Perovskite applied to the oxidative coupling of methane generated in the treatment of wastewater

Abstract

The use of methane generated in treatment of wastewater via oxidative coupling (AOM), in which occurs the direct conversion to ethene, eliminates the formation of synthesis gas and conversion in methanol followed by dehydration to ethene. During indirect conversion, the major part of the invested capital is associated to the generation of the synthesis gas, which makes the oxidative coupling economically attractive. Ethene is the simplest olefin and base product to produce polystyrenes, PVC and EVA. Its commercial production is an established process, but it depends on fossil feedstock. Therefore, considering treatment of wastewater as a source of methane and the possibility of a direct conversion of methane in C2 hydrocarbons, the present project aims the production of C2 hydrocarbons via oxidative coupling of methane generated in treatment of wastewater. This reaction, which requires temperature between 680-830°C, consists in three main steps: heterogeneous activation of methane, leading to formation of methyl radicals, followed by oxidative coupling of methyl radicals to form ethane and the dehydrogenation to ethene. MgO promoted with rare earth (La, Ce, Nd, Eu, Yb) was evaluated in the AOM reaction and showed activity and catalytic selectivity. La2O3 is active to AOM due to its ability of generating O2- centers and by the reaction between gas oxygen and oxygen vacancies on the surface. CeO2 has excellent redox properties due to easy reduction of Ce4+ to Ce3+ associated to the formation of oxygen vacancies in the crystalline lattice. A catalytic surface with larger quantity of oxygen vacancies promotes the adsorption and activation of molecular oxygen, favoring the activation of methane to methyl radical. Active catalysts should promote the generation and recombination of this radical. Perovskite oxides (ABO3) are promising catalysts once they allow the creation of electronic defects and oxygen vacancies by substitution of cations A or B and due to high thermal stability. Considering the promising results with oxides CeO2, La2O3 and MgO at AOM, the present project proposes the study and application of perovskite La1-CexTi1-yMgyO3 catalysts as well as the mixture of oxides in different proportions at the reaction of oxidative coupling of methane, in order to evaluate its activity and the doping effect at C2 hydrocarbons formation processes. (AU)