JPH0112530B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to gas separation membranes. For more details,
The present invention relates to a gas separation membrane containing polysiloxane amide as a main component and suitable for separating gas mixtures. Gas separation membranes are required to have high gas separation efficiency and high permeation rate. In order to satisfy such performance, a structure can be considered in which the membrane thickness that provides substantial separation performance is made as thin as possible, and this is maintained by a porous layer. Various methods have been devised to produce membranes having such a structure. For example, a method of superimposing a separately formed thin film on a porous membrane, a method of forming an asymmetric membrane in which a skin layer and a porous layer coexist at once, a method of directly polymerizing monomers by various methods on a multilayer membrane, etc. There are methods such as forming a thin film by coating the polymer with a solution of the polymer and then evaporating the solvent. Among these film-forming methods, the method of coating a porous membrane with a solution of another polymer material to form a thin film layer is a method that can be applied to relatively many types of polymer materials; If it is made thin enough, defects will occur and the separation performance will be lost, so it is necessary to coat it thicker than a certain level, and a thick coating has the disadvantage that the permeation rate decreases. Therefore, in order to compensate for these drawbacks, it is necessary to select a material that has relatively high gas permeability and separation performance. Organopolysiloxane is known as one of the polymer materials with the highest permeability coefficient for gases, especially carbon dioxide gas, but when it is made into a thin film with a thickness of several tens of microns or less, non-uniformity in thickness and pinholes occur. , does not show good gas separation performance. On the other hand, polyamides exhibit good gas separation performance, but have much lower permeability coefficients and unsatisfactory permeation rates compared to organopolysiloxanes. As a result of extensive studies, the present inventors have found that when polysiloxane amide is used as the main membrane material, a membrane with a higher gas permeation rate than conventional membranes can be created in the separation of gas mixtures while maintaining excellent selectivity. The present invention was achieved by discovering that it can be obtained. That is, the gist of the present invention is to combine an aromatic dicarboxylic acid chloride or an aromatic dicarboxylic acid ester and a siloxane diamine represented by the following general formula (). (In the formula, n is a number from 2 to 6, m is a number from 1 to 3,
and R ¹ and R ² represent an alkyl group). A feature of the polysiloxane amide-based membrane of the present invention is that it exhibits properties intermediate between those of organopolysiloxane membranes and polyamide membranes, while providing a gas permeation rate higher than either membrane. The present invention will be explained in more detail below. The polysiloxane amide used in the present invention is
It is obtained by polycondensation of an aromatic dicarboxylic acid chloride or an aromatic dicarboxylic acid ester and a siloxane diamine represented by the general formula (). The above-mentioned polysiloxane amide can be easily obtained by a known method of polycondensation of an amide and an acid chloride or an acid ester. For example, an interfacial polycondensation method using a dicarboxylic acid chloride dissolved in a water-immiscible hydrophobic organic solvent and an aqueous diamine solution containing an acid acceptor may be used. Examples of the aromatic dicarboxylic acid chloride or aromatic dicarboxylic acid ester include dicarboxylic acid chlorides or dicarboxylic acid esters derived from the aromatic dicarboxylic acid represented by the following formula. Examples of the ester include methyl ester, ethyl ester, phenyl ester, and the like.

[Formula] (terephthalic acid, sophthalic acid, phthalic acid),

[Formula] (Substituted product of the same as above.Formula (wherein, X represents a halogen or an alkyl group),

