Method for preparing cation exchange membrane from olefin sulfonic acid intermediate

Abstract

The invention relates to the technical field of separation membrane materials, in particular to a preparation method of an olefin sulfonate cation exchange membrane, which comprises the following steps: heating styrene sulfonic acid metal salt and inorganic acid in an organic solvent to react, filtering, and distilling filtrate to obtain an olefin sulfonic acid solution. Mixing the olefin sulfonic acid solution with a cross-linking agent and a polymerization initiator to obtain a membrane casting solution, and coating the membrane casting solution into a substrate to initiate cross-linking polymerization to obtain the cation exchange membrane. And the obtained membrane has good performance.

Description

Technical Field

[0001] The invention relates to the technical field of separation membrane materials, and discloses a homopolymeric cation exchange membrane and a preparation method thereof. Background Art

[0002] Ion exchange membranes can be used to manufacture electrodialysis, electro-desalting, diffusion dialysis and other devices, and are used in water desalination and seawater desalination, purification and concentration of brine or chemical aqueous solutions, separation of ions of different valence states, preparation of acids and alkalis by water dissociation, and other application fields. They can also be used in electrolytic hydrogen production, electrolytic alkali production and various battery devices.

[0003] For a long time, heterogeneous ion exchange membranes have dominated the market. Heterogeneous membranes are made by bonding ion exchange resin powders together with a binder and then reinforced with a fiber mesh. Its significant weakness is that the ion exchange resin particles are covered by the binder, which weakens its ion exchange function. The large mass ratio of binder and mesh makes its performance low; there is no chemical bond between the ion exchange resin, binder and mesh, so the stability is poor. The difficulty in preparing homogeneous ion exchange membranes and their high price limit their wider application. Common "alloy membranes" and homogeneous membranes prepared by the slurry coating method still do not solve the problem of weak bonding between ion exchange functional polymers, binders and meshes, and thus poor stability.

[0004] The preparation method of granular ion exchange resin is to initiate cross-linking polymerization of styrene and divinylbenzene into granules, and then functionalize the obtained cross-linked product. The functionalization includes sulfonation for preparing cation exchange resin and chloromethylation and quaternization for preparing cation exchange resin. Using similar chemical processes to prepare homogeneous ion exchange membranes can theoretically achieve higher exchange capacity and lower surface resistance. Using similar methods to prepare ion exchange membranes involves a more harsh chemical reaction process, which is not conducive to environmental protection and has higher costs.

[0005] Sodium styrene sulfonate is a cheap bulk chemical. Using this chemical as a raw material, obtaining a cation exchange membrane through cross-linking polymerization of its double bonds is an ideal route for manufacturing a cation membrane. The technical problem that needs to be solved is that sodium styrene sulfonate and a more ideal cross-linking agent (such as divinylbenzene) do not have a suitable common solvent. There are many technical solutions in the known technology for converting sodium styrene sulfonate into other salts to improve its solubility in organic solvents. U.S. Patent No. 4,029,640 discloses a technical solution for converting styrene sulfonate metal salts into inorganic ammonium salts; U.S. Patent No. 6,344,584B2 discloses a film-making method for styrene sulfonate lithium casting liquid. However, the solubility of various styrene sulfonates mentioned in these technical solutions in the relevant solvents is still too low, and the performance of the obtained ion exchange membrane is relatively low. Chinese Patent 201180060474 and US Patent US96111368B2 use vinylbenzene sulfonate metal salt and pyridine hydrochloride to react in an organic solvent, filter and remove the chloride metal salt (such as sodium chloride), and obtain a mixture of styrene sulfonate pyridinium salt, styrene sulfonic acid and the solvent; add divinylbenzene crosslinking agent and polymerization initiator to the mixture to obtain a positive film casting liquid, and dip-coat the casting liquid into the bottom liner to initiate crosslinking polymerization to obtain a positive film. However, the problem of this technical route is that: (1) The weight of the obtained "sodium chloride" reported in the patent document is much higher than the theoretical yield of sodium chloride, proving that the reaction is far from complete. Therefore, the obtained mixed solution contains residual pyridine hydrochloride and pyridine, a byproduct of generating styrene sulfonic acid, in addition to styrene sulfonate pyridinium salt, styrene sulfonic acid and the solvent. Therefore, the actual concentration of the active ingredient in the casting solution is much lower than the value reported in the patent; (2) the casting solution is a mixture of multiple mixtures, and the proportion of various substances in the mixture cannot be determined and controlled; (3) in order to effectively filter and remove the metal chloride salt, the viscosity of the mixture cannot be too high, so the concentration of the active ingredient is too low, and the obtained membrane is not dense and efficient enough; (4) the cost of commercially available pyridinium hydrochloride is too high. Chinese patent application 20191133375x also mentioned the technical solution of styrene sulfonate pyridinium salt. Summary of the invention

[0006] The purpose of the present invention is to disclose a method for preparing a cation membrane which uses olefin sulfonic acid metal salt as a main raw material, can finely control the composition and viscosity of the casting liquid, and has a lower cost.

