JPS588735A - Modification of porous membrane composed of aromatic polyimide - Google Patents

Abstract

PURPOSE:To obtain a porous membrane with good reproducibility, which has excellent separation performance and is suitable for use in the separation of mixed gases, by impregnating a porous membrane composed of an arom. polyimide with a weakly shrinking org. solven, and drying the membrane to shrink it to a given extent. CONSTITUTION:An arom. polyimide composed of at least 80% repeating unit of the formula (wherein R is a bivalent arom. residue derived from arom. diamines) is prepd. by polymerization and imidation reaction using a biphenyl-tetracarboxylic acid component and an arom. diamine component. A porous membrane i s produced from this polyimide. The porous membrane is impregnated with a weakly shrinking org. solvent capable of shrinking said porous membrane to an extent of 3-14%, such as benzene or n-hexane. The membrane is dried by heating to reduce the content of said solvent to 10wt% or lower, whereby a modified porous arom. polyimide membrane can be obtd.

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.

An asymmetric membrane having a dense layer (homogeneous layer) and a porous layer,
The asymmetric membrane was well known for its excellent permeability and separation performance, and its asymmetric membrane was created by coagulating a thin film of a doped solution of 9 polymers with an appropriate coagulating liquid, thereby forming a dense layer and a porous layer at the same time. layer.

Since it is necessary to create a coagulated film in which a film is formed, the manufacturing conditions are difficult, and it is difficult to create an asymmetric film with good reproducibility and stable performance.

The present inventors have already studied a method for producing a porous membrane made of aromatic polyimide.

Several patent applications have been filed, and as a result of various studies on how to modify these porous membranes to obtain high-performance separation membranes, we have found that virtually all of the porous membranes made of aromatic polyimide by impregnating the porous membrane with a shrinkable organic solvent that can cause the porous membrane to shrink by a certain amount over a period of time, and then drying and/or heating the porous membrane.

The present invention was completed by discovering that the present invention can be modified into a separation membrane with excellent separation performance.

That is, the present invention.

From an aromatic polyimide having 80% or more (preferably 90% or more) of repeating units represented by general formula (4) (wherein R is a divalent aromatic residue excluding the amine group of aromatic diamine) into a porous membrane.

When the porous membrane is immersed in each solvent alone and the porous membrane wetted with each solvent is dried, the porous membrane loses about 3 to 14% (
Shrinkage rate) 1 of weakly shrinking organic solvents that can cause shrinkage
The porous membrane is impregnated with the seed or two or more over substantially the entire surface thereof, and then the porous membrane is dried and/or heated to reduce the amount of weakly shrinkable organic solvent impregnated to about 10% by weight or less (the amount of solvent impregnated). /weight of porous membrane) 4. Modifying method of aromatic polyimide porous membrane. It is.

The method of the present invention is a method that is completely different from conventional separation membranes made of high molecular weight polymers, and is capable of producing high-performance separation membranes from porous membranes made of aromatic polyimide.

This method allows production with good reproducibility.

When the aromatic polyimide separation membrane obtained as a result of modification by the method of the present invention is used for separating and concentrating a mixed gas or for separating and concentrating a solution.

The permeation rate of each gas component or solution component is fast.

Moreover, 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 PH2 of 1X10-
"~I X l O-'ex"/ctn2・sec・Cf
rLHg + especially 5 X 10-1 to 5 X 10-'
Sub"/(@' ・sec-mlg), and the permeability ratio of hydrogen and carbon monoxide (PH2/Pcυ is 1.5 to 5
．． % may be about 2 to 4.5.

It is preferable that the aromatic polyimide represented by the general formula (I) is soluble in at least 3% by weight, preferably 5% by weight or more, in at least one type of phenolic solvent. The logarithmic viscosity measured with 1oOW11 solvent (a mixed solvent of 4 volumes of parachlorophenol and 1 volume of orthochlorophenol) is 0.3 to 7.0.
．． Especially 0, 4-5. O, more preferably 0.5-
A wide range of about 4.0 is sufficient.

The aromatic polyimide mentioned above is 3.3', 4.4'
-Biphenyltetracarboxylic acid component, 2,3.3',4
A biphenyltetracarboxylic acid component such as '-biphenyltetracarboxylic acid component and a general formula H2N -R-NH2
and an aromatic diamine component shown in

Any aromatic polyimide produced by any known method may be used as long as it is a polymer obtained by polymerization and imidization reaction (imide cyclization reaction).

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 as a dope.

For example, 9 is a method for manufacturing the porous membrane.

The above-mentioned homogeneous solution of aromatic polyamic acid or polyimide is coagulated with a suitable coagulating liquid mainly composed of water or lower alcohol to form a semipermeable membrane, and then the solvent has a solubility parameter of 9.3 or less. Once impregnated, the semipermeable membrane is dried and/or heated, if necessary.

A method for manufacturing a polyimide porous membrane by imide-cyclizing a polymer by heating to a high temperature can be mentioned.

