JPH0536094B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing composite membranes suitable for gas separation and to composite membranes obtained by such a method. The idea of separating low molecular weight gases based on differences in permeation rates through solid films is not new. About 150 years ago, it was observed that natural rubber is more permeable to some gases than others. However, it is only in the past few years that membrane separation methods for gas separation have become recognized as a practical alternative to conventional cryogenic separation methods. The need for simple and energy efficient commercial methods has led to a wave of interest in applying membrane technology for gas separation. In 1866, the theory was proposed that the permeation of gas through a solid film is a three-step process consisting of the following steps: (1) dissolution of gas at one interface of the membrane, (2) diffusion of gas to the opposite interface, and (3) desorption, or release, of gas at the opposite interface. This mechanism, known as the dissolution-diffusion model of permeation, remains a useful explanation of the permeation process and serves as the basis for modern permeability theory. First, if we consider the second stage of the permeation process, diffusion,
Fick's law can be used to quantitatively describe the transport of low molecular weight gases across isotropic and homogeneous membranes. For a flat sheet-like membrane, the flux J is expressed by the following equation: J=-D∂C/∂X (1) where D is the local interdiffusion coefficient and C is the concentration of the gas at a distance x from the membrane interface.
Applying this equation across the film thickness (x = 0 to x
=l), it leads to Fick's law of the following form. J=D( _C2 - _C1 )/l (2) where _C2 and _C1 are the concentrations of the permeating gas just inside the film at each interface. Equation (1)
and (2) only account for the second stage of permeation, namely diffusion across the membrane. Furthermore, it is difficult to measure the concentration of gas at a specific point inside the membrane;
It is necessary to relate these concentrations to some external, more easily measured variable. According to Henry's Law, the concentration of dissolved gas, C, for a dilute solution is proportional to the partial pressure of the gas in contact with the solution. C=Sp (3) In the above formula, S is the solubility coefficient (the reciprocal of the constant of Henry's law). Combining equations (2) and (3), the permeability of the membrane to gas is expressed by the following equation: J=DSΔp/l=PΔp/l (4) where is the average permeability coefficient defined as the product of the average diffusion coefficient and the average solubility coefficient S,
and Δp is the pressure difference between the two sides of the membrane. Depending on the polymer/permeate system currently considered, and (therefore) are influenced by pressure and temperature. However, for simple gases such as oxygen and nitrogen, and are usually considered constant over a reasonable range of temperature and pressure for most polymers. Although the permeability of a particular gas may vary over many orders of magnitude between different polymers, the permeability of a particular polymer to various permeates falls within narrower ranges. . The ratio of one of these permeability coefficients to the other is a useful measure of the relative permeation rate of gas and thus the permselectivity of the membrane.
This quantity is called the ideal separation factor (α _ij ) and is defined by the following expression. α _ij =P _i /P _j (5) where _i and _j are the component i and j transmission coefficients, respectively, with the subscript i usually representing the more transparent component. A general theory often cited when selecting materials for membrane separations is that polymers that exhibit high selectivity for one component of a gas mixture often have low permeability, while polymers that are highly permeable also exhibit high selectivity for one component of a gas mixture. This means that there are fewer distinctions between them. Examples of permeability coefficients and ideal separation coefficients for many oxygen and nitrogen polymers are shown in the following table.

Table: In the table above, it can be seen that varies over values of orders of four between the polymers, but the values of α are of the same order of magnitude. There is also a relationship between low permeability and high selectivity and vice versa, although there is considerable overlap. One of the reasons for this observation is the influence of the physical state of the polymer on the diffusion process. Polymers are classified as existing in either a glassy or rubbery state, although no true change of state is involved. When a polymer is allowed to cool from the melt, it first forms a rubber-like material, and then, as the temperature is further reduced, a hard, brittle, glass-like material. The temperature at which a polymer transforms from a rubber-like substance to a glass-like substance is the glass transition point.
