Houston Industries Inc. United States

At the beginning of the 1990s, Houston Industries developed an enzymatic process ( Enzymatic Coal Desulfurization ) protected in Canada and US [83,84], Although, the application was focused to coal desulfurization it may also be applicable to crude oil and fossil fuel-derived liquids. The processes claim the removal of both, organic as well as inorganic sulfur species. The process was described as using ground coal (10-50 p,m) slurried with water, while the oil was treated in an aqueous emulsion. 

The final step is a hydrolyzing step with sulfatase enzymes (E.C. number 3.1.6.1), such as limpet sulfatase, Aerobacter aerogenes sulfatase, Abalone entrail sulfatase, or Helixpomatia sulfatase. This step was suggested to be carried out in a CSTR or fluidized bed reactors, with counter-current flow between the aqueous and the oil phase. A more efficient removal of the sulfate into the aqueous stream is expected to occur in this cross-flow manner. A final separation of the reacting mixture was suggested to obtain sulfur-free product and aqueous enzyme solution for recycle. 

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