Selective oxycracking of associated petroleum gas into energy fuel in the light of new data on self-ignition delays of methane-alkane compositions

Abstract

Preliminary selective oxycracking of heavy methane homologues theoretically allows using associated petroleum gas (APG) for power generation in gas-piston engines thus significantly decreasing its flaring. But practical implementation of this possibility is impossible without clear understanding of the dependence of fuel characteristic of hydrocarbon gases on their composition. Experimental investigations in the temperature range 523–1000 K at p0 = 1 atm and φ = 1 of self-ignition delays of complex gas mixtures imitating real APG have shown that quantitative influence of the addition of all C2-C6 alkanes on the self-ignition delay of methane is almost the same. The addition of any C2-C6 alkane at a level of 1% two-three times decreases the self-ignition delay of methane. The addition of any C2-C6 alkane at a level of 10% makes self-ignition delay practically indistinguishable from the self-ignition delay of added alkane itself. The delay of self-ignition of complex methane-alkane mixtures is determined only by the total concentration of heavy alkanes and within the measurement errors does not depend on their component composition. Available kinetic mechanisms of low-temperature oxidation of paraffinic hydrocarbons C1-C5 confirm these results. Therefore, to obtain certified gas fuel for gas-piston engines, it is necessary to remove practically all C2+ alkanes. Selective oxycracking of C2+ alkanes provides 82–85% conversion of ethane and the almost complete conversion of all the heavier alkanes. When using air as an oxidizer, it allows converting into certified fuel associated gas containing up to 10% C2+ alkanes, that is, almost all gas from the first and second stages of associated gas separation.