Safe, Efficient Storage of Hydrogen in Liquid Ammonia and Ammonia-Based SolidChemicals

摘要

Pure anhydrous ammonia (NH3) provides an excellent storage medium forhydrogen, and two known solid organic chemicals related to ammonia, urea andguanidine, are also good storage media. Anhydrous ammonia is about 18 percenthydrogen by weight percent and has all of the advantages associated with a liquid fuel—high volumetric density, easy to store, easy to pump, easy to transport, and easy todeliver. It also has an existing and proven distribution infrastructure and is one of thehighest tonnage chemicals produced in the world. Furthermore, gaseous hydrogen can bereadily produced (reformed) from anhydrous ammonia at the highest efficiency of anyhydrogen-containing chemical. On the other hand, it is well known that ammonia is toxicwhich results in some handling/delivery safety concerns. We will discuss safe handling ofanhydrous ammonia. It turns out as well that both urea and guanidine (solids at standardtemperature and pressure) have essentially zero toxicity, are not explosive, and do notexhibit any other public or environmental hazard. Both are high in hydrogen content viatheir ammonia content, and both can be reacted with water under appropriate conditionsto provide ammonia, which can then be reformed to hydrogen as necessary. We willdiscuss the features of these two chemicals and their potential applications as safe,energy-dense hydrogen energy carriers.