Process for removing a nitrogen gas from mixture comprising N.sub.2 and CO or N.sub.2 ' CO.sub.2 and CO

A process for separating carbon monoxide and carbon dioxide from a feed gas comprising carbon monoxide, carbon dioxide and nitrogen through pressure swing adsorption by using at least two adsorption columns containing an adsorbent exhibiting selective adsorb property to carbon monoxide and carbon dioxide which comprises:

• (i) a step of pressurizing an adsorption column by the feed gas, in which the step (vi) was previously completed;
• (ii) a step of introducing the feed gas into the adsorption column, in which step (i) was previously completed, so as to adsorb carbon monoxide and carbon dioxide adsorbed on or in the adsorbent until the breakthrough point is reached or until just before that point is reached;
• (iii) a step of connecting the adsorption column, in which step (ii) was previously completed, to the other adsorption column in which step (v) was previously completed, to reduce the pressure in the former adsorption column to one atmosphere or a pressure close to it, and to increase pressure in the latter column;
• (iv) a step of purging nitrogen by passing product gas through the adsorption column, in which step (iii) was previously completed;
• (v) a step of desorbing carbon monoxide and carbon dioxide on the adsorbent of the adsorption column, in which step (iv) was previously completed, by vacuum pump to recover a product gas, and
• (vi) a step of connecting the adsorption column, in which step (v) was previously completed, to the other adsorption column in which step (ii) was previously completed to increase pressure in the former column,
• periodically switching the flow between or among said adsorption columns so as to repeat the above steps in all the adsorption columns.