Desulfurization of liquid transportation fuels is currently accomplished by high temperature and high pressure catalytic processes, while desulfurization of natural gas is performed by solvent extraction using amines. These are costly and energy intensive processes. Desulfurization by adsorption would be a simple and low-energy process. It is not being used because of the lack of good sorbents.
A class of pi-complexation sorbents has been discovered in our laboratory that has higher sulfur selectivities and higher sulfur capacities compared to all previously known sorbents, and the pi-complexation sorbents are fully regenerable. This is the case for desulfurization of both natural gas and transportation fuels. Only a very limited number of cations that are capable of forming pi-complexation bonds with sulfur molecules have been explored in our laboratory. Also, only a very limited number of large pore substrates have been studied as supports for pi-complexation sorbents. Our most recent studies showed that for both gas and liquid fuel desulfurization, pore diffusion causes severe limitation on the sulfur capacity in fixed-bed adsorption.
In this proposal, a systematic study of the most promising mesoporous, largepore, pi-complexation sorbents for desulfurization of both gaseous and liquid fuels is outlined. Salts and oxides of the most promising d-block metal cations will be spread in monolayer form on these large-pore substrates. These sorbents will have the highest sulfur selectivities and capacities. They will also be most stable and fully regenerable. They will have large pores in order to minimize diffusion resistance and consequently provide the highest fixed-bed adsorption capacities for sulfur.
Equilibrium isotherms and pore diffusivities (in terms of diffusion time constants) for both pure-component and mixtures of sulfur-containing molecules will be measured for these pi- complexation sorbents. A basic understanding of the adsorbed species and bonding on various pi-complexation sorbents will be obtained through molecular orbital theory calculations as well as spectroscopic studies. The possible benefit of using a dispersant for spreading monolayer pi- complexation salts on high-surface-area substrates will be examined by studying the metal dispersion and stability. Fixed-bed adsorber breakthrough curves will be measured for both gas and liquid fuels on various new sorbents. An understanding of the diffusion limitation on sulfur capacity will be obtained.
This project will involve active participation of a diversity of graduate as well as undergraduate students, particularly the minority and female students. The students will be active in disseminating the findings and discoveries at national meetings and through publications. The research will lead to entirely new technologies for desulfurization of both gaseous and liquid fuels, which will result in cleaner fuels at lower costs. Cleaner fuels with lower sulfur contents will reduce sulfur emission into the atmosphere. The sorbents developed in this work can be readily transferred to industrial applications. In addition, a basic understanding on the bonding between sulfur containing molecules and d-block metals (i.e., pi- complexation bonds) will be obtained.
