Oxidative desulfurization of tire pyrolysis oil over molybdenum heteropolyacid supported mesoporous catalysts

Abstract

Pyrolytic oil derived from waste tires consists of high sulfur content in the range of 7000–9000 ppm. To use as transportation fuels, its sulfur content needs to be lowered to 10–15 ppm. Though conventional hydrodesulfurization is suitable for sulfur removal in tire pyrolytic oil, its high cost provides the avenue for alternative desulfurization technologies to be explored. In this study, oxidative desulfurization, a low-cost technology was explored for desulfurization of tire pyrolytic oil at mild process conditions. Two categories of Ti-incorporated mesoporous supports with 20 wt.% loaded heteropoly molybdic acid catalysts (HPMo/Ti-Al2O3 and HPMo/Ti-TUD-1) were developed and tested for oxidative desulfurization of tire pyrolytic oil. Catalysts were characterized by X-ray diffraction, BET-N2 physisorption, and X-ray photoelectron spectroscopy. The surface acidity of catalysts was studied by temperature-programmed desorption of NH3 and pyridine FTIR analyses. The presence of titanium in catalysts was found to promote the ODS activity of phosphomolybdic acid. Ti-TUD-1 supported catalysts performed better than Ti-Al2O3 supported catalysts as the former retains its keggin structure from phosphomolybdic acid. Hydrogen peroxide and cumene peroxide were found to be better oxidants than tert-butyl hydroperoxide for ODS of tire pyrolytic oil. Process parameter optimization study along with the catalyst regeneration study was carried out with phosphomolybdic acid on Ti-TUD-1 (Ti/Si= 0.025) catalyst, which was found to be most suitable for the ODS process. ANOVA statistical analysis was carried out to elucidate the significance of process parameters. Kinetic study for oxidative desulfurization was confirmed to be a pseudo-first-order reaction over HPMo/Ti-TUD-1 catalyst.