Kinetics of Biodesulfurization of Diesel and Kerosene
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos
The biodesulfurization of diesel and kerosene was investigated. Soil samples were taken at various points of the Ijora petroleum products haulage terminal, in Lagos, Nigeria. Microorganisms capable of selectively abstracting sulfur from diesel and kerosene without reducing their fuel values were isolated by using a sulfur-reducing selective medium. The choice of the sulfur selective reductive pathway is informed by the fact that it is sulfur specific and so the calorific value is maintained because C – C bonds are not altered in the pathway. The reaction pattern is similar to hydrodesulfurization (HDS) with respect to the production of H2S. The H2S that is formed in anaerobic route can be treated with existing refinery desulfurization plants (e.g. Claus process). The organisms were tentatively identified as Desulfobacterium anilini and Desulfobacterium indolicum based on their differential cultural, morphological and biochemical characteristics and by reference to Bergey’s Manual of Determinative Bacteriology. The concentrations of various sulfur compounds were determined by Gas Chromatography with Pulsed Flamed Photometric Detector (GC-PFPD, type 5890A; Hewlett Packard, Mississauga, USA). These microorganisms were found to desulfurize at least 70% of the fuels in 72 hours. Furthermore, Desulfobacterium anilini desulfurized the sulfur containing organic compounds in the fuels better than Desulfobacterium indolicum at the end of 72 hours for all the cases considered. The rate expression for enzyme-catalyzed reactions was obtained by the method outlined by Boudart (1968) for the kinetics of heterogeneous catalysis. The rate expression obtained from the rate determining step has clearly shown that when the first step determines the rate (the formation of the enzyme-substrate complex from the reaction of the enzyme and substrate), the reaction is first order. On the other hand, the reaction follows the Michaelis-Menten kind of equation when the second step (conversion of the enzyme-substrate complex to the product) limits the rate of reaction.