Hydrogen Recovery by Membrane Separation

The purge gas is water scrubbed at 135 -145 bar, reducing the ammonia concentration to less than 200 ppm. The scrubbed purge gas is heated to 35 °C and sent directly to the Prism separators. Trace concentrations of ammonia and water vapor in the gas stream pose no problem to the membrane. Therefore, a dryer system is not required. 

The main advantages of the Prism separator system are simplicity, ease of operation, and low maintenance. Reference [962] compares membrane and cryogenic separation units for a large ammonia plant. 

Membrane technology is also offered by other licensors an example is the Polysep Membrane System of UOP [970], In addition to the systems based on hollow fibers, membrane modules have been developed in which the membrane is in the form of a sheet wrapped around a perforated center tube using spacers to separate the layers. The raw gas flows in axial direction in the high pressure spacer and the permeate is withdrawn in the low pressure spacer. Such a module, for example, is marketed under the name Separex [971], [972], 

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