Title

Supercritical water oxidation of 4-monochlorobiphenyl (4MCB): Reaction kinetics, destruction efficiency, and by-products

Date of Award

1998

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

Lawrence L. Tavlarides

Keywords

Monochlorobiphenyl, Supercritical water, Destruction efficiency

Subject Categories

Chemical Engineering

Abstract

The safe disposal of various hazardous wastes, such as polychlorinated biphenyls (PCBs), is a major task in the chemical and environmental industries. Recent studies have shown the feasibility of using the supercritical water oxidation (SCWO) to destroy organic wastes, including PCBs, effectively.

In this research, SCWO of one of the PCB congeners, 4-monochlorobiphenyl (4MCB) is studied to define conditions for complete oxidation of this compound and to examine the reactions and kinetics of this system. A specially designed and constructed laboratory-scale plug flow reactor unit is employed for acquisition of the data. The design of the SCWO reaction system is based on the requirement for the data acquisition process. The investigation is focused on determining the reaction kinetics of 4MCB oxidation and pyrolysis/hydrolysis in supercritical water, including the reaction rate models, destruction efficiency, effect of reaction temperature, residence time, and concentrations of oxygen and 4MCB. The possible reaction by-products are also investigated. In addition, the oxidation and pyrolysis/hydrolysis of methanol, the solvent used to dissolve and deliver 4MCB into the reactor, are studied to permit better understanding and modeling of the reaction kinetics of 4MCB.

The reaction experiments of 4MCB are conducted at a pressure of 250 atm, over a temperature range of 380-600°C and residence times of 2-47 s. The analysis of the kinetic data reveals that the rate model for destruction of 4MCB appears to be first-order in 4MCB concentration and zero-order in oxygen concentration with an activation energy of 31.8 kcal/mol for the oxidation reaction. The results also indicate that the rate model for the 4MCB pyrolysis/hydrolysis reaction is first-order in 4MCB concentration with an activation energy of 20.1 kcal/mol. Biphenyl is identified as a major reaction by-product in both pyrolysis and oxidation reactions. The analysis of methanol reaction data suggests that the reaction rate is first-order in methanol in concentration for both pyrolysis/hydrolysis and oxidation reactions. The oxidation experiments for 4MCB and methanol cover essentially the entire range of the organic reactant conversions.

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