Study On The Epoxidation Of Vegetable Oils With Different Degrees Of Unsaturation

Epoxidation of vegetable oils or fatty acid methyl esters produce important monomers which are widely used as plasticizers or stabilizers in the polymer industry. However, little attention has been focused on the influence of the alkenyl structure of the fatty acid on the efficiency and selectivity of their epoxidation reactions. In addition, a new method of epoxidation of vegetable oils have still been the research hotspot for chemists.Therefor, the influence of the alkenyl structure(the number of double bonds or degrees of unsaturation) of fatty acids on their epoxidation reaction has been investigated in this study. Three fatty acid methyl esters with 1 to 3 double bonds as the model compounds were epoxidized by peroxycarboxylic acid formed in situ with both a weak(formic acid) and a strong(sulfuric acid/acetic acid) acid system. It was found that fatty acid methyl esters with more double bonds have higher reactivities toward the epoxidation reaction. In addition, the electron-donating effect of the double bonds on the fatty acid chain tends to stabilize the resulting epoxide adjacent to it with the weak acid system. However, fatty acid methyl esters with more double bonds easily underwent side reactions with the strong acid system. Epoxidation of two vegetable oils with different degrees of unsaturation were also carried out with the same two acid catalyst systems. And the results were in agreement with those from the fatty acid methyl esters of degrees of unsaturation. The current findings could provide useful guidance for the epoxidation of different vegetable oils with different alkenyl structure compositions.Moreover, a heterogeneous mesoporous molecular sieve supported peroxycarboxylic acid oxidant, 2-percarboxyethyl silica, was successfully prepared in this study and used for the epoxidation of fatty acid methyl esters and vegetable oils. Four oxidants were prepared at different conditions, including the ratio and the adding order of the raw materials to investigate the effect of preparing conditions on the structure and reactivity of the oxidant. The oxidants were characterized by XRD, SEM, TEM and 13 C CP/MAS NMR. Among these oxidants, C-SiO2@(CH2)2COOOH(TEOS: CTES=2:1, added together) had the higher surface area, larger pore volume and higher peroxide value than other three oxidants. It also exhibited the highest activity for the epoxidation reactions. For methyl linoleate, 92.76% yield of epoxidized product was obtained at room temperature. Other unsaturated fatty acid methyl esters with 1 and 3 double bonds were also efficiently converted to their epoxides, their yield of epoxidized product were 85.7% and 84.1%, respectively. The oxidant was also successfully applied to the epoxidation of vegetable oil, olive oil and linseed oil, that have different degrees of unsaturation with high product yields at room temperature. Finally, the used oxidant was regenerated through a simple oxidation process with H2O2 and recycled for at least 5 times without much drop in the reactivity.