System and method for removing hydrocarbons from gaseous mixtures

A method and system for removing low molecular weight olefins from gases generated during the first five minutes of start-up of an internal combustion engine. The mixture is contacted with hydrophilic material to remove at least some of the water therefrom. The hydrophilic material can be molecular sieve having pores large enough for adsorption of water molecules and small enough to prevent molecules larger than water from being adsorbed, high surface area aluminas, precursors for high surface area aluminas, high surface area silicas, and combinations thereof. The mixture is then contacted with a downstream hydrocarbon-removing agent for removing the olefins. The hydrocarbon-removing agent can be at least one molecular sieve which can be pentasil zeolites, faujasite zeolites, mordenite, beta zeolites, carbon molecular sieve, metallophosphates, aluminophosphates, silicoaluminophosphates, and combinations thereof.