Desulfuration of organic compounds

The most catalytically active metals are Ni, Pd, Pt, and Rh. Nickel is used extensively in hydrogenation. It is frequently used in skeletal form as Raney nickel (Ra-Ni or RNi). The hydrogenation of almost all hydrogenatable functional groups can be accomplished over some form of Ra-Ni. Ra-Ni is also useful for desulfurization of organic compounds, but this is a stoichiometric reaction, not a catalytic reaction. 

Desulfurization of organic compounds over Ra-Ni is a well-known procedure.364-369 Ra-Ni exists in different forms (W1 to W8), differing in the preparation procedure and sometimes symbolized as Ni(H). Ra-Ni is sometimes called a catalyst however, it is used usually in large excess and the reaction is stoichiometric. Ra-Ni can desulfurize every C—S bond containing compound but it can also hydrogenate a lot of other functional groups. Unwanted side reactions are sometimes suppressed by using deactivated Ra-Ni. 

The overall rate of desulfurization for enabling commercialization has to be greater than 1.2mmol/g dcw/h [1,12,13], The rates of desulfurization of model compounds such as DBT is usually higher than that achievable for real feedstocks such as diesel and other middle distillates. Thus, it is estimated that a more than 100-fold improvement in rates for removal of total sulfur (not just DBT) over wild-type organisms is necessary to achieve rates suitable for commercialization. 

The desulfurization of organic sulfur compounds with Raney Ni using far greater amounts than a catalytic is not a catalytic hydrogenolysis in the strict sense but involves a stoichiometric chemical reaction, since the catalyst itself is converted into nickel sulfide. However, since it has found many useful applications with Raney Ni (a hydrogenation catalyst), this reaction has been treated in this section. 

It has been reported that metal-zeolite catalysts have high possibility as new hydrodesulfurization catalysts for petroleum [1-9]. The catalytic desulfurization of organic sulfur compounds over zeolites has been investigated systematically [10-12]. On the basis of fundamental catalytic studies, active zeolite-based hydrodesulfurization catalysts such as transition metal ion-exchanged Y zeolites(MeY)[13-16], MoS2/NiHY[17] and Rh/USY[18,19] were developed. 

Ohshiro, T. Izumi, Y. Microbial desulfurization of organic sulfur compounds in petroleum. Biosci. Biotechnol. Biochem. 1999, 62 (1), 1-9. 

Xue, M., Chitrakar, R., Sakane, K., Hirotsu, T., Ooi, K., Yoshimura, Y, Toba, M. and Feng, Q. (2006) Preparation of cerium-loaded Y-zeolites for removal of organic compounds from hydro-desulfurized gasoline and diesel oil. J. Colloid Interface Sci., 298, 535-542. 

The second Mycobacterium strain capable of DBT desulfurization was M. phlei WU-F1 [30], This strain was also reported to desulfurize naphtho[2,l-b]thiophene (NTH) and 2-ethyl-NTH to sulfur free products with the following intermediates for the latter molecule 2-ethyl-NTH sulfoxide, l-(2 -hydroxynaphthyl)-l-butene, and l-naphthyl-2-hydroxy-1-butene [94], Thus, this organism was reported to consist of a sulfur-specific pathway capable of desulfurization of broad range of sulfur compounds including symmetric and asymmetric molecules. 

Kohler, M. Genz, I.-L. Schicht, B., and Eckart, V., Microbial Desulfurization of Petroleum and Heavy Petroleum Fractions. 4. Anaerobic Degradation of Organic Sulfur Compounds. Zentralbl. Mikrobiol., 1984. 139 pp. 239-247. 

Van Afferden, M. Tappe, D. Beyer, M., et al., Biochemical-Mechanisms for the Desulfurization of Coal-Relevant Organic Sulfur-Compounds. Fuel, 1993. 72(12) pp. 1635-1643. 

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