TABLE OF CONTENTS Biodesulfurization (BDS) is the excision (liberation or removal) of sulfur from organosulfur compounds, including sulfur-bearing heterocycles, as a result of the selective cleavage of carbon-sulfur bonds in those compounds by the action of a biocatalyst. Biocatalysts capable of selective sulfur removal, without significant conversion of other components in the fuel are desirable. BDS can either be an oxidative or a reductive process, resulting in conversion of sulfur to sulfate in an oxidative process and conversion to hydrogen sulfide in a reductive process. However, the reductive processes have been rare and mostly remained elusive to development due to lack of reproducibility of the results. Moderate reaction conditions are employed, in both processes, such as ambient temperature (about 30 C) and pressure.
The development of biological catalysts for sulfur removal found its origin in coal desulfurization. Although, the organosulfur species in coal and crude oil are similar, the inorganic sulfur content is quite different. The major inorganic sulfur species in coal is iron pyrite, while the organic sulfur in coal as well as oil is made up of a diverse mixture of organosulfur compounds, which include thiols, sulfides, disulfides, and thiophene derivatives. Some of the early work on coal served as basis for development of biocatalysts for crude oil application and is included here.
Most of the biocatalytic routes for biorefining processes have been studied at a laboratory scale and at most the pilot scale. The largest of the oil biorefining effort has been concentrated on BDS, which has...
