Revamping of Merox LPG sweetening unit for deeper desulfurization

Liquefied petroleum gas (LPG) is often contaminated with acidic compounds such as H2S, CO2, COS, CS2, methyl and ethyl mercaptans. Mercaptans in lighter feeds such as gases, C3s, C4s, LPG and naphtha, are extracted with a caustic solution by Merox or Sulfrex type of processes. In this paper, focus has been first on the chemistry of mercaptan extraction and caustic regeneration processes based on the experimental data represented in the literature. Thereafter optimization of an existing plant, Iran’s SPGC 4 & 5, is performed while no similar studies based on plant data were reported earlier. Simulation is based on the empirical relations represented in this paper and the main operating variables which are discussed include extraction and regeneration temperatures, amount and concentration of circulating caustic as well as air injection rate to the oxidizer. Optimization of the existing unit will result in an overall net increase of 2.9-3.9 million $/year in sales.

Keywords:

sweetening , desulfurization , Merox process , Sulfrex process , LPG treatment , mercaptan removal