Question

During cryogenic CO2 purification, why is it critical to control the cooling rate and pressure to prevent the transition of carbon dioxide from a gas directly into a solid?

Accepted Answer

In cryogenic CO2 purification, carbon dioxide must remain in a liquid state during the cooling process to allow for efficient separation from impurities. If the cooling rate is too rapid or the pressure drops too low, carbon dioxide reaches its triple point, which is the specific temperature and pressure where a substance exists as a solid, liquid, and gas simultaneously. Below this triple point, carbon dioxide undergoes desublimation, a phase change where it transitions directly from a gas to a solid, known as dry ice. Forming solid dry ice inside purification equipment creates physical blockages that stop the flow of gas, a condition referred to as plugging. These blockages can damage delicate internal components, such as heat exchangers and valves, by creating excessive pressure buildup behind the solid mass. Additionally, solids reduce the heat transfer efficiency of the equipment, preventing the system from reaching the temperatures required for purification. To prevent this, operators must ensure the process stays above the triple point of 5.1 atmospheres of pressure and minus 56.6 degrees Celsius, maintaining a pressure-temperature relationship that ensures the carbon dioxide liquefies instead of freezing.

Home → All Courses → Engineering and Technology Courses → Carbon Capture Technology → Flashcard

During cryogenic CO2 purification, why is it critical to control the cooling rate and pressure to prevent the transition of carbon dioxide from a gas directly into a solid?