No abstract

Using the method of freezing radicals in conjunction with ESR spectroscopic measurements, the kinetics of the thermal oxidation of methane has been studied under atmospheric pressure depending on the temperature, composition of the mixture, and nature of the surface of the reaction vessel. It has been shown that in a reactor treated with boric acid, the intermediates methylhydroperoxide and hydrogen peroxide are responsible for chain branching. It has been established that the leading active centers of the reaction are the HOz radicals, while chain branching occurs as a result of the decomposition of peroxy compounds-methylhydroperoxide and hydrogen peroxide. In reactors treated with potassium bromide, the concentrations of radicals and peroxy compounds were found to be lower than the sensitivity of the method of measurement. Computations were performed for the scheme of methane oxidation a t 738 K for a reactor treated with boric acid. Satisfactory agreement was found between the experimental and computed kinetic curves of accumulation of main intermediates CH20, HzOz, CH300H. The influence of their addition on the kinetics of the reaction has been considered. It has been shown that the addition of formaldehyde does not lead to chain branching, however; it contributes to the formation of those peroxy compounds that bring about chain branching. Mathematical modeling confirmed conclusions made on the basis of experimental data concerning the nature of the leading active centers and the products that are responsible for the degenerate chain branching.

The high-temperature oxidation of formaldehyde in the presence of carbon monoxide was investigated to determine the rate constant of the reaction HOZ + CO = CO:! + OH (10). In the temperature range of 878-952°K from the initial parts of the kinetic curves of the HOz radicals and CO, accumulation at small extents of the reaction, when the quantity of the reacted formaldehyde does not exceed lo%, it was determined that the rate constant klo isA computer program was used to solve the system of differential equations which correspond to the high-temperature oxidation of formaldehyde in the presence of carbon monoxide. The computation confirmed the experimental results. Also discussed are existing experimental data related to the reaction of HOt with CO.On the basis of our detailed knowledge of the mechanism of the oxidation of formaldehyde in a reactor treated with boric acid, it was possible to attempt to determine the rate constant of the elementary reaction HO2 + CO=CO2 + O H I n the reaction mixture, which contained 1% formaldehyde and 99% air, part of the nitrogen was replaced by carbon monoxide. The mechanism of the oxidation of formaldehyde in the presence of carbon monoxide may be represented by the following reactions (Table I). The units of the rate constants are given in sec-', cm3/molec.sec, and cm6/molec2.sec for the reactions of the first, second, and third orders, respectively.Reactions (1 1)- (22) have been included because reaction (9) generates H atoms. The reaction O H + HO2 = H2O + 0 2 has not been included in the scheme because its velocity is noticeably less than the velocities of reactions (5) and (8). It follows from this scheme that the rate of formation of carbon dioxide is equal to d(C02)/dt = k9(0H)(CO) + klo(HOz)(CO). To evaluate the contribution of reaction (9)

No abstract

No abstract