Study On Catalystic Desulfurization Of Dibenzothiophene By Gordonia Sp.

With the strengthening of environmental protection, the sulfur content standard of fuel oil in the world become more stringent. However, the reaction conditions of HDS are strict and expensive. Meanwhile, the desulfurization efficiency of HDS to C_X-DBT is very low, which cannot meet the requirements of deep desulfurization. Biodesulfurization can efficiently remove sulfur-containing organic compounds at mild temperature and pressure, which is an environment-friendly desulfurization technology. In this paper, the research was carried out from the isolation and identification of Gordonia sp. JDZX13 and analysis of its desulfurization pathway. Through single factor experiments and orthogonal test, the optimal growth conditions of Gordonia sp. JDZX13 in a single aqueous phase system was obtained. The effect mechanism of the key limiting factors for Gordonia sp. JDZX13 on growth and desulfurization was initially established. The best bioprocess mode and reaction conditions were studied. The desulfurization ability for different simulated oil by Gordonia sp. JDZX13 was examined. The main study contents were listed as follows:（1） The isolation and identification of Gordonia sp. JDZX13 and analysis of its desulfurization pathway. Eleven isolates were screened from the Karamay oilfield in China which could metabolize dibenzothiophene, and the desulfurization capacity of strain JDZX13 was the strongest by among all isolates. Strain JDZX13 was identified as Gordonia sp. and named Gordonia sp. JDZX13 with morphological, physiological, biochemical and 16 S rDNA analysis. Gas chromatography-mass spectrometry（GC-MS） analysis of desulfurization products indicated that DBT was converted into 2-hydroxybipheny1（2-HBP） via the “4S” pathway. Meanwhile, the “4S” pathway of strain JDZX13 was further demonstrated by identification of DBT desulfurization related genes（dszA, dszB and dsz C）.（2） Optimization of growth conditions of Gordonia sp. JDZX13 in a single aqueous phase system by the single factor test and orthogonal design method. The optimum operating conditions were found as 15 g×L^-1 of sucrose, 2 g×L^-1 of NH4 Cl, 0.1 g×L^-1 of MgCl2, 1 mL of metal solution, pH 7.0 and temperature 35 °C. Under the optimum fermentation conditions, the cell density reached 4.44 g×L^-1 in 81 h, which was 3.7-fold of the value of previous optimization and DBT removal rate reached 98% in 48 h, resulting in shorter cultivation cycle（12 h）.（3） The effect of the key limiting factors for Gordonia sp. JDZX13 on growth and desulfurization. DBT in an appropriate concentration could promote cell growth, strengthen desulfurization enzyme activities and improve the desulfurization gene transcription. When the concentration of DBT was higher than 3 mmol×L^-1, cell growth and enzyme activity were both slightly inhibited; 2-HBP had a strong toxicity in cell growth and enzyme activity. When the concentration of 2-HBP was higher than 0.3 mmol L^-1, cell growth and enzyme activity were completely inhibited. The transcript levels of the desulfurization genes（dszA, dszB, dszC） were increased in low 2-HBP concentration(≤0.025 mmol×L^-1), which reached to 2.60, 2.73 and 2.66 times of original levels. However, the transcript levels of the desulfurization genes were inhibited when the concentration of 2-HBP was higher than 0.05 mmol×L^-1. SO42- could promote cell growth, but inhibit the desulfurization activity. In addition, it could also increase the transcript levels of the desulfurization genes in low SO42- concentration(≤0.05 mmol×L^-1), which reached to 3.61, 2.00 and 2.62 times of original levels, but limited the transcript levels of the desulfurization genes in higher SO42- concentration(≥0.1 mmol×L^-1), which only reached to 0.33, 0.144 and 0.53 times of original levels.（4） The research of desulfurization process in oil/water two phase system. Model II was proved to be the highest desulfurization efficiency by comparing with other four desulfurization modes in oil/water two phase system. Optimization of desulfurization conditions in oil/water two phase system was obtained by the single factor test and Box-Behnken test, and the optimum operating conditions were listed as follows: oil/water ratio 1:5, rotation 200 r×min^-1, β-CD 4.44 g×L^-1, nicotinamide 1.57 mmol×L^-1, riboflavin 20.7 μmmol×L^-1. The desulfurization capacities for oil of the country II, III, IV and V standard were invested respectively, the results showed that Gordonia sp. JDZX13 was very suitable desulfurization for oil of the country IV and V standard, which ultimately achieved a sulfur-free level.