JPS6223972B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for modifying a porous aromatic polyimide membrane. Conventionally, separation membranes made of high molecular weight polymers are
Asymmetric membranes having a dense layer (homogeneous layer) and a porous layer were well known as having excellent permeation performance and separation performance.
A thin film of a dope solution of a polymer solution must be coagulated with an appropriate coagulating liquid to create a coagulated film that forms both a dense layer and a porous layer at the same time. It has been difficult to create membranes with asymmetric performance. The present inventors have already researched methods for manufacturing porous membranes made of aromatic polyimide and have filed several patent applications. As a result of various studies on how to obtain a separation membrane, we found that substantially the entire surface of a porous membrane made of aromatic polyimide is impregnated with a shrinkable organic solvent capable of shrinking the porous membrane by a certain amount, and then, The inventors have discovered that by drying and/or heating the porous membrane, it can be modified into a separation membrane with excellent separation performance, and the present invention has been completed. That is, the present invention is based on the general formula () (However, R is a divalent aromatic residue excluding the amino group of an aromatic diamine.) , a weakly shrinkable organic material capable of shrinking the porous membrane by about 3 to 14% (shrinkage rate) when the porous membrane is immersed in each solvent alone and the porous membrane wetted with each solvent is dried. The porous membrane is impregnated substantially over its entire surface with one or more solvents, and then the porous membrane is dried and/or
Alternatively, a method for modifying a porous aromatic polyimide membrane, which comprises heating to reduce the impregnation amount of a weakly shrinkable organic solvent to about 10% by weight or less (weight of impregnated solvent/weight of porous membrane). It is. Here, the weakly shrinkable organic solvent is benzene substituted with an alkyl group having 1 to 6 carbon atoms, benzene substituted with up to 2 halogen atoms, and benzene having 5 to 6 carbon atoms.
selected from 8 alicyclic alcohols or ketones. The method of the present invention is a method that can produce high-performance separation membranes from porous aromatic polyimide membranes with good reproducibility, in a method that is completely different from conventional separation membranes made of high molecular weight polymers. be. The aromatic polyimide separation membrane obtained as a result of modification by the method of the present invention can be used to separate and concentrate mixed gases,
Alternatively, when used for separating and concentrating solutions, the permeation rate of each gas component or solution component is high, and the separation performance of each component is high. The method of the present invention will be explained in more detail below. The porous membrane used in the present invention is a porous membrane made of the aromatic polyimide described above, and has a hydrogen permeability P _H2 of 1×10 ^-1 to 1× as measured by the gas permeation test described below. 10 ^-6 cm ³ /cm ²・sec・cmHg,
^In particular, the permeability ratio of ^hydrogen and carbon ^monoxide ( ^P
_H2 /P _CO ) may be about 1.5 to 5, particularly about 2 to 4.5. It is preferable that the aromatic polyimide represented by the above general formula () can be dissolved in at least 3% by weight, preferably 5% by weight or more, in at least one kind of phenolic solvent.