[Formula] (Dicarboxylic acid such as naphthalene-1, 8-, -2,6-, -2,7-, etc.) Among these, isophthalic acid chloride and phthalic acid chloride are preferred. To give a specific example of the polycondensation method, a solution of an aromatic dicarboxylic acid chloride in a hydrophobic organic solvent that does not mix with water, such as methylene chloride tetrachloroethylene, carbon tetrachloride, chloroform, dichloroethane, or toluene, is used. , in air at a temperature around room temperature, the general formula () containing an acid acceptor such as sodium carbonate or sodium hydroxide in advance.
When mixed with an aqueous diamine solution shown in and vigorously stirred, polymerization proceeds easily to obtain polysiloxane amide. Generally, a single type of the aromatic dicarboxylic acid chloride and the diamine of the formula () used in the polycondensation are used, but if necessary, one can be of multiple types and the other can be of a single type. Alternatively, a plurality of types of both comonomers can be selected as appropriate. After the polymerization reaction is completed, the organic solvent is distilled off, and the polymer is deposited in an aqueous solution layer. This is washed with water and dried to obtain a purified polymer. The polymer obtained here is a polysiloxane amide obtained by polycondensation of an aromatic dicarboxylic acid chloride and a diamine represented by the general formula () to form an amide bond, and its weight average molecular weight (gel permeation chromatography) Based on the E method) is usually 5000 ~
It is 300000. The polymer or copolymer obtained by the above method (hereinafter simply referred to as the present polymer) can be used as a separation membrane by dissolving it in an organic solvent and coating it on a porous membrane. . Of course, depending on the polymer, it can be used as a homogeneous membrane or an asymmetric membrane obtained by casting the solution. As a porous membrane, it has a spongy structure,
A membrane with open pores on both sides, or a membrane with a dense layer on one side and open pores on the other, where the permeation rate of nitrogen gas is per unit area (1 cm ² ) per unit time. (1 second), unit pressure (1cmHg)
Examples include those having a permeation amount of 1×10 ^-4 cm ³ /cm ² ·sec·cmHg or more. The organic solvent used for coating the porous membrane is not particularly limited as long as it dissolves the present polymer, is easily desolvated after coating, and does not dissolve the porous membrane serving as the support. Although it depends on the material of the porous membrane, examples thereof include chloroform, dimethylformamide, dimethylacetamide, dimethylsulfoxide, and the like. The type of material for the porous membrane is not particularly limited, but examples include polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polymethyl methacrylate, polyacrylonitrile, polycarbonate, polyphenylene oxide, polyamide,
polysulfone, polyethersulfone, polysulfonamide, polypiperazine, cellulose acetate,
Examples include Teflon, polyvinylidene fluoride, and polyvinyltrimethylsilane. In addition, non-woven fabrics,
Inorganic materials such as woven fabric, paper, metal filters, glass, etc. can also be used. When this polymer is dissolved in an organic solvent and coated on a porous membrane, the solution concentration is the molecular weight of this polymer,
Although it varies depending on the molecular weight distribution and type of solvent, 1
% to 50% by weight, preferably 5% to 30% by weight. If the concentration is less than 1% by weight, the thickness of the coating membrane will be thin, and although the gas permeation rate will be high, sufficient separation performance will not be obtained.
If it exceeds % by weight, the thickness of the coated membrane becomes large, and although good separation performance can be obtained, the gas permeation rate becomes low. Usually, the amount of the polymer applied is selected to be 0.1 to 10 mg per cm ² of area of the porous membrane. The thickness of the porous membrane is not particularly limited, but is preferably 10μ to 1000μ. In addition, when using this polymer as an asymmetric membrane, a solution consisting of dimethylformamide, an inorganic salt such as LiCl, and this polymer is prepared according to a known method ("New Experimental Chemistry Course 21" Maruzen. p976). It is obtained by casting, forming a dense layer, and then coagulating in water. At this time, it is preferable that the total thickness is 10 to 1000 μm, and the thickness of the dense layer is 0.01 to 1 μm. The method of coating the porous membrane with the present polymer is not particularly limited, but examples include a method of immersing the porous membrane in a solution of the present polymer, or a method of casting a solution of the present polymer onto the surface of the porous membrane. This can be done by Porous membranes can be in the form of hollow fibers, tubes, or plates, and membranes coated with this polymer can be of the hollow fiber type, tubular type, spiral type, flat membrane type, etc. It can be used as a membrane device. Further, a coating layer can be further laminated on the surface of the membrane of the present invention by plasma polymerization or the like. The membranes of the invention can be used to separate gases from each other, especially gas mixtures containing at least one of the following gases: oxygen, nitrogen, carbon dioxide, carbon monoxide, hydrogen, helium, methane, argon. For example, separation of nitrogen and oxygen in the production of oxygen-enriched air, separation of methane and helium in the recovery of helium from natural gas, argon and hydrogen in the recovery of hydrogen from hydrogenation reaction waste gas, It can be applied to the separation of methane and hydrogen, nitrogen and hydrogen, the separation of carbon monoxide and hydrogen in the recovery of hydrogen from cracking gas, the separation of carbon dioxide and nitrogen in the recovery of carbon dioxide from combustion gas, etc. EXAMPLES The content of the present invention will be specifically explained below with reference to Examples, but the present invention is not limited only to these Examples. Reference example 1 Add 0.12 mol of bis(3-aminopropyl)tetramethyldisiloxane and 0.24 mol of sodium carbonate to water.
The solution was put into two stainless steel beakers at room temperature, and while vigorously stirring with a homomixer, a solution of 0.12 mol of purified isophthalic acid chloride dissolved in 192 ml of dry chloroform was added, followed by vigorous stirring and polymerization. After 15 minutes, stirring was stopped, the solution was transferred to a flask, and chloroform was distilled off, and a white viscous substance was observed in the remaining aqueous layer.
It was washed with water several times and dried in vacuum. Yield 39g (88
%). The melting point of the obtained polymer is 95℃ (melting start point)
~106°C (intersection temperature). The weight average molecular weight was 18,400. Examples 1 to 3 Polybis-3-propyltetramethyldisiloxane isophthalamide obtained in Reference Example 1 was dissolved in chloroform to give 8, 5, and 2% by weight solutions. A Millipore filter (Japan Millipore Co., Ltd., trade name) VSWP (thickness 90μ) was fixed on a glass plate.
The above solution was cast onto a glass plate, and the porous membrane was coated with the polymer using a 250μ roll coater. After evaporating the solvent and drying, a porous membrane whose surface was coated with the polymer was obtained. This membrane was installed in a permeation test device, and the permeation rates of hydrogen and nitrogen were measured. The surface area of the membrane is 14.52 ^cm2 , each gas is removed from the cylinder and brought into contact with the high pressure side of the membrane at a controlled pressure of 1 atmosphere, the permeate gas is collected on the reaction side of the membrane at atmospheric pressure,
The amount of permeation was measured over time using a gas filter. The gas and equipment temperature was 25°C. The permeation rate of each gas was expressed as the volume (cc) of gas permeating per unit area, per unit pressure difference (1 cmHg), per unit time (1 second), converted to standard conditions. The results are shown in Table-1. Comparative Example 1 The same operation as in Example 1 was performed except that the polymer concentration of the polymer solution was changed to 0% by weight. The results are shown in Table-1.

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Claims (1)

[Scope of Claims] 1 An aromatic dicarboxylic acid chloride or an aromatic dicarboxylic acid ester and a siloxane diamine represented by the following general formula () (In the formula, n is a number from 2 to 6, m is a number from 1 to 3,
and R ¹ and R ² represent an alkyl group) A gas separation membrane made of polysiloxane amide obtained by polycondensation. 2. The gas separation membrane according to claim 1, comprising a porous membrane coated with polysiloxane amide.