Studies on the Hydrogenation of Edible Oils. I.

Abstract

In a continuation of the studies of this series, two hydrogenation runs of a cottonseed oil (I.V. 109.8) were conducted with a commercial nickel catalyst under different conditions, one under selective (0.2% catalyst, 180°C, 1.0kg/cm2, 200rpm) and the other under non-selective (0.1% catalyst, 150°C, 3.0kg/cm2, 500rpm) conditions. The hydrogenation was continued until the iodine value has fallen into 50 approx. Five samples of hydrogenated oils were taken at different stages of hydrogenation, the iodine values of the corresponding samples being approximately same for both runs. Each sample was analyzed with respect to softening point, S.F.I., trans-isomer (%) and fatty acid composition. Each of hydrogenated samples and the original cottonseed oil was separated by argentation-TLC into 5 to 8 fractions. From the yield and fatty acid composition of each fraction, the proportions of ten glyceride types, i.e., G-000, G-001, G-011, G-002, G-111, G-012, G-112, G-022, G-122 and G-222 were calculated. Further, each sample was subjected to permanganate-periodate oxidation, and the resulting azelao-glycerides, as their methyl esters, were analyzed by GLC.Results of the experiments indicate that monoene-rich glycerides are predominantly formed in the selective hydrogenation, whereas relatively large amounts of fully saturated glycerides are formed in the non-selective hydrogenation. The slope of S.F.I.-curves for non-selectively hydrogenated samples is generally more gentle than that for selectively hydrogenated samples. The GLC-chart of the methyl esters of azelao-glycerides from the original cottonseed oil is well defined, but the charts from hydrogenated samples, especially those from selectively hydrogenated samples, show many unknown peaks besides those corresponding to known azelao-glyceride esters, presumably due to double bond migration during hydrogenation. As in the case with olive oil reported in the preceding paper of this series, it is postulated also in the case of cottonseed oil that in the selective hydrogenation the more unsaturated glyceride molecules are hydrogenated in preference to the less unsaturated glyceride molecules, whereas in the non-selective hydrogenation the double bonds remaining in the glyceride molecules once adsorbed on the calalyst surface are likely to be hydrogenated in some preference to the unsaturated fatty acid groups of other glyceride molecules.