Ammonia (NH3) is easily liquefied by compression at 1 MPa and 25°C, and has highest volumetric hydrogen density of 10.7 kg H2 /100L. It has high gravimetric hydrogen density of 17.8 wt%. The heat of formation of NH3 is about 1/10 of combustion heat of hydrogen. NH3 has advantages as a hydrogen carrier for fuel cell vehicles (FCVs).
ISO 14687-2:2012 specifies the quality characteristics of hydrogen fuel. The maximum concentration of NH3 and N2 for the FCVs is 0.1ppm and 100 ppm, respectively. The minimum H2 purity is 99.97%. We need component technologies to produce high-purity hydrogen from ammonia, together with those to improve hydrogen energy efficiency.
High-performance ruthenium supported on MgO cracking catalyst was prepared. For this catalyst, NH3 conversion was 99.8% at 0.1 MPa and 500°C which was almost the same as the chemical equilibrium value. We found that the remained NH3 concentration of 1000 ppm was reduced to below 0.02 ppm using the remover including zeolite packed column. The NH3 elimination quantity was 30-40 gNH3/L. The Zeolite adsorbed NH3 was recycled by annealing below 400°C. Hydrogen purification process with pressure swing adsorption (PSA) method was established to produce high purity hydrogen above 99.98% and to reduce nitrogen below 10 ppm. Micro-channel cracker with heat supply unit and H2 purifier with off-gas supply unit were produced experimentally to improve efficiency.
In conclusion, we have developed component technologies to produce 1Nm3/h-scale high-purity hydrogen from ammonia (NH3 <0.02ppm, N2 <10ppm, H2 >99.98%) and to improve hydrogen energy efficiency by combination of the NH3 cracker, the remover and the H2 purifier. Hydrogen purification efficiency (hydrogen recovery rate) using the H2 purifier was 90%. Hydrogen energy efficiency using the micro-channel cracker was 80 %.
I am greatly indebted to Professor T. Ichikawa and Associate Professor H. Miyaoka of Hiroshima University, Dr. T. Fujitani of AIST, Mr. T. Kuriyama of Showa Denko K.K., Mr. T. Adachi of Taiyo Nippon Sanso Corporation and Mr. H. Kubo of Toyota Industries Corporation for collaboration of this work. This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier” (funding agency : JST).