Linoleic acid isomerization on Ru/Al2O3 catalyst

Abstract

The selective double bond isomerization reaction of linoleic acid to cis-9,trans-11-conjugated linoleic acid and trans-10,cis-12-conjugated linoleic acid on commercial H2-preactivated Ru/Al2O3 catalyst studied at 135–165 °C under kinetic control in a slurry reactor under atmospheric pressure in n-decane solution using the linoleic acid-to-surface ruthenium molar ratios 2.5, 5, and 10, was investigated by mathematical modeling. Over such catalyst and at the conditions used, the reaction scheme involves competitive isomerization of linoleic acid to conjugated linoleic acid isomers as well as hydrogenation of linoleic acid to oleic acid. These competing steps are through a complex relation strongly affected by chemisorbed hydrogen on the Ru surface. The concentrations of chemisorbed hydrogen and adsorbed key intermediates on the ruthenium surface influenced the catalytic activity and the selectivities toward isomerization and hydrogenation products through a complex relation. The isomerization rate was enhanced by catalyst preactivation under hydrogen, but increased hydrogen coverage on the Ru surface also restrained the isomerization selectivity. A reaction network and mechanism were advanced. Mechanistic models were developed from proposed elementary stage mechanism and corresponding kinetic equations were derived. Data fitting allowed discrimination between rival mechanistic models, more specifically the influence of hydrogen on the isomerization kinetics.