Absorption process, metal hydride

Hydrides. Zirconium hydride [7704-99-6] in powder form was produced by the reduction of zirconium oxide with calcium hydride in a bomb reactor. However, the workup was hazardous and many fires and explosions occurred when the calcium oxide was dissolved with hydrochloric acid to recover the hydride powder. With the ready availabiHty of zirconium metal via the KroU process, zirconium hydride can be obtained by exothermic absorption of hydrogen by pure zirconium, usually highly porous sponge. The heat of formation is 167.4 J / mol (40 kcal/mol) hydrogen absorbed. 

Therefore, X-ray absorption spectrums, having information about character of Me-H bonds in metal-hydrides, can be used for studying influence on their thermal stability of different factors and processes. 

A high-temperature chemical heat pump system has been designed at JAERI to heat up waste heat of about 500 °C to above 1000 °C by using Ti/Cr metal hydride intermetallic compounds (Fig. 4-11). This method would improve the total energy efficiency of the hydrogen production system combined with the process heat provision by the HTTR. The system consists of a low-temperature and a high-temperature vessel with the metal hydride material. The exothermal process of hydrogen absorption by the metal is able to heat up helium to approx. 1000 °C as was demonstrated in a test system [36]. 

Pd catalyst has also been used for other metal hydrides, such as MgaNi and FeTi (Zaluska et al., 2001). Without the catalyst, an activation process is generally needed before hydrogen absorption, for example, FeTi needs to be activated by a series of long-term annealings at temperatures >400 °C. Moreover, if the material is subsequently exposed to air or water vapor, the activation process has to be repeated. With the addition of Pd nanoparticles, the FeTi nanoparticles could absorb hydrogen without activation. 

Depending on the purity required, hydrogen can be further processed by cryogenic adsorption, solvent absorption, pressure swing adsorption (PSA), cryogenic absorption using liquid nitrogen, membrane separation, and metal hydride adsorption. 

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