Membrane Permeation and Pressure Swing Adsorption (PSA) for the Production of High Purity Hydrogen

Summary

For a new hydrogenation process at DSM a hydrogen feed gas with a purity of at least 98% was required. There were four options in this case: separation of hydrogen by membranes or by Pressure Swing Adsorption (PSA), using hydrogen containing feed gas from either a naphtha cracker or a cryogenic recovery unit.

The naphtha cracker gas contains 90% hydrogen and 10% methane and has a pressure of 20 to 22 bar. By means of PSA it is possible to produce a hydrogen gas with a purity of 99.9% and a recovery of 84 to 89%. For a membrane unit the feed gas can be used at the available pressure or it can be compressed. By means of membranes it is possible to produce a hydrogen gas with a purity of 98 to 99%, with recoveries varying from 64 to 95%.

The product gas from the cryogenic unit contains 92.3% hydrogen and 6.2% nitrogen, the remainder being helium, argon and methane. The pressure is 70 bar. When membranes are used, the hydrogen product gas has a purity of 98.2% and the recovery is 93%. If the recovery of hydrogen has to be carried out by PSA, the feed pressure has to be lowered to 20 – 30 bar. The product gas has a purity of 99.6%, while the recovery is 80%.

Comparison of all options, including compiession of product gas to 100 bar, shows that membrane permeation with cryogenic product gas as feed is the best choice.