloyl chloride and trimesoyl chloride, taken in a mass ratio of (0.1-0.3):(0.05-0.2), is used. EFFECT: increased productivity and selectivity of the resulting composite polymer membrane, as well as increased stability of these indicators. 4 pr., 1 tab.

The invention relates to the recovery of acidic components from gas streams such as associated gases from wells or flue/exhaust gases using membranes containing a macromolecular self-organizing polymer. The specified gas stream (gas mixture) is brought into contact with the polymer (membrane). The polymer is a macromolecular self-organizing polymeric material. The self-assembling polymer (material) is selected from the group consisting of an ester-amide copolymer, an ether-amide copolymer, an ester-urethane copolymer, an ether-urethane copolymer, an ether-urea copolymer, an ester-urea copolymer, or mixtures thereof. Molecularly self-organizing polymer contains repeating self-organizing units of structural formulas (I)-(IV). 24 w.p. f-ly, 9 tab., 6 pr.

The present invention relates to a process for the production of butanol, which is of great industrial importance as a feedstock for the production of chemical and pharmaceutical products, as well as as a solvent and fuel. The method includes: step A, where the butanol-containing solution obtained by microbiological fermentation is filtered through a nanofiltration membrane, and the butanol-containing solution is isolated from the filtrate side; step B, wherein said butanol-containing solution obtained in step A is passed through a reverse osmosis membrane and thus concentrated so as to cause two phases to separate into a butanol phase and an aqueous phase; and step C, wherein the butanol is isolated from said butanol phase obtained in step B. The method of the present invention makes it possible to obtain high purity butanol. 9 w.p. f-ly, 2 ill., 10 tab., 15 pr.

The invention relates to methods for separating a fluid emulsion stream into a hydrocarbon stream and an aqueous stream. A method for separating a fluid emulsion stream having a continuous aqueous phase into a hydrocarbon stream and an aqueous stream, in which the fluid emulsion stream is passed through a microporous membrane to obtain a hydrocarbon product stream and an aqueous product stream, the membrane contains an essentially hydrophobic, polymeric matrix and is essentially hydrophilic, finely divided fine-grained, essentially water-insoluble filler, distributed throughout the matrix. The polymer matrix has an average pore size of less than 1.0 microns and the purities of the product streams are independent of the flow rate of the aqueous product stream and the pore size of the membrane. The technical result is an increase in the efficiency of separating oil from water in real time. 3 n. 17 w.p. f-ly, 9 tab.

The invention relates to the field of obtaining porous polymer membranes and can be used for filtering, analyzing and purifying various media in microbiological, biochemical and other industries

The invention relates to the field of membrane technology, and in particular to methods for manufacturing micro- and ultrafiltration membranes, and in particular to methods for manufacturing track membranes. The porous membrane, which is a film, contains at least two arrays of straight hollow channels having constrictions in the near-surface layer, while the axes of the channels are not parallel and at least one of the arrays consists of non-through channels starting on the surface and ending in the depth of the film, connected by intersections with the channels of another array, with the formation of a selective layer. The formation of a selective layer provides an increase in porosity, thereby reducing the hydrodynamic resistance of the membrane and increasing the specific productivity of the membrane in the filtration process. The method for producing such a membrane includes irradiating the polymer film with heavy charged particles, for example, accelerated ions, some of which have a range less than the film thickness, and subsequent chemical etching. The diameter and length of the pore channels, their angles of inclination, and the pore density are chosen so that the pores belonging to different arrays intersect in the volume of the membrane to form a selective layer. 2 n. and 11 z.p. f-ly, 15 ill.

The invention relates to the field of membrane technology, and in particular to methods for manufacturing micro- and ultrafiltration membranes, in particular to methods for manufacturing track membranes.

Porous membranes obtained from various polymers are currently widely used in modern technologies. There are homogeneous membranes, the structure and transport properties of which are the same in any section parallel to the surface, that is, they do not change in thickness. In order to increase the specific productivity in the separation of liquid media (ultrafiltration, microfiltration), asymmetric membranes have been developed and are widely used. A feature of their structure, which distinguishes them from homogeneous membranes, is the presence of a thin "selective" layer with small pores, lying on a thicker layer with larger pores. Asymmetric membranes outperform homogeneous membranes in performance because a thin selective layer has less hydraulic resistance than a symmetrical membrane with the same pore size. The coarsely porous layer acts only as a substrate and does not make a significant contribution to the resistance to mass transfer. One of the common ways to obtain asymmetric polymeric membranes is the solution molding method. The method is based on the process of phase inversion, as a result of which the polymer is transferred from solution to the solid state in a controlled way. This method mainly produces reverse osmosis, ultra- and nanofiltration membranes; these membranes consist of a dense surface layer or coating 0.5 to 5 µm thick on a porous substrate 50 to 150 µm thick. The effective size of pores in the surface layer can be fractions or units of nanometers. Methods have also been developed for obtaining asymmetric microfiltration membranes, that is, those that contain macropores (>50 nm) in the selective layer.

Closer (in terms of production technique) to the claimed invention is a method for producing porous membranes based on irradiating a thin monolithic polymer film with heavy ionizing particles and subsequent chemical treatment. The chemical treatment conditions are selected in such a way that traces of heavy particles (tracks) turn into hollow channels of the required diameter. For this, it is necessary that the reagent used for etching has the ability to destroy and dissolve the polymer layer by layer, and the dissolution rate in the tracks must significantly exceed the dissolution rate of the undamaged material. An example of such a process is the etching of tracks of uranium fission fragments in polycarbonate with a caustic alkali solution. When using 6 M NaOH at 60°, the polymer etching rate is about 1 µm/h, and the track etching rate is 100-1000 µm/h. Due to the large difference between these two values ​​in the initial phase of etching, a narrow through channel with a diameter of several nanometers is quickly formed at the place of the track. Subsequent etching leads only to an increase in the channel diameter. In this way, micro- and ultrafiltration membranes are obtained, the thickness of which usually lies in the range of 6-20 μm, and the pore diameter can be set anywhere from 10 nm to several micrometers. Membranes of this type, called track-etch membranes, differ from all other polymeric membranes in their precise pore size and narrow pore size distribution. The disadvantage of track membranes, especially in the case of small pore diameters (10-100 nm), is the low performance in the filtration of liquid media. Since the pore channels of track membranes are almost cylindrical, a channel 10 μm long and 10 nm in diameter has a very high resistance to the flow of a viscous medium.

A further improvement of track membranes and the method of their preparation was the method described in the patent. According to this method, a dielectric film irradiated with heavy ionizing particles is chemically etched on one side while the other side of the film is in contact with a neutralizing solution. The result is a membrane with conical pores, that is, uniformly increasing from one side to the other. The side of the membrane with the smaller pore diameter is actually the selective layer. The underlying film layer with expanding pores acts as a substrate. Asymmetric track membranes, with proper choice of pore cone angle and pore density, are characterized by higher specific filtration performance and at the same time high selectivity.

In the patent, this method is also extended to a continuous method for obtaining a membrane. It is based on the fact that three films stacked together (“sandwich”) are passed through the pickling solution, of which the upper and lower layers are a polymer irradiated with particles, and the middle layer is a porous material impregnated with a neutralizing agent. For example, if etching is carried out using a caustic alkali solution (NaOH, KOH), then an acid solution (for example, H 2 SO 4) serves as a neutralizing reagent. This method, acceptable in principle, has never been implemented in practice due to obvious difficulties. The pickling solution penetrates into the neutralizing layer through the ends of the three-layer "sandwich", disrupting the process. For this reason, obtaining a high quality membrane is impossible.

Subsequently, other methods for manufacturing asymmetric track membranes were proposed. In one of them, using plasma-chemical graft polymerization, a layer of polyallylamine or another polymer is deposited on one of the surfaces of a conventional (symmetrical) track membrane. Depending on the conditions and duration of the process, a layer is formed with a thickness from tenths to several micrometers. The pore diameters in this layer are smaller than those in the substrate membrane. Thus, the resulting structure has bottle-shaped pores. It is proposed to obtain a similar structure by treating a polymer film irradiated with ions with plasma under such conditions that the polymer is predominantly crosslinked in the near-surface layer (the formation of a "protective layer"). During subsequent etching, the cross-linked polymer is etched more slowly than the initial one. Therefore, in the plasma-treated layer, the pores have sharp narrowings. The disadvantage of both these methods is the complexity of the technical implementation. In order for the pore sizes in the selective layer to be uniform, very precise conditions must be maintained. Both plasma-chemical grafting and plasma-chemical crosslinking strongly depend, for example, on oxygen impurities in the reaction medium and in the processed polymer film. Small difficult-to-control impurities that disrupt the course of the process hinder the practical implementation of these methods.