It is sufficient that the logarithmic viscosity measured with 100 ml of solvent (mixed solvent of 4 volumes of parachlorophenol and 1 volume of orthochlorophenol) ranges from 0.3 to 7.0, particularly from 0.4 to 5.0, more preferably from 0.5 to 4.0. . The aromatic polyimide mentioned above is 3, 3', 4, 4'-
Biphenyltetracarboxylic acid component 2, 3, 3',
A biphenyltetracarboxylic acid component such as a 4'-biphenyltetracarboxylic acid component and a general formula H ₂ N-R
An aromatic polyimide produced by any known method as long as it is a polymer obtained by polymerization and imidization reaction (imide cyclization reaction) from an aromatic diamine component represented by -NH ₂ Good too. The porous membrane made of aromatic polyimide used in the method of the present invention is made of aromatic polyamic acid or aromatic polyimide produced by polymerizing the biphenyltetracarboxylic acid component and the aromatic diamine component in approximately equimolar amounts. It can be produced in various ways using a homogeneous solution of as a dope. As a method for manufacturing the porous membrane, for example, a semipermeable membrane is formed by coagulating a homogeneous solution of the aromatic polyamic acid or polyimide described above with an appropriate coagulating liquid containing water or a lower alcohol as the main component. and then drying and/or heating the semipermeable membrane while impregnated with a solvent with a solubility parameter below 9.3, if necessary by heating to elevated temperatures to imidocyclize the polymer. , a method for producing a polyimide porous membrane. In addition, as another method for producing the above-mentioned porous membrane, the above-mentioned aromatic polyamic acid or polyimide is dissolved in an organic polar solvent soluble in the above-mentioned polymer, which contains a small amount of a high-boiling point organic polar solvent in which the above-mentioned aromatic polyamic acid or polyimide is insoluble. The homogeneous solution, which is homogeneously dissolved, is used as the dope to form a thin film of the dope, and the film is dried and/or heated to gradually remove the solvent and, if necessary, For example, a method of manufacturing a polyimide porous membrane by heating a dry membrane to a high temperature and imide cyclizing the polymer can be mentioned. The biphenyltetracarboxylic acid component used in the above-mentioned method for producing a porous membrane of aromatic polyimide includes 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3'・4′-biphenyltetracarboxylic dianhydride is preferred, but
2,3,3',4'- or 3,3',4,4'-biphenyltetracarboxylic acid, or 2,3,3',
It may be a salt of 4'- or 3,3',4,4'-biphenyltetracarboxylic acid or an esterified derivative thereof, or a mixture of the above-mentioned compounds. Some of the above-mentioned biphenyltetracarboxylic acid components may contain other tetracarboxylic acid components, such as pyromellitic acid, 2,2-bis(3,4-dicarboxyphenyl)propane, bis(3,4-dicarboxyphenyl) phenyl)methane, bis(3,4-dicarboxyphenyl)sulfone, bis(3,4-dicarboxyphenyl)ether, bis(3,4-dicarboxyphenyl)thioether, or their acid anhydrides may be substituted with a compound, salt, or esterified derivative. Alternatively, a benzophenonetetracarboxylic acid component (for example, 3.
3', 4, 4'-benzophenone tetracarboxylic dianhydride, 2, 3, 3', 4'-benzophenone tetracarboxylic dianhydride, 2, 3, 3', 4'- or 3 -3,4,4'-benzophenonetetracarboxylic acid, or a salt or esterified derivative thereof). The aromatic diamine component represented by the general formula H ₂ N-R-NH ₂ used in the production of the above-mentioned aromatic polyimide porous membrane includes, for example, 4.4'-
Diaminodiphenyl ether, 3.3'-dimethoxy-4.4'-diaminodiphenyl ether, 3.
3'-dimethyl-4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether,
Diphenyl ether diamines such as 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl thioether, 3,3'-dimethyl-4,
4′-diaminodiphenylthioether, 3・3′-
diphenylthioether diamines such as dimethoxy-4,4'-diaminodiphenylthioether and 3,3'-diaminodiphenylthioether;
4,4'-diaminobenzophenone, 3,3'-diamino-dimethyl-4,4'-diaminobenzophenone, benzophenone diamines such as 3,3'-diaminobenzophenone, 3,3'-diamino Diphenylmethane diamines such as diphenylmethane, 4,4'-diaminodiphenylmethane, 3,3'-dimethoxy-4,4'-diphenylmethane, 2,2
-bis(4-aminophenyl)propane, 2.2
-Bisphenylpropane diamines such as bis(3-aminophenyl)propane, diphenylsulfone diamines such as 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-diamino diphenyl sulfoxide,
Diphenyl sulfoxide diamines such as 3,3'-diaminodiphenyl sulfoxide; diphenyl diamines such as benzidine, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine, and 3,3'-diaminobiphenyl; , o-, m-, or p-diaminobenzene, 2,6-diaminopyridine, 3,6-diaminopyridine, 2,5-diaminopyridine, and the like. In addition, a porous membrane made of an aromatic polyimide having a repeating unit represented by the above general formula (),
When a porous membrane soaked in each solvent alone and wetted (swollen) with each solvent is dried, the porous membrane
Examples of weakly shrinking organic solvents that can shrink by ~14% (shrinkage percentage) include toluene, xylene,
Alkyl groups such as ethylbenzene (1 to 1 carbon atoms)
6) benzene substituted with chlorobenzene, bromobenzene, dichlorobenzene, dibromobenzene, etc., benzene substituted with up to 2 halogen atoms, cyclohexanol, cyclohexane, etc., containing 5 to 8 carbon atoms; Mention may be made of cyclic alcohols or ketones. In the method of the present invention, the above weakly shrinkable organic solvent (organic solvent for modification) is impregnated (adhered) over the entire surface of a porous membrane made of aromatic polyimide. , it can be impregnated (adhered) almost uniformly over substantially the entire surface of the porous membrane, and the amount of impregnation is such that the porous membrane cannot be modified or the porous membrane cannot be made into a high-performance separation membrane. For example, the impregnating amount should be adjusted to 100 parts by weight of the organic solvent for modification, unless the amount is as follows.
