Steam cracking of methyl ester: A modeling study on the influence of the hydrocarbon backbone

Abstract

Biodiesel can be used to produce clean platform chemicals for the chemical industry, as an alternative to or blend with conventional steam cracking feedstocks. Research on the decomposition chemistry of biodiesel is crucial for understanding their combustion, aging and potential as source for base chemical production. Three methyl esters are studied with varying hydrocarbon chain length and a different degrees of saturation to evaluate the impact of these structural differences on the decomposition chemistry and the decomposition product composition. A new kinetic model is developed with the automatic kinetic model generation tool Genesys for the pyrolysis of methyl butanoate, methyl decanoate and methyl dec-4-enoate. New ab initio calculations are carried out for the pyrolysis of methyl butanoate and for retro-ene reactions in unsaturated hydrocarbons and methyl esters, because of their importance in the secondary decomposition chemistry. The first-principles based kinetic model is validated using in-house experimental data gathered in a tubular reactor and against literature experimental data gathered in a jet-stirred reactor for methyl decanoate pyrolysis. A rate of production analysis reveals the main channels towards the pyrolysis products. The presence of the double bond in the hydrocarbon chain leads to a higher production of aromatic species, at the cost of a lower ethylene and propylene production. The high selectivity to aromatics is caused by the fast formation of 1,3-cyclopentadiene from the unsaturated, resonantly stabilized radicals formed during the decomposition.