Novel repressurization of pressure swing adsorption system

An adsorption process for producing an enriched gas stream which comprises the sequential steps of:

• (a) passing a gaseous mixture, at an adsorption pressure selected from the range of from 3.0 to 8.0 bars through a first adsorption zone comprising a first and a second column of carbon molecular sieves connected in series to yield enriched gas, said enriched gas flowing to a product reservoir;
• (b) prior to breakthough, isolating said first column of the first adsorption zone, thereafter passing the gaseous mixture through solely the second column of said first adsorption zone, thereby producing lean gas and passing said lean gas from the second column of said first adsorption zone into the inlet end of a second adsorption zone comprising a first and a second column of carbon molecular sieves connected in series, to partially pressurize said second adsorption zone in the range of about 40 to 90% of said adsorption pressure thereafter halting said lean gas flow;
• (c) further pressurizing of said second adsorption zone to said adsorption pressure by introducing enriched gas from said product reservoir into the outlet end of said second adsorption zone;
• (d) venting said isolated first column of the first adsorption zone to the atmosphere through its inlet end, and countercurrently venting the second column of said first adsorption zone thereby producing vented gas and using said vented gas to countercurrently purge the previously vented first column in the zone;
• (e) passing said gaseous mixture through said fully pressurized second adsorption zone to yield enriched gas while regenerating said first adsorption zone by application of vacuum to the inlet end of said first zone in the range of 70 to 250 torr;
• (f) repeating the sequence, steps (b)-(e) treating said second zone as said first zone and said first zone as said second zone.