High Purity Hydrogen from Liquid NH3 - Proposal and Evaluation of a Process Chain

This study proposes a process chain to gain high purity hydrogen from liquid ammonia. The utilization of the stored hydrogen requires the endothermic decomposition of ammonia2 NH3 ? N2 +3 H2(1)and the subsequent purification of H2. A process model from liquid NH3 to high purity hydrogen was developed. The process model includes the reaction kinetics for the catalytic decomposition of NH3 using a catalyst, such as Ni-Pt/Al2O3, and the necessary purification steps. Based on the simulation, a final process chain is proposed. Finally, heat integration calculations were performed to optimize the energy efficiency of the process. The application of a polyimide membrane system is proposed. The performed calculations show that using membrane separation, a H2 purity of around 97 wt% can be achieved. For a final NH3 content of < 1 ppm, the study found acidic or adsorptive removal of remaining NH3 necessary even for high decomposition conversion rates. To achieve even higher H2 purity, the application of an additional pressure swing absorption separation is proposed. This application can ensure H2 purities of > 99 wt% suitable for PEM fuel cells.