Any method may be used as long as the proportion can be adjusted to 0.1 to 30 parts by weight, particularly 0.5 to 20 parts by weight, and more preferably 1 to 10 parts by weight. In the present invention, the method of impregnating (adhering) the organic solvent for modification into the porous membrane is, for example, a method that does not substantially dissolve the polymer and has a boiling point lower than the organic solvent for modification, particularly at 20°C or higher. 100 parts by weight of other organic solvents and 0.5 to 40 parts by weight of organic solvent for modification, especially 1 to 30 parts by weight
The porous membrane is placed in a mixed solvent with parts by weight for an appropriate period of time.
A method can be used in which other organic solvents with a low boiling point are removed by evaporation from the porous membrane that has been immersed and wetted with the mixed solvent to form a porous membrane impregnated with a modifying organic solvent. Alternatively, a porous membrane is once immersed in a low-boiling point solvent as described above to prepare a porous membrane impregnated with the solvent, and then the porous membrane is immersed as it is in the desired organic solvent for modification. It is also preferable to replace the impregnating solvent with the following steps, and then perform drying, heating, etc. Further, examples of the impregnation (adhesion) method include a method of applying the mixed solvent to the porous membrane using a brush, a roll, or the like. Furthermore, impregnation (adhesion) methods include a method in which the porous membrane is exposed to the vapor of an organic solvent for modification and the vapor is allowed to adhere to the vapor, and a method in which the organic solvent for modification is atomized and adhered to the porous membrane. can also be mentioned. In the above-mentioned mixed solvent, the above-mentioned aromatic polyimide-insoluble organic solvent with a low boiling point includes:
For example, benzene; alicyclic hydrocarbons such as cyclohexane and cyclopentane; n-pentane, n-
Aliphatic hydrocarbons such as hexane, n-heptane, n-octane; lower aliphatic alcohols such as methyl alcohol, ethyl alcohol, propanol, butanol; methyl ketone, ethyl ketone,
Lower aliphatic ketone solvents such as methyl ethyl ketone, methyl isopropyl ketone, and methyl isoamyl ketone; lower aliphatic carboxylic acid esters such as methyl acetate, ethyl acetate, ethyl propionate, and butyl propionate are It is suitable because it is compatible with the organic solvent for modification. In the method of the present invention, the porous membrane impregnated with the organic solvent for modification as described above is dried and/or heated to gradually remove the organic solvent for modification, thereby forming a polyimide porous membrane. It modifies the. To remove the solvent from the porous membrane, for example, dry it under reduced pressure or normal pressure at 5 to 80°C for 0.1 to 100 hours, then heat dry at a temperature of 80 to 160°C for 0.1 to 20 hours, Further 0.1-20 at temperatures of 160-300℃
Heating for an hour is preferred, but in particular, the solvent is gradually removed by drying or drying and heating drying at a temperature of 160°C or less for a time of about 0.3 hours or more, especially 0.5 hours or more, and then Heat treatment is preferably performed at a high temperature of 300°C. By such a method, the amount of impregnated organic solvent for modification impregnated into the porous membrane (weight of organic solvent for modification impregnated/weight of porous membrane) is reduced to about 10% by weight or less (preferably 7 to 1% by weight). Note that the drying or heating described above can also be performed under the flow of an inert gas. The separation membrane obtained as a result of modifying a porous aromatic polyimide membrane by the method of the present invention is, for example,
Hydrogen gas permeability P _H2 in the gas permeation test described below is 1×10 ^-3 to 5×10 ^-7 , especially 1×10 ^-4 to 1
×10 ^-7 cm ³ /cm ²・sec・cmHg, and the ratio of permeability between hydrogen gas and carbon monoxide gas (P _H2 /P _CO )
is about 6 to 60, especially about 8 to 60, making it an excellent gas separation membrane. Further, the above-mentioned separation membrane is also a reverse osmosis membrane that exhibits salt exclusion performance in a reverse osmosis membrane test performed on an aqueous solution of sodium chloride NaCl, for example. In the method of the present invention, both flat membrane-like and hollow fiber-like porous membranes can be used; therefore, flat membrane-like or hollow fiber-like separation membranes can be stably obtained by modifying these porous membranes. be able to. Examples are shown below. In an example, the gas permeation test
A gas separation membrane is installed in a 14.65 cm ² stainless steel cell, and hydrogen gas and carbon monoxide gas are separated by 0.5 at 25°C.
