QUASI-EQUILIBRIA OF GASEOUS SPECIES IN THE C-H SYSTEM

The influence of a constant concentration of atomic hydrogen on the st eady state gas-phase composition (quasi-equilibrium) and its developme nt in hydrocarbon-hydrogen mixtures was studied by means of computatio nal modeling. In the thermodynamic equilibrium, methane is virtually t he only stable gas species at temperatures below 1000-degrees-C, where as acetylene prevails at higher temperatures. The steady state of the gas phase in the presence of atomic hydrogen is also divided between t hese two stability regimes. The transition temperature between them, h owever, is considerably lowered even by small H concentrations. Concen trations of other species, especially CH3, are increased by several or ders of magnitude over their equilibrium concentrations, having peak v alues in the vicinity of this transition temperature. Cyclic reaction sequences, consisting of H-consuming reactions, result in a catalytic effect on atomic hydrogen recombination. Generally, atomic hydrogen ac celerates the development of a steady state, but not necessarily with a time constant decreasing with increasing temperature.