Adsorption process for recovering two high purity gas products from multicomponent gas mixtures

In the separation of a multicomponent gas mixture by pressure swing adsorption to recover as individual products a primary key component and a secondary key component, wherein the secondary key component is more strongly adsorbed than the primary key component and there is present in the multicomponent gas mixture one or more minor tertiary components at low concentrations which are less strongly adsorbed than the secondary key component, by passing the multicomponent gas mixture in an adsorption step through a first bed of adsorbent selective for retention of the secondary key component, passing the effluent from said first bed through a second bed of adsorbent selective for the retention of the secondary key component and of the one or more minor tertiary components, withdrawing from said second bed a high purity product stream of the primary key component, and continuing said passing of the multicomponent gas mixture through the first and second beds for a predetermined time period or until the concentration of the secondary key component in the effluent from the first bed or the concentration of at least one of the tertiary components in said high-purity stream of said primary key component from the second bed reaches a predetermined level;

• the improvement comprising discontinuation of flow of the multicomponent gas mixture through said first and second beds at the end of said adsorption step and thereafter during a mutually extending time period:
• (1) immediately following said discontinuation of flow through said first and second beds, depressurizing said first bed by withdrawing therefrom a gas stream comprising desorbed and void space gas;
• (2) purging said first bed by passing therethrough a stream of the secondary key component whereby substantially all remaining primary key component and substantially all remaining tertiary components are displaced from said first bed and are withdrawn in a first purge effluent stream;
• (3) evacuating said first bed by withdrawing therefrom a product stream comprising the secondary key component;
• (4) depressurizing said second bed by withdrawing therefrom a gas stream comprising desorbed and void space gas;
• and
• (5) purging said second bed by passing therethrough a stream of the primary key component whereby additional adsorbed components are desorbed and are withdrawn along with remaining void space gas in a second purge effluent stream;
• and thereafter following said mutually extending time period:
• (6) pressurizing said first and second beds to a pressure up to the pressure of the adsorption step by passing a portion of said high purity product stream of primary key component into and through said second bed and passing pressurization effluent from said second bed into said first bed, whereby both beds are prepared for another cycle beginning with said adsorption step.