Patent ID: 7740688

Claim:
A vacuum pressure swing adsorption (VPSA) process for the recovery of carbon dioxide from a feed stream, wherein the feed stream comprises a multi-component gas mixture comprising at least carbon dioxide and hydrogen, in a VPSA unit comprising at least one adsorption bed containing at least one CO 2 -selective adsorbent, the process comprising: (a) feeding at least a portion of the feed stream to the at least one adsorption bed at a first pressure within a first pressure range for a predetermined time to produce a hydrogen-enriched stream; (b) depressurizing the at least one adsorption bed in a first depressurization step from the first pressure to a second pressure within a second pressure range wherein the second pressure is lower than the first pressure in a same direction as or in a direction opposite to the feed flow; (c) depressurizing the at least one adsorption bed in a second depressurization step from the second pressure to a third pressure within a third pressure range wherein the third pressure is lower than the second pressure and in a same direction as or in a direction opposite to the feed flow; (d) depressurizing the at least one adsorption bed in a third depressurization step from the third pressure to a fourth pressure within a fourth pressure range wherein the fourth pressure is lower than the third pressure and close to ambient pressure, and in a same direction as the feed flow or in a direction opposite the feed flow to produce a CO 2 -rich stream, wherein a first portion of the CO 2 -rich stream is compressed and recycled into the feed stream and feeding the feed stream with said recycled first portion to the at least one adsorption bed at a first pressure within a first pressure range for a predetermined time to produce a hydrogen-enriched stream; and (e) evacuating the at least one adsorption bed from the fourth pressure range to a pressure below ambient in a direction opposite to or in a same direction as the feed flow to produce CO 2 product; (f) feeding a second portion of the CO 2 -rich stream of step (d) to the at least one adsorption bed at a pressure below ambient to equalize the pressure in said bed; (g) pressure equalizing the at least one adsorption bed in a second pressure equalization step in a direction opposite to or in a same direction as the feed flow; (h) further pressure equalizing the at least one adsorption bed in a third pressure equalization step in a direction opposite to or in a same direction as the feed flow; and (i) repressurizing the at least one adsorption bed in a repressurization step to the first pressure range; wherein the process is repeated cyclically.