JPH02268820A - Pervaporative separation method of organic matter aqueous solution - Google Patents

Abstract

PURPOSE:To allow water to permeate and vaporize selectively from an aq. soln. of org. matter and to highly maintain the permeation and vaporization by bringing the aq. soln. into contact with an asymmetric separating membrane formed with soluble arom. polyimide having a specified compsn. as a heat resistant polymer. CONSTITUTION:Soluble arom. polyimide is dissolved in a phenol type solvent. The polyimide contains 60-100mol repeating units represented by formula I and the remaining repeating units are units each produced from biphenyltetracarboxylic acids and an arom. diamine compd. having 2-5 benzene rings as an arom. diamine component. The resulting soln. is spread and brought into contact with a solidifying bath to form a flat membrane or a hollow fiber membrane as an asymmetric separating membrane. An aq. soln. of org. matter is brought into contact with the separating membrane to allow water to permeate and vaporize selectively from the aq. soln.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a tetracarboxylic acid component containing biphenyltetracarboxylic acids as a main component and an aromatic diamine component containing a specific aromatic diamine compound. Using an asymmetric separation membrane (for example, a flat membrane or a hollow fiber membrane) made of soluble aromatic polyimide, an aqueous organic substance solution is brought into direct contact with the asymmetric separation membrane to selectively remove water. Pervaporation separation method involves pervaporation, which involves removing water from an organic aqueous solution and concentrating or separating organic matter.

[Description of prior art]

Distillation is conventionally known as a method for separating an aqueous solution of organic matter into organic matter and water. However, with the distillation method, it is extremely difficult to separate azeotropic mixtures, near-boiling point mixtures, and organic compounds that are susceptible to chemical changes due to heat.

In order to solve these problems, separation methods using separation membranes are being researched. In the method of concentrating and separating organic substance aqueous solutions using a separation membrane, for concentrating some low-concentration organic substance aqueous solutions, the organic substance aqueous solution is brought into contact with the separation membrane and specific liquid components are selected by the difference in osmotic pressure. Reverse osmosis has been used to penetrate the membrane. However, the reverse osmosis method cannot be applied to high-concentration aqueous organic matter solutions where the osmotic pressure is high because it is necessary to apply a pressure higher than the osmotic pressure of the separation liquid.Therefore, there is a limit to the concentration range of organic matter aqueous solutions that can be separated. be.

In contrast, a pervaporation separation method that is not affected by osmotic pressure is attracting attention as a new separation method that uses a separation membrane. In this pervaporation separation method, an organic aqueous solution to be separated is supplied in liquid form to one side (feed side) of a separation membrane that exhibits permselectivity, and brought into direct contact with the feed side of the separation membrane. The other side (permeation side) of the separation membrane is placed in a vacuum or reduced pressure state, and as a result, substances (such as water) that selectively permeate from the supply side of the separation membrane to the permeation side are extracted in gaseous form, and the organic aqueous solution is concentrated. This is a method of separating organic matter from moisture.

On the other hand, aromatic polyimide has recently attracted attention as a material for separation membranes because it has extremely superior heat resistance and chemical resistance compared to polyamide membranes, cellulose membranes, cellulose acetate membranes, etc. Asymmetric separation membranes are also being proposed for water separation of vapors from aqueous organic solutions. However, when conventional aromatic polyimide membranes are in contact with an organic aqueous solution or water at high temperatures for a long time, the polymer begins to deteriorate due to the hydrolytic action of the aromatic polyimide, and the deterioration gradually progresses. As a result, the permeation performance and mechanical strength of the asymmetric separation membrane may be significantly reduced, leading to problems in durability, and membrane separation methods for aqueous organic solutions have not always been fully satisfactory. In addition, known aromatic polyimide membranes are
When used in a pervaporation separation method for an aqueous solution of organic matter, there is also the problem that the permeation rate of water, selective separation performance between organic matter and water, etc. are not necessarily satisfactory.

[Problems to be solved]

The purpose of this invention is to provide a pervaporative separation method for an aqueous organic substance solution using an asymmetric separation membrane made of aromatic polyimide.
An aromatic polyimide membrane that can efficiently and selectively separate water from an organic aqueous solution by pervaporation without the drawbacks of known pervaporation methods, and can be used industrially for long periods of time. An object of the present invention is to provide a pervaporative separation method using the method.