T _g . Below T _g , not enough thermal energy is available for anything other than a small range of cooperative motions of the chain segments. Above T _g , sufficient energy is available to move relatively long segments of the polymer chain. Free volume of the polymer is required to accommodate the motion of long chain segments. In addition to accommodating the chain segments, this free volume may be filled by permeate gas. Within rubbery polymers, the free volume should be considered as a dynamic system in which pores in the polymer matrix are successively created and filled by the movement of the chains. On the other hand, glassy polymers contain much less free volume than rubbery polymers, and the pores in the matrix are relatively spatially fixed. Because glassy polymers have a smaller total free volume, their permeability tends to be lower, while a narrower distribution of pore sizes makes it more difficult for these polymers to distinguish between molecules of different sizes. make it easy to do. When designing a permeation process for industrial gas separation, the primary concerns are product purity and production rate. Therefore, when selecting a membrane, a membrane is sought that exhibits a high specific permeability for the product and a low specific permeability for the other components of the mixture, i.e. a membrane that exhibits high permeability and high selectivity. . These properties are rarely found simultaneously in one polymer. This dilemma is an important factor in the development of membrane separation methods that are fully useful for industrial gas separation. Fortunately, membranes that exhibit high selectivity for one component of a gas mixture need not be abandoned solely because of low overall permeability. A closer look at equation (4) shows that the flux can be increased by increasing the pressure differential across the membrane or by decreasing the membrane thickness. Moreover, the permeator design also influences the flux as well as the membrane selectivity that can actually be achieved. In practice, membrane separation of gases is carried out by passing a feed stream of the gas mixture to be separated over the surface of the membrane, but allowing only a portion of the gas to permeate and leaving the unpermeated gas (ruffinate) Recirculate or send it to another permeation chamber. The driving force for gas permeation is the pressure differential across the membrane, which is maintained by either hydrostatic pressure on the feed side or vacuum on the product side of the permeation chamber, or both. Each passage of the gas mixture through the membrane is hereinafter referred to as a stage of separation, and the permeation fraction is referred to as the stage cut. The increase in the number of stages results in a product of higher purity than that obtained in a single stage process. However, the cost of recompressing the gas at each stage, as well as the cost of adding models, often makes implementation impossible. Stage cut also affects selectivity as well as permeation rate. The greater the amount of gas that is allowed to pass through, the lower the true degree of separation. The mode of gas flow across the surface of the membrane also affects the selectivity of the process. However, if the stage cut is very low, this effect will be minimal. Since the flux described in equation (4) is the permeation rate per unit area, another way to improve membrane productivity is by increasing the surface area of the membrane. Simply adding more modules is one way to increase surface area, but polymers often have low permeability to gases, requiring millions of square feet to produce a satisfactory permeation rate. This can make this method impractical. Considerable research has been devoted to the subject of packing membranes into structures that provide greater membrane surface per unit volume. The most successful 2
The types of seeds were spirally wound membranes and hollow fiber membranes. Hollow fibers in particular offer extremely high surface area to volume ratios. For example, a 0.3 m ³ membrane device contains a surface area as large as 500 m ² . In comparison, a spirally wound membrane has the same volume of 20 m ² . An additional advantage of using hollow fiber technology is the self-supporting nature of the hollow fibers, which minimizes the cost of manufacturing devices for housing the hollow fibers. It has been shown that the pressure difference across the membrane affects the membrane flux. It has been shown that the true separation of gas mixtures also depends on the pressure difference between the feed and product sides of the membrane. The ratio r of the pressure on the high pressure (feedstock) side of the membrane to the pressure on the low pressure (product) side of the membrane in the separation of two components, the molar fraction of the more permeable component in the feedstock X _A ,
Based on the ideal separation factor (α ^* ) as defined in equation (5), the following equation holds for the actual separation factor α: α = (α ^* +1) / 2 - (1 / r) (α ^* -1) / 2X _A -
1/2X _A ±{(α ^* −1/2) ² + (α ^* −1) − (1/r) [(α ^* ) ² −1]/2X _A + [(
1/r)(α ^* -1)+1/2X _A ] ² } ^1/2 (6) It can be seen that in the limit of infinite supply pressure, the actual separation factor approaches the ideal separation factor. With the high operating pressures required to maintain high fluxes and selectivities, comes the need for membranes and equipment that can withstand such conditions as well as increased energy consumption for compression of the feed mixture. Of all the research methods for maximizing membrane flux, perhaps no other has attracted as much interest as reducing the thickness of the membrane itself.
However, this research method has two major drawbacks that have been successfully overcome within the last 20 years. Gas molecules are so small that a pinhole (or even a microscopic defect in the membrane surface) is sufficient to render the membrane unusable for gas separation. It is extremely difficult to cast ultra-thin membranes without defects using conventional casting techniques. Irregularities on the surface onto which the membrane is cast are incorporated into the structure of the membrane, which for very thin membranes can be comparable in size to the thickness of the membrane. These irregularities create pinholes through which a large flow of gas occurs, thus causing a loss of permselectivity. Second, ultrathin membranes are extremely fragile and often cannot withstand the pressures they must undergo in membrane separation processes. An innovative solution to this problem came with the development of asymmetric cellulose acetate membranes. The term asymmetric refers to a membrane configuration in which a relatively dense, ultra-thin coating is placed over an underlying open porous structure. To cast this type of membrane, a solution of the polymer in a water-miscible solvent is first cast onto a glass plate in a conventional manner. After a short period of time for the solvent near the surface of the membrane to evaporate and concentrate the polymer, the glass plate is immersed in water, where the polymer condenses, the water diffuses into the solution, and the solvent also diffuses. As it comes out, it forms a porous matrix. Because the dense layers formed in this way represent only a small fraction of the total membrane thickness, the flux of these membranes is greater than that exhibited by dense isotropic membranes of comparable thickness. much higher.
