The Haber process currently helps feed more than half the world, producing 150m tonnes of ammonia a year. This is forecast to rise further, in line with the food demand of a growing world population.
And yet, it has serious drawbacks. In its traditional form, the process requires high temperatures – around 500°C – to make the extremely stable molecule nitrogen reactive.
The Haber process takes place at extremely high temperatures, similar to that of an average fire.
It also needs high pressure to shift the equilibrium towards the desired product. The process is sensitive to oxygen, meaning that nitrogen and hydrogen must be introduced as purified elements, rather than as air and water.
These requirements together make the process extremely energy-hungry; estimated to consume between 1% and 2% of global primary energy production. In 2010, the ammonia industry emitted 245m tonnes of CO2 globally, corresponding to half the UK’s emissions.
The Haber process was developed by Carl Bosch (left) and Fritz Haber (right) in the early 20th century. Image: Wikimedia Commons
In nature, the process relies on the highly complex enzyme nitrogenase, operating at an ambient pressure and temperature. But using the entire biological system would not be economical for large-scale industrial synthesis, and thus the search for an inorganic system that matches the performance of the biological has become an important challenge.
In recent years, novel electrochemical approaches and new catalysts have yielded promising results suggesting that, at least for small-scale synthesis, other ways may have a future.
The chemical reaction that feeds the world. Video: TED-Ed
‘The last [few] years brought some spectacular results on ammonia synthesis research,’ comments Hans Fredriksson from Syngaschem at Eindhoven, Netherlands.
‘On the catalyst side, there is the discovery of ‘super promoters’, helping N2 dissociation, allowing lower process temperatures, while optimised catalyst formulations yield significant improvements in activity.
‘Perhaps even more exciting are new approaches in processing, for example by electrochemistry, or simply running the reaction in an electric field, or bringing plasmas into play,’ he said.
In 2013, Shanwen Tao, then at the University of Strathclyde, Glasgow, UK, and colleagues demonstrated for the first time the production of ammonia from air and water, at ambient temperature and pressure, using a proton-conducting Nafion membrane in an electrochemical approach.
Nafion, a Teflon-like material that conducts cations but neither electrons nor anions, is also used in fuel cells.
‘Electrochemical synthesis of ammonia is an important new approach for efficient synthesis of ammonia using green renewable electricity as the energy source. This could be a key technology for a possible ‘ammonia economy’,’ where ammonia replaces or complements hydrogen as an energy carrier, says Tao.
Researchers hope new approaches will be supported by renewable energy, reducing CO2 emissions. Image: Pexels
Separate efforts using different routes are being developed in Japan, with a particular focus on ruthenium as an efficient catalyst. One approach is to apply super promoters to provide electrons that destabilise nitrogen by weakening the triple bond and making the molecule more reactive for ammonia synthesis.
This was first reported in 2012 by Hideo Hosono’s group at the Tokyo Institute of Technology, who used ruthenium catalysts in combination with ‘electrides’ – a new class of ionic materials where electrons serve as the anions.
The method operates at atmospheric pressure and temperatures between 250 and 400°C, and hydrogen poisoning of ruthenium catalysts is no longer a problem.
Ruthenium is a type of metal in the platinum group. Image: Metalle-w/ Wikimedia Commons
‘This catalyst exhibits the highest activity and excellent long-term stability,’ says Hosono, who sees the future of his methods in distributed, small-scale applications of ammonia synthesis.
Hans Niemantsverdriet, director of SynCat@Beijing, China, acknowledges the rapid progress being made, but also strikes a note of caution.
‘In spite of interesting discoveries, I find it hard to imagine that these improvements will be able to replace the current large-scale and fully optimised technology,’ he says. ‘In the fertiliser area, novel technology will at best become a niche market for very special situations. Also, the CO2 footprint is hardly diminished.’
Ammonia is a core component of fertiliser, feeding nitrogen to plants for photosynthesis. Image: Maurice van Bruggen/Wikimedia Commons
In the long term, Niemantsverdriet has hope for the ammonia economy as championed by Tao and others, providing carbon-free hydrogen from renewable energies.
‘I strongly believe that there will be scope for large industrial parks where this technology can be cleverly integrated with gasification of coal in China, and perhaps biomass elsewhere,’ he says. ‘If dimensioned properly, this has the potential to reduce the carbon footprint in the future.’
English wine is on the rise. In 50 years, production has increased by more than three orders of magnitude, from a negligible 1,500 bottles/year to a respectable 5.3 million.
Meanwhile, on the other side of the English Channel, grapes are harvested around two weeks before the traditional dates. In the Champagne region, harvest kicked off on 26 August 2017, while the average date for previous years was 10 September. In Burgoyne, home of Beaujolais wines, harvest began on 23 August, also two weeks ahead of schedule. Harvest workers in that area are also doing night shifts to reduce heat stress for the sensitive grapes.
French vineyards are struggling with the changes to traditional harvests. Image: Max Pixel
Both phenomena – the success of English wine and the earlier harvests in France – are linked to climate change. In a few decades, the favourable wine-growing conditions historically enjoyed by the Champagne region may have migrated to England.
As the life cycle of the grapevine – and therefore quality and quantity of the wine obtained – is extremely sensitive to temperature and weather extremes, wine growers have already been noticing the effects of climate change for years. Researchers have detailed how conditions have changed, how they are likely to change further, and what vineyards can do to adapt.
All agricultural products are likely to be affected by climate change at some point, but wine occupies a special position due to its high value. Therefore, wine growers have always watched the weather and its effects on their vineyards very closely, and recorded their observations.
Climate scientist Benjamin Cook from Columbia University at New York and ecologist Elizabeth Wolkovich from Harvard University, have analysed harvest data spanning more than 400 years, from 1600 to 2007, from European regions, together with the weather data.
While many studies have covered the last few decades, this one reaches back to the time before the Industrial Revolution.
Higher temperatures in spring and summer generally speed the whole process and lead to earlier harvests, like the one in 2017, while cool and rainy summers can delay the phrenology and thus the harvest time. Traditionally, the observation was that a warm summer and a period of drought just before grape picking is the best recipe for an early harvest.
Grape picking is easiest after a warm summer. Image: Pixabay
‘Our research, and other work, has clearly and unequivocally demonstrated that climate change is already affecting viticulture worldwide,’ explains Cook, adding that: ‘There are lots of opportunities for adaptation in various locations, such as planting different varieties, but the most important thing is for people to starting planning for the next several decades, when conditions are likely to get even warmer still.’
Adapt or move?
So, what could be changed? Short of pulling up Pinot Noir vines in Champagne and replanting them in Dorset, there are some steps wine-makers can take to ensure a good harvest.
The Chemistry of Wine. Video: Reactions
For instance, growers could add a few days to the ripening cycle by delaying the spring pruning, or by allowing the vines to grow higher above the ground, where the air is slightly cooler than just above the soil. While these changes are benign, other measures, such as reducing the leaf area, may have complex consequences that could interfere with the quality of the wine.
In selecting the plant material, growers could reverse the trends of the 20th Century, when it made sense to select rapidly ripening varieties. Simply by adapting the choice of variety from among the range of varieties already used in a given region to the changing climate, growers can to some extent mitigate the anticipated effects.
Alternatively, wine production could migrate closer to the poles. Wines now coming from California may be produced in Washington State, and the premium fizz we now call Champagne may one day be known as Devon or Kent.