[Means for solving problems]

The first invention of this application is a pervaporation separation method in which an aqueous solution of organic matter is brought into contact with an asymmetric separation membrane made of a heat-resistant polymer to selectively permeate mainly water from the aqueous solution of organic matter. An aromatic diamine in which the aggregate contains 60 to 100 moles of repeating units represented by general formula I, and the remaining repeating units are biphenyltetracarboxylic acids and other aromatic diamine compounds having 2 to 5 benzene rings. The present invention relates to a method for pervaporative separation of an aqueous solution of an organic substance, characterized in that the repeating unit formed from the components is a soluble aromatic polyimide.

Further, the second invention of this application is that in the pervaporation separation method similar to that in the first invention, the heat-resistant polymer has a repeating unit A represented by the general formula (■) and a general formula (2) or , a soluble aromatic polyimide consisting of a repeating unit B represented by general 2V and a molar ratio CA:B) of the repeating units ranging from 30 to 90:10. Concerning pervaporative separation of aqueous solutions.

Each requirement of each invention will be explained in more detail below.

Generally, the asymmetric separation membrane used in the pervaporation separation method of the present invention mainly has the above-mentioned general 2 I, or has repeating units A of the general formula (2) and repeating units B of the general formula (2), It is formed mainly from a soluble aromatic polyimide having an extremely thin homogeneous layer (preferably about 0.001 to 5
micrometer homogeneous layer) and a relatively thick porous layer supporting the homogeneous layer (preferably about 10 to 2 μm thick)
000 μm porous layer) and has the ability to selectively permeate water in an organic substance aqueous solution, for example, an asymmetric separation membrane in the shape of a flat membrane or hollow fiber ( This is a separation membrane that is not homogeneous in the thickness direction and has asymmetric micropores.

The soluble aromatic polyimide forming the asymmetric separation membrane has 6 repeating units represented by the general formula I.
0 mol% or more, preferably 65 to 95 mol%, especially 70 mol%
It contains ~90 mol%, and the remainder of the repeating unit consists of biphenyltetracarboxylic acids and 2 to 5 benzene rings, especially 2
It is a high molecular weight aromatic polyimide J that is soluble in phenolic organic solvents, etc., which is a repeating unit formed from an aromatic diamine component that is another aromatic diamine compound having ~4 units, or , mainly consists of a repeating unit A represented by the general formula (■) and a repeating unit B represented by the general formula (2), (2), or (preferably, the repeating unit A).
and B is about 90 mol% or more, particularly 95 mol% or more), and the molar ratio of the repeating units (A:B)
but 30 near 0 to 90:10, preferably 35:6
It is a high molecular weight aromatic polyimide J that is soluble in phenolic organic solvents with a ratio of 5 to 85:15.

Each of the above-mentioned aromatic polyimides contains, for example, an aromatic tetracarboxylic acid component containing 60 mol% or more, preferably 80 mol% or more of biphenyltetracarboxylic acids, (1) di(aminophenoxy)benzenes (general (2) (a) L4-bis(4-aminophenoxy)benzene (corresponding to the general formula ■) (A) and , (b) Diaminodiphenyl ethers (corresponding to general 2■), 1,3-di(aminophenoxy)benzenes (corresponding to general 2N) or 4,4-di(aminophenoxy)biphenyls (-general formula V (corresponding to) (B) and A:B is 30 near 0 to 90:10, preferably 35:6
5 to 85:15, approximately equimolar amount of r aromatic diamine component j, preferably containing about 80% or more, is added to a phenolic organic solvent, and while uniformly dissolving, the solution is heated to about 150% or more. By polymerizing and imidizing both components in the solution by heating to a high temperature of ~250°C or reacting in the presence of an imidizing agent at a low temperature of about 10 to 100″C. can be generated.

The above biphenyltetracarboxylic acids include 2.3
, 3°, 4°- or 3,3''-, 4,4'-biphenyltetracarboxylic acids, acid dianhydrides thereof, salts of these acids, or lower alcohol esters thereof.

