Abstract: A process for treating an engine exhaust gas stream is disclosed. The process involves arranging a catalyst bed and a molecular sieve bed side by side with a connecting pipe between and parallel to the two beds. When the engine is first started, the cool exhaust is flowed through the catalyst bed, then through the connecting pipe, then through the molecular sieve bed and finally discharged to the atmosphere. When the molecular sieve bed reaches a temperature of about 150.degree. C. to about 200.degree. C. the exhaust stream is diverted such that it is first flowed through the molecular sieve bed, to desorb the adsorbed hydrocarbons, and then through the catalyst bed and finally discharged to the atmosphere. Finally, when all the hydrocarbons are desorbed from the molecular sieve bed, the exhaust stream is diverted such that it is flowed through the catalyst bed and then discharged to the atmosphere.

Abstract: A pressure swing adsorption (PSA) process is provided for the size-selective separation of a feedstream into an adsorbate fraction employing a rapid blowdown step to induce a state of disequilibrium within an adsorbent bed and thereby increase the weight hourly space velocity of the process. The selective separation mechanism explored in the PSA process may also include equilibrium separation. The benefits include a reduced adsorbent bed size for new installations or increased feed rates for existing facilities. In one aspect of the invention the feedstream to be separated comprises iso and normal pentane.