Few in our society realize just how dependent we all are on a poison gas.
Ammonia has literally permitted about half the humans on earth today to exist at all. The vast majority of our food calories, and especially those of our food animals, are totally dependent on ammonia as the source of nitrogen fertilizer. And, so too, our major liquid biofuels (ethanol, biodiesel) are also quite dependent on ammonia.
How do we make ammonia? We make it by reacting hydrogen and nitrogen at high temperature and pressure over an catalyst, by a process that has been in massive use for over 100 years.
Nitrogen is very unreactive, so we need high temperatures and pressures- and a good catalyst- to make it react with hydrogen at a reasonable rate. However, at high temperatures, ammonia wants to “crack” and fall apart to N2 and H2 again, so the yield is low. Fritz Haber discovered that we could use Le Chatelier’s principle to drive the reaction to the ammonia by condensing out the ammonia as fast as it is produced to drive the equilibrium reaction to the desired product, though his osmium catalyst (a Pt group metal) was rare and expensive. Carl Bosch took Haber’s process and scaled it up to 20 tonnes per day by 1913, with the help of Alwin Mittasch who discovered the much cheaper and more effective iron catalyst that made the process truly practical. And for these discoveries, both Haber and Bosch received Nobel prizes.
Here, the ironies become rather deep and delicious. And those who are here for the technical stuff and don’t care about history (and hence don’t mind the risk of repeating it), may wish to skip the next section of this paper.
(History haters start skipping here…)
The first application of the Haber Bosch process was not to make fertilizers to end hunger for millions, but to permit Germany to avoid the British embargo on the world’s prior primary supply of nitrogen compounds: guano (bird dung) found in islands off South America. It is said that the British imagined that Germany would run out of munitions in a few short weeks, because they effectively controlled the world supply of nitrate from which explosives were made. Germany’s mastery of the Haber Bosch process permitted them to make all the nitrate they wanted from ammonia, made from nitrogen from the atmosphere and hydrogen made from coal. Not only therefore did Haber and Bosch therefore permit World War I to continue to its unimaginably bloody conclusion, but Haber added to this by being an active participant in Germany’s chemical weapons program during the war, standing by as a observer as chlorine was first used to deadly effect. His wife, also a chemist, committed suicide in shame over her husband’s actions.
Haber, being Jewish, found himself to be the wrong flavour when the Nazis came to power- his history as a putative German patriot and Nobel laureate was insufficient to insulate him.
As I already mentioned, Haber was awarded a Nobel prize, despite howls of protest about his wartime activities at the time- the award of course being made from Alfred Nobel’s estate. Nobel, whose invention of dynamite tamed the nitroglycerine that had accidentally killed his own younger brother and turned it into a tremendously beneficial explosive for construction and mining, bequeathed the Nobel Prize awards after reading a premature obituary titled “La marchand de la mort est mort” (the merchant of death, is dead). His own history as a munitions manufacturer was something he couldn’t live down, and the awards were putatively an attempt to put a better spin on his legacy.
(History haters can start reading again…)
I say the ironies are deep and delicious here, because the same ammonia that made explosives that killed millions during WWI, ultimately became- no joke- the very basis of human civilization. Per Vaclav Smil, humans are as big a part of the nitrogen cycle as nature, making as many tonnes per year of nitrogen compounds now as nature does via lightning and nitrogen-fixing plants and other
Smil estimated that if pre-ammonia agricultural yields still prevailed per the year 1900, we’d need four times as much arable land under till as we did in 2010 to feed our population at that time. Admittedly, other fertilizers (K, P), pesticides, yield-increasing crop strains and other improvements in agricultural technology also had a big part to play in that- but kid yourself not, human civilization is founded on ammonia and ammonia-derived nitrate and urea. Not only is about 50% of the nitrogen in the proteins in our bodies a result of the Haber-Bosch process, ammonia has been called the “detonator of the population explosion”: recall that world population was 1.6 billion in 1900, and had risen to 7.7 billion by 2018
If human society is founded on ammonia now, what is ammonia’s foundation?
That’d be hydrogen. Nitrogen is just lolling around as 79% of the atmosphere.
And what is hydrogen’s foundation? Fossil fuels.
Ammonia production alone is responsible for approximately 3-5% of world natural gas use, all to make hydrogen. It represents 1-2% of world primary energy use (and yeah, I hate primary energy as a measure, but in this case, it does provide some perspective).
In greenhouse gas emissions terms, things are even worse than you’d imagine. When nitrogen-containing fertilizers (including natural ones) are used, nitrous oxide (N2O) is released from the soil into the atmosphere. N2O is a surprisingly persistent and extremely powerful greenhouse gas. So we get a triple whammy from our current ammonia addiction:
1) we get fossil methane emissions from producing natural gas (86x CO2 as a GHG on the 20 yr time horizon, despite a short atmospheric half-life of about 7 yrs)
2) we get CO2 emissions from fossil fuel reforming to make hydrogen from which to make ammonia and
3) we get N2O emissions from excessive N-containing fertilizer use (298x CO2 as a GHG on the 100 yr timescale, with an atmospheric half life of 100+ yrs just like CO2 itself)
Man, we’ve got it bad for this molecule! And yet we really, really like to eat…
Ammonia In A Post-Fossil World
We’re going to need it- huge amounts of it- even once we finally kick the fossil monkey off our backs for good. So where are we going to get it from?
From Electrolytic (Green) Hydrogen Made from Renewable Electricity
This is where we’re going, folks. One day. But probably not too soon.
In 2016 we produced about 175 megatonnes of ammonia. At $500/tonne, that’s $87 billion dollars worth. Per year…for one chemical. We actually spent quite a lot more than that, because it costs more to make nitrate and urea from it.
Did I say we liked to eat?
Making it requires about 31 megatonnes of hydrogen just to satisfy stoichiometry. To make that at 55 kWh/kg H2 would have taken about 1700 TWh of electricity- almost all of the ~ 2,000 TWh of wind, solar and geothermal power we made in 2018 per the IEA. In fact, by the time we consider Haber Bosch’s energy efficiency of about 66% (starting with methane not hydrogen), we’d be close enough to say that every wind turbine, solar panel and geothermal facility on earth in 2018 would just about keep us eating- if we used all that energy JUST to make ammonia. It would take more still to make nitrate and urea from it to make it fully useful. (Thanks to @Karan Bagga for finding my error here- I had previously stated 76% which isn’t possible, given that making hydrogen from natural gas is only about 70% LHV efficient best case- getting to ammonia for 66% of the energy in the natural gas is already very impressive efficiency).
Needless to say, we’d be hard pressed to make all that ammonia from electricity. It is absolutely NOT IMPOSSIBLE, and one day we’ll have to do it that way. It will just cost a lot of money and will take up a lot of land and other resources to make that happen. And with an average capacity factors of wind and solar of perhaps 30%, the worst thing would be that we’d have to build about 1 terrawatt’s worth of electrolyzers- plus associated compressors and storage equipment- to make that much hydrogen. That’s 1000 GW worth, or approximately 41,666 of the world’s largest (24 MW) electrolyzers to do that job.
…and at 4-5x the cost of fossil hydrogen right now, green hydrogen isn’t on the table at all. It exists only in marketing bum-fodder and in the imaginations of people selling #hopium to extract money from credulous governments.
From Fossils Using Carbon Capture and Storage
Hydrogen right now is made 98.5% from fossil fuels- without carbon capture. But in return for $150/tonne CO2, we could cut the CO2 emissions of H2 production from natural gas by steam methane reforming (SMR) down by 70% without having to rebuild every SMR on the earth. Going to 100% would be really tough. And that would require us to bury a lot of CO2…at 9 kg of CO2 per kg of H2 and $150/tonne, we’re talking about spending $42 billion per year just to bury the resulting CO2 to make $87 billion worth of ammonia per year. That’d have a fairly significant impact on food prices, assuming we could find a place to dump all that CO2.