A dense separation layer is placed on a porous support matrix that provides mechanical strength to the membrane. These membranes have been very successful in reverse osmosis applications, but their utility in gas separation is questionable. Although it may be considered impermeable to liquids, even its dense coating contains pores larger than a typical gas molecule. for example,
Post-treatments such as annealing the film at high temperatures were used to reduce the size of the pores in the surface layer. However, for this post-treatment to be successful, the surface porosity must be less than 10 ^-6 % of the surface area. Moreover, these post-treatments tend to significantly reduce membrane flux. Another solution for eliminating the effects of surface porosity in asymmetric membranes was published by Henis and Tripodi in US Pat.
No. 4230463 (published October 28, 1980). This shows a porous substrate coated with polymer in closed contact. Hennis et al.'s research method deposits a thin layer of highly permeable polymer (e.g. silicone rubber) onto the surface of a porous asymmetric membrane that exhibits good specific selectivity for one component of the gas mixture to be separated. It was to let him do it. It has been found that by sealing the surface pores in this manner, much of the selectivity of the underlying porous polymeric material is maintained, yet the overall permeability remains very high. Membranes made of two (or more) laminated films are called composite membranes. Similar to the electrical current in an electrical circuit, the ultimate properties of these composite membranes are related to the resistance of each of their constituent parts. In this case, the coating material,
It relates to the resistance of the substrate and the filled pores to gas flow. The resistance R for a particular component of the composite membrane is given by the following equation: R=l/PA (7) where l is the thickness of the part, P is the average permeability of the material making up the part, and A is the surface area of the part. The total resistance R _T of a composite membrane to a given gas flow is calculated in the same way as that of the corresponding current. For the case of a composite membrane consisting of two stacked defect-free layers, R _T is simply the sum of the resistances of the individual layers. For a composite membrane of the type of Hennis et al., R _T is given by the following equation: R _T =R ₁ +R ₂ R ₃ /R ₂ +R ₃ (8) The subscript in the above formula represents the membrane part. Assuming that the pore area is small compared to the total surface area,
The thickness-corrected permeability (P/l) is given by the following equation: P/l=[l ₁ /P ₁ +l ₂ /P ₂ +P ₁ (A ₃ /A ₂ )] ^-1 (9) where A ₃ is the surface area of the pores and A ₂ is the total area of the membrane. It is the surface area. The ratio of thickness-corrected permeabilities for a pair of gases is likewise equal to the ideal separation factor as a ratio of average permeability coefficients. It is clear that the selectivity of composite membranes does indeed approach the intrinsic selectivity of the substrate up to relatively high surface porosity. It is therefore possible to achieve high fluxes and at the same time high selectivities. The separator in these composite membranes of Hennis et al. is the underlying asymmetric membrane. Therefore, the choice of separation material is limited to the polymer from which the asymmetric membrane is cast. Moreover, since most of the material in the composite membrane is within the underlying structure, the materials making up this layer must be inexpensive and easily synthesized polymers. Membrane manufacturing methods in which the separation layer is deposited as an ultrathin film on the surface of an inexpensive porous support allow the membrane to be constructed using small amounts of expensive or novel polymers as the permselective layer. . The use of such materials is advantageous from the point of view of their inherent permselectivity. This method actually predates the work of Hennis et al. and has generally become the most common method for developing high flux membranes for gas separation. Several methods have been investigated for depositing ultrathin films on the surface of porous supports. The simplest and most straightforward technique is simply to coat the support film by dipping it in some polymer or reactive monomer, followed by drying and/or heat curing. However, this method has been applied only to limited applications, mainly in the field of reverse osmosis membranes. A close relative of this technique is the interfacial polymerization of reactive monomers or polymers on the surface of a support. In such methods, a porous film is saturated with an aqueous solution of a monomer or polymer and then treated with a reactive intermediate dissolved in a water-immiscible solvent. Since the reaction between monomers or polymers occurs only at the interface,
The resulting separation layer is extremely thin. So far, this method has been applied commercially only to create membranes for reverse osmosis separations. The vapor phase deposition of polymers onto porous supports is a promising new technique that has been studied in the past, but there is no commercial application of this method yet. Another method of placing the film directly on the support layer is to cast the film separately and then laminate the ultrathin separating layer onto the porous support. Perhaps the easiest way to accomplish this is to dip a glass plate into a dilute solution of the polymer and
The idea is to pull up the plate and then evaporate the solvent. The remaining film is then removed from the glass surface by dipping the glass plate in water. Finally, one or more sheets of this film are carefully layered onto the porous support. The second method is to cast a polymer solution in a hydrophobic solvent onto the surface of water and spread the solution to form an ultra-thin film. After the solvent has evaporated, the film is picked up and placed on the support layer. These techniques have proven useful for casting essentially defect-free films as thin as 150 angstroms. The above membranes were laminated as single or multiple layers onto porous supports for use in gas separation. Although thin separation layers are advantageous in terms of increasing membrane flux, they complicate the membrane manufacturing procedure as these layers are easily damaged during lamination. Composite membranes consisting of a very thin glassy polymer film on a porous glassy polymer support are particularly sensitive to damage during handling. Browall and Saleem
Salemme in U.S. Pat. No. 3,874,986 (issued April 1, 1975) and Browall in U.S. Pat.
