JPS63182005A - Polyion complex separation membrane - Google Patents

Abstract

PURPOSE:To obtain a separation membrane having adequate durability, high permeable speed and separation properties by permitting formation of a polyion complex through the gathering of anionic polymers and cationic polymers under ion linkage effect on the surface of or in a membrane. CONSTITUTION:An aqueous solution of, for instance, salt of ammonium polyacrylate as a synthetic polymer containing the anionic group is poured and spread on a porous support of polyester sulfonic ultrafiltration membrane. After this, the aqueous solution is air-dried and the above-described process is repeated to create a complex membrane of salt of ammonium polyacrylate. This membrane is immersed in, for instance, a mixed solvent solution of ethanol of polyarylamine hydrochloride/water as a synthetic polymer containing the cationic group to obtain a polyion complex. The membrane obtained in this way has a high separation coefficient across a wide range of density areas of organic materials when an aqueous solution of organic materials or a mixed vapor of water and organic materials is separated by a permeation/evaporation method and a vapor permeation method. Besides the membrane has superior water-proofness and durability.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for separating water from an aqueous solution of an organic substance or a mixed organic substance/water vapor. More specifically, the present invention relates to a membrane for separating and concentrating an organic substance aqueous solution by a pervaporation method or an organic substance/water mixed vapor by a vapor permeation method.

(Prior Art and Problems) Reverse osmosis has been put into practical use for concentrating and separating some low-concentration organic matter aqueous solutions using membranes. However, reverse osmosis requires applying pressure to the liquid to be separated that is higher than the osmotic pressure of the separation liquid, so it cannot be applied to highly concentrated aqueous solutions where the osmotic pressure becomes high. There is a limit.

In contrast, pervaporation and vapor permeation methods, which are separation methods that are not affected by osmotic pressure, are attracting attention as new separation methods. Pervaporation is a method in which a separated liquid is supplied to the primary side of the membrane, and the separated substance is passed through the membrane in gaseous form by reducing the pressure on the secondary side (permeation side) of the membrane or by passing a carrier gas through the membrane. The vapor permeation method differs from the pervaporation method in that mixed vapor is supplied to the primary side of the membrane. The membrane-permeable substance can be collected by cooling and condensing the permeated vapor. Many research examples have been reported so far regarding the pervaporation method. For example, U.S. Patent 3,750.735 and U.S. Patent 4,0
67, 805, there is an example of organic matter/water separation by polymers having active anionic groups, and US Patent 2,95
No. 3,502 and No. 3,035,060 have examples of ethanol/water separation using cellulose acetate membranes and polyvinyl alcohol membranes, respectively. In addition, in Japan, JP-A-59-109.204 describes a cellulose acetate membrane and a polyvinyl alcohol membrane;
No. 55.305 has a polyethyleneimine crosslinked membrane.

However, the separation performance exhibited by the membranes described in these patents, especially the permeation rate, is low, and it can be said that they are of poor practical use. On the other hand, as an example of excellent separation performance, JP-A-60
-129,104 describes membranes made of anionic polysaccharides; however, in the case of membranes made of polysaccharides and polysaccharide derivatives,
Depolymerization by acid or alkali, decomposition by bacteria, etc.
There are unavoidable problems with natural polymer compounds, such as durability,
Chemical resistance cannot be expected.

As mentioned above, the conventional membranes used in pervaporation or vapor permeation methods require large area membranes due to low permeation rates, or have low separation coefficients that make it difficult to separate liquids. In order to concentrate to the desired concentration, it was necessary to circulate the highly concentrated permeate. These have been disadvantageous in increasing the equipment price or operating cost.

The permeation rate in the present invention is the amount of permeated mixture per unit membrane area/unit time, expressed in units of kg/rrf/hr. On the other hand, the separation coefficient (α) is the ratio of water and organic matter in the permeate gas to the ratio of water and organic matter in the feed liquid or feed vapor. That is, α=(X/Y)p/(X/Y)f
It is. Here, X and Y represent the respective compositions of water and organic matter in a two-component system, and p and f represent permeation and supply.

