Effects of Solvent Composition and Hydrogen Pressure on the Catalytic Conversion of 1,2,4,5-Tetrachlorobenzene to Cyclohexane
clean-up, dechlorination, dehalogenation, ethanol, hydrogenation, palladium, remediation, rhodium, soil, solvent extraction
Digital Object Identifier (DOI)
Toward the development of a “green” technology for cleaning soil contaminated by halogenated hydrophobic organic contaminants, here we demonstrate that combined use of palladium (Pd) and rhodium (Rh) catalysts enables the conversion of 1,2,4,5-tetrachlorobenzene (TeCB) to cyclohexane in mixtures of water and ethanol. We tested the hypotheses that, in batch reactors, (1) an increased ratio of water to ethanol in water/ethanol solvents would increase the reaction rates of both Pd-catalyzed hydrodehalogenation (HDH) and Rh-catalyzed hydrogenation, and (2) catalytic reaction rate coefficients would be constant above a hydrogen (H2) pressure threshold, but would decrease with decreasing H2 pressure below that threshold. These hypotheses were derived from a Langmuir–Hinshelwood model for the heterogeneous catalytic reactions. Complete conversion of TeCB to cyclohexane was achieved at all experimental conditions tested, suggesting that the proposed technology may be technically viable. Concentration data were consistent with an apparent first-order kinetic model in which Pd-catalyzed HDH and Rh-catalyzed hydrogenation occur in series. As expected, HDH and hydrogenation rate coefficients increased as the fraction of water in the solvent increased. However, contrary to expectations, HDH rate coefficients decreased when H2 pressure increased from 69 to 207 to 345 kPa. We attributed this to the displacement of TeCB by H2 on the catalyst surface at higher H2 pressures. No statistically significant effect of H2 pressure on hydrogenation rate coefficients was observed. The findings suggest that the proposed technology should be operated with at least 50% water in the solvent and a H2 pressure as low as 30–70 kPa.
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Citation / Publisher Attribution
Environmental Engineering Science, v. 31, issue 3, p. 156-166
Scholar Commons Citation
Cone, Margaret; Osborn, Claire; Ticknor, Jonathan L.; and Cunningham, Jeffrey A., "Effects of Solvent Composition and Hydrogen Pressure on the Catalytic Conversion of 1,2,4,5-Tetrachlorobenzene to Cyclohexane" (2014). Civil and Environmental Engineering Faculty Publications. 85.