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A multistage metal hydride hydrogen compression (MHHC) system uses a combination of hydride materials in order to increase the total compression ratio, whilst maximizing the hydrogenation rate from the supply pressure at each stage. By solving the coupled heat, mass and momentum conservation equations simultaneously the performance of a MHHC system can be predicted. In the current work a numerical model is proposed to describe the operation of a complete compression cycle. Four different MHHC systems are examined in terms of maximum compression ratio, cycle time and energy consumption and it was found that the maximum compression ratio achieved was 22:1 when operating LaNi 5 (AB 5 -type) and a Zr-V-Mn-Nb (AB 2 -type intermetallic) as the first and second stage alloys respectively in the temperature range of 20 °C (hydrogenation) to 130 °C (dehydrogenation).

Hydrogen separation membranes based on a heated metal foil of a palladium alloy, offer excellent permeability for hydrogen as a result of the solution-diffusion mechanism. Here, the possibility to separate hydrogen from the mixture of Natural Gas (NG) and hydrogen (NG+H 2) with various NG concentrations using Pd, PdCu 53 and PdAg 24 hydrogen purification membranes is demonstrated. Hydrogen concentrations above ~ 25% (for Pd and PdCu 53) and ~ 15% (for PdAg 24) were required for the hydrogen separation to proceed at 400 °C and 5 bar pressure differential. Hydrogen permeability of the studied alloys could be almost fully recovered after switching the feed gas to pure hydrogen, indicating no significant interaction between the natural gas components and the membranes surface at the current experimental condition. Hydrogen flux of the membranes at various pressure differential was measured and no changes in the hydrogen permeation mechanism could be noticed under (NG 50%+H 2) mixture. The hydrogen separation capability of the membranes is suggested to be mainly controlled by the operating temperature and the hydrogen partial pressure.