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The desulfurization kinetics of Nocardia globerula R-9 was investigated initially in a model system consisting of dibenzothiophene (DBT) dissolved in dodecane. The ability to desulfurize straight-run diesel oil by resting cells of this strain was also evaluated. The course of desulfurization of DBT in dodecane could be represented by the Michaelis-Menten equation. The desulfurization of DBT and 4,6-dimethyl dibenzothiophene (4,6-DMDBT) in a mixture of the two proceeded simultaneously without preference for either of them. The sulfur content of the straight-run diesel oil could be reduced from 1807 to 741 mg dm(-3) by treatment with resting cells of this strain, at a mean rate of 5.1 mmol sulfur kg(-1) h(-1). This showed that Nocardia globerula R-9 could be a potential bacterium for reducing the sulfur content of petroleum products. (C) 2003 Society of Chemical Industry.

The desulfurization of dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT) and their mixture by lyophilized cells ofPseudomonas delafieldii R-8 was studied in the presence of dodecane. The desulfurization rate for 4,6-DMDBT was found to be about 40% in comparison with that for DBT. The desulfurization process for DBT and 4,6-DMDBT proceeded simultaneously without preference for either one. The desulfurization rate for each compound was decreased when they were mixed together. The extent of desulfurization of 4,6-DMDBT was increased with the increase of cell concentration and the decrease of the volume ratio of oil-to-water used. The specific desulfurization rate for 4,6-DMDBT could be reached to 10.4 mmol sulfur kg−1 (cell) h−1 [approximately 0.33 mg sulfur g−1 (cell) h−1].Pseudomonas delafieldii R-8 showed high desulfurization capability for straight-run diesel oil (containing 1,807 mg/L of sulfur). About 1,000 mg/L of sulfur in diesel oil was removed by resting cells of this strain in 24 h of reaction. The specific desulfurization rate was 8.75 mmol sulfur kg−1 (cell) h−1.

The kinetics of base catalyzed racemization of ibuprofen enantiomers has been studied in DMSO-water mixed medium. The dynamic equilibrium rate of keto-enol tautomerism leading to racemization of ibuprofen enantiomers, is proportional to the concentrations of base catalyst and substrate. A kinetic model capable of predicting the time course of racemization, under different base and substrate concentrations, is established and experimentally verified.

It has been found in the present study that Re(VII) can be quantitatively separated from Mo(VI) in alkaline solutions by synergistic extraction with primary amine and neutral phosphorus esters. The mechanism of synergistic extraction was studied. Results of extraction with combinations of different donor and acceptor solvents indicated that during extraction hydrogen bonds were formed between perrhenic acid and active hydrogen atoms of primary amines as well as between the acid and active phosphoryl oxygen of neutral phosphorus esters. The composition of the synergistic extraction adduct was studied and its structure was also proposed. This newly found extraction system is important to the extraction and separation of Re(VII) and also to the studies of mechanism of synergistic extraction.