The above-mentioned biphenyltetracarboxylic acids include, in particular,
2,3.3',4'- or 3,3°,4.4'-biphenyltetracarboxylic dianhydride is preferred for producing soluble aromatic polyimides.

Examples of the above-mentioned tetracarboxylic acid component include pyromellitic acid, 3.3', 4.4'-biphenyl ether tetracarboxylic acid, 3.3', 4.4'-henyl in addition to the above-mentioned biphenyltetracarboxylic acid component i1M. A small proportion (particularly preferably 20 mol% or less, more preferably 1
They may be used in combination (at a ratio of 0 mol% or less).

In the above-mentioned methods for producing aromatic polyimides, if the content of biphenyltetocarboxylic acid in the tetracarboxylic acid component becomes too low, the resulting aromatic polyimide will have low solubility in phenolic organic solvents. This is not preferable because it may become impossible to produce an asymmetric separation membrane with stable crystallinity, or the separation performance of the obtained asymmetric separation membrane in pervaporation method will be poor.

The di(aminophenoxy)benzenes used as the main component of the aromatic diamine component for forming the repeating unit represented by the general formula (1) above are aromatic diamine compounds represented by the general formula (2), and include, for example, 1.
4-bis(4-aminophenoxy)benzene, ■, 4-
1.4-bis(aminophenoxy)benzenes such as bis(3-aminophenoxy)benzene, 1.3-bis(4
Preferred examples include 1,3-bis(3-aminophenoxy)benzenes such as -aminophenoxy)benzene and 1,3-bis(3-aminophenoxy)benzene.

Examples of the diaminodiphenyl ethers used as one of the main components of the aromatic diamine component to form the repeating unit represented by the above general formula (1) include 4,4''
-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 3,3'-diaminodiphenyl ether.

L used as one of the main components of the aromatic diamine component to form the repeating unit shown in the above general 2)
Preferred examples of the 3-di(aminophenoxy)benzenes include the 1,3-bis(3-aminophenoxy)benzenes shown above.

Furthermore, the 4,4-di(aminophenoxy)biphenyls used as one of the main components of the aromatic diamine component for forming the repeating unit shown in the general ② above are:
Examples include 4,4-bis(4-aminophenoxy)biphenyl and 4,4-bis(3-aminophenoxy)biphenyl.

The aromatic polyimide forming the separation membrane according to the first title of this application contains 60 mol% or more of the repeating unit represented by the above-mentioned general formula 1, and the remainder is biphenyltetracarboxylic acid. and an aromatic diamine component which is another aromatic diamine compound having 2 to 5 benzene rings.

Preferred examples of the other aromatic diamine compounds having 2 to 5 benzene rings include the aforementioned diaminodiphenyl ethers and di[(aminophenoxy)phenyl]ethers; Di(aminophenoxy)biphenyl 94, o-dianisidine, o
- Diaminobiphenyls such as tolidine and m-tolidine, diaminodiphenyl alkanes such as diaminodiphenylmethane and diaminodiphenylpropane, benzene rings such as diaminodiphenylthioethers, diaminodiphenylsulfones, diaminodibenzothiophenes, and diaminothioxanthines. aromatic diamine compounds having three benzene rings such as bis(aminophenyl)benzenes, or
Bis(4-(4-aminophenoxy)phenyl)ether, bis(4-(3-aminophenoxy)phenyl)ether, bis[3-(4-aminophenoxy)phenyl]
Aromatic diamine compounds having four benzene rings such as ether, bis[(aminophenoxy)phenyl]ethers such as bis(3-(3-aminophenoxy)phenyl)ether, and di[(aminophenoxy)phenylcoalkanes) can be mentioned.

In addition, the aromatic diamine component described above contains a small proportion (content ratio of 10 mol% or less) of an aromatic diamine compound j having one r-Hensen ring such as phenylene diamines and diaminobenzoic acids. Good too.

In particular, in the pervaporative separation method of the second invention of Ex.
or from a repeating unit (B) denoted by V,
+jl The molar ratio (A:B) of the repeating unit is 30 nia 0 ~
The use of a heat-resistant asymmetric separation membrane made of a soluble aromatic polyimide that is 90:1 O allows the separation membrane to have excellent water resistance and ethanol resistance. It is suitable because it is excellent in that it has a high retention rate of permeation performance and tensile strength after treatment with a hot ethanol aqueous solution (150' Cl2O hours).

