Midjourney generated image of supercritical CO2 changing phase explosively from pipeline
Supercritical CO2 Is Useful, Not Miraculous And Has Clear Risks
Be skeptical when the substance is invoked for energy generation and storage gains as fossil fuel CCS propaganda lurks
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Published in
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19 min read
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2 days ago
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Supercritical CO2 is having a moment in the sun again, at least from my admittedly odd point of view. The US DOE is once again touting the use of the substance in thermal electrical generation. The carbon capture and sequestration crowd are touting supercritical CO2 pipelines as the answer to the reality that burning fossil fuels makes CO2 that’s 2–3 times the mass and 450 times or more the volume of the fuels. And it’s being used in textiles and to extract interesting herbal elements from high-value plants that are legal in many jurisdictions. Heck, it’s even in heat pumps.
Phases Of Matter
There’s a lot to unpack here, so lets head back to the 19th century to figure out what the heck supercritical CO2 is. No, lets head back further to the ancient Greeks. And to be clear, it’s entirely probable that the ancient Chinese and ancient Arabians figured this out independently and possibly before Europeans did, but English-language histories were written by Europeans, so we’ll live with this version of the story. (If anyone has references to non-European scientists and phases of matter, please let me know. I love good parallel invention stories.)
Humans have known pretty much forever that water and ice are the same thing, with the difference between them being heat. Summer and winter with icing and melting are pretty obvious phenomena, and humans have been smart enough to remember and figure things out for probably 450,000 years. Gases took a lot longer to understand as another state of matter. The Greeks knew this and mistakenly thought that with water being able to exist in three states, everything in the universe was probably made of it.
It takes a lot of heat to change the phase of ice to water. The temperature of ice or any solid rises until it gets to the point where it’s going to turn to a liquid, and then it just sits there at that temperature as more and more heat is added until finally it becomes a liquid. Ditto for water turning to steam. Water gets to the boiling point and doesn’t get hotter. It sits there…
