Upgrading of methane under homogeneous thermal conditions: An environmental and economic imperative

After a brief outline of current estimates of the amount of methane annually injected into the atmosphere from fossil sources, we list various techniques that have been proposed and tested for converting methane to higher molecular weight hydrocarbons and alcohol to facilitate transport to locations where these chemicals could be utilized either directly to generate power or as feed stock for further processing. We propose a thermal conversion under homogeneous conditions that appears attractive, based on an extensive computer analysis of the kinetic mechanisms that control pyrolysis of methane when mixed with selected radical generators, at relatively modest temperatures (similar to 900 degrees C), that initiate C-H bond fission during the early stages of pyrolysis. Product distributions were computed to illustrate theoretically attainable temperature and time dependent levels of conversion. Therein, two key assumptions were made: ''kinetic trapping'' of radical-initiated products can be achieved; no solid deposits were generated. We utilize initiators available in commerce at low cost in bulk quantities. An extended series of tests were completed using a newly designed highly stirred ''batch'' reactor operating at pressures up to 25 atm that was later adapted for ''flow-through'' operation. It appears that conversion to a C/H solid deposit on the quartz-lined reactor walls does limit the amounts of hydrocarbons that can be recovered in the gasphase. Additional tests were run in a single-pulse shock tube, where the reactants are highly diluted in Ar and the residence time at the pyrolysis temperature is milliseconds. No C/H deposits were generated, and the analytical data confirmed the modeling calculations.