What is Liquid Nitrogen?

What is Liquid Nitrogen?

Written on 07/02/2019
Allie Brownlee

What is Liquid Nitrogen? 

Liquid Nitrogen, it sounds so mysterious and science-y, but what is it actually?

The Chemistry: 

Nitrogen is the 7th element on the periodic table. To humans, it is colorless, tasteless, odorless, and non-toxic. It is also non-corrosive and non-flammable. As a diatomic gas (di meaning two, atomic meaning atoms), it is nearly always found in the atmosphere as a pair of two atoms of nitrogen, which are triple-bonded. This triple bond makes it very stable and therefore relatively inert. The stability of inert gases is found in their not reacting chemically under normal conditions, nor with many substances. Although nitrogen is not quite as stable or inert as the noble gases, it’s pretty close. 

Nitrogen makes up 78.03% of Earth’s atmosphere by volume, 75.5% by weight. (For comparison, Mars’ atmosphere only measures at between 1.89% and 2.6% Nitrogen.) Nitrogen is a building block of organic compounds and found in all living tissues. Nitrogen atoms have 7 electrons and 7 protons with 5 electrons in the outer shell. It is the first in the series of pnictogens or pentels which make up group 15 on the periodic table. The “pent” in pentel means five, which references the "pentavalency" of nitrogen. Valency is a measure of an atom’s combining power with other atoms when it forms chemical compounds or molecules, so pentavalency means that Nitrogen and others in its group tend toward having 5 bonds with other atoms in a molecule, and they have 5 valence electrons or electrons that can form bonds with other atoms. Example: such as N2O5, which is two atoms of Nitrogen and 5 atoms of Oxygen. 

Nitrogen was first isolated from the atmosphere by Daniel Rutherford, a Scottish botanist, in 1972. He collected atmospheric nitrogen by removing oxygen from regular air by using a trapped mouse in a sealed container. The mouse helped to remove all the breathable air and after that he lit a candle then a piece of phosphorus to burn off all remaining oxygen. Lastly he passed the air through a solution that absorbed the carbon dioxide leaving only nitrogen, which he called “noxious air.“

In 1790 French chemist Jean Antoine Chaptal discovered that niter (potassium nitrate), a naturally occurring mineral that was commonly used as a fertilizer, contained the same gas discovered by Rutherford. Because of it’s connection with the niter he coined the word nitrogen by combining the word niter with the suffix -gen meaning "giving birth to." 

Niter made such good fertilizer because all life requires nitrogen, due to its role in cell walls, proteins, and DNA. Because of nitrogen’s tripple-bonded nature, it is extremely difficult for plants and animals to access atmospheric nitrogen, even though we are literally surrounded by nitrogen. That’s why fertilizers have nitrogen bonded to other elements, such as the potassium nitrate in niter, thereby making it easier for plants to get access to the nitrogen necessary for their growth. Not only is nitrogen necessary for plant growth but it is crucial for animals as well. For example, nitrogen makes up approximately 3% of human body weight. Nitrogen is also vital for many aspects of our modern life as well given that it is an important additive in chemicals such as cyanides (sodium or potassium cyanide are used in the extraction of gold and silver), dyes, antibiotics, and more.

What is air really and how does nitrogen compare to oxygen? 

Dry air contains, by volume, approximately 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and tiny amounts of other gases, on average. The amount of water vapor in the air also fluctuates, mostly by region, and is about 0.4% averaged through the whole atmosphere but closer to 1% at sea level. No matter how you put it, the air you breathe is mostly nitrogen.

Oxygen is slightly denser than nitrogen (4 g/mol) due to its heavier atomic weight at all temperatures and pressures. Since their weights are so similar and they don't generally separate from each other, there is really no reason to worry which is lighter or heavier. [Oxygen, having a heavier atomic weight, is denser than both air and nitrogen, at all temperatures and pressures, but only slightly. Since they don't separate from each other, we generally don't worry which is lighter or heavier. The difference in the density of nitrogen and oxygen gas comes from their molecular weight, which is small (4 g/mol).]

Regular air contains between 20.8 and 21% oxygen as compared to the 75 to 78% nitrogen. Small amounts make a bigger difference for oxygen though because it is immediately necessary for all life with 19.5% considered oxygen deficient and 22% considered oxygen enriched.

What Makes It LIQUID Nitrogen?  

