The commercial production of ammonia en masse began in the early 1900’s and since then it has played an increasingly important role in the world’s food supply. Prior to ammonia synthesis being realized, fertilization was achieved using either manure-based fertilizer or using nitrate salts which had to be mined.
The increasing need for nitrogen-based fertilizers in the early 20th century resulted in the development of the Haber-Bosch process, which uses high pressure and temperature, alongside a catalyst, to produce ammonia from nitrogen and hydrogen gas. Despite the extreme conditions, this reaction occurs at a very low efficiency, meaning ammonia production plants must use very large reactors.
The production of ammonia is the largest source of greenhouse gas emissions – the process uses 1% of the world’s energy consumption and is responsible for 1% of total greenhouse gas emissions. In addition to the energy consumed during its production, further emissions are associated with the transport of ammonia to sites of use.
Green Ammonia
As ammonia production is so important, and due to its current environmental inefficiency, a new cleaner method of producing ammonia must be developed.
On-site gas generation could play a role in this. Gas generators can be used to produce nitrogen via pressure swing absorption, and to produce hydrogen via electrolysis – neither of which emit greenhouse gases. Using green gas generation on-site, alongside a small Haber-Bosch reactor, allows ammonia to be produced at the point of need.
Localizing the production of ammonia, using renewable methods of gas generation, also removes the carbon dioxide emissions associated with the transportation of ammonia. Research conducted at The University of Minnesota showed that nitrogen and hydrogen generation could be driven by wind generation, with the gases produced reacted in a small-scale reactor.
However, it was also noted that extremely efficient methods of heating and cooling the reactor were required to counteract the negative impact the small reactor size has on efficiency. Heating is required to drive the process, whereas cooling is needed to condense the ammonia produced.
A Better Way of Producing Green Ammonia
The majority of the research around producing green ammonia has focused on using green hydrogen and nitrogen sources to minimize emissions; however, the main source of inefficiency is the method used to synthesize ammonia. For this reason, new methods of ammonia synthesis should be focused on.
It has been found that Alkaline Exchange Membranes (AEMs) can be used for the energy efficient synthesis of ammonia. Efficiency gains are achieved because AEMs use just one electrochemical reaction, without excessive heat or pressure, to produce ammonia, as opposed to three reactions in the Haber-Bosch process.
AEMs function in a similar way to Proton Exchange Membranes (PEMs) though they use basic chemistry as opposed to the acidic chemistry of PEMs. Base chemistry is required as an acid-based membrane would react with the ammonia produced, due to ammonia being basic. If used alongside an appropriate catalyst, AEM has the potential to be a greener alternative to the huge-scale production of ammonia using the Haber-Bosch process.
Nel Hydrogen has invested heavily in research into the electrochemical production of ammonia and hope that developments in AEM design, alongside the development of novel catalysts, will help green ammonia production become a reality.
This information has been sourced, reviewed and adapted from materials provided by Nel Hydrogen.
For more information on this source, please visit Nel Hydrogen.