Each of the asymmetric separation membranes made of aromatic polyimide used in the present invention uses a phenolic solvent solution of aromatic polyimide to form a thin film (flat membrane shape, hollow fiber shape) of the /'4 liquid. A wet method in which a thin film is formed by a casting method, an extrusion method, etc., and then the thin film is brought into contact with a relatively low-temperature coagulating liquid to solidify the thin film to form a flat or hollow fiber-like asymmetric I4 membrane. It can be manufactured by a film forming method, for example, JP-A-56-21602, JP-A-56-1.
It can be manufactured by a conventionally known film forming method such as that described in Japanese Patent No. 57435.

In the above method for producing an asymmetric separation membrane, the asymmetric separation membrane produced by the wet membrane forming method is prepared using a suitable organic solvent (for example, lower alcohol tn having 1 to 6 carbon atoms, and lower alcohol tn having 1 to 8 carbon atoms). After washing with a lower aliphatic or alicyclic hydrocarbon solvent, etc.) and thoroughly drying, the mixture is further heated at about 150 to 420° C., especially 1, in an atmosphere of gas such as nitrogen or air.
It is appropriate to carry out the heat treatment at a temperature of 80 to 400°C for about 0.1 to 5 hours.

The asymmetric separation membrane used in this invention is an organic matter aqueous solution (
When pervaporative separation is performed using organic matter concentration: 50% by weight), the permeation rate Q of selectively permeated water is about 0.2 kg/rr (・Hr or more, especially about 0.4~ 5
．． 0 kg/n (・Hr), and the separation performance between permeated water and unpermeated organic matter (separation coefficient α - water permeation rate/ethanol permeation rate, which will be described later) is 100
or more, especially 120 or more, more preferably 130 to 10
It is preferable that it is about 00.

The pervaporation separation method of this invention is as follows: (a) A separation membrane module containing an asymmetric separation membrane (flat membrane type, hollow type) made of aromatic polyimide as described in Ail is charged with organic water? (b) supplying the permeate side of the asymmetric separation membrane with a carrier gas, if necessary, and bringing the organic aqueous solution into direct contact with the feed side of the asymmetric separation membrane in the separation membrane module; While flowing (sweep gas) or by connecting to a vacuum pump installed outside the separation membrane module to create a reduced pressure state, water is removed from the supplied organic aqueous solution through the asymmetric separation membrane. selectively permeates and permeates, and vaporizes and separates, (C) Finally, permeates through the separation membrane from the unpermeated side (supply side) of the asymmetric separation membrane to the outside of the separation membrane module. The remaining concentrated organic matter aqueous solution that was not removed is taken out and collected, and at the same time, it is transferred from the permeate side of the asymmetric separation membrane to the outside of the separation membrane module.
The permeated vapor (permeated material) whose main component is water that has selectively permeated the separation membrane is taken out, and if necessary, the permeated vapor (permeated material) is cooled, condensed, and recovered.

In this invention, the organic aqueous solution supplied to the separation membrane module is about 25-120'C1, particularly preferably 50-120'C1
The temperature is preferably about 00°C.

In the pervaporation separation method of the present invention, the pressure applied to the separation method is usually such that the pressure on the permeate side of the separation membrane is lower than the pressure on the supply side, and the pressure on the supply side is from atmospheric pressure to 60 kg/cI.
II, preferably about atmospheric pressure to 30 kg/cml.

The permeation side of the asymmetric separation membrane in the separation membrane module may be subjected to a sweep gas or to a reduced pressure state when performing pervaporation separation of an aqueous organic solution, but the reduced pressure state is atmospheric pressure. It is sufficient if the pressure is lower, particularly preferably about 200 torr or less, and even more preferably about 100 torr or less.
Preferably, the pressure is reduced to below Torr.

