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New Process Promises Ammonia From Air, Water, and Sunlight

Posted by timothy on from the kid-tested-mother-shocked dept.

The synthesis of ammonia is one of the globe's most significant industrial applications of chemistry. PhysOrg reports the publication in the August issue of Science (sadly, article is paywalled) the description of a low-energy process to syntheize ammonia for fertilizer using just air, water, and sunlight, by zapping with electricity water bubbling through a matrix of iron oxide, and sodium and potassium hyroxide. Electricity isn't free, though — "Low energy" in this case means two-thirds the energy cost of the long-in-use Haber-Bosch process. Researcher Stuart Licht is getting some of the energy to run this reaction from a high-efficiency solar cell he's created, which creates hydrogen as a byproduct. 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 450C and 200 times atmospheric pressure as the Haber-Bosch process does. ... But even with Licht's method, [University of Bristol electrochemistry professor David] 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.

3 of 117 comments (clear)

  1. Ammonia fuel by floobedy · · Score: 4, Interesting

    Something not mentioned here is that ammonia is suitable as a fuel in internal combustion engines. Ammonia is liquid under modest pressures (like propane), is easily transported, and will burn inside an engine.

    If we made ammonia out of nitrogen and water vapor, then it would become nitrogen and water vapor again when burned. It's a closed cycle that would not alter the composition of the atmosphere at all.

    It probably wouldn't be suitable as a fuel for your car, because of safety issues (if you hammered a hole in the fuel tank, the fuel inside would flash boil and could shoot out into your eyes causing a chemical burn). However it would probably be fine for trains, airplanes, ships, and so on, where special handling procedures could be enforced and people could be required to wear goggles before working on the fuel tank.

    1. Re:Ammonia fuel by mlts · · Score: 5, Interesting

      How would that be more dangerous than propane? LP gas would do exactly as stated above, if someone poked a hole in a fuel tank with their drill, they would get sprayed by rapidly evaporating fuel.

      IMHO, this might be the way to have a hydrogen economy. If a nitrogen fixing process is easy and economical, making liquid ammonia is a lot easier and requires less pressure than converting water to hydrogen via electrolysis.

      The downside is that ammonia has a bad rep here in the US. Because it is a major ingredient in meth, anhydrous ammonia tanks tends to be a prime target for "lab assistants" to obtain their reagents. However, if done right, ammonia might just be what is needed to make the "hydrogen economy" a reality, because it has a decently high energy density.

      Of course what would be nice would be a fuel cell that uses ammonia directly without the conversion to hydrogen.

    2. Re:Ammonia fuel by floobedy · · Score: 5, Interesting

      How would that be more dangerous than propane? LP gas would do exactly as stated above, if someone poked a hole in a fuel tank with their drill, they would get sprayed by rapidly evaporating fuel.

      Ammonia is caustic and would cause a chemical burn on the surface of your eyes, unlike LP.

      IMHO, this might be the way to have a hydrogen economy. If a nitrogen fixing process is easy and economical, making liquid ammonia is a lot easier and requires less pressure than converting water to hydrogen via electrolysis.

      It seems much more sensible to use ammonia than hydrogen gas, because ammonia has handling and storage properties similar to propane which solves the major problem of hydrogen gas.

      It makes a big difference if you can store something as a liquid and transport it through pipelines. That explains why oil sells for 10x more than coal, per BTU, and several times more than natural gas.