阅读说明：本技术 碱金属氯化物电解用含氟离子交换膜 (Fluoride ion exchange membrane for alkali chloride electrolysis ) 是由 王丽 杨淼坤 滕培峰 张志浩 张永明 于 2019-11-27 设计创作，主要内容包括：本发明属于离子交换膜技术领域,具体涉及一种碱金属氯化物电解用含氟离子交换膜,所述的含氟离子交换膜包括包括具有羧酸型官能团的含氟聚合物层、含有磺酸型和羧酸型官能团的含氟聚合物层和具有磺酸型官能团的含氟聚合物层,其中,在所述具有磺酸型官能团的含氟聚合物层中包埋有增强材料,所述增强材料与所述具有羧酸型官能团的含氟聚合物层和含有磺酸型和羧酸型官能团的含氟聚合物层平行设置；所述含氟离子交换膜表面具有离子交换树脂与无机离子所共同构成的表面改性涂层。本发明可以降低碱金属氯化物电解时的电解电压且抑制多层复合膜在应用过程中发生层间剥离的缺陷,适合在新型高电流密度条件下的零极距电解槽中运行。(The invention belongs to the technical field of ion exchange membranes, and particularly relates to a fluorine-containing ion exchange membrane for electrolyzing alkali metal chloride, which comprises a fluorine-containing polymer layer with carboxylic acid type functional groups, a fluorine-containing polymer layer with sulfonic acid type and carboxylic acid type functional groups and a fluorine-containing polymer layer with sulfonic acid type functional groups, wherein a reinforcing material is embedded in the fluorine-containing polymer layer with sulfonic acid type functional groups, and is arranged in parallel with the fluorine-containing polymer layer with carboxylic acid type functional groups and the fluorine-containing polymer layer with sulfonic acid type and carboxylic acid type functional groups; the surface of the fluorine-containing ion exchange membrane is provided with a surface modified coating layer formed by ion exchange resin and inorganic ions. The invention can reduce the electrolytic voltage during the electrolysis of the alkali metal chloride and inhibit the defect that the multilayer composite membrane is stripped in the application process, and is suitable for running in a zero polar distance electrolytic cell under the novel high current density condition.)

1. A fluoride ion exchange membrane for electrolysis of alkali metal chloride is characterized in that: the fluorine-containing polymer coating comprises a fluorine-containing polymer layer (1) with carboxylic acid type functional groups and a fluorine-containing polymer layer (3) with sulfonic acid type functional groups, wherein a reinforcing material (4) is embedded in the fluorine-containing polymer layer (3) with the sulfonic acid type functional groups, and a fluorine-containing polymer layer (2) containing the sulfonic acid type functional groups and the carboxylic acid type functional groups is arranged between the fluorine-containing polymer layer (1) with the carboxylic acid type functional groups and the fluorine-containing polymer layer (3) with the sulfonic acid type functional groups; the reinforcing material (4) is arranged in parallel with the fluoropolymer layer (1) having carboxylic acid type functional groups and the fluoropolymer layer (2) containing sulfonic acid type and carboxylic acid type functional groups; the surface of the fluorine-containing ion exchange membrane is provided with a surface modified coating layer formed by ion exchange resin and inorganic ions.

2. The fluoride ion-containing exchange membrane for alkali chloride electrolysis according to claim 1, wherein: the polymer used in the fluorine-containing polymer layer (2) containing the sulfonic acid type functional group and the carboxylic acid type functional group is a blend of fluorine-containing polymers containing the sulfonic acid type functional group and the carboxylic acid type functional group, or a multipolymer of a functional monomer containing the sulfonic acid type functional group and the carboxylic acid type functional group and fluorine-containing olefin.

3. The fluoride ion-containing exchange membrane for alkali chloride electrolysis according to claim 1 or 2, wherein: the fluorine-containing polymer layer (2) containing sulfonic acid type and carboxylic acid type functional groups is of a main chain structure with perfluorocarbons.

