HYDROGEN STORAGE AND GENERATION PROPERTIES OF AMMONIA AND ALKALI METAL HYDRIDE SYSTEM

摘要

Ammonia NH_3 is an attractive hydrogen carrier because of high gravimetric and volumetric hydrogen density 17.8 mass% and 10.7 kg/100L, respectively, in liquid state under about 0.8 MPa of pressure at room temperature. However, synthesis and thermolysis of NH_3 requires high pressure (＞ 10 MPa) and temperature (＞ 400 ℃). Kojima et al. and Yamamoto et al. proposed the following reaction between NH_3 and alkali metal hydride MH (M = Li, Na, K) as hydrogen storage system, NH_3 + MH ⇄ H_2 + MNH_2. The H_2 generation of the systems proceeds at room temperature by exothermic reaction to form amide MNH_2 as product. MNH_2 is recycled back to NH_3 and MH below 300 ℃ under H_2 flow condition, in which the equilibrium state of the endothermic reaction is shifted by reducing partial pressure of NH_3 around the reaction field. Thus, the NH_3-MH systems is recognized as the promising hydrogen storage system because of the lower H_2 desorption and absorption temperature than 300 ℃. In addition, by performing the reaction between liquid NH_3 and LiH in a closed reactor, more than 20 MPa of compressed hydrogen can be produced without any heat sources and mechanical compressor. Therefore, the H_2 generation reaction of the NH_3-LiH system can be utilized as chemical compressor as well. This work was partially supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), -energy carrier" (Funding agency: JST).