Sciencemadness Discussion Board - Shop-made supercritical CO2 chamber

Shop-made supercritical CO2 chamber

watson.fawkes - 12-9-2011 at 05:44

Ben Krasnow built his own chamber to hold supercritical CO2:
http://www.youtube.com/watch?v=-gCTKteN5Y4
Here's what happens when you don't put a release valve on it:
http://www.youtube.com/watch?v=M4CTkicgKtE

The builder had access to machine tools, but there's nothing at all fancy about the machining. This kind of project is well within the bounds of a typical community college machine shop.

Magpie - 12-9-2011 at 07:28

That's the first time I have ever seen liquid CO2 or a supercritical fluid. Thanks for sharing.

unionised - 12-9-2011 at 13:06

It seems that doing something plainly stupid is within the bounds of a community college.
Why would you want to do that?

AndersHoveland - 12-9-2011 at 13:34

very nice, thanks for sharing!

although it would be extremely dangerous, one wonders about the possibility of dissolving N2O5 in the liquid CO2 for performing extreme nitrations. http://www.sciencemadness.org/talk/viewthread.php?tid=17304

[Edited on 12-9-2011 by AndersHoveland]

watson.fawkes - 12-9-2011 at 17:20

Quote: Originally posted by unionised

It seems that doing something plainly stupid is within the bounds of a community college.
Why would you want to do that?

In the US, many community colleges have shop classes whose equipment may be used for the cost of the generally very cheap tuition. For many people, it's an ideal way to do some occasional projects.

drago57 - 12-9-2011 at 22:14

I've been using supercritical/liquid CO2 most days for the last 4 years for my PhD project. I wouldn't be so rash as to suggest I'm an expert, but if anyone has any questions about system design or whatever I'd be happy to have a go answering them.

bahamuth - 12-9-2011 at 23:21

Extracting limonene using liquid/supercritical carbon dioxide

If this really exhibits supercritical levels I'm not sure, but it works.

Done this for fun at the lab in cheap VWR 50ml centrifuge tubes, and only one of three-four trials ruptured the cap, possibly due to reuse of the cap.

bbartlog - 13-9-2011 at 06:06

Quote: Originally posted by unionised

It seems that doing something plainly stupid is within the bounds of a community college.
Why would you want to do that?

Because it looks cool, and with a little more work could be used to do some interesting extractions or even just reactions with the CO2 itself? Seriously, the guy did the appropriate calculations and for his first run pressurised the thing remotely (viewing via TV). Still risky, but do you just want to write off any possible amateur experiments with supercritical CO2?
Granted the lack of a release valve was a nice piece of foolishness...

peach - 28-9-2011 at 04:24

These are from 'periodicvideos' on youtube, who produce educational science videos at Nottingham University to engage the public.

The videos are always interesting and feature the whacky professor's hair. The professor studies supercritical fluids and has a demonstration model in his office, and new videos are put up regularly so you can subscribe and click for email updates.

If you scroll down on the channel page to "Brady's other channels", you'll see there's a channel for physics (sixty symbols) and other related topics.

<iframe sandbox width="640" height="360" src="http://www.youtube-nocookie.com/embed/trhXiCxvzu4" frameborder="0" allowfullscreen></iframe>

<iframe sandbox width="640" height="360" src="http://www.youtube-nocookie.com/embed/0dSMzg0UPPo" frameborder="0" allowfullscreen></iframe>

watson.fawkes - 5-10-2011 at 14:49

Ben Krasnow has a new video up on his chamber. Effect of long-term high pressure CO2 on acrylic. Teaser: foamy acrylic.

There's a reason they use sapphire windows on the professional versions. For him, the easiest thing to do would be to use an off-the-shelf sight glass, an optical disk of glass, available in borosilicate, that's used to see into boilers and tanks and the like. Use the acrylic for mechanical stability. Mount the sight glass in a recess therein.