4. The fluoride ion-containing exchange membrane for alkali chloride electrolysis according to claim 1, wherein: the molar ratio of the sulfonic acid functional group to the carboxylic acid functional group in the fluoropolymer layer (2) containing the sulfonic acid functional group and the carboxylic acid functional group is 1: 9-9:1.

5. The fluoride ion-containing exchange membrane for alkali chloride electrolysis according to claim 1, wherein: the fluoropolymer layer (3) having sulfonic acid functional groups has an ion exchange capacity of 0.9 to 1.5mmol/g dry resin and a thickness of 30 to 120 μm.

6. The fluoride ion-containing exchange membrane for alkali chloride electrolysis according to claim 1, wherein: the fluoropolymer layer (1) having carboxylic acid type functional groups has an ion exchange capacity of 0.8 to 0.95mmol/g dry resin and a thickness of 5 to 30 μm.

7. The fluoride ion-containing exchange membrane for alkali chloride electrolysis according to claim 1, wherein: the fluoropolymer layer (2) containing sulfonic acid type and carboxylic acid type functional groups has an ion exchange capacity of 0.85-1.2mmol/g dry resin and a thickness of 1-50 μm.

8. The fluoride ion-containing exchange membrane for alkali chloride electrolysis according to claim 1, wherein: the ion exchange capacity between the layers of the fluorine-containing polymer layer (3) with the sulfonic acid type functional group, the fluorine-containing polymer layer (2) with the sulfonic acid type functional group and the carboxylic acid type functional group and the fluorine-containing polymer layer (1) with the carboxylic acid type functional group is gradually reduced.

9. The fluoride ion-containing exchange membrane for alkali chloride electrolysis according to claim 1, wherein: the reinforcing material (4) is a porous material, has an aperture ratio of 20-90%, is formed by weaving perfluorocarbon reinforcing wires and hydrocarbon polymer soluble wires, and has a thickness of 30-100 microns.

10. The fluoride ion-containing exchange membrane for alkali chloride electrolysis according to claim 1, wherein: the inorganic ions in the surface modified coating are inorganic oxide particles with the particle size of 20 nanometers to 10 micrometers, the ion exchange resin is perfluorinated ion exchange resin which is a perfluorinated polymer with at least one ion exchange group, and the ion exchange capacity is 0.7 to 1.1 mmol/g.

Technical Field

The invention belongs to the technical field of ion exchange membranes, and particularly relates to a fluorine-containing ion exchange membrane for electrolysis of alkali metal chlorides.

Background

Ion exchange membranes have been widely used in electrolytic oxidation and reduction operations due to their excellent permselectivity. The use of perfluorinated ion exchange membranes in the salt electrolysis industry has led to a revolutionary change in the chlor-alkali industry. In addition, the method has wide application in the fields of potassium carbonate preparation by potassium chloride electrolysis, sodium carbonate preparation by sodium chloride electrolysis, sodium sulfite preparation by sodium chloride electrolysis, caustic soda preparation by sodium sulfate electrolysis, sulfuric acid preparation and the like. In recent years, in order to improve production efficiency and reduce energy consumption, an ion exchange membrane with more stable performance is continuously required, and it is desired that the ion exchange membrane can perform electrolysis under conditions of high current density, low cell voltage and high alkali solution concentration.

In order to ensure the selective permeability of the membrane, a fluoropolymer having a carboxylic acid functional group used for the ion exchange membrane is often used which has a lower ion exchange capacity and a lower water content than a fluoropolymer having a sulfonic acid functional group. Therefore, in the ion exchange membrane used at present, in order to reduce the membrane resistance, increase the ion exchange capacity of the sulfonic acid layer and ensure high current efficiency, the difference in the exchange capacity between the sulfonic acid layer and the carboxylic acid layer in the ion exchange membrane increases the difference in the water content, and separation (so-called blisters) due to the difference in the water of electrodialysis may occur between the two layers of the composite membrane. In order to ensure low power consumption, the thickness of the carboxylic acid layer of the industrial membrane is about 10-15 microns, and the carboxylic acid layer after delamination is very easy to damage in the process of rubbing with an electrode, so that the selectivity of the membrane in the electrolytic process is sharply reduced, the membrane replacement period is greatly shortened, and the operation cost is increased.

