(A) study on the development of diesel oil biodesulfurization process

Abstract

Desulfurization characteristics as well as hydrocarbon bioavailability of Gordonia nitida CYKS1 were investigated. CYKS1 could utilize long chain aliphatic hydrocarbons such as dodecane, hexadecane, and 2-, 6-, 10- and 14-tetramethylpentadecane for its growth. The activities of two desulfurization enzymes (DszA and DszC) and the enzyme for $FMNH_2$ regeneration (DszD) in cell extract were examined. The activities of DszA, DszC, and DszD from the cells incubated with DBT as the sole sulfur source were 8.0, 9.5 and 46.3 mU/mg, respectively. On the other hand, when the cells were cultured with $MgSO_4$, no activities of DszA and DszC were observed with a DszD activity of 27.18 mU/mg, suggesting that these desulfurization enzymes were induced by DBT. The activity of another desulfurization enzyme, DszB could not be measured for technical reasons. When LGO (light gas oil) was desulfurized by resting cells at various oil-to-water ratios (or oil fractions), its sulfur content only slightly decreased from 0.1 wt% to 0.09 wt% and no sulfate resulting from the desulfurization was detected in the aqueous phase, implying that CYKS1 uptake sulfur as much as for its cell growth only. For this reason, growing cells were used for the subsequent experiments. An immobilized-cell air-lift reactor system was set up and its performance was investigated. A draft tube was placed inside the reactor and a patched type impeller was used for improving circulation of oil/water mixture. String-shaped nylon fiber bundles were used as the support for cell immobilization. The reactor performance was examined by repeated batch desulfurization of hydrotreated diesel oil. Sulfur content of diesel oil decreased from 500 ppm to 50 ppm at 10% of oil fraction and even at 50% of oil fraction. By GC-SCD chromatogram, it was identified that the remaining sulfur compounds were recalcitrant to CYKS1. Sucrose addition could improve the desulfurization efficiency at a high oil fraction. It was observed ...