The purpose of the present invention is to provide sufficient durability, high permeation rate, and separation coefficient for a wide range of concentration ranges of organic matter when separating organic matter aqueous solutions or mixed vapors of organic matter and water by pervaporation and vapor permeation methods. The objective is to obtain a separation membrane having the following characteristics.

(Means for Solving the Problems) As a result of intensive study on the above points, it has been found that the above problems can be solved by the following method.

(1) A synthetic polymer having an anionic group and a synthetic polymer having a cationic group are associated with each other through ionic bonds to form a polyion complex on the membrane surface and/or within the membrane. Polymer membrane for water/organic separation using pervaporation or vapor permeation.

(2) The membrane according to item 1 above, wherein the anionic group-containing synthetic polymer constituting the polyion complex is crosslinked with a crosslinking agent that forms a covalent bond with the polymer.

(3) The membrane according to item 1 or 2 above, wherein the anionic group-containing synthetic polymer constituting the polyion complex is polyacrylic acid, a metal salt of polyacrylate, or an ammonium salt of polyacrylate. .

(4) Item 1 above, wherein the cationic group of the cationic group-containing synthetic polymer constituting the polyion complex is a primary, secondary, tertiary, or quaternary amine; Alternatively, the membrane according to item 2 or 3.

(5) The membrane according to item 4 above, wherein the cationic group-containing synthetic polymer constituting the polyion complex is polyallylamine.

(6) The membrane according to item 4 above, wherein the cationic group-containing synthetic polymer constituting the polyion complex is polyethyleneimine.

(7) The membrane form is a composite membrane having a porous polymer membrane as a support, and the thickness of the active skin layer is 5 μm or less, or the above item 1, or 2, or 3, or The membrane according to item 4, or 5, or 6.

In order to selectively permeate water from an organic substance aqueous solution or an organic substance/water vapor mixture, it is preferable to introduce into the membrane a functional group having a large ability to coordinate water.Water coordinated to these membranes is called bound water in contrast to the free water of the bulk liquid. Therefore, it is thought that the selective water permeability of the membrane can be dramatically increased by introducing an electrolytic group that selectively coordinates water while excluding organic substances. Based on this idea, the aforementioned U.S. Patent No. 3,750,735 and U.S. Patent No. 4,067.805
describes that the decomposition coefficient increases by introducing anionic groups into various nonionic polymers. However, most of the polymers that have a large number of electrolytic groups, such as polyacrylic acid, polymethacrylic acid, carboxymethyl cellulose, or their salts, are water-soluble or have the property of swelling greatly in water. When used as a membrane, it can be used if the liquid to be separated is an aqueous solution of organic substances with a high concentration, but if the liquid to be separated is an aqueous solution of organic substances with a low concentration, the membrane will dissolve or swell significantly, making it difficult to use as a separation membrane. It is clear that function is significantly reduced. Therefore, by crosslinking polymers with these anionic groups to make them three-dimensional, it is possible to increase the resistance to the separation of aqueous solutions of organic substances with a wide range of concentrations. However, crosslinking of membranes usually tends to reduce the permeation rate. It is in.

As a result of intensive studies on crosslinking methods for polymers having anionic groups, the inventors of the present invention found that by associating the polymer with a cationic polymer through ionic bonds, a membrane with high separation performance and water resistance can be obtained. I found out.

In general, polymer molecules are associated with each other through many ionic bonds, resulting in a three-dimensional structure called a polyion complex.
Alternatively, it is called a polymer ion complex, and the present invention uses such a polyion complex to develop a membrane that has excellent solvent resistance, high permeation rate, and high separation performance.

The present invention will be explained in more detail below.

The anionic polymer constituting the polyion complex has a carboxyl group (-COOH) in the molecular side chain.
, or those having a sulfonic acid group (-3o, H) are preferred. The cationic polymer constituting the polyion complex is preferably one having a primary amine, a tertiary amine, a tertiary amine, or a quaternary amine in its main chain or side chain.

Polyion complexes are generally insoluble in solvents because their molecular chains are associated with each other through ionic bonds.

Therefore, in order to apply this to a membrane, (1) Prepare a mixed solution of an anionic polymer and a cationic polymer with a solution composition that does not cause ionic association between the two, and after casting on a smooth surface such as glass, A method of creating a complex film by vaporizing or replacing the solvent.

