Sometimes something dangerous can also be life saving. This is anhydrous ammonia. It's
critical to putting food on your table, both as a fertilizer and as a refrigerant. 50% of the food
that you eat is directly thanks to ammonia. And without it, the world population would starve.
This means that there's lots of it moving around the world by truck train and even pipeline.
So sometimes accidents happen. In 1976, a truck carrying in anhydrous ammonia crashed in Houston,
killing seven people and injuring 200 more.
In 2002 a train derailment sent a cloud of anhydrous ammonia over Minot, North Dakota,
killing one person and injuring at least 95 others. And in 2019, a mechanical failure on a
farm tractor towing, anhydrous ammonia released a cloud of gas that sent 83 people to the hospital.
And those are just the headline-making accidents: between 1996 and 2011 there
were over 900 accidents at places that store anhydrous ammonia resulting in 19 deaths.
You're probably familiar with household ammonia in things like glass cleaner at the molecular level.
Ammonia is a nitrogen with three hydrogen stuck to it, and it's normally found solubilized in water.
It's typically about 90 to 95% water and five to 10% ammonia in your typical household ammonia.
But in anhydrous ammonia, that ratio is very different. Usually about 99.98% ammonia, and just
a little bit of water. And that first part of the name gives it away. Anhydrous means without water.
At room temperature, it exists as a gas though. It can be pressurized into a liquid,
which is how it's usually transported. Since you can store a lot of it in a small space
that makes it easier and safer to transport by pipelines, trained cars and trucks, to farmers
across the country who use it as fertilizer. Nitrogen is incredibly important for plant growth.
Plants use it to make everything from amino acids to the chlorophyll that they
need for photosynthesis. Nitrogen serves an important structural role because it can form
bonds with weird angles. Each nitrogen atom has five valence electrons, three of them like to
form bonds. And two of them often hang out in a pair and participate in hydrogen bonds.
So you can get really cool structures for things like amino acids and the bends in DNA helices.
And then you can stick things together with those hydrogen bonds. It's a win-win for
chemical synthesis. But plants can't use the nitrogen gas or dinitrogen that's in the air.
That's because of those three valence electrons that we talked about before
in dinitrogen. Those electrons form bonds with each other, making a super stable triple bond
that plants just don't have a way to break apart and use. So instead of getting nitrogen directly
from the inert dinitrogen in the air, plants typically get it by way of bacteria in the soil.
The bacteria are able to break the dinitrogen down and combine it with hydrogen and create
ammonia that the plants can use to make all of those proteins in chlorophyll and nucleic
acids that they need. This process of turning inert dinitrogen into other
more reactive and useful nitrogen containing molecules is called fixation. The nitrogen
fixation abilities of bacteria end up being a big rate limiting step for food production.
So if you are a farmer and you wanna grow more crops than the bacteria on your land can support,
you've gotta get more bioavailable ammonia from somewhere.
This is why back in the 19th century wars were fought over islands of guano used for fertilizer.
Guano. That sounds so familiar. It’s bat droppings.
It was one of the only ways to get a rich source of nitrogen.
And without that nitrogen, they couldn't produce enough crops to feed everyone.
There were real worries about running out of food. They solved those worries with poop.
But in the early 1900s, German chemists, Fritz Haber and Carl Bosch developed a process that
could artificially fix nitrogen and hydrogen to create usable ammonia. So how does that work?
First, you gotta make hydrogen gas. You can do this with a process called
natural gas or steam reformation. You mix methane and steam at super high pressures with a catalyst
and you get out hydrogen, carbon monoxide, and carbon dioxide. Then you combine nitrogen from
the air with the hydrogen gas and a catalyst under high pressure at a moderate temperature
of 500 degrees Celsius. And bam, you get anhydrous ammonia farmers use that anhydrous ammonia to
grow food. They can inject it straight into the ground as a liquid where it will rapidly expand,
turn into a gas and ideally get stuck in the damp soil due to its water loving nature.
This way farmers can cut out the bacteria middlemen when trying to feed their crops.
This process made the manufacturing of ammonia for fertilizer possible.
Without it, we wouldn't be able to grow the huge amount of crops that we need to feed the world.
Once the Haber Bosch process was implemented on a large scale, the increase in food production
allowed the world's population to rise from 1.6 billion to 6 billion during the 20th century.
