Transient Adsorption Studies of Automotive Hydrocarbon Traps

A chromatographic adsorption unit was designed and built to study the adsorption of alkanes in zeolites for the hydrocarbon trap systems in three-way catalysts, to assist in the selection of optimal materials for this application. The experimental apparatus used a zeolite bed in place of the column in an ordinary gas chromatograph and could be accurately modeled to determine the adsorption equilibrium constants for simple alkanes in MFI zeolites. The adsorption of isopentane was studied in BEA zeolites with varying Si/Al-2 ratios, before and after ex situ zeolite aging simulating engine exhaust, and in the presence of water vapor. The elution times were shown to depend directly on the zeolite adsorption capacity. The primary effect of water was to decrease the iso-pentane adsorption capacity by partial filling of the zeolite pores through adsorption of water at acid sites. Some implications of this work for choosing the best materials for hydrocarbon trapping are discussed. (C) 2014 American Institute of Chemical Engineers