Heterogeneous Isomerization of Ethylene Oxide to Acetaldehyde

Abstract

Surface catalyzed isomerization of (CH2)2O to CH3CHO occurs in a small, Pyrex reactor containing 15 or 230 Torr (CH2)2O at temperatures in the range 339.2 °C to 461.4 °C. Ro(CH3CHO), the initial rate of formation of CH3CHO, depends on the number of successive pyrolyses and on the evacuation time between pyrolyses, which is not true of the initial rates of formation of H2, CO, CH4, CH2CO, and C2H6. Ro(CH3CHO) also depends on the reactor S/V and on pretreatment of the reactor with product gases, particularly H2. The reproducible and limiting values of Ro(CH3CHO) are independent of the (CH2)2O pressures used. Above 385 °C these initial rates exhibit an Arrhenius temperature dependence while below 385 °C they pass through a maximum.Analysis of the Langmuir–Hinshelwood, low surface coverage mechanism shows that the T > 385 °C isomerization is partially or totally controlled by CH3CHO desorption and that −ΔHads < (55 ± 10) kcal mol−1, for CH3CHO on this surface.Ea = 57 kcal mol−1 for the homogeneous first order decomposition of (CH2)2O, in the 15 Torr pyrolysis at temperatures in the range 374.0 to 406.7 °C, and any vibrationally excited CH3CHO, formed in the gas phase at this pressure (and possibly even at 230 Torr), dissociates into chain initiating radicals.