How to break a water-detergent-oil emulsion

[nnovillo]

Hi there,

We have a plant that manufactures iron furniture. The iron bars come from the provider plant with a cover of mineral oil. After cutting, folding and putting together the pieces, there is a rinse process with water and detergent to take out the oil cover. The remaining emulsion of water+detergent+oil is gathered into a recipient, and is reused for 15 days, when the solids are separated and the remaining liquids discarded.

I would like to know if there is a substance or a particular chemical that would allow us to break the emulsion physically separating the phases so we can remove the oil through a mecanical method, prolonging the useful life of the water we are using and obtaining a less contaminant residue.

Thanks!

 

[chemisttree]

If your detergent is an anionic one like a tall oil or a soap, adding acid will do the trick. Acid will protonate the anionic surfactant and eliminate it's ability to emulsify. The oil and the surfactant will separate out. You will need to add additional surfactant afterwards and adjust the pH to slightly basic. If your system uses a mixture of nonionic and anionic surfactants (VERY common) this might not work.

Sometimes you can chill the solution to just above freezing and the emulsion will become less stable and separate out with the surfactant. If that works, you will need to add more surfactant, of course.

In general, if you intend to recycle your wash water, a surfactant system must be carefully chosen to accomplish that. For example you might want to use a surfactant that is solid at room temperature but melts and works effectively at elevated temperatures. You would use this system at elevated temperature and chill the system to strip it back out.

 

[nnovillo]

Thanks for your reply Chemisttree, it was very helpful. Cheers, V.

If your detergent is an anionic one like a tall oil or a soap, adding acid will do the trick. Acid will protonate the anionic surfactant and eliminate it's ability to emulsify. The oil and the surfactant will separate out. You will need to add additional surfactant afterwards and adjust the pH to slightly basic. If your system uses a mixture of nonionic and anionic surfactants (VERY common) this might not work.

Sometimes you can chill the solution to just above freezing and the emulsion will become less stable and separate out with the surfactant. If that works, you will need to add more surfactant, of course.

In general, if you intend to recycle your wash water, a surfactant system must be carefully chosen to accomplish that. For example you might want to use a surfactant that is solid at room temperature but melts and works effectively at elevated temperatures. You would use this system at elevated temperature and chill the system to strip it back out.