I built a pressure vessel from aluminum and acrylic, and filled it by placing pieces of dry ice inside. The dry ice melts under high pressure, and forms a liquid and gas phase. When the vessel is heated, the CO2 becomes supercritical -- meaning the liquid and gas phases merge together into a new phase that has properties of a gas, but the density of a liquid.
Supercritical CO2 is a good solvent, and is used for decaffeinating coffee, dry cleaning clothes, and other situations where avoiding a hydrocarbon solvent is desirable for environmental or health reasons.
If you have a suggestion for what I should do with the supercritical CO2, please leave a comment.
CO2 can be liquefied in plastic bottle preforms:
It may be important to open the container before all of the solid melts. When there is still some solid CO2 present, the pressure will be close to the triple point. Once the solid completely melts, the pressure will increase quickly to about 750 psi depending on the ambient temp. I really doubt those plastic containers could hold 750 psi.
My first look at supercritical fluids:
Another youtuber interested in supercritical CO2:
Added engineering recap and formulas: