Making Ethylene (Refrigerant R1150)
256,933
Published 2023-04-21
youtube.com/@Exotic_Chem_Lab
In this video, I'll be making Ethylene (also called "Ethene", but not to be confused with "Ethane") gas to use as a refrigerant in the second stage of a two-stage vapor-compression system.
Ethylene has the formula C2H4 (as opposed to Ethane, which is C2H6), and has a boiling point of -104C. However, at a pressure of about 16 bar, its boiling point rises to -37C. This means if i compress it to at least 16 bar and then cool it with the evaporator coil from my propane-based vapor compression system, i can force it to liquify, and then expand it in an evaporator to below -100C. This would technically qualify as cryogenic, at least according to US EPA specifications, which considers any temperature below -90C to be "cryogenic".
Typically, a cascade refrigerator would use R508 as its second stage refrigerant, but this substance is no longer produced for environmental reasons, so it's prohibitively expensive. This makes Ethylene the only practical alternative for a hobbyist. Ethylene is also sold as "R1150" refrigerant, but difficult and expensive to acquire in this form. In some countries it may require a license to buy.
Fortunately, DIY production is relatively simple. By boiling ethanol and passing the vapors over an activated alumina (Al2O3) catalyst, the ethanol molecule is dehydrated as follows: C2H6O = C2H4 (gas) + H2O (gas). The output gases are then bubbled through liquid water, and the steam condenses, leaving behind the ethylene gas.
The only catch is that the dehydration has to proceed within a certain temperature range. The optimal temperature for ethylene production is about 450C +/-50C or so. Once the catalyst drops below 350-400C, the majority of the ethanol becomes diethyl ether or (C2H5)2O. Above about 500C, the ethanol molecule starts to decompose entirely, producing pure hydrogen and pure carbon. For this reason, it's necessary to use a thermocouple in the catalyst vessel to ensure optimal temperature is maintained.
Ethylene has a very distinct smell that many people describe as "faintly sweet and musky". To me, the smell is very similar to rotting/overly ripe fruit. It quickly becomes nauseating and can cause dizziness depending on the concentration. A more serious hazard of this gas is that it has almost exactly the same density as air. This means if undisturbed, a cloud of highly flammable ethylene can sit in one spot instead of sinking to the floor like propane or floating up and escaping like methane or hydrogen.
For storage, i collected the ethylene gas in a beach ball then used a fridge compressor to force it into a 2.5 gallon (9.5L) air tank, which had been evacuated, flushed with propane multiple times, then evacuated again to ensure no explosive mixture would occur. This will then be fed into the low-pressure side of the second stage of my vapor compression system when it's built.
Music Used:
Fortaleza - Topher Mohr and Alex Elena
Lobby Time - Kevin MacLeod
Bossa Antigua - Kevin MacLeod
All Comments (21)
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Really impressive video!
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one thing that absolutely shocks and impresses me about this channel is the pace at which videos are coming out, the last 6 months seems like years worth of work
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Dietary supplement for sea turtles f**king savage.
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Absolutely love this video. As someone who got a degree in chemical engineering and therefore spent many, many, MANY hours learning every minute detail of designing and building plug flow reactors, understanding their governing thermodynamic equations, solving differential equations to characterise the fluid dynamics of the packed catalyst beds, understanding the materials science of the various alloys used to build them and the physical chemistry involved with zeolite-catalysed reactions, drilling down into details of details of details I never could have imagined existing before... It absolutely blew my mind to see someone casually building a packed-bed plug-flow reactor from plumbing parts and unspecified alumina beads in his garage, and the damn thing actually working! Seriously, well done! (Deep down I'm almost insulted by the fact you managed to get a decent yield without doing any equations to work out the reaction rate, and therefore flow rate and reactor length required 😂) I think your "missing mass" is probably unreacted ethanol and possibly some diethyl ether that makes it past the collector bottle (I'd call that a blowdown drum 😂) and dissolves into the bubbler water and or adsorbs onto your silica gel dessicant. The bubbler will probably catch nearly all the ethanol, and a bit of the ether (particularly as it picks up more ethanol) The burning of your collected liquid looks to me like it's due mainly to ethanol burning, nice and calm and blue. I'd expect ether to burn off much more excitingly if it were the major component. I suspect a good fraction (half?) of the diethyl ether your reactor produces is ending up in your final product and I would suggest trying to do a thorough job of removing it because it's just such an horrific fire hazard. Although its boiling point is like 35*C, it has an insanely high vapor pressure so most of it will stay as vapor at atmospheric pressure even when cooled below this. Even at 0 degrees its vapor pressure is something like 1/3 of an atmosphere so that's why I suspect you have a lot in your collected product.
