Study of the mechanism of double-bond isomerization in methyl 9-octadecenoates

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

“…Equal hydrogenation rate constants of O and E were also assumed by Grau et al (1986Grau et al ( , 1987b, in calculating global pseudofirst-order reaction constants. Their assumption of equal hydrogenation rates of O and E (k 1 ) k 3 ), based on the suggestion of Van der Plank and Van Oosten (1975), is justified by our study.…”

“…The adsorption of the double bonds of O and E on the supported nickel surface (A1 and B1) is usually assumed to be at equilibrium (Vandenheuvel, 1956;Van der Plank, 1972a,b;Zwicky and Gut, 1978;Gut et al, 1979), though nonequilibrium adsorption was also incorporated to fit experimental data (Tsuto et al, 1978;Grau et al, 1986;Mu ¨nzing et al, 1986). Van der Plank and Van Oosten (1975) concluded from migration of double bonds of monoene FAME molecules that the first hydrogen insertion should be rate determining. In deriving our rate equations, we allowed for any possible combination of rate-determining steps.…”

“…Van der Plank (1972b) studied migration effects of monoene FAME (liquid phase, 323 e T e 448 K) and proved that if a FAME molecule enters the pores, in the absence of diffusion limitation, a migration reaction only occurs once before the FAME leaves the pores. Van der Plank and Van Oosten (1975) concluded from these data that the adsorption process must be relatively fast compared to the migration reaction and suggested that the ratelimiting step should be the insertion of hydrogen into the half-hydrogenated intermediate (the second hydrogen insertion, step C2). The migration studies thus showed a relatively fast adsorption process, which is supported by model A2B2, but from our analysis step C2 could not be a rate-determining step.…”

“…In monoene hydroge-nation, also undesired products are formed, due to migration and cis-trans isomerization of double bonds. The cis-trans isomerization was explained from the formation of a half-hydrogenated surface intermediate (Allen and Kiess, 1955;Hashimoto et al, 1971;Gut et al, 1979;Albright, 1985;Grau et al, 1988) by its easy rotation at the surface (Dutton et al, 1968;Heertje et al, 1974;Van der Plank and Van Oosten, 1975), whereas migration occurs via the π-allyl intermediate, the latter of which being mainly present at low hydrogen pressure (Heertje et al, 1974;Van der Plank and Van Oosten, 1975). In this study, we focus on the formation of the half-hydrogenated intermediate only.…”

Sunflower oil hydrogenation mechanisms and kinetics

“…To study accurately the dependency of hydrogen pressure on the isomerization reactions, some authors did not consider the hydrogenation of edible oils (which are complex mixtures of triglycerides) but that of fatty acid methyl esters (FAME) instead. The advantages of the latter are the same reactivity as the fatty acid chains on triglycerides [26], but a higher effective diffusivity within the catalyst, hence avoiding internal mass transfer limitations [27]. In this context, Grau et al [28] examined methyl oleate saturation and isomerization through an intermediate species, following once again the Horiuti-Polanyi reaction mechanism.…”