Stating it simply, everything has three possible states: gas, liquid, and solid. Which state something is in depends on temperature and composition, and every element and molecule is different. Freezing point is when something goes from a liquid state to solid, and boiling point is when it turns from a liquid into a gas. For water, 32° F is its freezing point, and 212° F is its boiling point, so we most often find water in a liquid state on earth. Nitrogen’s boiling point is -320° F and freezing point is -346° F, so it does not naturally occur as a liquid or solid on earth. Humans have discovered ways of creating conditions where nitrogen condenses into a liquid, and this is how we get liquid nitrogen today. 

How did people first discover liquid nitrogen?   

Science was making incredible progress in the early 19th century. Early on people became enthralled by the stages of matter or state of aggregation, and the race was on to be the first to turn gasses into liquids. By controlling temperature and pressure various gasses had been able to be condensed and turned into a liquid fairly early on though many gasses such as oxygen, carbon dioxide, and nitrogen proved to be more elusive. On April 15, 1883, Zygmunt Wróblewski and Karol Olszewski were the first people in the world to successfully (in a stable state) condense oxygen nitrogen, and carbon dioxide from the air.

Zygmunt Wróblewski was born in what is now Belarus, had studied at Kiev University and was finally introduced to the method of condensing gasses at the École Normale Supérieure graduate school in Paris by a Professor Caillet. Wróblewski later went on to work at Jagiellonian University in Kraków Poland where he started working with Karol Olszewski. Karol was a Polish chemist who studied mathematics, physics, chemistry, and biology at Jagiellonian University. Like many scientists of his day, he was fascinated with the condensation of gasses and conducted his first experiments with a compressor of his own making and was able to compress carbon dioxide into a vapor, which is as successful as anyone had been up to that point. He later went on to be the first to liquefy hydrogen and argon though he failed to liquefy helium. 

Today liquid gasses are made using the same principles used by Wróblewski and Olszewski. Liquid gasses are produced industrially by the method known as “fractional distillation.” When air is cooled below its boiling point you can slowly warm the mixture and as it warms up the separate gasses (having different boiling points) can be refined and separated, hence the name fractional distillation because you can distill and sperate (or fractionalize) the gasses from the air. 

 

 

Research:

[Nitrogen was first liquefied at the Jagiellonian University on 15 April 1883 by Polish physicists, Zygmunt Wróblewski and Karol Olszewski.

It is produced industrially by fractional distillation of liquid air. This is how they do it.

Liquid nitrogen is often referred to by the abbreviation, LN2. 

Liquid nitrogen is a diatomic liquid, which means that the diatomic character of the covalent N bonding in N2 gas is retained after liquefaction.

  • Di meaning two, atomic meaning atoms, or two atoms that form a molecule. If these atoms are the same element, the molecule is called homonuclear, homo meaning the same, nuclear meaning relating to the nucleus, which is defined as “the central and most important part of an object, movement, or group, forming the basis for its activity and growth” more specifically as it relates to physics and chemistry, “the positively charged central core of an atom, consisting of protons and neutrons and containing nearly all its mass.” The same at their core. N2. There are only 7 diatomic elements, 1. Hydrogen (H2), 7. Nitrogen (N2), 8. Oxygen (O2), Fluorine (F2), Chlorine (Cl2), Iodine (I2), and Bromine (Br2).

Liquid hydrogen is most commonly used as rocket fuel. 

Liquid nitrogen's efficiency as a coolant is limited by the fact that it boils immediately on contact with a warmer object, enveloping the object in insulating nitrogen gas. This effect, known as the Leidenfrost effect, applies to any liquid in contact with an object significantly hotter than its boiling point.]

How is liquid nitrogen made? 

[Liquid nitrogen is made through cryogenic distillation by compressing air and cooling it enough to cause the various gasses to separate out of the pressurized gas. After the air has been pressurized and cooled it is depressurized which causes the various gasses to transform from their gaseous form into their liquid form, known as the Joule–Thomson effect. Since each gas has a different boiling point you can extract pure liquid gasses at different points in the distillation process. A modern liquid air plant produces liquid oxygen, nitrogen, and argon and is capable of producing 3,000 tons of liquid air products per day.]

There are other ways to make liquid nitrogen. At its simplest, if you could get dry, pure nitrogen gas next to something colder than -321°F, liquid nitrogen would condense onto the cold thing, and you could theoretically drip that condensed liquid nitrogen into a dewar for holding and storage. It would probably be prolonged though, and perhaps not very practical or cost-effective. It’s not easy to get things that cold. So, in the end, making liquid nitrogen is best left to professionals making large quantities if you want ease and cost-effectiveness. 

How do they store liquid nitrogen? What is a Dewar and why is it needed?  