A similar technical solution is a track membrane described in RF patent No. 2220762. The membrane is a polymer film pierced by hollow channels having a shape close to cylindrical over most of the film thickness and tapering towards one of the surfaces. A method for producing such a membrane includes irradiating a polymer film with a stream of heavy charged particles, for example, an accelerated ion beam, and subsequent chemical etching, characterized in that chemical etching is carried out in a solution containing at least two dissolved components, one of which is an etching agent, and the second - surfactant, as well as carry out additional processing, providing partial destruction and hydrophilization of one side of the film, which is carried out before chemical etching. Such a membrane has a higher specific performance than a conventional track membrane with the same pore diameter, since its resistance is determined by a thin selective layer. The thickness of this layer is about 1 µm. The rest of the membrane thickness (typically 9-20 µm) is actually the substrate. The diameter of the pore channels in the substrate is several times (2-4) larger than in the selective layer. The maximum porosity (volume fraction of pores) of the substrate is limited by the required level of mechanical strength and is 15–30% depending on the membrane thickness. In connection with the above ratio between the diameters of the channels in the substrate and in the selective layer, the maximum porosity of the selective layer does not exceed 7-8%. As the degree of asymmetry increases, the porosity on the selective surface becomes even smaller. The low porosity in the selective layer limits the specific performance of the membrane. This circumstance is a disadvantage of the membranes obtained according to the patent of the Russian Federation No. 2220762.

In order to eliminate this shortcoming, it was proposed to create a track membrane with an additional array of pores in the selective layer. To do this, it is proposed to modify the structure of the track membrane so that the selective layer contains pores ending in the depth of the film and oriented at an angle to the array of through pores. It was assumed that due to the non-parallelism of the axes of the channels in these arrays, the pores would have intersections. Thus, blind pores will contribute to the transport of a viscous medium across the membrane. Due to non-through pores, the porosity in the selective layer increases and the mechanical strength of the substrate layer (in which the number of pores does not increase) is preserved. The disadvantage of this technical solution is that the sign of "non-parallelism of the axes of the pore channels" as such does not solve the problem. To ensure the operability of the entire pore system, it is necessary that all non-through pores intersect with the pores of another array that has exits to the other side of the membrane. Arrays of non-parallel pores may practically not intersect in the following cases:

If the thickness of the layer in which the channels of the two considered arrays are located is small;

If the volumetric porosity of the membrane is insufficient, and therefore the pore channels are structural elements separated by large distances;

If the angle between the axes of the channels of the arrays under consideration is not large enough;

If all three or any two of the factors listed above are active at the same time.

Thus, the technical solution proposed in was rather a statement of the problem than its solution. It did not ensure the operability of an additional array of non-through pores.

The present invention considers the technical solution as the closest analogue and solves the problem of increasing the efficiency of the selective layer of the track membrane and, thereby, the problem of increasing the specific productivity of the membrane in the filtration process.

This problem is solved by the fact that the porous membrane, which is a film containing at least two arrays of straight hollow channels with constrictions in the near-surface layer, and the axes of the channels belonging to different arrays are not parallel, and at least one of the arrays consists of non-through channels starting at the surface and ending in the depth of the film, contains a layer in which the channels of the non-through array are connected by intersections with the channels of another array that has exits to the other side of the membrane.

Thus, unlike the solution (the closest analogue), we introduce a feature that gives the membrane a new topological property - the requirement that the channels of a non-through array must be connected with the channels of another array by mutual intersections. In other words, the volume of pores belonging to both arrays under consideration must be a connected space (whereas arrays of simply nonparallel pores do not generally form a connected space). The layer in which the required number of intersections is provided can be called a connectivity layer. This layer can be located either near one of the membrane surfaces or in depth. Since there are pores in at least two massifs simultaneously in the connectivity layer, the volumetric porosity of this layer is higher than in the adjacent layers. In this regard, a useful solution is to place this layer deep in the membrane, which reduces the risk of damage to the selective layer by mechanical impacts on the membrane. This possibility, provided by the proposed technical solution, is another difference from the closest analogue, providing an advantage. In the following explanations, examples of the structure of the membrane are given when the connectivity layer is located in the thickness of the membrane.

The essence of the invention is illustrated in Fig.1-6. Within the framework of the proposed invention, several specific technical solutions are possible to achieve a beneficial effect. Fig.1-6 illustrate options for technical solutions.

Figure 1 shows one of the simplest structures of the proposed membrane. It contains an array of through pores 1, perpendicular to the surface and tapering to both surfaces of the membrane. The method for obtaining such pores is known (see, for example). In addition to this array, the membrane contains an array of inclined channels 2 starting at one of the film surfaces and ending in the thickness of the film. Due to the presence of an additional array of inclined channels, the total pore area on the lower surface of the membrane is significantly increased. Due to the fact that the channels belonging to different arrays are not parallel, they intersect each other; as a result, blind pores contribute to the permeability of the membrane. In practice, for example, in the case of a track membrane with a thickness of 23 μm, the density of through channels is 2 10 8 cm -2, the density and length of non-through channels are 2 10 8 cm -2 and 6 μm, respectively, the diameter of the channels in the thickness of the membrane is 0.2 μm , the angle between the through and non-through channels is 45°, and the random distribution of pores over the surface, the average number of intersections per channel is at least 2. Thus, the channels belonging to different arrays form a single porous system.

Figure 2 shows a section of a membrane having one array of through channels 1 and two arrays of non-through channels, one on each side (2 and 3). Due to this, an increase in porosity is achieved in both selective layers of the membrane.

3 shows the structure of a membrane containing two arrays of intersecting blind channels (3 and 4). Arrays can contain a different number of channels; channels can be of different lengths - this achieves a change in porosity in thickness according to the desired law. The structure in figure 3 is a demonstration of the possibility of manufacturing a membrane with a thickness greater than the path length of charged particles in the film. In practice, this possibility is very important.

Figure 4 illustrates another version of the structure of the membrane containing two arrays of mutually intersecting non-through channels, while the diameter of the channels decreases in the near-surface layer only on one side of the membrane. The array of non-through tracks 7 has no constrictions near the surface. Thus, the membrane has one selective layer 5 on the bottom surface of the membrane. Inclined blind channels 2 serve to increase the porosity of the selective layer 5. Layer 6, containing only one array of channels (in Fig.4 - the upper part of the membrane), is a substrate that provides the mechanical strength of the membrane and at the same time provides high permeability. Layer 5 with pores narrowing towards the surface determines the selective properties of the membrane. Layer 10 contains two arrays of pores - in this layer, the channels intersect, forming a single pore system of the membrane.

Figure 5 shows a configuration with a single selective layer consisting of two arrays of intersecting channels 3 and 2. The array of cylindrical channels 7 provides a certain porosity and permeability of the "substrate" layer of the membrane. Arrays of pores 2 and 3 tapering to the surface provide the necessary porosity in the selective layer. Layer 10 is marked in the thickness of the membrane, inside which there is an intersection of pore channels belonging to different arrays.

In order to increase the number of intersections, the number of arrays of both end-to-end and non-through channels can be significantly larger. Fig.6 shows a variant when the membrane contains two arrays of inclined through channels 8 and 9 and one array of non-through channels oriented perpendicular to the surface.

For the manufacture of membranes having the described structure, the following method is proposed that solves the problem.

The problem is solved by the fact that in the method of manufacturing a porous membrane, which is a film containing at least two arrays of straight hollow channels having constrictions in the near-surface layer, moreover, the axes of the channels belonging to different arrays are not parallel, and at the same time at least one of arrays consists of non-through channels starting at the surface and ending in the depth of the film, which includes irradiation of the polymer film with heavy charged particles and subsequent chemical etching, the membrane contains a layer in which the channels of the non-through array are connected by intersections with the channels of another array that has exits to the other side of the membrane , moreover, an array of non-through channels is obtained by irradiating the film at an angle α i to the normal to the film surface with particles with a range R i , fluence n i , and the values ​​α i and R i are selected from the condition R ic cos α i

Hdn i sinβ ij / cosα i ≥1,

where H is the thickness of the layer in which the i-th and j-th arrays of channels intersect, β ij is an acute angle formed by the intersecting axes of the channels belonging to the i-th and j-th arrays.

