Reactive Adsorption Of Sulfur Compounds In Gasoline On Ni/ZnO

With the development of enconomy, industry of vehicle developed quikly, airpollution caused by automobile exhaust gas become more seriously. Production ofultra-low-sulfur gasoline was needed in order to solve the problem of pollution causedby automobile exhaust gas. Altough the conventional hydrodesulfurizaiton (HDS)could effectively remove the majority of sulfur-containing compounds, investment offacilitu was high, further more, the large loss of the octane number. Reactiveadsorption of sulfur compounds was the common method for removal of these sulfurcompounds because of its high performance and low operational. Reactive adsorptiondesulfurization had been reported to be a complementary and alternative technique forHDS.The adsorbents were prepared by co-precipition of corresponding nitrates withurea and sodium dodecyl sulfate. Experiments of reactive adsorption desulfurization(RADS) of model gasoline and commercial gasoline over Ni/ZnO adsorbent wascarried out in a fixed bed reactor at hydrogen atmosphere in order to evaluate thedesulfurization performance of the adsorbent for producing ultra-low-sulfur gasoline,further more, the adsorption of thiophene on Ni/ZnO was investigated using densityfunctional theory based slab calculations.The results showed that Ni was the main active site for the adsorbent, asprereduction could improve the desulfurization capability of the adsorbent. Theoptimal adsorptive conditions are673K and1.0MPa, and small LHSV couldimprove the desulfurization ability of Ni/ZnO, under which the sulfur breakthroughloading of the adsorbent (taking10mg/L as the criterion for sulfur breakthrough)would be399mg/g, and the octane number loss of commercial gasoline (with sulfurcontention88mg/L) would be0.4.The alkene has more influence on absorptive desulfurization than aromaticcompounds, but the heats of model compounds on Ni/ZnO were followed the order:3-methylthiophene> toluene>2-methy-2-butylene> thiophene>2,3-dimethyl-1-butylene. The main reactions in reactive adsorption desulfurization(RADS) are the hydrogenation of sulfur compounds and olefins, however,hydrogenation of aromatics is almost non-existent, so aromatics has little effect on the RSDS performance.DFT simulations showed that thiophene was adsorbed over the Ni/ZnO via S-Niinteractions, however, olefins and aromatics were adsorbed via π-complexation. Thedesulfurization mechanism of thiophene over Ni/ZnO adsorbent can be explained by adirect hydrogenolysis of the C-S bond, which results in the formation of NiS andolefins in hydrogen atmosphere. The active Ni in adsorbent is regenerated in situunder the synergistic action of hydrogen and ZnO.XRD analysis showed that NiS and ZnS decreased the reaction activity.Combination of regeneration by heat method and regeneration by reduction methodhas relatively high regeneration performance, and the sulfur capacity of adsorbent canbe recovered by regeneration.