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

Abstract

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.

Innovative metal oxides (CaO, SrO, MgO) impregnated waste-derived activated carbon for biohydrogen purification

“…Based on the technical feasibility considered in terms of stability, simplicity and productivity, the dark fermentation is the technical challenge 2 . Via this successive process, the principal compositions of produced biohydrogen are H 2 and CO 2 3 , in which approximately 56% of H 2 was obtained at 35 °C and 1 atm 4 . A high H 2 purity of the produced biogas can be obtained using various purification processes such as cryogenic process 5 , absorption 6 – 8 , membrane separation 6 , 9 – 11 or their combined process 12 , 13 .…”

“…Nevertheless, each process exhibits both technical benefits and drawbacks. For example, the cryogenic process exhibits the capability to purify the CO 2 -rich gas stream (CO 2 ~ 90%) and able to produce liquid CO 2 , but it is the energy intensive and complex 3 . The absorption is able to recover high CO 2 quantity from a low pressure gas stream with low energy requirement for H 2 compression; however it requires extensive energy for solvent recovery and has a solvent loss 3 , 7 .…”

“…For example, the cryogenic process exhibits the capability to purify the CO 2 -rich gas stream (CO 2 ~ 90%) and able to produce liquid CO 2 , but it is the energy intensive and complex 3 . The absorption is able to recover high CO 2 quantity from a low pressure gas stream with low energy requirement for H 2 compression; however it requires extensive energy for solvent recovery and has a solvent loss 3 , 7 . The membrane separation requires the minimal utility in operation and allows an in-situ and continuous flow of biohydrogen, but it gives a low product purity and recovery and also requires the pre-filter/coalescer and/or the gas compression system 3 , 9 .…”

“…The absorption is able to recover high CO 2 quantity from a low pressure gas stream with low energy requirement for H 2 compression; however it requires extensive energy for solvent recovery and has a solvent loss 3 , 7 . The membrane separation requires the minimal utility in operation and allows an in-situ and continuous flow of biohydrogen, but it gives a low product purity and recovery and also requires the pre-filter/coalescer and/or the gas compression system 3 , 9 . Another possible process might be the adsorption 14 – 16 , because of its high efficiency to produce high purity biohydrogen, environmentally friendly, ease of operation and control 3 , 17 – 19 .…”

“…The membrane separation requires the minimal utility in operation and allows an in-situ and continuous flow of biohydrogen, but it gives a low product purity and recovery and also requires the pre-filter/coalescer and/or the gas compression system 3 , 9 . Another possible process might be the adsorption 14 – 16 , because of its high efficiency to produce high purity biohydrogen, environmentally friendly, ease of operation and control 3 , 17 – 19 .…”