Process for treating a gaseous mixture by adsorption

A process for recovering by adsorption at least one preferentially adsorbable constitutent of a gaseous feed mixture, said process employing only three adsorbers and comprising the following cycle of operations for each adsorber:

• (a) an adsorption stage in which the feed mixture is admitted into the adsorber through an inlet end thereof and comprising an isobaric adsorption sub-stage at a high pressure of the cycle for absorption of said preferentially adsorbable constituent, the mixture, at least during said isobaric sub-stage, circulating through the adsorber and being withdrawn therefrom through an outlet end thereof, the direction of circulation of the mixture being termed cocurrent, said isobaric sub-stage being conducted until an adsorption front has reached said outlet end;
• (b) a first stage for cocurrent decompression of the adsorber to a medium presure of the cycle;
• (c) a second stage for countercurrent decompression of the adsorber to a low pressure of the cycle, the gas withdrawn in the course of this second stage being the production gas containing the desired content of said adsorbable constituent, at least a portion of the gaseous mixture extracted from the absorber in the course of stage (b) being richer in said adsorbable constituent than said gaseous feed mixture and being recycled to the inlet end of another adsorber and admixed with said feed mixture during at least one part of the stage (a) of said other absorber;
• and
• (d) a recompression stage to raise the pressure in said adsorber from said low pressure to an initial pressure of said stage (a) by introduction of gas cocurrently withdrawn from another adsorber.

A process for recovering by adsorption at least one preferentially adsorbable constituent of a gaseous feed mixture, said process employing only four adsorbers and comprising the following cycle of operations for each adsorber:

• (a) an adsorption stage in which the feed mixture is admitted into the adsorber through an inlet end thereof and comprising an isobaric adsorption sub-stage at a high pressure of the cycle for adsorption of said preferentially adsorbable constituent, the mixture, at least during said isobaric sub-stage, circulating through the adsorber and being withdrawn therefrom through an outlet end thereof, the direction of circulation of the mixture being termed cocurrent, said isobaric sub-stage being conducted until an adsorption front has reached said outlet end;
• (b) a first stage for a cocurrent decompression of the adsorber to a medium pressure of the cycle;
• (c) a second stage for countercurrent decompression of the adsorber to a low pressure of the cycle, the gas withdrawn in the course of this second stage being the production gas containing the desired content of said adsorbable constituent, at least a portion of the gaseous mixture to be treated in said adsorption stage (a) being successively (i) said gaseous feed mixture, (ii) gas extracted from another adsorber in stage (b), mixed with said gaseous mixture, and (iii) gas extracted from said other adsorber in stage (b);
• and
• (d) a recompression stage to raise the pressure in said adsorber from said low pressure to an initial pressure of said stage (a) by introduction of gas cocurrently withdrawn from another adsorber.

A process for recovering by adsorption at least one preferentially adsorbable constituent of a gaseous feed mixture, said process employing a plurality of adsorbers and comprising the following cycle of operations for each adsorber:

• (a) an adsorption stage in which the feed mixture is admitted into the adsorber through an inlet end thereof and comprising an isobaric adsorption sub-stage at a high pressure of the cycle for adsorption of said preferentially adsorbable constituent, the mixture, at least during said isobaric sub-stage, circulating through the adsorber and being withdrawn therefrom through an outlet end thereof, the direction of circulation of the mixture being termed cocurrent, said isobaric sub-stage being conducted until an adsorption front has reached said outlet end;
• (b) a first stage for a cocurrent decompression of the adsorber to a medium pressure of the cycle;
• (c) a second stage for countercurrent decompression of the adsorber to a low pressure of the cycle, the gas withdrawn in the course of the second stage being the production gas containing the desired content of said adsorbable constituent, at least a portion of the gaseous mixture extracted from the adsorber in the course of stage (b) being richer iin said adsorbable constituent than said gaseous feed mixture and being recycled to the inlet end of another adsorber and admixed with said feed mixture during at least a portion of stage (a) of said other adsorber;
• and
• (d) a recompression stage to raise the pressure in said adsorber from said low pressure to an initial pressure of stage (a) by means of gas cocurrently withdrawn from another adsorber.