By 2006, the Environmental Protection Agency aims to have lowered the sulfur standards for gasoline and diesel fuel to less than a tenth of the current standards. Findings described yesterday at the spring meeting of the American Chemical Society could help fuel producers meet those new requirements more easily. Scientists from Pennsylvania State University announced they have developed a low-temperature, low-pressure process that removes sulfur from liquid fuel without need for any additional reactive gases.
One hindrance to extricating sulfur from hydrocarbon fuels is the element's tendency to bind to aromatic compounds, molecules that contain rings of six-carbon atoms. The trick is to remove only the sulfur, which comprises less than 1 percent of the fuel, while leaving the more prevalent aromatics behind. The new technique, dubbed selective adsorption for removing sulfur (SARS), utilizes transition metal alloys perched atop a non-reactive porous surface. When the liquid fuel comes in contact with this surface, sulfur molecules in the fuel attach to the transition metals while other aromatic compounds such as benzene and napthalene remain in the fuel. "The absorbent transition metals can clean 10 times their volume of fuel," graduate student Michael Sprague notes, "but eventually the system becomes saturated with sulfur." Still, the system can be regenerated, the scientists say, and the sulfur further processed for other uses.
Though it remains to be seen whether the technology will make its way into refineries, the researchers note that diesel and gasoline are not the only fuels that could be cleaned using the new procedure. "Fuel cells need essentially zero sulfur to operate," notes project leader Chunsan Song. "Small adsorption sulfur removal systems might be used at gas stations on special clean fuel pumps for fuel cell vehicles to ensure that all sulfur is removed from the fuel."