Various organic aqueous solutions can be used to which the pervaporative separation method of organic compound mixtures in the present invention can be applied. Examples of the organic substances include methanol, ethanol, n- Propatool, Isopropatool, n-butanol, 5e
Aliphatic alcohols such as c-butanol 1, tert-butanol, and ethylene glycol, alicyclic alcohols such as cyclohexanol, aromatic alcohols such as benzyl alcohol, organic carboxylic acids such as formic acid, acetic acid, propionic acid, and butyric acid, butyl acetate, Organic carboxylic acid esters such as ethyl acetate and methyl malonate, acetone,
Ketones such as methyl ethyl ketone, cyclic ethers such as tetrahydrofuran and dioxane, acetonitrile,
Examples include nitriles such as acrylonitrile, aldehydes such as formaldehyde and heptaldehyde, and mixtures of two or more thereof may be used.

In the pervaporation separation method of the present invention, the concentration of the organic substance aqueous solution is not particularly limited, and an organic substance aqueous solution containing organic substances in any proportion can be separated or concentrated.

The structure, format, etc. of the separation membrane module described above are not particularly limited, but examples thereof include a plate-and-frame type module, a spiral type module, a hollow fiber membrane type module, etc. It is preferable.

〔Example〕

EXAMPLES Hereinafter, examples and comparative examples regarding the pervaporative separation method of the present invention will be shown, and the present invention will be explained in more detail.

In Examples and Comparative Examples, the permeation rate Q and separation coefficient α are determined by cooling and condensing the vaporized components that have passed through the membrane, collecting them, measuring their weight, and adding dehydrated n- Propatool was added, and the weight ratio of water to organic matter was measured by TCD-gas chromatography, and calculated using the formula shown below.

In the reference examples, the abbreviations of each compound used for the aromatic tetracarboxylic acid component and the aromatic diamine component are shown below.

4.4゛DADt! ; 4.4'' Diaminodiphenyl ether 3.4'-DADE;3.4' Diaminodiphenyl ether M; 4,4'' Diaminodiphenylmethane TSN PASN; 〇-Toridine sulfone: to bis(4-aminophenyl) sulfone DAB;
3,5-Diaminobenzoic acid reference example 1 [Preparation of aromatic polyimide solution] A tetracarboxylic acid component consisting of 100 mol% of 3.3',4.4'-biphenyltetracarboxylic dianhydride;
■, 4-bis(4-aminophenoxy)benzene (TP
EQ) (85 mol%) and a diamine component consisting of 15 mol% of 4,4''-diaminodiphenyl ether (DADE) were polymerized in equimolar amounts in parachlorophenol (PCP) at a temperature of 180 °C for 20 hours. The resulting high molecular weight aromatic polyimide PCP solution (concentration = 17% by weight)
) was prepared.

[Spinning of hollow fiber membrane of aromatic polyimide] The above-mentioned aromatic polyimide solution was supplied to a spinning device equipped with a hollow fiber spinning nozzle, and the coagulation liquid (temperature: 5°C, ethane-water based coagulation liquid) An asymmetric hollow fiber separation membrane was formed by a wet membrane forming method using the following method, and heat treated at the heat treatment temperature shown in Table 1 to produce a hollow fiber separation membrane for aromatic polyimides.

The hollow fiber membrane has an outer diameter of 432 μm and an inner diameter of 2
It was a continuous long hollow fiber with a thickness of 66 μm (film thickness was approximately 83 μm).

The tensile strength (kg/fiber) and elongation rate (
%), as well as the retention rate (%) of tensile strength and elongation after being immersed in hot water or hot ethanol aqueous solution at 150°C for 20 hours.

Reference Examples 2 to 15 A PCP solution of aromatic polyimide having the concentration and rotational viscosity shown in Table 1 was prepared in the same manner as in Reference Example 1, except that a diamine component having the type and composition shown in Table 1 was used. were prepared, respectively, and the obtained aromatic polyimide solution was used and heat treated at the heat treatment temperature shown in Table 1, but by the same wet film forming method as in Reference Example 1. Hollow fiber membranes made of asymmetric separation membranes made of aromatic polyimides and having the same outer diameter, inner diameter, and wall thickness as the hollow fiber membranes were manufactured.

Table 1 shows the tensile strength and elongation of each hollow fiber membrane, as well as the retention of the tensile strength and elongation after being immersed in 150°C hot water or hot ethanol aqueous solution for 20 hours.