This problem was solved by inserting an interlayer of organopolysiloxane-polycarbonate copolymer between the microporous layer and the non-porous layer. In this case, the above-mentioned intermediate layer serves as a cushion and an adhesive. Another disadvantage of separately casting the support structure and permselective layer is the limitations of the technology for coating planar sheet membranes. The advantages over planar sheet membranes in the form of hollow fibers have already been mentioned above. In Japanese Patent Publication No. 57 [1982]-105203 (published on June 23, 1982, filed by Toray Industries, Inc.), Hirose and Kurihara describe an aminopolysiloxane consisting mainly of repeating units of the following general formula. describes a selectively permeable membrane prepared by crosslinking.

[expression] and

[Formula] In the above formula _, , and i and j represent the mole fraction, i+j=
1.0, 0.1i1 and 0j0.9 conditions are satisfied. Hirose and Kurihara describe aminopolysiloxanes as crosslinking agents, such as acid chlorides, acid anhydrides, isocyanates, thiocyanates, sulfonyl chlorides, epoxides, or compounds containing two or more functional groups such as active halogens in each molecule. It states that crosslinking is achieved by If the crosslinking agent is soluble in water or alcohol, a solution of the aminopolysiloxane and the crosslinking agent are mixed and coated onto the porous support. If the crosslinker is insoluble in water or alcohol, or if the crosslinker reacts with these solvents, the membrane is produced by surface condensation. The aminopolysiloxane is first applied onto the porous support and the polymer solution is allowed to penetrate into the pores for a certain period of time, preferably from a few seconds to 30 minutes. The surface of the support can be dried with hot air. The surface of the support coated with the aminopolysiloxane film is then contacted with a solution of a polyfunctional crosslinking agent capable of reacting with the amino groups in the aminopolysiloxane. Preferred solvents for polyfunctional crosslinkers are usually hydrocarbon solvents, such as petroleum ether, hexane, or heptane. The appropriate concentration of crosslinking agent in the solvent varies depending on the reaction substrate, crosslinking agent, and solvent, but about 0.1 to 2% by weight gives good results.
Heating is usually required to complete the crosslinking reaction;
Generally heated at 50° to 180°C for 1 to 30 minutes. The present invention relates to a method for producing a composite material suitable for increasing the oxygen gas content in an oxygen-nitrogen gas mixture by passing the mixture through said composite material. The method comprises (a) coating a polysiloxane with aminoorganic functionality on at least one surface of a highly porous polymeric substrate with a thickness of 20 to 250 μm, the polysiloxane having a thickness of 0.1 μm to 20 μm;
and the polysiloxane consists essentially of aminosiloxane units having 1 to 9 mol % of primary amino organofunctionality and 91 to 99 mol % of aminosiloxane units having primary amino organic functionality. consisting of a random copolymer of other repeating siloxane units and having the following general formula: (r and s in the above formula are the following formula 1 to 9 mol% of aminosiloxane units are present,
and the average total number of siloxane units per molecule is
100 to 800); (b) forming a film in which the polysiloxane coated on the substrate is cross-linked with a solution of a diisocyanate and an organic solvent that is non-reactive to isocyanate; and (c) contacting the cross-linked membrane with a sufficient amount of poly(phenylene oxide) to produce an extremely thin layer useful as a gas-selective film. b) Further processing of the product obtained in the step. One object of the present invention is to provide a method of manufacturing a membrane for concentrating oxygen in air.
