Chemical evolution of liquid redox processes

A multitude of processes have been proposed for removal of hydrogen sulfide from gaseous streams. Removal of H 2 S from sour natural gas streams is particularly difficult since low outlet concentrations must be reached before the gas is put into a pipeline. Liquid redox sulfur recovery (LRSR) processes use a solution containing an oxidizing agent that absorbs H 2 S from the gas stream and oxidizes it to sulfur. The chemistry of these processes has undergone considerable evolution in the last 30 years. A number of tradeoffs must be considered in designing LRSR processes. For example, the rate of reaction of the oxidized agent with H 2 S often determines the scrubbing efficiency, but excessive rates of sulfur formation in the scrubber can lead to plugging. Systems based on vanadium and/or anthraquinone disulfonates (ADA) as the redox catalyst had several drawbacks, most of which can be traced to sluggish redox agent kinetics. Current LRSR processes use chelated iron as the catalyst for sulfur recovery. This gives faster scrubbing and re-oxidation kinetics, but chemical degradation of the chelating agent can affect the economics of the process. Plugging of sorption vessels continues to be a problem in some applications. New nonaqueous solvent-based or biological processes may overcome these problems.