Hydrogenation Of Soybean Oil In Supercritical And Subcritical Carbon Dioxide Conditons

Hydrogenated vegetable oils have widespread applications and great market demands infood industry, because they can be used as materials of margarine, shortening and cacoa buttersubstitute. Trans fatty acids content of the hydrogenated vegetable oils obtained by means ofthe existing industry technology is generally high, which is harmful to human, so it isimperative to research new hydrogenation technologies to produce healthy hydrogenatedvegetable oils of lower trans fatty acids content.In this experiment, hydrogenation of soybean oil was attempted in supercritical andsubcritical carbon dioxide, based on mechanisms of oil hydrogenation and properties ofsupercritical fluids. Amount of catalyst, pressure of hydrogen, time of hydrogenation,temperature of hydrogenation, stirring rate were studied. Catalytic activity k1NHwas set asevaluation index, and the optimum conditions obtained by orthogonal test for hydrogenationof soybean oil were as follows: the amount of Pd/C catalyst was0.08%, pressure of hydrogen3MPa, pressure of carbon dioxide6MPa, temperature of hydrogenation140℃, time ofhydrogenation70min. Under the conditions, the catalytic activity k1NHwas the best, the valueof which was9.456×10-4, and the content of trans fatty acids in the product was21.24%withIV of96.46, whereas the product of similar IV obtained in common industry hydrogenationtechnology had as much trans fatty acid as28.36%. The linear relations among iodine value,melting point and refractive index of hydrogenated soybean oil were established.Kinetic analysis of the hydrogenation of soybean oil in supercritical and subcriticalcarbon dioxide was studied, on the basis of the hydrogenation modeling and Sketchy MethodAlternately proposed by AI Hong-tao. The radio of hydrogenation reaction rate constants oflinolenic, linoleic and oleic was42.9:1.5:1in higher pressure supercritical carbon dioxidecondition,24.5:9.1:1in medium pressure supercritical carbon dioxide condition,14.4:5.7:1in lower pressure subcritical carbon dioxide condition,9.3:2.7:1in pure hydrogencondition,9.1:5.5:1in common industry hydrogenation technology. In supercritical andsubcritical carbon dioxide conditions, the total reaction rate was retarded, while theselectivties of linolenic and linoleic both rised.According to the specified hydrolysis of triglyceride by porcine pancreas lipase and thetheory of1,3-random-2-random Distribution, the hydrogenation reaction rates of unsaturatedfatty acids distributed among different positions of triglyceride in higher pressure supercritical,medium pressure supercritical and lower subcritical conditions were researched. Under the above conditions, the hydrogenation reaction rates of unsaturated fatty acids among Sn-1,3position were higher than those among Sn-2position. As a result, we concluded that thehydrogenation rates of unsaturated fatty acids were different among the different positions oftriglyceride.