The role of homogeneous steam reforming of acetylene in the partial oxidation of methane to syngas in matrix type converters

Abstract

The conversion of natural gas to syngas is a key and most expensive stage of modern gas chemical technologies. As a promising alternative to existing technologies, a non-catalytic matrix conversion of natural gas to syngas was proposed. However, the reaction products, in addition to CO and H2, also contain unreacted methane, CO2 and acetylene. The latter is the most problem impurity, as it is a precursor of soot and other heavy products. In this work, the kinetic analysis of changes in the composition of the products during the matrix conversion of rich methane-air mixtures up to the establishment of the thermodynamic equilibrium was carried out. Three characteristic stages of the process were identified. The first stage of fast reactions involving oxygen is completed in a very short time (∼10−2 s at 1500 K) with almost complete oxygen consumption and the formation of CO, H2, CO2, H2O and some minor products of methane pyrolysis, mainly acetylene, but at their ratio, far from equilibrium. At the second stage, slow reactions of steam reforming of the formed products significantly increase the amount of hydrogen. The ratio [CO2][H2][CO][H2O] reaches an equilibrium value, but not the concentration of individual products due to incomplete conversion of acetylene and methane. At the third and longest stage, the system reaches equilibrium, and acetylene is not among the equilibrium products. The results of kinetic modeling and experimental study of partial oxidation of methane in matrix-type reformers have shown the important role of acetylene steam conversion in the post-flame zone. This reaction leads to a substantial decrease of methane and acetylene with a simultaneous increase in the yields of hydrogen and CO.