H2S extraction proceeds readily as long as free NaOH is available. RSH extraction proceeds readily for
the lightest mercaptans (C1-SH and C2-SH) but slows considerably with increasing molecular weight. For
Reaction 2 to be effective, the concentration of free NaOH in the caustic solution must be considerably
higher than what is required for Reaction 1. To maintain a high NaOH concentration, the caustic solution
flows through the extraction system in a single pass and is sent back to a regeneration system. Without
benefit of regeneration, a much larger amount of caustic would be required to successfully accomplish
mercaptan extraction and meet product specifications.