PHOTOCATALYZED OXIDATION OF ETHANOL AND ACETALDEHYDE IN HUMIDIFIED AIR

Photocatalyzed oxidation of ethanol and acetaldehyde in humidified air was carried out to establish a first complete kinetic model for a pho tocatalyzed multispecies network. Two photocatalysts were examined in a batch, recirculation reactor, near-UV illuminated TiO2 (anatase) coa ted (i) on the surface of a nonporous quartz glass plate and (ii) on a porous ceramic honeycomb monolith. The former contained only illumina ted (active) surfaces, the latter consisted of substantial ''dark'' su rfaces coated with a thin layer of illuminated (active) catalyst. Etha nol was photooxidized to acetaldehyde and formaldehyde intermediates, and eventually to carbon dioxide and water products. The catalyst and monolith surfaces adsorbed appreciable fractions of the trace ethanol, acetaldehyde, formaldehyde, carbon dioxide, and water present. Ethano l, acetaldehyde, and carbon dioxide adsorption isotherms were measured on both catalysts; the formaldehyde adsorption isotherms were assumed identical to those of acetaldehyde. On the fully illuminated glass pl ate reactor, all four species were accounted for, and closure of a tra nsient carbon mass balance was demonstrated. Completion of a transient carbon balance on the monolith reactor required inclusion of addition al reaction intermediates (acetic and formic acids), which appear to r eversibly accumulate on only the dark surfaces. The ethanol and acetal dehyde photocatalyzed oxidation kinetic networks were modeled using La ngmuir-Hinshelwood rate forms combined with adsorption isotherms for r eactant, intermediates, and product CO2 For both the quartz plate and monolith catalysts, satisfactory kinetic models were developed to pred ict the entire time course of ethanol and acetaldehyde multicomponent batch conversions. (C) 1996 Academic Press, Inc.