Talk:Supercritical carbon dioxide

Safety

Does anyone know if there are any safety concerns with CO2 in its supercritical sate?

This is in refrence to Geosequestration (a type of CSS). —Preceding unsigned comment added by 203.29.214.2 (talk • contribs)

I know that the process has many safety requirements since it is always done under very high pressure. Besides that, I don't know of any environmental of health safety concerns since the CO2 used is always (I think) reclaimed. Sjschen 16:07, 22 August 2006 (UTC)

The article says: "The unique properties of supercritical CO2 ensure that it will remain out of the atmosphere". None of the three references give an account of why CO2 would not emerge from a subterranean storage such as an old oilfield, nor how that is linked to supercritical CO2's "unique properties". After all, the oil that used to be in there did come out and according to what I've managed to learn about supercritical fluids, they will expand to fill every volume, which means that unless the oilfield is completely tight, CO2 should be expected to leak out. This seems to be different for brine, but there as well, it's not the properties of supercritical CO2 but rather the fact that brine formations are usually sealed tight due to their geological nature. In fact, it would appear to me (based on the information in the article) that supercritical CO2 is probably much more difficult to contain than most regular fluids, due to not having surface tension. It would be good if someone who is more knowledgeable could shed some light on this.138.250.80.173 (talk) 17:49, 3 March 2015 (UTC)

Surfactants?

I've read that some companies have produced surfactant molecules that dissolve in supercritical CO₂ to assist it's properties in dry cleaning. Interestingly, these surfactants form inside-out micelles (tails pointing outwards). Can anyone expand on this, by any chance? --Xanthine 18:35, 1 September 2006 (UTC)

Cleanup need

All those http links within the text should be treated thusly:

1. click on those http links, and get a heading/author from the links,
2. rewrite http link from http://www.here.org/ to [http://www.here.org/ heading/author some such]
3. surround [http://www.here.org/ heading/author some such] with <ref></ref> so that the link constitutes a nice link

And near the end of the article add the lines

==References==

<references/>

I would do it myself, but I'm a little busy for now. Said: Rursus 21:02, 20 May 2007 (UTC)

done just that. Uwezi 12:04, 24 May 2007 (UTC)

re-directing to supercritical fluid

I have been planning for a while to delete this article and re-direct to supercritical fluid. I have transfered much of what was good over to that article, and there is not much here not covered by that or supercritical fluid extraction. Anyone think this subject heading needs keeping?Stainless316 (talk) 16:37, 15 October 2008 (UTC)

Do you realize that the version on which you placed the "merge" tag had been badly vandalized on 10Sep2008, when an anon IP deleted most of the lead paragrph? The prior version was much better, but subsequent editors (including yourself) made no attempt to find or revert the obvious vandalism. Please always check the page history for vandalism prior to making any edits.

Anyway, I think this should remain a separate article, since it is about a specific (and quite important) supercritical fluid, while supercritical fluid deals with the general topic of such fluids. --Seattle Skier (talk) 22:02, 26 December 2008 (UTC)

I am OK with leaving it separate, but I think you are a bit quick to assume vandalism for the edits made on 10 September. The definition may not have been as comprehensive as the earlier one, but was essentially correct, and could have been an attempt to make the intro more succinct.Stainless316 (talk) 15:14, 20 January 2009 (UTC)

Image

made image better —Preceding unsigned comment added by 72.75.206.180 (talk) 23:23, 22 December 2008 (UTC)

Greenie-weenie nonsense

Removed from the Uses section:

"Because supramics consume and sequester carbon as stable compounds in useful products, they may serve to reduce carbon that would otherwise be released into the environment."

