Preparation And Properties Of Y-zeolites Their Deep Desulfurization Diesel Fuels

Due to the growth of demand and use of fuel oil, the environmental problems arising from sulfur compounds have drawn great attention from the public. Countries around the world have set stringent standards of sulfur content in fuel oil, and deep desulfurization of fuel oil has become one of the worldwide important issues. Adsorption desulfurization by zeolites is efficient in selectively removing sulfur organic compounds in fuel oil under ambient temperatures and pressures, with high adsorption capacities for thiophene and its derivatives, which are difficult for removal by catalytic hydrodesulfurization. However, the recent researches focuse mostly on adsorption of thiophene and benzothiphene other than dibenzothiophene, which is widely accepted as the most difficult to remove due to steric hindrance. Therefore, the objective of this research is to investigate selectively desulfurization over cation-exchanged Y zeolotes with dibenzothiophene as the adsorption target, and improve their desulfurization capacities by optimizing the preparation and adsorption conditions.NiY zeolites were selected for high sulfur adsorption capacities and their properties and desulfurization performance were systematically studied. The results showed that the BET surface area was 585 m2/g and average pore diameter was 0.89 nm, which is larger than the dynamical molecular diameter of DBT (0.8 nm) and conductive to DBT adsorption. The strong adsorption was the result of theπ-complexation between Ni2+ and dibenzothiophene. The optimal conditions for preparing NiY zeolite were the concentration of Ni(NO3)2 solution 0.1mol/L, the ion exchange temperature 95℃and the activation temperature 450℃. The decrease of adsorption temperature and increase of adsorption dose enhanced the sulfur removal of NiY. Co-existing aromatics decreased the sulfur removal due to its competitive adsorption. The adsorption isotherm at 25℃was well fitted by the Freundlich equation and Langmuir-Freundlich (L-F) equation.In order to decrease the effects of co-existing aromatics on NiY zeolites, Ce4+ was loaded on NiY zeolites to produce NiCeY zeolites. Their properties and desulfurization performance were studied. The results showed that the BET surface area was 568 m2/g and average pore diameter was 0.88 nm, which is conductive to DBT adsorption as well. The higher adsorption capacity in the presence of toluene was due to the synergistic effects of theπ-complexation between Ni2+ and DBT, and S-M bond between Ce4+ and DBT, indicating that NiCeY zeolites is a more pratical adsorbents. The optimal conditions for preparing NiCeY zeolites were the concentration of Ni(NO3)2 and Ce(NO3)3 solution 0.1mol/L and Ni2+ was loaded before Ce3+. The increase of adsorption dose and decrease of adsorption temperature enhanced the sulfur removal. Langmuir-Freundlich equation adjuseted best for the adsorption isotherm of NiCeY zeolite at 25℃, and so did Freundlich at 50℃.