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For your calculations, the mass you distilled from the flask of everclear wouldn't be 100% ethanol because ethanol and water form an azeotrope. A mixture of 8% water and 92% ethanol has the lowest boiling point, so that was probably what you distilled over. Making your own ethene is astounding. Impressive yield.
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Ether as a byproduct? This reaction keeps getting better!
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As an (Bio-) Petrochemical AND Open Source Hardware nerd who wants to be able to make like all the things at a community/makerspace scale, this is AMAZING! Granted may need to be modified etc, and some things require larger scale (i wrote some wiki page on this), but having this chemical at this scale is an amazing addition to the toolkit! Really neat video, keep up the great work!
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Very cool video! I suspect that the liquid you collected after passing the ethanol over the catalyst is mostly a mixture of water and unreacted ethanol. Diethyl ether is immiscible with water, and only slightly soluble, so you would expect to see a separate layer if an appreciable quantity of ether was produced. Ethanol is also less dense than water, but fully miscible with water, so this may explain the lower density of the mixture. A lower concentration ethanol/water mixture isn't super flammable though, so you may be right that there is a little bit of diethyl ether dissolved in the water which caused the mixture to ignite. If you distilled the mixture to determine the composition, I suspect you'd find that it is mostly unreacted ethanol and water. I'm excited to see you use the ethylene as a refrigerant and look forward to that video! Great job.
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As a refrigeration mechanic I love the content and interesting take on all this. I’m currently sourcing all the parts I need for a cascade system.. Keep up the great content 👍
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Wow, this is awesome! One thing that might improve your yield is actually pre-heating the ethanol vapor. It's hitting the catalyst at ~100C, so it takes the first few inches in the catalyst bed to actually get it up to 450C, so you're running with low selectivity on the first bit of the reactor. You could accomplish this by filling the first several inches with an inert material with a high thermal capacity to get the ethanol up to temperature so when it hits the catalyst it's at your target temp. Broken/ground glass should do the trick if you don't want anything fancy!
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I wish my chemistry teachers had been half as interesting as you.
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This is really interesting since a way of creating ethylene that I'm familiar with (and you kinda hinted at it in the beginning) is using sulfuric acid, the entire reaction uses sulfuric acid heated to 180°C: Ethanol ---(H2SO4 @ 180°C)---> ethylene + water you can see the benefits of that since it requires a much lower temperature that the method you used. Interestingly enough you could also use the same setup but at 140°C to make ethers as well and I think Neilred used it to make diethyl ether from ethanol quite a while back.
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Sir, I admire your pirate attitude. Can't be any freeer as a person than when you take simple chemistry and apply it carefully to obtain difficult to get components. Your thoroughness in calculating yields and identifying by products are a testament to your interest in handling this stuff safely. I want to be like you when I grow up.
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I’ve been following this closely. I do HVAC Service for work, and have played with my own R290/Propane system before that had great results. I built my own tiny little system from scrap Dehumidifier parts, and I’ve also used it in a Window AC for shiggles. Both worked great! I’ve got so many random parts, this project seems like something I should try myself!
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I want to subscribe, but I feel like it’ll get me placed on some kinda watch list. Ehh, what the hell. These videos are worth it.
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Been watching this channel for a while but this project has made this my all time favorite channel. I've wanted to make a cryocooler for a while now and the amount of information with detailed explanation of the build and data analysis is GOLD. Can't wait till you get your first drop of cryogenic liquid!
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smell-test is not a great thing for cancerogenic anesthetic, but it works. I've made ethylene with the same method in lab, with just a butane torch heating it. FTIR showed almost complete conversion and MS showed lots of ethanol with the gas. your cleaning steps are very nice. i did run my catalyst in quartz tube, so i could eyeball the yellowing of the catalyst, and ethanol I evaporated in the same quartz tube from mineral wool. but I did not need 60 liters. Good Luck!
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great video series! thank you for taking the time to put together these videos.
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Found your channel a couple of days before and watched all of your videos with great pleasure. It's so nice to see someone explaining such complex topics and building real-life working prototypes. Thank you for making videos at such an incredible pace, but please, don't get burnt out from such an overwhelming load. Wish you success in all your experiments and steady growth to your channel. You definitely deserve a million subs at least!
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This is the best experiment series on youtube, i cannot wait to see your next cooler design and to really get those low temps
