Did you ever think you could make liquid nitrogen in your own garage? This is an industrial process so how can an individual do this? Still doubt me? Intrigued? Read on.

As a lover of science I tried to think of a challenging project that was out of the ordinary. After going through the internet web and Youtube I realized that no one had made liquid nitrogen in his home. Yes, I did see some videos where some would use a Stirling Cooler from a cryorefrigerator and use this to condense nitrogen on the exterior of the cold-head. While one is making liquified gas, this is done using a prefabricated machine. I wanted to make the machine that liquefies the gas. Furthermore, a cryocooler has a very low production rate. You will only get about 500 - 1000ml per day. On the following pages I will walk you through the basics of how to build your own liquid nitrogen generator. Using easily obtained materials you can liquefy nitrogen or air. The unit cools to -320F in under 50 minutes. The production rate is about 350 cc/hr.

A full tutorial and plans are at http://homemadeliquidnitrogen.com This page goes over theory, thermodynamics and more detail on where to get components and how to build this. This Instructable serves as a general introduction to how this baby is put together.

I have just added a new web tutorial on how to make your own N2 gas from the air. I will add this as a new Instructable in the next few days. You can get a link for it at the end of this one.

I have also built a high-precision cryogenic digital LCD thermometer for this project, which you can buy for yourself. You can see how it compares with an Omega digital thermometer here.

Ok. The video above gives you a quick 3 minute overview of the project. At the end of this tutorial I briefly mention the PSA I made for making the pure N2 from the air for the generator. If you're ready for 320 degrees below zero we can begin...

Step 1: Overview

The liquefication generator has a few basic components. Starting in order:

1. Scrubber - This removes CO2 and H20 from the gas stream. Without this the water and CO2 would freeze and clog the tubing and valves

2. Filter - We need to remove any micro-particles that can clog our compressor valves

3. Compressor - This compresses the gas to high pressure. Two important factors are the pressure and flow rate. This project uses an oil-free scuba compressor delivers a pressure of 3500 psi at a flow rate of 3 SCFM (I jacked it up to 4 SCFM). It is possible to use a regular refrigerator compressor, but the production rate will be significantly reduced

4. Pre-cooler - This cools the hot, compressed gas before entering the cooling tower.

5. Regenerative cooling tower - Hot compressed gas flows through a counter-current system to cool the gas to cryogenic temperatures. Expanded, non-liquid gas returns to get recompressed.

6. Throttle - This is a needle-valve that enables a controlled expansion of the gas without losing the pressure behind it.

7. Baffle - This reduces the velocity of the expanded gas so it does not dissipate the cooled liquid into the gas-stream. It also provides a larger surface area for condensation.

7. Reservoir- This is the collection system that collects the gas. Heat exchange with the environment is minimal.

Above is a picture of an early version of the generator using a recycle can. Later you will see an improved version.

Step 2: Compressor Filter

You need to protect the compressor's valves and cylinders from debris and water. You can purchase an inexpensive vacuum filter from a distributer. I bought a Vaccon 10 um filter. The part number is VF500F.

Step 3: Compressor

This is the most expensive component. I used a RIX oil-free SA-3E. This delivers 3 SCFM @ 3500psi (230 ATM). I modified the motor and pulleys to deliver 4 SCFM. A higher flow gives you a faster cool-down and production rate. The high pressure allows you to have a larger temperature drop when you throttle the gas to a lower pressure. You can use a regular refrigerator compressor, but you will be waiting a long time to drop 400 degrees Fahrenheit from the ambient temperature to -320F if you only have 40 ATM of pressure.

My compressor allows me to get to -320F in 45 minutes. I am guessing that a standard compressor at 40 ATM will take 6 times longer, or 4 1/2 hours. Of course, if the flow rate is less then you have to add more time.

Step 4: The Scrubber

You can make this components out of PVC pipe. I used 4" PCV. You need to get the correct fittings to get to a pipe size that you can then attach to your compressor. The scrubber uses a material called zeolite, or molecular sieve. I specifically used 13x molecular sieve and added some 4A sieve material that had a color indicator added so I know when it has reached saturation. You determine the size of the scrubber based on your flow rate. If you want 3-4 SCFM then you need about 10-15lbs of the material and size the scrubber based on this.

