Pressure swing adsorption process

In a pressure swing adsorption process for the separation and recovery of a less readily adsorbable component of a feed gas mixture in an adsorption system capable of selectively adsorbing a more readily adsorbable component from said gas mixture, the adsorption system containing at least four adsorbent beds, each of which undergoes, on a cyclic basis, a processing sequence that includes (1) adsorption at an upper adsorption pressure level with discharge of the less readily adsorbable component as product effluent from the product end of the bed, (2) cocurrent depressurization with release of void space gas from the product end of the bed and the passage of said gas to other beds in the system initially for pressure equalization and then for provide purge purposes, (3) countercurrent depressurization to lower adsorption pressure with release of said more readily adsorbable component from the feed end of the bed, (4) purge at said lower desorption pressure, (5) partial repressurization by pressure equalization with void space gas from other beds, and (6) repressurization to upper adsorption pressure, the improvement comprising:

• (a) passing void space gas released from the product end of the bed during cocurrent depressurization from said upper adsorption pressure to an upper intermediate pressure to one other bed in the system being partially repressurized to said upper intermediate pressure, while simultaneously passing said void space gas to a second other bed as purge gas for said other bed at its lower desorption pressure level;
• (b) discontinuing the passage of said void space gas to said partially repressurized bed upon said bed being depressurized and said partially repressurized bed reaching said upper intermediate pressure;
• (c) further continuing to pass void space gas released from said bed being depressurized solely to said second other bed as purge gas, after completion of step (a), said bed being depressurized thereby being depressurized further from said upper intermediate pressure to an intermediate pressure level;
• (d) passing additional void space gas released from the product end of the bed being depressurized upon further cocurrent depressurization thereof from said intermediate pressure to another bed in the system initially at a lower pressure for pressure equalization therebetween at said lower intermediate pressure, while simultaneously countercurrently depressurizing said bed by the discharge of gas from the feed end of the bed;
• (e) discontinuing the passage of said void space gas to said bed initially at lower pressure upon said bed being depressurized and said bed initially at lower pressure reaching said lower intermediate pressure;
• and
• (f) further continuing to countercurrently depressurize said bed being depressurized after completion of said step (d) down to the lower desorption pressure of said bed, whereby enhanced adsorbent productivity, bed capacity and product recovery can be obtained at minimized overall cycle times without degradation of product effluent purity.