GAS-PHASE OXIDATION-KINETICS OF TOXIC METALS AT INCINERATOR TEMPERATURES - THE REACTIONS OF CHROMIUM ATOMS WITH HCL, N2O, CL-2, AND O-2

The need for kinetic data on individual reactions to develop combustion control strategies for alleviation of toxic metal species production is discussed. In this work such data are obtained at realistic incinerator temperatures. Measurements on the Cr + HCl reaction, made by both the High-Temperature Fast-Flow Reactor(HTFFR), and Metals High-Temperature Photochemistry (Metals-HTP) techniques, are found to be in good agreement. The other reactions were studied by the Metals-HTP technique only. These techniques are briefly described. The N2O and Cl-2 results are compatible with O and Cl abstraction, respectively, while the HCl mechanism needs further study. These three reactions are independent of pressure. The previously studied O-2 reaction involves a pressure-independent abstraction, and a pressure-dependent addition component. The following rate coefficient expressions in cm(3) molecule(-1)s(-1) were obtained: Cr + HCl k(811-1449 K) = 1.6 x 10(-12) (T/K)(0.74) exp(- 5802 K/T); Cr + Cl2 k(277-344 K) = 2.1 x 10(-11) (T/K)(0.69) exp(-396 K/T); Cr + N2O k(278-1150 K) = 2.2 x 10(-12) (T/K)(0.55) exp(-2851 K/T). The data from the latter reaction agree well with measurements elsewhere at the temperature extremes to yield an overall recommendation of k(278-2570 K)= 3.2 x 10(-12) T-0.50 exp(-2605 K/T)cm(3) molecule(-1)s(-1); this temperature dependence is shown to be in good agreement with that predicted by a recently developed semi-empirical theoretical method.