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[–] NassTee 1 points 2 points (+3|-1) ago 

They start with wet ice, then they dry it out.

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[–] aileron_ron 0 points 2 points (+2|-0) ago 

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[–] scorinth 0 points 1 points (+1|-0) ago  (edited ago)

Carbon dioxide can't exist as a liquid at atmospheric pressure (which is why dry ice is "dry"), but if you cram it into a pressure tank, it can condense into a liquid.

Dry ice production starts with this liquid carbon dioxide in a pressure tank, and then you open a valve into a second container that's at atmospheric pressure. The liquid shoots out of the tank because of the pressure difference, and once it's at atmospheric pressure, it boils into a gas. Now, it takes heat to make a liquid boil, and that heat comes from the rest of the CO2 liquid, that makes part of the CO2 cold enough to freeze into a solid.

So, to recap, you have all of this CO2 that was a liquid, but it can't be a liquid anymore. Some of it changes into a gas, and some of it changes into a solid. At this point, you basically have CO2 "snow" shooting out of a valve at high speed, so now you have to catch the solid snow and squeeze it together to form a solid block. This is the dry ice that you can buy in shops.

Fun fact: You can replicate this process at home with a CO2 fire extinguisher and a pillowcase. And here's a video about CO2 at high pressure in a home workshop. All the stuff about "supercritical" CO2 isn't important to your question about dry ice - it happens at even higher pressures than liquid CO2.

And, finally, where do dry ice manufacturers get the liquid CO2 from? I have no idea. But it's probably the same source that soda manufacturers use. shrug

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[–] jokersmild 1 points 1 points (+2|-1) ago 

When mommy dry ice and daddy dry ice love each other very much they give each other a, um, special hug. ..

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[–] Stavon 0 points 1 points (+1|-0) ago 

Similar as how a refrigerator or an aircon works. Only it's carbon dioxide you cool down, not food or air.