Study On Adsorptive Deep Desulfurization Of Gasoline By Oxidation Modified Activated Carbon

Deep desulfurization of transportation fuels is receiving increasing attention among world research community due to more and more stringent regulations for environmental protection. Adsorptive desulfurization is a promising approach for selective removal of sulfur-containing compounds from fuels. Current researches in this field have been concentrated on simply screening of adsorption materials, and the adsorption mechanism studies are weak. In this study, coconut shell activated carbon was modified by oxidation as adsorption materials for liquid adsorptive desulfurization of thiopenic compounds in both model gasoline and FCC gasoline.Firstly, activated carbon was oxidized by ammonium persulfate and ozone. The adsorptive desulfurization performance was evaluated by both static and dynamic adsorption experiments for thiophene-cyclohexane binary solution. Optimum oxidation conditions were determined by criteria of capacity of thiophene adsorption. Results showed that after modification, the equilibrium thiophene adsorption capacity was increased from 8.47 mg/g to 15.52 mg/g and 21.50 mg/g, respectively. Meanwhile, breakthrough thiophene adsorption capacity was increased from 2.03 mg/g to 8.10 mg/g and 14.21 mg/g, respectively. The influence on adsorption by competitive adsorption constituents in gasoline was investigated as well. Results indicated that alkanes had minor influence on adsorption, while aromatics and alkenes exhibited strong competitive adsorption with thiophene. Desulfurization rate decreased distinctively with competitive substances, while the influence of aromatics was more adverse. Porous structure of the activated carbon, which was characterized by N2 adsorption, and the surface chemistry described by Boehm titration and FT-IR were correlated to the adsorption performance. Results implied that the enhancement of thiophene adsorption by modified activated carbon was mainly ascribed to increased surface oxygen containing groups produced by oxidation. Adsorption process of thiophene on activated carbons both before and after modification was studied comparatively. The adsorption data can be fitted to the Langmuir isotherm. Thermodynamics investigation showed that the adsorption process is exothermic, entropy-decreasing and spontaneous. The oxidation modification of activated carbon improved their affinity to thiophene molecules. Kinetics study indicated that the adsorption rate of thiophene on activated carbon can be described as a pseudo-second order rate equation. Intro-particle diffusion was the control step of adsorption, which also was influenced by inter-particle diffusion.The ozonation is comparatively more preferable for activated carbon in FCC gasoline desulfurization. Under optimized adsorption and regeneration conditions, the initial effluent in dynamic adsorptive desulfurization of FCC gasoline with sulfur concentration of 796μg/g can be reduced to 18μg/g. After the saturated activated carbon was regenerated with ethanol and recycled for 3 times, the initial effluent concentration was still as low as 45μg/g.