Two-feed pressure swing adsorption process

Claim 1

An improved pressure swing adsorption process for the separation and purification of hydrogen contained in a gas stream having a relatively high concentration of carbon dioxide therein comprising: (a) pretreating at least about 30% up to about 80% by volume of said gas stream to remove a substantial portion of said carbon dioxide therefrom, the unpretreated gas stream having a carbon dioxide content of at least about twice that of the thus-pretreated gas stream; (b) passing the pretreated gas stream at an elevated adsorption pressure to the feed end of an adsorbent bed capable of adsorbing carbon dioxide and other impurities of said stream, a purified hydrogen stream being withdrawn from the product end of the bed having an advancing adsorption front therein; (c) upon completion of step (b), passing the unpretreated gas stream to said feed end of the bed at essentially the same pressure as in step (b), a second adsorption front being created at the higher concentration and adsorption loading of carbon dioxide, a purified hydrogen stream continuing to be withdrawn from the product end of the bed; (d) concurrently depressurizing said bed to release void space gas from the product end of the bed; (e) countercurrently depressurizing said bed to a lower desorption pressure to desorb and release carbon dioxide and other impurities from the feed end of the bed; (f) repressurizing said bed to said elevated adsorption pressure; and (g) repeating said steps (b)-(f) for the separation and purification of additional quantities of hydrogen; whereby the recovery of purified hydrogen is enhanced at a significant savings in equipment and operating costs as compared with the pretreatment of all of the gas stream for removal of carbon dioxide therefrom.