* CO2 is already a gas at room temperature and pressure: CO2 becomes a liquid under high pressure, but it readily reverts back to a gas when released. Preheating is usually necessary for substances that need to be heated to a specific temperature before they can be effectively used or transported.

* Preheating could be dangerous: Heating a compressed CO2 cylinder could increase the internal pressure to unsafe levels, potentially causing a catastrophic failure.

* CO2 systems rely on pressure regulation: CO2 systems rely on regulators to control the flow and pressure of the gas. These regulators ensure the CO2 is delivered at the correct pressure for its intended use.

However, there are some specific scenarios where a preheater might be used with CO2:

* Special applications requiring very high flow rates: In some industrial processes, very high flow rates of CO2 might be needed. In such cases, a preheater might be used to help vaporize the liquid CO2 faster.

* CO2 used in extremely cold environments: If CO2 is being used in a very cold environment (e.g., outdoors in winter), a preheater might be used to help prevent the CO2 from freezing.

Overall, preheaters are not a standard feature of CO2 cylinders. They are only used in specific applications where they are necessary for the safe and efficient operation of the system.