Catalytic wet air oxidation of wastewaters

Succinic acid was chosen as a model pollutant to study the catalytic wet air oxidation (CWAO) of aqueous solutions of carboxylic diacids (5g 1(-1)). Using a 5%Ru/C catalyst, the destruction of succinic acid was rapid and substantially complete within one hour, at 190 degrees C and 5 MPa total pressure. Acrylic and acetic acids were formed as reaction intermediates and were further oxidized to CO2 and H2O. Acetic acid was most difficult compound to oxidize, but at the end of the reaction, only traces could be detected and a total organic carbon (TOC) removal efficiency of more than 99% was observed within 4 hours. No leaching of ruthenium from the catalyst was detected, and the heterogeneous catalyst could be removed by simple filtration. Under the same operating conditions, during the oxidation of succinic acid in solutions containing high salt concentrations (NaCl) or mineral acids, the oxidation of succinic acid was only slightly slowed down, while the oxidation of the acetic acid intermediate was diminished. The rate of oxidation was much slower at neutral or basic pH. Preliminary experiments have demonstrated that CWAO over Ru/C was also feasible for treatment of other carboxylic acids (adipic, glutaric, malonic, propionic and acetic acids).