10/10/2023 0 Comments Anode cathode picHydrogen, which is usually treated as exhaust gas in the chlor-alkali industry, may become the major fuel used on a large scale in the future as the most promising clean energy. This membrane has low electrical resistance and high ion-selective permeability and can work in a highly corrosive electrolyte environment. The first-generation membrane can only work at low corrosive concentrations, whereas the state-of-the-art membrane is made of a perfluorosulfonic acid (PFSA) polymer layer, where a polytetrafluoroethylene (PTFE)-reinforced fabric and a perfluorocarboxylic acid (PFCA) polymer are bonded together. This membrane rejects the passage of chloride ions (negatively charged) but allows sodium ions (positively charged) to pass through. A cation-selective permeation membrane is placed between the anode and cathode compartments, and a saturated sodium chloride solution is injected into the anode compartment, which usually produces 32%–35% caustic soda (Fig. The perfluorinated membrane method is currently recognized as the most energy-efficient chlor-alkali process in the world. Thus, the replacement of the diaphragm method with ion membrane technology is an inevitable trend. Compared with diaphragm electrolytic cells, the membrane counterpart offers high-purity sodium hydroxide. Membrane electrolysis cells use highly conductive IEMs instead of traditional asbestos felt to separate Cl 2 and H 2, which greatly reduces the operating voltage and pollutant emissions. Therefore, these two technologies above rely on highly toxic mercury and asbestos respectively, resulting in serious environmental pollution. Therefore, in diaphragm electrolyzers, asbestos felt is often used to separate the products (Cl 2 and H 2), although the chemical instability of asbestos itself causes the severe swelling of pure asbestos diaphragm under a high current load. The negatively charged membrane can inhibit the back diffusion of OH −. A diaphragm is introduced to separate the anode and cathode reactions to prevent the cathode product (NaOH) and the anode product (Cl 2) from crossing over to generate sodium hypochlorite. Then, NaHg is transferred to another electrolytic cell to release Na + (NaHg → Na + + Hg + e −), forming NaOH in the electrolyte. In mercury electrolysis cells, mercury as the liquid cathode reacts with sodium ions to form sodium amalgam (Na + + Hg + e − → ∙NaHg), whereas Cl 2 is formed on the anode. At present, membrane electrolytic cell technology accounts for approximately 81% of the global chlor-alkali capacity. The chlor-alkali industry has experienced a long development process from mercury, diaphragm electrolytic cells to ion exchange membrane (IEM) electrolytic cells. Therefore, energy saving and emission reduction in the chlor-alkali production process are important development directions. However, the current chlor-alkali process is one of the industries with high energy consumption, releasing large amounts of pollutants and causing serious environmental problems. NaOH is also a common chemical raw material that is widely used in the production of detergents, herbicides, pesticides, medicines, plastics, and soaps. Chlorine has been used in a variety of applications, including the production of building materials such as polyvinyl chloride, organic synthesis, metallurgy, water treatment, and the manufacture of titanium dioxide. Each ton of chlorine consumes about 2200–2600 kW∙h of electricity, and the global chlor-alkali industry needs to consume over 150 TW∙h of electricity every year, accounting for about 10% of global electricity. The global annual production of chlorine exceeds 75 million tons. The chlor-alkali process is one of the most basic chemical industries, mainly producing chlorine (Cl 2) and sodium hydroxide (NaOH).
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