Hydrothermolysis and Oxidation of Hydrocarbons in Supercritical Water at High Pressures

This paper will present results on the investigation of different chemical reactions in supercritical water, i.e. the oxidation of methane, the hydrothermolysis of methane and the hydrothermolysis of methanol. Hydrogen, carbon monoxide, carbon dioxide and methanol constitute the main products in the oxidation of methane with oxygen in supercritical water. From the change of the methane concentration with time, it is possible to obtain a gross rate coefficient for a reaction of the first order for the oxidation of methane in supercritical water. With an Arrhenius plot the rate coefficients for the oxidation of methane in supercritical water of three different research groups are compared. In connection with studies on the oxidation of methane, the question arises, to what extent the decomposition of pure methane occurs. Our studies have shown that methane is still predominantly stable at temperatures up to 873 K. As reaction products carbon dioxide, carbon monoxide, hydrogen and ethene are produced. Under specific reaction conditions, the methanol concentration assumes relatively high values in the oxidation of methane. Decomposition of methanol in supercritical water at 60 MPa and temperatures between 673 K and 773 K mainly produces carbon dioxide, methane and hydrogen. Methanol remains rather stable in supercritical water up to 673 K