The principle of creating arrays of pores that intersect each other at a certain angle is illustrated in Fig.7. In a film of thickness L, intersecting channels are shown, belonging to different arrays, having lengths R i and R j, and entering the film at different angles. The film layer in which the channels intersect is characterized by the thickness H.

8 and 9 show how an increase in the angle β ij between channels belonging to different arrays leads to an increase in the number of channel intersections, with the same layer thickness H and the same number of channels per unit area of ​​the film surface in each of the arrays.

10 illustrates the fact that as the angle α i increases, the number of intersections of channels belonging to different arrays also increases. When interpreting FIGS. 8-10, it should be remembered that they are two-dimensional projections of three-dimensional objects. This means that the intersection of channels on projections does not necessarily mean the intersection of pore channels in space. However, the number of intersections on two-dimensional projections is proportional to the number of intersections in space (ceteris paribus). In addition to the angular characteristics of arrays of pores, the probability of their intersection in three-dimensional space is affected by the density and diameter of the pores. In order for the pore belonging to the j-th array to almost certainly intersect with at least one pore of the i-th array, it is necessary that the channels of the pores of the i-ro array form a “solid palisade” interactions. Mathematically, this condition is expressed as follows:

Р≥1, where Р=Hdn i sinβ ij /cosα i .

In this expression, the value of H/cosα i is the length of the section of the pores of the i-th array, located in a layer of thickness H. The value of Hdsinβ ij /cosα i is the projection area of ​​the specified section on the plane perpendicular to the pores of the j-th array. When calculating the projection area, we neglect the change in the pore diameter in the near-surface layer, since the thickness of the latter is less than 1 μm. The value of Hdn i sinβ ij /cosα i is the total area of ​​the projections of the pore sections localized in the layer of thickness H and belonging to the i-th array per unit area of ​​the membrane surface. In the case when the value of Hdn i sinβ ij /cosα i is several times greater than unity, each pore of the j-th array experiences several intersections with the pores of the i-th array. Accounting for tangent merging of pore channels doubles the number of intersections.

Non-fulfillment of the condition introduced by us (P≥1) leads to the absence of the desired technical result. For example, with a combination of parameters H, d, n i , β ij and α i such that P takes a value of 0.1, only a small fraction of the pores of the non-through array is associated with the main pore structure of the membrane. At the same time, this array of pores practically does not contribute to the performance of the membrane, but worsens its mechanical strength. At P=0.01, the non-through array of pores does not completely participate in the transport of a viscous medium through the membrane. The use of the proposed method is especially important if it is required to form a small thickness connectivity layer. In this case, an intuitive choice of structure parameters or a trial and error method have little chance of success.

To obtain pores according to the proposed method, the method of selectively etched tracks produced by high-energy heavy charged particles in dielectrics is used. The principle of creating intersecting arrays of pores is illustrated in Fig.11. The polymer film 11 is transported in the direction indicated by the arrow 14. A beam of heavy charged particles 12, such as accelerated heavy ions from an accelerator, passes through the film, leaving tracks penetrating the film from one surface to another. A beam of heavy charged particles of lower energy 13 falls on the film at a different angle and leaves tracks in it that end in the thickness of the film at a certain depth. By adjusting the energy of the particles, tracks of the required length are obtained. Irradiation of a polymer film with beams of particles with different energies can be carried out sequentially: first, the film is treated with a beam of particles of one energy, and then with a beam of particles of another energy.

To obtain arrays of tracks of different lengths entering the film at different angles, one and the same beam of heavy charged particles can be used; in this case, the formation of different arrays occurs simultaneously. Figure 12 shows the film 11, enveloping the cylindrical shaft 15 at the moment of irradiation. The beam of charged particles 12, for example, accelerated heavy ions, passes through the window 16, the upper and lower sections of which are covered with a thin metal foil 17 (here the term "thin" means that the film is not thick enough to completely trap the particles passing through it). Particles passing through the open part of the window fall on the film and leave through tracks in it. Particles passing through the metal foil (they are conditionally shown in Fig.12 by shorter arrows) lose some of their energy and do not penetrate the film through. They leave tracks in the film that stop in the thickness of the film. By changing the thickness of the metal foil, non-through tracks of the desired length are obtained.

Irradiation of a film on a cylindrical shaft makes it possible to create arrays of tracks that fill a certain interval of angles. In this regard, the mathematical expressions for the conditions for the formation of the membrane structure are somewhat modified. If an array of non-through channels is obtained by irradiating the film in the range of angles [α i   max , α i   max ] to the normal to the film surface, then the values ​​α i   min , α i   max and R i are chosen from the condition that R icos α i

Hdn i (sinβ ij) cp /(cosα i) cp ≥1,

where H is the thickness of the layer in which the i-th and j-th arrays of channels intersect, (sinβ ij) cp is the average value of the sine of the acute angle formed by the intersecting axes of the channels belonging to the i-th and j-th arrays, (cosα i ) cp is the mean value of the cosine in the range of angles [α i   min , α i   max ].

The polymer film, in which arrays of intersecting tracks are created using the methods described above, is subjected to chemical treatment (etching), as a result, a system of hollow channels is formed in the film. Thus, a porous membrane is obtained. By carrying out chemical etching in the presence of a surfactant, as described in , channels are obtained with constrictions in the surface layer on both sides of the membrane, that is, the structures depicted in Figs. 1-3. If the original polymer film has denser surface layers that are more resistant to chemical etchants than the material in the thickness of the film, then such structures can be obtained without adding surfactants to the etching solution. For example, this can be achieved using polycarbonate films. When using polyethylene terephthalate films, which are generally uniform in thickness, it is necessary to add surfactants to the etch solution. The permeability of pores narrowing to the surface and the strength of the membrane depend on the ratio of the diameter of the pore channels on the surface to the diameter of the channels in the thickness of the membrane. As shown by us in , the optimal ratio for track membranes is characterized by a wide maximum lying in the range from 1:1.5 to 1:5. In this range, an increase in productivity (permeability) is achieved without loss of mechanical strength.

Membranes with an asymmetric structure, the pores of which are narrowed only on one side of the membrane (see Fig.4-6), are obtained by processing the polymer film, which provides partial degradation and hydrophilization of the polymer on one side of the film. Processing is carried out before chemical etching. This treatment consists of exposure to ultraviolet radiation or plasma in an oxygen-containing atmosphere. As a result of exposure to radiation, a partial destruction of the near-surface layer of the film material occurs. When using UV radiation, its wavelength is selected so that it is absorbed in a thin near-surface layer. In other words, the desired wavelength lies near the material's transparency limit with respect to electromagnetic radiation. For example, in the case of a polyethylene terephthalate film, the required wavelength is 310-320 nm, and in the case of a polycarbonate film, 280-290 nm. The rate of etching of the destructed near-surface layer during the subsequent immersion of the film in the etchant is higher than for the undestructed material. Therefore, the shape of the pore channels formed during etching is asymmetric: on the untreated side of the film, the pores have a sharp narrowing, while on the treated side, the narrowing is less pronounced. With further etching, the destructed layer on the machined side is completely removed. Thus, an asymmetric membrane is obtained, consisting of a large-pore substrate and a thin selective layer with small pores. In this case, the number density of pores in the substrate and in the selective layer is different. Due to the above methods of irradiation with heavy charged particles, the number of pores per unit area of ​​the selective layer is greater than the number of pores per unit area of ​​the reverse side of the membrane (substrate).