White Yeti - 9-10-2011 at 10:48

Strange...
I read that you need some kind of synthetic sapphire window in order to be able to see the supercritical CO2. This goes without saying that such a window would be outrageously expensive. So, I would not look at this in terms of feasibility, but I would instead consider the financial limitations associated with making such a chamber. It better be a chamber you'd use often, or else you're throwing one and a dozen grant out the window.

You technically don't need a window, you could substitute it with a thermocouple, a pressure gauge and a phase diagram.

I know this is a hypothetical thread, so I will present you with a hypothetical question; what would you use this chamber for? Extracting caffeine? Extracting essential oils? Extracting smells from flowers? Looks like an awesome project, but not something that a single person can undertake.

watson.fawkes - 10-10-2011 at 04:28

Quote: Originally posted by White Yeti

So, I would not look at this in terms of feasibility, but I would instead consider the financial limitations associated with making such a chamber. It better be a chamber you'd use often, or else you're throwing one and a dozen grant out the window.

You technically don't need a window, you could substitute it with a thermocouple, a pressure gauge and a phase diagram.

Using an opaque chamber is just fine once you've debugged the apparatus, but being able to see inside is very useful before that point. It's worth the expense.

And that expense isn't even all that much. Search for "borosilicate sight glass". A 4" diameter disk of 1/4" thickness (~ 100 mm x 6 mm) is only about $26. It needs reinforcement for strength, but the chamber in the original post shows that's eminently feasible. The gasket material can seal against the glass, so the acrylic is then used only for strength and optical clarity, not chemical resistance.

Quote:

Looks like an awesome project, but not something that a single person can undertake.

I will answer this defeatist attitude. This is easily a single-person project.

Admittedly you need access to the right tools to do this, but even this isn't particularly difficult. There are many routes to access. As I've said before, your typical community college machine shop has all the equipment. You can gain the skill to do this with one or two semesters of night classes.

A serious person of modest means can just go purchase the equipment these days. Tormach sells a line of inexpensive CNC gear. They are not designed for continuous production manufacturing but rather for prototyping and serious hobbyists. If you could afford a second car payment, you can readily finance a complete shop.

If you're in a city with a TechShop, join that. They've priced their membership to be comparable to a gym membership. Indeed the economics are rather similar. A well equipment shop has about the same capital cost as a well-equipped gym.

If you're enrolled at a major university, there's always at least one student-available shop on campus. It's usually in the physics department. Talk your way in; it's a good skill to practice for later life.

Edit: Fixed the price. the 3" one is $21.

[Edited on 10-10-2011 by watson.fawkes]

peach - 10-10-2011 at 08:54

I like the borosilicate backed window idea.

That just leaves the seal. Suggestions on material?

Also, if you haven't already, suggest it to Ben.

Quote:

I know this is a hypothetical thread, so I will present you with a hypothetical question; what would you use this chamber for?

That's like asking what you'd use a bottle of solvent, soxhlet or still head for.

Rather than trying to think of really specific applications (like caffeine) think of what it fundamentally is and how it compares to other things.

The supercritical CO2 is an organic solvent, with the dissolving capacity of a liquid but the flow properties of a gas. So, instead of sitting on the surface of things, stuck in place by it's surface tension (like a liquid solvent), it will flow through them.

This has major potential for performing reactions in solvent systems that are very different to normal liquids and gases.

It is also an under explored area of science, as creating such supercritical systems, in a highly controlled manner, is something that requires a fair bit of materials and engineering technology.

For instance, until society had easy, cost effective access to high vacuums and pure inert gas in cylinders, the whole area of studying atmospherically sensitive materials and reactions was out of bounds. That was not very long ago at all.

White Yeti - 10-10-2011 at 11:23

Quote: Originally posted by peach

The supercritical CO2 is an organic solvent, with the dissolving capacity of a liquid but the flow properties of a gas. So, instead of sitting on the surface of things, stuck in place by it's surface tension (like a liquid solvent), it will flow through them.

Right, but considering the size of the chamber shown in the video, you can't extract much of anything. There's probably enough room for the CO2 and a dozen coffee beans. You'll get a yield of a fraction of a gram if you get lucky. What I'm saying is that this chamber would be great for demonstrations of supercriticality, but putting such a small chamber to use is a different story.

Of course you can scale this up, but as soon as you scale this up, the walls will need to get thicker, the window will get thicker and more expensive and things start to get dangerous. There's a reason why sapphire windows are used in large chambers.

I think the most profitable use for such a small chamber would be extracting essential oils from flowers to make perfumes. That's why I asked what the OP was going to do with this chamber. No one mentioned it and everyone kept talking about extracting caffeine from coffee beans instead. I don't know why everyone has an obsession with extracting caffeine. What about extracting essential oils instead? For once you could extract something that is actually pretty valuable, oils are sold for quite high prices.

peach - 10-10-2011 at 12:32

I think Watson was posting it merely to show something interesting and that it's possible at home.

Why is extracting flowers more advanced than extracting caffeine?

We'd get an equally poor mass of essential oil out of those as well. And neither process needs a windows, it's only there so us fickle humans can get excited by what the windows to our soul tell us.

The big deal with supercritical solvents now is not just extracting things but doing reactions and forming novel products in that supercritical solvent.

Quote:

putting such a small chamber to use is a different story

It's only a problem if you plan to run your own commercial caffeine extraction plant from that chamber.

The vast majority of experimental work starts in the micro-scale first, even processes for plants producing millions of tons of product per year.

Really special products are still made on a comparatively micro-scale compared to things like sulphuric acid, which is made by the megaton. The guys who make sulphuric acid will look at the pharmaceutical companies as if they're playing with that CO2 chamber.

We could equally well say the same thing about CERN. That is one big and expensive chamber, yet all it does is fire a tiny quantity of atoms into each other and produce nothing that is of any immediate, tangible worth. It can technically turn lead into gold, if you want a few atoms of gold for the few billion it cost to build and run that accelerator.

Imagine you're trying to make an anticancer or HIV drug that is as powerful as adrenaline is stimulating, or LSD psychoactive. But that happens to be best made in supercritical solvents. That chamber could contain enough to treat thousands and thousands of people. So it certainly has it's use.

[Edited on 10-10-2011 by peach]

White Yeti - 10-10-2011 at 13:18

Quote: Originally posted by peach

...Really special products are still made on a comparatively micro-scale compared to things like sulphuric acid, which is made by the megaton...
[Edited on 10-10-2011 by peach]

That's my point. Flower extracts (perfumes) are still made on a relatively small scale, while caffeine extraction is done on a really, REALLY large scale. Caffeine extracted from tea and coffee then goes into "energy drinks", which is a huge multimillion market.

Whether experimentation starts out on a small scale or not, you'll have to scale it up eventually and that's when you will hit financial obstacles.

This method for making CO2 chambers is great for a small scale if you don't want to do anything except look at supercritical CO2.

watson.fawkes - 12-10-2011 at 05:36

Quote: Originally posted by peach

That just leaves the seal. Suggestions on material?

I'd guess lots of fluoropolymers might be appropriate, but I certainly can't say definitively. It's not like material compatibility tables regularly have a column for liquid CO2. Viton is the most readily available of these for this applications, as you can get off-the-shelf O-rings. McMaster-Carr carries a huge variety. You could also machine hard gaskets from PTFE or PVDF. Assuming a 4" glass disk for a somewhat smaller window, they'd be somewhere between $10-$20 each in materials.

watson.fawkes - 12-10-2011 at 05:58

Quote: Originally posted by White Yeti

Whether experimentation starts out on a small scale or not, you'll have to scale it up eventually and that's when you will hit financial obstacles.

This method for making CO2 chambers is great for a small scale if you don't want to do anything except look at supercritical CO2. If a cubic inch of homemade aerogel isn't proof enough of your kewlness, you're trying to impress the wrong people.

What you're doing is complaining that you have to invest in capital equipment in order to start a business. Duh.

I can't think of a reason for scaling up that's not production or research for production. If you're doing science, the modest size of this chamber is just fine. If your cubic inch of homemade aerogel doesn't adequately show off your kewlness, you're trying to impress the wrong people.

