Long-chain bio-olefins production via oxidative dehydrogenation of oleic acid over vanadium oxides/KIT-6 catalysts

Abstract

Long-chain α-olefins (≥ C10) are normally applied in detergents, lubricants, and oil field chemicals. Due to the abundance of palm oil, the derivatives derived from palm oil, such as oleic acid (OA), can be converted to long-chain olefins via oxidative dehydrogenation (ODH) over a series of vanadium oxides (VxOy) incorporated with KIT-6 (nV-KIT-6 catalysts) synthesized by a direct hydrothermal method. Various ammonium metavanadate/tetraethyl orthosilicate molar ratios (V/Si) were evaluated over the range of 0.01–0.09. The results obtained from X-ray diffractometry, hydrogen-temperature programmed reduction, and X-ray photoelectron spectroscopy analyses revealed that the VxOy were mainly in a tetrahedral form when the V/Si molar ratios were lower than 0.05. Above this point, the formation of V2O5 crystallites was observed. The ODH of OA was performed in a continuous flow fixed-bed reactor under atmospheric pressure in the absence of solvent to avoid the interference of by-products generated from solvent oxidation. The results showed that the OA conversion and selectivity towards the desired products strongly depended on the V/Si molar ratio and the reaction temperature. The highest selectivity of olefins (alkenes + dienes) with carbon atoms in the range of C7–17 was 44%. Moreover, the selectivity to aromatics at 24% was observed at a 76% OA conversion level when the ODH was activated using the 0.05 V-KIT-6 catalyst under a 1/1 (v/v) oxygen/nitrogen gas mixture at a flow rate of 100 mL min−1 at 450 °C. Although the high selectivity towards alkenes was promoted by a higher dispersion of VxOy species on the catalyst, overdose of V/Si molar ratios produced more oxygenate compounds. The reaction mechanism for the ODH of OA was likely to be decarboxylation and decarbonylation followed by dehydration. The 0.05 V-KIT-6 catalyst also exhibited reusability over two cycles.