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 k₁, k₇/k^1/2₄ and k₈. HCHO + O₂→ HO₂+ HCO (1), HO₂+ HO₂→ H₂O₂+ O₂(4), HO₂ [graphic ommitted] ½ H₂O + O₂(7), H₂O₂ [graphic ommitted] H₂O +½ O₂. (8). Comparison of the experimental values for k₇/k^1/2₄ and k₈ with those calculated from diffusion theory indicates that the destruction of HO₂ at the surface is fully diffusion controlled, whereas the destruction 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 k₁ have been obtained, the values being 7.65 × 10^–1, 2.08 × 10^–1, 8.50 × 10^–2 and 2.20 × 10^–2 dm³ mol^–1 s^–1 at 542.5, 500, 471 and 440.5°C, respectively. These values give the Arrhenius parameters A₁= 2.04 × 10¹⁰ dm³ mol^–1 s^–1, E₁= 38.9 ± 1.5 kcal mol^–1. The absence of any diameter effect on the value of k₁ confirms that the parameters refer to the homogeneous process.