CO2 dry cleaning what is the process

Question

From what I understand CO2 drycleaning is essentially heating and pressurizing Co2 until it is at a supercritical state and then using it as a solvent to wash clothing. I just don't understand why clothing that comes out of the resulting process would be cold. Doesn't supercritical carbon dioxide require temperatures of at least ~300 Kelvin to form? Anyway, I would greatly appreciate it if someone with more knowledge on the subject could provide a basic outline as to how CO2 dry-cleaning works. There are very few resources that go into detail on the process.

Thanks!

Answer 1

Like aliphatic cleaning solvents such as hexane, both liquid and supercritical $\ce{CO2}$ are effective solvents for fatty stains. According to Green America, though, "[L]iquid CO2 is pumped into the mix. Clothes are rotated in a cycle that lasts five to 15 minutes at room temperature."

The phase diagram for $\ce{CO2}$ shows that it is a supercritical fluid above ~300 K, just above room temperature, at ~80 kg/cm², so that it may be either liquid or supercritical during the cleaning. However, at the end of the cycle, "[T]he liquid CO2 is pumped back into the storage tank, to be reused again, if possible. The remaining CO2 is released in the air." That implies a bit of a pressure drop at the end, with concomitant adiabatic cooling.