The Study Of Soybean Oil Epoxidated By Heterogeneous Catalyst

Epoxidation of double bonds is one of important chemical modification methods to expand industrial application of vegetable oil. By now, epoxidized vegetable oil and their derivatives such as fatty acid methyl esters have been commercially used as non-toxic, environmental friendly plasticizers and stabilizers in chlorine-containing polymer, as additives in lubricants, or as components in thermosetting resins.To develop green, economical technological process of epoxidation, the research in last decade focused on synthesizing new catalysts to allow hydrogen peroxide as oxidants. Among these catalysts, phosphotungstic acids have a high catalytic efficiency and are easily synthesized with low cost for the epoxidation of double bonds. Several reports about epoxidation of vegetable oil catalyzed by phosphotungstic acids have been published. Although the conversion of double bonds was satisfied, separation and recovery of phosphotungstic acids after epoxidation reaction were difficult and tedious. For multi-phase epoxidation of vegetable oil system, the key problem is to reduce the mass transfer resistence and the recycling problem of catalyst. To overcome the above disadvantage, immobilization of phosphotungstic acids is essential for industrial application.Halloysite nanotubes (HNTs) is a two-layered aluminosilicate clay mineral, having a hollow and open-ended tubular structure, measuring typically 0.5μm～2μm long, 20nm-30nm inner diameter and 15nm-20nm shell thichness. The typical hollow and open-ended tabular structure makes halloysite nanotubes to be a petentially good catalyst supporter.Halloysite nanotubes were selected as catalyst carrier and and a heterogeneous catalyst had been successfully prepared by immobilizing phosphotungstic acids through ion exchange with quaternary ammonium anchored onto the surface of halloysite nanotubes in this paper. Prior to immobilization, silylation and quaternary ammonation of HNTs were conducted in order to introduce quantitively the grafting function groups, providing a platform for immobilizng the active centre of phosphotungstic acids by ion exchange method. At last, the prepared catalysts were evaluated by catalyzing the epoxidation of double bonds of soybean oils. The effects of additional ligands, way of stirring and adding methods of hydrogen peroxide were studied. The results show that:phosphotungstic acids was loaded in the molecular state on the halloysite nanotubes, the combination of mechanical stirring and ultrasonication was helpful to accelerate the mass transfer of the reacting agents, additional ligand and batch by batch feeding of hydrogen peroxide all contributed to the epoxidation of double bonds. The heterogeneous catalyst can be reused three times and regenerated by a simple activate methods.