Hector Hernandez - Supercritical Water Desulfurization of Organic Sulfides Is Consistent with Free-Radical Kinetics

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      Publication Details (including relevant citation   information):

      Patwardhan, Pushkaraj R., Timko, Michael T., Class, Caleb A.,   Bonomi, Robin E., Kida, Yuko, Hernandez, Hector H., Tester,   Jefferson W., Green, William H. Energy & Fuels  2013 27 (10) 6108-6117

      Abstract: Supercritical water desulfurization   (SCWDS) has potential as a technique for removing sulfur from   feedstocks such as heavy oil and bitumen. However, a fundamental   understanding of SCWDS (such as the underlying chemical   mechanisms, relative rates of desulfurization, and the role of   SCW and hydrocarbons) is limited. In the present work, we have   gained molecular-level insights into this process by measuring   the kinetics of decomposition of a variety of organic sulfides in   the presence of hydrocarbons and supercritical water in a   continuously fed stirred-tank reactor (CSTR). The results are   consistent with a free-radical mechanism, with hydrogen   abstraction from the sulfide as the rate-determining step. The   decomposition rates of the aliphatic and aromatic sulfides varied   depending on their molecular structure, with conversions after 31   min at 400 °C ranging from less than 3% (our detection limits) to   more than 90%. These differences in the reactivity correlate with   the estimated heats of reaction for the critical hydrogen   abstraction. The decomposition rates of the sulfides were   affected by the presence of hydrocarbon carriers, with the rates   being higher in the presence of alkanes than in the presence of   toluene, as expected for a free-radical process. Product   distributions and rates of radical-induced alkane cracking during   this process were likewise affected by the presence of different   sulfides. The decomposition of several different sulfides is   consistent with 3/2 power kinetics, providing further evidence   that the reaction proceeds via a radical mechanism. The knowledge   developed in the current work provides a fundamental basis for   further improvements in SCWDS.

      Address (URL): http://dx.doi.org/10.1021/ef401150w