Selective photo-oxidation of ethanol to acetaldehyde and acetic acid in water in presence of TiO2 and cupric ions under UV-simulated solar radiation

The selective oxidation of ethanol to acetaldehyde and acetic acid in aqueous solution, through sacrificial TiO2 photocatalysis in the presence of cupric ions at ambient temperature, under acidic conditions and artificial sunlight, has been investigated. Different commercial TiO2 photocatalyst samples and loads have been tested. The influence of starting cupric ion and ethanol concentrations has been investigated. Ethanol conversion, overall product selectivity, and product yield have been calculated and compared with the aim of maximizing the recovery of valuable commodity chemicals. For the run corresponding to optimal values of ethanol conversion, overall product selectivity and yields, a value of process photoefficiency equal to 33% has been calculated. Based on the experimental results, the main focus of the study has been the development of a photo-oxidation mechanism and a new kinetic model constituted by a set of mass balance equations for the main species involved in the photocatalytic oxidation process. The model has been employed for analyzing data collected at different starting substrates and cupric ion concentrations. A reliable prediction of the concentrations of cupric ions and organic species during selective photo-oxidation runs has been achieved. The modeling investigation has allowed to estimate for the first time the kinetic parameters not available in the literature review, such as the equilibrium adsorption constants and the rate constants for the hole-capture by sacrificial agents. A new alternative strategy to convert ethanol from biorefinery wastewaters into valuable fine chemicals, by using water as solvent, a low-cost catalyst, solar radiation and ambient temperature, has been proposed and kinetically characterized. The model presented can be easily applied to other photocatalytic systems for the oxidation of organic species over metal doped photocatalysts.