A Combined Flash Photolysis/Shock‐Tube Study of the Absolute Rate Constants for Reactions of the Hydroxyl Radical with CH₄ and CF₃H around 1300 K

Abstract

A combined flash photolysis/shock‐tube technique for the direct investigation of the rates of bimolecular reactions of the OH radical at temperatures between 1000‐1500 K is described. In this technique shock heated mixtures of approximately 0.5% of H2O in Ar and containing small amounts of a selected reactant, are subjected to flash photolysis as an instantaneous source of OH. The shock wave only serves to heat the gas mixture; thermal decomposition does not occur. Formation and subsequent decay of OH are monitored by time resolved UV resonance absorption. – First results with this technique have been obtained for the reactions (1) OH + CH4 r̊ CH3 + H2O and (2) OH + CF3H r̊ CF3 + H2O. Rate constants were found to be k1 (1300 K) = (2.5 ± 0.8) 1012 and k2 (1350 K) = (4.0 ± 1.0) 1011 cm3/mol · s. The result for reaction (1) is shown to confirm previously suggested non‐Arrhenius behaviour for this reaction, and in combination with low temperature data yields k1(T) = 106.19 (T/K)2.13 exp(‐1234 K/T) cm3/mol · s. The dependence of k1, on temperature is described in terms of transition state theory.

Containment of dioxin emissions from refuse fired thermal processing units - prospects and technical issues

“…The end results obtained, rate expressions for desorption and catalyzed dioxin formation are reasonable [22,3]. The observation that a substantial activation energy for desorption may be expected is consistent with a report that dioxins are apparently irreversibly adsorbed on fly ash at moderate temperatures [32]. However, unlike the situation in the gas phase, activation energy limits for surface induced processes are rather wide.…”

“…In high temperature combustion such as incineration, the hydroxyl radical is the most important small inorganic radical present under typical incinerator operating conditions [10,11,[30][31][32][33][34]. Furthermore, there is evidence that a local thermodynamic equilibrium between small inorganic radicals rapidly develops in the combustion flame zone [10,11,34].…”

Sensitivity and correlation analysis of the physical parameters in absorption, four‐wave mixing, and Schlieren experiments

“…(81, and an additional row and column of matrix elements, eqs. (6) and (7), which contain the reduced sensitivity coefficient for the pi term. The importance, or weight, of a parameter is given by the relative magnitude of the diagonal element that corresponds to the parameter [31, Wi = Dii/Trace [D].…”

Modelling of CF2HCl Consumption in H2/O2/Ar Flames

“…Most of these compounds used as propulsive gases, as refrigerants or as fire extinguishers have been regulated in the Montreal Protocol (1987). The rate coefficients of their reaction with reactive radicals like H, 0 and OH have been generally determined by flow tube experiments (Jeong andKaufman 1982, Jourdain et al 1978 or Miyoshi et al 1993) or by shock tube experiments (Ernst et al 1978). Our approach is to investigate the action of chlorofluorocarbons in flames, which can be considered as a "reactor" containing reactive species at high temperature.…”