Agricultural waste-based microporous catalysts for oxidative desulfurization of highly sour heavy gas oil

Abstract

In recent years, the use of abundant and low-cost biomaterials such as agricultural wastes in the preparation of activated carbon has been receiving a lot of attention. Besides, the conventional middle and heavy fuel cuts require a substantial and cost-effective sweetening process because sulfur in transportation fuel was found as one of the main causes of air pollution. The present work explored the preparation and characterization of microporous activated carbon (AC) catalysts prepared from olive stone by tubular furnace (Fe/AC1) and microwave (Fe/AC2) heating methods using H3PO4 (85 wt%) as chemical activating agents. The kinetics of the oxidative desulfurization process (ODS) of a highly sour diesel fuel (sulfur content = 7361 ppm) was determined. The effect of the heating method on the texture and morphological structure, surface area, and surface chemistry of the carbons produced was investigated. Fe/AC1 was prepared in a horizontal tabular furnace at 650 °C calcination temperature and 90 min residence time under a nitrogen atmosphere, while Fe/AC2 was performed in a microwave reactor with 565 W and 7 min microwave power and irradiation time respectively. The catalysts were characterized by N2- adsorption-desorption, SEM-EDX, FTIR, XRD, XRF, TGA, PSD, and elemental analysis. It was found that the use of a tubular furnace for heating the olive seeds resulted in a higher surface area and yield. Also, the characterizations of the Fe/AC1 catalyst showed that it has a large surface area of 1175 m2/g and micropore volume of 0.6954 cm3/g whereas Fe/AC2 had a surface area of 854 m2/g and micropore volume of 0.6936 cm3/g. Moreover, SEM-EDX results indicated that Fe/AC1 was dispersed uniformly better than Fe/AC2. Also, TGA/DTA results revealed better results for Fe/AC1 than Fe/AC2 making it favorable in ODS experiments. The difference in texture and chemical properties is caused by the heating methods. The desulfurization removal was investigated under different temperatures (80, 90, 100, 110 °C) and reaction time (30–90 min). The kinetics of the ODS were conducted over the efficient Fe/AC1 catalyst prepared. It was shown that the ODS reaction followed pseudo-first-order kinetics with a fairly low activation energy over the catalyst was 40.71 kJ/mol.