Zeolite is a naturally occurring, finely porous material. By fine I mean the holes are only angstroms in size. Molecular sieve is man-made, but the structure is the same. CO2 and water enter and bind within the pores, letting the other gases, like O2 and N2, to pass through. The color-indicator will change from light blue to gray when the material can not adsorb any more water. One regenerates the material by heating to 350F, driving off the CO2 and water.

Now, back to the device. I cut a disc of 200 micron screening. This holds the 10 lbs of material in place so it does not get sucked into the compressor, but still allows for air-flow. I glued this material between the 4-to-2 inch reducer and the coupler fitting. We need to filter smaller material, so I took 11 MERV air-conditional filter material and cut it into a large circular disc. This should filter 1-3um particles. If you can get a 12 MERV this is better. I fashioned a circular ring of stainless steel that I got at a hardware store and fixed the filter material on top of the 200um screening. Then, poured in 10 lbs of 13x and 4A sieve. I then made another filter disc out of the air-conditioning material and fixed it on the top with a stainless steel ring. This keeps the material clean. You don't want particles clogging the sieve's pores.

The top of the scrubber needs three inputs. One is to allow for fresh gas input. The other connects to the regenerated gas. This is gas from the cooling tower that did not liquefy. The gas is already cool, free of CO2 and water, and in my case is 98.5% nitrogen. I don't want to waste this gas to the atmosphere so I reuse it, reducing the amount of fresh N2 that I need to make. This is why it is called regenerated gas because it comes from the original gas I fed into the tower. The third input allows any excess gas to vent out.

The only other connection is at the bottom where you connect the scrubber to the compressor. I placed a 10um vacuum water trap between the scrubber and the compressor. This will remove particles that can fowl up the compressor, and also serve as a check that no water gets into the cylinders. I also used this spot as a place to insert a gas-analysis meter that I made to monitor the purity of the N2.

You will need to buy a pipe/tube bender to make the coils and rings. I've shown a picture of one above. Mine is meant to bend 1/4" tubing/rod.

Step 5: Pre-cooler

The compressed gas leaving the compressor is hot. You want to remove this heat using an ice bath. The pre-cooler is sized to fit into a large bucket.

Basically, the precooler is a long coil of tubing. I used 20 feet of 1/4" 304 seamless stainless steel with a 0.035" wall thickness. Again, one could go to 0.027" wall, but this got too thin for me. I did not want a wall rupture at 3500 PSI. I go through the engineering calculations for verifying the integrity of the tubing at the tutorial site.

I added 0.016" thick aluminum fins which increased dT/dt even further by allowing better heat transfer. I carefully drilled a hole 1/64" smaller than the tubing. I then cut the square and snapped the fin in place. I can then submerse the cooler in an ice bath or expose it to sub-freezing outdoor temperatures when available.

Step 6: Regenerative Cooling Tower

This is the part that will take the most work. My final tower uses a large concrete cardboard form container that is 50 inches high and 24 inches in diameter. However, I had good success with an earlier version that used a 36 gallon plastic recycle can. The compressed gas goes into the tower through a long helical coil and re-expands through a needle valve at the end into the reservoir. The cold gas that did not liquefy returns through Teflon tubing around this coil. This cold gas cools the steel tubing further. This process repeats until the steel tubing is cold enough to liquefy the gas.

I used 305 stainless steel 1/4" tubing with a 0.035" wall thickness. There are many places that sell this near you. If you are going to do this with a standard refrigerator compressor than you can use copper tubing. Just make sure it is rated for the pressure from the compressor. Now the PTFE (Teflon) tubing is critical. It is one of the few materials that is flexible and can withstand cryogenic temperatures. I used plastic tubing in the beginning, but it would eventually crack.

My tower uses 80 feet of tubing. You can do this with 40-60 feet, but this increases the cool-down time. Again, everything is about tradeoffs. You need to insert the steel coil into the Teflon tubing. You want the Teflon tubing diameter to be a little bigger than the coil. Mine was 1" corrugated tubing which allows it to be flexible. This wraps over the 1/4" stainless tubing.

