CN114345136A - Preparation method of fluorine-containing ion exchange membrane for chlor-alkali industry - Google Patents
Preparation method of fluorine-containing ion exchange membrane for chlor-alkali industry Download PDFInfo
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Abstract
The invention belongs to the technical field of ion exchange membrane processing, and particularly relates to a preparation method of a fluorine-containing ion exchange membrane for chlor-alkali industry. The preparation method comprises the following steps: (1) and (3) melting coextrusion molding: the transverse tension and the longitudinal tension of the control film are both less than or equal to 10N; (2) hot-pressing and compounding: the transverse tension and the longitudinal tension of the control film are both less than or equal to 30N; (3) modification treatment: the tension applied to the film in the transverse direction and the longitudinal direction is less than or equal to 100N; (4) coating of a coating: the tension applied to the film in the transverse direction and the longitudinal direction is less than or equal to 80N. The prepared fluorine-containing ion exchange membrane has longer service life and improves the comprehensive use performance by carrying out targeted adjustment design and independent control on the transverse and longitudinal tensions of the membrane in each process step.
Description
Technical Field
The invention belongs to the technical field of ion exchange membrane processing, and particularly relates to a preparation method of a fluorine-containing ion exchange membrane for chlor-alkali industry.
Background
Ion exchange membranes, a selectively permeable material, are widely used in electrolytic operations. The application of the perfluorinated ion exchange membrane in the chlor-alkali industry greatly reduces the use and generation of harmful substances in the environment during the production process of producing alkali and chlorine by electrolysis, and is a revolutionary technical progress in the chlor-alkali industry. With the continuous progress and development of the technology, the technology is increasingly popularized 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 further improve the electrolysis production efficiency and reduce the energy consumption per ton of alkali, high current density, low cell voltage and high alkali liquor concentration are the main directions for the development of the technology. The ion exchange membrane is applied to electrolysis production, and has the most important properties of high current efficiency, low cell voltage, low impurity content of products, long service life and the like. In the processing process of the ion exchange membrane material, the tension control of the membrane material is one of the very key control technologies, especially when the membrane is at a higher temperature or secondary processing and post-treatment modification are carried out on the preliminarily shaped multilayer composite thin film material. If the membrane tension is not well controlled in the preparation process, even if the ion exchange membrane with good micro-morphology just starts to operate for a certain time under the normal working condition of chlor-alkali electrolysis, the phenomena of micro-cracks and the like can be seen through the micro-analysis of the apparent morphology. Therefore, control of the tension is important throughout the processing of the film. For a flexible film, unstable traction tension can also cause irregular deformation of the film, and particularly during long-time soaking treatment and transformation modification, the unstable traction tension can easily cause irregular distribution or concentration of internal stress of the film, so that the produced film can be permanently deformed or damaged under certain specific conditions (such as temperature, humidity, physical external force, chemical action and the like) when applied to an industrial device.
In addition, the tension stability during film coating is also important for coating quality, and unmatched tension control can cause cracking or falling off of the coating layer, and the tension can also influence the extrusion of the coiled material on a winding and unwinding roller to cause damage of the coating layer.
Chinese patent ZL201210545793.6 discloses a preparation process method of a fluorine-containing ion exchange membrane for the chlor-alkali industry, wherein in the whole preparation process of the ion exchange membrane, the temperature, humidity and chemical environment of the processes of extrusion of a perfluorinated ion exchange membrane base membrane, compounding of a reinforcing mesh, hydrolytic transformation of the reinforced ion exchange membrane after compounding, coating of a gas release coating and the like are different, and the dimensional stability of the ion membrane has larger difference.
In the production process of the ion exchange membrane, whether the factors such as temperature change, environmental humidity change and the like of the membrane are matched with the tension and the stability can influence various performances of the ion exchange membrane. In different process steps of the actual production of the ion exchange membrane, the tensile action of a transverse stretching roller (vertical to the extrusion direction, TD direction), a traction roller (along the extrusion direction, MD direction) and the tension of other hot pressing rollers and tracking rollers directly influence the appearance, application performance, service life and other performances of the finished ion exchange membrane in different aspects.
When the ion exchange membrane is subjected to larger tension at a processing temperature, a local thinning phenomenon can occur, local abnormal points are difficult to find in the detection of a production process and become weak points in the long-term operation process of an electrolytic cell, the current density at the local abnormal points is increased due to the low local thickness, the aging failure of the electrolytic cell is accelerated, even the local abnormal points become leakage points, and the service life of the membrane is seriously shortened.
In summary, the fluorine-containing ion exchange membrane is subjected to different tensions during the processing process, and has a great influence on the electrochemical performance of the final membrane. The problem of unstable tension in the preparation process of the ion exchange membrane, and the problem of matching of the tension and the stretching effect under different temperatures, humidity and chemical environments of the ion exchange membrane in the preparation process can cause the problems of flatness such as warping and wrinkling of a product after molding or in a working environment, peeling and cracking of different composite layers and coatings, and the like. In order to ensure the comprehensive use performance of the ion exchange membrane, the problem of tension matching degree control in the production and preparation process of the ion exchange membrane needs to be solved urgently.
Disclosure of Invention
The invention aims to provide a preparation method of a fluorine-containing ion exchange membrane for chlor-alkali industry aiming at the defects. The preparation method carries out targeted adjustment design and independent control on the transverse and longitudinal tension of the membrane in each process step, so that the prepared fluorine-containing ion exchange membrane has longer service life and improves the comprehensive use performance.
The technical scheme of the invention is as follows: a preparation method of a fluorine-containing ion exchange membrane for chlor-alkali industry comprises the following steps:
(1) and (3) melting coextrusion molding: firstly, adopting a melt coextrusion casting mode to obtain two layers of composite fluorine-containing ion exchange resin base films, then shaping the fluorine-containing ion exchange resin base films under the stretching action of a transverse stretching roller and a traction roller, wherein the transverse tension and the longitudinal tension of a control film in the process are less than or equal to 10N. When the tension exceeds the tension, the prepared ion exchange membrane has sharp reduction of current efficiency and chlorine purity after running for a certain time, the content of salt and chlorine in alkali in a product is obviously increased, micro cracks and other phenomena can be seen through microscopic analysis of the membrane, repeated and intensive research is carried out for finding out the reason and the solution of the problem, and the result shows that the occurrence of the micro cracks and the mismatch of the internal stress of the ion exchange membrane during extrusion molding have a large relationship. The casting processing temperature of the fluorine-containing ion exchange resin film is 270-290 ℃, the invention controls the transverse and longitudinal traction tension values of the fluorine-containing ion exchange resin film in the forming process by adjustment, so that the stress borne by the base film in the casting process is smaller than the maximum tolerable tension, the traction between chain segments is in a recoverable state, the internal structure of the film cannot be damaged by the tension, and the normal operation of the ion exchange film can be ensured.
When the tension is too large, the mutual movement distance between polymer chains in the membrane exceeds the recoverable amount, good entanglement between the polymer chains is damaged, so that the tolerance of the main structure of the ion exchange membrane to severe environment is reduced, a mechanical property defect area appears in the ion exchange membrane, the thickness uniformity also has a larger problem, the number of local thin points is increased rapidly, the mechanical property of the ion exchange membrane is reduced, the chemical tolerance is reduced, the ion selective permeability is reduced, the comprehensive use performance of the ion exchange membrane is reduced, the generation of the defects can directly cause the yield of the membrane to be reduced, the service life to be reduced, the ion exchange membrane can be suddenly degraded in the operation process more seriously, the short circuit between electrodes is caused, the production safety accident is caused, and the serious economic loss is caused.
(2) Hot-pressing and compounding: thermally compounding a reinforcing material into the fluorine-containing ion exchange resin base membrane obtained in the step (1) to form a reinforced composite membrane, wherein the thermal compounding temperature is 200-240 ℃, and the horizontal and longitudinal tension of the membrane is controlled to be less than or equal to 30N in the process; the thermal compounding temperature is 200-240 ℃, and the tension values of the transverse traction and the longitudinal traction enable the stress borne by the base film to be smaller than the maximum tolerable tension of the base film under the conditions of the thermal compounding temperature and the like, so that the internal structure of the film cannot be damaged, and the normal operation of the ion exchange film can be ensured.
(3) Ionization modification treatment: hydrolyzing the reinforced composite membrane obtained in the step (2) in alkali metal hydroxide to obtain an ion exchange membrane with an ion cluster channel, wherein the horizontal and longitudinal tension of the control membrane in the process is less than or equal to 100N;
(4) coating of a coating: and (4) coating the ion exchange membrane obtained in the step (3) to obtain the fluorine-containing ion exchange membrane for chlor-alkali industry, wherein the horizontal and longitudinal tension of the control membrane in the process is less than or equal to 80N.
The fluorine-containing ion exchange resin-based membrane in the step (1) is a layered fluorine-containing ion exchange resin-based membrane, and comprises a fluorine-containing polymer layer with a sulfonic acid type functional group and a fluorine-containing polymer layer with a carboxylic acid type functional group.
The reinforcing material in the step (2) is formed by weaving reinforcing wires containing perfluorocarbons and soluble wires of hydrocarbon polymers, and has a knot and hole structure.
The coating component in the step (4) comprises at least one of perfluorinated ion polymer, perfluorinated phosphoric acid polymer, metal oxide particles and pore-forming agent.
The total thickness of the fluorine-containing ion exchange resin base membrane in the step (1) is 95-170 mu m.
The total thickness of the fluorine-containing ion exchange resin base membrane is 95-130 mu m.
A fluorine-containing ion exchange membrane for chlor-alkali industry prepared by the preparation method.
The invention has the beneficial effects that: according to the preparation method, according to the state of the membrane under each environmental condition such as temperature and the like, the transverse and longitudinal tensions of the membrane in each process step are subjected to targeted adjustment design and independent control, for example, after ionization modification, the strength of the membrane is increased, and the tension control considers the influence factor of the strength; while in the coating step the film needs to be subjected to two temperatures, one above the ionization phase and one below, the tension control of which is more affected by the process temperature. Through the control of each step of horizontal and longitudinal tension which looks like being isolated but is buckled with each other in a ring manner, the stress damage of a fluorine-containing ion exchange membrane matrix caused by larger tension in the processing process is avoided, so that the defects of microcracks, local thinning and even leakage points of the ion exchange membrane and the like in the ion exchange membrane matrix are prevented, the ion exchange membrane can bear a harsh electrochemical environment without being locally damaged, the stability of the cell voltage of the membrane under a complex use working condition is ensured, the current efficiency, the chlorine purity and other key parameters are not obviously reduced, the ion exchange membrane can be operated efficiently for a long time in electrolytic production, and the comprehensive performance of the fluorine-containing ion exchange membrane is improved. Thereby leading the fluorine-containing ion exchange membrane to have longer service life and improving the comprehensive use performance.
The fluorine-containing ion exchange membrane prepared by the method 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, impurity ion tolerance and long-period performance stability.
Detailed Description
The present invention will be described in detail below with reference to examples.
Example 1
The preparation method of the fluorine-containing ion exchange membrane for chlor-alkali industry comprises the following steps:
(1) carrying out melt casting by a screw extruder in a coextrusion mode to obtain a fluorine-containing ion exchange resin base film compounded by a fluorine-containing polymer layer with a sulfonic acid type functional group and a fluorine-containing polymer layer with a carboxylic acid type functional group, carrying out hot pressing on a reinforcing material through a high-temperature hot roller, enabling weaving nodes of the reinforcing material to deform and fix, compounding the reinforcing material with the cast resin base film, introducing the reinforcing material between film forming press rollers, embedding the reinforcing material into resin on the S layer side under the action of pressure between the rollers to obtain a precursor material of the film, and controlling the transverse and longitudinal tensile forces of the film to be 5-7N in the step of obtaining two layers of compounded fluorine-containing ion exchange resin base films by melt extrusion;
(2) sequentially placing an isolation material with a porous material and the precursor material (S layer downwards) of the membrane obtained in the step (1) on a hot table with a vacuumizing function, embedding a reinforcing material in the S layer under the condition of high-temperature vacuum to form a reinforced composite membrane, wherein the transverse and longitudinal tensions of the membrane are controlled to be 15-20N in the process. The compounding method includes but is not limited to the following steps: the reinforcing mesh, the fluorine-containing ion exchange membrane base film (the side of the sulfonic acid membrane faces the mesh) and the release paper are stacked and combined in sequence and then placed on a heating plate of a laminator. Then, the reinforcing mesh layer is embedded in the perfluorosulfonic acid resin film by hot-press lamination under vacuum (or negative pressure) and heating. And then peeling off the release paper to obtain the sacrificial fiber mesh cloth reinforced fluorine-containing ion exchange membrane.
(3) Hydrolyzing the reinforced composite membrane obtained in the above working procedure by using alkali metal hydroxide at a certain temperature, and adding an organic solvent with a certain composition into the reinforced composite membrane to swell the membrane during hydrolysis so as to accelerate the hydrolysis reaction rate, wherein the organic solvent is dimethyl sulfoxide and dimethylformamide, and the weight ratio of the dimethyl sulfoxide to the dimethylformamide is 1: 1 mass ratio of the resulting solution. In the step, functional groups in the reinforced composite membrane are converted into-COONa to form the ion exchange membrane with ion cluster channels, and in the process, the horizontal and longitudinal tension of the membrane is controlled to be between 90 and 100N.
(4) Dissolving 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 water, isopropanol and a nitrogen-containing organic solvent DMF, and the weight ratio of the DMF to the water is 1: 0.8: 0.2, homogenizing the inorganic particles and the obtained resin solution to form a stable dispersion liquid;
(5) and (4) transferring the dispersion liquid obtained in the step (4) to the surface of the ion exchange membrane formed in the step (3), and drying and curing to form a stable surface coating. In the step of coating the ion exchange membrane to obtain the fluorine-containing ion exchange membrane, the horizontal and longitudinal tensions of the membrane are controlled to be between 60 and 70N.
Example 2
The preparation method of the fluorine-containing ion exchange membrane for chlor-alkali industry comprises the following steps:
(1) carrying out melt casting by a screw extruder in a coextrusion mode to obtain a fluorine-containing ion exchange resin base film compounded by a fluorine-containing polymer layer with a sulfonic acid type functional group and a fluorine-containing polymer layer with a carboxylic acid type functional group, carrying out hot pressing on a reinforcing material through a high-temperature hot roller, enabling weaving nodes of the reinforcing material to deform and fix, compounding the reinforcing material with the cast resin base film, introducing the reinforcing material between film forming press rollers, embedding the reinforcing material into resin on the S layer side under the action of pressure between the rollers to obtain a precursor material of the film, and in the step of obtaining the two-layer compounded fluorine-containing ion exchange resin base film by melt extrusion, wherein the horizontal and longitudinal tensile forces of the film are less than or equal to 10N;
(2) sequentially placing a separation material with a porous material and a precursor material (S layer downwards) of the membrane obtained in the step 1 on a hot table with a vacuumizing function, embedding a reinforcing material in the S layer under the condition of high-temperature vacuum to form a reinforced composite membrane, wherein the transverse and longitudinal tensions of the membrane are less than or equal to 20N in the process;
(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 is propanol. In which the functional groups in the reinforced composite membrane are converted to-SO3Na to form an ion exchange membrane with ion cluster channels, wherein the transverse and longitudinal tension of the membrane is less than or equal to 90N in the process;
(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 ethanol and diethylene glycol according to the weight ratio of 1: 0.75 mass ratio, homogenizing the inorganic particles and the obtained resin solution to form stable dispersion liquid;
(5) and (3) attaching the dispersion liquid obtained in the step (4) to the surface of the ion exchange membrane formed in the step (3) in a roller coating mode, and drying and curing to form a stable surface coating. In the step of coating the ion exchange membrane to obtain the fluorine-containing ion exchange membrane, the transverse and longitudinal tensions of the membrane are less than or equal to 60N.
Example 3
The preparation method of the fluorine-containing ion exchange membrane for chlor-alkali industry comprises the following steps:
(1) carrying out melt casting by a screw extruder in a coextrusion mode to obtain a fluorine-containing ion exchange resin base film compounded by a fluorine-containing polymer layer with a sulfonic acid type functional group and a fluorine-containing polymer layer with a carboxylic acid type functional group, carrying out hot pressing on a reinforcing material through a high-temperature hot roller, enabling weaving nodes of the reinforcing material to deform and fix, compounding the reinforcing material with the cast resin base film, introducing the reinforcing material between film forming press rollers, embedding the reinforcing material into resin on the S layer side under the action of pressure between the rollers to obtain a precursor material of the film, and in the step of obtaining the two-layer compounded fluorine-containing ion exchange resin base film by melt extrusion, both the transverse and longitudinal borne tension of the film are less than 8N;
(2) sequentially placing a separation material with a porous material and a precursor material (S layer downwards) of the membrane obtained in the step 1 on a hot table with a vacuumizing function, embedding a reinforcing material in the S layer under the condition of high-temperature vacuum to form a reinforced composite membrane, wherein the transverse and longitudinal tensions of the membrane are less than 24N in the process;
(3) hydrolyzing the reinforced composite membrane obtained in the above working procedure by using alkali metal hydroxide at a certain temperature, and adding an organic solvent with a certain composition into the reinforced composite membrane to swell the membrane during hydrolysis so as to accelerate the hydrolysis reaction rate, wherein the organic solvent is ethanol and ethylene glycol according to the weight ratio of 1: 0.3 mass ratio of the resulting mixed solvent. In which the functional groups in the reinforced composite membrane are converted to-SO3Na to form an ion exchange membrane with ion cluster channels, wherein the horizontal and longitudinal tension of the membrane is controlled to be 60-85N in the process;
(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 water and DMSO, and the weight ratio of the polar solvent to the DMSO is 1: 1.2, homogenizing the inorganic particles and the obtained resin solution to form stable dispersion liquid;
(5) and (4) spin-coating the dispersion liquid obtained in the step (4) on the surface of the ion exchange membrane formed in the step (3), and drying and curing to form a stable surface coating. In the step of coating the ion exchange membrane to obtain the fluorine-containing ion exchange membrane, the horizontal and longitudinal tension of the membrane is controlled to be 70-75N.
Comparative example 1
The method for manufacturing the fluorine-containing ion exchange membrane comprises the following steps:
(1) carrying out melt casting by a screw extruder in a coextrusion mode to obtain two layers of composite fluorine-containing ion exchange resin base films, carrying out hot pressing on a reinforcing material through a high-temperature hot roller, enabling a weaving node of the reinforcing material to deform and fix, compounding the reinforcing material with the cast resin base film, introducing the reinforcing material between film forming press rollers, embedding the reinforcing material into resin on the S layer side under the action of pressure between the rollers to obtain a precursor material of the film, and controlling the horizontal and longitudinal tension of the film to be between 40 and 70N in the step of obtaining the two layers of composite fluorine-containing ion exchange resin base films by melt extrusion;
(2) and (2) sequentially placing the isolation material with the porous material and the precursor material (S layer downwards) of the membrane obtained in the step (1) on a hot table with a vacuumizing function, embedding the reinforcing material in the S layer under the condition of high-temperature vacuum to form a reinforced composite membrane, wherein the transverse and longitudinal tensions of the membrane are controlled to be 25-30N in the process.
(3) Hydrolyzing the reinforced composite membrane obtained in the above working procedure by using alkali metal hydroxide at a certain temperature, and adding an organic solvent with a certain composition into the reinforced composite membrane to swell the membrane during hydrolysis so as to accelerate the hydrolysis reaction rate, wherein the organic solvent is dimethyl sulfoxide and dimethylformamide, and the weight ratio of the dimethyl sulfoxide to the dimethylformamide is 1: 1 mass ratio of the resulting solution. In the step, functional groups in the reinforced composite membrane are converted into-COONa to form the ion exchange membrane with ion cluster channels, and in the process, the horizontal and longitudinal tension of the membrane is controlled to be 130-150N.
(4) Dissolving 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 water, isopropanol and a nitrogen-containing organic solvent DMF, and the weight ratio of the DMF to the water is 1: 0.8: 0.2, homogenizing the inorganic particles and the obtained resin solution to form a stable dispersion liquid;
(5) and (4) transferring the dispersion liquid obtained in the step (4) to the surface of the ion exchange membrane formed in the step (3), and drying and curing to form a stable surface coating. In the step of coating the ion exchange membrane to obtain the fluorine-containing ion exchange membrane, the horizontal and vertical tensions of the membrane are controlled to be 110-120N.
Comparative example 2
The method for manufacturing the fluorine-containing ion exchange membrane comprises the following steps:
(1) carrying out melt casting by a screw extruder in a coextrusion mode to obtain two layers of composite fluorine-containing ion exchange resin base films, carrying out hot pressing on a reinforcing material through a high-temperature hot roller, enabling a weaving node of the reinforcing material to deform and fix, compounding the reinforcing material with the cast resin base film, introducing the reinforcing material between film forming press rollers, embedding the reinforcing material into resin on the S layer side under the action of pressure between the rollers to obtain a precursor material of the film, and controlling the horizontal and longitudinal tension of the film to be 15-35N in the step of obtaining the two layers of composite fluorine-containing ion exchange resin base films by melt extrusion;
(2) and (2) sequentially placing the isolation material with the porous material and the precursor material (S layer downwards) of the membrane obtained in the step (1) on a hot table with a vacuumizing function, embedding the reinforcing material in the S layer under the condition of high-temperature vacuum to form a reinforced composite membrane, wherein the transverse and longitudinal tensions of the membrane are controlled to be 40-45N in the process.
(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 is propanol. In which the functional groups in the reinforced composite membrane are converted to-SO3Na forms an ion exchange membrane with ion cluster channels, and in the process, the transverse and longitudinal tension of the membrane is controlled between 160-170N.
(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 ethanol and diethylene glycol according to the weight ratio of 1: 0.75 mass ratio, homogenizing the inorganic particles and the obtained resin solution to form stable dispersion liquid;
(5) and (3) attaching the dispersion liquid obtained in the step (4) to the surface of the ion exchange membrane formed in the step (3) in a roller coating mode, and drying and curing to form a stable surface coating. In the step of coating the ion exchange membrane to obtain the fluorine-containing ion exchange membrane, the horizontal and longitudinal tensions of the membrane are controlled to be between 60 and 70N.
Comparative example 3
The method for manufacturing the fluorine-containing ion exchange membrane comprises the following steps:
(1) carrying out melt casting by a screw extruder in a coextrusion mode to obtain two layers of composite fluorine-containing ion exchange resin base films, carrying out hot pressing on a reinforcing material through a high-temperature hot roller, enabling a weaving node of the reinforcing material to deform and fix, compounding the reinforcing material with the cast resin base film, introducing the reinforcing material between film forming press rollers, embedding the reinforcing material into resin on the S layer side under the action of pressure between the rollers to obtain a precursor material of the film, and controlling the horizontal and longitudinal tension of the film to be 8-9.5N in the step of obtaining the two layers of composite fluorine-containing ion exchange resin base films by melt extrusion;
(2) and (2) sequentially placing the isolation material with the porous material and the precursor material (S layer downwards) of the membrane obtained in the step (1) on a hot table with a vacuumizing function, embedding the reinforcing material in the S layer under the condition of high-temperature vacuum to form a reinforced composite membrane, wherein the transverse and longitudinal tensions of the membrane are controlled to be 75-80N in the process.
(3) Hydrolyzing the reinforced composite membrane obtained in the above working procedure by using alkali metal hydroxide at a certain temperature, and adding an organic solvent with a certain composition into the reinforced composite membrane to swell the membrane during hydrolysis so as to accelerate the hydrolysis reaction rate, wherein the organic solvent is ethanol and ethylene glycol according to the weight ratio of 1: 0.3 mass ratio of the resulting mixed solvent. In which the functional groups in the reinforced composite membrane are converted to-SO3Na, forming an ion exchange membrane with ion cluster channels, in the processThe tension of the film in the transverse and longitudinal directions is controlled between 220N and 230N.
(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 water and DMSO, and the weight ratio of the polar solvent to the DMSO is 1: 1.2, homogenizing the inorganic particles and the obtained resin solution to form stable dispersion liquid;
(5) and (4) spin-coating the dispersion liquid obtained in the step (4) on the surface of the ion exchange membrane formed in the step (3), and drying and curing to form a stable surface coating. In the step of coating the ion exchange membrane to obtain the fluorine-containing ion exchange membrane, the horizontal and longitudinal tension of the membrane is controlled to be between 90 and 100N.
The ion exchange membrane samples obtained in the examples and the ion exchange membrane samples obtained in the comparative examples were subjected to an electrolysis test under the same electrolysis conditions (the same saline conditions, current density: 5.5kA), and the cell voltage, current efficiency and chlorine gas purity of the samples were measured every 10d, with the following results:
the cell voltage changes of the fluorine-containing ion exchange membranes obtained in the first and second examples and comparative example in the electrolytic test are shown in table 1 below.
TABLE 1 cell Voltage Change in the use of the ion-exchange membranes obtained in examples 1 to 3 and comparative examples 1 to 3 for electrolysis
As can be seen from the data analysis in table 1, the cell voltage of the sample prepared in the comparative example decreases after a certain period of electrolysis, which is actually caused by microcracks in the base membrane, which deteriorates the selectivity of the base membrane to ions, resulting in an increase in the ion conduction rate on both sides of the ion exchange membrane, and finally shows a decrease in the cell voltage.
Second, the change of the current efficiency of the fluorine-containing ion exchange membrane obtained in each example and comparative example in the electrolysis test is shown in table 2.
TABLE 2 Change in Current efficiency when the ion-exchange membranes obtained in examples 1 to 3 and comparative examples 1 to 3 were used for electrolysis
Third, the change of the chlorine purity when the fluorine-containing ion exchange membrane obtained in each example and comparative example was used for electrolysis is shown in table 3.
TABLE 3 change in purity of chlorine gas when the ion-exchange membranes obtained in examples 1 to 3 and comparative examples 1 to 3 were used for electrolysis
As can be seen from the data analysis in tables 2 and 3, the current efficiency and the chlorine purity of the sample prepared by the comparative example are significantly reduced, which is the same reason as the reduction of the cell voltage, the internal part of the ion exchange membrane is subjected to excessive tension in the processing process, which causes the entanglement between the main chains in the internal part of the membrane to be damaged or micro-cracks to be generated, the damage is not easy to be found in the conventional detection of the membrane, and after a certain period of electrolysis production, the damaged parts are deteriorated, which causes the selective permeability of the whole membrane to ions to be reduced, and OH is reduced-The ions are conducted from the negative side to the anode side, resulting in an increase in the oxygen content of the chlorine gas and a decrease in the purity of the chlorine gas. The current efficiency is the ratio of the actual alkali yield to the theoretical alkali yield, and the selective permeability of the ion exchange membrane is reduced, so that the alkali yield is reduced, and the current efficiency is reduced.
In addition, the fluorine-containing ion exchange membrane samples obtained in the examples were compared with the fluorine-containing ion exchange membrane samples obtained in the comparative examples in terms of dimensional stability. The dimensional stability test method is as follows: taking a dry sample film of 1m multiplied by 1m, marking the film in the transverse and longitudinal directions, drawing ten lines in each direction of the film by using a marking pen, testing the increase percentage of the drawn line length compared with the original length after different soaking time, recording the increase percentage as swelling ratio, respectively calculating the standard deviation of the swelling ratio in the two directions, and taking the size of the standard deviation as an index for measuring the dimensional stability, wherein the smaller the standard deviation is, the better the dimensional stability is. The specific indexes are shown in Table 4.
TABLE 4 Standard deviations of swelling ratios in two directions for the samples obtained in examples 1 to 3 and comparative examples 1 to 3
As can be seen from the data analysis in table 4 above, the sample prepared by the comparative example has significantly poorer dimensional stability than the sample prepared by the example, which also indicates that, in the processing process, after the ion exchange membrane is damaged by excessive tension, the absorption capacity of the ion exchange membrane to moisture also has significant difference, so that the ion exchange membrane has regions with locally excessive swelling or too small swelling, when the ion exchange membrane is electrolyzed, the difference in local water content can cause the ion transport capacity to be different, so that the currents conducted by different regions are different, and the service life of the region with excessively large current is inevitably reduced.
Claims (7)
1. A preparation method of a fluorine-containing ion exchange membrane for chlor-alkali industry is characterized by comprising the following steps:
(1) and (3) melting coextrusion molding: firstly, casting by adopting a melt coextrusion mode to obtain two layers of composite fluorine-containing ion exchange resin base films, and then shaping the fluorine-containing ion exchange resin base films under the stretching action of a transverse stretching roller and a drawing roller, wherein the transverse tension and the longitudinal tension of a control film in the process are both less than or equal to 10N;
(2) hot-pressing and compounding: thermally compounding a reinforcing material into the fluorine-containing ion exchange resin base membrane obtained in the step (1) to form a reinforced composite membrane, wherein the thermal compounding temperature is 200-240 ℃, and the horizontal and longitudinal tension of the membrane is controlled to be less than or equal to 30N in the process;
(3) modification treatment: hydrolyzing the reinforced composite membrane obtained in the step (2) in alkali metal hydroxide to obtain an ion exchange membrane with an ion cluster channel, wherein the horizontal and longitudinal tension of the control membrane in the process is less than or equal to 100N;
(4) coating of a coating: and (4) coating the ion exchange membrane obtained in the step (3) to obtain the fluorine-containing ion exchange membrane for chlor-alkali industry, wherein the horizontal and longitudinal tension of the control membrane in the process is less than or equal to 80N.
2. The method for preparing the fluoride ion-exchange membrane for chlor-alkali industry as claimed in claim 1, wherein said fluoride ion-exchange resin base membrane of step (1) is a laminar fluoride ion-exchange resin base membrane comprising a fluoropolymer layer having sulfonic acid type functional groups and a fluoropolymer layer having carboxylic acid type functional groups.
3. The method for preparing the fluoride ion-exchange membrane for chlor-alkali industry as claimed in claim 1, wherein in said step (2), said reinforcement material is woven of reinforcement threads containing perfluorocarbon compounds and hydrocarbon polymer solution threads, and has knot and pore structure.
4. The method for preparing the fluorine-containing ion exchange membrane for chlor-alkali industry as claimed in claim 1, wherein the coating component in step (4) comprises at least one of perfluoroionomer, perfluorophosphoric acid polymer, metal oxide particles and pore-forming agent.
5. The method for preparing the fluorine-containing ion exchange membrane for the chlor-alkali industry according to claim 1, wherein the total thickness of the fluorine-containing ion exchange resin base membrane in the step (1) is 95 to 170 μm.
6. The preparation method of the fluorine-containing ion exchange membrane for chlor-alkali industry as claimed in claim 5, wherein the total thickness of the fluorine-containing ion exchange resin base membrane is 95-130 μm.
7. A fluorine-containing ion exchange membrane for chlor-alkali industry prepared by the preparation method of any one of claims 1 to 6.
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