JPH0644977B2 - Desalination method for organic compounds using amphoteric ion exchange membrane - Google Patents

Description

The present invention relates to a method for removing an inorganic salt from a mixture of an inorganic salt and an organic compound, which is carried out by using an amphoteric ion exchange membrane prepared by using a block copolymer.

Sugars, antibiotics, oligopeptides, coenzymes, vitamins,
The process of removing inorganic salts from an aqueous solution containing low molecular weight organic compounds such as amino acids and nucleic acids and inorganic salts at a low cost and without impairing the activity of necessary components is now becoming more and more important industrially. It is becoming. In the crystallization separation method and the method using an ion exchange resin which are generally used at present, acid,
It consumes a large amount of alkali, salts, water, etc., and consumes a large amount of electricity in the electrodialysis method. Furthermore, in these methods, the apparatus and the operation are complicated, and there is a high risk that the necessary components are denatured by the influence of heat, contact with resin, or voltage. On the other hand, when an ultrapermeation membrane or a reverse osmosis membrane is used, it is usually impossible to efficiently separate a low molecular weight organic compound and an inorganic salt. In recent years, researches on new separation membranes have been actively conducted, but a decisive method for replacing the conventional method has not been found yet.

The present inventors have used an amphoteric ion exchange membrane composed of a block copolymer having a polymer polyA ⁻ having a cation exchange group and a polymer polyB ⁺ having an anion exchange group as a part of constituent components, As a result of research on means for removing an inorganic salt from an aqueous solution containing a high molecular weight organic compound or a low molecular weight organic compound and an inorganic salt, one side of such an amphoteric ion exchange membrane contains the organic compound and the inorganic salt. Aqueous solution I
The other surface is contacted with phase II, and the other surface is contacted with phase II, which is an aqueous solution of water or an inorganic salt thinner than the phase I or an organic compound of an appropriate concentration and an inorganic salt of a concentration lower than the phase I, and if necessary, I
It has been found that if pressure is applied to the phase, it is possible to move the inorganic salt from the I phase to the II phase through the membrane with high efficiency while leaving the I phase organic compound in the I phase. .

Hereinafter, the method of the present invention will be described in detail.

The amphoteric ion exchange membrane used in the present invention is a polymer polyA capable of introducing a cation exchange group, a polymer polyB capable of introducing an anion exchange group, and a polymer not introducing an ion exchange group.
polyC is, for example, polyA-polyC-polyB, polyC
-PolyA-polyC-polyB, polyA-polyC-polyB-
Using an original multi-block copolymer which is linked like polyC, polyC-polyA-polyC-polyB-polyC, cation exchange groups and anion exchanges in the polyA and polyB parts before or after film formation, respectively. It is obtained by introducing a group and, if necessary, crosslinking the polyA, polyB and polyC moieties.

Generally, in the case of a block copolymer, in the solid state,
It is known that component blocks composed of different kinds of monomers do not mix with each other to form spherical, rod-shaped or layered microdomains determined for each block by the degree of polymerization of the blocks. In the amphoteric ion exchange membrane used in the present invention, the domain having a cation exchange group and the domain having an anion exchange group are present separately from each other by utilizing such a microphase separation phenomenon to prevent the formation of a polyion complex. The feature is that

Hitherto, in amphoteric ion exchange membranes made from such block copolymers, the pressure difference generated between the two surfaces was used as the driving force, and the salt solution on the high pressure side in contact with the membrane was made to have a higher concentration than that and the low pressure side was used. It has been known that desalination and purification of organic substances can be performed by utilizing this. In this case, much higher pressure is required to increase efficiency. The present inventors have found that when there is no pressure difference between both sides of an amphoteric ion exchange membrane made from a similar block copolymer, the salt moves through the membrane from the high salt concentration solution side to the low salt solution side at high speed. Furthermore, it was discovered that salt permeation can be promoted by applying pressure to a solution with a high salt concentration while causing a difference in salt concentration, or adding an organic compound that does not ionize to a solution with a low salt concentration. However, these phenomena are applied to desalination of organic compounds. That is, the present invention is characterized in that the concentration difference of the salt generated between both sides of such an amphoteric ion exchange membrane is used as a driving force, and one side of the membrane is an aqueous solution of an organic compound to be desalted. (I
Phase) and the other surface is contacted with water or an aqueous solution containing a salt at a concentration lower than that of the aqueous solution of phase I or an aqueous solution (phase II) containing any organic compound that does not ionize. By applying a relatively low pressure to the phases, it is possible to efficiently move the salt from phase I to phase II. In this case, if only the salt concentration difference is used as the driving force, as the concentration of the organic compound in the phase I increases, the permeation of the salt greatly hinders the salt permeation.
In such a case, it is effective to pressurize the phase II or add an arbitrary organic compound to the phase II.