The ends of the tubing need high-pressure, stainless steel fittings and adapters. I got mine from Swagelok, but there are other companies that sell similar parts.

You then insert the coil into the garbage can or container. Industrial manufacturers fill the container with perlite and create a vacuum to prevent heat from entering from the environment. I filled my container with alumina silica high-temperature wool. This is normally used to insulate furnaces to contain the heat. Well, guess what? It also contains the heat of the outside from getting to our coils. You need to loosely fill the container with the material so it stays fluffy. Air is also an excellent insulator.

The pictures above show me using the 36 gallon recycle container. At the end of this tutorial you will see the concrete form container which houses a bigger run of coil. The stainless steel tubing is surrounded by the Teflon tubing. This, in turn, is wrapped with polypropylene foam to further decrease heat penetration.

Step 7: Throttle

The gas expands using a needle valve as mentioned earlier. One controls the pressure by finely tuning the orifice opening with a large lever/knob. I made a large lever because the standard knob handle is too small for fine control. Furthermore, as the temperature drops one finds difficulty turning the knob because it gets frozen in position. A large lever makes this fact mute.

I extended the stem so it would reach the outside. I insulated the connection to the stem with Teflon to reduce any heat transfer through the stem from the outside.

Step 8: Baffle

The expanded gas distal to the needle valve moves at a high velocity. This can agitate the liquefied gas in the reservoir and blow it back out into the gas stream. You need to slow the gas down to allow the droplets to collect and drop into the container. Until I figured out this simple step I was never collecting a lot of liquid.

Making this is very easy. I used a fitting and attached it to 1/4" copper refrigerator tubing. I drilled a few holes with a 1/8" drill bit on the other end and fixed some copper abrasive scrubbing sponge that I got at a food store. Make sure the copper wool (abrasive scrubber) does not come off. The other pictures show how this part relates to the needle valve and reservoir.

Step 9: Reservoir

The reservoir holds the collected liquefied gas, whether that is N2 or air. A simple stainless steel vacuum bottle, or a thermos as many of you would know it, serves this purpose very nicely. Such a simple solution that eluded me for some time. The trick is to fashion an adapter that allows you to contain the expanding gas and direct it to the regeneration Teflon tubing that surrounds the high pressure stainless steel tubing. The details, along with all the other methods I tried, can be found at my extensive tutorial at http://homemadeliquidnitrogen.com

Basically, the baffle connects to the output of the needle valve. The inflow to the valve connects to a tube fitting on the end of the high pressure tubing. A Teflon cylinder surrounds this and just fits over the orifice of the thermos. Small screws keep this fixed so the pressure of the expanding gas does not push it off. A small tube of Teflon goes from the bottom of the thermos to the outside through an insulated jacket to allow the liquefied gas to escape. A small plug keeps the liquid contained until you are ready to drain the system.

In addition to these connections, there is a small opening for a RTD probe for monitoring the temperature. I am currently using a unit I bought, which is seen in the video at the beginning of this Instructable. I have developed a low-cost LCD cryogenic thermometer that is accurate to 0.1F. I plan on posting this as a new Instructable in the near future.

Step 10: Summary

This project allows an individual to do what only commercial industry has done in the past. You can generate your own liquid air or nitrogen with a high production rate. The cool-down period depends on your compressor, length of regeneration tubing and how well you can insulate your system. In the past, making liquid nitrogen in your garage seemed impossible. Not any more.

Good luck and stay cool.

Step 11: Making Pure N2 for Liquefication

I have gotten a lot of comments suggesting that I am making liquid air, which contains O2, and not liquid N2. I made a pressure swing adsorper that removes the O2 from the air, leaving 98.5% pure N2. If I used a second stage I could get 99.999% pure N2. I feed this N2 into the liquid nitrogen generator. I am putting out about 30 L/min of 98.5% N2.

I have just finished writing a web tutorial on this subject which you can find here. This can also be used for having a pure source of N2 in your garage. I use it for filling my tires. I will write this as its own Instructable in the next few days.

You can click on the this link to see a video I made, showing my PSA device.

Do you turn nitrogen gas to liquid when pressed 230 atm?
<p>When N2 is above -147 C (that is the case here), it does not liquefy no matter the pressure. This is the critical temperature.</p>
The N2 is compress and cooled. Without the cooling there is no pressure you can achieve to get liquid N2. I compress between 3000-3400 psi so that's close to 205-230 atm as you stated. The expanding gas at the needle valve (throttle) drops the temperature and this cooler gas chills the compressed, unexpanded gas further. Eventually, the gas gets cold enough to liquefy. This is all explained in great detail at the website tutorial I mention in this instructable.
The gas cools itself?
The principle of liquefaction of nitrogen<br>1. pressure of 200-230 atm<br>2. throttle<br>3. Stretch<br>4. When compressed gas dilate absorbs heat even par with boiling point<br>5. cooled until -196 Celsius<br>6. The result liquid nitrogen
What is the gas used for cooling up to 320 degrees below zero, and what is the pressure before and after the compressor<br>Please explain how to make the cooling circuit video
<p>Air. You should read the full explanation at www.homemadeliquidnitrogen.com</p>
Now it became clear idea<br>It is by nitrogen pressure<br>And not reduce temperature
I do not speak English language<br><br>I just want a detailed explanation of the cooling method and what is the necessary pressure to become liquid nitrogen<br><br><br>I own a heat exchanger and used the Freon r22 I have become the temperature -37 Celsius degree and I need -170 / -180 Celsius heat<br>What are the required supplies<br>Thank you
<p>Hey,</p><p>Your unit is so great!!! I need a liquid nitrogen generator that can produce liquid nitrogen about 20-25 liter per day. Can you make one for me? please email me at info@cmlabpro.com. Thank you very much. </p>
<p>You can get a better idea of the parts and cost at my tutorial website:</p><p>http://homemadeliquidnitrogen.com</p>
<p>What are the other possible uses for the Nitrogen produced other than filling up tires as you stated? The production of Ammonia could be the nest step forward using the nitrogen gas along with a source of electrolysed hydrogen to try and replicate the Haber process since it is such a clean usage for the Nitrogen.</p><p>I can almost guarantee noone has tried making an industrial Ammonia producer at home from natural products such as nitrogen and hydrogen gas. One of the main issues being the high pressures and temperatures associated. It would be a pretty cool project though...</p>
<p>There is a pretty good reason why you people have not tried that because it requires high pressure and high temperatures and is frankly stupid to try at home.</p>
<p>small minded people refuse to dream big and look at the bigger picture -</p><p>it was only a question for scientific perusement, there is no need to be insulted</p>
<p>i use liquid oxygen for scientific glass blowing. would you help design one for liquid oxygen/</p>
If I understand what's going on in this process just use the &quot;exhaust gas&quot; from the PSA instead of the N2
Can you adapt it to liquify NO2?
Could this make liquid hydrogen?
<p>In theory, yes. However, you would have to provide the unit with a gas mixture containing pure hydrogen. That seems like an added cost and danger factor that I wouldn't want to deal with. This system is relatively safe because the gases involved are inert under usual conditions, and the only comparable risk to a hydrogen explosion during liquid nitrogen production is a pressure buildup from boiling nitrogen.</p>
Ignoring the danger, an electrolysis device could provide the machine with pure hydrogen. Also you can liquify the oxygen.
<p>what would be a minimum pressure rating you would recommend? i have a higher volume fan but is only rated somewhere between 1 and 5 psi</p>
<p>HI I am an engineering technologist looking to build a hydrogen fuel cell and to use a system very similar to this to cool it. You say a refrigerator compressor would work. Would there have to be an oil remover between the cooling tower and compressor? Are we talking about a dry compressor? Running a couple of these in parallel is a bad idea? Thanks.</p>
<p>oil less compressor</p>
Where do you buy 13x molecular sieve quality zeolite? I keep seeing zeolite clinoptolite online and am not trying to buy the wrong stuff in bulk. Also I'd like to point out the person who tried to give you a grammar lesson on your homemade pressure swing absorption liquid nitrogen generator instructable..... &quot;Allude&quot; &quot;elude&quot; dude air is being split apart into basic liquid forms, cut the author a break on this 20 page instruction manual which was generously posted for people like us. Sometimes people forget what their reading, I don't think this instructable is called really cold grammar. I for one thought everything was extremely well written. Thank you for posting.
