An evaluation of the metal hydride hydrogen extraction efficiency from biological gas streams

Selectivity of metal hydrides to reversibly absorb hydrogen makes them promising candidates for hydrogen extraction or separation from different gas mixtures. In combination with their high volumetric capacity, safety and simple maintenance metal hydrides provide to construct highly efficient hydrogen separation systems. LaNi₅ based intermetallic compounds have superior overall characteristics such as variable hydrogen equilibrium pressure, fast kinetics, impurity resistance and good cyclic stability. Present study aims to investigate metal hydride alloys in terms of applicability to hydrogen separation from dilute hydrogen gas mixtures in a flow-through tubular metal hydride reactor. Samples of AB₅-type alloys LaNi_4.4Fe_0.3Al_0.3 and LaNi_4.6Mn_0.2Al_0.2 were prepared and their properties were measured. Due to low equilibrium pressures (0.35 bar for LaNi_4.4Fe_0.3Al_0.3 and 0.4 bar LaNi_4.6Mn_0.2Al_0.2 at 25 °C) they are potential candidates for biohydrogen purification. Analytical solution for hydrogen separation efficiency (recovery) is obtained and possibility of hydrogen extraction from a biohydrogen stream (1 bar, 50% H₂, 10 and 25 °C) is analyzed.