The characteristics required for this membrane are good oxygen permeation selectivity (ideal separation coefficient of 3 to 4), moderately high flux,
and adaptation to hollow fiber technology. Composite membranes prepared by direct deposition of component layers onto a supporting surface are best suited to the membrane requirements described above. A second object of the invention is to provide an improved intermediate layer within a plurality of membranes. In particular, this layer serves to cushion the separation layer and also acts as a ``gutter layer'' that channels permeated gases into the surface pores of the polysulfone (PSF) support, thus providing a barrier to the composite membrane. by increasing the effective surface area of the separating film. The method of manufacturing the composite material of the present invention is similar to the method used by Hirose and Kurihara in Japanese Patent Publication No. 105203/1982. The process of the invention is characterized by a low content of aminosiloxane units in polysiloxanes with aminoorganic functionality, i.e. 1
Allows the use of ~9 mole % aminosiloxane units. These amino-organofunctional polysiloxanes are cross-linked with diisocyanates on porous substrates to produce cross-linked films, which are contacted with poly(phenylene oxide)s to form gas-selective films. By being produced on membranes, composite materials can be made that are useful for gas separation, especially for oxygen enrichment of gas mixtures such as air. According to the teachings of Hirose and Kurihara, a polysiloxane cannot be sufficiently crosslinked unless it has 10 mole percent or more aminosiloxane units. The method of the present invention not only uses less than 10 mole percent aminosiloxane in the polysiloxane, but also reduces the permeability coefficient of the resulting composite material to that of the polysiloxane.
It has been discovered that the weight ratio of the polysiloxane to the diisocyanate used to crosslink can be controlled. Increasing the ratio results in a decrease in the permeability coefficients of gases such as oxygen and nitrogen for the composite material. Changes in the transmission coefficient do not cause substantial changes in the separation factor (SF, α). The support layer may be, for example, a sheet or a hollow fiber, and may be made of highly porous polymers such as polysulfone (PSF), polystyrene, and other US Pat. ) can be manufactured from polymers as defined in ). Such porous substrates are known in the art, and many are commercially manufactured. Preferably, the porous substrate is polysulfone. The porous substrate preferably has a thickness of 20 to 250 μm, and the pore diameter is desirably in the range of 0.01 to 0.1 μm. At least one surface of the porous substrate is coated with a polysiloxane having aminoorganic functionality. Preferably,
The dense surface is coated and is also the surface in contact with the feed gas. Preferably, the polysiloxane is in solution in an organic solvent when applied onto the porous substrate. The organic solvent used in making the polysiloxane solution is one that is substantially a non-solvent for the porous substrate and is non-reactive with the porous substrate and the polysiloxane, such as hexane. See US Pat. No. 4,230,463 for further information regarding suitable solvents for dissolving polysiloxanes and not acting on porous substrates. Polysiloxane is placed on the porous base material in a thickness of 0.1 μm ~
It is applied in an amount sufficient to give a 20 μm thick cured coating. The concentration of polysiloxane in the organic solvent is preferably within the range of 1 to 20% by weight, but may vary outside this range depending on the nature of the solvent and polysiloxane. The most practical concentration of polysiloxane in a solvent is 1
~10% by weight. For sheet materials, the polysiloxane solution may be cast onto a porous substrate to provide a uniform coating on the surface. Other methods of applying a uniform coating may be suggested by the structure of the porous substrate. For example, the surface of a hollow fiber (tubular) can be coated by passing a solution through the tube. One or more passes can also be made to build up the coating thickness to provide a given system for gas separation. After applying the polysiloxane solution to the porous surface, the solvent is evaporated. The siloxane then forms a non-crosslinked polysiloxane film. The polysiloxane film is then crosslinked with diisocyanate to form an elastic film. The diisocyanate is applied to the polysiloxane as a solution in an organic solvent. The concentration of diisocyanate in the organic solvent can be varied, but must be sufficient to crosslink the polysiloxane. Preferably, the concentration of diisocyanate is between 0.1 and 5% by weight, most preferably between 0.2 and 4% by weight. After the diisocyanate is spread on the polysiloxane film, the diisocyanate is left with the polysiloxane to provide a crosslinking amount in the polysiloxane. Usually a time of 5 to 30 seconds is sufficient. Excess diisocyanate solution is removed from the surface of the polysiloxane film, either by washing it away or pouring it out of the hollow fibers. After pouring off the excess diisocyanate solution, the surface of the treated polysiloxane film was dried at room temperature and then
Further curing can be achieved by heating at 150°C for 1 to 30 minutes. The polysiloxane with amino organic functionality is 1
It has ~9 mol% aminosiloxane units and is a random copolymer. The composite membrane of the present invention contains an aminoorganofunctional polysiloxane having an average of 100 to 800 siloxane units per molecule. The above polysiloxane has the general formula (r and s in the above formula are the following formula 1 to 9 mol% of aminosiloxane units are present,
and the average total number of siloxane units per molecule is
100 to 800), preferred random polysiloxanes have the following average formula: (r and s in the above formula are the following formula of aminosiloxane units are present, and the average total number of siloxane units per molecule is about
300), and also (where r and s in the above formula have a value such that about 2 mole % of aminosiloxane units are present, and the average total number of siloxane units per molecule is about
Contains 100% polysiloxane. ) The diisocyanates may be aromatic, aliphatic or cycloaliphatic, such as toluene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, benzene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, and metaxylene diisocyanate. A preferred diisocyanate is toluene diisocyanate (TDI). The composite material prepared as above is 2.4~
SF (separation factor) of 2.9 and 18× for oxygen
10 ^-10 ~ 180 × 10 ^-10 cm ³ cmsec ^-1 cm ^-2 (cmHg) ^-1 permeability coefficient and 6 × 10 ^-10 ~ 75 × 10 ^-10 cm ³ for nitrogen
It can have a transmission coefficient of cmsec ^-1 cm ^-2 (cmHg) ^-1 . The composite material described above, consisting of a porous substrate coated with a film of polysiloxane having cross-linked aminoorganic functional groups, is useful for the separation of gases, e.g. to increase the oxygen content in oxygen-nitrogen mixtures. However, poly(2,6-dimethyl-1,4
Composites prepared by placing an ultrathin layer of PPO (phenylene oxide) (PPO) on top of a film of polysiloxane with crosslinked aminoorganic functional groups offer more advantages and broader utility. To provide a composite material having The separation factor can be higher, the crosslinked polysiloxane can act as a gutter layer, and the surface can be
Does not easily attract contaminants such as dust particles. PPO is a brominated compound with up to 60% or more repeating units containing -CH ₂ Br as much as 1 to 60%.
It can be a PPO. Preferred brominated PPO is 20000 ~
has a molecular weight of 500000, and

【formula】

【formula】

【formula】

[expression] and

It can have repeating units selected from the formula:
Brominated PPO can be used as a separating layer exhibiting high separation coefficients. Separation factor values of greater than 8 can be obtained for oxygen-nitrogen mixtures. Other poly(phenylene oxides) are also expected to serve as separation layers in bilayer composite membranes. An ultrathin PPO film is deposited as a separate layer on a crosslinked polysiloxane film. the
PPO layers can be deposited to a thickness of 2 μm, but are commonly deposited from organic solvents to a thickness of 0.5 μm or less. The combined thickness of the gutter layer and PPO layer may be as thin as about 1 μm. film,
That is, the performance of the composite material depends on the relationship between the thickness of the underlying layer, the porosity of the substrate, and the percentage of defects in the separation layer. Less damage to the separation layer results in no overall loss of membrane performance. Also, severe damage to the separation layer (eg, 2% or more surface defects) will reduce the separation performance of the membrane to that of the gutter layer (intermediate crosslinked polysiloxane layer). The crosslinked polysiloxane layer has increased separation coefficient and increased inertness. Also, if the top layer (separation layer) is damaged, it can be recoated to restore the membrane's original performance even within the model. In certain embodiments of the present invention, particularly useful separation membranes include a supporting matrix of porous polysulfone (PSF) cast sheets and an amino-organic membrane cross-linked in situ with TDI deposited thereon. It was a two-layer composite membrane prepared from an ultrathin layer of functionalized polysiloxane and an ultrathin layer of PPO. The air is concentrated by passing through this membrane, and the gas mixture is
Produced 40-50% oxygen. The following examples are presented for illustrative purposes and are not to be construed as limitations on the invention, which is precisely delineated in the claims. Example 1 A composite membrane was coated with a polysiloxane with amino-organic functionality on one side of a cast sheet (approximately 7 x 14 cm) of rectangular porous anisotropic polysulfone fixed in a frame devised for this purpose. (The concentration and type of polysiloxane used were as shown in Table 1) by uniformly spreading a hexane solution of A small amount of solution (enough to give the desired film thickness) was injected into one end of the frame, and then the frame was tilted to allow the solution to flow evenly over the surface. After being left on the surface for 15 minutes, excess solution was removed and the film adhering to the polysulfone surface was allowed to dry for 2 minutes. After evaporating the solvent, a 2% by weight toluene-2,4-diisocyanate (hereinafter referred to as TDI) hexane solution was spread on the surface in the same manner as the polysiloxane solution.
The solution was left on the polysulfone surface for 15 minutes and then unreacted solution was allowed to flow off the surface. TDI formed a cross-linked polysiloxane coating, which was dried at room temperature for 5 minutes and then in a convection oven for 10-12 minutes.
A crosslinked polysiloxane-polysulfone composite film was formed by curing at a temperature of 90° to 95°C. The thickness of these composite films was measured using a scanning electron microscope (SEM).
The ideal separation coefficient, actual separation coefficient, and permeability coefficient for nitrogen gas and oxygen gas were also measured for each composite membrane. The two-layer composite membrane is made of the aforementioned crosslinked polysiloxane.
Poly(2,6-dimethyl-
1,4-phenylene oxide) (hereinafter referred to as PPO).