[0007] The method for preparing a cation membrane of the present invention comprises:

[0008] (1) organic solvent 1 and organic solvent 2 are mixed into a mixed solvent, and a small amount of polymerization inhibitor is added;

[0009] (2) adding an olefin sulfonate metal salt to the mixed solvent under stirring;

[0010] (3) adding anhydrous inorganic acid dropwise to the suspension, heating the suspension to obtain a styrene sulfonic acid solution in which an inorganic salt is suspended;

[0011] (4) filtering and removing solid matter to obtain an olefin sulfonic acid solution;

[0012] (5) distilling the organic solvent 1 to obtain a solution of olefin sulfonic acid and solvent 2 (solution A);

[0013] (6) mixing solution A with a cross-linking agent and a polymerization initiator to obtain a casting solution;

[0014] (7) applying the casting solution to the substrate, and heating to induce cross-linking polymerization to obtain a cation exchange membrane;

[0015] The solvent 1 includes but is not limited to methanol, ethanol, propanol, butanol, dioxane, diacetone, butanone and a mixture thereof.

[0016] The solvent 2 includes, but is not limited to, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, triethyl phosphate, dipropylene glycol, diethylene glycol and a mixture thereof.

[0017] The ratio of solvent 1 to solvent 2 in the mixed solvent is 0:100-20:1.

[0018] The olefin sulfonates include, but are not limited to, sodium, potassium, calcium, magnesium and mixtures thereof of aromatic olefin sulfonates, such as sodium styrene sulfonate; sodium, potassium, calcium, magnesium and mixtures thereof of ester olefin sulfonates, such as sodium vinyl sulfonate.

[0019] The inorganic acid includes, but is not limited to, concentrated sulfuric acid, concentrated phosphoric acid, and mixtures thereof.

[0020] The crosslinking agent is any single molecule compound or mixture containing two or more double bonds, such as divinylbenzene and ethylene glycol dimethacrylate.

[0021] The use temperature of the solution A in step (6) is between 25-70°C

[0022] The polymerization initiator is any compound or mixture thereof that can initiate carbon-carbon double bond polymerization at 60-150° C., and the compound includes but is not limited to azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, and tert-butyl peroxyethylhexanoate.

[0023] The beneficial effects of the homopolymeric cation exchange membrane of the present invention are:

[0024] (1) By obtaining pure styrene sulfonic acid, the concentration and composition of the active ingredients in the casting solution can be selected to improve the performance of the resulting membrane. (2) This technical solution has lower costs. DETAILED DESCRIPTION Example 1

[0025] (1) Add 80 g of N-methylpyrrolidone (NMP), 250 ml of ethanol, and 0.5 g of hydroquinone into a 500 ml conical flask;

[0026] (2) Add 51.5 g of dry sodium styrene sulfonate while stirring;

[0027] (3) Slowly add 12.5 g of concentrated sulfuric acid (98% purity) dropwise and heat under reflux for 6 hours;

[0028] (4) filtering at room temperature to obtain a styrene sulfonic acid solution; the obtained solid was washed with ethanol, dried and weighed to 22.5 g;

[0029] (5) distilling the solution obtained in step 4 to 120° C. to obtain 115.2 g of styrene sulfonic acid NMP solution (calculated composition: approximately 64% NMP, 36% styrene sulfonic acid);

[0030] (6) heating the styrene sulfonic acid NMP solution obtained in step (5) to 60° C., taking 20 g of the solution, adding 2.0 g of divinylbenzene and 0.30 g of benzoyl peroxide, and stirring to react to obtain a colorless and transparent casting solution;

[0031] (7) The casting solution is dip-coated into a polypropylene microporous membrane with a thickness of 70 μm and a porosity of about 45%, protected by a polyester film, and pressurized and heated at 90 degrees for 6 hours in a vacuum to obtain a cation exchange membrane.

