THE ROLE OF CATALYST IN SUPERCRITICAL WATER OXIDATION OF ACETIC-ACID

The oxidation kinetics of acetic acid in supercritical water (1.02 les s than or equal to T-r less than or equal to 1.15 and 1.04 less than o r equal to P-r less than or equal to 1.13) was examined in the homogen eous phase as well as in the presence of a solid catalyst consisting o f supported copper, zinc, and cobalt oxides. For the conditions studie d, the uncatalyzed oxidation reaction was found to be first order in a cetic acid and 0.3 order in oxygen, with an activation energy of 182 k J mol(-1). The rate of catalyzed oxidation was found to be well descri bed by means of the power-law kinetic formulation based on non-uniform surfaces. It is postulated that oxygen is adsorbed on active sites an d that a reaction between adsorbed species and organic molecules from the van der Waals sublayer forms a carbonate complex which further dec omposes to carbon dioxide and water. The apparent activation energy of catalyzed oxidation is 110 kJ mol(-1). The observed products in uncat alyzed supercritical water oxidation were carbon monoxide, carbon diox ide, and water. The oxidation of acetic acid over transition metal oxi des favors the production of carbon dioxide over carbon monoxide.