PPO was coated onto the surface of a crosslinked polysiloxane-polysulfone composite material that had been previously cut to fit the permeation chamber, using a method slightly different from that used to apply polysulfone. This change in coating technique was necessary to evaluate the same membrane before and after PPO processing. PPO was applied to the crosslinked polysiloxane surface of these composite membranes by fixing the membrane to the outside of a cylinder with a diameter of about 10 cm. The cylinder was held on top of a small dish filled almost to the brim with a 1% by weight CCl ₄ solution of PPO such that the meniscus of the solution was above the rim of the dish. The cylinder was then lowered to contact the membrane with the solution. Finally, the cylinder was rotated to contact the entire surface of the membrane with the solution. The membrane was removed from the solution and dried, thus forming a two-layer composite membrane. The thickness of the PPO film was measured with a scanning electron microscope, and the ideal separation coefficient, actual separation coefficient, and permeability coefficient were measured for nitrogen and oxygen gases.
The results were as shown in Table 1. The table also shows predicted values for comparison with actual values. The polysulfone cast sheet was manufactured by UOP Inc., San Diego, California and is designated E-183, and is a precast microporous polysulfone membrane (air permeable) laminated to a paper backing. degrees = 95×10 ^-15 gcm ^-2 sec ^-1 atm ^-1 ). The polysiloxane with amino organic functionality used here had the following general formula. In the above formula, x had an average value of about 276 and y had an average value of about 24, which is about 8 mole percent aminosiloxane units. Ideal Separation Factor The ideal separation factor of these composite membranes in oxygen/nitrogen separation was calculated from the ratio of the membrane's permeability coefficients for the two gases. Place the membrane in a permeation cell,
Its permeability to pure oxygen or nitrogen was measured. For permeability testing, pure gas is supplied to the cell through the inlet, the outlet is used for fine adjustment of pressure, and the permeate is sent to a soap bubble flow meter. Flow rate was measured by measuring the time required for a bubble to travel a fixed volume within the flow meter at a fixed pressure. The flow rate divided by the surface area of the membrane exposed to the gas equals the flux. The flux, pressure difference, and membrane pressure (measured with a scanning electron microscope) are used to calculate the permeability coefficient. However, for a single membrane, all other parameters being the same, it is only necessary to measure the fluxes of the two gases at constant pressure. Actual Separation Factor The actual separation factor of the composite membrane in oxygen/nitrogen separation was determined using essentially the same equipment. Actual separation coefficients were determined for membranes exposed to air under pressure and also for vacuum conditions on the product side of the membrane. In both methods, air was supplied to the cell by an outlet that was always open to maintain a low stage cut. The permeate was sent through the sample loop of a gas chromatograph (F&M model 720). The retentate was led to another gas chromatograph. The compositions of raw materials and products were determined from the peak areas of gas chromatograms. The area was calculated by multiplying the height of the peak by the width at half its height. The composition of oxygen and nitrogen was given by the following relation. %O ₂ =A _O2 /A _O2 +A _N2 %N ₂ =A _N2 /A _O2 +A _N2 In the above formula, A _O2 and A _N2 are the areas of the oxygen and nitrogen peaks, respectively. The following equation was used to calculate the actual separation factor. α=X _O2 /X _N2 /Y _O2 /Y _N2 In the above formula, X _O2 and X _N2 are the percentage of oxygen and nitrogen in the product, and Y _O2 and Y _N2 are the percentage of oxygen and nitrogen in the raw material. . The actual separation coefficient is calculated from the product side at ambient pressure (approximately 1 atm).
Measured at feed pressures from 10 psig to 100 psig. Alternatively, the feed stream was maintained at a constant pressure (typically 20 psig) and the product side was vacuumed to 0.1-1 psig absolute. For each pressure reading, three samples were injected into the gas chromatograph for analysis. Scanning Electron Microscopy Examination The thickness of the coating as well as other characteristics of the film morphology were determined by scanning microscopy. After the composite membranes were evaluated using the method described above, samples were cut from each membrane. The samples were fractured with liquid nitrogen and then mounted along the edges onto sample stubs with neoreube dry film lubricant. Approximately 1 x 0.5cm
Two samples of were attached to each stub. The samples were coated with gold/palladium film on a Hummer using two pulses of 100 mA for 90 seconds each. Samples under ETEC scanning electron microscope
Inspected under 20KV beam. The photos were taken with Polaroid Type 55 positive/negative film. Comparison of the thickness of the layer in the photograph and the micron bar double printed on the photograph was used to calculate the thickness. A composite membrane consisting of a single coating of crosslinked polysiloxane on polysulfone was prepared and evaluated as described above. The first test these membranes underwent was the determination of ideal separation factors from oxygen and nitrogen flux measurements. Fluxes were first measured at a feed pressure of 20 psig to give an indication of their potential. Membranes exhibiting an ideal separation factor greater than or equal to the ideal separation factor of silicone rubber (approximately 2) were further tested. A defect-free membrane should exhibit a linear relationship between flux and pressure difference across the membrane. Linearity was observed for all films, demonstrating the absence of any substantial defects. To coat a thin film of PPO on the surface of a crosslinked polysiloxane-polysulfone composite membrane,
