Oxidation of Formaldehyde in KCl-coated Vessels

Abstract

In the temperature range 440-540’C, the oxidation of HCHO in KCl-coated vessels is reproducible and of short chain length for HCHO concentrations in the range 0.05-4 Torr. Interpretation of the [CO] against time profile permits evaluation of the unknown parameters A'i, k7jk^ and ka. HCHO + O2->HO2 + HCO HO2 + HO2->H2O2 + O2 surface HO2---->4H2O + JO2 surface H2o2—>H2O + 4O2. (1) (4) (7) (8) Comparison of the experimental values for k7/kf and ka with those calculated from diffusion theory indicates that the destruction of HO2 at the surface is fully diffusion controlled, whereas the destruc tion of H2O2, though moderately efficient, is not fully diffusion controlled. From measurements at HCHO concentrations below 0.5 Torr, where the chain length is close to unity, effectively direct measurements of ki have been obtained, the values being 7.65 x 10~’, 2.08 x 10-1, 8.50 x IO-2 and 2.20x 1CF2 dm3 moF* s_1 at 542.5, 500, 471 and 440.5°C, respectively. These values give the Arrhenius parameters At = 2.04x 1010 dm3 moF1 s~l, £\ = 38.9 ± 1.5 kcal moF1. The absence of any diameter effect on the value of k, confirms that the parameters refer to the homogeneous pro cess.