Control of the product distribution in the hydrogenation of vegetable oils over nickel on silica catalysts

Abstract

Several nickel on silica catalysts, prepared by impregnation or precipitatioddeposition, and a commercial catalyst were tested for activity and selectivity in the sunflower seed oil hydrogenation. An average turn-over frequency of 2.57 s-I was found for the catalysts, assuming inaccessibility of nickel in pores smaller than 2 nm and a constant nickel surface concentration poisoned by the reaction mixture. After studying the mass-transfer steps, the effect of temperature (373-453 K) and pressure (101-608 kPa) on reaction rates in the kinetic regime was analyzed, and the corresponding apparent activation energies and reaction orders were obtained. Conclusions on the effect of temperature and pressure on the selectivity to the preferential hydrogenation of polyunsaturates (So) and to the formation of trans-isomers ((SEo,,J0) in the kinetic regime were derived from the results. Finally, a similar analysis was carried out when diffusion limitations were known to be present.Plusieurs catalyseurs de nickel sur de la silice, prepares par impregnation ou precipitationldep6t. en un catalyseur commercial ont ete testes en termes de leur selectivite dans I'hydrogenation d'huile de tournesol. On a trouve une frequence de renouvellement moyenne de 2,57 s-' pour les catalyseurs, en supposant I'inaccessibilite du nickel dans les pores inferieures a 2 nm et une concentration de surface de nickel constante empoisonnee par le melange de la reaction. Apres avoir etudie les etapes du transfert de matiere, on a analyse I'effet de la temperature (37-53 K) et de la pression (101408 kPa) su; les vitesses de reaction dans le regime cinetique, et on a obtenu les energies d'activation apparentes correspondantes. A partir des resultats, des conclusions ont ete tirees sur I'effet de la temperature et de la pression sur la selectivite a I'hydrogenation preferentielle des polyinsatures (So) et a la formation de trans-isomeres ((Spqn,J0) dans le regime cinetique. Enfin, une analyse similaire a ete menee lorsqu'on a su qu'il y avait des limitations de diffusion.

Revisiting the hydrogenation of sunflower oil over a Ni catalyst

“…Some authors (González-Marcos, Gutiérrez-Ortiz, González-Ortiz de Elguea, Alvarez, & González-Velasco, 1998;Susu, 1982;Veldsink, Bouma, Schöö n, & Beenackers, 1997) propose to estimate the magnitude of the different mechanisms for mass transport by plotting the reciprocal of the hydrogenation rate versus the inverse of the catalyst mass according to the following equation: where C H 2 is the H 2 concentration in the liquid-gas interphase, r H 2 is the initial reaction rate, k l is the coefficient of transfer between the bubble and the liquid, k s is the coefficient of transfer in the boundary layer that surrounds the catalyst, k is the reaction constant, a l and a s are the areas of transfer between the gas and the liquid, and between the liquid and the solid respectively, g is the effectiveness factor and m the mass of the catalyst. In agreement with this equation, the intercept at the y-axis is associated with the magnitude of the mass transfer resistance between the gas and the liquid, whereas the slope depends on the mass transport processes associated with the catalytic solid.…”

Kinetics, Gas−Liquid Mass Transfer, and Modeling of the Soybean Oil Hydrogenation Process

“…The first mechanistic kinetic model for vegetable oil hydrogenation was developed in 1949 by Bailey, who proposed consecutive reactions of the unsaturated triglycerides in which Ln, L, OL, EL, and S represent linolenic, linoleic, oleic, elaidic, and stearic acid, respectively: The reaction rates for the mechanism given in eq 1 were found to be pseudo-first-order with respect to the oil triglycerides. − Colen et al and Santacesaria et al employed eq 1 and assumed a 3:2:1 ratio between the equilibrium adsorption constants of the monounsaturated triglycerides, corresponding to the probability of a double bond to react at the catalyst surface. Other investigators, including Gut et al, Susu and Ogunye, Susu, Jonker et al, and Gonzáles-Marcos et al, modified eq 1 by incorporating the cis−trans isomerization of monoenes as given in eq 2: Gut et al proposed a kinetic model to account for the formation of the cis and trans isomers during the hydrogenation of sunflower seed oil, and a Langmuir−Hinshelwood adsorption kinetic equation was used to determine the reaction rates of the fatty acids. Their model assumed that both cis and trans fatty acids (TFAs) are adsorbed identically on the catalyst surface and that the adsorbed double bond could isomerize at the catalyst surface.…”

Production of Butylamine in the Gas Phase Hydrogenation of Butyronitrile over Pd/SiO2 and Ba-Pd/SiO2

“…60 The nitrile consumption rate delivered by Pd/SiO 2 (I) and Ba-Pd/ SiO 2 (II) passed through maxima at 523 and 493 K, respectively, as shown in Fig. 8.…”