Patent CN107075703A alleviates the problem of interlayer peeling due to the difference in water absorption between layers by adding a sulfonic acid layer with lower exchange capacity between the carboxylic acid layer and the sulfonic acid layer. CN107949664A achieves control of the blister phenomenon by matching the ion exchange capacity of the sulfonic and carboxylic acid layers optimally. In order to solve the contradiction between the generation of blisters and low power consumption, CN109154091A uses a sulfonic acid resin having a bifunctional group on a side chain to suppress the difference in water absorption with a carboxylic acid layer caused by an excessively large water absorption of the sulfonic acid layer.

Although the problem of delamination is somewhat alleviated by continued technological advances, as electrolytic techniques continue to evolve, further increases in process current density are required, resulting in higher demands on the bubble resistance of the ion exchange membrane by the electrolytic process. The increase in process current density causes the acceleration of ion conduction, resulting in the formation of pressure of bound water between the layers, while the increase in current density causes the increase in the amount of gas generated per unit time, which are responsible for the foaming of the ion exchange membrane. In order to ensure the performance stability of the ion exchange membrane under long-term operation conditions, the prior patent technology mainly focuses on reducing the internal pressure formed at the interface by matching the difference of water absorption rates between the two layers to slow down the interlayer peeling, but because of the property problem of the material, the compatibility of the polymer of the fluorine-containing functional compound containing carboxylic acid groups and the polymer of the fluorine-containing functional compound containing sulfonic acid groups is poor, and the problem of low interlayer bonding force cannot be solved. Therefore, it is very important to develop a novel ion exchange membrane which has good interlayer binding property and can stably realize high current efficiency and low power consumption operation for a long time in the most advanced electrolytic cell and electrolytic process.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the fluorine-containing ion exchange membrane for electrolyzing the alkali metal chloride can stably and efficiently process the solution of the alkali metal chloride with wide-range concentration, is suitable for running in a zero-polar-distance electrolytic cell under the novel high-current-density condition, and has excellent electrochemical performance and long-period performance stability. The fluorine-containing polymer layer simultaneously having sulfonic acid type functional groups and carboxylic acid type functional groups is adopted, so that the interlayer interface adhesive force is increased on the premise of not influencing the conductivity of the membrane, the contradiction between the foaming resistance and the ion conductivity of the membrane is solved, and the comprehensive performance of the membrane is improved.

The fluorine-containing ion exchange membrane for alkali metal chloride electrolysis comprises a fluorine-containing polymer layer with a carboxylic acid type functional group and a fluorine-containing polymer layer with a sulfonic acid type functional group, wherein a reinforcing material is embedded in the fluorine-containing polymer layer with the sulfonic acid type functional group, and the fluorine-containing polymer layer with the sulfonic acid type and carboxylic acid type functional groups is arranged between the fluorine-containing polymer layer with the carboxylic acid type functional group and the fluorine-containing polymer layer with the sulfonic acid type functional group; the reinforcing material is disposed in parallel with the fluoropolymer layer having carboxylic acid type functional groups and the fluoropolymer layer containing sulfonic acid type and carboxylic acid type functional groups; the surface of the fluorine-containing ion exchange membrane is provided with a surface modified coating layer formed by ion exchange resin and inorganic ions.

