The Study On The Adsorbent Of FCC Gasoline Reactive Adsorption Desulfurization By S-Zorb Process

FCC gasoline, accounting for more than 80% of commercial gasoline in China, contains very high levels of sulfur compounds. More than 90% of sulfur compounds in commercial gasoline come from FCC gasoline. The removal of sulfur compounds traditional by hydrodesulfurization (HDS) techniques will inevitably result in the saturation of many olefins and cause serious octane number lost. Therefore, the application of the traditional HDS techniques in producing ultra-low sulfur containing gasoline is limited. Reactive adsoption desulfurization (RADS) is effective for deep desulfurization because it combines the advantages of the catalytic HDS and adsorption. S-Zorb process for desulfurization follows the mechanism of reactive adsorption and it is a novel green process with extensive development space and application prospects. Adsorbents play a vital role in S-Zorb process. In this paper, Ni-ZnO based adsorbent were chosen as main research basement and model fuel was chosen as treatment object to explore the performance of adsorbents with different types of supports and active components on RADS using a lab fixed bed continuous flow reactor. The adsorbents were characterized by BET, XRD, H2-TPR, TG-DTA and FT-IR in order to find out the influence of specific types of surface chemistry and structural characteristics on the sulfur adsorptive capacity. The regeneration property and stability and the adsorption Mechanism have been studied. The main and important results are described as follows:The model fuel(thiophene-n-octane) was chosen as treatment object and ZnNi/diatomite-Al2O3 adsorbents were prepared by kneading method. According to the activity measurement results, the optimal composition for ZnNi/diatomite -Al2O3 was diatomite:Al2O3=25%:25%, Zn/Ni molar ratio=0.4.The optimal preparation condition for the adsorbent was Tcalcination =600℃, tcalcination=1h. The optimal reduction condition for the adsorbent was LH2=30ml/min, Treduction=370℃, Preduction=0.5MPa. The optimal reaction condition for the adsorbent was Treaction=400℃, Preaction=1 MPa,H2/oil=400. Under these conditions, the adsorptive capacity of ZnNi/diatomite-Al2O3 adsorbent was about 1.073%.Next, the model fuel(thiophene-n-octane) was chosen as treatment object and Ni-ZnO chosen as active components to explore the performance of adsorbents with different types of supports (caly-Al2O3, zeolites, metal oxides) on RADS. The adsorption results shown that the adsorptive capacity of different support adsorbents is in the following order:NiZn/Ti-Zr> NiZn/Ti> NiZn/Al-clay> NiZn/Al-diatomite. The commercial FCC gasoline contains amounts of olefins. To examine the effect of olefin on the adsorption of thiophene, the adsorptive desulfurization of the model fuel (thiophene -1-octene -n-octane) over the five different support adsorbents at the same reaction conditions was examined. The results showed that the desulfurization rate of the five different support adsorbents samples decreased in various degrees. The adsorptive capacity of NiZn/HY and NiZn/Al-diatomite samples decreased only slightly, while the adsorptive capacity of NiZn/Ti sample decreased extensively(Reduction rate was 30.39%). The olefin saturation rate of NiZn/ HY sample (70.19%)was higher than that of the other four samples, implying that the HY-supported adsorbent will lead to a great loss of octane number for gasoline, while, the olefin saturation rates of NiZnO/diatomite-Al2O3,NiZnO/ZrO2-TiO2和NiZnO/TiO2 were relatively low. On the basis of comprehensive compare, ZrO2-TiO2 was the most suitable support of the adsorbent.The model fuel(thiophene-l-octene-n-octane) was chosen as treatment object. The four Ni/ZnO-based adsorbents with different ZnO precursors of ZnO,2ZnCO3·3Zn(OH)2 (ZN), ZnCl2(ZC) and Zn(NO3)2·6H2O(BZC) were prepared in this study. The RADS performance of the four different ZnO textures was evaluated in the same conditions. According to XRD patterns, the characteristic XRD peaks of ZnO crystalline phase for the modified ZnO precursor adsorbents (NiZnO(BZC)/ZrO2-TiO2, NiZnO(ZC)/ZrO2-TiO2and NiZnO(ZN)/ ZrO2-TiO2) become much boarder than that for the NiZnO/ZrO2-TiO2, implying that Zn(NO3)2·6H2O, ZnCl2 and 2ZnCO3·3Zn(OH)2 as ZnO precursors can significantly improve the dispersion of ZnO on the support surface. In addition, for NiZn/Ti-Zr sample the crystallite phases of TiO2 are attributed to the anatase phase and the rutile phase;however, there are, X-ray diffraction data indicated only the anatase phase of TiO2 at the NiZnO(BZC)/ ZrO2-TiO2, NiZnO(ZC)/ ZrO2-TiO2 and NiZnO(ZN)/ZrO2-TiO2 samples, without detection of rutile phase. This indicates that the addition of 2ZnCO3·3Zn(OH)2, ZnCl2 or Zn(NO3)2·6H2O can inhibit the transformation of anatase to rutile, thus improve the desulfurization activity of the adsorbents. The effect of types of hydrogenated active components(Mo,Co,Ni) was investigated, the results shown that the desulfurization performances of Mo series adsorbents were higher than Co series and Ni series adsorbents, while the olefin saturation rates of Mo series adsorbents were higher than that of Co series and Ni series adsorbents, implying that the Mo series adsorbents will lead to a great loss of octane number for gasoline. The olefin saturation rate of Ni-Co series adsorbents was the lowest. The optimal composition for CoNZnO/ZrO2-TiO2was Co(wt%)=35%, ZnO(wt%)=15%, the adsorptive capacity and the olefin saturation rate of CoNZnO/ZrO2-TiO2 adsorbent were 1.245% and 27.20% separately. The muticycle fixed-bed tests show promise for adsorption desulfurization over the Ni/ZnO-based adsorbents.A two-step regeneration schemes are deemed to be appropriate to return the adsorbent to its original state.The thiophene RADS reaction mechanism was proposed and it was proved to be convenient and accurate. Firstly, S-M adsorbed thiophene in the model fuel is first decomposed on surface Ni of the adsorbent to form Ni3S2 while the C4 hydrocarbon portion of the molecule is released back into the process stream, followed by the reduction of Ni3S2 to form H2S in the presence of H2, and then H2S is rapidly stored in the adsorbent accompanied by the conversion of ZnO into ZnS. The above conclusion can provide practice experiences for the Localization of S-Zorb process adsorptive desulfurization adsorbent.