Development of biocatalysts for petroleum desulfurization

Abstract

Several strains capable of desulfurizing dibenzothiophene(DBT), which is representative of organic sulfur compounds in petroleum were isolated in this study. Among them, three strains named as Gordona sp. CYKS1, Nocardia sp. CYKS2 and Nocardia sp. CYKNII9 were found to be capable of desulfurizing DBT via sulfur-specific pathway, which is considered to be advantageous due to no loss of fuel value. The dead-end metabolites of DBT were found to be 2-hydroxybiphenyl(2-HBP) and sulfate. The strains Gordona sp. CYKS1 and Nocardia sp. CYKS2 showed an ability of desulfurizing about 15 other organic sulfur compounds than DBT encompassing thiols, sulfides, disulfides and thiophene derivatives. About 0.2 mM of DBT was entirely desulfurized in 60 hours and the cell concentration reached about 2.8 g/L in a batch fermentation A model oil(DBT/hexadecane) system which 10 mM of DBT was dissolved in hexadecane, the major component of diesel oil, was used to simulate the desulfurization of actual oils. The model oil was treated with cell suspended in MSM. The strains Gordona sp. CYKS1 and Nocardia sp. CYKS2 were found to adhere to the oil phase to utilize sulfur compounds in it than secrete solubilizers. About 10 mM of DBT in hexadecane was desulfurized in 60 hours by Gordona sp. CYKS1. The volumetric desulfurization rate was 0.255 mg-sulfur/L-dispersion/h. The desulfurization rate increased as the initial DBT concentration in hexadecane increased. However, there was little change in the desulfurization rate as the ratio of oil to aqueous phase changed. In the case of real unhydrotreated diesel oils treatment, two types of diesel oils with different sulfur contents were used. When the phase ratio was 1/20, light gas oil(LGO) which had a relatively low sulfur content(0.3 wt%) was desulfurized to 0.187 wt% in 48 hours by Gordona sp. CYKS1. However, no further decrease of sulfur content was observed after 48 hours. Middle distillate unit feed(MDUF) which had a high sulfur content (1...