[0032] The performance indicators of the obtained membrane were tested according to the Chinese industry standard HY / T 166.1-2013. The test results are shown in Table 1. Table 1 Example 1 Cation exchange membrane parameters parameter thickness Dry film exchange capacity Moisture content Sheet resistance Selectivity unit mm mmole / g ％ <![CDATA[Ω / cm 2 ]]> ％ Measured value 0.68 1.05 34.5 1.65 94.2 Example 2

[0033] (1) Add 70 g of dipropylene glycol (DPG), 250 ml of ethanol, and 0.5 g of hydroquinone into a 500 ml conical flask;

[0034] (2) Add 37 g of dry sodium propylene sulfonate under stirring;

[0035] (3) Slowly add 12.5 g of concentrated sulfuric acid (98% purity) dropwise and heat under reflux for 6 hours;

[0036] (4) filtering at room temperature to obtain a propylene sulfonic acid solution; the obtained solid was washed with ethanol, dried and weighed to 19.4 g;

[0037] (5) distilling the solution obtained in step 4 to 120° C. to obtain 94.8 g of propylene sulfonic acid DPG solution, with a calculated composition of approximately 67% DPG and 33% propylene sulfonic acid);

[0038] (6) heating the DPG solution of propylene sulfonic acid obtained in step (5) to 60° C., taking 20 g of the solution, adding 1.2 g of divinylbenzene and 0.20 g of benzoyl peroxide, stirring and reacting to obtain a colorless and transparent casting solution;

[0039] (7) The casting solution is dip-coated into a polypropylene microporous membrane with a thickness of 70 μm and a porosity of about 45%, protected by a polyester film, and pressurized and heated at 90 degrees for 6 hours in a vacuum to obtain a cation exchange membrane.

[0040] The performance indicators of the obtained membrane were tested according to the Chinese industry standard HY / T 166.1-2013. The test results are shown in Table 1. Table 1 Example 1 Cation exchange membrane parameters parameter thickness Dry film exchange capacity Moisture content Sheet resistance Selectivity unit mm mmole / % ％ <![CDATA[Ω / cm 2 ]]> ％ Measured value 0.39 1.08 35.1 1.43 95.2

Claims

1. A method for preparing a styrene sulfonate cation exchange membrane, characterized in that The following steps are involved: (1) organic solvent 1 and organic solvent 2 are mixed into a mixed solvent, and a small amount of polymerization inhibitor is added; (2) adding olefin sulfonate metal salt to the mixed solvent under stirring: (3) adding anhydrous inorganic acid dropwise to the suspension, heating the suspension to obtain a styrene sulfonic acid solution in which an inorganic salt is suspended; (4) filtering and removing solid matter to obtain an olefin sulfonic acid solution; (5) distilling the organic solvent 1 to obtain a solution of olefin sulfonic acid and solvent 2 (solution A); (6) mixing solution A with a cross-linking agent and a polymerization initiator to obtain a casting solution; (7) Dip-coating the casting solution into the substrate, and heating to induce cross-linking polymerization to obtain a cation exchange membrane.

2. The method for preparing a styrene sulfonate cation exchange membrane according to claim 1, characterized in that The solvent 1 includes but is not limited to methanol, ethanol, propanol, butanol, dioxane, diacetone, butanone and a mixture thereof.

3. The method for preparing a styrene sulfonate cation exchange membrane according to claim 1, characterized in that The solvent 2 includes, but is not limited to, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, triethyl phosphate, dipropylene glycol, diethylene glycol and a mixture thereof.

4. The method for preparing a styrene sulfonate cation exchange membrane according to claim 1, characterized in that The ratio of solvent 1 to solvent 2 in the mixed solvent is 0:100-20:

1.

5. The method for preparing a styrene sulfonate cation exchange membrane according to claim 1, characterized in that The olefin sulfonates include, but are not limited to, sodium, potassium, calcium, magnesium and mixtures thereof of aromatic olefin sulfonates, such as sodium styrene sulfonate; sodium, potassium, calcium, magnesium and mixtures thereof of ester olefin sulfonates, such as sodium vinyl sulfonate.

6. The method for preparing a styrene sulfonate cation exchange membrane according to claim 1, characterized in that The inorganic acid includes, but is not limited to, concentrated sulfuric acid, concentrated phosphoric acid, and mixtures thereof.

7. The method for preparing a styrene sulfonate cation exchange membrane according to claim 1, characterized in that The crosslinking agent is any single molecule compound or mixture containing two or more double bonds, such as divinylbenzene and ethylene glycol dimethacrylate.

8. The method for preparing a styrene sulfonate cation exchange membrane according to claim 1, characterized in that The polymerization initiator is any compound or mixture thereof that can initiate carbon-carbon double bond polymerization at 60-150° C., and the compound includes but is not limited to azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide tert-butyl peroxyethylhexanoate.

9. The method for preparing a styrene sulfonate cation exchange membrane according to claim 1, characterized in that The use temperature of the solution A in step (6) is between 25-70°C.