An experimental investigation was carried out for the separation and recovery of butane vapor (10 to 40 vol%) from nitrogen using Westvaco BAX activated carbon in a twin-bed pressure swing adsorption (PSA) system utilizing a 4-step Skarstrom-type cycle. Twenty-four runs, covering a broad range of process and initial column conditions, were performed to investigate the transient and periodic process dynamics. In all cases the approach to the periodic state was very slow, taking up to 160 cycles depending on the initial condition of the beds; and peak bed temperatures of up to 105 degrees C were observed depending on both the initial condition of the beds and the process conditions. Also, the periodic state of each run was unique when approaching a new periodic state from less contaminated beds. The uniqueness of the periodic states, together with the exceedingly high peak temperatures, inferred much about the practice of preconditioning beds to avoid high temperature excursions. The periodic enriched butane vapor concentration histories also gave considerable insight into new cycle designs for improved solvent vapor enrichment.