Preparation And Evaluation Of Sorbents For Deep Desulfurization Of Diesel Fuels By Liquid Adsorption

Today the clean diesel oil instead of gasoline used as the primary transportation fuels has become a trend due to energy shortage and environmental pollution. Expanding use of diesel depends greatly on the deep desulfurization technology and the deep desulfurization of diesel fuels by liquid adsorption which possessing the advantages of simple equipments, mild operation conditions and lower cost becomes an active research field. As the basis research for the industrialization of adsorptive desulfurization, this paper focused on the study of the preparation, evaluation and regeneration of the desulfurization adsorbents.Based on the review of the references, the adsorbents were prepared considering two aspects: the different kinds of active metals and the supports with various diameters, and the mechanisms of desulfurization were studied accordingly. A series of adsorbents were prepared by ion exchange methods and solution impregnation methods. Ni, Re, Ce were used as the active metal component and Na-Y zeolite, 13X zeolite and ZSM-5 zeolite as the support respectively. The metal content of the adsorbents were analyzed by the Energy Dispersive Analysis by X-ray (EDAX). A micro- and mesoporous composite material Y/MCM-41 was synthesized in laboratory, structure of which was characterized by the X-ray Diffraction pattern (XRD) and the N₂ Adsorption-Desorption Isotherm. The BET surface area was 909m²/g and average micro- and mesopore pore size of that material were 0.98nm and 2.91 nm respectively.Static adsorptive desulfurization method was referred to evaluate the adsorption properties. The Ni-Y adsorbent with the nickel ion exchange ratio of 67.5% was tested to be the best. The equilibrium adsorption capacity of Ni-Y was calculated to be 17.16mgS/g (sorbent) with the model diesel containing 840ppmw sulfur and with a fuel/adsorbent ratio of 20. The Nickel supported on the adsorbent by ion exchange method behaved obviously more active than that by the solution impregnation one. The desulfurization capacity of the adsorbents had the same trend with the nickel ion exchange ratio. Experiment results also indicated that the dibenzothiophen in the model diesel was preferentially adsorbed than benzothiophene, agreeing well with the Ï€-complexation mechanism.According to the pore size selection mechanism, the adsorption capacity was significantly affected by the aperture of supports. Detailed study of the pore size showed that Na-Y zeolite with pore size of lnm performed the best in sulfur adsorption capacity comparing with the ZSM-5 zeolite with 0.53nm and the mesoporous composite materials with 3nm in pore size.The adsorption capacity of the selected Ni-Y adsorbent was further evaluated in a fixed-bed reactor. The results showed that 31.1mL ultra-low-sulfur model diesel (S<5ppmw) was obtained by one gram absorbent from the original model diesel (S≈840ppmw). The saturated sulfur capacity of this adsorbent was calculated to be 33.6 mgS/g (sorbent).The dynamic regeneration of adsorbents was pilot studied by means including calcinations in oxygen, washing with ethanol and sweeping by high temperature vapor. The highest sulfur content was 14.08 mgS/g (sorbent) which was obtained by the third way.This paper was a preparatory research of the preparation of adsorbents for the liquid desulfurization of diesel fuels, the results would provide a basis for further study.