When pressure is applied to phase I to improve desalination efficiency, it is desirable that the pressure be equal to or higher than the osmotic pressure caused by the organic compound. In order to improve the desalting efficiency, it is desirable that the molar concentration thereof is equal to or higher than that of the organic compound contained in the phase I. However, even if the pressure of the phase I or the concentration of the organic compound of the phase II is lower than the above values, the effects corresponding to those values can be exhibited.

Among the polymers constituting the original block copolymer used in the present invention, the polymer polyA capable of introducing a cation exchange group needs to be capable of easily introducing a carboxyl group, a sulfone group, a phosphoric acid group or the like. is there. Among these, the carboxyl group is an unsaturated carboxylic acid ester (for example, acrylic acid ester, methacrylic acid ester, crotonic acid ester, conjugated diene carboxylic acid ester, etc.)
Alternatively, it can be obtained by hydrolyzing a monomer having a cyano group such as acrylonitrile, methacrylonitrile, or vinylidene cyanide, or a polymer such as an alkyldenmalonic acid ester or α-cyanoacrylic acid ester,
The sulfone group can be obtained by hydrolyzing a polymer of styrenesulfonyl chloride or by sulfonating a polymer of styrene, α-methylstyrene, vinyltoluene or diphenylbutadiene by a known method.

The polymer polyB capable of introducing an anion exchange group needs to be able to introduce a functional group such as an ammonium group, a sulfonium group or a phosphonium group. These functional groups are, for example, vinyl pyridines (2-vinyl pyridine, 4 which are vinyl compounds having a nitrogen atom-containing heterocycle).
-Vinyl pyridine, 2-methyl-5-vinyl pyridine, etc.), vinyl pyrimidines, vinyl quinolines, vinyl carbazoles, vinyl imidazoles, or (N = 1 to 3, R ₁ and R ₂ are each an alkyl group having 1 to 12 carbon atoms). It is obtained by quaternizing a polymer of styrene derivative amines such as o, m, p-vinylbenzylalkylamines or forming a tertiary ammonium salt.

Or (R ₁ is hydrogen or an alkyl group having 1 to 12 carbon atoms,
R ₂ and R ₃ are each an alkylamino acrylate represented by an alkyl group having 1 to 12 carbon atoms, (R ₁ is hydrogen or an alkyl group having 1 to 12 carbon atoms,
R ₂ and R ₃ can also be introduced by quaternizing a polymer of a dialkyl acrylamide represented by an alkyl group having 1 to 12 carbon atoms) or forming a tertiary ammonium salt. Furthermore, quaternary amines or tertiary amines can be easily introduced into halomethylstyrene polymers such as chloromethylated styrene by known methods.

A diene monomer is suitable as a monomer species constituting the polymer polyC in which the remaining ion-exchange group is not introduced,
For example, butadiene isoprene, pentadiene, cyclohexadiene and the like.

In the case of a block copolymer having a neutral block composed of such a diene-based monomer, this portion is easily cross-linked by a known method using peroxide, sulfur, sulfur monochloride, concentrated sulfuric acid, or ultraviolet light. can do. Also, hydrogenation can be performed by a known method. These increase the strength of the material.

