High-Temperature Stabilities of Hydrocarbons

Article abstract of DOI:10.1021/j100263a027

A chemical thermodynamic analysis of hydrocarbon molecules from 1500 to 3000 K is presented for species C_2nH_2m, n=1-21, m=1-8.With group additivity as the primary estimation method, the nature and chemical thermodynamic properties of the most stable molecules ( stabilomers ) are found.Concentrations of these molecules are then examined in equilibrium with acetylene and molecular hydrogen after taking into account numbers of isomers.Thermodynamically favored pathways leading to large, condensed polyaromatic species are examined in detail.Two general types of paths are found.At higher H2/C2H2 ratios (>=1), most species on these paths are polycyclic aromatic molecules and, depending on partial pressures of C2H2 and H2, a free energy barrier appears in the range 1400-1800 K which increases sharply with increasing temperature.At lower H2/C2H2 ratios, many smaller species are cyclic, and as this ratio becomes smaller the barrier declines and becomes less sensitive to temperature.A brief dicussion of the connection between these results and the kinetics of carbon polymerization is then presented.