Deaeration removes gas bubbles, usually air, from a liquid, for example from a gel. Deaeration is also needed to remove dissolved gases from liquid raw materials. Otherwise, they would later escape in the finished product and form bubbles there.
Why air in the product is harmful
Mixing processes often require subsequent deaeration, because processing liquid to highly viscous materials frequently creates air and gas inclusions. These can:
- Make fats and oils go rancid
- Cause oxidation and discolouration
- Change smell and taste
- Make coated surfaces porous and full of holes
Deaerated products, on the other hand, are chemically more stable and last longer. In industry, for example, water degassing is important wherever the lowest oxygen levels are required, such as in chemicals, pharmaceuticals and beverages. An everyday example is opening a bottle of sparkling mineral water.
How gases are released
Liquids release the most gas when they are heated and the pressure drops at the same time. This depends on the solubility of the gases, which according to Henry's law decreases with falling partial pressure and rising temperature. Gases can also be released naturally, for example when foams outgas.
Applications
Degassing matters above all for oxygen-sensitive products and wherever bubbles impair product properties. Both apply to cosmetics: oxygen shortens shelf life, and gas bubbles accelerate the coalescence of the dispersed phase. Further examples:
- Battery compounds: oxygen would make the finished product unusable
- Oils and lubricants: degassing before pumping reduces wear from cavitation
- Paints: degassing before curing or use
- Beverages and sauces: degassing inhibits aerobic microbes and extends shelf life
- Shampoo: its own surfactants make it foam, so filling would be impossible without degassing
What matters in deaeration
The vacuum deliberately enlarges the air bubbles so that they rise in the product. Agitation is closely linked to efficiency.
- The vessel must be large enough for the expanded mass, without it wetting the lid or being drawn into the vacuum pump
- The agitator must not break up the air bubbles
- However, it must mix well so that the bubbles reach the surface faster and burst there
- Without an agitator, everything would depend on the rising speed of the bubbles and take a very long time
It becomes difficult when surface-active substances stabilise the gas bubbles. These additives are meant to stabilise the emulsion or dispersion, but they also surround the bubbles and make them very robust. The solution is conveying-optimised agitators: large ring surfaces carry the product to the surface and help the bubbles burst there, even in foam. This shortens the process considerably. The counterpart is aeration.
Other processes
Frequently Asked Questions about deaeration
Why do products need to be deaerated?
Air and gas inclusions can lead to oxidation, rancidity of fats and oils, discolouration and changes in smell and taste. Deaerated products are chemically more stable and have a longer shelf life.
How does vacuum deaeration work?
Under vacuum, the air bubbles expand and rise faster. The vessel must be large enough for the expanded product mass, and the agitator provides mixing without breaking up the bubbles.
Why is deaerating shampoo and shower gel difficult?
Surfactants stabilize the gas bubbles and tend to foam. Conveying-optimized agitators with large annular surfaces bring the product to the surface and significantly shorten deaeration.
Which physical effects does deaeration use?
Gas solubility decreases with falling partial pressure and rising temperature (Henry’s law). This is why pressure reduction and, if necessary, heating are used.