FUELS – HYDROGEN PRODUCTION | Gas Cleaning: Pressure Swing Adsorption

Abstract

The present drive to develop a hydrogen-based economy poses several technological challenges that must be addressed to provide an ample supply of pure hydrogen to meet future energy demands. The purification of hydrogen to the levels required by certain end-use technologies, particularly fuel cells, is a key issue. Four proven technologies are commercially available, namely membrane separation, cryogenic distillation, solvent extraction, and pressure swing adsorption (PSA). On a small scale, filtration through a hot palladium membrane has been used in the electronic industry to produce ultrapure hydrogen for reducing traces of oxides in semiconductor wafers. The high cost of palladium and the operating condition limit scale-up of this technique. Both cryogenic distillation and solvent extraction are energy intensive, and in the latter method, the disposal of spent solvent is hazardous. By contrast, PSA is very economical for the purification of bulk amounts of hydrogen. Modern PSA plants can handle up to 100 000 N m 3 h −1 of hydrogen with a purity close to 99.99%. The large size, capital cost, and sensitivity to both feed composition and flow are some of the issues that still need to be addressed with the PSA technology. Nevertheless, in terms of energy demand and operational cleanliness, the PSA technology is far superior to membrane separation, cryogenic distillation, and solvent extraction technologies. This article describes the current state-of-the-art and future challenges of hydrogen purification by PSA.