One of the main advantages of the proposed method is that it can be easily implemented in the industrial production of track membranes. All stages of film material processing are carried out in a continuous mode. The film in the form of a roll 20-60 cm wide and tens-thousand meters long enters the operation of irradiation with heavy charged particles, where it is rewound at a speed of 1-100 cm/s under a scanning particle beam. Part of the beam is passed through a metal or other foil of the required thickness in order to reduce the energy of the particles to the desired level. The film is transported in such a way that particles of different energies fall on the film at different angles (for example, as shown in Fig. 12). The resulting roll of particle-irradiated film then proceeds to a second stage of treatment, for example with UV light, where it is rewound so that only one side of the film faces the radiation source. The rewind speed is chosen so that the required exposure is achieved. Depending on the number and intensity of UV radiation sources, the film rewind speed can be 1-100 cm/min. In the third stage, the film passes through an etching machine, as in the usual method for producing track membranes.

Specific options for implementing the proposed method are illustrated by the following examples.

Example 1 A polyethylene terephthalate (PET) film 23 µm thick, 320 mm wide and 2 m long was irradiated perpendicular to the surface with a scanning beam of accelerated krypton ions with an energy of 250 MeV so that the ion track density was 2×10 8 cm -2 . During irradiation, the ions pierced the film through. Next, the film was divided into two parts (A and B), 1 m each. Part A was left as a control. Part B was re-irradiated from both sides with a scanning beam of Kr ions with an energy of 20 MeV at an angle of 45° (cosα i =0.707) at the same beam intensity n i as during the first irradiation. The range of 20-MeV krypton ions in the polymer was 5 μm. The thickness of the intersection layer H was about 3.5 μm. Further, both parts A and B were exposed for 60 minutes to air with filtered radiation from LE-30 UV lamps, so that the spectrum of radiation incident on the samples contained only a component with a wavelength of more than 315 nm. The power of the incident UV radiation was 5 W m -2 . Samples A and B thus sensitized were immersed in 6 M NaOH supplemented with 0.01% sodium dodecylbenzenesulfonate surfactant and treated at 60° for 6 minutes. The resulting membranes and their cleavages were examined in a scanning electron microscope. The average pore diameter on the surface was 0.1 µm. The pore density was 2×10 8 cm -2 in sample A and 4×10 8 cm -2 in sample B. The average pore diameter d in the depth of the film was determined on the chips of the samples and amounted to 0.25 μm. The intersection of through and non-through arrays of pores was achieved due to the fact that the value of the parameter Hdn i sinβ ij /cosα i was 1.7 (this value is the sum of the values ​​H=3.5×10 -4 cm, d=0.25×10 - 4 cm, n i =2×10 8 cm -2 , sinβ ij =0.707, cosα i =0.707). The strength of the resulting membranes was studied by determining the differential pressure destroying the membrane covering a round hole with an area of ​​1 cm 2 . For specimens A and B, the fracture pressure was 0.32 and 0.27 MPa, respectively. The initial specific productivity of membranes in distilled water was measured at a pressure drop of 0.1 MPa and amounted to 4 and 7 ml/min/cm 2 for samples A and B, respectively. Thus, the application of the proposed method made it possible to obtain a membrane with the same pore diameter in the selective layer and significantly better performance with a slight loss of mechanical strength.

Example 2 A polyethylene terephthalate (PET) film 23 µm thick, 320 mm wide and 2 m long was irradiated perpendicular to the surface with a scanning beam of accelerated krypton ions with an energy of 250 MeV so that the ion track density was 2×10 8 cm -2 . During irradiation, the ions pierced the film through. Next, the film was divided into two parts (A and B), 1 m each. Part A was left as a control. Part B was repeatedly irradiated from one side with a scanning beam of Kr ions through an ion energy-reducing foil at angles of ±45° at the same beam intensity as during the first irradiation. Further, both parts - A and B - were exposed for 120 minutes in air with unfiltered radiation from LE-30 UV lamps on one side. The power of the incident UV radiation was 5 W m -2 . Samples A and B thus sensitized were immersed in 6 M NaOH supplemented with 0.01% sodium dodecylbenzenesulfonate surfactant and treated at 60° for 6 minutes. In this way, membranes corresponding to the structure shown in FIG. 5 were obtained. The resulting membranes and their cleavages were examined using a scanning electron microscope (SEM). SEM images are presented in Fig.13. Fig.13a shows the structure of the sample A, containing one array of parallel through channels, tapering at the top (selective) surface. 13b shows the structure of sample B containing two additional arrays of blind pores intersecting the array of through pores at angles of ±45°. The electron micrographs clearly show the intersections of pores belonging to different massifs, which ensure the formation of a single pore system. The thickness of the layer in which the intersections of pore arrays are localized is 5 μm. The pore density was 2×10 8 cm -2 in sample A and 4×10 8 cm -2 in the selective layer of sample B. Images of the non-selective and selective surfaces of sample B are shown in Figs. 13c and 13d, respectively. The average pore diameter on the selective surface was 0.14 µm. The average pore diameter on the non-selective side and in the depth of the membrane was 0.3 μm. On the SEM image in Fig. 13d, pore openings belonging to different arrays are clearly distinguishable: dark objects are channels extending inward perpendicular to the film surface; lighter objects are inclined pores belonging to non-through massifs and extending deeper at an angle of 45°. From the given geometric characteristics of the membrane, it is easy to calculate that for each of the non-through arrays, the value of Hdn i sinβ ij /cosα i is 1.5.

The strength of the resulting membranes was studied by determining the differential pressure destroying the membrane covering a round hole with an area of ​​1 cm 2 . For specimens A and B, the fracture pressure was 0.32 and 0.27 MPa, respectively. The initial specific productivity of membranes in distilled water was measured at a pressure drop of 0.1 MPa and amounted to 4 and 6.5 ml/min/cm 2 for samples A and B, respectively. Thus, the application of the proposed method made it possible to obtain a membrane with the same pore diameter in the selective layer and significantly better performance with a slight loss of mechanical strength.

Example 3 A polyethylene terephthalate (PET) film 23 µm thick, 320 mm wide and 2 m long was irradiated with a scanning beam of accelerated krypton ions with an energy of 250 MeV so that the ion track density was 1.5×10 8 cm -2 . During irradiation, the film went around a cylindrical roller, the diameter of which and the vertical size of the beam were chosen so that the ions created tracks in the film in the range of angles from -30° to +30° relative to the normal to the surface. The ions penetrated through the film. Next, the film was divided into two parts (A and B), 1 m each. Part A was left as a control. Part B was repeatedly irradiated from one side with a scanning beam of Kr ions with an energy of about 30 MeV and with the same angular distribution (±30° relative to the normal to the surface). The density of the tracks created during the second irradiation was 2×10 8 cm -2 . Further, both parts - A and B - were exposed for 180 minutes in air with unfiltered radiation from LE-30 UV lamps. The power of the incident UV radiation was 8 W m -2 , while the power of the incident radiation in the ranges >320 nm and<320 нм составляла соответственно 5 Вт м -2 и 3 Вт м -2 . Сенсибилизированные таким образом образцы А и Б погрузили в 6 М NaOH с добавлением 0,025% поверхностно-активного вещества сульфофенокси додецилдисульфонат натрия и обрабатывали при 70° в течение 6 минут. Полученные мембраны и их сколы исследовали в сканирующем электронном микроскопе. Средний диаметр пор на поверхности, на которую падало УФ-излучение, составил 0,4 мкм. Средний диаметр пор на противоположной поверхности составил 0,2 мкм. Плотность пор составила 1,5×10 8 см -2 на обеих сторонах мембраны А. В мембране Б плотность пор на стороне с большим диаметром составила 1,5×10 8 см -2 , а на стороне с меньшим диаметром - 3,5×10 8 см -2 . Средний синус угла β ij между треками, принадлежащим двум массивам в образце Б, составил 0,48 (он рассчитывается как среднее значение синуса в интервале углов от 0 до 60°). Средний косинус угла α i наклона треков несквозного массива по отношению к нормали к поверхности составил 0,96. Таким образом, набор величин, определяющих вероятность пересечений массивов пор, выглядит следующим образом: Н=4,8×10 -4 см, d=0,4×10 -4 см, n i =2×10 8 см -2 , (sinβ ij) ср =0,48, (cosα i) cp =0,96. Численное значение параметра, определяющего вероятность пересечений каналов, составляет 2. Прочность полученных мембран была исследована методом определения разностного давления, разрушающего мембрану, закрывающую круглое отверстие площадью 1 см 2 . Для образцов А и Б давление разрушения составило 0,30 и 0,25 МПа, соответственно. Начальная удельная производительность мембран по дистиллированной воде была измерена при перепаде давления 0,1 МПа и составила 11 и 20 мл/мин/см 2 для образцов А и Б, соответственно. Точка пузырька, измеренная при смачивании мембран этанолом, найдена одинаковой для А и Б и равной 0,28 МПа. Таким образом, применение предложенного метода позволило получить мембрану с тем же диаметром пор в селективном слое и существенно лучшей производительностью при незначительной потере механической прочности.