This was evidently injected by some ignorant, brainwashed greenie-weenie who slept through high school biology and doesn't realize that there's something called a "carbon cycle" in nature. This kind of bullshit should be removed from Wikipedia "on sight".—Quicksilver^{T @} 21:18, 5 February 2010 (UTC)

use in solving essential oils

sco2 is used sometimes (particularly in woods), but I think far more often it is liquid CO2 extraction that is used. The whole thing leads to confusion in suppliers, many offering "hypercritical" extractions to distinguish from the common misuse of supercritical for liquid CO2 extraction. At the other end of the spectrum, hypercorrection occurs, with many places offering "sub-supercritical" co2 extracted essences. Regular (liquid) CO2 extraction is a less complete extraction, avoiding the terpenes that would otherwise spoil the traditional scents associated with the essential oils. There is a video of an orange rind extraction done in a test tube, which clearly shows the solid melt and liquid phase in action, but being in a simple test tube with plastic cap it can't be far beyond the triple point. I'm not sure of the source (and I can't remember if the numbers are in kPa or psi) but I remember reading that pressures beyond 200 exceed optimal extractions for traditional essential oils. --173.66.61.78 (talk) 21:11, 8 July 2011 (UTC)

My understanding is that you don't have stable liquid CO2 above 31 degrees centigrade regardless of how much pressure in the vessel. So anything which dissolves above 31 degrees would require supercritical CO2 to extract. And you need a vessel which will contain over 1100 PSI regardless of which you're using. My experience is limited and outdated -I haven't worked as a chemist for over 30 years- but if I understand it correctly there is a great deal of variability as to what temperatures are tolerated by the various oils. So I would agree with you that liquid CO2 extraction may be preferable for super light and volatile oils but it is a whole 'nother ball of wax. Pardon the pun. Trilobitealive (talk) 15:57, 9 July 2011 (UTC)

Supercritical CO2 at 500C and 20 MPa

I think this part should be deleted, because nobody heats CO2 to 500 C and 20 MPa. To me, these look like parameters that were scaled more for water... from CO2. Although it is 2 MPa below the critical point of water... — Preceding unsigned comment added by 69.17.253.18 (talk) 22:40, 29 January 2012 (UTC)

mislabeled vertical axis?

Am I confused or is the diagram mislabeled? In both the "supercritical fluid" and "supercritical carbon dioxide" articles, the diagram has a vertical axis in P(bars), and shows the critical point of CO2 at about 7 bars. The text in both places gives the critical pressure as 7.38 MPa, aka 73.8 bars. I'm not confident enough in this area to go altering the diagram (which in any case would require me to learn how to edit SVG), but it certainly looks to me like the diagram is wrong. I'd love an explanation one way or the other. Paleolith (talk) 17:30, 12 March 2012 (UTC)

It looks ok to me. Are you sure you aren't confusing the critical point with the triple point? This one is around 7 bar (looks more like 5 bar to me, but I'm not very good at placing the intermediate marks on logarithmic-scale axes) while the actual critical point looks about 75 bar just fine. --Wtrmute (talk) 18:37, 3 March 2013 (UTC)

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Density

What is the density at the critical point? This seems like a basic fact to list. JWB (talk) 19:47, 25 April 2018 (UTC)

Reaction with metal at high temperatures

Does supercritical Carbon Dioxide react with metals at high temperatures? If so, which metals, which temperatures and which reactions? Hobbitschuster (talk) 16:48, 15 January 2022 (UTC)

Magnesium will, as will lithium, potassium, sodium, calcium, and aluminium. (not necessarily an exhaustive list) It will strip one of the oxygen off. Come to think of it, elemental carbon might be bad, under the right conditions as well. (as in passing CO2 over a bed of carbon or coke will produce CO) Then you will have carbon-monoxide that can react pretty easily with iron and nickel, see the Nickel_tetracarbonyl wikipedia entry. Putting something reactive with CO2 has the potential of cascading dangerously. — Preceding unsigned comment added by 2601:243:1202:D9F0:B15E:6CDD:8E56:8D68 (talk) 02:45, 4 February 2022 (UTC)

But relatively more noble metals should be fine(r) right? Like iron/steel or zirconium or something of the sort.... Hobbitschuster (talk) 15:39, 4 February 2022 (UTC)

Dealing with the high pressure required

How do you wash caffeine out of green coffee beans with something at 73 atm? How do you do anything with something at 73 atm? Reading this article, I'm sure you can, and I'm sure people are doing, but my instinct has it that the beans could not stand 73 atm, and the CO2 would not stay supercritical at a pressure the beans could stand. This apparent incongruity is not really about coffee, but about ALL the uses of sCO2 where other things are involved. Does the article need a bit of an explanatory addition here, or is it just my failing imagination? Nick Barnett (talk) 17:49, 31 October 2023 (UTC)