Applications of titanium in the chemical industry

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:Due to its excellent corrosion resistance, mechanical properties, and processability, titanium is widely used in many sectors of the national economy. Especially in chemical manufacturing, replacing stainless steel, nickel-based alloys, and other rare metals with titanium as corrosion-resistant materials is of great significance for increasing production volume, improving product quality, extending the service life of equipment, reducing consumption, lowering energy costs, cutting expenses, preventing pollution, improving working conditions, and enhancing productivity. In recent years, the scope of titanium use in China’s chemical industry has been continuously expanding, with consumption increasing year by year; titanium has become one of the main corrosion-resistant materials in chemical equipment. As a corrosion-resistant structural material used in chemical plants, titanium has established its reputation, and as an ideal material for chemical equipment, it is attracting increasing attention from engineering professionals. I. Chlor-alkali industry The chlor-alkali industry is an important basic raw materials industry, and its production and development have a significant impact on the national economy. This is because titanium has better corrosion resistance to chloride ions than common stainless steels and other non-ferrous metals. Currently, titanium is widely used in the chlor-alkali industry to manufacture metal anode electrolyzers, ion-exchange membrane electrolyzers, wet chlorine coolers, refined brine preheaters, dechlorination towers, chlorine gas cooling and washing towers, etc. In the past, the main components of these devices were often made of non-metallic materials such as graphite and polyvinyl chloride. Due to the unsatisfactory mechanical properties, thermal stability, and processability of these non-metallic materials, the devices became bulky, consumed large amounts of energy, had a short lifespan, which affected product quality and caused environmental pollution. Therefore, since the 1970s, our country has begun to gradually replace graphite cells with metal anode cells and ion-exchange membrane cells, as well as graphite coolers with titanium wet chlorine coolers, all of which have yielded good results. For example: the application of titanium wet chlorine coolers. The electrolytic production of caustic soda from table salt generates large amounts of high-temperature, humid chlorine gas, with temperatures typically ranging from 75 to 95°C; this gas must be cooled and dried before it can be used. In China, the production of chlorine through the electrolysis of salt used to be affected by unreasonable cooling processes or corrosion of cooling equipment, which impacted both the yield and quality of chlorine produced, and it also caused severe environmental pollution. Titanium coolers resistant to high-temperature and humid chlorine corrosion were put into production, changing the landscape of chlorine production in the chlor-alkali industry. Titanium is highly resistant to corrosion in high-temperature, humid chlorine environments. In chlorine water at room temperature, the corrosion rate of titanium is 0.000565 mm/a; in chlorine water at 80°C, the corrosion rate of titanium is 0.00431 mm/a ； In 95% wet chlorine gas, the corrosion rate of titanium at room temperature is 0.00096 mm/a. Many chlor-alkali plants use titanium wet chlorine coolers; some of them have been in use for nearly 20 years and are still in perfect condition. II. Soda ash industry Soda ash is one of the most fundamental chemical raw materials, and it is directly related to the development of the national economy. In the soda ash production process, the gaseous media are mainly NH3 and CO2, while the liquid media consist of solutions with high concentrations of NaCl, NH4Cl, NH4HCO3, and Cl-. The main equipment used for reactions such as carbonation, including the small tubes in the carbonation towers, heat mother liquor coolers, coolers, and crystallization external coolers, is made of carbon steel or cast iron; such materials are not resistant to corrosion, leading to severe corrosion and leakage, and their service life does not exceed three years. From 1975 to 1977, the Tianjin Alkali Plant and Dalian Chemical Industry Company established facilities to carry out demonstration projects on the use of titanium. The application of components such as carbonization tower cooling tubes with dimensions of Φ63×2 mm, titanium plate heat exchangers, titanium external coolers, titanium pumps, CO2 turbine compressor rotors, and Ti-6Al-4V alloy impellers proved to be very effective. These projects served as a model for the entire industry in carrying out upgrades using titanium technology, as well as for the construction of three new plants capable of producing 600,000 tons of soda ash per year. For example, in the ammonia condenser at the top of the distillation tower of a soda ash plant, pure titanium tubes are used instead of cast iron tubes. The ammonia condenser is a device used in the soda ash production process to condense the ammonia gas evaporated from the distillation tower. It consists of two cast-iron cooling chambers, each with a diameter of 2.5 meters and a height of 1.2 meters. These chambers are equipped with 214 cast-iron tubes of dimensions Φ63×6×2986 mm, for a total of 428 tubes in the two chambers combined. The inside and outside of the tube are protected against corrosion using thermosetting phenolic varnish; the medium outside the tube is NH3, CO2, and H2O vapor, at a temperature of around 95°C. The NH4Cl mother liquor flows inside the tube, where it exchanges heat with the medium outside the tube. Under these conditions, cast iron pipes suffer severe corrosion; some of them develop corrosion-induced perforations after just one year of use, and by the end of two years they are so severely damaged that they can no longer be used. To address the severe corrosion of the cast iron pipes in the ammonia condenser, all such pipes were replaced with TA2 titanium pipes, with specifications of Φ60×2×3010 mm. The ends of the titanium pipes are sealed against the cast iron grating using O-ring rubber seals. This is the first distillation tower in our country’s soda ash industry whose cooling tubes are made of pure titanium. More than two years after it was put into use, a macroscopic inspection was conducted by removing the pipe, and no signs of corrosion were found. Its expected service life is over 20 years, which is 10 times longer than that of cast iron pipes. Due to the corrosion resistance of titanium tubes, their heat transfer efficiency remains high (in contrast, cast iron tubes exhibit good heat transfer efficiency at the beginning of a 3-year maintenance period, poor efficiency in the middle phase, and eventual failure). Preheating the NH4Cl mother liquor inside the tubes allows for the recovery of heat, thereby increasing the temperature of the mother liquor before it enters the distillation tower; this helps to save a large amount of steam, resulting in significant economic benefits.