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Production process of sodium sulfite

Addtime:2022/8/11 hits:

 Production process of sodium sulfite

 
1、Traditional production process of sodium sulfite with sulfur as raw material
 
The traditional production process of sodium sulfite is to produce SO₂ from monomeric sulfur, and then react with soda ash (Na2CO3) and caustic soda (NaOH) to produce sodium sulfite and sodium bisulfite, and then neutralize, concentrate and dry to produce finished products. The chemical reactions involved in the production process are as follows.
S+O₂=SO₂
3SO₂+2Na₂CO3+H₂O=Na₂SO3+2NaHSO3+2CO₂
NaHSO3+NaOH=Na₂SO3+H₂O
 
The traditional production process of sodium sulfite has better product quality, mature technology and unrestricted raw materials, but the required raw materials sulfur and soda ash have higher prices and higher production costs, and a large amount of waste gas (CO2) is generated.
China's natural alkali resources are abundant, and the natural alkali containing salt, nitrate and water insoluble matter and other impurities (solar alkali) as raw materials, sulfur powder burning SO₂, using sodium carbonate-sodium bicarbonate absorption SO₂ method to directly produce industrial anhydrous sodium sulfite, the product conforms to national standards, and has the characteristics of low raw material costs, advanced technology, significant economic benefits, for the comprehensive utilization of natural alkali and deep processing opened up a It opens up a new way for the comprehensive utilization and deep processing of natural alkali.
Li Chunping et al. studied the reaction of natural mannite, lime and SO₂ to produce sodium sulfite. This method compared with soda ash to produce sodium sulfite, due to the different raw material route, the unit cost was greatly reduced and the economic efficiency was significantly improved, which opened up a new field for the raw material source of sodium sulfite.
Lu Haifen uses three raw materials, namely, underground brine, waste sulfur and ammonium bicarbonate, to produce sodium sulfite. The waste sulfur mainly comes from recycled waste from enterprises such as fertilizer plants, power plants and coking plants that use coal as raw material. The brine and ammonium bicarbonate undergo a complex decomposition reaction to produce sodium bicarbonate, and then use the sodium bicarbonate lye to absorb the SO₂ generated by the combustion of waste sulfur to obtain sodium sulfite, while producing ammonium chloride by-products. Although the raw material cost of the process has been reduced, the process route is more complicated, more equipment, occupies more space, and the product quality is not stable enough.
 
2、Production of sodium sulfite with SO₂ industrial tail gas as raw material
 
Large-scale thermal power plants, non-ferrous metal smelters and industrial boilers produce a large amount of industrial tail gas containing SO₂. The content of SO₂ in these industrial tail gas can be as low as several hundred ppm and as high as 10% (volume fraction), and industrial tail gas with SO₂ content greater than 1.5% can produce industrial sulfuric acid. However, according to the current technology and equipment level, on the one hand, sulfuric acid production has certain requirements on SO₂ content and emission scale in flue gas, and on the other hand, the product sulfuric acid is restricted by storage, transportation and market, etc. How to further develop new products by using industrial tail gas flue gas containing SO₂ is of great significance to control the environment and reduce sulfur resources loss. Using SO₂ flue gas from smelting production, a set of sodium sulfite production line with an annual capacity of 20,000t has been established by liquid alkali production process, with advanced technology and stable product quality. The production of sodium sulfite by SO₂ industrial tail gas can not only solve the pollution of environment by industrial tail gas containing SO₂, but also reduce the production cost of sodium sulfite.
 
3、Other methods of sodium sulfite production
 
Sodium sulfite is produced by absorbing SO₂ escaping from the production of sodium saccharin with sodium hydroxide solution, and the absorbed solution is subject to iron removal, sedimentation, decolorization, filtration, concentration, centrifugal separation, drying and other processes to obtain anhydrous sodium sulfite with a content of 96% or more.
To produce sodium sulfite from sodium metabisulfite, sodium metabisulfite is hydrolyzed with water to produce NaHSO3, then neutralized with sodium hydroxide solid, dried and dewatered to produce the product. This method not only shortens the process flow, reduces the amount of equipment used, but also greatly reduces the generation of "three wastes" in the production process. The quality indexes of sodium sulfite products produced by this method can meet and exceed the requirements of national standards for superior products.

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