Electron micrographs of the two surfaces of the membrane A are shown in Fig.14, a and b. Figs. 14c and d show electron micrographs of two surfaces of membrane B. Comparison of Figs. 14b and d shows that sample B significantly outperforms sample A in hole density on the selective side. Fig.14e shows a cleavage of membrane B, on which arrays of intersecting pores are visible. The membrane faces the side with the larger pore diameter up. The lower layer of the membrane, about 8 µm thick, contains an additional array of inclined (at different angles) channels.

15 shows the performance of the proposed membrane compared to existing track membranes of the same rating (0.2 µm). Graphs of the dependence of the volumetric flow rate of water on the filtration time are presented for membrane B from this example (curve 3), for an asymmetric track membrane obtained according to the method (curve 2), and for a track membrane of a conventional structure (curve 1). Filtration was carried out at a pressure drop of 0.02 MPa, using a filter holder with an area of ​​17 cm 2 . The presented dependencies show that the proposed membrane has an even greater advantage in terms of the volume of liquid filtered over a relatively long period of time than in terms of initial performance.

Example 4. A polycarbonate film 20 µm thick, 300 mm wide and 2 m long was irradiated with a scanning beam of accelerated krypton ions with an energy of 250 MeV in the range of angles ±30° to the normal so that the ion track density was 2×10 9 cm -2 . During irradiation, the ions pierced the film through. Next, the film was divided into two parts (A and B), 1 m each. Part A was left as a control. Part B was repeatedly irradiated from both sides with a scanning beam of Kr ions with an energy of 20 MeV and the same angular distribution (±30°). The track density during repeated irradiation was 3×10 9 cm -2 . Further, both parts - A and B - were exposed for 20 minutes in air with filtered radiation from LE-30 UV lamps. Samples A and B thus sensitized were immersed in 3M NaOH supplemented with 0.01% sodium dodecylbenzenesulfonate surfactant and treated at 70° for 2.5 minutes. The resulting membranes and their cleavages were examined in a scanning electron microscope. The average pore diameter on the surface was 30 nm. The pore density on both surfaces was 5×10 9 cm -2 in sample B and 2×10 9 cm -2 in sample A. The average pore diameter in the depth of the film was determined on the chips of the samples and amounted to 90 nm. The initial specific productivity of membranes in distilled water was measured at a pressure drop of 0.1 MPa and amounted to 0.35 and 0.6 ml/min/cm 2 for samples A and B, respectively.

Example 5. A polyethylene phthalate film 23 μm thick, 300 mm wide and 2 m long was irradiated with a scanning beam of accelerated xenon ions with an energy of 150 MeV at an angle of 0° to the normal so that the ion track density was 2×10 9 cm -2 . During irradiation, the ions penetrated the film to a depth of 20 μm. Next, the film was divided into two parts (A and B), 1 m each. Part A was left as a control. Part B was repeatedly irradiated from the opposite side with a scanning beam of Xe ions with an energy of 40 MeV at angles of ±45° to the normal. The track density during repeated irradiation was 3×10 9 cm -2 . Further, both parts - A and B - were exposed on one side for 200 minutes in air with unfiltered radiation from LE-30 UV lamps. In this case, sample B was exposed from the side with a lower track density. The power of the incident UV radiation was 8 W m -2 . Samples A and B thus sensitized were immersed in 3 M NaOH supplemented with 0.025% sodium sulfophenoxy dodecyl disulfonate surfactant and treated at 90° for 4 minutes. The average pore diameter on the surface not exposed to UV radiation was 35 nm. The average pore diameter on the reverse side of the membrane was 60 nm.

The numerical value of the parameter that determines the probability of crossing the channels, the sum of the values ​​H=6×10 -4 cm, d=0.06×10 -4 cm, n i =3×10 9 cm -2 , sinβ ij =0.707, cosα i = 0.707 and is 1.1.

The initial specific productivity of membranes in distilled water was measured at a pressure drop of 0.1 MPa and amounted to 0.4 and 0.7 ml/min/cm 2 for samples A and B, respectively.

Thus, the presented materials show that the proposed technical solution makes it possible to obtain track membranes with selective layers of high porosity, which ensures an increase in the specific performance of track membranes.

Literature

1. Loeb S., Sourirajan S. Adv. Chem. Ser. 38 (1962) 117.

2. Mulder M. Introduction to membrane technology. M., Mir, 1999, p.167.

3. Price P.B., Walker R.M. Pat. US 3,303,085, B01D, 2/1967.

4. Bean C.P., DeSorbo W. Pat. US 3,770,532,11/1973.

5. Dytnersky Yu.I. et al. Colloid Journal, 1982, vol. 44, No. 6, p. 1166.

6. Nechaev A.N. and other membranes. VINITI, M., 2000, No. 6, p.17.

7. Apel P.Yu., Voutsadakis V., Dmitriev S.N., Oganesyan Yu.Ts. Patent RF 2220762. Prior. 09/24/2002. Published 01/10/2004.

8. Apel P.Yu., Dmitriev S.N., Ivanov O.M. application RU 2006124162, publ. 01/20/2008, B01D 67/00, (abstract), BIPM, 2008, No. 2, p.114.

9. Apel P.Yu. and Dmitriev S.N. Membranes, VINITI, M., 2004, No. 3 (23), p.32.

10. Apel P.Yu. and others. Colloid journal, 2004, v.66, No. 1, p.3.

1. A porous membrane, which is a film containing at least two arrays of straight hollow channels with constrictions in the near-surface layer, while the axes of the channels belonging to different arrays are not parallel, and at the same time, at least one of the arrays consists of non-through channels , starting at the surface and ending in the depth of the film, characterized in that the membrane contains a layer in which the channels of a non-through array are connected by intersections with the channels of another array.

2. The membrane according to claim 1, characterized in that the channels have constrictions at only one surface of the membrane, and at least one array of non-through channels extends to this surface.

3. The membrane according to claim 1, characterized in that the channels have constrictions at both surfaces of the membrane.

4. The membrane according to claim 3, characterized in that it contains at least two arrays of blind channels, at least one of which faces one surface, and at least one of which faces another surface.

5. The membrane according to claim 1, characterized in that the ratio of the diameter of the channels on the surface to the diameter of the channels in the thickness of the membrane is in the range from 1:1.5 to 1:5.

6. A method for manufacturing a membrane, which is a film containing at least two arrays of straight hollow channels having constrictions in the near-surface layer, while the axes of the channels belonging to different arrays are not parallel, and at the same time, at least one of the arrays consists of non-through channels starting at the surface and ending in the depth of the film, and including irradiation of the polymer film with heavy charged particles and subsequent chemical etching, characterized in that the membrane contains a layer in which the channels of a non-through array are connected by intersections with the channels of another array, and an array of non-through channels is obtained by irradiation of the film at an angle α i to the normal to the film surface by particles with range R i , fluence n i , and the values ​​of α i and R i are chosen from the condition
R i cosα i where L is the film thickness;
in this case, etching is carried out until the diameter of the channels in the thickness of the membrane d is reached, which is selected from the condition
Hdn i sinβ ij /cosα i >1,
where H is the thickness of the layer in which the i-th and j-th arrays of channels intersect;
β ij - acute angle formed by the intersecting axes of the channels belonging to the i-th and j-th arrays.

7. A method for manufacturing a membrane according to claim 6, characterized in that the etching is carried out in a solution containing a surfactant.

8. A method for manufacturing a membrane according to claim 6, characterized in that, in order to obtain narrowing of the channels on only one side of the membrane, before chemical etching, the polymer film is treated on one side with ultraviolet radiation in an oxygen-containing atmosphere.

9. A method for manufacturing a membrane according to any one of claims 6 to 8, characterized in that a polyethylene terephthalate film is taken as a polymer film.