The fluoropolymer layer having a sulfonic acid-type functional group and a carboxylic acid-type functional group as the intermediate layer is composed of a fluoropolymer having both a sulfonic acid-type functional group and a carboxylic acid-type functional group. The polymer can be a blend of a plurality of polymers, and can also be a multipolymer of a functional monomer containing a sulfonic acid type functional group, a monomer containing a carboxylic acid type functional group and fluorine-containing olefin. The total ion exchange capacity thereof is 0.85 to 1.2mmol/g (dried resin) while the ratio of the number of moles of the carboxylic acid type functional groups to the sulfonic acid type functional groups contained therein is 1:9 to 9:1, more preferably 3:7 to 7:3, and when the ratio of the functional groups is lower than the lower limit or higher than the upper limit, the adhesion to the fluoropolymer layer having the sulfonic acid type functional groups or the fluoropolymer layer having the carboxylic acid type functional groups is lowered. If a multi-resin blending structure is adopted, the ion exchange capacity of each polymer is between 0.8 and 1.2mmol/g, and the polymer is subjected to high-temperature mixing at the temperature of 220 ℃ and 300 ℃ before processing, so that the uniform performance of the blend is ensured. The multipolymer of the functional monomer containing a sulfonic acid type functional group, the monomer containing a carboxylic acid type functional group and the fluorine-containing olefin mentioned therein may be a multipolymer obtained by using any of polymerization systems of fluorine-containing hydrocarbons. In order to provide better chemical stability, the fluorine-containing olefin is optimally selected to be tetrafluoroethylene. Due to the reactive nature of the carboxylic acid type functional group, the production system is preferably a nonaqueous polymerization system, and the reaction medium is a fluorine-containing alkane or fluorochlorohydrocarbon or the like, such as trifluorotrichloroethane, perfluorotetramethylcyclobutane, 2, 3-dihydro-10 fluoropentane, perfluoromethylcyclohexane, perfluorobenzene, perfluorooctane or the like. The processing temperature range of the polymer is 220-300 ℃. The fluoropolymer layer containing sulfonic acid type and carboxylic acid type functional groups has good compatibility with the fluoropolymer layer containing carboxylic acid type functional groups and the fluoropolymer layer containing sulfonic acid type functional groups as a transition layer, the water content and the surface resistance of the fluoropolymer layer are both between the fluoropolymer layer containing carboxylic acid type functional groups and the fluoropolymer layer containing sulfonic acid type functional groups, and the thickness of the fluoropolymer layer is 1-50 micrometers, preferably 3-30 micrometers, and more preferably 3-15 micrometers.

Among these, the carboxylic acid type functional group-containing monomer is preferably one or more monomers represented by the following formula (1) from the viewpoint of excellence in production cost of the monomer, reactivity with other monomers, characteristics of the resulting fluoropolymer, and the like.

CF₂＝CF-(O)_P-(CF₂)_q-(CF₂CFX)_r-(O)_S-(CF₂)_t-(CF₂CFX’)_U-A₁(1)

Wherein X is a fluorine atom or a trifluoromethyl group. X' is fluorine atom or trifluoromethyl. X and X' may be the same or different. A. the₁A group that can be converted into a carboxylic acid type functional group. P is 0 or 1, q is an integer from 0 to 12, r is an integer from 0 to 3, S is 0 or 1, t is an integer from 0 to 12, and U is an integer from 0 to 3, wherein P and S are not 0 at the same time, and r and U are not 0 at the same time. Among them, preferred are compounds in which P ═ 1, q ═ 0, r ═ 1, S ═ 0-1, t ═ 1-3, and U ═ 0-1. For example CF₂＝CF-O-CF₂CF₂CF₂-COOCFCH₃、CF₂＝CF-O-CF₂CF(CF₃)-OCF₂CF₂COOCH₃、CF₂＝CF-O-CF₂CF₂-COOCH₃And the like.

The monomer containing the sulfonic acid functional group is preferably one or more of monomers shown in the following formula (2) or formula (3):

CF₂＝CF-O-R_f1-A₂………..(2)

CF₂＝CF-R_f2-A₂……………(3)

R_f2the perfluoroalkylene group has 1 to 20 carbon atoms, may contain an etheric oxygen atom, and may be either linear or branched. A. the₂Being groups convertible into functional groups of the sulphonic acid type, e.g. SO₂F、-SO₂Cl, and the like. For example CF₂＝CFOCF₂CF₂SO₂F、CF₂＝CFCF₂CF₂SO₂F、CF₂＝CFOCF₂CF(CF₃)OCF₂CF₂SO₂F, and the like.

