| More restrictive regulations are implemented on sulfur content in transportation fuels due to the environment problems.Therefore,the National V standard of gasoline will be implemented in all the country,with sulfur content no more than 10 ?g/g,so clean gasoline production has become an inevitable trend.In addition,a majority of the commodity gasoline is FCC gasoline.Deep desulfurization of FCC gasoline must be realized.In recent years,selective adsorption desulfurization has become a focus with a high selectivity,small loss of octane.One of the cores of this technology is the preparation of adsorbents,requiring high selectivity for thiophene,and high sulfur capacity.Therefore,removal of sulfur compounds in FCC gasoline by selective adsorption desulfurization was researched in this thesis.The sorbents were developed using Y zeolite modified by an active metal.Moreover,adsorptive desulfurization performance was investigated,meanwhile,the effects of olefins or aromatics on thiophene removal was studied.The propertites of sorbents were characterized,such as XRD,BET,SEM,IR,etc.Adsorbents were evaluated on a small fixed bed desulfurization device,and competitive adsorption mechanisms of olefins and aromatics were studied by In Situ FT-IR.By selecting different loaded metals,metal loading methods and loading content,a series of adsorbents were evaluated by selective adsorption desulfurization in a fixed bed.The results showed that Ni IE performed better in desulfurization among all the sorbents prepared by ion exchange,and per unit of Ni IE can deal with 30 m L of clean gasoline;NiY sorbents performed better in desulfurization among all the sorbents prepared by the incipitent wet impregnation,and per unit of NiY can deal with 28 m L of clean gasoline.Morever,it can be found that Ni20 displayed better desulfurization performance in Ni loadings study,and per unit of Ni20 can deal with the largest volume of clean gasoline.In order to increase the sulfur content of gasoline and selectivity of thiophene on NiY,NiY adsorbents further modified by loading K or La,as well as precious metal Pd,were evaluated by adsorption desulfurization in the fixed bed reactor,and examined the effects of olefins and aromatics on thiophene adsorption.The results were as follows: firstly,for M-I,only containing thiophene and cyclohexane,HY exerted a high adsorption desulfurization rate.Because competitive adsorption did not exist in M-I,the larger surface area and pore volume of HY provided a great advantage for adsorption desulfurization.Morever,thiophene was adsorbed on HY by ? complexation and protonated reaction occurred on the center of B acid.Therefore,adsorption desulfurization rate of HY was 97 %.The adsoption modes of thiophene on NiY were S-M and ? complexations.Especially S-M complexation improved the selectivity of thiophene.Only the Ni Pd Y adsorbent can improve the selectivity of thiophene greatly.Secondly,compared with HY,adsorption desulfurization rate of NiY improved 15.2% in the olefin-containing M-II,indicating that the selectivity of thiophene was improved on NiY.Furthermore,compared with NiY,the adsorption desulfurization rates of KNiY,LaNiY and Ni Pd Y further improved by 26.0,13.8,and 30.6 % respectively,indicating that K,La and Pd additives improved the selectivity of thiophene in olefins,and Pd performed the best.Because protonated reaction of 1-hexene occurred on the center of B acid,which inhibited thiophene adsorption.The introduction of K?La or Pd decreased the amount of B acid sites,which promoted thiophene adsorption.Thirdly,the desulfurization rate of HY was only 21.8 % in the aromatic-containing M-III,while the desulfurization rate of NiY was up to 73.1 %.The introduction of K decreased the amount of B acid sites and increased the amount of L acid sites,so the protonated reaction of thiophene was weakened and increased complexation adsorption of thiophene.The introduction of La decreased the amount of L acid sites,and the surface area and pore volume decreased,which weakened complexation adsorption of thiophene.However,the desulfurization rate of Ni Pd Y further improved by 19.0 % compared with NiY,indicating that the introduction of Pd can further improve the thiophene selectivity in olefins or aromatics.Because Pd had a certain adsorption activity towards sulfide itself,and the amount of B acid was reducd and the amount of L acid was increased by introduction of Pd,which all promoted the thiophene adsorption.In conclusion,the acid properties of the adsorbents,the modes of complexation adsorption(? and S-M),pore structure and surface structure of adsorbents can affect the selectivity of thiophene and sulfur adsorption capacity. |
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