Solvent free epoxidation of vernonia oil using Ti-SBA-15 with tailor made particle morphology and pore size

Abstract

[EN] Vernonia galamensis is a native weed of Ethiopia containing high concentration of naturally epoxidized oil (glyceryl trivernolate) in its seeds, which could be used as a potential substitute for currently used epoxy oils. Apart from an epoxy group, vernolic acid contains a double bond that could be further epoxidized yielding a low viscosity, high oxirane, non-edible oil. Epoxidized vegetable oils are usually produced at industrial scale mainly by the peracid process. Soluble mineral acids are essential for this process but these acidic components lead to several drawbacks. Our study deals with a solvent free epoxidation of vernonia oil using heterogeneous catalysts. Ordered mesoporous materials are good candidates as catalysts for epoxidation reactions of large molecules such as vernonia oil (MW =926 g/mol). The aim of this work is to obtain titanium containing SBA-15 catalysts with tunable pore size and convenient particle morphology to avoid diffusion problems. Titanium was incorporated in SBA-15 catalysts by co-condensation as well as grafting methods in order to compare their catalytic performance. Ti-SBA-15 materials with hexagonal symmetry, surface area between 368 and 888 m/g, high pore volume (0.75-1.41 cm/g) and average pore diameter ranging from 7.2 to 14.3 nm have been successfully synthesized. The long fibers commonly observed in SBA-15 could be avoided obtaining small crystals with plate morphology having the channels running along the short axis of the crystal. DR UV-vis and ICP-OES studies revealed that Ti has been successfully incorporated as isolated Ti(IV) species in SBA-15 while maintaining good textural properties. Ti was also incorporated in hydrophobic PMO supports by co-condensation and grafting for comparative purposes. Epoxidation of vernonia oil was carried out using anhydrous TBHP as an oxidant without any organic solvent at 70 °C. Titanium-grafted, large-pore size SBA-15 (TiCgESBAL) yielded 71% conversion with more than 80% selectivity, while short-channel Ti-SBA-15 and Ti-PMO showed the highest selectivity towards epoxide.