Preparation Of Hierarchical Molecular Sieves For Deep Desulfurization Of Gasoline

Selective adsorption is a new approach for deep desulfurization to remove organic sulfurcompounds from liquid fuels. The process could be operated at ambient temperature andatmosphere, without using H₂, which is very effective for ultra-deep desulfurization of liquidfuels. The key issue for the commercialization of deep desulfurization by adsorption is todevelop new adsorbents with higher sulfur capacity, higher sulfur selectivity and stability.According to the unique advantage character of the larger cavity of the hierarchical molecularsieves combining the good ion-exchange and ordered mesoporous sieves, the topic commitsto the preparation of the composite molecular sieves and applies them to the deepdesulfurization of liquid fuels. In this paper, two kinds of composite molecular sieves wereprepared and used in the adsorption desulfurization of the model gasoline.MSU-S series materials Al-MSU-S and MSU/Beta were self-assembled synthesizedusing nanaoclustered Y zeolite orβzeolite seeds templated by CTAB or TEAOH,respectively, then were exchanged by Ag⁺. The characterizations of XRD, FT-IR, TEM andN₂ adsorption confirm that the adsorbents are pure mesoporous composite molecular sieves.The adsorbents were used in deep desulfurization of model gasoline. Thiophene or DBT wasdiluted in sulfur-free n-octane with sulfur concentrations both being 600 ppm (0.06% byweight) and used as model gasoline. All the samples collected during experiments wereanalyzed with a GC-7890â…¡gas chromatograph. The results show that (1) the sulfur capacityincreases with the increasing Al contents incorporated in the silicate framework and Ag⁺exchange can effectively improve the desulfurization performance; (2) at thiophene modelgasoline system, for per gram Ag⁺/20%Al-MSU-S having better adsorption effect, the processis capable of processing 5 cm³ of sulfur-free model gasoline; (3) at DBT model gasolinesystem, for per gram Ag⁺/20%Al-MSU-S and Ag⁺/MSU/Beta, the process can get 20 cm³ and12 cm³ of sulfur-free model gasoline, respectively.MCM-41/Y and ZMC/ZSM-5 were synthesized by using Y zeolite and HZSM-5 zeoliteas silica seed, respectively. After exchanged by Ag⁺, the adsorbents were characterized andanalyzed by XRD, FT-IR and confirmed to be composites of microporous and mesoporousmolecular sieves. The results of desulfurization of the model gasoline show that (1) atthiophene model gasoline system, Ag⁺/MCM-41/Y and Ag⁺/ZMC/ZSM-5 process 7 cm³ and 5cm³ of sulfur-free model gasoline per gram adsorbent respectively. It is obviously more effective than MCM-41/Y and ZMC/ZSM-5, which almost can not get sulfur-free modelgasoline; (2) at DBT model gasoline system, per gram Ag⁺/MCM-41/Y can get 25 cm³ ofsulfur-free model gasoline, however, Ag⁺/ZMC/ZSM-5 with small aperture size, almost cannot get sulfur-free model gasoline.From the experiment results above, we can see that desulfurization of adsorbents is moreeffective for DBT than thiophene, and follow the molecular size selective mechanism andÏ€-complexation adsorption mechanism. The adsorbents can be regenerated through simplycalcination in air at 350℃, and the adsorbent 20%Al-MSU-S did not lose sulfur adsorptioncapacity after regenerated for six times, indicating the better adsorption and regenerationperformance of the adsorbents for deep desulfurization of transportation fuels.