Studied On Synthesis And Adsorption Desulfurization Performance Of Hierarchically Porous ZSM-5 Zeolites

The aim of this work is to develop highly efficient adsorbents for adsorption desulfurization. Thus, three hierarchically porous ZSM-5 molecular sieves used as adsorbent supports were synthesized in this thesis. To meet the need of low-sulfur fuel oil and the demand of environmental protection, the adsorption desulfurizatopn performances of the adsorbents for dibenzothiophene(DBT) were evalued.Based on the previous work of the lab, microporous ZSM-5 was synthesized by a hydrothermal method using silicasol, Na Al O2 and tetrapropyl ammonium bromide(TPABr) as silica, alumina source and template respectively. By controlling the crystallization time, ZSM-5 nanocrystal clusters were prepared. Further, hierarchically porous ZSM-5/MCM-41(ZMC) and ZSM-5/SBA-15(ZS) composite molecular sieves were synthesized by using the nanocrystal clusters as precursors and using hexadecyl trimethyl ammonium bromide(CTAB) and tri-block copolymer PEO20-PPO70-PEO20(P123) as a template, respectively. And, p H values, the crystallization temperature, and the ratio of template to silica were invesitigated. In addition, nanocrystal-sheet mesoporous ZSM-5(NCMZ) was synthesized by a one-pot method and using C18-6-6N2Br2 as a template. The sample synthesis factors, including the precursor crystallization temperature, the ratio of template to silica, template types and crystallization methods were investigated.Furthermore, the samples were characterized with several methods including X-ray diffraction(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM), fourier transform infrared spectroscopy(FTIR), pyridine adsorption fourier-transform infrared(Py-FTIR) and N2 physical adsorption/desorption. The results agreed that the hierarchically porous ZSM-5 possessed more excellent properties for specific surface areas and pore structures than a traditional microporous ZSM-5. They have stronger acidity and more proper acid types compared to mesoporous molecular sieves. Meanwhile, the synthetic samples including ZMC and ZS were proved to be the micro-mesopore composite molecular sieves instead of mechanical mixtures, while the mesopores of NCMZ built up with some similar nanocrystal sheets.In this work, desulfurization adsorbents with different contents of active metal nickel were prepared by a solid-state ion exchange method. And, the performances of the adsorbents were evalued by a fixed-bed dynamic adsorption equipment. The mixture of DBT and cyclohexane were used as a model fuel oil. The evaluation results exhibited that the desulfurization performances of Ni/NCMZ(Ni N) had an obvious advantage over those of Ni/ZSM-5(Ni Z), Ni/ZMC(Ni ZMC) and Ni/ZS(Ni ZS). Moreover, the optimum supported Ni O content was 10%, the breakthrough adsorption capacity of sulfur was 0.274 mmol·g-1 and the saturated adsorption capacity of sulfur was 0.528 mmol·g-1. The good result may be ascribed to the high specific surface area(434.4 m2·g-1), large pore size(3.99 nm) and proper acidity of the material.