As my memory serves me, CO2 becomes super critical in the neighborhood of 1100 psi and 89F. Actually pretty low and easily achievable.
At the cryogenic temperatures reached as the pressure is released, carbon steel becomes a grenade, so typically 300 series stainless is used.
A piece of 4" Schedule 160 stainless pipe is more than adequate for a 1500 psi operating pressure, and still maintain a 3X safety factor.
Liquid C02 at atmospheric pressure is called dry ice, so some pressure is required to just keep it liquid.
A 50 gallon Dewar of liquid C02 with a dip tube, would allow you to pre-pressurize your vessel to ~150psi with the 250psi gaseous head pressure to keep it liquid, and still have transfer pressure using the liquid dip tube.
Per Boyles ideal gas law:
of an amount of gas
is determined by its pressure, volume, and temperature. The modern form of the equation is:
is the absolute pressure
of the gas; V
is the volume
of the gas; n
is the amount of substance
of the gas, usually measured in moles
is the gas constant
(which is 8.314472 J
−1 in SI units
); and T
is the absolute temperature
You can heat the reaction vessel with simple pipe heaters, to hit whatever operating pressure you wish. If a back pressure regulator is placed in the system that limits backpressure to 1500psi before venting to atmosphere, you can operate in super critical range without overpressuring and exploding the vessel.
By starting with liquid C02, it eliminates the need for pumps and a refrigeration system.