Quote: Originally posted by White Yeti

Of course you can scale this up, but as soon as you scale this up, the walls will need to get thicker, the window will get thicker and more expensive and things start to get dangerous.

This is just mechanical nonsense. When you scale up such a reactor, you don't just scale up the dimensions of a test reactor. The Krasnow test chamber is essentially just a pair of sight glasses opposite each other, without a separate tank structure. A larger reactor would be a pressure tank of typical design, a cylinder with a pair of spherical or ovoid end caps. If you want sight glasses in your reaction, weld on bits of pipe for sight glasses. You shouldn't have to change the design of the sight glass mounting and sealing from what's used in the test chamber. You don't even have to change the dimensions.

Wizzard - 12-10-2011 at 07:01

Indium or lead may make a very good, hard seal. You could always use aluminum but that may not work really well with glass, but should work well with the plastics.

White Yeti - 12-10-2011 at 13:00

Quote: Originally posted by watson.fawkes

If you're doing science, the modest size of this chamber is just fine.

What kind of "science" are you planning on doing with such a chamber? Just out of curiosity.

I have a feeling that you would start by extracting caffeine from coffee (and the like) before using it for anything else. Anders suggested dissolving N2O5 in the liquid CO2 to perform nitrations, but other than that, I don't see what use such a chamber would have, besides extractions of chemicals from raw materials.

Be careful when using the word "science". Call me whatever you want, I don't care, but I take the words "science" and "experiment" very seriously. Extracting chemicals is not "science" per say, it's just an industrial process.

watson.fawkes - 12-10-2011 at 18:56

Quote: Originally posted by White Yeti

Failing to have anything further to say about construction of such apparatus, you proceed to attack the messenger of your small experience with building things. Then you pose a straw man about what I myself might want, wholly out of your small imagination. Your small actions speak louder than any names I might call you.

UnclearReactor - 30-10-2011 at 16:24

Eminently doable. Sapphire windows. Prices start under $200 U.S. http://www.mpfpi.com/sapphire.html

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unionised - 31-10-2011 at 11:59

"Indium or lead may make a very good, hard seal. "
Possibly the only time you will ever see indium and lead described as hard.

He Blew an O-Ring in the Second Video... XD

Retrical - 1-10-2013 at 03:06

Quote: Originally posted by watson.fawkes

Ben Krasnow built his own chamber to hold supercritical CO2:
http://www.youtube.com/watch?v=-gCTKteN5Y4
Here's what happens when you don't put a release valve on it:
http://www.youtube.com/watch?v=M4CTkicgKtE

The builder had access to machine tools, but there's nothing at all fancy about the machining. This kind of project is well within the bounds of a typical community college machine shop.

He Blew an O-ring taking the thing apart, LOL.

Master Triangle - 25-12-2013 at 06:07

The first thing about supercritical CO2 is that the pressures and temperatures are not as high as most people think, look up a table for it. As you see in one of Ben Krasnow's videos where he makes aerogels you can just make a chamber out of steel pipes and that is well more than you need, I have a calorimetry bomb that I was considering using for this sort of thing but am selling now. If you can get some short lengths of bolt-flange pipe like this would be perfect as you really want a large chamber. You could just start with straight tube or a sawn-up nitrogen tank and weld bolt flanges to that, most welding shops would be happy to do that, just make sure they understand it needs to be gas-tight and very secure.

If you do not mind minor gas leakage then any sealing material that does not completely fall apart under intense solvents will do, even "liquid gasket" will probably work. For the viewing window you can use thin glass on the inside with thick perspex supporting it (careful with big windows >15cm, the perspex may flex too much to support the glass adequately), then only the glass is exposed and needs a seal, have a steel flange with bolts holding the sandwich to the surface or just put the bolts straight through the perspex like Krasnow did. For a small pipe vessel something like this would provide a good flat surface that can be bolted to.

You really do not need a viewing window as it increases complexity a lot and you only need to know the temperature and pressure, but who doesn't like to see their experiment bubbling away?

Heating would be best done with a electric heating band like Krasnow did, have a look around Aliexpress for a good one.