In addition, as another method for manufacturing the above-mentioned porous membrane, the above-mentioned aromatic polyamic acid or polyimide is a polymer-soluble organic polar solvent containing a small amount of a high-boiling point organic polar solvent insoluble in the above-mentioned polymer. A homogeneous solution uniformly dissolved in a solvent is used as a dope, a thin film of the dope is formed, and the thin film is dried and/or heated to gradually remove the solvent.

If necessary, a method of manufacturing a polyimide porous membrane by heating the dry membrane to a high temperature to imide-cyclize the polymer can be mentioned.

The biphenyltetracarboxylic acid component used in the method for producing the aromatic polyimide porous membrane described above includes:
3.3',4.4'-bipheny A/7-tracarboxylic dianhydride and 2,3.3',4'-biphenyltetracarboxylic dianhydride are preferred.

2, 3, 3', 4'- or 3.3', 4.4'
-biphenyltetracarboxylic acid, or 2,3,
It may be a salt of 3', 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 be combined with other tetracarboxylic acid components 1, such as pyromellitic acid, 2.
2-bis(3,4-dicarboxyphenyl)propane,
Bis(3,4-dicarboxyphenyl)methane, bis(
3,4-dicarboxyphenyl)sulfone, bis(3,
4-dicarboxyphenyl)ether, bis(3,4-
dicarboxyphenyl) thioether, or.

Their acid anhydrides, salts or esterified derivatives, etc.
May be replaced. Alternatively, a benzophenone tetracarboxylic acid component, (eg.

3.3', 4.4'-benzophenone tetracarboxylic dianhydride, 2,3.3', 4'-benzophenone tetracarboxylic dianhydride, 2,3,3', 4'- or 3.3 '.

4'-benzophenonetetracarboxylic acid, or a salt or esterified derivative thereof).

One example of the aromatic diamine component represented by the general formula H2N-R-NH used in the production of the above-mentioned aromatic polyimide porous membrane is 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'-diaminodiphenylthioether, 3.3'-dimethyl-4,4'-diaminodiphenylthioether, 3.3'-dimethoxy-
4,4'-diaminodiphenylthioether.

3. Diphenylthioether diamines such as 3'-diaminodiphenylthioether, 4.4'-diaminobenzophenone, 3,3'-diamino-dimethyl-4
, 4'-diaminobenzophenone, 3,3'-diaminobenzophenone and other benzophenone diamines.

3.3'-diaminodiphenylmethane, 4.4'-diaminodiphenylmethane, 3.3'-dimethoxy-4,
diphenylmethane diamines such as 4'-diphenylmethane, 2.2-bis(4-aminophenyl)propane,
2゜Bisphenylpropane diamines such as 2-bis(3-aminophenyl)propane, 4.4'-diaminodiphenylsulfone, 3.4 diphenylsulfone diamines such as 3'-diaminodiphenylsulfone, 4.4
'-Diamino diphenyl sulfoxide, 3.3'-Diamino diphenyl sulfoxide, which diphgonyl sulfoxide diamines, benzidine, 3.3'-dimethylbenzidine, 3.3'-dimethoxybenzidine, 3.3'-
Diaminobiphenyl is a diphenyl diamine, Q-
, m-, or p-diaminobenzene, 2,6-diaminopyridine, 3,6-diaminopyridine, 2,5-diaminopyridine, and the like.

Further, a porous membrane made of an aromatic polyimide having a repeating unit represented by the above general formula (I).

A weak acid-condensing organic solvent that can shrink the porous membrane by about 3 to 14% (shrinkage rate) when the porous membrane is wetted (swollen) with each solvent and dried. An example of this is toluene.

Alkyl groups such as xylene and ethylbenzene (1 carbon number
Benzene, cyclohexanol, cyclohexane substituted with up to 2 halogen atoms such as benzene, chlorobenzene, bromobenzene, dichlorobenzene, dibromobenzene, etc. substituted with ~6), cyclohexanol, cyclohexane with 5 carbon atoms in either corner
-8 alicyclic alcohols or ketones may be mentioned.

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. Unless.

For example, the amount of impregnation is changed to 100 parts by weight of the porous membrane.
・Organic solvent for J 01 to 30 parts by weight, especially 0.5 to 20 parts by weight, more preferably 1, and any method can be used as long as it can be made into a proportion of about 1 to 10 M parts. good.

In the present invention, a porous membrane is impregnated with an organic solvent for modification (Appendix M).
9. For example, use a method that does not substantially dissolve the polymer and has a boiling point lower than the above-mentioned organic solvent for modification, especially 20C or higher.
100M parts of other organic solvent and 0 parts of organic solvent for modification.
．． A porous membrane is immersed in a mixed solvent of 5 to 40 parts by weight, especially 1 to 30 parts by weight, for an appropriate period of time, and other organic solvents with a low boiling point are removed from the porous membrane moistened with the mixed solvent. After the porous membrane is once immersed in a boiling point solvent to prepare a porous membrane impregnated with the solvent.

