Ammonia synthesis gas purification

Claim 1

In the purification of a reformed gas mixture following water gas shift conversion to produce a purified ammonia synthesis gas stream, the improved processing sequence consisting essentially of: (a) selectively catalytically oxidizing the residual carbon monoxide content of said gas mixture to carbon dioxide so as to reduce the carbon monoxide content of said gas mixture to less than about 20 ppm, said selective catalytic oxidation being carried out with an excess of air, with said excess oxygen being catalytically reacted with a small amount of hydrogen so that the residual oxygen level is reduced to less than about 3 ppm; (b) removing the bulk of the carbon dioxide content of said gas mixture by liquid absorption; (c) removing residual amounts of carbon monoxide, carbon dioxide and water by selective adsorption on the fixed beds of a thermal swing adsorption system, a dry, purified ammonia synthesis gas stream containing less than a total of 10 ppm of carbon monoxide and carbon dioxide being recovered from said thermal swing adsorption system; (d) passing the resulting dry, purified ammonia synthesis gas stream having a low content of methane to an ammonia production operation without intermediate passage of said ammonia synthesis gas stream to a methanation unit or to a cryogenic unit for removal of carbon monoxide and carbon dioxide therefrom; whereby the efficiency of the overall purification operation and the effective utilization of hydrogen are enhanced.