Directly From Electricity
A recent paper in Energy and Environmental Science Communications touted itself as a giant new discovery in ammonia production, out of two Australian universities. A new process consisting of two steps: production of NOx from nitrogen using a submerged nonthermal plasma, followed by reduction of NOx back to ammonia by nanowire-catalyzed electrolysis, was touted as the next best thing since sliced bread by the media. Here’s just one of many such breathlessly enthusiastic articles about this new discovery:
Many who are looking for something cool and profitable to do with excess wind and solar energy (and Australia is a hotbed of such work) are looking at ammonia, and hope to do something other than water electrolysis followed by conventional Haber Bosch for a couple reasons:
1) Haber Bosch plants need to be made very large to be profitable, because any commodity chemical like ammonia needs to be made at giant scale to achieve sufficiently low capital intensity- not the best if your resource is distributed in space like wind and solar, as it means you’ll need a big grid to feed a huge energy resource into a sufficiently large plant. It also means a huge capital investment- a $300 million ammonia plant is small in current world scale terms
2) Haber Bosch plants, operating at high temperatures and pressures, need to be operated continuously- 24/7- not just to use their large capital efficiently, but to keep them from destroying themselves due to thermal and pressure cycling. That means storing both hydrogen feedstock AND energy to run them- not the best if your energy source is intermittent, and yet MORE cost
So…people have been looking for alternative ways to make ammonia that don’t involve high temperatures and pressures. Electrochemistry to the rescue!
Sadly, it doesn’t work very well. And this process may well be a big improvement in comparison to the world state of the art, but it’s still terrible- because the world state of the art for direct ammonia synthesis is just that much more terrible.
From the paper, the NOx conversion takes 3.8 kWh per mole of NOx, and the conversion of NOx back to ammonia electrochemically takes another 0.51 kWh per mole. Converting moles to mass, they get 253 kWh of electricity per kg of ammonia. Remember that hydrogen takes only 55 kWh per kg to make from water, and even THAT is too expensive and too energy inefficient- and there are only 3 kg of H2 per 17 kg of ammonia…
How did the media go so far in the ditch on this one? Usually you can’t blame the authors of the technical paper, but in this case, you can. The paper is frankly laden with self-promoting hyperbole- no doubt in an effort to attract more research grant money. But the real problem here is that the authors make a true but deceptive statement on p. 3 of their paper:
“…the theoretical energy limit for NOx generation via non-thermal plasma is 5.56x 10^-2 kWh/mol NOx (in vacuum). This consumption is at least 2.5 times lower than Haber-Bosch process (0.13 to 0.4 kWh/mol NH3)”
0.13 to 0.4 kWh/mol ammonia is about 7.6 to 24 kWh/kg ammonia, quoted for Haber-Bosch but without a reference given in the paper. Not only is that 10.5 to 33 TIMES BETTER than what they managed to achieve with their process, in favour of Haber-Bosch, it doesn’t jibe with what the Australians in the know- from CSIRO- say about ammonia production:
They claim that Haber-Bosch production of ammonia is about 76% energy efficient when produced from methane, or about 1.41 MWhr/tonne ammonia. That’s 1.41 kWh/kg, not 7.6 much less 24 kWh/kg.
Sadly, this hyperbole-laden stuff is the truck and trade of the internet media in relation to ANY innovation related to energy these days. It could easily be a full-time job for someone like me to take apart these articles on a daily basis- but the pay for doing so, really sucks! (In case you’re wondering, nobody pays me to write my articles- I’m writing this one as my Friday night entertainment in lieu of watching Netflix)
Ammonia as a Fuel or Hydrogen Carrier
I’ll leave you not only without solutions for this absolutely existential problem for my children’s future, I’ll sour your day further with a little rant:
Since there is no green ammonia right now, because there is no green hydrogen to make it from, nor any process better than Haber-Bosch to make it by, anyone planning to either a) burn ammonia as a fuel or b) thermally crack ammonia back into hydrogen and nitrogen, is an energetic and environmental vandal.
Yes, I’m talking to you, CSIRO!
(The Ammonia Energy Association paper above is far more readable than CSIRO’s paper itself. CSIRO has been a shameless promoter of ammonia-for-energy schemes as it sees them to be in Australia’s national interest. But in my view they should focus on making Australia the world’s largest producer of green ammonia for fertilizer purposes- starting that effort by lobbying for Australia to have carbon taxes, which are the only way anybody will make hydrogen from non-fossil resoures at scale)
Yes, I’m talking to you, Air
Actually, that Ammonia Energy Association distillation of CSIRO’s more technical paper that I linked above is excellent- top notch work. It states clearly the problems with using ammonia as a fuel or especially as a way to make hydrogen and thereby, electricity again.
…and who can blame Air Products? Somebody in Europe told them, with a straight face, that there were going to be millions of hydrogen-fuelled trucks and busses to fuel one day, and that they (Europe) were going to pay through the nose for “green” hydrogen from anywhere they could get it. Cha-ching! Who could resist those cash register bells ringing?
Remember that best case, going from electricity to hydrogen, to storage, to electricity again- bleeding edge, uneconomic best case- is 37% round-trip efficiency. Terrible, compared to anything using a lithium ion battery.
What is it when you get ammonia involved?
11 to 19% And though that’s a range, it’s likely an optimistic one.
Ammonia is a toxic gas, but one which is a liquid at a modest pressure and temperature. Accordingly, crazy people desperate to find ways to move hydrogen in bulk, reach for ammonia. And not only is that just a bad, bad idea from an energetic perspective given the round-trip efficiency, from a terrorism perspective it’s just not even worth thinking of. Imagine a tanker full of gigantic quantities of toxic liquefied gas, parked in a major port, and what a tempting target that would be for some politically or religiously-motivated misanthropes.
Then there’s the fact that making ammonia is exothermic where you have the energy to make it, i.e where you already have excess energy- and cracking ammonia is endothermic, i.e. requiring energy where you don’t have enough. (That’s true of other hydrogen carriers like the methylcyclohexane/toluene organic hydrogen carrier pair too, by the way).
And on top of it, ammonia is a poison to PEM fuelcell catalysts. So you have to waste about 15% of your product hydrogen in the gas purification train just to get rid of the tramp ammonia. Not a problem if you’re burning it in a turbine of course- but then, when you burn ammonia in air, you get NOx- but of course you have plenty of ammonia around to feed the SCR catalyst with to reduce that back to nitrogen.
Not to mention the obvious problem that black ammonia will rush in to fill the market vacuum left by the non-existent green stuff. And using it, is at least (100-76) =24% worse than using the natural gas you could have used instead, plus all the extra cost for the H-B plant. Without carbon capture. That’s what the fossil fuel industry is counting on, by the way- they have no intention of making green hydrogen.
Be watching the ammonia space in the future. Expect more crazy stuff, misinformation, misunderstandings, disinformation and #hopium slinging to cloud the public policy discourse, just like with ammonia’s big brother hydrogen. You know it’s coming- because when people start to realize just how hard, lossy and expensive it is to move hydrogen- the reason that 85% of European hydrogen per IRENA is used right where it’s made- they’ll reach for ammonia out of desperation.
And methanol, too. But that’ll be the subject of a future paper.
DISCLAIMER: I wrote this myself, based on long experience with chemical engineering and hydrogen, but only a little experience with ammonia. Nobody paid me to write it. No shares are riding on it. And my employer, Zeton Inc., would greatly prefer that I shut up about this stuff. If you have a problem with anything I’ve said here, please take it up with me. And if I’ve made a mistake somewhere, in fact or analysis- I’m human, so my apologies in advance. If you point it out to me with a good reference, I promise to revise the paper to correct my error, with my thanks to you for finding it.
If you didn’t get angry- or even if you did- please SHARE my paper so people read it. And go to my profile and read my others, which are all featured there. And share them. Otherwise I’ll go back to watching Netflix…