(537e) Thermochemical Production of NH3 Used for Fertilization

Millions of people around the world suffer from chronic food deficits, including about 20% of the population in developing countries. Artificial nitrogen fertilizers are credited in part with the "green revolution" that started in the 1940's and more of these chemicals will be needed in the future to satisfy food demands. Globally, the Haber-Bosch process to produce NH3 mainly for fertilizers consumes up to 5% of all natural gas produced and 2% of the total energy production, with significant fossil-based CO2 emissions. The Haber-Bosch process cannot easily be scaled down or performed in developing countries due to the required temperature, pressure, natural gas, and utilities. Our goal is a solar-thermochemical and essentially fossil-fuel free process to produce NH3 that is scalable and can be performed in developing countries mainly due to near-atmospheric operating pressure and the absence of the need for natural gas as reactant. No catalyst will be needed.

A solar thermochemical process has been shown by Steinfeld et al. at ETH to produce ammonia at near atmospheric pressure and 1500-2000°C. Here we report on a modification that would allow the solar-driven ammonia production from water, carbon (biomass), and air to proceed near atmospheric pressure at about only 1000°C. This should alleviate some engineering issues since a significant array of materials is available for operation at 1000°C while 1500-2000°C is more challenging.

Based on thermodynamic considerations, a new reaction scheme employing vanadium, chromium, or manganese to produce NH3 was developed. The use of a mixture of water and air as oxidizing agent is proposed to avoid the need for N2 separation from air. CO2 produced is reacted to CO employing solar-thermal biomass gasification. A laboratory scale Fresnel lens based tubular solar thermochemical reactor will be used to establish feasibility of the thermochemical cycle proposed here.