Bi-phasic bio-conversion of sulfur present in model organo-sulfur compounds and hydro-treated diesel

Bacterial strain of Rhodococcus sp. (JUBT1) isolated from petrol/diesel station has been used for the desulfurization of different model organo-sulfur compounds like DBT, substituted DBT, etc. which are difficult to remove in the conventional hydro-desulfurization of diesel fraction. The initial concentration of organo-sulfur compounds has been varied in the range of 100–1000 mg/dm³. Under the present experimental range, the bacterial growth has been observed to follow Haldane-type kinetics characterizing the presence of substrate inhibition. The extent of inhibition by the substrate has been observed to increase with the number of substituents in the same range of initial concentration of different organo-sulfur compounds. The values of intrinsic kinetic parameters, like maximum desulfurization rate, v_max, half saturation constant, K_S, inhibition constant, K_Si and the maximum substrate concentration, C_Smax, corresponding to the maximum uninhibited rate of desulfurization, have been determined using each organo-sulfur compound having different number of substituents as limiting substrate. Relative changes in the values of the kinetic parameters have been correlated to the number of substitutions. Separate studies have also been conducted to determine the kinetics of bio-desulfurization of a hydro-treated diesel fraction. The concentration of sulfur in diesel was selected in the range of 100–500 mg/dm³.

The effect of aqueous to non-aqueous ratio on the rate of specific desulfurization of hydro-treated diesel fraction in the range from 1:9 to 9:1 has also been studied in the present investigation. Mathematical models have been developed to predict the conversion of sulfur during batch-type bio-desulfurization of model compounds as well as diesel having known distribution of organo-sulfur compounds. The predictions of the model satisfactorily compare with the experimental results.