The impregnating solvent is replaced by immersing the porous membrane as it is in the desired organic solvent for modification.

A method of drying, heating, etc. is also preferred.

Further, as an impregnation (adhesion) method, a method of applying the mixed solvent to the porous membrane with a brush, a roll, etc. can also be mentioned.

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 membrane, and a method in which the fabric ia solvent for modification is atomized and adhered to the porous membrane. etc. can also be mentioned.

In the above-mentioned mixed solvent, the above-mentioned aromatic polyimide is insoluble and the organic solvent with a low boiling point includes 9 examples: t, benzene; alicyclic hydrocarbons such as cyclohexane and cyclopentane; n-pentane, n-hexane; n-hebutane,
Aliphatic hydrocarbons such as n-octane; methyl alcohol.

Ethyl alcohol, propatool, lid/ru.

lower aliphatic alcohols such as; methyl ketone;

Ethyl ketone, methyl ethyl ketone, methyl isopropyl ketone, methyl isoamyl ketone.

Lower aliphatic solvents such as methyl acetate.

Lower aliphatic carboxylic acid esters such as ethyl acetate, ethyl propionate, and butyl propionate are suitable because they are compatible with the organic solvent for modifying the aromatic polyimide porous membrane.

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 above solvent from the porous membrane, 1. For example, dry under reduced pressure or normal pressure at 5 to 80C for 0.1 to 100 hours, and then heat dry at a temperature of 80 to 160C for 0.1 to 20 hours. and further 0.1 to 2 at a temperature of 160 to 300C.
It is preferable to heat for 0 hours, but especially for drying or drying at a temperature of 160C or less and heat drying, heating for about 0 hours is preferable.
．． Gradually remove the solvent by spending more than 0.5 hours at 1% for more than 3 hours and then at a high temperature of 160-300C.

Heat treatment is preferred. With this method,
Amount of the organic solvent for modification impregnated into the porous membrane (weight of the organic solvent for modification impregnated/weight of the porous membrane)
is 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 the aromatic polyimide porous membrane by the method of the present invention has a hydrogen gas permeability PH2 of lXl0-
3 to 5 x 1O-7, especially lXl0-' to lX 10-7
cm”/cv?・sec・atrHg, and the permeability ratio between hydrogen gas and carbon monoxide scum (PH2/Poo)
Or 6-60. It is an excellent gas separation membrane with a ratio of 8 to 60 compared to bamboo.

Further, the above separation membrane may be 9, for example, sodium chloride NaC
It is also a reverse osmosis membrane that exhibits salt rejection performance in reverse osmosis membrane tests conducted on water bath liquids.

In the method of the present invention, both flat membrane and hollow fiber porous membranes can be used, so it is possible to stably obtain flat or hollow fiber separation membranes by modifying these porous membranes. can.

Examples are shown below.

In the example, the gas permeation test was performed on a 9 area 14.65c
A gas separation membrane is installed in the stainless steel cell of tfI2-,
Hydrogen gas, - carbon oxide gas at 25C.

The gas volume passing through the 9 separation membranes was measured using a flowmeter under pressure of 0.5 to 3 k and 70 m2.

The permeation IP of each gas was calculated using the 9th order equation.

[Examples 1 to 3 and Comparative Example 1] 3.3',4.4'-biphenyltetracarboxylic dianhydride 40 rrrnol, 4,4'-diaminodiphenyl ether 40 mmo and parachlorophenol 1989 were mixed with a stirrer and Place it in a separable flask equipped with a nitrogen gas inlet tube and pass nitrogen gas through it.

While stirring, the temperature of the 9 reaction solution was raised from room temperature to 180C4 in about 50 minutes, and the reaction solution was further held at 1800C for 8 hours to perform one-stage polymerization and imide cyclization to obtain a viscous polyimide solution. .

The polyimide solution has a polymer concentration of 10% by weight and a polymer imidization rate of 95% or more (as determined by infrared absorption spectrum analysis).

Furthermore, the logarithmic viscosity of the polymer (50C, 0.5g/100
1 parachlorophenol) was 2.2.

Polyimide solution prepared as described above.

Claims (1)

[Scope of Claims] A porous material made of an aromatic polyimide having 80% or more of repeating units represented by the general formula (wherein R is a divalent aromatic residue excluding the amine group of aromatic diami/) A weakly shrinkable organic solvent is added to the membrane, which can shrink the porous membrane by about 3 to 14% when the porous membrane is immersed in each solvent alone and the porous membrane wetted with each solvent is dried. Substantially the entire surface of the porous membrane is impregnated with one or more of them, and then the porous membrane is dried and/or heated to reduce the impregnation amount of the weakly shrinkable organic solvent to about 10% by weight or less (by weight of the impregnated solvent). /
1. A method for modifying an aromatic polyimide porous membrane, characterized in that the porous membrane is modified by: