Enhanced perfluorinated sulfonic acid ion exchange membrane for alkali chloride electrolysis and preparation method thereof
Technical Field
The invention belongs to the technical field of ion exchange membranes, and particularly relates to a reinforced perfluorinated sulfonic acid ion exchange membrane for alkali chloride electrolysis and a preparation method thereof.
Background
Ion exchange membranes have excellent permselectivity and have been widely used in electrolytic oxidation and reduction operations. 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. As a high energy consumption industry, the development of lower power consumption electrolysis technology has been the direction of effort. With the development of technology, the cell voltage can be effectively reduced by reducing the cell gap between the anode and the cathode. However, when the distance between the electrodes is reduced to a certain distance, bubbles generated during the electrolysis are easily adhered to the surface of the membrane and are difficult to release because the membrane is tightly attached to the electrodes. A large number of bubbles are gathered on the surface of the membrane to block a current channel, so that the effective electrolysis area of the membrane is reduced, the local polarization effect is obviously increased, and the cell pressure is increased.
At present, perfluorosulfonic acid ion exchange membranes all have the problems of high exchange capacity, low mechanical strength, high mechanical strength and low exchange capacity. In addition, in practical application, the requirements on the mechanical strength and the service life of the diaphragm are quite high, and the existing perfluorinated sulfonic acid ion exchange membrane cannot meet the requirements. In the prior art, a great deal of research is carried out on the coating of the ion exchange membrane, however, fillers in the coating can block an ion transmission path, so that the membrane resistance is larger, the coating cannot be applied to a zero polar distance electrolytic cell under the condition of high current density, and the application field of the coating is greatly limited.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: overcome prior art's not enough, provide an alkali metal chloride electrolysis with reinforcing perfluorosulfonic acid ion exchange membrane, through increase perfluoropolymer reinforcing net in perfluorosulfonic acid membrane simultaneously at the inside fretwork tunnel that has prepared of membrane, have lower membrane resistance concurrently when making it have better mechanical properties, prepare porous structure on membrane surface simultaneously, can promote membrane surface roughness, reduce its adhesion to the bubble, improve the effective electrolysis area of membrane, reduce local polarization phenomenon. The invention also provides a preparation method of the compound, which has simple and reasonable process and is easy for industrial production.
The reinforced perfluorinated sulfonic acid ion exchange membrane for alkali metal chloride electrolysis comprises a perfluorinated sulfonic acid polymer layer, wherein a functional surface coating is coated on the surface of the perfluorinated sulfonic acid polymer layer, the functional surface coating consists of a perfluorinated polymer and a metal oxide and has a porous rough structure, a reinforcing material layer is embedded in the perfluorinated sulfonic acid polymer layer, and the reinforcing material layer is provided with a hollow tunnel structure.
The thickness of the perfluorinated sulfonic acid polymer layer is 50-250 μm, preferably 70-200 μm, and the Ion Exchange Capacity (IEC) is 0.6-1.5mmol/g, preferably 0.8-1.2 mmol/g.
The perfluoropolymer in the functional surface coating is a perfluoropolymer with an ion exchange function, the perfluoropolymer is one or more of perfluorosulfonic acid polymer, perfluorocarboxylic acid polymer or perfluorophosphoric acid polymer, preferably perfluorosulfonic acid polymer, and the Ion Exchange Capacity (IEC) of the perfluoropolymer is 0.5-1.5mmol/g, preferably 0.8-1.2 mmol/g.
The amount of the metal oxide contained in each square meter of the functional surface coating is more than 0g, less than 20g, preferably 0.1-12g, and the particle size is 5nm-10 mu m, preferably 20-800nm, and the metal oxide is the oxide of zirconium, hafnium or cerium in IVB group, preferably zirconium oxide.
The perfluorinated sulfonic acid polymer layer contains criss-cross hollow tunnels; the distance between two adjacent main fibers in the reinforcing material net is 0.5-1.5mm, and the two adjacent main fibers contain 32-500 hollow tunnels; the diameter of the single tunnel is 1 to 50 μm, preferably 5 to 20 μm. The tunnel is in the shape of regular or irregular circle, ellipse, square, triangle and the like. The hollow tunnels can be arranged in a single way or can be formed by twisting a plurality of hollow tunnels to form a large channel.
The functional surface coating has porous rough structure inside and on the surface, the coating thickness is 10nm-30 μm, preferably 1-6 μm, the Ra value of the surface roughness of the functional surface coating is 10nm-5 μm, preferably 50nm-2 μm, the Ra value of the surface roughness of the functional surface coating is 300nm-10 μm, preferably 1-5 μm. The pores can be distributed on the surface of the coating or in the coating or can be distributed in a designated area in a concentrated manner, the pores can be in a regular or irregular structure which is orderly or disorderly arranged, such as regular or irregular circles, ellipses, squares, rectangles and the like, and the volume of the pores in the functional surface coating accounts for 5-95% of the volume of the functional surface coating.
The functional surface coating has extremely low bubble adhesion in 0-300g/L saline water environment, and the adhesion of 3 mu L of bubbles and the functional surface coating is 0-400 mu N, preferably 0-120 mu N.
The functional surface coating has a 5 mu L bubble contact angle of more than or equal to 130 degrees in 250g/L saline environment at 25 ℃.
The preparation method of the enhanced perfluorinated sulfonic acid ion exchange membrane for alkali chloride electrolysis comprises the following steps:
(1) obtaining a perfluorinated ion exchange resin base membrane from perfluorinated sulfonic acid resin by adopting an extrusion casting mode, and compounding a reinforcing material net with the perfluorinated ion exchange resin base membrane after soaking treatment by using a solvent so as to form a perfluorinated sulfonic acid ion exchange membrane precursor;
(2) carrying out overpressure treatment on the perfluorinated sulfonic acid ion exchange resin base membrane obtained in the step (1), and then carrying out hydrolysis treatment in an alkali metal hydroxide solution to convert the perfluorinated sulfonic acid ion exchange resin base membrane into a perfluorinated ion exchange membrane with an ion exchange function;
(3) adding the perfluoropolymer into a solvent for homogenization treatment to form a perfluoropolymer solution;
(4) adding a pore-forming agent and a metal oxide into the perfluoropolymer solution obtained in the step (3), and performing ball milling to obtain a dispersion liquid;
(5) and (3) attaching the dispersion liquid obtained in the step (4) to the surface of the perfluorinated ion exchange membrane with the ion exchange function obtained in the step (2) in a coating mode, and etching the surface to form a porous rough structure after drying and curing.
The reinforcing material net in the step (1) is formed by weaving perfluorocarbon reinforcing threads and hydrocarbon polymer soluble threads, has a porosity of 20-99%, preferably 60-80%, and a thickness of 40-200 μm, preferably 50-100 μm.
In the step (2), when the hydrolysis treatment is carried out in the alkali metal hydroxide solution, an organic solvent can be added to swell the membrane so as to accelerate the hydrolysis reaction rate, wherein the organic solvent is one or a mixture of more than one of dimethyl sulfoxide, dimethyl formamide, propanol, ethanol or ethylene glycol. In which the functional groups in the membrane are converted to-SO3Na forms an ion exchange membrane with an ion cluster channel, and meanwhile, a dissolving and discarding line in the reinforcing material net is dissolved and discarded in the step to form a hollow tunnel structure.
The solvent used in step (3) is a polar solvent, and is usually one or more selected from water, low-boiling monohydric alcohol, dihydric alcohol, and nitrogen-containing organic solvent.
The pore-forming agent in the step (4) is one or a composition of more than one of silicon oxide, aluminum oxide, zinc oxide, titanium oxide, potassium carbonate, silicon carbide, sodium carbonate, polytrimethylene terephthalate fiber, polyurethane fiber, polyvinylidene fluoride and polyethylene terephthalate fiber.
The film coating mode in the step (5) is one of spraying, brushing, roller coating, transfer printing, dipping or spin coating; the etching is one or more of alkaline hydrolysis, acid hydrolysis and hydrolysis.
Compared with the prior art, the invention has the following beneficial effects:
1. the perfluorinated polymer reinforcing net is added in the perfluorinated sulfonic acid membrane, and the hollow tunnel is prepared in the membrane, so that the perfluorinated sulfonic acid membrane has better mechanical property and lower membrane resistance.
2. The ion exchange membrane prepared by the invention has lower membrane resistance, and has good performances of preventing bubble adhesion, reducing the voltage of an electrolytic cell and saving electric energy through a rough surface structure consisting of metal oxide and perfluoropolymer in a functional surface layer.
3. The perfluorinated sulfonic acid ion exchange membrane prepared by the invention is suitable for running in a novel zero-polar-distance electrolytic cell under a high-current density condition, and can obviously reduce the cell voltage.
4. The preparation method is scientific and reasonable, simple and easy to operate, and easy for industrial production.
Detailed Description
The present invention will be further described with reference to the following examples.
The starting materials used in the examples are commercially available unless otherwise specified.
Example 1
The preparation method of the reinforced perfluorinated sulfonic acid ion exchange membrane for alkali chloride electrolysis comprises the following steps:
(1) obtaining a perfluorinated ion exchange resin base membrane by adopting a perfluorinated sulfonic acid resin extrusion casting mode with IEC (0.8 mmol/g), wherein the thickness of the perfluorinated sulfonic acid resin layer is 70 mu m, soaking a reinforced material net compounded and woven by polytetrafluoroethylene and silk into a trifluoro trichloroethane solvent subjected to ultrasonic treatment for 1.5 hours, wherein the thickness of a porous reinforced material is 40 mu m, the volume ratio of the polytetrafluoroethylene to the silk is 1:1, the porosity of the reinforced material net is 30%, taking out, drying and then compounding the reinforced material net with the perfluorinated ion exchange resin base membrane in a rolling mode, thereby forming a perfluorinated sulfonic acid ion exchange membrane precursor;
(2) performing overpressure treatment on the perfluorinated ion exchange membrane precursor prepared in the step (1) at the temperature of 180 ℃ and under the pressure of 120 tons at the speed of 45 m/min by using an overpressure machine, immersing the perfluorinated ion exchange membrane precursor into a mixed aqueous solution containing 18 wt% of dimethyl sulfoxide and 20 wt% of NaOH at the temperature of 85 ℃ for transformation for 80 minutes after the overpressure treatment, converting the perfluorinated ion exchange membrane precursor into a perfluorinated ion exchange membrane with an ion exchange function, and simultaneously dissolving and discarding silk in a reinforcing material net to form a hollowed-out tunnel structure; in the obtained ion exchange membrane, the distance between two adjacent main fibers in the reinforcing material net is 0.8 +/-0.2 mm, and 189 hollow tunnels are contained in the two adjacent main fibers; the diameter of the single tunnel is 8 +/-1 mu m;
(3) preparing ethanol and isopropanol into a mixed solution according to the weight ratio of 1:1, adding perfluorinated sulfonic acid resin with the exchange capacity of 1.2mmol/g, and treating for 3 hours at 230 ℃ in a closed reaction kettle to obtain a uniform perfluorinated sulfonic acid solution with the weight percent of 3;
(4) adding sodium carbonate particles with the average particle size of 1 mu m and zirconia powder with the particle size of 700nm into the perfluorosulfonic acid solution obtained in the step (3) according to the mass ratio of 1:2, and carrying out ball milling for 36 hours to obtain a 20 wt% dispersion solution;
(5) adopting a spraying method to attach the dispersion liquid obtained in the step (4) to the two side surfaces of the perfluorinated ion exchange membrane base membrane with the ion exchange function obtained in the step (2), and controlling the ZrO content in each square meter of coating2The content is 8g, and the mixture is dried for 2 hours at 150 ℃;
(6) and (3) treating the film containing the coating obtained in the step (5) in a 10 wt% nitric acid solution for 3 hours at normal temperature.
Performance testing
The surface roughness Ra of the prepared perfluorinated sulfonic acid ion exchange membrane is 350nm at 10 mu m multiplied by 10 mu m, and the surface roughness Ra of the prepared perfluorinated sulfonic acid ion exchange membrane is 4.5 mu m at 240 mu m multiplied by 300 mu m. The adhesion was 80. mu.N in 250g/L NaCl solution, measured with 3. mu.L air bubbles.
Carrying out an electrolysis test on the prepared perfluorosulfonic acid ion exchange membrane in an electrolytic cell by using a sodium chloride aqueous solution, wherein 290g/L of the sodium chloride aqueous solution is supplied to an anode chamber, water is supplied to a cathode chamber, and the concentration of sodium chloride discharged from the anode chamber is ensured to be 200g/L and the concentration of sodium hydroxide discharged from the cathode chamber is ensured to be 31%; the test temperature was 75 ℃ and the current density was 6.0kA/m2After 60 days of electrolysis experiments, the average cell pressure is 3.31V, and the average current efficiency is 98.5%.
According to the criterion SJThe sheet resistance of the film obtained by the T10171.5 method test was 0.38. omega. cm-2。
Comparative example 1
An ion membrane-based film and a perfluorosulfonic acid solution were prepared in the same manner as in example 1, and then a dispersion was prepared in the same manner, except that sodium carbonate was not added to the dispersion, and only ZrO having an average particle size of 700nm was added2The particles were homogenized in a ball mill to form a dispersion with a content of 20% by weight. A perfluorosulfonic acid ion-exchange membrane was obtained in the same manner as in example 1, with the ZrO content in the coating layer controlled per square meter2The content was 12 g.
Performance testing
The surface roughness Ra of the prepared perfluorinated sulfonic acid ion exchange membrane is 110nm at 10 mu m multiplied by 10 mu m, the surface roughness Ra of the prepared perfluorinated sulfonic acid ion exchange membrane is 3.8 mu m at 240 mu m multiplied by 300 mu m, and the adhesion is 190 mu N measured by 3 mu L of air bubbles in 250g/L NaCl solution.
An electrolytic test of a sodium chloride solution was carried out under the same conditions as in example 1, and after an electrolysis experiment for 60 days, the average cell pressure was 3.5V, the average current efficiency was 98.5%, and the sheet resistance was 0.43. omega. cm-2。
Example 2
The preparation method of the reinforced perfluorinated sulfonic acid ion exchange membrane for alkali chloride electrolysis comprises the following steps:
(1) obtaining a perfluorinated ion exchange resin base membrane by adopting a perfluorinated sulfonic acid resin extrusion casting mode with IEC (International electrotechnical Commission) of 1.32mmol/g, wherein the thickness of the perfluorinated sulfonic acid resin layer is 250 mu m, soaking a reinforcing material net compounded by polytetrafluoroethylene and silk into a trifluoro trichloroethane solvent subjected to ultrasonic treatment for 1.5 hours, wherein the thickness of a porous reinforcing material is 40 mu m, the volume ratio of the polytetrafluoroethylene to the silk is 1:1.2, the void ratio of the reinforcing material net is 25%, taking out, drying and then compounding the reinforcing material net and the perfluorinated ion exchange resin base membrane in a rolling mode, thereby forming a perfluorinated sulfonic acid ion exchange membrane precursor;
(2) performing overpressure treatment on the perfluorinated ion exchange membrane precursor prepared in the step (1) at the temperature of 180 ℃ and under the pressure of 120 tons at the speed of 45 m/min by using an overpressure machine, immersing the perfluorinated ion exchange membrane precursor into a mixed aqueous solution containing 18 wt% of dimethyl sulfoxide and 20 wt% of NaOH at the temperature of 85 ℃ for transformation for 80 minutes after the overpressure treatment, converting the perfluorinated ion exchange membrane precursor into a perfluorinated ion exchange membrane with an ion exchange function, and simultaneously dissolving and discarding silk in a reinforcing material net to form a hollowed-out tunnel structure; in the obtained ion exchange membrane, the distance between two adjacent main fibers in the reinforcing material net is 1.3 +/-0.2 mm, and the two adjacent main fibers contain 124 hollow tunnels; the diameter of the single tunnel is 10 +/-1 mu m;
(3) preparing ethanol and isopropanol into a mixed solution according to the weight ratio of 1:1, adding perfluorinated sulfonic acid resin with the exchange capacity of 0.95mmol/g into the mixed solution, and treating the mixture for 3 hours at 230 ℃ in a closed reaction kettle to obtain a 7 wt% uniform perfluorinated sulfonic acid solution;
(4) adding sodium carbonate particles with the average particle size of 2 mu m and zirconia powder with the particle size of 500nm into the perfluorosulfonic acid solution obtained in the step (3) according to the mass ratio of 1:2, and carrying out ball milling for 36 hours to obtain a 20 wt% dispersion solution;
(5) adopting a spraying method to attach the dispersion liquid obtained in the step (4) to the two side surfaces of the perfluorinated ion exchange membrane base membrane with the ion exchange function obtained in the step (2), and controlling the ZrO content in each square meter of coating2The content is 4g, and the mixture is dried for 2 hours at 150 ℃;
(6) and (3) treating the film containing the coating obtained in the step (5) in a 10 wt% nitric acid solution for 3 hours at normal temperature.
Performance testing
The surface roughness Ra of the prepared perfluorinated sulfonic acid ion exchange membrane is 210nm at 10 mu m multiplied by 10 mu m, and the surface roughness Ra of the prepared perfluorinated sulfonic acid ion exchange membrane is 6 mu m at 240 mu m multiplied by 300 mu m. The adhesion was measured in 250g/L NaCl solution with 3. mu.L air bubbles and was 50. mu.N.
Carrying out an electrolysis test on the prepared perfluorosulfonic acid ion exchange membrane in an electrolytic cell by using a sodium chloride aqueous solution, wherein 300g/L of the sodium chloride aqueous solution is supplied to an anode chamber, water is supplied to a cathode chamber, and the concentration of sodium chloride discharged from the anode chamber is ensured to be 200g/L and the concentration of sodium hydroxide discharged from the cathode chamber is ensured to be 31.6%; the test temperature was 78 ℃ and the current density was 4kA/m2After 60 days of electrolysis experiment, the average cell pressure is 2.61V, and the average current efficiency is 98.9 percent。
The sheet resistance of the resulting film was measured to be 1.3. omega. cm by the standard SJ/T10171.5 method-2。
Comparative example 2
An ion membrane-based film and a perfluorosulfonic acid solution were prepared in the same manner as in example 2, and then a dispersion was prepared in the same manner, except that sodium carbonate was not added to the dispersion, and only ZrO having an average particle diameter of 500nm was added2The particles were homogenized in a ball mill to form a dispersion with a content of 20% by weight. A perfluorosulfonic acid ion-exchange membrane was obtained in the same manner as in example 1, with the ZrO content in the coating layer controlled per square meter2The content was 6 g.
Performance testing
The surface roughness Ra of the prepared perfluorosulfonic acid ion exchange membrane is 180nm at 10 mu m multiplied by 10 mu m, the surface roughness Ra of the prepared perfluorosulfonic acid ion exchange membrane is 4.9 mu m at 240 mu m multiplied by 300 mu m, and the adhesion is 185 mu N measured by 3 mu L of air bubbles in 250g/L NaCl solution.
An electrolytic test of a sodium chloride solution was carried out under the same conditions as in example 2, and after an electrolysis experiment for 60 days, the average cell pressure was 2.9V, the average current efficiency was 98.7%, and the sheet resistance was 1.57. omega. cm-2。
The performance data for the perfluorosulfonic acid ion exchange membranes prepared in examples 1-2 and comparative examples 1-2 are shown in Table 1.
TABLE 1 Performance data for perfluorosulfonic acid ion exchange membranes prepared in examples 1-2 and comparative examples 1-2
Of course, the foregoing is only a preferred embodiment of the invention and should not be taken as limiting the scope of the embodiments of the invention. The present invention is not limited to the above examples, and equivalent changes and modifications made by those skilled in the art within the spirit and scope of the present invention should be construed as being included in the scope of the present invention.