Intrinsic Kinetics of 9-Monoenic Fatty Acid Methyl Ester Hydrogenation over Nickel-Based Catalysts

Abstract

The monoenic fatty acid methyl ester hydrogenation and isomerization over a supported nickel catalyst was studied at 0.02 e P H 2 e 0.50 MPa and 333 e T e 443 K. Batch hydrogenations at constant and variable hydrogen pressure were carried out to investigate the rate-determining steps. On the basis of the Horiuti-Polanyi mechanism, involving a half-hydrogenated surface intermediate, kinetic rate equations were systematically derived following the Langmuir-Hinshelwood-Hougen-Watson approach. Each set of rate equations was tested by means of a χ 2 method on its ability to describe the experimental curves simultaneously. The χ 2 was minimized by a stepwise optimization of model parameters. Furthermore, we used Bartlett's test to reduce the set of most-likely rate expressions. The statistically most significant model assumes the formation of the half-hydrogenated surface intermediate as the rate-determining step and an equilibrium associative hydrogen adsorption. The rate equations are R O )

Mathematical modeling of the partial hydrogenation of vegetable oil in a monolithic stirrer reactor

“…Triglyceride and H 2 adsorption are assumed to be at equilibrium. The fractions of the surface occupied by the intermediates are negligible due to their high reactivity. The location of the double bonds does not affect the reaction rates. The probability of diene adsorption is twice as much as the monoene adsorption The same overall effectiveness factor is assumed for the different reactions because reaction rates and diffusivities have the same order, thus simplifying the calculation (Overall effectiveness factor section). The reaction rate is controlled by adding the first hydrogen in the double bond …”

Selectivities in Partial Hydrogenation

“…In 1983, Beyens and Dijkstra [6] reported that linoleic acid present in triglycerides with two or more linoleic acid moieties reacted more slowly than when it was the only linoleic acid moiety present in triglycerides. Finally, deviations from the common pool kinetics, which have been linked to pore diffusion limitations [7,8], may be at least partially explained by abandoning the common pool concept [9]. Since the definitions of the fatty acid selectivities are based on the common pool concept, their meaningfulness is severely curtailed.…”

Kinetics of the Hydrogenation of Sunflower Oil over Alumina Supported Palladium Catalyst

“…Also working with a nickel-based catalyst, Jonker et al (1997Jonker et al ( , 1998 derived kinetic rate equations for methyl esters of fatty acids (FAME) following the Langmuir-Hinshelwood-Hougen-Watson approach. These authors considered cis-trans isomerization only and followed the Horiuti-Polanyi mechanism involving a halfhydrogenated surface intermediate.…”