That is huge. In the US, most of our anhydrous ammonia is made on the Gulf coast
and piped across large agricultural areas via a huge pipeline, but it's
also transported by train cards and trucks and stored in facilities across the country.
In 2020, the US produced 14 million metric tons of the stuff. To put that into perspective, an
average African elephant weighs about six metric tons. So that's over 2.3 million elephants worth,
and it isn't just used fertilizer. It's a really important chemical precursor for everything from
plastics to pesticides to explosives. It's also often used as a refrigerant in big
industrial cooling systems like warehouses and factories. It's more efficient than commonly used
hydrocarbons and many technicians actually prefer to work with it because you can smell a leak
quickly giving you more time to get away or solve the problem than other odorless
refrigerants. Anhydrous ammonia has also been suggested as a potential way to transport large
amounts of hydrogen to support fuel cell cars. Talked about that in another video.
So this all sounds great, but in order to use this stuff, we have to actually move
it from the industrial plants where it's made to the farms and facilities where it's used.
And by virtue of the fact that we're moving so much of it, there's a chance that things
could go wrong if it isn't stored properly, or if it ends up in a train or car crash.
When anhydrous ammonia leaks from a high pressure container, one of two things could have happened.
In the first scenario, ammonia leaking from a high pressure source will often
cool down as it expands and turns from a liquid into a gas. This cold vapor can be dense causing
it to stay close to the ground, but usually warm surrounding air can mix into it, heating it up
so that it's buoyant and lighter than air. And then it can drift upwards and disperse
away. But if the pressurized liquid ammonia leaks out through a small hole in the tank,
it can aerosolize the ammonia creating tiny droplets stuck in a cloud of vapor. This aerosol
is just like the tiny hairspray droplets sprayed from a can. That gets stuck in a cloud of gas. Oh.
The liquid ammonia droplets make the aerosol cloud heavy. And it takes a lot of energy.All
of those droplets up the aerosol that forms is also pretty stable. So there's not a lot
of chance for warmer surrounding air to mix in. This means the cloud stays cool and dense for a
long time giving it its distinctive creeping shape rather than just dissipating quickly.
The very first thing to know about an ammonia leak is that if you can see a cloud, you should
absolutely not enter it. Your body is mostly water and ammonia is really good at dissolving in water.
When ammonia and water mix, you get ammonium hydroxide and ammonia reacts with moisture,
absolutely anywhere. It can find it on your body, your eyes, nose, mouth, and especially your lungs.
The resulting ammonium hydroxide burns through your tissue, and breaks down your cell membranes
in a process known as saponification. When you inhale it, it can burn the moist inner
surfaces of your nose and throat eventually leading to respiratory distress or failure.
Once ammonia gets into your lungs and on your mucus membranes,
much of the medical care you get is based on just allowing your body to rebuild.
Doctors can decontaminate you with a lot of water and assist your breathing and try and
rehydrate you, keeping you alive so that your body can repair, but that's about it.
So this small version of the ammonia fountain experiment can show how even a small amount of
ammonia gas can quickly turn a watery solution basic. So first I'm gonna fill this pipette bulb
with ammonia gas. I'm gonna do that by placing on top of another pipette bulb filled with household
ammonia and warming it up gently. I can then take my ammonia gas filled pipette and dip it into a
flask filled with water and a pH indicator. When I draw just a tiny bit of water up into the bulb,
you can see that the pH indicator rapidly turns blue indicating that the pH is very alkaline.
So are we all in danger of an anhydrous ammonia accident all the time?
No. And anhydrous ammonia is moved and stored around the country a lot,
but if properly contained and transported, it's not dangerous. The kinds of accidents that make
the headlines are typically tragedies, but also aren't caused by the ammonia itself. Trained
derailments and car crashes can happen no matter what's being transported. To keep everyone safe,
the containers used to transport anhydrous ammonia are rugged, reinforced and checked regularly.
Since it boils at negative 33 degrees Celsius, the containers have to be able to handle pressures of
up to 250 PSI to make sure that it stays liquid. Even when outside temperatures
reach 37 degrees Celsius, they also can't be made out of copper or zinc alloys as the ammonia will
react with them and eat straight through the container. And you've gotta test the tanks
regularly to keep everyone safe, but with proper testing precautions in PPE anhydrous ammonia
continues to move around the world safely every day. We would all be a lot hungrier without it.