Selective Hydrogenation of Soybean Oil on Copper Catalysts as a Tool Towards Improved Bioproducts

Abstract

The liquid-phase soybean oil hydrogenation was studied on silica-supported Cu and ternary Cu-Zn-Al catalysts. Cu/SiO2 samples were prepared by incipient-wetness impregnation (Cu/SiO2-Imp) and chemisorption-hydrolysis (Cu/SiO2-CH) while two Cu-Zn-Al mixed oxides containing 8 (Cu(8)-Zn-Al) and 15% Cu (Cu(15)-Zn-Al), respectively, were prepared by coprecipitation. Copper dispersion (DCu) was 23% on Cu/SiO2-CH and this sample showed a high activity for soybean oil hydrogenation; in contrast, Cu/SiO2-Imp was inactive, probably because Cu was poorly dispersed (DCu = 2%). The oil hydrogenation activity on Cu(15%)-Zn-Al (DCu = 9%) was lower than on Cu/SiO2-CH, while Cu(8%)-Zn-Al (DCu = 23%) was also inactive. Citral hydrogenation used as a test reaction showed that the intrinsic Cu0 activity was not significantly changed by the kind of support or the catalyst preparation method. These later result suggested that differences in soybean oil hydrogenation should be explained as changes in accessibility of the triglyceride molecules to Cu active sites. In ternary Cu-Zn-Al samples, access to catalytic sites was hampered by the narrower structure of the catalyst. Copper exhibited unique properties for obtaining proper lubricants from soybean oil hydrogenation because selectively hydrogenated unsaturated linolenic (C18:3) and linoleic (C18:2) fatty acids to unsaturated oleic acid (C18:1) without forming saturated stearic acid (C18:0).