A sequential process of pressure swing adsorption-desorption has been investigated experimentally and numerically. Two mathematical models have been developed. The exact model includes the momentum balance, apart from the mass balances, whereas the lumped model assumes that both individual steps of the process are isobaric. Experimental separation of a gaseous mixture of water and ethanol over a zeolitic adsorbent has been carried Out. Regeneration of the adsorbent was performed under lowered pressure by purging the bed with unhydrated ethanol. The predictions of both models were compared with the experimental results and a satisfactory agreement was found only in case of the exact model. The lumped model tended to overestimate the efficiency of regeneration of bed during the purge step. It was concluded that, under conditions applied in measurements, a model adequately representing the process should include the momentum balance because a pressure drop arising over the purge step is significant in relation to the total pressure. (C) 2009 Elsevier B.V. All rights reserved.