Wet Air Oxidation of Methyl-tertiary-butyl-ether (MTBE) in a fixed bed tubular reactor over a Ruthenium-Cerium/Alumina catalyst

International audienceTreatment of polluted industrial wastes is one of the challenging research topics that occupy an important position in various chemical processes. Among the various types of processes which can be used for treating aqueous wastes polluted with organic matter, the biological and chemical treatments, as well as the incineration are the most commonly used techniques. Each of the mentioned techniques can be used separately or combined with other procedures in order to optimise the global operating conditions. The choice of the process depends upon the nature of the waste and its final destination. Although, the operating cost is an important factor which determines the possibility to exploit the process in large scale. Wet air oxidation is a destructive technology based upon the oxidation of organic and inorganic pollutants in aqueous solutions. The system uses molecular oxygen or air as a potential source of oxidant. Wet air oxidation can be either a non-catalysed process or can occur in the presence of homogeneous or heterogeneous catalysts.Destruction of Methyl-tertiary-butyl-ether (MTBE) is a research subject of growing concern since the recognition of this compound as an environmental pollutant. MTBE is commonly added to gasoline as an octane enhancer and has been used for the last two decades. It is highly soluble in water and transports easily in ground and surface water. As a result, it is found frequently in groundwater and some surface water. We have focused our research on the catalytic decomposition of this compound using a wet air oxidation process. Some typical results are presented, pointing out the most important parameters of the process and showing the specific behaviour of a Ruthenium/Cerium catalyst during the oxidation of MTBE. The main part of the process consists of one fixed bed tubular reactor centred in an electrical automated oven. The substrate mixed to pure oxygen is oxidised over the catalyst bed and the emergent effluent is therefore cooled into a condenser thus liquid and gas phases could be separated hereafter. Catalysts are prepared by co-impregnation process of metallic chloride precursors (RuCl3.H2O and CeCl3.7H2O) onto commercial alumina (Merck-Prolabo; BET = 331 m²/g) support commonly used in the industrial catalytic processes. Therefore, catalysts are calcinated at 450°C under airflow in order to remove impurities at the surface, then reduced at the same temperature under pure hydrogen flow for 3 hours. Feed solution of MTBE giving 2500 ppm of COD (Chemical Oxygen Demand) was prepared in distilled water. The oxidation runs have been carried out at 150°C under 2 bar of pure oxygen pressure during 3 hours. The catalyst presenting 3 % of Cerium concentration showed the best result regarding the abatement of COD and TOC (Total Organic Carbon). Higher concentrations of cerium have negative effects on the oxidation reaction. This could be explained by the presence of chlorine which inhibits the active metallic sites. AOSC (Average Oxidation State of Carbon) has been calculated according to the measured COD and TOC values. Here again, the optimal oxidation state was obtained with the catalyst of 3 % of Cerium concentration