The fluoropolymer layer having a sulfonic acid type functional group in the present invention is a fluoropolymer having a sulfonic acid group, and is preferably a perfluorosulfonic acid resin because a structure having perfluorocarbon in its main chain provides better chemical stability, and the exchange capacity of the perfluorosulfonic acid resin is 0.9 to 1.5mmol/g (dry resin). In view of taking into consideration both the mechanical properties and ion conductivity of the membrane, it is preferable that the exchange capacity is from 0.95 to 1.4 mmol/g. The fluoropolymer layer having sulfonic acid type functional groups is 30 to 120 microns thick, with a more preferred thickness of 50 to 100 microns. Wherein the fluoropolymer layer having sulfonic acid type functional groups has a reinforcing material embedded therein. The reinforcing material is disposed in parallel with the aforementioned fluoropolymer layer having carboxylic acid type functional groups and fluoropolymer layers containing sulfonic acid type and carboxylic acid type functional groups.

The fluoropolymer layer having carboxylic acid type functional groups in the present invention is a fluoropolymer having carboxylic acid groups, preferably a perfluorocarboxylic acid resin, and the exchange capacity of the resin is 0.8 to 0.95mmol/g (dry resin). The fluoropolymer layer having carboxylic acid type functional groups has a thickness of 5 to 30 microns, more preferably 7 to 20 microns; the ion exchange membrane comprises a fluorine-containing polymer layer with a sulfonic acid type functional group, a fluorine-containing polymer layer with a sulfonic acid type functional group and a carboxylic acid type functional group, and a fluorine-containing polymer layer with a carboxylic acid type functional group in sequence from an anode side to a cathode side. While the ion exchange capacity between the layers is such that the fluoropolymer layer having sulfonic acid type functional groups > the fluoropolymer layer having sulfonic acid type and carboxylic acid type functional groups > the fluoropolymer layer having carboxylic acid type functional groups.

The reinforcing material used in the present invention is woven by using a reinforcing thread of perfluorocarbon and a solvent-laid thread of hydrocarbon polymer, the most preferable material of the reinforcing thread is polytetrafluoroethylene long fiber, the thickness of the reinforcing material is 30-100 μm, and the reinforcing material is a porous material with an open porosity of 20-90%, preferably 50-85%. Too low an open porosity results in increased film resistance, and too high an open porosity reduces the mechanical properties of the film. The reinforcing material is located on the side close to the fluoropolymer layer having sulfonic acid type functional groups, and it may be partially located in the fluoropolymer layer containing sulfonic acid type and carboxylic acid type functional groups.

The inorganic ions in the surface modified coating are preferably inorganic oxides, and the inorganic oxides are selected from one or more of oxides, hydroxides and nitrides of IV-A group elements, IV-B group elements, V-B group elements and III-B group elements. One or more of zirconia, silica, zirconium nitride, yttria and the like are preferred. The particle size of the inorganic substance is in the range of 20 micrometers-10 nanometers.

The ion exchange resin in the surface modified coating is preferably a perfluorinated ion exchange resin, which is a perfluorinated polymer having at least one ion exchange group and has an ion exchange capacity of 0.7 to 1.1 mmol/g.

The fluorine-containing ion exchange membrane for electrolyzing alkali metal chloride comprises the following preparation steps:

(1) melt-casting the three-layer composite fluorine-containing ion exchange resin base film by a screw extruder in a coextrusion mode, carrying out hot pressing on a reinforcing material through a high-temperature hot roller, enabling a weaving node of the reinforcing material to generate deformation and fix, compounding the reinforcing material with the cast resin base film, introducing the reinforcing material between film forming press rollers, and embedding the reinforcing material into resin on the side of a fluorine-containing polymer layer with a sulfonic acid type functional group under the action of pressure between the rollers so as to obtain a precursor material of the film;

(2) placing a separation material with a porous material and a precursor material (a fluorine-containing polymer layer with a sulfonic acid type functional group faces downwards) of the membrane obtained in the step 1 on a hot table with a vacuumizing function in sequence, and embedding a reinforcing material in the fluorine-containing polymer layer with the sulfonic acid type functional group under the condition of high-temperature vacuum to form a reinforced composite membrane;