Liquid nitrogen is most commonly stored and transported in a funny container called a dewar. A dewar is essentially an extremely insulated container, usually made of silvered glass or metal. It is double-walled, with an inner wall and an outer one, which creates a space between them which is turned into a vacuum. Because of the complete lack of atoms, a vacuum is one of the best-known insulators. You can often find mini vacuums used in other instances to reduce heat transfer such as in thermoses and fancy water bottles. This double-walled feature also protects the carrier from the cryogenic temperatures inside, though safety measures such as insulated gloves should always be used when transporting liquid nitrogen, no matter how insulated the container. 

Surprisingly, dewars are open at the top and non-pressurized. This is important because no matter how well you insulate a container, there will always be a tiny bit of heat exchange due to the extreme temperature difference compared to room temperature (also called the ambient temperature). This tiny bit of heating eventually warms some of the liquid nitrogen past its boiling point, and small amounts begin to vaporize and leak away. An open container allows the gas to simply escape and rejoin the natural air. But, in a closed container, the nitrogen will expand as it vaporizes, thus increasing the pressure until is it released via a pressure relief valve or the container explodes. The rate of vaporization varies according to ambient temperature, size, and other factors. It can be as low as 0.4% or as high as 3% of the container’s volume per day.

Liquid nitrogen has a 1 to 696 liquid to gas ratio at 70 °F, which means that 1 cubic foot of liquid nitrogen would expand to 696 cubic feet of nitrogen gas. 

[This is referred to as head pressure. The head pressure will build in the container and periodically vent via the pressure relief valve. Vaporization rates will vary and may be as low as 0.4% or as high as 3% of the container’s volume per day.]

There are several types of containers used to store and ship liquid nitrogen, depending on the amount the end user wants. The types of containers in use are the dewar (a non-pressurized container with sizes ranging from approximately 5-52 gallons), cryogenic liquid cylinder (insulated, vacuum-jacketed pressure vessels with sizes ranging from approximately 21-119 gallons), and cryogenic storage tank (large consumer installations with capacities ranging from 500-420,000 gallons). Since the liquid nitrogen is always warming up, heat leak is always present and vaporization takes place continuously. How fast the nitrogen vaporizes varies depending largely on the design of the container and the volume stored. All containers are designed according to specifications for the temperatures and pressures involved in storing the liquid nitrogen. 

How cold exactly is -321° Fahrenheit? 

Let’s put how cold that is into perspective.  

Liquid Nitrogen is 3x colder than the coldest place on earth. 

The lowest naturally occurring temperature ever directly recorded at ground level on Earth was −128.6 °F (−89.2° C) at the Soviet Vostok Station in Antarctica on 21 July 1983 by ground measurements.] Liquid Nitrogen is nearly 200 degrees colder!

On ice-covered Antarctica, the average temperature during the dark winter months is around -30°F (-34.4°C),  

With new satellite methods, scientists estimate that under the right conditions, temperatures could drop to nearly -148°F (-100°C), which, they said, is probably the coldest it can naturally get on Earth, at least while the sun still shines.  

What happens when you douse something in liquid nitrogen?   

A penny shatters easily when hit with a hammer after being cooled with liquid nitrogen. 

Liquid oxygen condenses on the bottom of the bowl because a bowl cooled by liquid nitrogen where it is pooling in the bottom gets cold enough to hit the Leidenfrost point of oxygen, which then condenses out of the air and gathers in tiny droplets on the bottom of the bowl. It’s just the same as that water on the outside of your ice cold drink on a hot day, except instead of water condensing out of the air, it’s oxygen!

Feeling liquid oxygen dripping on my head, it’s so cold! But then you’re instantly dry. There’s no wet effect left. I touch my hair in wonder. It’s hardly even cold. But the sensation I felt was very real. But liquid oxygen is −297 °F, (−182 °C), wouldn’t it cause cold burns? Nope, because of evaporation and the Leidenfrost effect. 

The Leidenfrost effect is a physical phenomenon where a liquid, when it gets close to something that is significantly warmer than the liquid's boiling point, produces a layer of vapor that insulates the liquid and keeps it from boiling rapidly. This thin layer of vapor gets trapped between the droplet and the hot surface, making the droplet hover over the surface rather than making physical contact. 

You can see this effect at home when you drop water onto a hot pan and the water seems to skitter and dance over the surface. If the pan's temperature is at or above the Leidenfrost point, which is approximately 379° F (193° C) for water, 

He sets the still cold bowl down on a table and it begins hydroplaning as it finally warms up enough to condense liquid water from the air onto the bottom.   

What’s that cloud liquid nitrogen makes? 