■ A membrane consisting of either an anionic polymer or a cationic polymer is cast and formed in advance, and a counterionic polymer solution is cast on the surface of the membrane to form a membrane near the interface between the two polymer layers. A method for forming polyion complexes.

■ Similar to ■, a membrane made of either an anionic polymer or a cationic polymer that has been formed in advance is immersed in a counterionic polymer solution, and the membrane surface is adsorbed by the counterionic polymer in the solution. A method to form a polyion complex nearby.

It is necessary to use a film forming method such as In the case of ■■, the polyion complex is thought to exist in a very thin layer at the interface or surface, but exhibits sufficiently high separation performance.

In addition to association between ionic groups, by providing a crosslinked structure consisting of covalent bonds, the durability and solvent resistance of the membrane can be further improved. Furthermore, in membranes made of highly hydrophilic materials as shown in the examples of the present invention, by providing both a polyion complex structure and a crosslinked structure by covalent bonds, swelling of the membrane by an aqueous organic substance solution to be separated can be prevented. even lower, and the separation factor remains high. The covalent bond crosslinking described here may be one that utilizes an electrolytic group such as a carboxyl group or an amino group, but
It must not be of such a degree that it consumes all or most of these electrolytic groups and eliminates the ability of the material to form polyion complexes. It is preferable that the crosslinking agent is dissolved in a solution of the polymer used as the membrane material and reacted in the solution by heating or the effect of an appropriate catalyst. Specifically, polyfunctional epoxy, methylolated melamine, diamine, Polyfunctional isocyanate compounds and the like can be used.

It is preferable that the film is as thin as possible if there are no pinholes, but specifically, the film thickness is preferably 10 μm or less, particularly 5 μm or less. However, a membrane with a thickness of 1Oμ or less lacks mechanical strength and is generally difficult to use as a separation membrane that is used by applying a high pressure difference on both sides of the membrane. Therefore, it is preferred to use it in the form of a composite membrane coated as an active skin layer on a porous support. After adding a crosslinking agent as necessary to a solution consisting of an anionic polymer, a cationic polymer, or a mixture thereof, which is a membrane material, on the porous support, an applicator such as a doctor blade or a wire bar is used. A composite membrane is obtained by casting, heating and drying, and ion complexing treatment.

The support is a support having micropores of tens to thousands of angstroms on its surface, and is a support made of known materials such as polysulfone, polyethersulfone, polyacrylonitrile, cellulose ester, polycarbonate, polyvinylidene fluoride, etc. Includes: In order to reduce the thickness of the skin layer of the composite membrane, the solid content concentration of the mixed solution coated on the porous support is lowered, or the coating thickness is reduced. The membrane of the present invention can be a flat membrane, a tube membrane, or a hollow membrane. The flat membranes can be stacked as is, or they can be formed into pleats or spirals to form modules.

The membrane prepared in this manner can be prepared using water/organic mixtures such as alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and n-butanol, acetone,
Ketones such as methyl nityl ketone, ethers such as tetrahydrofuran and dioxane, organic acids such as formic acid and acetic acid,
Aldehydes such as aldehyde and propionaldehyde,
1 or 2 consisting of amines such as pyridine and picoline
It is used to separate aqueous solutions containing the above compounds or vapor mixtures with water.

(Effect of the invention) A membrane in which a polyion complex is formed within the membrane or on the membrane surface has a higher separation performance, especially a higher separation coefficient, than a membrane consisting of a single anionic or cationic polymer. It also has excellent water resistance and durability.

(Example) Next, the present invention will be explained in more detail with reference to Examples.

1 (1) Creation of polyacrylic acid ammonium salt composite membrane An aqueous solution of polyacrylic acid polymerized in the laboratory (1% aqueous solution viscosity - 24 centiboise) was neutralized with an ammonia aqueous solution, and then diluted with water. 0.5 of polyacrylic acid ammonium salt
% aqueous solution was prepared. A 0.5% aqueous solution of the prepared polyacrylic acid ammonium salt was placed on a polyethersulfone ultrafiltration membrane (manufactured by Daicel Chemical Industries, Ltd., DUS-40) using a wire bar with a winding diameter of 0.151. It was cast and air-dried using dust-free air on a clean bench. The same coating was repeated once on the polyacrylic acid ammonium salt coating layer obtained by drying to obtain a composite film having a skin layer thickness of 0.4 μm.

