Separation of multicomponent gas mixtures by pressure swing adsorption

Claim 1

In the separation of a multicomponent feed gas mixture in a system comprising a plurality of first and second sorbent beds, 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 sorbed by the sorbent employed than the primary key component and there is present in said mixture at least one other tertiary gas component, which is present in dilute concentrations and which is more strongly sorbed than both the primary key and the secondary key component; the method which comprises in an adiabatic pressure swing cycle the sequential steps of (a) an adsorption step during which such multicomponent feed gas mixture at initial superatmospheric pressure is passed through a first sorbent bed selective for preferential retention of tertiary gas component(s) and then through a second sorbent bed selective for retention of said secondary key component, and discharging from said second sorbent bed 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 second sorbent bed, while retaining essentially all of the tertiary gas component(s) in said first adsorbent bed; (b) thereafter interrupting feed gas flow to said first bed and discontinuing gas flow communication between said first and second beds; and (i) rinsing said second sorbent bed at about initial feed pressure by flowing a stream of essentially pure secondary product gas component therethrough until said second bed is saturated with said secondary component; and meanwhile (ii) first reducing to an intermediate level the pressure in said first bed by gas withdrawal therefrom, and (iii) then further reducing the pressure in said first bed to substantially ambient level by further gas withdrawal therefrom, and; (c) thereafter, reducing the pressure of the said second bed to substantially ambient pressure level by gas withdrawal therefrom comprising substantially pure secondary key component, and during such pressure reduction of said second bed (i) purging said first bed with part of the gas being withdrawn from said second bed; and (ii) purging another second bed, which is then undergoing the high pressure rinse step defined in (b), with part of the gas being withdrawn from the first mentioned second bed after compressing the said withdrawn gas to about the initial feed pressure; (d) following reduction of pressure in said second bed to substantially ambient pressure level, evacuating said bed to lowest pressure in the operating sequence thus further desorbing secondary key component therefrom; and (e) repressuring the previously evacuated second bed to feed pressure level by flow thereinto of primary product gas and while said second bed is being thus repressured, (i) first bringing said first bed to an intermediate pressure level by flow thereinto of a gas stream comprising the desorbed gas from another first bed then undergoing the pressure reduction step defined in step (b), and (ii) then re-establishing flow between said second and first beds and flowing primary product gas through said second bed into said first bed until said first bed is brought to initial feed gas pressure level, and (f) when said first and second beds are at feed gas pressure at the conclusion of step (e) above, repeating the above-recited sequence of operations beginning with step (a) above.