union With salt, ammonia and carbon dioxide, a by-product of synthetic ammonia industry, as raw materials, soda ash and ammonium chloride are produced simultaneously. The reaction equation can be summarized as the following two steps.
(1) Introduce carbon dioxide into the saturated solution of sodium chloride in ammonia water to separate sodium bicarbonate with low solubility from the solution:
(2) Sodium bicarbonate crystals are obtained through filtration. NaHCO 3 has poor thermal stability and is easy to decompose when heated:
According to NH four The principle that the solubility of Cl at room temperature is greater than that of NaCl, but at low temperature is smaller than that of NaCl. When NaCl is added to the mother liquor at (5 ℃~10 ℃), NH four Cl is separated out to obtain chemical fertilizer, which improves the utilization rate of NaCl.
The combined alkali production method has the following advantages:
The advantages of ammonia alkali method are retained and its disadvantages are eliminated, so that the utilization rate of table salt is increased to more than 96%; In addition, it makes comprehensive use of carbon dioxide from ammonia plant and chloride ion from alkali plant, and produces two valuable products - soda ash and ammonium chloride. The waste gas carbon dioxide from the ammonia plant is converted into the main raw material of the alkali plant to produce soda ash, thus saving the huge lime kiln used to produce carbon dioxide in the alkali plant; The useless component of the alkali plant, chloride ion (Cl -), is used to replace the expensive sulfuric acid to fix ammonia in the ammonia plant to produce ammonium chloride as a nitrogen fertilizer. Thus, calcium chloride, which is useless and difficult to treat, is no longer generated, which reduces environmental pollution, and greatly reduces the cost of soda ash and nitrogen fertilizer, fully reflecting the advantages of large-scale joint production. [2]
