Hydrodechlorination of polychlorinated biphenyl

Rene B. LaPierre, Laszlo Guczi, Wilmer L. Kranich, Alvin H. Weiss

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Abstract

The catalytic hydrodechlorination of a complex polychlorinated biphenyl (PCB) mixture was studied in a batch reactor using a 61% Ni on kieselguhr catalyst from 25 to 100 °C at 50 atm of H2. Ethanol was used as a solvent and NaOH as an acid acceptor. Aromatic hydrodechlorination of chlorinated biphenyls is a consecutive single-step process; ortho-substituted chlorine is the least labile due to steric effects. In the reaction sequence below, φφi indicates a biphenyl molecule substituted with i chlorine atoms distributed over the two rings. First-order pseudo-homogeneous relative rate constants for the liquid phase study are noted: {A figure is presented} Similar behavior was observed in a gas-phase pulse microreactor over a series of 0.00, 0.05, 0.10, and 0.35 wt% Pd on α-Al2O3 catalysts at 220 ± 5 °C, 2.3 atm of H2, and space time of ~10-2 sec (based on H2 carrier gas flow rate). The corresponding values of the relative rate constants were 1.0, 0.85, 0.50, 0.70, and 0.95. These values of relative rate constants pass through a minimum as a result of the combined influence of statistical and steric factors. Highly ortho-substituted materials cannot adsorb in a planar configuration. The relative first-order rate constant for ortho to (meta + para) hydrodechlorination ko kmp = 0.52 for the nickel catalyst. Reaction behavior is consistent with the mechanism requiring adsorption of the benzene ring and charge delocalization at the aromatic chlorine: {A figure is presented} For hydrodechlorination, the {A figure is presented} carbon-chlorine double bond is regarded as the reactive species.

Original languageEnglish
Pages (from-to)230-238
Number of pages9
JournalJournal of Catalysis
Volume52
Issue number2
DOIs
Publication statusPublished - Apr 1978

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ASJC Scopus subject areas

  • Catalysis
  • Physical and Theoretical Chemistry

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