Poly constituting the block copolymer used in the present invention
When a plurality of each of A, polyB, and polyC is contained as a constituent component of the block copolymer, these may be the same polymer or different polymers. Component polymer polyA, poly
The molecular weight of each of B and polyC is preferably 10 ³ to 10 ⁶ g / mol. More preferably 10 ^{4 to} 5 × 10 ⁵ g / m
ol. As is well known, in a block copolymer, the volume fraction of the compatible interface region formed between two adjacent domains formed by microphase separation increases as the molecular weight decreases. For this reason, in a sample having a low molecular weight, polyion complex formation is large, and the effect of simultaneously presenting a cation domain and an anion domain is weakened by microphase separation. According to the experimental facts published so far for various block copolymers, it is considered that almost no phase-separated structure is formed when the molecular weight of each block is 10 ³ or less. On the other hand, in the case of a sample having a large molecular weight, the viscosity of the sample in a solid or solution state increases, and molding may become difficult.

The raw block copolymer must contain the component polymer polyA that introduces a cation exchange group and the component polymer polyB that introduces an anion exchange group in a weight fraction of 5% or more. The reason for this is that if the component segment having a cation or anion exchange group in the finally obtained amphoteric ion exchange membrane is less than 5%, the effect due to the simultaneous presence of amphoteric ions is significantly reduced. Is. In addition, since the neutral component polymer polyC separates the strength of the membrane from the microphase-separated polyA and polyB parts, the weight fraction is 30%.
It is desirable that the above content is included.

The block copolymer used in the present invention is produced by a living anion polymerization method. According to this method, it is possible to obtain a block copolymer having a uniform degree of polymerization.

As the living anionic polymerization initiator, known butyl lysium (including n, sec, tert, etc.), 2-methyl butyl lysium, sodium naphthalene, sodium anthracene, α-methylstyrene tetramer sodium, sodium biphenyl, etc. are used. Polymerization is carried out in a group hydrocarbon, a tubular ether or an aliphatic hydrocarbon (generally benzene, toluene, tetrahydrofuran, n-hexane, cyclohexane etc.) under vacuum or in an inert gas atmosphere such as nitrogen gas or argon gas. Be done.

The film formation from the original block copolymer can be easily performed by a solvent evaporation method or the like. At this time, many organic solvents such as benzene, toluene, xylene, cyclohexane, dioxane, tetrahydrofuran, chloroform and dichloroethane can be used. Further, in order to increase the strength of the film, a suitable fine screen, porous thin film, cloth or the like may be used as the support. These supports are preferably made of a material having excellent solvent resistance such as polyvinyl chloride, Teflon, polyethylene, polypropylene and glass. For amphoteric ion exchange membranes, after forming the original block copolymer, or before or at the same time as the membrane formation, the nitrogen portion is converted to a quaternary or tertiary ammonium salt, and then this treatment is performed before the membrane formation. Can be obtained by forming a film and subjecting it to crosslinking, hydrogenation, sulfonation, hydrolysis and the like. The quaternization of nitrogen is carried out by a known method, that is, by reacting with an alkylhalogen compound, but if a solvent containing an alkylhalogen compound is used, quaternization can be performed simultaneously with film formation. Halomethylstyrene can be converted to a quaternary amine with trimethylamine or the like. Further, the nitrogen portion can be converted to a tertiary ammonium salt with hydrochloric acid or the like.
Sulfonation of aromatic rings is performed with concentrated sulfuric acid, fuming sulfuric acid, sulfur trioxide, chlorosulfonic acid, etc. (New Experimental Chemistry Course, 14-III
Vol., P1776), and the hydrolysis of the carboxylic acid ester can be carried out by a known method using an aqueous solution of sodium hydroxide or the like.

Furthermore, by suppressing the swelling of water in the part with ion-exchange groups,
In order to obtain a denser film, those portions may be crosslinked. Friedel-Crafts catalysts (eg, AlCl ₃ , SbCl ₅ , SnC) can be used to crosslink moieties with cation exchange groups.
l ₄ , TiCl ₄ etc.) and a compound having an aromatic ring such as polystyrene and a compound represented by Cl (CH ₂ ) _n Cl in which n is 2 or more, for example, an aromatic polyfunctional compound represented by the following formula In order to cross-link the moiety having an anion-exchange group, the quaternization of the nitrogen moiety can be performed by, for example, _n represented by Br (CH ₂ ) _n BR or I (CH ₂ ) _n I being 2 The above compounds may be used.

