Facilitating analysis of trace impurities in hydrogen: Enrichment based on the principles of pressure swing adsorption

Abstract

A laboratory-scale gas sampling and impurity enrichment device (GSIED) based on the principles of pressure swing adsorption (PSA) has been designed, fabricated, and tested to show that such a device provides an effective method to enrich trace impurity species in hydrogen by a factor of 10 or more. With the availability of a high pressure sample gas at the hydrogen refueling stations, the device uses only a pressure sequence to enrich the impurities without need of a temperature cycle. Enrichment of the impurities allows the use of simpler and less expensive analytical instruments for hydrogen quality monitoring and certification purposes. A series of experiments was conducted using activated carbon as the PSA sorbent for impurity enrichment in a hydrogen gas containing N2, CO, CH4, and CO2. The enrichment factor varied for the different species according to their affinity of adsorption. The measured impurity enrichment factors agreed well with theoretical analyses, and are functions of the pressure ratio (adsorption/desorption pressures) and adsorption affinity relative to hydrogen (selectivity). Depending on the species of interest and the volume of the enriched sample needed for analysis, the device can be designed to enrich the impurities in hydrogen in 40 min or less.