In the separation of a multicomponent feed gas mixture with the individual recovery of a primary key component and a secondary key component present in such mixture, by selective sorption, wherein said secondary key component is more strongly adsorbed than the primary key component and there is present in said mixture at least one minor dilute tertiary gas component less strongly sorbed than the secondary key component;
- the method which comprises, in an adiabatic adsorption pressure swing cycle the steps of:
- (a) passing such multicomponent gas mixture at initial super-atmospheric pressure and in selected flow direction through a first sorbent column (A) packed with an adsorbent selected for preferential retention of said secondary key component and then passing the effluent from said first column through a second sorbent column (B) packed with an adsorbent selective for retention of said tertiary component(s) as opposed to said prima key component, and discharging from said second sorbent column unadsorbed primary key component, said passing of the multicomponent gas mixture being continued for a controlled time period until or short of breakthrough of said secondary key component from said first sorbent column, while retaining all of the said tertiary components in said second sorbent column;
- (b) thereafter discontinuing gas flow communication between said first and second sorbent columns, and
- (i) rinsing said first column by flowing a stream of relatively pure secondary key component therethrough at substantially the initial feed pressure level for a controlled time period effective to purge most of the void and displaced gases from the said first column, and during this time period (b),
- (ii) lowering the pressure in said second column to an intermediate level by withdrawing a gas stream therefrom including void and desorbed gases, and thereafter;
- (iii) further depressuring said second column to near ambient pressure followed by:
- (iv) purging the second column at near ambient pressure with a stream of primary key component;
- (c) after said rinsing step in (b) above reducing the pressure in said first column to an intermediate level by desorption of gas therefrom including previously sorbed secondary key component and during this step (c), repressuring the second column to an immediate pressure level by flow thereinto of gas essentially free of the secondary key component;
- (d) following step (c) above further desorbing gas from said first column to lower the pressure therein to substantially ambient level, and thereafter;
- (e) evacuating said first column to subatmospheric level;
- (f) after attaining the subatmospheric level in the said first column, introducing thereinto a gas stream substantially free of the secondary key component to bring said first column to an intermediate pressure level, and thereafter;
- (g) further repressurizing said first column to initial super-atmospheric feed pressure level by flowing thereinto primary key product gas via a second column already pressurized to the intermediate pressure level (step c), thereby bringing both columns of the feed pressure level and making them ready to repeat the defined sequence of steps beginning with the reintroduction of the multicomponent feed gas mixture into the said first sorbent column;
- the improvement which comprises:
- (h) passing to storage the gas withdrawn from a second column during the further depressuring of said second column to near ambient pressure;
- (j) also passing to storage the effluent obtained in the purging of said second column with a stream of primary key component;
- (k) withdrawing the gas stored during steps (h) and (j) and passing said withdrawn gas through a third adsorption column packed with adsorbent selective for adsorption of the secondary key component as well as said minor tertiary gas component, while collecting unsorbed gas discharged from said third column consisting essentially of primary key component;
- (l) discontinuing passing of stored gas into said third column and countercurrently desorbing said column to near ambient pressure;
- (m) at the attained near ambient pressure rinsing the third column countercurrently, using part of the unsorbed gas collected during step (k);
- and
- (n) repressuring the rinsed third column with another portion of the unsorbed gas collected during step k.