Supercritical pyrolysis of the endothermic fuels methylcyclohexane, decalin, and tetralin

The pyrolysis of the potential endothermic fuels methylcyclohexane, decahydronaphthalene (decalin), and tetrahydronaphthalene (tetralin) under supercritical conditions can be of great import and is the focus of this dissertation. Supercritical fluids, essentially gases with a liquid-like density, are a unique environment for chemical kinetic studies. Because the solvent properties of a supercritical fluid vary strongly with pressure (unlike liquids or gases), elementary reactions in a supercritical environment can have strong pressure dependence. The influence of these solute/solvent interactions on kinetic rates can have important implications in the context of the fuel-fouling problem.; Supercritical methylcyclohexane pyrolysis was investigated in a specially constructed silica-lined flow reactor. Experiments in which the temperature and pressure were varied independently revealed a product distribution substantially different from numerous higher temperature gas-phase pyrolysis studies. Major products identified at 820 K and 45 atm included methane, ethane, propene, ethene, dimethylcyclopentane, propane, 1-methyl-1-cyclohexene, and ethylcyclopentane. As pressure was increased at 782 K, the selectivity of dimethylcyclopentane increased and was consistent with a mechanism that incorporated caging effects. Some observations related to polycyclic aromatic hydrocarbons (PAH) and solid formation were a natural extension of this research effort. PAH products observed included indene, methylnaphthalenes, dimethylnaphthalenes, fluorene, pyrene, methylanthracene, and benzo[ghi]perylene.; A gas-phase model of methylcyclohexane pyrolysis was constructed and compared with experimental data from a sister effort in this laboratory. This model, along with two others currently being developed at Princeton, is the first elementary-reaction-based cycloalkane decomposition model ever created. Excellent agreement was found between the gas-phase model and experimental data for the major products observed. Preliminary steps were taken to extend this model to supercritical conditions through detailed consideration of the solute/solvent interactions present in the supercritical fluid and modifications made to the ideal gas model.; Supercritical pyrolysis mechanisms of decalin and tetralin were also investigated. Major products of supercritical decalin pyrolysis included light alkanes and alkenes, methylhexahydroindane, indene, methylcyclohexenes, and indane. Major products of supercritical tetralin pyrolysis included: naphthalene, methylindane, ethane, methane, ethene, and phenylbutane. Quantification of the major products indicated that C₆ to C₅ ring contraction was found to occur preferentially with increasing pressure, consistent with the caging hypothesis.