Why Liquid Carbon Dioxide Is Not Used as an Aerosol Propellant?

When formulating aerosol products, choosing the right propellant is critical for product performance, safety, and manufacturing efficiency. With the growing demand for eco-friendly alternatives to traditional VOCs (Volatile Organic Compounds), carbon dioxide (CO2) often comes up in discussions.

However, there is a fundamental misconception in the industry: while CO2 is used as a compressed gas propellant, liquid carbon dioxide is never used as an aerosol propellant in standard packaging.

If you are an aerosol manufacturer optimizing your production line, understanding the physics behind propellants is essential for selecting the right aerosol filling machine and ensuring consumer safety. Here is the technical breakdown of why liquid CO2 is incompatible with standard aerosol packaging.

The Physics of CO2: The Extreme Pressure Problem

The primary reason liquid carbon dioxide cannot be used in traditional aerosol cans boils down to vapor pressure. For a gas to exist as a liquid at room temperature (around 70°F or 21°C), it must be kept under its specific vapor pressure.

Standard Aerosol Cans Cannot Withstand the Pressure

Standard tinplate or aluminum aerosol cans used in the cosmetic, household, and industrial sectors are engineered to handle internal pressures of about 90 to 180 PSI. The burst limit for most commercial cans is around 250 to 270 PSI.

If you were to inject liquid CO2 into a standard aerosol can, the internal pressure would immediately exceed the structural limits of the packaging. The can would buckle, deform, and ultimately rupture explosively on the aerosol filling line, posing a catastrophic safety hazard to operators and consumers.

Compressed Gas vs. Liquefied Propellant: What’s the Difference?

To use CO2 in aerosols, manufacturers must use it as a compressed gas, not a liquefied gas. Understanding this distinction is vital for optimizing your propellant filling process.

The Liquefied Propellant Advantage (LPG, DME, Fluorocarbons)

When a liquefied propellant (like LPG) is inside a can, it exists in two phases: liquid at the bottom (mixed with the product) and gas at the top. As the consumer sprays the product, the head space increases, and some of the liquid propellant instantly vaporizes to replace the lost gas. This ensures a constant, steady spray pressure from the first spray to the last drop.

The Compressed Gas Limitation (CO2, Nitrogen)

When CO2 is used, it is injected as a compressed gas that sits in the head space above the liquid product. It does not mix as a liquid.

• The Drawback: Because there is no liquid propellant reserve to vaporize and replace the expelled gas, the internal pressure drops every time the nozzle is pressed.
• The Result: A weaker spray pattern as the can empties, often leaving unused product at the bottom of the can.

While compressed CO2 is highly desirable for its non-flammability and zero VOC status (often used in hair sprays or automotive dusters), it requires highly precise gas filling equipment to inject the exact volume of gas without compromising the can's integrity.

How Propellant Choice Impacts Your Aerosol Filling Machine

Your choice of propellant directly dictates the engineering requirements of your aerosol packaging equipment.

• Explosion-Proof Requirements: If you use traditional liquefied hydrocarbon propellants (LPG, Butane), your filling environment and aerosol filling machine must be strictly explosion-proof (pneumatic driven, ATEX certified).
• High-Pressure Gas Fillers: If you opt for compressed CO2 or Nitrogen, your gas filling heads must be designed to handle high-pressure gas injection accurately. Over-pressurization by even a small margin can lead to can buckling.
• Alternative Packaging (Bag-on-Valve): Because compressed gases like CO2 experience pressure drops, many manufacturers are switching to Bag-on-Valve (BOV) filling machines. In BOV systems, compressed air or nitrogen/CO2 is squeezed between the can and a product-filled bag, ensuring 99% product emptying and a continuous spray without the propellant mixing with the formula.