Precipitation from solution was considered the most desirable from the viewpoint of application to coating hollow membranes. The actual separation coefficient of the composite membrane containing a surface layer of PPO was also greater than that of the membrane coated with crosslinked polysiloxane alone. In order to study the influence of the interlayer on the permeation behavior of these membranes, a series of membranes were prepared by coating polysiloxanes with varying concentrations of aminoorganic functionality onto a polysulfone support, thus allowing crosslinking. Composite membranes with various thicknesses of polysiloxane were obtained. After crosslinking the polysiloxane with TDI, these composite membranes were
Permeability was tested over a range of 10-50 psi for pure oxygen and pure nitrogen. These same membranes were then soaked and coated in a 1% by weight solution of PPO as described above. They were then subjected to the same tests as single coating membranes. Although the relationship is far from perfect, there was certainly a tendency that the higher the concentration of the coating liquid, the thicker the film accordingly. It was observed that the permeability of a single coated membrane decreases over a wide range of values. Example 2 Polysiloxane with amino organic functionality/
The effect of the weight ratio of TDI on the permeability and selectivity of polysulfone-polysiloxane composite membranes was determined. Three composite membranes were prepared as described in Example 1, with the following differences. The surface of the polysulfone cast sheet was coated with a hexane solution of polysiloxane as described in Example 1 by allowing the polysiloxane to sit on the polysulfone for 20 seconds and then air dry for 2 minutes. A 2% by weight hexane solution of TDI is applied to the polysiloxane surface, TDI is brought into contact with the surface for 20 seconds, unreacted solution is removed, and air-dried.
It was then heated in a convection oven at 90°C for 10 minutes. The concentration of polysiloxane for each experiment is listed in the table.
The oxygen and nitrogen permeability and actual separation coefficient were measured as shown in Table 1.

EXAMPLE 3 A polysulfone cast sheet coated with a crosslinked polysiloxane was prepared as described in Example 1. Composite membrane C was coated with a CCl ₄ solution containing 1% by weight of brominated PPO with the general formula: In the above formula, the sum of m, n, p, and r has a molecular weight of approximately
80,000 and 45% of the units contain -CH ₂ Br. The coating procedure is Example 2
It was the same as described in. The membrane thus obtained has a real separation coefficient αO ₂ /N ₂ =8.2, which corresponds to a permeation rate for oxygen gas of 8×10 ¹⁰ cm ³ cmsec ^-1 cm ^-2
(cmHg) ^-1 .

【table】

【table】

【table】

Claims (1)

[Claims] 1. A method for producing a composite material suitable for increasing the oxygen gas content in a composite material by passing an oxygen-nitrogen gas mixture through the composite material, comprising: (a) 20-250 μm coating a polysiloxane with aminoorganic functionality on at least one surface of a highly porous polymeric substrate with a thickness of 0.1 μm to 20 μm.
and the polysiloxane consists essentially of aminosiloxane units having 1 to 9 mol % of primary amino organofunctionality and 91 to 99 mol % of aminosiloxane units having primary amino organic functionality. consisting of a random copolymer of other repeating siloxane units and having the following general formula: (r and s in the above formula are the following formula 1 to 9 mol% of aminosiloxane units are present,
and the average total number of siloxane units per molecule is
100 to 800); (b) forming a film in which the polysiloxane coated on the substrate is cross-linked with a solution of a diisocyanate and an organic solvent that is non-reactive to isocyanate; and (c) contacting the cross-linked membrane with a sufficient amount of poly(phenylene oxide) to produce an extremely thin layer useful as a gas-selective film. b) further processing the product obtained in step); 2. The method according to claim 1, wherein the poly(phenylene oxide) used in step (c) is poly(2,6-dimethyl-1,4-phenylene oxide). 3 The poly(phenylene oxide) used in step (c) is brominated poly(2,6-dimethyl-1,
4-phenylene oxide). 4 has 1 to 9 mol % of siloxane units with primary amino organofunctionality and 91 to 99 mol % of other siloxane units and has the following general formula: (r and s in the above formula are the following formula 1 to 9 mol% of aminosiloxane units are present,
and the average sum of siloxane units per molecule is
20-250 μm thick with closely adhered gutter layer of highly gas-permeable rubber obtained by cross-linking an amino-organofunctional polysiloxane with a value such as 100-800 A two-layer bonded membrane suitable for gas separation, consisting essentially of a porous polymer substrate and a gas separator of poly(phenylene oxide)s closely coated on the gutter layer. 5 The polysiloxane is cross-linked with diisocyanate, the gutter layer is 0.1-20 μm thick and the gas separator is poly(2,6-dimethyl-1,4-phenylene oxide) and 2 μm thick.
The composite membrane according to claim 4, having a thickness of not more than m.