Adsorption Desulfurization Over Modified Y Zeolite

Transition-metal ions are often introduced into NaY zeolites for removing the sulfur compounds from fuels to obtain ultra clean fuels with low energy consumption, easier equipment operation and non-pollution. However, the loaded transition-metal ions were washed away during the adsorptive desulfurization and regeneration of adsorbent. Thus, the stability of the obtained adsorbents was poor. In this dissertation, NaY zeolites modified with NaOH aqueous solution were prepared. The adsorptive desulfurization of simulated diesel oil was employed as a probe reaction. The optimal modified conditions were as followed:0.09 mol/L of NaOH solution,20℃ and 15 h. The sulfur removal reached to 99.9% and 15%, and the adsorption capacity was 1.65 and 0.75 mg benzothiophene/g of the adsorbent in simulated diesel oil and No.0 diesel oil. The results of the SEM, XRD, and N2 adsorption-desorption isotherms analyses showed that mesopores appeared on the surface of the adsorbent. Py-IR and NH3-TPD analyses indicated that the adsorption of benzothiophene occurred on the weak Lewis acid sites on the adsorbent. The adsorptive desulfurization of NaY zeolites modified HCl, H2SO4, phosphoric acid, and citric acid have also been investigated in the same probe reaction. The results showed that both the introduction of mesopores and the increase in the weak Lewis acid sites were responsible for the improvement in the adsorptive desulfurization of NaY zeolites. For the adsorptive desulfurization of simulated diesel oil, the sulfur removal of the modified NaY zeolites maintained above 85% after the eighth cycle of desulfurization, which was better than CeY (5%). Besides, the results showed that the adsorptive desulfurization of NaY zeolites modified with NaOH is better than that modified with citric acid. Again, the adsorptive desulfurization of NaY zeolites modified with organic acid is better than that modified with inorganic acid. Finally, the above-mentioned modification methods were integrated to obtain the better desulfurization rate in No.0 diesel oil (21% and 1.05 mg/g), the NaY zeolites modified with tetramethylammonium hydroxide and CeO2 loading in series.