Recovery of hydrogen from ammonia synthesis purge gas

In a process for the recovery of hydrogen from purge gas withdrawn from a recycling gas stream of an ammonia synthesis, which process comprises

• at superatmospheric pressure cooling the purge gas to sub-ambient temperature to form a condensate comprising components having a boiling point above that of hydrogen and uncondensed gas rich in hydrogen and separating said uncondensed gas from said condensate;
• providing refrigeration for said cooling by expanding condensate and passing said expanded condensate and said uncondensed gas separately in indirect countercurrent heat exchange relationship with said purge gas, with evaporation of said expanded condensate;
• and
• lowering the partial pressure of said expanded condensate by withdrawing a bleed stream from said uncondensed gas prior to said heat exchange, expanding said bleed stream and injecting it into said expanded condensate prior to said heat exchange;
• the improvement wherein the bleed stream contains less than 10% impurities and the minimum temperature of said bleed stream after said expansion thereof is prevented from falling below 77.degree. K.