Microbial Desulphurization of Refractory Organic Sulphur Compounds from Transportation Fuels

Abstract

The sulphur content in crude oil ranges from 1000 to 3000 ppm but the environmental regulations require less than 10 ppm sulphur to meet the stringent protocols on reduced SO2 emission by transportation fuels. Hydrodesulphurization (HDS), which is the most employed technology to reduce sulphur (S) suffers from severe and hazardous operation conditions, inefficiency, high capital and operating costs, generation of the hazardous H2S end product etc. During the last decades, several advances have been made in developing chemical, physical and biological technologies complementary to HDS to achieve ultra-low sulphur fuel. Biodesulphurization (BDS) is one of these emerging nonconventional technologies that can be merged with other desulphurization technologies, such as the oxidative desulphurization process, to produce S-free fuels. The BDS process involves the use of free or immobilized microorganisms, their enzymes or cellular extracts, as catalysts to remove the S present in fuels. The most extensively studied and utilized microorganisms for BDS processes are Gram-positive bacteria. Gram-negative bacteria with high tolerance to organic solvents and metals, broad metabolic versatility and easy genetic manipulation also make them ideal candidates for the purpose. This chapter reviews research findings of utilization of mesophilic, thermophilic and Gram-negative bacteria for desulphurization of gasoline, jet and diesel fuel to be used as transportation fuel.