Clay and ammonium catalyzed reactions of alkanols, alkanoic acids and esters under flash pyrolytic conditions

Abstract

Pyrolysis of an alkanol, an alkanoic acid and a wax ester is shown to be affected by the presence of clay and/or ammonium. The alkanol dehydrates and is mainly converted into an 1-alkene, trans and cis 2-alkenes, and a variety of mid-chain alkenes due to double bond migration (‘scrambling’). The alkanoic acid is less affected than the alkanol, although a series of alkenes, alkanes and alkanones is produced in the presence of clay. Furthermore, a large portion is converted into the corresponding alkyl nitrile due to reaction with ammonium, which is promoted by clay. Pure clay does not cause bond breaking of the wax ester upon pyrolysis, but in the presence of ammonium ions the ester bond is cleaved to some extent yielding the alkanol and the alkanoic acid moieties. The products released (i.e. alkanol and alkanoic acid) undergo subsequent reactions. Comparison of pyrolysates of a mixture of grass material and clay with a soil sample taken from the grassland showed great resemblance in the aliphatic part consisting mainly of n-alkenes and n-alkanes, while a large difference with the pyrolysate of grass leaves (alkanols and alkanoic acids) alone was observed. This suggests that mineral particles, especially clay, present in soil samples, can generate compounds upon pyrolysis not directly derived from plant biopolymers.