Making Big Dry Ice Blocks With Low Pressure CO2

Although the term ‘dry ice’ is generally used for solid CO₂, it’s much more accurate to call this ‘dry snow’, as, rather than being actual solid blocks, they are effectively snow that’s been compressed really tightly. While not really necessary for most applications of dry ice, it is possible to make blocks of actual CO₂ ice, and thus [Hyperspace Pirate], as someone with a healthy obsession with cold things had to make some of his own.

As a first step, you, of course, have to chill down CO₂ in a container, for which Mr. [Pirate] used a Joule-Thomson cryocooler, with a 15% butane, 35% propane, and 50% ethylene gas mixture. Of course, as ethylene is only easy to get if you have a lot of money to spend, you will want to make it yourself from ethanol. This involves boiling and 400°C aluminum oxide to capture the produced ethylene.

With the CO₂ pressure chamber cooled in its refrigerated bath, the process didn’t take long. After opening the pressure chamber, the results were interesting to say the least. Although there was definite ice formation along the sides that contacted the metal chamber the closest, the closer to the center, the more the CO₂ resembled the usual fluffy, compressed dry ice.

This is encouraging as it shows that it’s definitely possible to make nice ice pucks or cubes, but the method needs further refinement to get more ice and less snow.