New Sorbents for Separation and Purification Processes

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

New Sorbents for Separation and Purification Processes As a means of meeting more stringent sulfur standards for gasoline and diesel fuels, adsorption under ambient conditions has become an attractive alternative (to hydrodesulfurization, which is a high-pressure catalytic process). In prior work pi-complexation has been exploited for fuel desulfurization. Thiophene in benzene was used as the model system to represent sulfur compounds and gasoline, respectively. Preliminary results showed that Cu(I)Y and AgY zeolites both adsorbed thiophene at low concentrations much more strongly than NaY, which is among the best sorbents for desulfurization. Molecular orbital calculations showed stronger pi-complexation bonds between these zeolites and thiophene than with benzene. Based on these promising results, a comprehensive study of both vapor-phase and liquid-phase adsorption has been undertaken. Two classes of pi-complexation sorbents are used: ion exchanged zeolites and monolayer salts supported on high-surface-area substrates involving Cu+ and Ag+ as well as other promising d-block cations. The study investigates thiophene, benzothiophene, and dibenzothiophene dissolved benzene and toluene. Also, the study examines the unique and promising adsorption properties of carbon nanotubes. Preliminary results showed that 2.5% (wt.) of hydrogen could be stored in alkali-doped nanotubes at 1 atm H2, and up to 1% (wt.) H2 could be stored in Ni-containing nanotubes, also at 1 atm H2. The project studies H2 adsorption by multi-wall and single-wall carbon nanotubes and graphite nanofibers doped with alkali metals, noble metals, and transition metals. Experimental conditions include hydrogen pressures up to 1000 psig, temperatures up to 500oC, and nanotubes of various inner diameters. The mechanisms of hydrogen storage in nanotubes are studied theoretically through molecular orbital and Monte Carlo calculations. Multiwall nanotubes appear to be effective for dioxin removal from combustion gases, exhibiting much better capacity that activated carbon so this application is also being tested. This project is aimed at developing efficient sorbents for desulfurization of gasoline and diesel fuels under ambient conditions. Success of this program will enable refiners to meet easily the new (2006) sulfur standards. The second aim of this program is to develop carbon nanotubes as sorbents for hydrogen storage as well as to explore other unique sorbent properties of carbon nanotubes. The results of this program will make a significant advance in the applications of carbon nanotubes and contribute to protection of the environment.