Effects of operation conditions on removal rate constant and quantum yield of gaseous chlorobenzene degradation in a photochemical reactor.

A photochemical reactor with a low-pressure mercury ultraviolet (UV) lamp was established to treat waste gas containing chlorobenzene. Operation conditions such as light intensity, gas humidity, and inlet chlorobenzene concentration were varied. Two significant parameters, the removal rate constant and the quantum yield (relating to removal kinetic and light energy utilization), were investigated under each set of conditions. The experimental results indicated that the removal of chlorobenzene by UV irradiation in the gas phase followed a first-order kinetic model at inlet chlorobenzene concentrations ranging from 200 to 2500 mg x m(-3). With increasing light intensity from 10 to 37 microW x cm(-2), the chlorobenzene removal rate constant rose from 0.004 to 0.011 sec(-1), whereas the quantum yield maintained the same value of 0.60. The effects of gas humidity on the parameters indicated that the highest humidity of 80% could achieve the highest removal rate constant (0.046, 0.029, and 0.015 sec(-1)) and the highest quantum yield (1.91, 1.19, and 0.60) among the tested gas humidities at the inlet concentrations of 400, 1000, and 2500 mg x m(-3), respectively. An increase in inlet chlorobenzene concentration from 200 to 2500 mg x m(-3) resulted in reduction in both removal rate constant (from 0.060 to 0.014 sec(-1)) and quantum yield (from 2.50 to 0.56) that may be attributable to competition between the intermediates and chlorobenzene. On the basis of the quantum yield, the total power expended per mass of chlorobenzene was calculated as 483 kWh x kg(-1) under the conditions of an inlet concentration of 200 mg x m(-3) and an empty-bed residence time of 27 sec.