10. A method for manufacturing a membrane according to any one of claims 6 to 8, characterized in that a polycarbonate film is taken as a polymer film.

11. A method for manufacturing a membrane according to any one of claims 6-8, characterized in that a polyethylene naphthalate film is taken as a polymer film.

12. A method for manufacturing a membrane according to any one of claims 6-8, characterized in that multiply charged ions accelerated on an accelerator, for example, a cyclotron, are used as heavy charged particles.

13. A method for manufacturing a membrane according to claim 12, characterized in that to create arrays of through and non-through channels in the membrane, the same beam of accelerated ions is used, at least one part of which is passed through a foil that reduces the energy of ions, the thickness and material of which is chosen depending on the ion energy from the condition R i cosα i

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The invention relates to a technology for producing composite membranes for membrane separation of liquid and gaseous media with a selective layer containing multiwalled carbon nanotubes (CNTs). The method includes forming a selective CNM layer on a polymeric microporous substrate using an ultrasonic disperser and subsequent drying. A selective layer 6-8 µm thick of CNTs and a solvent in the form of a stable colloidal mixture is formed by passing a 0.005-0.1% solution of this mixture through a substrate at a given pressure until a given selectivity is achieved. The invention provides an increase in the stability of the manufacturing process of a composite membrane with desired transport properties (selectivity and permeability) for membrane treatment of various media. 3 w.p. f-ly, 1 tab., 3 pr.

The invention relates to the field of membrane technology, and in particular to methods for manufacturing micro- and ultrafiltration membranes, and in particular to methods for manufacturing track membranes

Methods for obtaining membranes

membranes -(from Greek "partition") a device in the form of a thin dividing wall, which is inherent in semi-permeability, that is, the ability to pass some components of solutions (or mixtures) and retain others.

Membranes are classified according to five classification criteria.

For the nature of the material from which the membrane is made: polymeric, non-polymeric (inorganic). In turn, polymer membranes, depending on the chemical composition of the polymer, can be: cellulose, cellulose acetate, polyamide, polysulfone. polysulfonated copper, polyvinyl chloride, etc. Inorganic membranes: metal, ceramic, graphite, glass, polyphosphazene, etc.

Behind the porous structure: non-porous (diffuse) and porous. Porous are divided into isotropic and anisotropic, including asymmetric anisotropic. Isotropic membranes are characterized by the same pore diameter throughout the membrane volume. Anisotropic membranes are characterized by a gradual change in the pore diameter in their cross section, that is, the pore diameter gradually increases from the working to the membrane surface. Asymmetric anisotropic membranes are also characterized by an increase in the pore diameter from the working to the surface, but in this case, the membrane layers are clearly distinguished, within which the pores are approximately the same and differ markedly in size from the pores in the layers located above and below them.

In particular, asymmetric anisotropic membranes include the so-called composite membranes, in which the working (selective) and layers, as a rule, are obtained from porous materials different in chemical composition. Composite membranes also include heterogeneous ion-exchange membranes and filled membranes, including polymer-polymer membranes.

By geometric shape: membranes in the form of films, plates, tubes, cavity fibers. Films and plates are made in the form of disks, squares, rectangles, ellipses, etc. The thickness of film membranes is 100-150 microns, plates - 2-3 gg. tubes with an inner diameter of 5-25 mm, and cavity fibers with an inner diameter of 20-100 microns and a wall thickness of 10-50 microns.

For functional features: dialysis, electrodialysis (ion exchange), microfiltration, nanofiltration, ultrafiltration, reverse osmosis, pervaporation, gas separation, membranes with additional functions.

For the method of receipt and condition: dry, wet (swollen in a solvent) polymer, track, liquid (unlined and lined), dynamic, rigid structure membranes, which are obtained by application, spraying, deposition, seepage, sintering.

semi-permeable membranes. One of the important tasks in the implementation of the process of reverse osmosis and ultrafiltration is the choice of membranes, which should have: high permeability, selectivity, resistance to the action of separated solutions, sufficient mechanical strength, invariability of characteristics during operation and storage, low cost. Cellulose acetate type membranes treated for water permeability with magnesium perchlorate are most suitable. These membranes with pores of 0.3-0.5 nm are characterized by a high water transmission rate, separate salts and other substances, and have a high degree of swelling.

The performance of membranes in water after a few hours of operation under pressure is reduced by 30--50%, which is associated with their shrinkage (decrease in porosity). Dependences of selectivity and permeability on the operating time of the membranes are shown in Fig. . 3.1

The service life of membranes depends on the type, concentration of substances dissolved in water and other factors and ranges from several months to several years. However, these membranes are disadvantages: instability in acidic and alkaline environments, low mechanical strength, the need for storage and transportation in a wet state, aging.

A variety of racing semi-permeable membranes are hollow polymer fibers having an inner diameter of 20-100 microns with a wall thickness of 10-50 microns.

To improve the physical and mechanical properties of cellulose acetate membranes, it is recommended to apply the material on the surface of a porous substrate to form a semipermeable layer. These membranes are called dynamic. As a porous substrate, fibrous cellulose acetate treated with epoxy resin and withstanding a pressure of 4.5-7 MPa, polyelectrolyte films, porous carbon tubes, porous glass fiber tubes, metal and porcelain filters, etc. are used. Depending on the substrate material, the pore diameter ranges from 30 -6 to 50-4 cm.

Colloidal solutions of metal hydroxyls are used to form a semipermeable layer on substrates. (for example, Fe, Al, Zn, Zr, etc.), natural clays, finely divided ion exchangers, nylon threads, organic polyelectrolytes, etc.

Permeability up to 500-600 l/(m 2 h) was obtained on dynamic membranes with high selectivity reaching 90% for salts. Dynamic membranes are easy to manufacture, capable of self-healing by introducing small amounts of membrane-forming additives into wastewater.

Metal membranes, as well as membranes made of microporous glass, have rigidity, high chemical resistance, and are not destroyed by bacteria.

Methods for obtaining membranes. Among the materials that are used to make membranes, polymers will sit prominently. To a lesser extent, ceramics, graphite, glass, clay minerals and metals are used.

Methods for obtaining polymeric membranes are the most diverse, the most common and traditional is the coagulation method, or phase-inversion (soluble), a method that is used to obtain almost all types of membranes, with the exception of ion-exchange ones. The content of this method, which in technological practice has three options (dry-wet, dry and wet), consists in the fact that a concentrated polymer solution in the form of an applied gel film or fiber under the influence of external factors (precipitator, evaporation) is amenable to phase-dispersed transformations with the formation of a rather rigid porous film or fiber. Actually, the name of the method "coagulation" or "phase-inverse" reflects the physical content of the method. Technologically, the coagulation method is quite complex and multi-stage.

The main stages of the dry-wet version of this process are: the dissolution of the polymer in an organic solvent, which is freely miscible with water; purification of the solution from mechanical impurities; its degassing and composition adjustment; reformation of the membrane (partial evaporation of the solvent from the surface of a thin film of the solution poured onto the lining); sedimentation (coagulation) of the membrane with water (precipitant); flushing the membrane with water; hydrothermal treatment at 80-95 °С; defectoscopy; winding into rolls.

The dry version of the membrane formation consists in the complete evaporation of the polymer solution, that is, the membrane formation process ends at the stage of solvent evaporation, but not partial, as in the case of the dry-wet version, but complete. The dry version is used to obtain pervaporation and gas separation membranes that are non-porous (diffuse).

The wet version includes all steps except for preforming. It is used to obtain microfiltered membranes.

Resin Requirements. The polymer must: form a film from its concentrated solutions; dissolve well in solvents that are unrestrictedly miscible with water, which is a precipitant during membrane formation; be not brittle and not very hard, but not be an elastomer; be measured as hydrophilic when forming reverse osmosis, nano- and ultrafiltered membranes; be in a powdery state, which facilitates its dissolution.

Among other, less common methods for obtaining polymeric membranes, the following can be mentioned: formation of polymers from melts; thermal gelation (inversion); formation from polyelectrolyte complexes at the moment of their formation; irradiation of films with high-energy heavy particles with further etching of radiation tracks (track, or nuclear, membranes).

