What are the extraction methods of bromine

The production methods of bromine include: steam distillation method, air purge method, continuous double-process vacuum bromine extraction method, resin method, liquid membrane method, semi-permeable membrane method, solvent extraction method, etc. Among them, the steam distillation method and the air purge method are common methods. Bromine is mainly extracted by steam distillation. At present, China's bromine production are using water vapor distillation and air blowing. Steam distillation accounts for about 10% of China's bromine production capacity. The blast method accounts for about 90 per cent of the country's bromine production capacity.
1. Steam distillation
In the 1950 s and 1960 s, steam distillation with brine as raw material was the main bromine production method for bromine manufacturers. The principle is that br ions in brine are oxidized to Br2 with Cl2 as an oxidant, and then Br2 is evaporated with Br2, which has a different volatility from water. Evaporated liquid automatic stratification. The upper layer is an aqueous layer containing a small amount of bromine, and the lower layer is a crude bromine layer containing a small amount of water and chlorine. The refined bromine is obtained from the crude bromine. Steam distillation has the characteristics of mature process, simple process, high efficiency and low cost. Through the continuous improvement of steam distillation process and equipment, the purity of refined bromine reached 99.5%, and the recovery rate of bromine increased to more than 95%. However, this process requires a high bromine content in the feedstock, typically greater than 3G/L in the brine. In the Chinese salinization plant using steam distillation to produce bromine, the raw material is the mother liquor after the separation of carnallite in the production of potassium chloride (bromine content is usually 2.5~3G/L). A large amount of steam is consumed in the bromine production process, and the production cost is high, which limits its scope of use.
2. Overview of bromine extraction
At present, China's bromine production are using water vapor distillation and air blowing. Due to process technology and other problems, the utilization rate of bromine resources in China is only about 65%. This has led to a large waste of bromine resources in China, shortened the service life of bromine resources, and the bromine content in underground brine is also rapidly declining. China's bromine resources are facing a crisis.
3. Blowing method
Bromine production from underground brine by air blast method. It was successful in the early 1970 s. The principle is that Cl2 is added to the acidified raw material to oxidize br-to Br2, and then the feed liquid is sent to the purge tower and poured from the top of the tower. The bottom of the column was filled with compressed air to blow out Br2 in the feed liquid. After being introduced into the absorption tower, it is absorbed with an absorbent. After absorption, the bromine-containing compound is decomposed into free bromine with an acid. The feed solution containing free bromine is then distilled with steam. Refined bromine is obtained by condensing and separating the products at the top of the column. The process flow is shown in Figure 2.
At present, the raw materials of the blowing method are generally concentrated seawater and underground brine in the salt drying process. A variety of absorbents are used in the bromination process, mainly including soda or caustic soda solution, sulfur dioxide, iron filings and low temperature bromine salt solution. In China, the acid absorption process accounts for about 85% of the total production capacity of the blast method, and the alkali absorption process accounts for about 15%. Jiangsu, Sichuan, Zhejiang and Tianjin mostly use alkali absorption process, Shandong mostly use acid absorption process. The blast method has strong adaptability to the bromine content of raw materials and is easy to automatically control, but its disadvantages are large equipment and high energy consumption.