Process for the recovery of hydrogen from ammonia purge gases

TLDR: In this paper, a purge stream from an ammonia synthesis loop is treated to reduce its ammmonia content to less than about 0.5 volume percent, and the purge stream is then contacted at a pressure of at least substantially the superatmospheric synthesis pressure of the ammonia synthesis with the feed side of a separation membrane which exhibits selective permeation of hydrogen as compared to the permeations of each of methane and argon.

Abstract: Ammonia synthesis processes are disclosed which provide enhanced conversion of hydrogen values to ammonia. In the processes, a purge stream from an ammonia synthesis loop is treated to reduce its ammmonia content to less than about 0.5 volume percent. The purge stream is then contacted at a pressure of at least substantially the superatmospheric synthesis pressure of the ammonia synthesis with the feed side of a separation membrane which exhibits selective permeation of hydrogen as compared to the permeation of each of methane and argon. A total pressure differential is maintained across the membrane to provide a driving force for hydrogen permeation through the membrane. A hydrogen-rich permeating gas is obtained on the permeate exit side of the membrane. The permeating gas is combined with gas passing to the ammonia synthesis reaction zone for conversion to ammonia. For instance, the permeating gas can be combined with synthesis feed gas or directly introduced into the ammonia synthesis loop. A non-permeating gas is removed from the feed side of the separation membrane at substantially the same pressure at which the purge stream is contacted with the separation membrane and provides a valuable source of energy due to its high pressure and combustible gas content.