CATALYTIC WET AIR OXIDATION OF CARBOXYLIC ACID

Abstract

Today, the survival of process industries is increasingly dependent upon the environmental sustainability of their technologies. There is growing concern about the problems of waste minimization. Waste streams from various industries constitute high BOD, COD, pH, temperature, color, obnoxious odors. Rising concern about environment, strict implementation of environmental norms and the need to survive in competitive green pollution free market are slowly forcing the industries to upgrade and improve the waste minimization and treatment techniques. Among the various types of processes which can be used for treating aqueous wastes polluted with organic matter, wet air oxidation (WAO) is very attractive. The basic idea of the process is to enhance contact between molecular oxygen and organic matter to be oxidized. High temperature conditions convert the organic matter to carbon dioxide and water. The liquid phase is maintained by high pressure which also increases the concentration of dissolved oxygen and thus the oxidation rate. In this process insoluble organic matter is converted to simpler soluble organic compounds which in turn oxidized to carbon dioxide and water without emissions of NOx, SO2, HCI , dioxins, furans, fly ash etc. The last residual organic compounds are fatty acids , especially acetic acid. In the present work, CWAO of carboxylic acid (butyric acid) was carried out in a pressurized reactor at a partial pressure of air 4 kg/cm2 and temperature from 140°C to 180°C to reduce the COD of butyric acid. The catalysts tested in CWAO of butyric acid include both homogeneous (CuSO4 and FeSO4 ) and heterogeneous [ Co:Bi (5:1) and Mn:Ce (1:1) catalysts. The characterization of catalysts by SEM and XRD proves that heterogeneous catalysts are far better than homogeneous catalysts. iii The percent COD reduction of the butyric acid was found to be a function of initial pH of the solution and temperature. It has been found that it works more effectively at a certain pH for a given individual catalyst. The percent COD reduction was found to increase with temperature in the range 140°C to 180°C. An increase in the temperature from 140°C to 180°C increases the % COD reduction from 40.0% to 83 % with Mn : Ce (I: I) after 4 hour reaction time. Maximum COD reduction of 83% was obtained with catalyst Mn : Ce (1: 1) at I80°C and 14 kg/cm2 pressure after a reaction time of four hours. iv