There are also dynamic membranes, which are obtained by applying mineral dispersions to the surface of a porous lining. Lipid-based liquid membranes exist in the free state as spherules filled with one or more components of a system that is separating, or liquid membranes on a porous lining. Inorganic membranes are obtained from mineral dispersions by sintering, sputtering, curing, precipitation or from colloidal solutions of certain metal oxides and hydroxides using sol-gel technology.

In recent years, work on the creation and industrial development of inorganic membranes has been developing rapidly. Already at present, about 10% of the membranes used for micro- and ultrafiltration are inorganic.

According to the chemical composition of the materials from which porous inorganic membranes are formed, they are divided into ceramic, glass, graphite, metal and composite (cermets, carbon graphite, ceramics on graphite, etc.).

Compared with polymeric inorganic membranes, they have a number of advantages that allow them to be used under specific technological conditions and, therefore, they do not replace, but primarily supplement, polymeric membranes.

The most important advantages of inorganic membranes are the following:

Ability to separate mixtures and solutions at high temperatures.

At high temperatures, the viscosity of the system to be separated decreases and, consequently, the specific performance of the membrane increases.

Elevated temperatures make it possible to remove a number of problems that arise during the cleaning and regeneration of membranes. They can be washed with hot strong solvents, including concentrated acids, alkalis, etc. If necessary, inorganic membranes can be purged with gas at high temperatures and pressure, which is unacceptable with respect to polymer membranes.

Spent inorganic membranes, in contrast to polymeric ones, can be regenerated by burning out the organic precipitate that has penetrated into their pores.

Stability in chemically and biologically aggressive environments, various solvents. Ceramic membranes can be used at any pH value of the medium. Ceramic membranes based on oxides of aluminium, zirconium and titanium have especially high chemical resistance.

3. The possibility of obtaining membranes with special properties and the regulation of these properties: for example, membranes can have catalytic properties; have a different surface charge; be hydrophobic or hydrophilic.

4. Ceramic membranes retain their properties when heated up to 1000 С, are capable of operating under high pressure (1-10 MPa), can be periodically subjected to steam sterilization at a temperature of 120 С (to obtain a stably sterile ultrafiltrate) or calcined to remove contaminants at a temperature 500 С.

However, the essential disadvantages of inorganic membranes are their high cost and fragility. One way to eliminate brittleness is to form composite membranes. This assumes the use of macroporous ceramic substrates as the basis for membranes, which can lead to an improvement in the functional characteristics of inorganic membranes and their physical and mechanical properties.

The functional characteristics of inorganic membranes are determined by many factors that must be taken into account during their production: accurate dosing of membrane-forming components and compliance with specified technological regimes at all stages of membrane production, the use of substances, reagents, solvents and inert gases of a high degree of purity, the state of the surface of the porous substrate and fine powders if they are used.

The high cost of ceramic membranes (3-5 times more than polymer membranes) is also compensated by their higher permeability up to 20,000 l/(hm 2 MPa) instead of 5000 l/(hm 2 MPa) for polymer membranes and a service life of up to 10 and more years instead of 1 year for polymeric membranes. Thus, the use of ceramic membranes quickly pays off due to higher performance and long service life.

The proportion of ceramic membranes is 58% of all inorganic membranes. Alumina occupies a dominant position among the ceramic materials used to obtain membranes (with the development of scientific research, other materials appear (silicon carbide, sialon, RuO 2, TiO 2, etc.) that can successfully compete with alumino-ceramics).

To date, industrial methods have been developed abroad for obtaining micro- (pore diameter of the order of 0.1–10 μm) and ultrafiltration membranes with pores in a selective layer with a diameter of ~ 10–50 nm.

A more difficult task is to obtain ceramic membranes for reverse osmosis processes. But it is likely that reverse osmosis ceramic membranes will be widely used in the future, which will make it possible to treat and desalinate hot, aggressive and highly polluted wastewater from various industries.

In recent years, for fine purification of liquid media, composite ceramic micro- and ultrafiltration membranes have been used, which consist of a substrate with a pore size of 1–15 μm, one or two intermediate layers (0.1–1 μm thick) and an upper working layer (3– 100 nm). The top layer can be chemically modified. The combination of the first two layers, called the primary membrane, is used for microfiltration. The secondary membrane is designed for ultrafiltration, while the chemically modified membrane is designed for reverse osmosis or gas separation.

Ceramic membranes for microfiltration are obtained from dispersed powders (usually oxides) with additions of hydroxides, carbonates, silicates, etc. by sintering them to form a cellular structure.

In the case of the formation of ultrafiltration membranes, the sol-gel process, various methods of applying fine dispersions, as well as the method of obtaining membranes based on anodic oxidized aluminum, are suitable.

At present, methods for obtaining ceramic membranes based on dispersed alumina have been most fully developed. Such membranes are characterized by mechanical strength and thermal stability. In addition, they are suitable for obtaining composite membranes using oxides of other multiply charged metals, since their linear expansion coefficients are close.

The traditional method for producing porous ceramic substrates is the sintering of powders (fillers) of a certain dispersion (quartz, glass, metal oxides) with binders, which can be liquid glass, clay minerals (kaolinite, montmorillonite), aluminophosphate binder, polymers. To increase the porosity of ceramics, in some cases, burnable (sawdust, flour, starch) or gas-forming (calcite, megnesite) additives are introduced. By adjusting the dispersion of powders, the amount and nature of binders, additives and the method of heat treatment of the mixture, a ceramic substrate with different porosity and permeability is obtained.

Ceramic membranes based on aluminum oxide powders have a porous structure with pore sizes of relatively large diameter (of the order of 100 nm - 10 μm) and are suitable for microfiltration.

The main indicators of a porous ceramic substrate obtained on the basis of aluminum oxide powders are affected by changes in the technological parameters of the process (pressing strength, corundum fineness, firing temperature, isothermal holding time, as well as the type and amount of binder).

The necessary strength properties of a porous ceramic substrate after formation and drying, as well as its physical and technical properties after sintering, are largely determined by the nature and amount of binders used. An increase in the amount of binder leads to a change in the water absorption of the total open porosity of the ceramic, as well as to a certain drop in the specific water permeability. In addition, an increase in the binder content results in a significant increase in the mechanical strength of ceramics and a slight increase in its shrinkage.

Resistance to aggressive media depends to a large extent on the nature and amount of binder used. Due to the fact that the structure of the porous material is a framework of corundum particles surrounded by a glassy phase of the binder, between which there are pores communicating with each other and the atmosphere, the chemical stability of the material is determined primarily by the stability of the glass located on the surface of the filler particles. Therefore, the process of destruction of such a material and its resistance to aggressive media is ultimately determined by the mineralogical composition of the cutting and the composition of the glass phase, the perfection of the structure of the resulting crystalline phases, as well as the nature of the aggressive agent and the temperature of exposure. Such glasses are intensively hydrolyzed under the action of alkali or acid, forming metal hydroxides and colloidal silicic acid as products. The latter remains on the glass surface in the form of a thin layer, and the course of further destruction already depends on the diffusion of water and hydrolysis products through this protective layer.

As a rule, industrial ceramic filters have a tubular shape, the production of which consists of two stages: first, a substrate is made, then a working layer (the membrane itself) is applied to it.

From aluminum oxide powders, which are characterized by a high uniformity of particles in size, tubular substrates with a wall diameter of 1-2 mm are obtained. The average pore size is 0.2-4 µm.

The manufacturing technology of ceramic tubular membranes from aluminum oxide powders differs in the composition of pastes (suspensions) and firing temperatures.

The method of obtaining ceramic substrates based on metal oxides is widely used in industry due to its economy, availability, and a number of other advantages. However, to ensure high performance of porous substrates, special care is required in the preparation of molding masses.

The use of standard methods of powder metallurgy by selecting a ceramic filler of the appropriate granulometric composition with its subsequent sintering makes it possible to obtain porous ceramic substrates with the required set of properties.

Composite ceramic membranes consist of two or more layers with different pore sizes.

The thickness of the inner microporous layer is usually in the range of 1-5 µm. A thin selective layer should have a uniform pore size adapted to the characteristics of the filtered material, good adhesion to the substrate.

Finely dispersed oxides are used as the starting material for applying the microporous layer. The formation of thin selective layers on the surface of a coarsely porous base is carried out by the methods described below.