As described above, when the above block copolymer is used as a raw material, chemical modification can be performed while maintaining the microphase separation structure that was initially formed, and finally, a dense and defect-free zwitterion exchange. A membrane can be obtained. In fact, if the anion and cation exchange capacities of such a membrane were measured independently by a commonly known titration method, 1 g of dry membrane was obtained.
It was confirmed that 0.3 meq or more was obtained and that the anion and cation exchange group regions were present at the same time.

In the present invention, organic compounds that can be desalted by being placed in phase I include glucose, fructose, maltose, xylose, saccharose, raffinose, and other sugars such as oligosaccharides, various vitamins, oligopeptides,
Antibiotics, coenzymes, amino acids, alcohols, amines, organic acids and other food additives, pharmaceuticals, flavors, biochemicals and other low molecular weight organic compounds known as general chemical products, or starch. Natural polymers such as high molecular weight polysaccharides, various proteins, nucleic acids and enzymes, and water-soluble synthetic polymers such as polyvinyl alcohol, polyethylene glycol and polyvinylpyrrolidone. Further, the organic compound added to the phase II in order to increase the desalting efficiency may be appropriately selected from the above depending on the purpose.

Hereinafter, the present invention will be described with reference to examples.

Example 1 In benzene purified through a sodium mirror, styrene and 4-vinylbenzyldimethylamine (hereinafter, referred to as 4-vinylbenzyldimethylamine) with 3.4 × 10 ⁻⁴ mol of sec-butyllithium as an initiator.
Abbreviated as VBDMA) and isoprene, 7 g of isoprene,
Styrene 15g, isoprene 7g, 4-VBDMA25
g and isoprene 7 g in this order to carry out polymerization by sequentially adding monomers in 5 steps to obtain polyC ₁ -polyA -polyC ₁ -poly
A raw block copolymer of B-polyC ₁ type was obtained. Prior to the polymerization, styrene was dried with calcium hydride, distilled under reduced pressure, further purified with sodium benzophenone, and vacuum distilled. Isoprene was dried over calcium hydride and sodium and then distilled. 4-VBDMA was dried over calcium hydride, distilled under reduced pressure, further purified by a triphenylmethyllithium-lysium bromide system, and vacuum distilled.

5% by weight of the raw block copolymer thus obtained
A raw film having a thickness of about 50 μm was prepared by a solvent evaporation method on mercury using the benzene solution described in 1. This raw film was quaternized with an amine moiety in methyl iodide vapor, and
After cross-linking the isoprene moiety with a 20% by volume solution of sulfur monochloride in nitromethane, the styrene moiety was further sulfonated with a 2% solution of chlorosulfonic acid in 1,2 dichloroethane.

Observation of the film with a transmission electron microscope at each step of these chemical treatments showed that the three-phase microstructure of the original film remained essentially unchanged. The cation exchange capacity of the finally obtained membrane was 0.95 meq and the anion exchange capacity was 0.60 meq per 1 g of dried resin.

The cell used for the dialysis test was an I chamber separated by a membrane.
It consists of room II, and is designed so that room I contains an aqueous solution containing an organic substance to be desalted, and room II contains dialysate from the outside. The obtained amphoteric ion exchange membrane was attached to this dialysis cell, and 0.10 mol / saccharose and 0.1
A dialysis test was conducted by filling an aqueous solution containing 10 mol / min of sodium chloride, and agitating this liquid while pouring 10 ⁻³ mol / min of saline into chamber II. At this time, atmospheric pressure was applied to the aqueous solution in each chamber. Twenty hours after starting the dialysis, the salt concentration of the aqueous solution in the chamber I was reduced to 0.021 mol / about 1/5, but the saccharose concentration was 0.097 mol /, which was almost unchanged. Further, at this time, the volume of the aqueous solution in the chamber I was almost unchanged.

Example 2 In the dialysis test of Example 1, when the dialysis test was conducted by flowing pure water into the II chamber, almost the same effect as that of Example 1 was obtained.

Example 3 In the dialysis test of Example 1, chamber I was filled with an aqueous solution containing 0.30 mol / saccharose and 0.10 mol / salt, and chamber II was filled with 0.30 mol / sucrose and 10 ⁻³ mo.
When dialysis was performed by flowing an aqueous solution containing l / salt,
After 20 hours, the salt concentration and the saccharose concentration in the chamber I were 0.016 mol / and 0.30 mol /, respectively, and the volume of the aqueous solution in the chamber I was almost unchanged.

