Experimental study on removal of mercaptans from gas streams by 1-butyl-3-methyl-imidazolyl alanine

Abstract

Mercaptans as volatile organic sulfur compounds would cause environmental pollution. Researches are focused on the removal of mercaptans by solvent absorption method. In this work, a new efficient absorbent of 1-butyl-3-methylimidazolyl alanine ([Bmim]Ala) was prepared and evaluated by the removal of mercaptans from the model gas containing methyl mercaptan (MeSH, 307.6 mg/m3), ethyl mercaptan (EtSH, 201.1 mg/m3) and propyl mercaptan (PrSH, 149.9 mg/m3) in nitrogen. The results showed that the removal rate of MeSH, EtSH and PrSH was 97.77, 98.12 and 100.00%, respectively, at a temperature of 35 °C and a pressure of 1.00 bar for 2 min. After 6 recycling times, [Bmim]Ala remained a good performance for the removal of mercaptans. The desulfurization mechanism was proposed that the absorption sites were mainly on the alanine anion (Ala−) and Ala− could be replaced by the thiol anion (RS−) to form a new ionic liquid 1-butyl-3-methylimidazolyl thiolate ([Bmim]+RS−). Meanwhile, since the electrostatic interaction between -COO− in Ala− and H-g on the imidazolium cation could be destroyed by the -SH group, the -COO− group would interact with mercaptans to form a strong H-bond. The amino in Ala− and the -SH group could form Lewis acid-base compounds.