It’s not a cloud of nitrogen gas, which is invisible to the human eye but is just like the clouds we see in the sky. The physics behind making the nitrogen clouds is the same as that for making normal clouds.

A cloud is made up of millions of very tiny droplets of water. Water vapor is always in the air and on hot, humid summer days you can feel that water vapor as humidity. The air high up in our atmosphere is very cold and near the freezing point of water. Because it is so cold, the water vapor in the air condenses into tiny liquid water droplets. These droplets reflect light giving clouds their white color. When the droplets get too big, gravity causes them to begin to fall. As they fall, the droplets collect more and more water to make raindrops.

To make a nitrogen cloud all that is needed is lots of liquid nitrogen. The liquid nitrogen is heated until it boils, which is at -320o F so it is still very cold. The cold nitrogen cools the air around it. Just like in the sky, the water vapor in the cold air condenses forming tiny water droplets. This makes the cloud. If you stand close enough you can feel how cold the air really is.

Other gases in the atmosphere (particularly oxygen, carbon dioxide, and water vapor) also absorb light, but at ultraviolet and infrared wavelengths that we can’t see. There’s a sweet spot between the absorption spectra of oxygen and water where not much light gets absorbed. Lo and behold, that’s exactly the range of light that we’ve evolved to see!

So it’s not that gases are invisible, as such, it’s just that we can’t see atmospheric gases as they don’t have a color in the visible range.

Why is nitrogen invisible? 

Long story short, nitrogen gas is visible in the infrared light spectrum. The visible light spectrum ranges from 400-700 nm and nitrogen falls largely outside that spectrum, therefore it is invisible to our eyes. This is actually a really good thing because we all glad for that since nitrogen makes up 78% of Earth’s atmosphere, it would make for constant incredibly foggy days if we could see it! 

What else is liquid Nitrogen used for besides making ice cream? 

Liquid nitrogen has been used in computers and technology as a coolant, and in the field of medicine for removing warts, unwanted skin such as tags, and even pre-cancerous cells. It can also be used to preserve biological samples and there have been experiments on using liquid nitrogen to preserve live organs without damage from water crystals forming because of the fastness of the freezing effect which doesn’t allow ice crystals much time to form or grow. 

Using this theory of liquid nitrogen preservation, some people have been frozen after they’ve died, with the hope of being restored sometime in the future when medicine has advanced far enough to save them. Obviously, this is a quite expensive procedure and therefore very rare and generally reserved for the rich and eccentric, but before you ask, no, contrary to popular rumor, Walt Disney is not one of those frozen. He was cremated. 

Scientists also use liquid nitrogen in cryogenics or the study of the effects of extreme cold temperatures on various materials. Liquid nitrogen is also widely used by the food industry and professional chefs in various culinary effects from flash freezing chocolate to nitrogenating beer. 

How safe is liquid nitrogen to use? 

The safety concerns of liquid nitrogen have been raised many times, but really there’s nothing to worry about if you think about it in the right way. Dangerous materials have been used in cooking since man discovered fire. We’re just so accustomed to these dangers that we hardly notice them anymore. We don’t often run into liquid nitrogen, so it feels exotic and mysterious, but also unfamiliar and therefore a little scary. Liquid nitrogen is simply very cold. Think of it the same way you would about something very hot. You would not plunge your hand into a pot of boiling water, nor would you try to drink it, pour it over yourself, etc. Neither should you do these things with liquid nitrogen. You would use oven mitts to take something very hot out of an oven, so you should use insulated gloves to handle anything that might be very cold from liquid nitrogen. It’s just the other side of the coin. 

If all of the right processes are followed, the mitigated safety concerns. Mitigation for frostbite is Leidenfrost, third is the contained pressure, but every tank has multiple back up systems for relieving pressure. Functional redundancy. You have to know the risks and then mitigate them. 

Because of cool science, some of these things are theoretically possible to do without injury, and you might even find videos of it on the internet, but these science experiments should always be left to professionals.

Fractional distillation: liquefaction of gases, Airgas, AirLiquide, Matheson Gas, liquid natural gas is very similar. 

Walt Chamberlain: first to do it in a mixer. Played with it in the 70s. 

If it weren’t for NASA, they wouldn’t have started mass-producing liquid nitrogen. They created the need. 

https://www.livescience.com/62918-coldest-place-on-earth.html

 

1. Tilden, William Augustus (2009). A Short History of the Progress of Scientific Chemistry in Our Own Times. BiblioBazaar, LLC. p. 249. ISBN 1-103-35842-1.