چكيده به لاتين
The presence of sulfur compounds in transportation fuels has been one of the most important issues in academic and industrial societies. In recent years, investigation of appropriate desulfurization systems has attracted much attention due to universally adopted policies to deal with environmental problems. In this research, oxidative desulfurization and adsorptive desulfurization methods were adopted to remove dibenzothiophene (DBT) from simulated fuel with the aid of zeolite catalysts. First, mesoporous zeolitic catalysts and adsorbents as mordenite, NaP, Faujasite and LTA (pore diameters of 2-5 nm) were hydrothermally synthesized under different synthetic conditions and characterized. In addition, final products were modified with active components Mo, Ce and Ni via impregnation and ion-exchange processes (Mo-MOR,
Ce-Ni/MOR, Ce-Ni/P, Mo-FAU, and Ce/LTA). Then, different desulfurization systems were designed and the effects of various parameters such as reaction time, the amount and type of oxidant (hydrogen peroxide (H2O2) and tert-butyl hydroperoxide (TBHP)), catalyst dosage, initial concentration of sulfur compound, rival N-compound (indole) and S-compound (benzothiophene), and loading percent of active component on ODS efficiency were assessed. Moreover, the catalytic performances of modified mesoporous zeolites were compared to those of unmodified ones and modified microporous zeolites. Desulfurization rate of 71.88 percent was obtained for 50 ppm S, catalyst Mo-MOR and in the presence of TBHP. With increase in the initial concentration of sulfur (300 ppm) and H2O2 existence, yield of 91.33 percent was achieved. In TBHP/Ce-Ni/P ODS system, the yield of 67.86 percent was obtained and as TBHP replacement with H2O2, it improved 10.72 percent and reached 78.58 percent. In the other ODS system (H2O2/Mo-FAU), for 19.03 w% loading of Mo as the optimum amount of active component, 100.00 and 89.83 percent DBT removal were achieved for S-content of 50 and 300 ppm, respectively. The yield of ODS process in H2O2/Ce/LTA system was determined 64.04 percent. Moreover, the synthesized catalyst Ce/LTA demonstrated higher efficiency (50.46 percent) in comparison with Ce-modified commercial microporous zeolite 4A. In general, in the presence of indole, DBT removal efficiency reduced or increased depending on the system. In H2O2/Mo-MOR and H2O2/Mo-FAU ODS systems, elemental analysis of the catalysts separated from oil by hot filtration and partial reduction in the extent of the active component (0.11 and 0.00 w%, respectively) confirmed the structural stability and heterogeneous nature of the catalysts prepared by impregnation method. Regeneration and reusability of the synthesized catalysts were investigated in 5 to 6 sequential desulfurization cycles, too. Drying, washing with solvents and calcination treatments were chosen to activate the used catalysts. These methods showed both positive and negative impacts on the performances of the catalysts in different systems. Pseudo first-order kinetic model was also studied for ODS processes. Assessment of adsorpntive desulfurization systems with zeolites Ce-Ni/MOR, Ce/LTA and Ce-Ni/P did not demonstrat any efficiency in DBT removal from simulated fuels. In confront, zeolites
Mo-MOR and Mo-FAU played a great role in sulfone (as S-contained reaction products) adsorption in addition to their efficient catalytic performances.