Example 4 In the dialysis test of Example 3, while supporting the membrane using a stainless mesh, 10 ⁻³ mol / saline solution was flown into the II chamber,
When a dialysis experiment was conducted by applying a pressure of 5 atm to the chamber I,
After 20 hours, the concentrations of sodium chloride and sucrose in room I were 0.018 mol / and 0.29 mol /, respectively.

Example 5 In the dialysis experiment of Example 1, room I was filled with an aqueous solution containing 0.10 mol / vitamin B ₁₂ and 0.10 mol / salt, and a dialysis test was conducted under the same conditions. The concentration of vitamin B ₁₂ and salt in the chamber is 0.0 each
It became 99 mol / and 0.022 mol /.

Example 6 sec-Butyllithium 1.3 × 10 ⁻⁴ mol was used as an initiator in the same manner as in Example 1 to obtain butadiene 3.4.
g, styrene 6.6 g, isoprene 6.8 g, 4-VB
DMA 9.8 g and butadiene 3.5 g are sequentially added,
A polyC ₁ -polyA-polyC ₂ -polyB-polyC ₁ type five-block copolymer was synthesized, and the polymerization yield was about 10
It was 0%, and the number average molecular weights of the intermediate polymer and the final polymer and the results of elemental analysis of the final polymer were in good agreement with the calculated values. The film prepared from the dioxane solution of the quaternary block copolymer was introduced with an ion exchange group and crosslinked in the same manner as in Example 1 to obtain 1 g of a dried film.
As a result, an amphoteric ion exchange membrane having 1.2 meq of cation exchange group and 0.98 meq of anion exchange group was obtained.

This amphoteric ion-exchange membrane was attached to the dialysis cell used in Example 1, and the chamber I was filled with an aqueous solution containing 10 g / dl and 0.1 mol / mol of polyvinyl alcohol having a molecular weight of 10 ⁴ and potassium chloride, respectively. ^When a dialysis test was conducted by flowing a ^-3 mol / potassium chloride aqueous solution, the concentrations of potassium chloride and polyvinyl alcohol in chamber I were 0.020 mol / and 9.9 g / dl, respectively, 20 hours after the start of dialysis. The volume of the aqueous solution in chamber I did not change much.

Example 7 In the dialysis test of Example 6, 0.050 mol /
When a dialysis test was conducted under the same conditions with an aqueous solution containing glycine and 0.10 mol / salt of sodium chloride, the concentrations of glycine and sodium chloride in room I were 0.047 mol / s after 20 hours.
And 0.019 mol /, and the volume of the aqueous solution remained almost unchanged.

Claims (6)

[Claims] 1. An amphoteric ion exchange membrane comprising a block copolymer having a polymer polyA ⁻ having a cation exchange group and a polymer polyB ⁺ having an anion exchange group as a part of its constituent components. It is in contact with the I phase which is an aqueous solution of an organic compound containing an inorganic salt, and contains water or an aqueous solution of an inorganic salt thinner than the I phase on the other side or an organic compound which does not ionize at any concentration and an inorganic salt having a lower concentration than the I phase. A method for desalting an organic compound using an amphoteric ion exchange membrane, which comprises contacting with phase II which is an aqueous solution and selectively removing the inorganic salt from the aqueous solution of the organic compound containing the phase I inorganic salt. 2. An aqueous solution of an organic compound containing an inorganic salt, I.
A method according to claim 1, characterized in that pressure is applied to the phases. 3. An amphoteric ion exchange membrane is a positive block copolymer composed of a polymer capable of introducing a cation exchange group, a polymer capable of introducing an anion exchange group and a polymer not capable of introducing an ion exchange group. Claim 1 or 2 which is obtained by introducing an ion exchange group and an anion exchange group.
The method described in the section. 4. The polymer part of the amphoteric ion exchange membrane which does not introduce an ion exchange group is crosslinked.
The method described in the section. 5. The method according to claim 3, wherein the polymer portion introduced with the cation exchange group of the amphoteric ion exchange membrane is crosslinked. 6. The method according to claim 3, wherein the polymer portion introduced with the anion exchange group of the amphoteric ion exchange membrane is crosslinked.