ARGON RECOVERY FROM HYDROGEN DEPLETED AMMONIA PLANT PURGE GAS

A gas stream comprising hydrogen, nitrogen, methane and argon is subjected to the following steps: (i) separation of methane and most of the nitrogen in the gas stream in a pressure swing adsorption system 2 using molecular sieve or activated carbon material. (ii) separation of most of the hydrogen in a membrane separator 5. The separated hydrogen may be used as purge gas for regeneration of the pressure swing adsorption system 2 of step (i). (iii) separation of the nitrogen and residual hydrogen in a cryogenic distillation unit 8 to obtain essentially pure liquid argon product. In a Step (ii) above may be eliminated and separation of hydrogen is then accomplished by cryogenic separation in to combination with step (iii). In a further alternative, separation of most of the hydrogen is accomplished by metal hydride adsorption in place of membrane separation. The present process is applicable to the recovery of argon from ammonia synthesis plant purge gas stream, which is pre-heated typically in a membrane to reduce its hydrogen content. The pre-treatment may also include an ammonia removal step.