Soot-Ozone Reaction Kinetics: Spectroscopic and Gravimetric Studies

Abstract

Studies on the kinetics of soot-O3 reactions, at various soot and ozone concentrations, have been conducted under flow conditions with ozone ranging from 50 to 15,000 ppm and soot from 2 to 350 mg. At lower concentrations, the initial rates of CO2 and CO formation are found to be half order with respect to soot and first order with respect to ozone. At higher concentrations, CO2 formation exhibits a more complex pattern. The initial rate for the formation of CO2 for a first stage is half order with respect to soot and 1.5 order with respect to O3, while the second stage is zero order in both species. Differences between data at higher and lower concentrations are discussed, and mechanisms for the formation of CO2 CO, and carboxylics during ozonation are suggested. Mass balance calculations on low concentration data reveal that only a small portion of the ozone is used to produce CO2, CO, H2O, and carboxylic species, most of it being decomposed catalytically over soot. At higher concentrations of O3 the rate of formation of carboxylic functionalities during the hexane soot-ozone reaction under static conditions has been examined. The initial rate, as determined by the Elovich equation, suggests that the soot-ozone reaction is nearly 6 times faster under equivalent conditions than the sool-NO2/N2O4 reaction reported earlier from this laboratory.