Degradation of maleic acid in a wet air oxidation environment in the presence and absence of a platinum catalyst

摘要

Over a temperature range of 415-478 K, the catalytic and non-catalytic degradation of an aqueous solution of maleic acid (0.03 M) has been studied both in the presence of oxygen and under an inert atmosphere (nitrogen). These reactions were first-order for maleic acid. The non-catalytic oxidation reaction was zero-order in oxygen over a partial pressure range of 0.4-1.4 MPa. The apparent activation energies for the non-catalytic removal of maleic acid under both a nitrogen (66.7 kJ mol~(-1)) and an air (131.5 kJ mol~(-1)) environment have been calculated. The use of 0.5 wt.% platinum on #gamma#-alumina catalyst significantly enhanced the degradation rate of maleic acid. A kinetic expression was developed accounting for both homogeneous and heterogeneous routes in maleic acid elimination. Although maleic acid removal was zero-order for oxygen concentration, the presence of oxygen is shown to result in significant chemical oxygen demand (COD) removal in both the catalytic and the non-catalytic process. Finally, the stability of a platinum catalyst has been tested for eight consecutive runs without any noticeable loss in catalyst activity.