Effect of СО₂ Additives on the Noncatalytic Conversion of Natural Gas into Syngas and Hydrogen

Abstract

A kinetic analysis of the noncatalytic carbon dioxide reforming of CH₄ has been carried out in the temperature range of 1500–1800 K under conditions of variable temperature behind the reflected shock wave. The stages of methane conversion into syngas, the characteristic time intervals corresponding to these stages, and the most important elementary reactions have been established. At the first stage, as a result of thermal pyrolysis, methane molecules are sequentially converted into ethane, ethylene, and then acetylene, the most stable hydrocarbon in this temperature range. At the second stage, acetylene is normally converted into CO and H₂ and also into soot particles in the case of rich mixtures. The conversion of CO₂ proceeds at the second and third stages, when CH₄ conversion is almost complete. It occurs as a result of the interaction of CO₂ molecules with ${{{\text{H}}}^{\bullet }}$ atoms arising in the reacting system and leads to the formation of CO molecules and ${\text{O}}{{{\text{H}}}^{\bullet }}$ radicals. Acetylene is predominantly consumed in the reaction with ${\text{O}}{{{\text{H}}}^{\bullet }}$ radicals. The high concentration of acetylene during methane reforming promotes active formation of soot nuclei, for which acetylene makes the highest contribution to the rate of their surface growth. At the same time, acetylene itself is not a precursor of soot particle nuclei, which mainly form from ${{{\text{C}}}_{{\text{3}}}}{\text{H}}_{3}^{\bullet }$ radicals.