Abstract: A process for removing methane and argon from crude ammonia synthesis gas, which method comprises the steps of:(a) cooling said crude ammonia synthesis gas in a heat exchanger;(b) distilling the cooled crude ammonia synthesis gas to provide purified ammonia synthesis gas and a liquid fraction containing methane, argon and nitrogen;(c) expanding said liquid fraction containing methane, argon and nitrogen;(d) introducing at least part of the liquid from step (c) into indirect heat exchange with vapor from the top of said distillation column to condense part of said vapor and provide reflux for said distillation column while simultaneously separating said liquid into a liquid stream rich in methane, and a gaseous stream rich in nitrogen;(e) warming said gaseous stream from step (d);(f) compressing at least part of the warmed gaseous stream from step (e);(g) cooling at least part of the compressed gaseous stream from step (f);(h) expanding at least part of the cooled gaseous stream from step (g); and(i) passing t

Abstract: A method for purifying crude argon containing argon, oxygen and nitrogen comprises the steps of reducing the amount of nitrogen in the crude argon to between a trace and 0.15% (by volume) and passing the remaining oxygen and argon, together with residual nitrogen, through 4A molecular sieve to separate the oxygen and argon. The 4A molecular sieve is particularly effective if steps are taken to ensure that all the remaining oxygen and nitrogen has to pass through a volume of 4A molecular sieve which is wholly at or below -250.degree. F.