Selective hydrogenation of oleic acid to fatty alcohols over a Rh-Sn-B/Al2O3 catalyst. Kinetics and optimal reaction conditions

CHRISTIAN FONSECA BENITEZ; VANINA MAZZIERI; CARLOS VERA; VIVIANA BENITEZ; CARLOS PIECK

Reaction Chemistry & Engineering

Royal Society of Chemistry

Lugar: Londres; Año: 2021 vol. 6 p. 726 - 746

2058-9883

The selective hydrogenation of oleic acid to oleyl alcohol over a Rh(1wt%)-Sn(4wt%)-B/Al2O3 catalyst was studied. The comprehensive set of experimental data was also used for elucidating the reaction mechanism. For the kinetic study, models were written that considered the whole network of reactions taking place: double bond hydrogenation, acid hydrogenation to alcohol, esterification of acids and alcohols. Each of these reactions was decomposed into elementary steps. Different combinations of elementary steps led to the formulation of a big number of models that were tested against the experimental data.Models posing the surface reactions as rate-limiting fitted the data better. Adsorption of the acids, the alcohols or hydrogen, were not rate-limiting. The best-fit model had the following hypotheses: (i) only one kind of adsorption site is needed for all species and reactions; (ii) H2 is dissociatively adsorbed; (iii) fatty molecules are adsorbed on only one site; (iv) pairwise insertion of H is the rate-limiting step to fatty molecule; (v) reduction of the carboxylate group occurs via an aldehyde intermediate that is subsequently hydrogenated to the corresponding alcohol; (vii) hydrogen and oleic acid are the main adsorbates; (vii) heavy esters are formed but do not contribute as intermediates of the main mechanism.