Separation of hydrogen-lean mixtures for a high-purity hydrogen by vacuum swing adsorption.

High purity hydrogen is commercially produced by pressure swing adsorption from hydrogen rich mixtures. In this work, a vacuum pressure swing adsorption cycle was used to produce high purity hydrogen from a hydrogen lean binary mixture using zeolite 5A as the sorbent. The effects of different process variables on separation performance were studied. The purity of hydrogen product increases at low throughput, high feed pressure, high end pressure of cocurrent depressurization, low end pressure of countercurrent evacuation and short cycle time. Also, it was found that for a H2 lean mixture, the separation was improved at higher ambient temperature. In addition, a new "vacuum purge" step was found to improve the separation and is therefore a promising step for commercial application.