The pressure was increased to ~3 Kg/cm ² and the volume of gas passing through the separation membrane was measured using a flow meter. The permeability P of each gas was calculated using the following formula. Permeability P = gas permeation amount (STP)/membrane area x permeation time x pressure difference ( ^cm3 / ^cm2・sec・cmHg) Examples 1 to 4 and Comparative Example 1 3・3′・4・4′− 40 mmol of biphenyltetracarboxylic dianhydride, 40 mmol of 4,4'-diaminodiphenyl ether, and 198 mmol of parachlorophenol
g into a separable flask equipped with a stirrer and a nitrogen gas introduction tube, and flowing nitrogen gas through it.
While stirring, heat the reaction solution from room temperature to 180℃ for about 50 minutes.
The reaction solution was heated at 180° C. for 8 hours, and polymerization and imide cyclization were performed in one step to obtain a viscous polyimide solution. The polyimide solution has a polymer concentration of 10% by weight, a polymer imidization rate of 95% or more (based on infrared absorption spectrum analysis), and a polymer logarithmic viscosity (50°C, 0.5g/100ml parachlorophenol). ) was 2.2. The polyimide solution produced as described above was
A thin liquid film with a thickness of 0.2 mm was formed by casting on a glass plate at 25°C, and the liquid thin film was immersed in a methanol coagulation solution at 25°C for about 20 hours to solidify and form a semipermeable membrane. The coagulated film was immersed in n-hexane for 20 hours, then taken out from the n-hexane, dried at 30°C for 20 minutes under air circulation, and then dried at 100°C for 1 hour.
The mixture was further heated at 200° C. for 3 hours to produce an aromatic polyimide porous membrane. The polyimide porous membrane had a thickness of about 25μ. Table 1 shows the results of a gas permeation test performed on this porous membrane (Comparative Example 1). The above aromatic polyimide porous membrane was immersed in n-hexane at 25°C for 20 minutes to impregnate the porous membrane with n-hexane, and then the porous membrane was taken out from the n-hexane and shown in Table 1. Soak in the solvent shown in . This immersion was carried out under reduced pressure at 25°C for 20 minutes, then dried at room temperature under air circulation for 2 hours, then heated at 100°C for 1 hour and further at 200°C for 2 hours to form a solvent-impregnated porous material. A membrane was obtained. The results of a gas permeation test conducted on each solvent-impregnated porous membrane are shown in Table 1 along with the results of Comparative Example 1 above. 【table】

Claims (1)

[Claims] 1. General formula (However, R is a divalent aromatic residue excluding the amino group of an aromatic diamine). When a porous membrane soaked in a solvent alone and wetted with each solvent is dried, the porous membrane can be contracted by about 3 to 14%, and moreover, it can be substituted with an alkyl group having 1 to 6 carbon atoms. benzene substituted with up to 2 halogen atoms, and a weakly shrinkable organic solvent selected from alicyclic alcohols or ketones having 5 to 8 carbon atoms. , the porous membrane is impregnated substantially over its entire surface, and then the porous membrane is dried and/or heated to reduce the amount of the weakly shrinkable organic solvent impregnated to about 10% by weight or less (weight of the solvent impregnated/porous membrane). weight)).