(2) Polyion complex formation The polyacrylic acid ammonium salt composite membrane obtained in (1) above was added to a 0.5% solution of polyallylamine hydrochloride using an ethanol/water (-1/1) mixture as a solvent at room temperature. A polyion complex membrane was obtained by immersion in water for 10 minutes. The solution is weakly acidic (P
) I 3.5).

(3) Evaluation of separation performance Ethanol/water (=9515 weight ratio) at a temperature of 70°C and a gauge pressure of 0.1 kg/aa on the primary side (skin layer side) of the membrane obtained in (2) above When the secondary side of the membrane was made into a closed system, the pressure of this system rose to 8 amHg due to the mixed vapor of ethanol/water permeating through the membrane. The total number of moles of the mixed vapor permeating through the membrane was calculated from the volume of the closed system and the time required for the pressure to rise.

Furthermore, the permeation rate and separation coefficient were calculated by analyzing the composition of the feed liquid and the mixed vapor of this closed system by gas chromatography. The values of the permeation rate and separation coefficient obtained in this way were consistent with the values of the permeation rate and separation coefficient calculated from the weight and composition analysis of the permeated mixed vapor trapped in liquid nitrogen. .

(4) Evaluation results It is shown in Table 1.

In (2) of Example 1, 0.5% polyallylamine hydrochloride is used to soak the polyacrylic acid ammonium salt composite membrane.
The same procedure as in Example 1 was carried out except that the solution was adjusted to be weakly basic (PH9, 2) with a 10% ammonia aqueous solution in advance. Table 1 shows the evaluation results of separation performance.

The polyacrylic acid ammonium salt composite membrane prepared in (1) of Example 1 was evaluated as it was in (3) of Example 1. The results are shown in Table 1.

Compared to the membranes in which polyallylamine was adsorbed in Examples 1 and 2, the separation coefficient α was significantly smaller and the permeation rate Q was also lower.

(1) Preparation of polyacrylic acid potassium salt composite membrane Example 1
The aqueous solution of polyacrylic acid used in (1) was neutralized with a 1N aqueous potassium hydroxide solution, and then diluted with water to prepare a 1.0% aqueous solution of potassium polyacrylate salt. A 10% aqueous solution of the prepared potassium polyacrylate salt was filtered using a polyethersulfone ultrafiltration membrane (manufactured by Daicel Chemical Industries, Ltd.).
DU S-40) using a wire bar with a winding diameter of 0.15 mm, and air-dried with dust-free air in a clean bench. On the coated layer of polyacrylic acid potassium salt obtained by drying, the same coach infrastructure was further repeated once to obtain a composite membrane having a skin layer thickness of 0.6 μm.

(2) Polyion complex formation example 3 (1)
The polyacrylic acid potassium salt composite membrane obtained in ) was made into a polyion complex in the same manner as in Example 1 (2).

(3) Evaluation of separation performance The same procedure as in Example 1 (3) was carried out.

(4) Evaluation results It is shown in Table 1.

In (2) of Example 3, the 0.5% solution of polyallylamine hydrochloride in which the polyacrylic acid potassium salt composite membrane is immersed is made basic (PH10,0 ) was carried out in the same manner as in Example 3, except that it was adjusted to . Table 1 shows the evaluation results of separation performance.

The polyacrylic acid potassium salt composite membrane prepared in Example 3 (1) was evaluated as it was in Example 1 (3).

The results are shown in Table 1.

1/1 (1) Creation of polyacrylic acid melamine crosslinked composite membrane Add 0.5% aqueous solution of hexamethoxymethylmelamine to the same 0.5% aqueous solution of polyacrylic acid as in Example 1 (1) to polyacrylic acid: Add xamethoxymethylmelamine = 8:2 (solute mixing ratio), and apply it on a polyethersulfone ultrafiltration membrane (manufactured by Daicel Chemical Industries, Ltd., DUS-40).
It was cast using a wire bar with a winding diameter of 0.15 am (7) and heated in a clean open at 100°C for 10 minutes to obtain a crosslinked composite membrane.

