International. Since the early twentieth century, ammonia is produced by the Haber-Bosch process. This is a chemical process that converts nitrogen and hydrogen into liquid ammonia. The reaction, which takes place at temperatures of about 400 °C and pressures of up to 20 MPa, absorbs between 1 and 2% of the world's total energy production [1][3]. According to the Industrial Productivity Institute, it caused the emission of approximately 451 million t of CO2 in 2010.
Ammonia is used as a refrigerant in the refrigeration industry. It is an interesting alternative to HFCs as it has a GWP of 0.
A team of researchers from UNSW Sydney and the University of Sydney has published a paper [2] in Energy & Environmental Science examining a way to produce ammonia at a lower cost, with renewable energy and on a smaller scale than usual.
One of the paper's authors, Dr. Jalili, says that trying to convert atmospheric nitrogen (N2) directly into ammonia using electricity "has posed a significant challenge for researchers over the past decade, due to the inherent stability of N2 that makes it difficult to dissolve and dissociate." [3]
Dr. Jalili and his colleagues devised proof-of-concept lab experiments that used plasma (a form of lightning made in a tube) to convert air into an intermediate known to chemists as NOx, either NO2- (nitrite) or NO3- (nitrate). The nitrogen in these compounds is much more reactive than the N2 in the air.
"Working with our colleagues at the University of Sydney, we designed a range of scalable plasma reactors that could generate the NOx intermediate at a significant rate and with high energy efficiency," he says.
"Once we generated that intermediate in water, designing a selective catalyst and scaling the system became significantly easier. The advancement of our technology was the design of high-performance plasma reactors along with electrochemistry."
Professor Patrick Cullen, who led the team from the University of Sydney, adds: "Atmospheric plasma is increasingly finding applications in green chemistry. By inducing plasma discharges within water bubbles, we have developed a means to overcome the challenges of energy efficiency and process scale, bringing the technology closer to industrial adoption."
The "green" method of the ammonia production team could solve the problem of storing and transporting hydrogen energy.
"Hydrogen is very light, so you need a lot of space to store it, otherwise you will have to compress or liquefy it," says Professor Amal, co-director of the ARC Training Centre for the Global Hydrogen Economy [3].
"But liquid ammonia actually stores more hydrogen than liquid hydrogen itself. That is why interest has increased in the use of ammonia as a potential energy vector for a carbon-free economy."
Sources:
[1] ALBONETTI S., PERATHONER S., QUADRELLI E. A., Horizons in sustainable industrial chemistry and catalysis, vol. 178. Amsterdam: Elsevier, 2019, 444 p. Link.
[2] SUN J., ALAM D., DAIYAN R., et al. A hybrid plasma electrocatalytic process for sustainable ammonia production. Energy & Environmental Science. 2021. DOI: https://doi.org/10.1039/D0EE03769A
