Kinetics of Liquid Phase Catalytic Hydrogenation of Impure Soy Lecithin

Hydrogenation was carried out at different temperatures, hydrogen pressures and catalyst loadings and the observ-ations were used to tune parameters of a kinetic model. The reaction products were analyzed by Wijj’s method to find iodine value, which quantitatively yielded the degree of unsaturation; hence conversion. Impure soy lecithin was hydrogenated using 10% Pd/C catalyst in pressure reactor at comparably low pressure such as 1.5 Mpa until iodine number values drops in the range of 10-30 gI2/100g from initial 105gI2/100g. The best fits were obtained for a reaction that occurs in three stages: adsorption of lecithin onto the catalyst surface (rate controlling step), hydrogenation of adsorbed lecithin and desorption of the hydrogenated product. The order of the rate determining step with respect to lecithin and catalyst is 0.81 and 0.53 respectively while the activation energy is 3.0 kcal/mol. The order with respect to hydrogen pressure is 0.6. The enthalpy of hydrogenation and desorption was determined to be -18.61 kcal/mol and 20.35 kcal/mol respectively. The speed of agitation was sufficiently high enough to eliminate diffusional resistance. Hydrogenated lecithin provides products with increased stability with respect to oxidation, mostly applied in cosmetics and pharmaceutical preparations.