ShareNew energy-efficient way to make ammonia
The traditional way of manufacturing ammonia leaves a huge carbon footprint. An Australian team of researchers have found a cheaper and greener way to make ammonia from air, water, and renewable electricity.
Since the beginning of the 20th century, ammonia has been produced using 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 around 400°C and at pressures of up to around 20 MPa, absorbs between 1 and 2% of the world’s total energy production [1][3]. According to the Institute for Industrial Productivity, 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 since it has a GWP of 0.
A team of researchers from UNSW Sydney and from the University of Sydney has published a paper [2] in Energy & Environmental Science examining a way to produce ammonia at lower cost, with renewable energy, and on a smaller scale than usual.
One of the authors of the paper, Dr Jalili, says that trying to convert atmospheric nitrogen (N2) directly into ammonia using electricity “has posed a significant challenge to researchers for the last 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 N2 in the air.
“Working with our University of Sydney colleagues, we designed a range of scalable plasma reactors that could generate the NOx intermediary at a significant rate and high energy efficiency,” he says.
“Once we generated that intermediary in water, designing a selective catalyst and scaling the system became significantly easier. The breakthrough of our technology was in the design of the high-performance plasma reactors coupled with electrochemistry.”
Professor Patrick Cullen, who led the University of Sydney team, adds: “Atmospheric plasma is increasingly finding application in green chemistry. By inducing the plasma discharges inside water bubbles, we have developed a means of overcoming the challenges of energy efficiency and process scaling, moving the technology closer to industrial adoption.”
The team’s "green" method of ammonia production 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 have to compress or liquify it,” says Professor Amal, co-director of ARC Training Centre for Global Hydrogen Economy [3].
“But liquid ammonia actually stores more hydrogen than liquid hydrogen itself. And so there has been increasing interest 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