Pressure swing adsorption process for gas separation

An improved pressure swing adsorption process for the recovery of the more readily adsorbable component of a feed gas mixture containing said component and a less readily adsorbable component in an adsorption system having at least two adsorbent beds containing adsorbent material capable of selectively adsorbing said more readily adsorbable component, with the feed gas mixture being introduced to the feed and of the bed, the more readily adsorbable component being withdrawn from said feed end, and the less readily adsorbable component being discharged from the discharge end of the bed, each bed, on an alternating cyclic basis, undergoing a processing sequence comprising:

• (a) introducing less readily adsorbable component enriched gas into the discharge end of the bed to partially countercurrently repressurize the bed from its subatmospheric desorption pressure level to an intermediate pressure level, such countercurrent backfilling of the bed serving to displace previously adsorbed more readily adsorbable component toward the feed end of the bed, thereby enhancing the sharpness of the mass transfer zone being the less and more readily adsorbable components of the feed gas mixture and increasing the amount of said more readily adsorbable component recoverable from the feed gas mixture;
• (b) passing the feed gas mixture to the feed end of the bed, the bed being cocurrently repressurized from said intermediate pressure to its upper adsorption pressure, with said more readily adsorbable component being selectively adsorbed, and with a less readily adsorbable component stream being withdrawn from the discharge end of the bed, a portion of said stream being withdrawn from the system, the remaining portion of said less readily adsorbable component stream being passed directly to another bed in the system for said countercurrent backfilling repressurization of step (a) or for the purging of the bed and/or being passed to a surge tank for subsequent use in such backfilling or purge steps;
• (c) passing more readily adsorbable component gas to the feed end of the bed at said upper adsorption pressure so as to cocurrently purge said bed and displace less readily adsorbable component retained in the void spaces thereof, said less readily adsorbable component continuing to be withdrawn from the discharge end of the bed, said withdrawn gas either being passed to said surge tank for subsequent use in backfilling or purge steps, being passed directly to another bed for use in said steps, or being withdrawn from the system, the bed being cleaned out of less readily adsorbable component by said purge prior to the recovery of high purity more readily adsorbable component from the bed;
• (d) countercurrently depressurizing the bed by discharging more readily adsorbable component from the feed end of the bed, the pressure of the bed thereby being reduced from the upper adsorption pressure to an intermediate pressure level;
• (e) further countercurrently depressurizing the bed by discharging additional quantities of said more readily adsorbable component from the feed end of the bed, the pressure of the bed thereby being reduced from said intermediate pressure to the subatmospheric desorption pressure level;
• (f) countercurrently purging the bed by introducing less readily adsorbable component gas to the discharge end of the bed, with additional quantities of the more readily adsorbable component being discharged from the feed end of the bed, thereby increasing the adsorptive capacity of the bed prior to the next succeeding pressurization adsorption step and increasing the sharpness of the mass transfer zone of more readily adsorbable component in the bed, the more readily adsorbable component removed from the feed end of the bed in this step (f) and in countercurrent depressurization steps (d) and (e) being either withdrawn from the system as high purity product gas or stored in a surge tank for use as purge gas in step (c);
• and
• (g) repeating steps (a)-(f) on a cyclic basis with additional feed gas being passed to the bed during the carrying out of step (b) therein,
• whereby, said more readily adsorbable component of the feed gas mixture is conveniently obtained as a high purity, low cost product in said simplified vacuum processing cycle.