Homogeneous Catalysis in the Oxidation of P-Chlorophenol in Supercritical Water
Yang, Helen Hsien
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https://hdl.handle.net/2142/69795
Description
Title
Homogeneous Catalysis in the Oxidation of P-Chlorophenol in Supercritical Water
Author(s)
Yang, Helen Hsien
Issue Date
1988
Doctoral Committee Chair(s)
Eckert, Charles A.
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Abstract
This work is an investigation of the kinetics of the uncatalyzed and homogeneously catalyzed oxidation of p-chlorophenol in water near the critical point. The temperatures and pressures studied range from 310$\sp\circ$C to 400$\sp\circ$C and 75 to 240 atm, respectively. The rate expression for the disappearance of chlorophenol appears to be first order in the organic at low concentrations and second order at high concentrations. It does not appear to be a function of the concentration of oxygen. Under the conditions studied, the same rate expression holds at subcritical and supercritical conditions, which suggests that the reaction proceeds by the same mechanism in the two regions.
Homogeneous catalysts studied were copper(II) tetrafluoroborate, manganese(II) chloride, and manganese(II) acetate. The first two resulted in modest increases in the rate constant, less than two-fold, while the latter showed no effect. Not all of the catalyst was recovered in the liquid effluent; a high percentage was lost in the reactor, possibly due to the formation of non-soluble metal oxides. The presence of the homogeneous catalyst does not appear to change the mechanism.
When the surface to volume ratio of the reactor was increased, an acceleration in rate was observed. This suggests that perhaps wall initiation is important. Possible mechanisms for both the uncatalyzed and homogeneously catalyzed reactions are presented, which include solvolysis and free radical oxidation. The rate expressions derived from these mechanisms contain a first order term primarily accounting for solvolysis and a second order term mainly accounting for free radical oxidation.
The most significant liquid intermediate was 1,4-benzoquinone. Other intermediates were present only in trace amounts. Gaseous products include carbon dioxide, carbon monoxide, ethane, ethylene, methane, and hydrogen. Carbon dioxide was by far produced in the greatest quantity.
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