Process for separating carbon monoxide having substantially constant purity

Claim 1

A process for separating carbon monoxide with substantially constant purity from a feed gas containing at least carbon dioxide, carbon monoxide and nitrogen through pressure swing adsorption (PSA) in a two-stage adsorption operation which comprises a first adsorption stage and a second adsorption stage wherein: (1) the first adsorption stage comprises pressure swing adsorption whereby adsorption and desorption are alternated by using at least two adsorption columns containing an adsorbent exhibiting a selective adsorbing property relative to carbon dioxide in order to remove carbon dioxide from said feed gas; and (2) the second adsorption stage comprises a process for separating carbon monoxide from the gaseous mixture which has been withdrawn from the first adsorption stage through PSA by using at least two adsorption columns containing an adsorbent exhibiting a selective absorbing property relative to carbon monoxide; the second adsorption stage repeating at least a step of pressurizing the column, a step of adsorbing carbon monoxide, and a step of desorbing the carbon monoxide, characterized in that the CO concentration in the feed gas, the CO concentration in the effluent gas withdrawn from the first adsorption stage, or the CO concentrations in both gases are monitored, and when the CO concentrations in the feed gas or effluent gas decreases below a predetermined amount, part of the CO product gas is circulated into the feed gas, the effluent gas, or both gases.