Nearly all ammonia is produced using methane via the Haber-Bosch process, which requires high-temperature and high-pressure operation. A new portable prototype device developed by researchers from Stanford University (Stanford, Calif.; www.stanford.edu) and King Fahd University of Petroleum and Minerals (Dhahran, Saudi Arabia; www.kfupm.edu.sa) has demonstrated the production of ammonia from ambient air without any external electricity or radiation source.
Using wind as its motive force, air is drawn through a special catalyst mesh consisting of magnetite (Fe3O4) and Nafion fluoropolymer. Capturing nitrogen from the air and hydrogen from water-vapor microdroplets, the catalyst-mesh structure facilitates the reaction to form an ammonia-rich aqueous solution within the device. This solution is collected by a condenser plate to separate it from any unreacted air or water vapor in the reaction chamber. The performance of the device depends on many environmental factors, such as humidity and wind speed, as well as the size, salt content and acidity of the water droplets. The researchers tested the device in the field at nine different locations in California’s Bay Area to verify its performance over a wide range of relative humidities, temperatures and wind speeds. The device has demonstrated its ability to produce ammonia solution of sufficient concentration (25 to 120 μM in 1 hour, depending on local relative humidity) for use as a hydroponic fertilizer.
Ammonia synthesis could be integrated with agricultural irrigation systems
Other properties that were tuned to improve ammonia synthesis included the pore size of the mesh and the size distribution of water microdroplets entering the chamber. Larger pore sizes led to less-effective catalytic interaction, while pores that were too small condensed the gas and water before they could pass through the mesh and react.
The ability to generate ammonia onsite for fertilizer applications is extremely beneficial, as it eliminates the need for storing and transporting materials. The researchers hope that the device could eventually be integrated with irrigation systems, enabling localized, on-demand ammonia production for agricultural sites. They are currently working to expand the mesh-system size to produce larger volumes of ammonia.