On the coating layer made of the polyacrylic acid melamine crosslinked product obtained by heating, the same coating was further repeated once to obtain a polyacrylic acid melamine crosslinked composite membrane.

(2) Conversion to potassium salt The polyacrylic acid melamine crosslinked composite membrane obtained in (1) of Example 5 was added to a 0.1% potassium hydroxide aqueous solution for 10 min at room temperature.
The polyacrylic acid was converted to potassium salt by soaking for a minute.

(3) Polyion complex formation example 5 (2
) The polyacrylic acid potassium salt melamine cross-linked composite membrane obtained in 1.
Polyallylamine hydrochloride adjusted to pH 10.0).
It was immersed in a 5% solution to form a polyion complex.

(4) Evaluation of separation performance The same procedure as in Example 1 (3) was carried out.

(5) Evaluation results It is shown in Table 1.

The polyacrylic acid potassium salt melamine crosslinked composite membrane obtained in Example 5 (2) was evaluated as it was in Example 1 (3). The results are shown in Table 1.

Although the separation coefficient α was slightly larger than that of the membrane adsorbed with polyallylamine in Example 5, the permeation rate Q was about one third.

The polyacrylic acid melamine crosslinked composite membrane obtained in (1) of Example 5 was evaluated as it was in (3) of Example 1.

The results are shown in Table 1.

Compared to the membrane in which polyallylamine was adsorbed in Example 5, the separation coefficient α was significantly smaller and the permeation rate Q was also smaller.

(1) Preparation of polyacrylic acid epoxy crosslinked composite membrane Add 18 Wt of 0.5% water of diglycidyl ether to the same 0.5% aqueous solution of polyacrylic acid as in Example 1 (1). Glycidyl ether was added at a ratio of 9:1 (solute mixing ratio), and a polyether sulfone ultrafiltration membrane (manufactured by Daicel Chemical Industries, Ltd., DO3-40) was added with a winding diameter of 0.
Cast using a 15mm wire bar, i o o
The mixture was heated in a clean oven for 10 minutes to obtain a polyacrylic acid epoxy crosslinked composite film.

(2) Conversion to potassium salt The polyacrylic acid epoxy crosslinked composite membrane obtained in Example 6 (1) was converted to potassium salt in the same manner as in Example 5 (2).

(3) Formation into a polyion complex The polyacrylic acid potassium salt epoxy crosslinked composite membrane obtained in Example 6 (2) was formed into a polyion complex in the same manner as in Example 5 (3).

(4) Evaluation of separation performance The same procedure as in Example 1 (3) was carried out.

(5) Evaluation results It is shown in Table 1.

Comparison 5i The polyacrylic acid potassium salt epoxy crosslinked composite membrane prepared in Example 6 (2) was evaluated as it was in Example 1 (3). The results are shown in Table 1.

Compared to the membrane in which polyallylamine was adsorbed in Example 6, both the permeation rate Q and the separation coefficient α were extremely small.

The polyacrylic acid epoxy crosslinked composite membrane prepared in Example 6 (1) was evaluated as it was in Example 1 (3). The results are shown in Table 1.

The separation coefficient α was much smaller than that of the membrane adsorbed with bo-realylamine in Example 5.

(1) Creation of polyacrylic acid diamine cross-linked composite membrane Add 1 to 4.7% aqueous solution of polyacrylic acid, the same as in Example 1 (1).
．． 0.19% of 3-diamino-2-hydroxypropane
The aqueous solution was added so that the ratio of polyacrylic acid:1,3-diamino-2-hydroxypropane was 6jl (solute mixing ratio), and it was rolled onto a polyethersulfone ultrafiltration membrane (manufactured by Daicel Chemical Industries, Ltd., DUS-40). It was cast using a wire bar with a wire diameter of 0.15 (Foundation) and heated in a clean oven at 140"C for 30 minutes. On the coated layer of the composite film obtained by heating, a similar coating was further applied. This was repeated twice to obtain a composite membrane.

(2) Conversion into potassium salt The polyacrylic diamine crosslinked composite membrane obtained in Example 7 (1) was converted into potassium salt in the same manner as in Example 5 (2).