Spraying from a dispersion spray gun onto a heated (35-40С) surface of the substrate. In this case, the thickness of the resulting layer is varied by the deposition time at a fixed distance between the spray gun head and the substrate surface. A modification of this method is that the surface is rotated. This approach makes it possible to obtain selective layers on a flat surface, but it is difficult to implement in the case of tubular porous substrates.

By applying dispersion onto the substrate surface rotating at a fixed speed. The layer thickness is determined by the slip concentration and its volume deposited on the substrate. This method is more economical than spraying according to the dispersion consumption.

sedimentation precipitation from the suspended dispersion of fractions containing particles of different sizes. First of all, large particles settle, as they settle, the size of the particles remaining in the volume decreases. This method is only suitable for flat substrates.

Immersion coated substrate into dispersion. This method is the most economical. The working layer of the membrane is obtained both on the outer and on the inner surface of the porous tubes. In the first case, the substrate tubes are dipped into a suspension with a total solid phase concentration of 10–20%. In the second case, the suspension is pumped through the tubes under a slight overpressure. Tubes with an outer diameter of 20 mm and a wall thickness of 2 mm fired at 1800°C have a porosity of 35%.

The inner filter layer with an average pore size of 1-2 μm is obtained by pouring the suspension onto the inner surface of the tube. The film remaining after pouring the suspension is dried and fired at 1550°C. The thickness of the resulting layer is 20-30 microns.

Sol-gel technology is that on the surface of the substrate there is a transition of the colloidal solution from the free-dispersed state (sol) to the bound-dispersed (gel).

Since sol particles can be obtained with almost the same size and spherical shape, membranes with fine pores and a narrow size distribution in the working layer can be made from them.

Sol-gel technology includes three main stages: obtaining a sol; depositing it on a porous substrate to form a gel; drying and roasting.

Sol for the preparation of ceramic membranes from metal hydroxides is obtained by hydrolysis of metal salts and alkoxides.

The stability of the sol depends on the pH of the medium. The gelation process proceeds most intensively at pH values ​​close to neutral.

The stability of the sol has a strong effect on the characteristics of the resulting gel: the more stable the sol, the denser the structure of the gel and the fewer macrocavities filled with the liquid phase.

To obtain uniform gel films on substrates, various macromolecular compounds (cellulose derivatives, polyvinyl alcohol) are added to the sol. Their number regulate the viscosity of the system.

The amount of high molecular weight additives and plasticizers is usually 2-5% of the total mass of the sol.

An important advantage of the sol-gel method is that firing temperatures are usually low (400–600°C and rarely exceed 1000°C), while powder sintering requires temperatures of the order of 1200–1800°C.

The membranes obtained by the sol-gel method are characterized by a narrow pore size distribution. The fraction of large nonselective pores is small in the working layer.

The disadvantages of the sol-gel technology are the shrinkage during sintering, the fragility of the membrane after drying, and the high cost of the initial organometallic compounds.

The high cost of the method can be reduced by switching from organic raw materials to salts of these elements capable of hydrolysis.

In addition to those described above, other methods for producing ceramic membranes are known, for example, doctor blade formation of thin layers from a disperal on a flat substrate. At the first stage of the process, a dispersion of the powder in a liquid is prepared, followed by the introduction of additives to obtain a suspension, which is then applied to the substrate using a doctor blade. After drying, the film is removed from the substrate, cut and laminated. The last operation - burning out organic additives and sintering is carried out under carefully controlled temperature conditions.

A known method involves the use of ceramic foam to obtain porous membranes. The essence of the foam method lies in the mixing of a refractory material with a foaming agent or with a separately prepared foam formed during the mechanical treatment of aqueous solutions of some surfactants. According to the ability to give fine-meshed foam, colloidal pore formers are arranged in a row: saponin, gelatin, albumin, pectin, casein. When ceramic slip and foam are mixed, solid particles are adsorbed and held onto the foam films, forming a mineralized foam. Further, drying and reaction sintering in nitrogen are carried out.

Ceramic foam technology is similar to water suspension casting technology, so much attention is paid to slip preparation. Also of great importance is the viscosity of the suspension, associated with humidity and pH. The foam method can produce materials and products with a very high porosity of 85-95%.

The method for obtaining a ceramic-crystalline material consists in obtaining a porous ceramic workpiece by foaming a slip based on Al 2 O 3, mullite ZrO 2 , SiC, etc. 400С and firing blanks at a maximum temperature of 1300С.

The disadvantages of this method are:

Insufficient fluidity of the foam mass, resulting in a heterogeneous structure of products with cracks and voids both on the surface and in a fracture;

High humidity of foam mass (up to 200% by weight);

Large volumetric shrinkage during drying (about 72%).

A feature of the structure of membranes obtained by this technology is a high porosity of 60–90% (pore diameter 0.1–0.4 mm).

Ceramic foam filters have high mechanical strength, allow steam treatment (120 С), and operate at low pressures.

Testing of porous ceramic foam membranes under industrial conditions confirms their chemical resistance and efficiency, however, this area of ​​membrane technology has not yet left the research stage.

Along with the methods described for the preparation of porous ceramic membranes, the method of obtaining membranes based on anodic oxidized aluminum is of considerable interest.

The ability of aluminum to form porous films with a defined morphology upon anodic oxidation makes them suitable for use as membranes having a narrow pore size distribution, high pore density and fineness.

A feature of the porous structure of membranes obtained by this method is the presence of a large number of parallel pores penetrating a densely packed hexagonal cellular structure.

It has been established that initially a thin dielectric layer is formed on the metal, which is called a barrier layer. The distance between the pores is approximately twice the thickness of the barrier layer, which in turn is proportional to the applied voltage with a coefficient of ~ 1.0 nm/V and inversely proportional to the rate of oxide dissolution in the electrolyte. Therefore, the size and density of the membrane pores are inversely proportional to the anodic potential.

The main problem in this method of obtaining membranes is the existence of a barrier layer that closes the base of the pores. Therefore, in order to apply the process of anodic oxidation of aluminum to obtain porous membranes, it is necessary to remove the barrier layer.

Four generations of ceramic membranes are currently being produced. The first generation membranes are isotropic tubes and plates, the second generation are anisotropic tubes, and the third generation are asymmetric composite tubes. The fourth generation membranes, which are composite multichannel monoliths with an asymmetric structure, have the highest performance characteristics. Fifth generation membranes have now been developed - with an ultra-thin working layer, which have catalytic activity.

Tubular ceramic elements are produced with a membrane channel diameter of up to 10-40 mm. To increase the mechanical strength, they are braided or made in stainless steel shells with linear expansion coefficients close to those of ceramics. If the latter condition is met, filter elements are obtained that are operable at temperatures up to 400 С.

Tubular elements with a membrane channel diameter of the order of 10-25 mm are usually successfully used for cleaning emulsions containing fats and oils with high adhesion to the membrane material. In such devices, it is possible to create the most developed turbulent regime of movement of the liquid to be purified.

Unlike polymer membranes, ceramic membranes do not compact with a significant increase in pressure, as a result of which their water permeability does not decrease.

The properties of ceramic membranes, their selectivity, and permeability depend on the firing temperature. For example, membranes annealed at 400°C show selectivity for polyethylene glycol and dextran with a molar mass of 3000, while membranes annealed at 800°C are selective for compounds with a molar mass of 20000.

Selectivity is regulated not only by the firing temperature of the ceramic membrane, but also by the amount of microadditives. However, the preparation of highly selective membranes that allow the separation of liquid mixtures of macromolecular compounds into narrow fractions still remains a complex and difficult task.

For the successful use of ceramic membranes, as well as membranes made of other materials, it is very important to create good hydrodynamic conditions in the apparatus, ensuring a low value of concentration polarization, and preventing the formation of gel and sediment on the membrane surface. With an increase in the turbulence of the flow of the separated solution, the retention coefficient of the membrane sharply increases.

According to their performance characteristics, ceramic microfilters have an advantage over metal ones. They not only have a higher water permeability, but are also characterized by a slower decrease in water permeability.

Until now, little attention has been paid to the technology of manufacturing flat ceramic membranes on a substrate. Ceramic membranes have been produced mainly in the form of tubes, however, the ability to pack several membranes into packages and thus produce compact elements with a much larger filtering surface per unit volume makes flat membranes more attractive for many applications.

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