4452
Ind. Eng. Chem. Res. 2004, 43, 4452-4456
Method for Determining Performance of Sulfur Oxide Adsorbents for Diesel Emission Control Using Online Measurements of SO2 and SO3 in the Effluent Liyu Li and David L. King* Materials Division, Pacific Northwest National Laboratory,† P.O. Box 999 (K2-44), Richland, Washington 99352
Upcoming regulations regarding diesel engine emissions require substantial reductions in particulate matter and nitrogen oxides through aftertreatment methods. Because sulfur oxides in the exhaust greatly reduce the performance of the aftertreatment system, a dedicated trap for the removal of sulfur oxides has been considered. Most adsorbents are more effective in removing SO3 than SO2; hence, oxidation catalysts have been employed to maximize the concentration of SO3 in the effluent. Although SO2 concentrations are easily measured, SO3 is less easily quantified. As a result, the only figure of merit for SOx trap performance has been total capacity, provided by post-characterization. In this paper, we describe a chromatographic method for the measurement of SO2 and SO3 adsorption in real time that provides adsorbent performance data on breakthrough capacities and sulfur slip. We also provide experimental measurements of breakthrough capacities for SO2 and SO3 adsorption for some common metal oxide adsorbents using this analytical system. Introduction Diesel engines are gaining increasing attention in the U.S. because of their higher fuel economy compared to the gasoline internal combustion engine.1 However, the combustion process in a diesel engine results in the production and emission of carbon-based particulates and nitrogen oxides (NOx).1,2 Allowed levels of these polluting species are continually being decreased through regulation, with very challenging standards now set for the years 2006 and 2010.3 Engine manufacturers are seeking to meet these standards through the introduction of sophisticated emission control technologies based on combining particulate filters with NOx reduction catalysts or NOx adsorbers.1 Durability remains a significant challenge for these systems. One of the reasons for concern about the durability of diesel emissions aftertreatment devices is the presence of sulfur oxides (SOx) in the exhaust. Sulfur oxides, although not specifically regulated, contribute significantly and deleteriously to the overall performance of emission aftertreatment systems. Sulfur oxides come from the combustion of the sulfur-bearing molecules in the fuel and from the sulfur present in the lubricating oils. Fuel sulfur levels are mandated to be
