Desulfurization of light gas oil in immobilized-cell systems ofGordonasp. CYKS1 andNocardiasp. CYKS2

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Abstract
Desulfurizations of a model oil (hexadecane containing dibenzothiophene (DBT)) and a diesel oil by immobilized DBT-desulfurizing bacterial strains, Gordona sp. CYKS1 and Nocardia sp. CYKS2, were carried out. Celite bead was used as a biosupport for cell immobilization. Seven–eight cycles of repeated-batch desulfurization were conducted for each strain. Each batch reaction was carried out for 24 h. In the case of model oil treatment with strain CYKS1, about 4.0 mM of DBT in hexadecane (0.13 g sulfur loil−1) was desulfurized during the first batch, while 0.25 g sulfur loil−1 during the final eighth batch. The mean desulfurization rate increased from 0.24 for the first batch to 0.48 mg sulfur ldispersion−1 h−1 for the final batch. The sulfur content in the light gas oil was decreased from 3 to 2.1 g loil−1 by strain CYKS1 in the first batch. The mean desulfurization rate was 1.81 mg sulfur ldispersion−1 h−1, which decreased slightly when the batch reaction was repeated. No significant changes in desulfurization rate were observed with strain CYKS2 when the batch reaction was repeated. When the immobilized cells were stored at 4°C in 0.1 M phosphate buffer (pH 7.0) for 10 days, the residual desulfurization activity was about 50∼70% of the initial value.