A role for ammonia in the hydrogen economy

Ammonia (NH 3) is a non-polluting fuel which produces only water and nitrogen as products of combustion. Therefore, it could be an alternative to hydrogen for vehicle motive power in the hydrogen economy. For this role 'electrolytic ammonia' would be prepared by catalytic combination of electrolytic hydrogen and atmospheric nitrogen. The background and developmental status of hydrogen and ammonia as motor-vehicle fuels are reviewed. Engine tests have demonstrated that ammonia can replace gasoline or diesel fuel for motor vehicles, giving near-theoretical values of engine power and efficiency. Ammonia is superior to hydrogen as a vehicle fuel for several reasons: it can be stored and transported as a liquid at ambient temperatures in low-pressure containers; per unit volume ammonia has 1.3 times the heating value of liquid hydrogen; ammonia is distributed internationally in quantities of over 100 million tons per year, and procedures and facilities are established world-wide for its safe handling and distribution. These factors would greatly facilitate the commercial adoption of ammonia as a practical replacement for carbonaceous fuels. The projected cost of supplying 'electrolytic ammonia' to motor vehicle filling stations is estimated to be roughly half the cost of supplying electrolytic liquid hydrogen for the same purpose, i.e. $10.5–12.5 GJ ‑1 for ammonia vs $25–30 GJ ‑1 for LH 2 (1988$). A summary is presented of the physical and thermo-chemical characteristics and estimated costs of ammonia in comparison with hydrogen, as liquid, compressed gas or stored as metal hydride. Properties of gasoline, methanol, ethanol and liquified methane are also listed.