(618e) Future of Ammonia Production: Improvement of Haber-Bosch Process or Elecrochemical Synthesis?

Ammonia, the second largest produced chemical in the world (176 million tons in 2014), is manufactured at large plants (1,000 – 1,500 t/day) using Haber-Bosch process developed more than hundred years ago. A simple reaction of nitrogen and hydrogen (produced by steam methane reforming or coal gasification) consumes about 2% of world energy, in part due to the use of high pressure and temperature. With world transition from fossil fuels to intermittent renewable energy sources there is a need in long term storage and long range transmission of energy, for which ammonia is perfect fit. To make it practical, it is necessary to match ammonia production scale with scale of renewable energy sources at the same or better capital cost per ton of NH₃ and reduce the energy consumption.

The Advanced Research Projects Agency (ARPA-E) invests in transformational, high risk early stage research to create America’s future technologies for generation, use, and storing energy thus ensuring US technological lead. The Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program funds the development of transformational technologies to reduce the barriers to widespread adoption of intermittent renewable energy sources by enabling the conversion of energy from these sources, water and air to energy-dense zero-carbon liquid fuels, mainly focusing on ammonia.

REFUEL program funds projects related to two major paths that may potentially reduce both capital and energy costs of ammonia production: dramatically improving conventional Haber-Bosch process or its replacement it with direct electrochemical synthesis. New generation of Haber-Bosch chemistry should work at lower pressure and temperature, which can be achieved by using of more active catalysts or combination of catalysts with physical activation and by continuous ammonia removal from reaction zone thus shifting the equilibrium. To make it competitive with conventional process, the process efficiency should be >86% and catalyst should provide reaction rate at least 7x10^-7 mol cm^-2 s^-1. Direct electrochemical ammonia synthesis from nitrogen and water has a potential for big energy savings due to reduction of number of process steps and pressure/temperature. In addition, electrochemical technologies are easily scaled down to allow for low capital, modular plants that match the scale of renewable energy production. REFUEL program very challenging target for the electrochemical process is 60% energy efficiency at current density > 300 mA cm^-2 and 90% coulombic efficiency. In this presentation a comparison of these two future ammonia production technologies will be made and REFUEL projects targeting various approaches to ammonia synthesis as well as related projects supported by ARPA-E through OPEN program will be highlighted.