An excellent material for anodes in the chlor-alkali industry—titanium
The melting point of titanium is 1680 degree and the density is 4.54g/cm3. It is heavier than aluminum but 43% lighter than steel. Titanium is very strong, 6 times stronger than aluminum. Therefore, among structural materials, titanium has a very high specific strength. Another great advantage of titanium is its strong corrosion resistance to a variety of substances.
Titanium is widely used in the chlor-alkali industry, firstly because of its excellent corrosion resistance to wet chlorine and sodium chloride solutions, and secondly because its electrochemical properties make it suitable for use as an anode material. The United States began manufacturing chlor-alkali equipment as early as the 1960s, and this application has developed rapidly, with a compound annual growth rate of 8%. In 2021, approximately 50% of global chlorine production uses ruthenium-titanium coated anodes. In Russian chlorine production, more than 80% of equipment and pipes are made of titanium. The entire chlor-alkali industry, which produces chlorine and other oxides, toxic chemicals, chloramines and bleaching powder, accounts for more than 60% of the titanium equipment used in the chemical sector. In the chlor-alkali industry, Japan uses titanium anodes, which are the most widely used titanium products in Japan. Since the early 1980s, my country's chlor-alkali industry has begun to use titanium anodes and has achieved good economic benefits.
Titanium anode is currently the single product that uses the most titanium in the chemical industry. In the past, graphite anodes were commonly used in chlor-alkali industrial electrolyzers, which had short lifespan and high power consumption. The advantages of using titanium anodes are: anode size stability, long life, low power and steam consumption, high product quality, large production capacity, and good working conditions. After Shanghai Liaoyuan Chemical Company switched its 20-meter-long electrolytic cell to titanium anodes, experts determined that its production capacity doubled compared to that of graphite anode electrolytic cells. The current density of graphite electrodes is mostly 1100A/m2, and the current density of titanium anodes can reach >2000A/m2; the anode has a long life. Graphite anodes can only be used for about 0.5 years, while titanium anodes can be used for >4 years; saving about 15% of electricity and about 5% of steam. Product quality is good. The caustic soda produced by the graphite anode tank is reddish purple, while the caustic soda produced by the titanium anode tank is colorless and has low organic impurity content; the asbestos diaphragm has a long life. The graphite anode tank diaphragm can only be used for about 180 days, while the titanium anode tank diaphragm has a long service life because it is not blocked by graphite particles, which not only saves asbestos, but also requires less maintenance work; titanium anodes do not use asphalt and lead, and are green and environmentally friendly.
In the chlorine production process of the chlor-alkali company, the chlorine gas discharged from the electrolytic cell not only has a high temperature, but also contains a large amount of moisture. Must be cooled and dried before use. The cooling process includes direct method and indirect method. Direct water spray cooling will not only form a large amount of chlorine-containing water, but also pollute the environment. The loss of chlorine is large, the consumption of H2SO4 is large, and the working conditions are also poor. If a stainless steel indirect cooler is used for cooling, the service life is difficult to exceed 10 days, while a graphite cooler can only be used for about 90 days. Titanium is an excellent material for manufacturing coolers and has extremely strong resistance to wet chlorine corrosion, with a corrosion rate of Less than or equal to 0.0025 mm/year. Therefore, the use of titanium coolers in chlor-alkali processing can shorten the cooling and drying time, reduce the loss of chlorine, and reduce environmental pollution. Secondly, it can create the necessary conditions for stable operation and complete drying of compressed gas.
In the U.S. chemical industry, >50% of titanium is used in coolers for chlor-alkali production. Allied's cooling tubes made from graphite only lasted 2 to 3 years. After switching to titanium tubes, they can be used for more than 10 years. The use of thin-walled titanium tubes eliminates the need for inlaying graphite strips on the cooler and can withstand extremely high heat conduction. For example, a 78m2 titanium cooler conducts as much heat as a 140m2 graphite cooler. The coolers used in the Soviet Union and Russia's chlor-alkali industry are all made of titanium. Wet chlorine cooling economic indicators, Shanghai Liaoyuan Chemical Company graphite tube, titanium tube cooler technical and economic indicators. It can be seen from these data that indirect cooling with wet chlorine is much more effective than direct spray cooling with water.
After Shanghai Liaoyuan Chemical Company switched to indirect titanium coolers, it can save 400,000 tons/year of water, 1,360 tons/year of sulfuric acid for drying, and 1,400 tons/year of chlorine gas. Titanium tube coolers last much longer than graphite tube coolers.
Titanium pumps that use membrane methods or mercury electrolysis to produce chlorine can achieve the highest economic benefits. The titanium pump from the American company Piffic has a service life of up to 10 years. Beijing Chemical Plant No. 2 used cast titanium 6BA-12 pumps, Dg100 and Dg150 stop valves, and HTB-7011 water ring ceramic vacuum pump titanium impellers in the vacuum dechlorination process. After 1.5 years of operation, they are still intact. No signs of corrosion. Various titanium valves can be effectively used under high pressures from normal pressure to 5000N/cm2.
