Preparation And Property Of CeO₂ Or Ag Modified Activated Carbon And Their Performance On Desulfurization Of Fuel

Sulfur compounds in fuels have caused serious envirmental problems, and domestic department has published stringent standard to limit the sulfur content in fuels. According to the latest fuel standard of China, National V fuel standard, the sulfur content in fuel is limited below 10 ppm?mg/kg?. Conventional hydrodesulfurization?HDS? is not economically reasonable and expends vast amount of resourse to meet the standard while the quality of fuel decreases when more sulfur compounds are removed by HDS. Thus, it is necessary to develop new methods to remove sulfur compounds in fuels. Adsorption desulfurization is supported as a promising method for its mild operation conditions and excellent desulfurization capacity and has got great attention from researchers.In this thesis, series adsorbents of silver or cerium loaded on activated carbon were prepared by ultrosound assisted impregnation method. The optimum preparation conditions were investigated. Static and dynamic experiments were carried out to investigate the desulfurization performance of adsorbents. The isothermals, kinetics and thermodynamics of adsorption desulfurization process were explored as well. Conclusions were as follows:?1? CeO₂/AC with a Ce content of 1% and calcinaed at 500 ? had the best desulfurization performance compared with other candidates in this thesis and had the sulfur capacity of 0.82 mmol/g. The ultime sulfur capacity of Ag/AC?3 wt%, calcinaed at 450?? reached 0.78 mmol/g comparied with other candidates in this work. The sulfur capacities of CeO₂/AC and Ag/AC recovered 85% of fresh adsorbent sulfur capacity after using 5 times. Through competitive adsorption of aromatic hydrocarbon, the sulfur capacities of CeO₂/AC and Ag/AC decreased apparently at the present of 20% benzene or methylbenzene in model fuel. CeO₂/AC performanced better than Ag/AC for competitive adsorption.?2? The adsorption isotherm curves of CeO₂/AC and Ag/AC in the desulfurization process were belong to the second type of L style summarised by Giles. Experimental datas could well fitted by the Langmuir, Freundlich and Temkin isothermal equations, while the realtionship between coverage rate and heat of adsorption showed that Langmuir isothermal equation was not suitalbe to describe the isothermals in this thesis. The heat of adsorption values showed that CeO₂/AC adsorption desulfurization process was exothermal when the coverage rate was low, and turned to be endothermal when the coverage rate was higher. Ag/AC adsorption desulfurization was an endothermal process within the coverage rate range in this thesis. The larger heat of adsorption value of CeO₂/AC than Ag/AC under zero coverage rate indicated that sulfur compounds had a higher affinity with CeO₂/AC than Ag/AC.?3? Entropy change values of adsorption desulfurization process showed that degree of freedom of CeO₂/AC desulfurization process decreased under low coverage level and increased when the coverage was higher. While degree of freedom of Ag/AC desulfurization process increased within the coverage range in this thesis. The positive values of Gibbs free energy change of CeO₂/AC and Ag/AC desulfurization indicated that adsorption desulfurization processes in this thesis were non-spontaneous and chemical adsorption happened.?4? Kinetics studies results indicated that CeO₂/AC and Ag/AC desulfurization processes were pseudo-second order process. Higher desulfurization temperature was conducive to increasing the rate of adsorption. External and internal diffusion of sulfur compound both had the significant effect on desulfurization rate. Higher sulfur content in model fuel was conducive to improving the desulfurization rate but the effect of film diffusion on desulfurization process was increased as well.