Closed-system pyrolysis of butyl ethyl ether and sec-butyl ethyl ether at 20 MPa—Mechanistic insights

Abstract

Natural macromolecular organic matter (kerogen) possesses a complex structure with a variety of subunits with a multitude of functional groups (e.g. numerous ether bonds). During thermal maturation, a preferential cleavage of labile bonds leads to fragmentation and the gradual liberation of CO2, H2O and organic compounds (e.g., hydrocarbons). Though, a detailed understanding of the kinetics and mechanisms of individual thermochemical reactions during maturation is difficult due to the complex structure, but would enable an improved prediction of the composition of released organic products or gas pressures. Pyrolysis studies of organic model compounds are one approach for a better understanding of individual bond cleavage pathways in kerogen and for the derivation of kinetic parameter.Here we present the results of closed-system pyrolysis experiments of the model compounds butyl ethyl ether (BEE) and sec-butyl ethyl ether (SBEE) at elevated pressure (20MPa) and temperatures (150–345°C).C1–C4 alkanes and carbonyl compounds (CO or butanone) account for the pyrolysis’ main products together with alkenes as byproducts. A detailed radical chain reaction mechanism is proposed to explain the formation pathways of the main products. The activation energy for H abstraction from CH bonds in the ether model compounds controls the formation of favored ether radicals whose decomposition gives rise to the main products. CO2 and several esters are byproducts whose formation can be attributed to the reaction of alkoxy radicals with CO or aldehydes – or to some extent ether decomposition processes induced by oxygen impurities.