A Short Review on Various Purification Techniques Suitable for Biohydrogen-Mixed Gases

The need of establishment of biohydrogen purification techniques is due the fact that biohydrogen production will be completely transformed into industrial scale soon or later. For biohydrogen process development to be commercially feasible, all the process involved, including purification should be low cost, practical and efficient; particularly when the biohydrogen production is technically challenging. In any case, carbon dioxide and other gaseous impurities are usually evolved during hydrogen production, and highly purified hydrogen is desirable in fuel cells application and other hydrogenation processes. Particularly, is critical to achieve high purity of hydrogen especially in a fuel cell application where it requires 99.9% only hydrogen. This paper reviews four main principle methods that are suitable for biohydrogen mixed gases, namely cryogenic separation, absorption, adsorption and membrane separation. The comparison based on their strengths and weaknesses, regarding the rate and yield of hydrogen, energy requirement and efficiency in terms of hydrogen selectivity, recovery and purity for fuel cell application. Cryogenic separation is among the earliest technique used for hydrogen purification. Though, due to the low temperature requirement, cryogenic separation is least preferred as gas separation is energy intensive and costly. Cyrogenic separation is commonly combine with membrane separation. It was also acknowledged that the membrane separation technique is widely used for biohydrogen purification. Most of research mostly in advancement of the membrane for high selectivity for hydrogen and low selectivity for carbon dioxide.Another method, pressure swing adsorption (PSA) is one of commonly used in conventional hydrogen purification. The hydrogen purity produced by PSA was higher than absorption but the cost to operate it is the same at the expense of low hydrogen recovery. Also, chemical absorption of hydrogen separation from mixed gaseous mixture is discussed due to its simplicity of operation and possible to operate using existing common absorber.