(3) the reinforced composite membrane obtained in the above procedure is hydrolyzed by alkali metal hydroxide at a certain temperature, and organic solvent with certain composition can be added into the composite membrane to swell the membrane during hydrolysis so as to accelerate the hydrolysis reaction rate, wherein the organic solvent can be one or more of dimethyl sulfoxide, dimethyl formamide, propanol, ethanol, glycol and the like. In which the functional groups in the reinforced composite membrane are converted to-SO₃Na or-COONa to form an ion-exchange membrane having ion cluster channels;

(4) dissolving the fluorine-containing resin with ion exchange functional groups in a polar solvent with a certain composition at high temperature and high pressure to form a stable resin solution, wherein the polar solvent is usually one or more of water, low-boiling monohydric alcohol, dihydric alcohol and some nitrogen-containing organic solvents, the nitrogen-containing organic solvents are one or more of DMF, DMSO and the like, and homogenizing inorganic particles and the obtained resin solution to form a stable dispersion liquid;

(5) and (3) attaching the dispersion liquid obtained in the step (4) to the surface of the ion exchange membrane obtained in the step (3), and drying and curing to form a stable surface coating. There are many ways of attachment, including: spraying, roll coating, dipping, transferring, spin coating, and the like, and spraying and roll coating are preferable. The process operation is carried out according to the prior art. The membrane can be used in the electrolytic preparation process of alkali metal chloride after being balanced by dilute alkali liquor.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention adopts the resin layer with the sulfonic acid functional group and the carboxylic acid functional group as the transition layer, which increases the interface compatibility between the fluorine-containing polymer layer with the sulfonic acid functional group and the fluorine-containing polymer layer with the carboxylic acid functional group, thereby improving the interlayer adhesive force and solving the problem of interlayer peeling in the electrolytic process.

2. When the sulfonic acid functional group-containing resin and the carboxylic acid functional group-containing resin are blended, the blend can be ensured to be uniform on a molecular level through an early high-temperature mixing process, the sulfonic acid functional group-containing fluoropolymer layer and the carboxylic acid functional group-containing fluoropolymer layer can form random distribution of two functional groups in a molecule when a multipolymer simultaneously containing the sulfonic acid functional group and the carboxylic acid functional group is adopted, ion clusters formed by the two functional groups can be formed in any mode, and the condition that the membrane performance is damaged by salt analysis caused by difference of transmission performance in the ion transmission process is avoided.

3. The invention adds the fluorine-containing polymer layer containing sulfonic acid type and carboxylic acid type functional groups into the multilayer composite film, increases the binding force between interfaces, overcomes the technical requirement that the difference of the water content between the fluorine-containing polymer layer containing sulfonic acid type functional groups and the fluorine-containing polymer layer containing carboxylic acid type functional groups is strictly needed to inhibit layering in the prior art, enlarges the adjustable range of the ion exchange capacity of each layer, and can further reduce the electrolytic voltage when the metal chloride is electrolyzed on the premise of keeping the original film performance stability and current efficiency.

4. The method is suitable for the electrolysis industry of alkali metal chloride, can stably and efficiently process alkali metal chloride solution with wide concentration range, is suitable for operation in a zero polar distance electrolytic cell under the novel high current density condition, and can obviously reduce the cell voltage while improving the product purity. The preparation method of the invention has simple and reasonable process and is easy for industrialization.

Drawings

FIG. 1 is a schematic view showing the structure of a fluorine-containing ion exchange membrane for alkali chloride electrolysis according to the present invention;

in the figure: 1. a fluoropolymer layer having carboxylic acid type functional groups; 2. a fluoropolymer layer containing sulfonic and carboxylic acid functional groups; 3. a fluoropolymer layer having sulfonic acid type functional groups; 4. a reinforcing material.

Detailed Description

The present invention will be further described with reference to the following examples.