The Study Of Reducing The Content Of Trans Acid Of The Hydrogenation Process

With the increasing requirement of food quality and safety, trans fatty acids inhydrogenated products are hold attention by more and more people. There were somedrawbacks for nickel and copper catalysts used in the traditional industrial production. Thenickel catalyst caused carcinogenicity; and copper catalysts produced large amounts of transfatty acids, which increased incidence of heart disease and diabetes. In the paper, trans fattyacids content of hydrogenated vegetable oil was investigated using GC. The factors that affectthe trans fatty acids content of hydrogenation products were evaluated. Two kinds ofpalladium catalysts were prepared, which were used to hydrogenate sunflower oil. The effectof hdrogenation conditions on trans fatty acids content were also studied. The reuse ofcatalyst, catalyst characterization,catalytic activity of catalysts and trans acid content in thedifferent oils were also investigated.The optimum preparation conditions of the Pd/SiO₂catalyst were as follows: reductiontime4h, the impregnating solution pH11, impregnation time4h. Under the followingconditions: hydrogenation temperature100℃, hydrogen pressure0.15MPa,25g sunflower oil,and0.5gPd/SiO₂, the trans fatty acids content of hydrogenated product was32.16%（iodinevalue75）.The optimal preparation conditions of supported Pd/Al2O3catalyst were as follows:impregnating solution pH1,8h of soaking time, restore time9h, restore temperature of60℃,not roasting and direct restoring. Under the following conditions: hydrogenation temperatureof100℃, hydrogen pressure of0.15MPa,25g sunflower oil, and1.5gPd/Al2O3, the trans fattyacids content of hydrogenated product was27.66%（iodine value75）.The reuse of the Pd/Al2O3catalyst was studied, and the results showed that iodine valueof the hydrogenated products increased at the9th time, and catalyst activity was reduced.Trans fatty acids decreased gradually with the increase of reuse for about13%. TEM resultsof the catalyst prepared showed that: smaller crystalline grain and intensive distribution ofpalladium on the support carriers silica; larger crystalline grain and good dispersion ofpalladium on the support carriers alumina.Compared the above two catalysts in the catalyst activity, trans fatty acids content, aftertreatment of products, Pd/Al2O3was selected for studing the effect of hydrogenation conditions （reaction time, pressure, catalyst amount, temperature） on the trans fatty acidscontent of the hydrogenation sunflower oil. By optimizing the hydrogenation parameters,combined with the actual production requirements, the best conditions of low trans fatty acidhydrogenation were obtained: reaction temperature of52℃, the reaction pressure of1.87MPa,the amount of catalyst was2.97g. Under the above conditions, the trans fatty acid content ofthe hydrogenation sunflower oil was12.01%. The hydrogenation of the palladium catalyst inthe different oils showed that: various fatty acid content of raw oils have different effects oncatalytic activity and trans fatty acids content.