"Kinetic modeling of FAMEs hydrogenation over Ni/Al2O3 catalysts, recognizing the differences in the molecular sizes of the organic species and hydrogen"

MARÍA I. CABRERA; RICARDO J.A. GRAU

Seoul, Korea

Congreso; 14th International Congress on Catalysis; 2008

Seoul National University

Scope: New findings in reaction mechanism. Kinetics, modelling, and computational analysis. Abstract Nº PICC08-0598. The kinetics of the hydrogenation of methyl linoleate on a Ni/a-Al2O3 catalyst was studied in the absence of mass-transport limitation, at 398 £ T £ 443 K and 3.7 £ PH2 £ 6.5 bar. The kinetic modeling was performed on the basis of a new reaction mechanism including p and 2p-adsorbed dienes, and s and s-p bonded half-hydrogenated intermediates strongly adsorbed, and p-adsorbed monoenes (cis and trans methyl oleate), which was found to be capable of explaining the observed kinetic behavior. Admitting a distinction between occupied-sites and covered-sites by the large molecules of the fatty acid methyl esters (FAMEs), a rigorous method was applied to link the kinetic models corresponding to the extreme models of competitive and non-competitive adsorption, without having to draw the usual distinction between two types of surface sites. General rate equations were then formulated without expressing a priori opinion on whether the adsorption regime is competitive or non-competitive. Then, typical LHHW rate equations for both extreme adsorption regimes were directly derived as special cases for f=1 and f®0, respectively. Statistical results demonstrated the inadequacy of the models approaching non-competitive adsorption to describe the experimental data but results did not allow a definite discrimination between rival models with competitive and semi-competitive adsorption. However, the kinetic model featuring semi-competitive adsorption proved to be the best candidate to describe the experimental data satisfactorily with physically reasonable parameters. The semi-competitive model additionally indicates that the adsorbed molecules of methyl linoleate and methyl oleate could cover up to 14 and 7 surface sites, respectively. These values are in adequate agreement with those expected from a rough computational.