Effects of Pressure on the Non-Catalytic Thermal Conversion of Methane in Various Gases

A detailed kinetic model based on the NUI Galway mechanism for light hydrocarbon oxidation was used to investigate the effects of pressure on the non-catalytic conversion of methane in various gas atmospheres (Ar, H2, CO, CO2, H2O). The study also evaluated the impact of H2O addition on the conversion of CH4 in mixtures with H2 and CO. For CH4 mixed with Ar, CO, or H2, the methane pyrolysis rate exhibits a power-law dependence on pressure (W = APn), with the exponent n ranging from ~0.4 to ~0.65 in the 1400–1800 K temperature range. The achievable CH4 conversion decreases significantly with rising pressure, particularly for CH4–H2 mixtures. For the non-catalytic conversion of CH4 in mixtures with H2O and CO2, the initial pyrolysis rate is similar to that in an argon atmosphere. At high pressures, however, the CH4 concentration profile subsequently passes through a rising region. This is attributed to the interaction of C2H2 and CO products with H2O, which generates additional H2 and consequently shifts the equilibrium of the reaction system (2CH4 ↔ C2H4 + 2H2 ↔ C2H2 + H2) to the left.