It is often desirable to remove acid gases, such as, for example, CO.sub.2, H.sub.2 S, SO.sub.2, CS.sub.2, HCN, COS, and sulfur derivatives of C.sub.1 to C.sub.8 hydrocarbons, from gas streams. Gas streams from which these acid gases must be removed can be from many sources. One common source of such gas streams is from natural gas wells. The gas removed from natural gas wells is often rich in methane and other combustible gases, but contains concentrations of acid gases such as H.sub.2 S, CO.sub.2 and the other acid gases described above. High concentrations of H.sub.2 S inhibit pipe line shipment of the natural gas because of environmental considerations and government regulation. High concentrations of CO.sub.2 in natural gas reduce the heating value of the gas because CO.sub.2 is not combustible. Mercpatans, i.e., sulfur derivatives of C.sub.1 to C.sub.8 hydrocarbons, have an offensive odor and are corrosive.
The removal of mercaptans can be particularly difficult. One process proposed for the removal of mercaptans from a gas stream is described in U.S. Pat. No. 3, 716,620, issued Feb. 13, 1973. The process includes the step of contacting a gas containing hydrogen sulfide or a mercaptan with a solution of iodine in an organic solvent, e.g., an ether of a polyalkylene glycol, and an amine. The presence of iodine in processes such as described in the above-referenced patent is generally undesirable because the iodine must be regenerated in an oxidation process which increases the complexity and adds cost to the overall acid gas removal process.
Accordingly, processes and absorption solvents are desired for the removal of mercaptans from gas streams by absorption which do not require the presence of iodine or suffer the disadvantages described above.