Example 1-13 and Comparative Examples 1 to 7 After heat-treating the asymmetric hollow fiber separation membranes manufactured in each reference example at the heat treatment temperature shown in Table 1, four fibers were bundled to form a fiber bundle, and the fibers were Seal one end of the bundle with epoxy resin,
A separation membrane module is manufactured by creating a hollow bundle element and placing the hollow bundle element inside a container having an inlet for supplying an aqueous organic solution, an outlet for taking out unpermeated matter, and an outlet for taking out permeated matter. did.

An 80% ethanol aqueous solution is supplied to the separation membrane module at 90°C, and permeation is carried out under a reduced pressure of 3 torr or less inside the hollow fibers of the hollow fiber elements in the separation membrane module. was cooled and collected.

Table 2 shows the permeation rate Q in pervaporation and the separation coefficient α between water and organic matter.

The asymmetric hollow fiber separation membranes produced in each reference example were subjected to the following hot water resistance test, and the test results are shown in Table 2.

After holding the hollow fiber membrane in hot water at 150°C for 20 hours, it was dried under reduced pressure at room temperature, and a mixed solvent of parachlorophenol (PCP) and orthochlorophenol (OCP) (PCP10CP= 4/1 weight ratio) to dissolve the polyimide forming the hollow fiber membrane, and
The logarithmic viscosity at °C was measured and the retention rate was calculated using the following formula.

Table Examples 14 to 16 and Comparative Example 8 Reference Example 5, Reference Example 9, Reference Example 10 and Reference Example) The asymmetric hollow fiber separation membrane made of aromatic polyimide obtained in 1.
It was immersed in water at 50°C or a 60% by weight ethanol aqueous solution for 20 hours.

After drying the asymmetric hollow fiber separation membrane made of aromatic polyimide heat-treated as described above at 60°C under reduced pressure, a hollow bundle element and a separation membrane module were produced in the same manner as in Example 1. Then, add 80% by weight ethanol aqueous solution to 9
Table 3 shows the permeation rate Q and the separation coefficient α between water and organic matter in pervaporation when the water is supplied at 0°C.

[Actions and effects of the present invention]

The pervaporation separation method of the present invention is a separation method related to pervaporation using an asymmetric separation membrane made of a specific aromatic polyimide, so it can be used to separate and concentrate aqueous solutions of various organic substances. It can be used with organic matter aqueous solutions with a wide range of concentrations, and has sufficient heat resistance.
It has water resistance, solvent resistance and durability, and also
Since an asymmetric membrane made of a specific polyimide having high water permeability and separation performance is used, stable separation by pervaporation can be performed for a long time.

Patent applicant: Ube Industries Co., Ltd.

Claims (2)

[Claims] (1) In a pervaporation separation method in which an aqueous organic matter solution is brought into contact with an asymmetric separation membrane made of a heat-resistant polymer to selectively permeate mainly water from the aqueous organic matter solution, the heat-resistant polymer has the general formula I ▲There are mathematical formulas, chemical formulas, tables, etc.▼ Other aromatic aromatic compounds containing 60 to 100 moles of repeating units shown in (I), and the remaining repeating units having biphenyltetracarboxylic acids and 2 to 5 benzene rings. 1. A method for pervaporative separation of an aqueous solution of an organic substance, characterized in that the soluble aromatic polyimide is a repeating unit formed from an aromatic diamine component which is a group diamine compound. (2) In a pervaporation separation method in which an organic matter aqueous solution is brought into contact with an asymmetric separation membrane made of a heat-resistant polymer to selectively permeate mainly water from the organic matter aqueous solution, the heat-resistant polymer has the general formula II ▲There are mathematical formulas, chemical formulas, tables, etc.▼(II) Repeating unit A shown by General formula III ▲There are mathematical formulas, chemical formulas, tables, etc.▼(III) General formula IV ▲There are mathematical formulas, chemical formulas, tables, etc. ▼(IV) Or, the general formula V ▲There are mathematical formulas, chemical formulas, tables, etc. ▼(V) It mainly consists of the repeating unit B shown by the general formula V, and the molar ratio (A:B) of the above repeating units is 30:70 ~ A method for pervaporative separation of an aqueous solution of organic matter, characterized in that it is a soluble aromatic polyimide with a ratio of 90:10.