The Application of Titanium Anode in Chlor-alkali Industry

The chlor-alkali industry is a chemical industry that produces chlorine gas and caustic soda by electrolyzing saline solution. It has a history of more than 100 years. The chlor-alkali industry is also the earliest application of titanium in the chemical industry.
 

Chlor-alkali production processes include mercury electrolysis, diaphragm electrolysis and ionic membrane electrolysis. Chlor-alkali anodes have been using graphite anodes in the past. In 1956, the Dutchman Henry Beer (H. Beer) first proposed the use of metal anodes in electrolytic cells, also known as Dimensionally Stable Anodes (DSA), and obtained the patent in 1965. Dimensionally stable anodes are coated with platinum on titanium substrates. Electrodes of noble metal oxides. In 1968, DeNore in Italy first realized the industrialization of titanium anodes in the chlor-alkali industry. Around 1970, the United States, Italy, Japan, Germany, France and other countries quickly switched to metal anodes instead of graphite anodes. In Japan, thousands of tons of titanium materials have been used as the base material for metal anodes, and about 5 titanium materials are needed to produce 10,000 tons of caustic soda.

With the development of my country's chlor-alkali industry, the main equipment (electrolyzer) for caustic soda production has undergone three major changes. The first change was the vertical tank instead of the horizontal tank. In the early 1960s, (vertical adsorption diaphragm electrolyzer) was used to replace the traditional horizontal tank, which greatly increased the production of caustic soda in my country, from 193,000 in 1957. Ton increased to 693,000 tons in 1966, an increase of 3.6 times.

The second change is that the metal anode electrolyzer replaces the graphite anode electrolyzer. In the 1970s, the metal anode (DSA) was used instead of the graphite anode. my country has carried out titanium anodes in Shanghai Tianyuan Chemical Plant and Tianjin Chemical Plant since 1972. In 1973, the 20m metal anode diaphragm electrolytic cell test was started, and the 30m metal anode electrolytic cell was gradually used in 1974. In 1978, the country carried out the task of metal anode technical transformation of 400,000 tons of diaphragm caustic soda. As of 1981, 17 chlor-alkali plants across the country used a total of 1,217 metal anode electrolytic cells, forming an annual production capacity of 670,000 tons of caustic soda with diaphragm metal anodes, accounting for 30% of the national caustic soda production capacity, and 95,000 tons of mercury-based electrolysis capacity. DSA. As of 1996, there were 99 chlor-alkali factories in the country with a total of 8,409 metal anode diaphragm electrolyzers, with an annual production capacity of 4.2 million tons of caustic soda, accounting for 70% of the national caustic soda production capacity. Except for a few large chemical factories such as Tianyuan, Tianhua, Daguhua and other factory-made metal anode electrolyzers, most of them are manufactured and supplied by professional factories such as Beijing Chemical Machinery Factory and Shanghai 4805 Factory.

The third change is the use of ionic membrane electrolyzers. In the mid-1980s, the energy-saving and efficient ionic membrane method was promoted to produce caustic soda. my country introduced ionic membrane caustic soda technology and devices from Japan and other countries, forming a production capacity of 10,000 to 50,000 Tons of serialized devices, the main equipment includes ion membrane electrolyzer, titanium anolyte circulation tank, light brine tank, vacuum dechlorination tower, heat exchanger, tubes and pump valves, etc. Titanium equipment and titanium tubes are mainly used in the anolyte circulation system , light brine system, dechlorination system, wet chlorine gas delivery system and chlorine water circulation system. Titanium pumps are mainly used to transport refined brine, anode circulating fluid, light brine and chlorine water, etc. A set of 10,000-ton equipment uses about 8 tons of titanium. In June 1986, the Yanguoxia Chemical Plant introduced the technology of Asahi Glass from Japan for the first time, with an annual output of 10,000 tons of caustic soda equipment. Except for the three-dimensional electrolyzer and the anolyte titanium pump supplied by Japan, the other six titanium equipment were all provided by domestic manufacturers. Jinxi Chemical Machinery Factory undertakes the supply. By 1990, 11 chlor-alkali plants had adopted ion-exchange membrane caustic soda plants, with a production capacity of 295,000 tons. In 1995, 27 chlor-alkali plants had adopted ion-exchange membrane caustic soda plants, with a production capacity of 827,000 tons. In 2000, the annual caustic soda production capacity of my country's chlor-alkali industry was 7.5 million tons, in 2005 it was 14.71 million tons, and in 2010 it was 23.99 million tons.

In the ionic membrane electrolyzer, the temperature of the cathode and anode chambers is about 90°C, the anode chamber has chlorine gas and salt solution, and the cathode chamber has a 30%~35% concentration of caustic soda solution. The general operating current density of the ion membrane electrolyzer is 30~40A/ dm. Under such harsh conditions, the material usage and anti-corrosion structure of the electrolytic cell must be fully considered when designing the electrolytic cell. For the anode part of the ion-exchange membrane electrolyzer (referring to the anode and the part in contact with the anolyte), all countries in the world have chosen titanium metal (or corrosion-resistant titanium alloy) with good corrosion resistance in the anolyte without exception.

The schematic diagram of the ion exchange membrane of caustic soda, as shown in the figure, the two electrodes are separated by the ion exchange membrane, and the salt water is added from one side, and the pure water is added from the other side. After passing an electric current, chlorine gas is generated from the anode side and hydrogen gas is generated from the cathode side. The ionic membrane only allows the passage of sodium ions, so sodium hydroxide is produced from the cathode side.

In addition to the electrolyzer of the main equipment of the ion-exchange membrane caustic soda plant, the application parts of titanium equipment mainly include: brine system - liquid level gauge; anolyte system - anolyte tank and chlorine gas scrubber; light brine system - dechlorination tower, Light salt water distributor, instrument cooler; sodium hypochlorite system - cooling, absorption tower, distributor; chlorine gas system - wet chlorine gas cooler; pest removal system - heat exchanger, pest removal fan.