Argon recovery from hydrogen depleted ammonia plant purge gas utilizing

Abstract

An improved process is provided for the recovery of argon from a gas mixture comprising hydrogen, nitrogen, methane and argon. An example of such a gas mixture is purge gas from an ammonia synthesis plant which has been subjected to the conventional steps of ammonia absorption and a membrane separation to obtain hydrogen for recycle to the ammonia plant. In a first embodiment, the gas mixture is treated in a pressure swing adsorption (PSA) system to remove the methane, residual moisture and most of the hydrogen, the resulting gas mixture is treated in a membrane separator to remove most of the hydrogen, which may be used as purge gas for the PSA system, and the resulting stream treat by cryogenic distillation to separate the nitrogen and residual hydrogen to obtain an essentially pure argon product. In a second embodient, the second treatment is eliminated and all of the hydrogen is removed by the cryogenic distillation. In a third embodiment, metal hydride adsorption is used in place of the membrane to separate the hydrogen. The process is enhanced by the recycle of vent gas from the PSA unit to the process itself or to the ammonia synthesis plant. Alternatively, a cocurrent depressurization product from the PSA plant can be recycled into the process.