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Multi-column pressure swing adsorption process for simultaneous production of ammonia synthesis gas and carbon dioxide from a reformer off gas having hydrogen, nitrogen and carbon dioxide as major components accompanied by minor quantities of methane, carbon monoxide and argon as impurities. The PSA

Multi-column pressure swing adsorption process for simultaneous production of ammonia synthesis gas and carbon dioxide from a reformer off gas having hydrogen, nitrogen and carbon dioxide as major components accompanied by minor quantities of methane, carbon monoxide and argon as impurities. The PSA system features two groups of adsorbent columns in which CO2 is adsorbed in adsorbers of the first group, the essentially CO2-freed effluent being charged to an adsorber of the second group for removal of minor impurities while discharging an effluent gas having an H2/N2 content stoichiometric for NH3 synthesis. The CO2 recovered from the first group of adsorbers is available at a high purity for reaction with the ammonia product for production of urea.

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The method of separately recovering high purity carbon dioxide and ammonia synthesis gas composed of hydrogen and nitrogen at near the 3:1 stoichiometric ratio, from a starting gas mixture containing hydrogen, carbon dioxide and nitrogen as bulk components and less than a total of 10 mol % on a dry

The method of separately recovering high purity carbon dioxide and ammonia synthesis gas composed of hydrogen and nitrogen at near the 3:1 stoichiometric ratio, from a starting gas mixture containing hydrogen, carbon dioxide and nitrogen as bulk components and less than a total of 10 mol % on a dry basis of minor components which comprises: (a) passing the starting gas at super atmoshperic pressure into and through a first bed of solid adsorbent wherein carbon dioxide is selectively adsorbed; discharging unadsorbed gas from said first bed into and through a second bed of adsorbent effective in retaining at least part of said minor components of said starting gas; and discharging from said second bed as primary effluent the unadsorbed portion of the gas passed therethrough; (b) rinsing said first bed with a stream of high purity carbon dioxide passed into the bed for a time short of complete breakthrough of a carbon dioxide front at the effluent end while discharging effluent gas therefrom and mixing said effluent gas with fresh starting feed gas; (c) desorbing carbon doxide from said first bed by gas withdrawal to near ambient pressure level; (d) lowering the pressure in said first bed by evacuation to subatmospheric level thereby obtaining an effluent rich in carbon dioxide; (e) partly repressuring the evacuated first bed by flow of gas into said bed from a second bed which is at superatmospheric pressure level, to bring said first and second beds to substantially equal pressure; and (f) further repressuring said first bed to superatmospheric pressure level to prepare the same for further adsorption of CO2 from the starting gas; said further repressuring being carried out by introduction of a nitrogen-containing gas stream in a direction counter to that employed in step (a); and during the said rinsing of said first bed regenerating the impurity-containing second bed by the sequence of steps comprising: (i) passing gas from the second bed to an evacuated first bed to equalize the pressure level in these beds; (ii) further withdrawing gas from said second bed to bring the same to near ambient pressure level; (iii) purging the second bed at said near ambient pressure level with nitrogen-containing gas; (iv) then repressuring the bed with nitrogen-containing gas to restore the same to initial adsorption pressure level for repetition of the recited cycle.