(3) Polyion complex formation example 7 (2)
) The polyacrylic acid potassium salt diamine crosslinked composite membrane obtained in Example 5 (3) was treated with a base (PH10,
0) to form a polyion complex.

(4) Evaluation of separation performance The same procedure as in Example 1 (3) was carried out.

(5) Evaluation results It is shown in Table 1.

The polyacrylic acid potassium salt diamine crosslinked composite membrane prepared in Example 7 (2) was evaluated as it was in Example I (3). The results are shown in Table 1.

Compared to the membrane in which polyallylamine was adsorbed in Example 7, both the permeation rate Q and the separation coefficient α were extremely small.

Hokkai Charcoal The polyacrylic acid diamine crosslinked composite membrane obtained in Example 7 (1) was evaluated as it was in Example 1 (3).

The results are shown in Table 1.

Compared to the membrane in which polyallylamine was adsorbed in Example 7, the permeation rate Q was higher, but the separation coefficient α was significantly smaller.

(1) Creation of polyacrylic acid epoxy cross-linked composite membrane A 1.0% aqueous solution of diglycidyl ether was added to the same 1.0% aqueous solution of polyacrylic acid as in Example 3 (1).Polyacrylic acid; diglycidyl Ether was added so that the ratio of solutes was 8:2, and the winding diameter was 0.15 m on a polyether sulfone ultrafiltration membrane (manufactured by Daicel Chemical Industries, Ltd., DUS-40).
The mixture was cast using a No. 1 wire parr and heated for 10 minutes in a clean oven at 100°C to obtain a polyacrylic acid epoxy crosslinked composite film. A similar coating was further repeated once on the resulting coating layer made of the crosslinked polyacrylic acid epoxy product to obtain a composite membrane.

(2) Polyion complex formation example 8 (1)
The polyacrylic acid epoxy crosslinked composite membrane obtained in ) was immersed in a basic (PH 10,0) 0.5% polyallylamine solution as in (3) of Example 5 to form a polyion complex.

(3) Evaluation of separation performance The same procedure as in Example 1 (3) was carried out.

(4) Evaluation results It is shown in Table 1.

(1) Creation of polyacrylic acid-polyethyleneimine-based polyion complex membrane The polyacrylic acid epoxy crosslinked composite membrane obtained in Example 8 (1) was mixed with an ethanol/water (= 1/1) mixed solution. 1 in a 0.5% solution of polyethyleneimine in solvent at room temperature.
A polyion complex membrane was obtained by immersion for 0 minutes.

(2) Evaluation of separation performance The same procedure as in Example 1 (3) was carried out.

(3) Evaluation results It is shown in Table 1.

The polyacrylic acid epoxy crosslinked composite membrane prepared in (1) of Example Day A was evaluated as it was in (3) of Example 1. The results are shown in Table 1.

The separation coefficient α was extremely small compared to the polyion complex membranes of Examples 8 to 10.

Table 1 5. Contents of correction October l1, 1986

Claims (7)

[Claims] (1) A synthetic polymer having an anionic group and a synthetic polymer having a cationic group are associated with each other through ionic bonds to form a polyion complex on the membrane surface and/or within the membrane. Polymer membrane for water/organic separation using pervaporation or vapor permeation. (2) The membrane according to claim 1, wherein the anionic group-containing synthetic polymer constituting the polyion complex is crosslinked with a crosslinking agent that forms a covalent bond with the polymer. (3) Claim 1 or 2, wherein the anionic group-containing synthetic polymer constituting the polyion complex is polyacrylic acid, a metal salt of polyacrylate, or an ammonium salt of polyacrylate. The membrane described. (4) The cationic group of the cationic group-containing synthetic polymer constituting the polyion complex is primary or
The membrane according to claim 1, 2, or 3, which is a secondary, tertiary, or quaternary amine. (5) The membrane according to claim 4, wherein the cationic group-containing synthetic polymer constituting the polyion complex is polyallylamine. (6) The membrane according to claim 4, wherein the cationic group-containing synthetic polymer constituting the polyion complex is polyethyleneimine. (7) Claims 1, 2, or 3, wherein the membrane is a composite membrane having a porous polymer membrane as a support, and the thickness of the active skin layer is 5 μm or less; Or the fourth
The membrane according to item 1, or 5 or 6.