Hydrogen Membrane Separation Techniques

About 80% of the present world energy demand comes from fossil fuels. Unlike using fossil fuels, using hydrogen as an energy source produces water as the only byproduct. Use of hydrogen as an energy source could help to address issues related to energy security including global climate change and local air pollution. Moreover, hydrogen is abundantly available in the universe and possesses the highest energy content per unit of weight compared to any of the known fuels. Consequently, demand for hydrogen energy and production has been growing in the recent years. Membrane separation process is an attractive alternative compared to mature technologies such as pressure swing adsorption and cryogenic distillation. This paper reports different types of membranes used for hydrogen separation from hydrogen-rich mixtures. The study has found that much of the current research has been focused on nonpolymeric materials such as metal, molecular sieving carbon, zeolites, and ceramics. High purity of hydrogen is obtainable through dense metallic membranes and especially palladium and its alloys, which are highly selective to hydrogen. Thin membranes would not only reduce the cost of materials but also increase the hydrogen flux. Metal alloys or composite metal membranes have been used for hydrogen purification. However, metallic membranes are sensitive to some gases such as carbon monoxide and hydrogen sulfide. Therefore, ceramic membranes, inert to poisonous gases, are desirable. Inorganic microporous membranes offer many advantages over thin-film palladium membranes. More importantly, in microporous membranes, the flux is directly proportional to the pressure, whereas in palladium membranes, it is proportional to the square root of the pressure. The paper also discusses the advantages and disadvantages of different hydrogen separation membranes. Also, the paper reports performance of selected membranes in terms of hydrogen selectivity and permeability.