Water and air are all you need to make ammonia—one of world's most important chemicals

Aug 08, 2014 by Jake Jacobs, The Conversation
Greener fertilisers are coming your way. Credit: James T M Towill, CC BY-SA

Researchers have developed a method to produce ammonia simply from air and water. Not only is it more energy efficient than the century-old Haber-Bosch process currently in use all over the world, but it is also greener.

Ammonia – made up of three parts hydrogen and one part (or NH3) – has had a momentous impact on society. Without the of this chemical, it is estimated that as many as a third of us won't be alive. This is because its main use is to make fertilisers, which have helped improve and sustain a large population.

Developed in 1909, the Haber-Bosch process – often cited as the most important invention of the 20th century – involves heating purified nitrogen and at very high temperature and pressure in presence of an . The presence of the catalyst, which doesn't take part in the reaction but lowers the energy threshold of the reaction, is vital. Despite which, 's production – about 140m tons in 2012consumes nearly 2% of the world's energy supply.

Apart from large energy requirements to achieve reaction conditions, the current production method is inefficient because it needs hydrogen gas, which is obtained by processing . The byproduct of the process is carbon dioxide. Stuart Licht and his colleagues at the George Washington University thought they could do better if they could find a way of using water instead of natural gas as a source of hydrogen.

Previous attempts at combining water (made up of two parts hydrogen and one part oxygen) with air (which consists of 78% nitrogen) to form ammonia have been less successful. Licht's solution was to bubble wet air through a mixture of tiny particles of iron oxide and molten chemicals (made up of sodium and potassium hyroxide) that is zapped with electricity.

Any chemical reaction is basically the exchange of electrons between atoms. In this case, those electrons are necessary to tease out the hydrogen from water and then combine with nitrogen. "When electricity is applied, the iron oxide captures electrons to permit water and air to directly react to form ammonia," Licht said.

This method claims to use only two-thirds of the energy of the Haber-Bosch process. Along with the elimination of the need to produce hydrogen from natural gas, the overall emissions are reduced quite significantly. The whole process also takes place at milder conditions, not requiring 450°C and 200 times atmospheric pressure as the Haber-Bosch process does.

These are not all that make Licht's method attractive. Some of the energy is sourced through another technology Licht has developed called solar thermal electrochemical production, or STEP. It is considered to be one of the most efficient solar cells currently in use. STEP when applied to making ammonia leads to production of as a byproduct.

This byproduct would be suitable for hydrogen fuel cells, another popular avenue for clean-energy enthusiasts, according to David Fermin, professor of electrochemistry at the University of Bristol. "Hydrogen generated in this manner is significantly cleaner," he said.

However, it is one thing to show off the success of chemical production in labs and quite another to replicate it on an industrial scale. Licht admits that there is room for improvement but he is confident that it could work. Fermin has a caveat to add, "Before going for full scale up, a better understanding of the mechanism in this complex multi-electron transfer will be required."

But even with Licht's method, Fermin points out that we are far away from being able to replicate nature's efficiency at converting nitrogen from the air to useful chemicals, which is done by nitrogen-fixing bacteria. "What is truly remarkable is that nature does it incredibly efficiently at low-temperature," Fermin added.

And yet, if something more efficient can replace the Haber-Bosch process, it would lower the energy input of the production of one of the worlds most important chemicals and lead to a notable reduction in global CO2 emissions.

Explore further: Scientists discover channel used by catalyst to produce ammonia, vital for food and fuel crops

More information: "Ammonia synthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3," by S. Licht et al. Science, www.sciencemag.org/lookup/doi/… 1126/science.1254234

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User comments : 11

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shavera
not rated yet Aug 08, 2014
What's the catch here?
rhsthjnty
4 / 5 (4) Aug 08, 2014
The catch is that it hasn't been upscaled yet.
Pexeso
not rated yet Aug 08, 2014
Currently about 2% of total energy production is consumed just for production of ammonia.
Scottingham
5 / 5 (1) Aug 08, 2014
my bet is that the ' molten chemicals (made up of sodium and potassium hyroxide)' are hella caustic and difficult to deal with at industrial levels.
tadchem
not rated yet Aug 08, 2014
This process combines the chemical reaction of the Haber process with the chemical reaction of the reduction of water to yield hydrogen. Energy is required to liberate hydrogen from the water molecule. The thermodynamic energy requirements per unit of product (NH3) of the combined reaction are thus greater than those of the original Haber process.
Chemical engineers recognize that estimation and measurement of the energy requirements of a bench-top process are a long way from those of a pilot plant scale, let alone those of a scale-up for bulk production.
Assuming that the scale-up could achieve similar efficiencies to the Haber process, the actual energy requirements will still be higher.
tadchem
5 / 5 (1) Aug 08, 2014
my bet is that the ' molten chemicals (made up of sodium and potassium hyroxide)' are hella caustic and difficult to deal with at industrial levels.

These problems are well known and manageable. I am a bit concerned about the presence of free oxygen with ammonia under elevated temperature and pressure. Ammonia gas is flammable (Autoignition temperature: 651 °C) and can form explosive mixtures with air (16–25%).
antialias_physorg
5 / 5 (2) Aug 08, 2014
The thermodynamic energy requirements per unit of product (NH3) of the combined reaction are thus greater than those of the original Haber process.

You're forgetting two things:
1) There's a different catalyst involved here. The temperature at which this works is lower. So this speaks for lower energy consumption.
2) To give a fair comparison you have to add the energy needed for creating H2 to the Haber Bosch synthesis method.

EnricM
not rated yet Aug 09, 2014
wrong. without the Haber-Bosch process what would happen is that we wouldn't have 1/3 of the cheap meat we have to throw it into landfills.
irongamer
not rated yet Aug 10, 2014
The catch is it will perpetuate the industrialized mono-culture farming methods that are causing a number of other long term problems. Soil erosion, soil degradation, algae blooms, ripe environments for pests thus requiring an increased need for pesticides, etc, etc.
Whydening Gyre
5 / 5 (1) Aug 10, 2014
Title
Water and air are all you need to make ammonia—one of world's most important chemicals

From my own experience cleaning horse stalls in my youth -
Ya don't need horse pee and straw, too?
Greg Vezina
5 / 5 (2) Aug 10, 2014
Many technologies to make or use NH3 as an energy currency, fuel and storage process are viable today and have been for many years. Vehicles have been powered by ammonia for over 100 years, eleven buses ran more than 100,000 km in Belgium in 1944-46, Canadian Alternative Energy Corp. drove a Hydrofuel® ammonia powered Chev across Canada in 1981 and in 2007 sister company Hydrofuel Inc. converted a Dodge Ram 3500 to a diesel/ammonia dual fuel system. New NH3 engine and Fuel Cell technologies have been developed including one patented in the US by the University of Ontario (UOIT) in Oshawa, Canada, an Apparatus for using ammonia as a sustainable fuel, refrigerant and NOx reduction agent, US 8272353 B2, that uses the chemical properties of ammonia to provide heating and cooling without consuming fuel, substantially reducing operating costs. youtube.com/watch?v=8vwmzkn0paM AND nh3fuel.com AND google.com/patents/US8272353

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