(657b) Development of a Pressure Swing Adsorption Reactor to Produce NH3 for Use As Naval Fuel

Decarbonizing the U.S. Naval fleet is a key goal of the U.S. Department of Defense (DoD) to curb CO₂ emissions. If the DoD were a sovereign nation, they would be the 56^th largest greenhouse gas emitter, surpassing countries like Switzerland, Peru, and Denmark. Two viable alternatives to hydrocarbon-based Naval fuels are H₂ and NH₃ or both. The synthesis of NH₃ at sea from air (N₂ source) and water (H₂ source) presents numerous challenges. Process intensification would certainly mitigate some of these challenges.

One way to intensify a process is to carry out reaction and separation in the same vessel. The concept of a pressure swing reactor that can do reaction and separation in the same vessel has been around for several decades. However, this concept has yet to be commercialized, although several patents have been issued and some novel approaches have been tested at various scales.

A pressure swing adsorption reactor (PSAR) combines a pressure swing adsorption (PSA) process and a heterogeneous catalytic reaction in such a way that a higher conversion can be achieved via Le Chatelier's principle. The difficulty is to find a suitable adsorbent that operates at or near the conditions of the catalytic reactor, i.e., at high temperature and pressure. High pressure is conducive to adsorption, but high temperature is not. In fact, most adsorbents are regenerated at temperatures far below the conditions of a catalytic reactor. Nevertheless, there are some catalytic systems that present an excellent opportunity for the design of a PSAR. The synthesis of ammonia from hydrogen and nitrogen is one such system.

Initial process simulations of a PSAR for NH₃ production have shown that very high conversions can be obtained by using a commercial adsorbent that reversibly adsorbs ammonia at high temperature by carrying out a relatively simple pressure swing cycle. The goal of this work is to experimentally validate the simulation results. For this purpose, a bench-scale PSAR has been set-up that is being used to study 1) rection kinetics of the conversion of H₂ and N₂ to NH₃ under dynamic and steady state conditions using a commercial catalyst and 2) to study the conversion of H₂ and N₂ to NH₃ in the absence and presence of the adsorbent. This presentation will present the latest results obtained from this effort.