Characteristics and catalytic behavior of supported NiMgAg/D catalysts in the partial hydrogenation of soybean oil

Diatomite supported NiMgAg catalysts, NiMgAg/D, were prepared by the precipitation-deposition method followed by drying, reduction and passivation. The preparation of the catalysts was performed with different loading of silver ranging from 0.16 to 5.88 wt% and constant molar ratios of SiO2/Ni and Mg/Ni equal to 1.07 and 0.1, respectively. The characterization of the catalysts was performed with N2-physisorption, mercury intrusion porosimetry, H2-chemisorption, X-ray diffraction, temperature programmed reduction, and scanning electron microscopy-energy dispersive X-ray analysis. The partial hydrogenation of soybean oil from initial to final iodine value of 90 was carried out at 160 °C and H2 pressure of 0.16 MPa using stirred semi-batch reactor. Soybean oil was hydrogenated over NiMgAg/D catalysts and NiMg/D catalyst (without silver addition) that was prepared using the same procedure as used for catalysts modified with silver. The selectivity towards trans fatty acid and saturated fatty acid formation was determined for both types of catalysts. By comparing the selectivity of the NiMgAg/D catalysts with the NiMg/D catalyst the promoting effect of silver modifier on the catalyst behavior in the hydrogenation of soybean oil was observed, and correlated with changing of the catalyst surface characteristics caused by the different Ag loading. It was found that the addition of silver to NiMg/D catalyst decreased both the selectivity towards trans fatty acids formation and the selectivity towards saturated fatty acids. For the same iodine value decay, the catalyst with the highest Ag loading (5.88 wt%) had the lowest level of both trans fatty acids and saturated fatty acids in the hydrogenation of soybean oil under studied operating conditions. The hydrogenation activity of NiMgAg/D catalysts is lower than NiMg/D catalyst and decreases with increasing Ag loading. The correlation between adsorption characteristics of the catalysts and their hydrogenation activities was established. The proposed simplified kinetic model to describe the kinetics of soybean oil hydrogenation gave a good description of the experimental data.