A Study Of The Effect Of Pore Size Of Zeolite Beta On Desulfurization Performance

In recent years, increasing attention has been focused on the environmental protection. The burning of organic sulfur compounds in fuel oils can lead to severe environmental pollution and the regulated sulfur limits are becoming lower and lower in gasoline. Deep desulfurization of fuel oils therefore is becoming a serious issue. At present, hydrodesulfurization (HDS) processe widely used in industry is not suitable for removing heterocyclic sulfur compounds from gasoline distillation to a deeper level, since HDS processe will result in the saturation of olefins and significant reduction of octane number. Hence, it is necessary to develop non-HDS technology to meet the urgent need for gasoline with low sulfur content.Adsorptive desulfurization is regarded as one of the most promising methods because of the simple operation, no pollution and low cost. Zeolite has been paid more attention in the field of adsorptive desulfurization of fuel oils, due to its stable skeleton structure, abundant pores and exchangeable metal cations. So far, the adsorption modes of the organic sulfur compounds on the adsorbents are regarded as a key factor in the desulfurization performance, and the effect of acid properties on the adsorptive desulfurization is being paid more and more attention. But another factor, the pore size of the absorbent that might play important role in the desulfurization performance due to the diffusion limit and pore-filling effect of adsorbent has not been systematically studied. This dissertation focuses on the effect of pore size of adsorbent on desulfurization performance.The modification of the pore size of zeolite Beta can be achieved by alkaline treatment with NaOH solution. In the model fuels without competitor, zeolite beta with lager pore size displayed evidently enhanced desulfurization performance for the four sulfur compounds. Although the desulfurization abilities of microporous and mesoporous zeolites beta were decreased by the addition of toluene or cyclohexene, a more gentle reduction was observed on the adsorbent with enlarged pore size.Ion-exchanged adsorbent was prepared by liquid-phase ion-exchange method, and the acid properties and the adsorption modes are found to be changed with the introduction of silver or cerium ions. The existence of competitor generally reduce the desulfurization performance, but the introduction of silver or cerium ions to some extent improve the desulfurization selectivities of the adsorbents. These results indicate that the desulfurization performace of adsorbent is co-decided by the pore size of the adsorbent and the adsorption modes of the adsorbates.Beta/MCM-41micro-mesoporous composite materials have been synthesized by using alkali-treated zeolite Beta and hexadecyltrimethylammoniumbromide (CTAB) as silica-alumina source and the template. The micro-mesoporous structure of Beta/MCM-41is maintained after the introduction of silver or cerium ions. Compared with microporous zeolite Beta, Beta/MCM-41with a special micro-mesoporous composite structure showed evidently increased desulfurization capacity, indicating that the pore size of the adsorbents is one of the key factors of the desulfurization capacity.