Alkaline sweetening of gas is used to remove sulfur compounds. As an alkaline sweetening of gas usually described process of mercaptan removal from gases. Alkaline sweetening of gas is carried by extraction of mercaptans from gas with alkaline solutions according to reaction (1):
CH3SH + NaOH = CH3SNa + H2O (1)
The only mercaptan in gas is methyl mercaptan. Mercaptide saturated alkaline solution after extraction is supplied to regeneration. Regeneration proceeds in the presence of phthalocyanine catalyst, oxygen, air and mercaptide saturated alkaline solution at temperature of 50÷70°C and pressure of 0.5 MPa according to reaction (2):
2CH3SNa + 0,5O2 + H2O → CH3SSCH3 + 2NaOH (2)
Dimethyl disulfide formed during regeneration of alkali is separated from the alkaline solution by settling.
Sometimes, as an alkaline gas sweetening described hydrogen sulfide and mercaptan removal from gas. In this case, solution saturated with inorganic sulfides (NaHS, Na2S) and mercaptides needs to be sweetened by oxidation of inorganic sulfides to thiosulfate and sulfate, and of mercaptans to water-soluble thiosulfonates.