No 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.

No abstract

No abstract