<p>if u want better zeolite...try zeo chem 12-07 lithium zeolite</p>
<p>ebay...i just built a oxygen concentrator and got the zeolite from ebay. </p>
<p>Would decreasing the volume of the entire system and using a compressor from a fridge increase efficiency so that It will not take as long to get to pressure? Would it also be possible to catch the pure O2 from the zolelite after it reaches saturation to then cool into a liquid form?</p>
Did I read you correctly? You're getting 30 liters per minute? If that's not a typo then that production is incredible. Is it correct?
<p>It says 350cc/hr. this is the same as 350ml/hr, or approximately 0.03 liters per minute. :)</p><p>This is still a rather efficient production rate for diy.</p>
I have a business opportunity for you. You could make a lot of money with me. Please contact me at barfknecht.air.force@gmail.com if you are interested. I'm talking multimillions
how can you be sure liquid oxygen isn't made and your house doesn't burn down in 4 seconds flat?
I have an oxygen analyzer that is reading 1% O2 for the liquid. I'm using 99% N2 for my gas.
what about using it for ac. is that a good idea?
<p>How much does this entire thing cost? I want to make one and I am fine using a smaller compressor, but would running it for that long cause problems?</p>
<p>This is awesome. I want to build one now. I don't have any reason to have it, but I'm sure I could find some. :)</p>
<p>could you use car brake pipe ( also 1/4 inch, but copper and seamed) for the coolers to replace the stainless steel? Its an awful lot cheaper</p>
<p>Check the manufacturer specifications on the line before considering it. Cars can see around 1,000 psi in their brake system. He specifies that this system can see 3,000 psi. I did a quick search and found 25' x 3/8&quot; zinc coated steel brake line for $25. It claims 16,000 psi burst pressure, but doesn't specify the wall thickness.<br><br>Trust but verify. The first time you load it up, expect it to catastrophically fail. You should do that anyways. One little manufacturing defect can make a rather large mess very quickly. By &quot;mess&quot;, I mean rapid disassemble of the unit and anything around it, including you.</p>
<p>car brake pipes are copper coated steel. The copper is to help prevent rusting</p>
<p>In the UK, car brake pipes are usually steel direct from the manufacturer. However, both pure (relative term) copper and cunifer (copper/nickel alloy) is available. I imagine these are available elsewhere in the world? I have friends in the USA who use both copper and cunifer..</p>
<p>I'm not familiar with this tubing. You first have to make sure that it can handle the pressure. Second, you want to make sure it is thin enough to readily allow heat transfer.</p>
<p>based on your title, i thought you were making a generator that ran on liquid nitrogen. maybe that can be your next project!! :)</p>
<p>That could be done. Look at Sterling engines and/or TEC/TEG (seeback and peltier) modules. They can make mechanical or electrical energy from temperature differentials. I would think that would be horribly inefficient, but it could do something. :)</p>
About what, would you say this cost...? Where did you find all of these parts?
Absolutely incredible. Thanks for sharing.
<p>I'd love to make this, but I'm unsure of how I could put this liquid N2 to work.</p>
<p>well, if the T1000 comes along, this'd be rather handy don't you think? :P</p><p>Hope this comment doesn't break posting rules! </p>
<p>liquid nitrogen is used in many shop/industrial applications. I need it for cryo-treating certain alloys, shrinking parts for interference fit, purging oxygen from containers. Freezing corpses...</p>
<p>i agree with u:)</p>
<p>I was wondering if this in the first steps scrubs/removes CO2 from the air why couldn't you use the CO2 as dry ice to help cool the gas in the pre-cooler?</p>
<p>In step 9 ...</p><p>&quot;Such a simple solution that alluded me&quot; should be &quot;Such a simple solution that eluded me&quot; ... in this usage, allude = &quot;to refer casually or indirectly; make an allusion (usually followed by to): He often alluded to his poverty.&quot; ... elude = &quot;to escape the understanding, perception, or appreciation of: The answer eludes me.</p><p>Otherwise, good project!</p>

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