A Study on Photocatalytic Oxidative Desulfurization of Diesel

Abstract

The supply of environmentally friendly petroleum products has extreme importance in ensuring a reliable healthy climate globally. The elimination of obstinate sulfur complexes is an enormous task in the current challenging legislative situation for fuel refining companies. The thesis is dedicated to the experimental investigation of various photocatalysts such as LaVO4, V2O5, etc. for the removal of sulfur from hydrocarbons. The as-synthesized photocatalysts were characterized by several techniques, including SEM, FTIR, UV-Vis DRS, Raman, PL, STEM, and N2 physisorption analyses, etc. Herein, the mesoporous LaVO4 was synthesized hydrothermally using a KIT-6-based template etching for deep desulfurization. The synthesized material offered a large surface area and enlarged pore size with a narrow bandgap (2.05 eV) and reduced particle size with a dominant monoclinic phase of LaVO4, making it suitable for capturing more light photons, offering plentiful active sites, and reducing electron-hole recombination rate compared with standard techniques; this results in an enhanced visible-light-driven APODS performance. The optimum parameters such as reaction temperature, solution pH, oxygen flow rate, solvent/oil ratio, catalyst dosage, and agitation rate for APODS were determined to be 20 oC, pH 4, 100 mL/min, 1:5 (v/v), 3 g/L, and 750 rpm, respectively. The mesoporous LaVO4 was tested on commercial diesel fuel containing 410 ppm sulfur over a visible-light irradiation period of three hours, exhibiting excellent performance in desulfurizing diesel up to 88.17%, which was more than twice that of conventional LaVO4. Similarly, the pure LaVO4 photocatalyst was prepared using the hydrothermal approach and employed for deep oxidative desulfurization application in the aerobic environment under visible-light irradiations. The photocatalytic material was employed for the removal of sulfur from different petroleum refinery diesel pool streams including hydrodesulfurization unit diesel rundown, mild hydrocracking unit rundown gas oil, heavy kerosene oil, and the ultimate diesel oil blend, containing organosulfur compounds ranging from disulfides to the stringent organosulfur compounds, with the quantity lying between 57 to 863 ppm. Likewise, the V2O5 microspheres were synthesized by hydrothermal approach for investigating the potential of the photocatalytic oxidation technology for the deep desulfurization of diesel oil blend (DOB) and straight-run diesel (SRD). The desulfurization investigation revealed that the proposed technology is significant in the desulfurization of the diesel oil blend, but is restricted for the photocatalytic application for the desulfurization of straight-run diesel. Moreover, the effect of using various polar solvents was investigated revealing that the 2-ethoxyethanol is the best solvent for the photocatalytic oxidative desulfurization reaction. In this study, the kinetic study demonstrated a good fit with the pseudo-first-order kinetic reaction model, and the possible reaction mechanism was suggested. The developed photocatalytic materials also exhibited excellent regeneration and recyclability.