Can Carbon Dioxide Be Liquefied? Understanding the Critical Conditions and Applications

Introduction

Carbon dioxide (CO2) is a common substance that plays a crucial role in various industrial and environmental applications. While it is primarily found in a gaseous state under normal atmospheric conditions, it can indeed be liquefied. This article explores the critical conditions required for the liquefaction of CO2 and its various applications.

Understanding the Critical Conditions for CO2 Liquefaction

Critical Temperature

The critical temperature of CO2 is approximately 31.1°C or 88.0°F. This means that at any temperature above this critical point, CO2 cannot be liquefied, regardless of the pressure applied.

Critical Pressure

The critical pressure of CO2 is about 7.38 MPa, which is equivalent to 73.8 bar or around 1070 psi. If CO2 is subjected to a pressure above this critical pressure, it can exist as a liquid at temperatures below its critical temperature.

The Liquefaction Process

Compression

The first step in the liquefaction process involves compressing CO2 gas to a pressure above 7.38 MPa. This high-pressure state is crucial for the process to proceed.

Cooling

Once the gas is compressed, the next step is to cool it to a temperature below its critical temperature. By doing so, CO2 can transition from a gaseous state to a liquid state.

Applications of Liquefied CO2

Liquefied CO2 finds applications in various fields, including:

Refrigeration: CO2 is used in industrial refrigeration systems due to its low boiling point and high heat absorption capabilities. Carbonated Beverages: CO2 gas is dissolved in water to create carbonated beverages, providing a desired fizz and effervescence. Fire Extinguishers: CO2 fire extinguishers are commonly used in industrial and commercial settings due to their non-conductive and non-toxic properties. Chemical Processes: CO2 is an essential reactant in various chemical processes, such as the production of urea and certain organic chemicals.

Comparison with Other Substances

It is worth noting that pure CO2 has only two phases: gas and solid. It does not have a liquid phase at pressures below 5.1 standard atmospheres (520 kPa) or temperatures above its critical point. To liquefy CO2, high pressure must be applied.

Comparing the phase diagrams of CO2 and liquid nitrogen (N2), it becomes evident that N2 can be liquid at much lower temperatures and pressures. This makes nitrogen a highly versatile and commonly used cooling agent due to its cost-effectiveness and wide-ranging applications.

Understanding the critical conditions and the liquefaction process is essential for the effective use of CO2 in various industrial and environmental applications. By harnessing the unique properties of liquefied CO2, we can optimize its utility and contribute to more sustainable practices.