Two-Step Selective Bromination of Thiophenic Compounds for Gasoline Desulfurization Under Mild Conditions

The removal of trace amount of refractory thiophenic compounds from fuels has raised intense concern globally. The development of less energy-intensified desulfurization process is under great demand. In this work, we proposed a new approach of two-step selective bromination of thiophenic compounds for gasoline desulfurization under mild conditions. The Ag modified MoO₃ nanorods (AMO) were synthesized and characterized by XRD, HRTEM and N₂ adsorption, and evaluated in selective bromination of thiophenic compounds. Results showed that (a) thiophenic compounds in model gasoline can be selectively brominated over AMO catalyst with the addition of Br₂, and their bromination production can be removed selectively by followed-up extraction. (b) At the optimized Ag loading of 10%, the apparent rate constants for T and BT reached as high as 95.8h^-1 and 142.7h^-1, respectively under ambient conditions, much higher than those cases in oxidative desulfurization, adsorptive desulfurization, etc. Product analyses showed that the portion of dibromo-thiophenes increased dramatically with increasing loading of Ag, due likely to the formation of MoAg₂O₄. (c) The bromination selectivity of thiophenic compounds reached four orders of magnitude than those of aromatic compounds in fuel. Meanwhile, the competition from olefins can be strategically suppressed by HBr pretreatment. (d) With the integration of the 2^nd-step of extraction, desulfurization capacity of thiophenes reached as high as 30 mg-S/g-cat, while the integrated system showed excellent bromination desulfurization capacity of thiophene at ~260 mg-S/g-cat under high fuel-to-catalyst mass ratio of 5000. The adsorption of various bromides over MoAg₂O₄ was simulated to elucidate the desulfurization mechanism. The fast kinetics, high desulfurization capacity and selectivity of the proposed two-step approach under mild conditions make it promising for gasoline desulfurization.

Keywords: desulfurization, gasoline, selectivity, Ag modified MoO₃