New method for producing green ammonia – News

Ammonia is widely used in fertilizer production, and green ammonia could enable more sustainable agriculture

RESEARCHERS from Monash University, Australia, have discovered a method of producing green ammonia that could benefit agriculture, as well as transport.

Ammonia is an important product for the production of fertilizers. Typically, it is produced using the Haber-Bosch process, an established technology that requires high temperature (300-500°C) and pressure (20-30 MPa). According to the Royal Society, the process is responsible for around 1.8% of global CO2 emissions. While demand for ammonia is expected to increase, green production is essential to keep the world on the path to net zero emissions.

Monash researchers have discovered a method of electrochemical production that relies on a phosphonium cation as a proton shuttle. Researcher Bryan Suryanto said the reaction can produce ammonia “at room temperature. at high and convenient rates and efficiency”. Importantly, the Monash team showed that the phosphonium cation is recycled during the process.

Doug MacFarlane, professor of chemistry at Monash, explained that the process developed takes place in an electrochemical cell, where water and nitrogen gas (separated from air) are introduced. At the cathode, the presence of nitrogen leads to the reduction of lithium ions. (in the electrolyte) to lithium nitride, which is then protonated to release ammonia (NH3). This leaves the cell in the gas stream and is then separated from the circulating nitrogen. It can then be compressed and liquefied, then stored.

After donating a proton, the phosphonium cation becomes a ylide, which passes to the anode where it is reprotonated to its phosphonium form by reacting with the protons of hydrogen.

In 20-hour experiments, under 0.05 MPa of hydrogen and 1.95 MPa of nitrogen, the research team achieved production rates of 53 ± 1 nmol/s/cm2. Since publishing their work, the team has increased throughput, and according to MacFarlane, they are working to achieve a unit that produces 100g/d of ammonia this year. MacFarlane added that this is a production scale that would be useful in small hydroponic and commercial greenhouses.

A future goal for the team is to create shipping container-sized plants that generate 1 t/d of ammonia, consuming 1 MW of energy, that could be sited and used by farms. The power plants could be powered by dedicated solar and wind farms.

Small, localized plants are a potential advantage offered by this technology over Haber-Bosch, which cannot be economically realized on a smaller scale due to the need for high temperature and pressure conditions.

Another potential benefit of small, localized facilities is that they could help avoid the polluting effects of fertilizers. MacFarlane said that in some settings, the ability to produce fertilizer “on demand” would allow farmers to apply it in small amounts more frequently, or even continuously, rather than adding it in bulk at certain stages of the growing cycle. plant growth. As a result, fertilizers would not be left in the ground for long periods of time and would oxidize to by-products such as nitrates – which can run off and seep into groundwater – or greenhouse gas nitrous oxide, which evaporates from the fields.

The work to achieve the scaling goals is a mission of Jupiter Ionics, the spin-off company working on commercial application development.

In addition to fertilizer production, ammonia can be used to replace fossil fuels in many applications, such as in the transportation sector, and by acting as a hydrogen carrier and energy store.

Considering other applications for ammonia, particularly use in the energy system, MacFarlane stressed the need to be aware of potential pollution issues. Using ammonia as a fuel can cause fugitive losses from engines of polluting compounds such as ammonia, nitrous oxide and other nitrogen oxides. He warned that it is therefore important to employ mitigation measures, to avoid damaging the environment with nitrogen compounds as we have done with CO2 and other carbon compounds.

Science: https://doi.org/gkh2q3

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