Can any chemists out there explain the chemistry of adding salt to a naptha and base solution to remove residual emulsion? And can the salt be iodized or not? I have heard conflicting opinions concerning the addition of iodized table salt. Just trying to understand a little more of the chemistry behind the mystery!!

Thanks,

JBArk

Adding salt (NaCl) to the solution of a basified emulsion of water and some other non-polar solvent tends to break down emulsions. This is true for some emulsions.

Some emulsions are caused by compounds that are soluble in both water and the non-polar solvent and because they don’t prefer either, they tend to cause both to mix, forming a third layer of emulsion. Sometimes the emulsion is so bad that there’s only 1 layer, no water layer or non-polar layer present.

Salt works by raising the polarity of the water, making less molecules soluble in it. This makes many molecules that are soluble in both the water and the non-polar solvent more soluble in the non-polar solvent. Part of this is caused by the salt taking up space in the water. The more salt you have in the water, the less space there is for other compounds. As the water becomes saturated with salt, many compounds becomes insoluble in the water and get pushed out by the salt. This technique doesn't work for all emulsions and actually makes some emulsions worse!

If you’ve ever done a salt based harmala extraction, it works by saturating the water with salt, causing many hydrochlorides to be insoluble in water. It just so happens that harmine and harmline HCl are insoluble is salt water, so they precipitate out of the water.


After adding the salt to clean an emulsion, it’s a good idea to heat the solution (no fire or sparks of course) to about 90 C or 10 C below the lowest boiling point of the non-polar solvent. This can help break the emulsion much faster. Be careful with this. With some solvents like naphtha, this is a fire hazard. But with solvents like DCM, there’s no danger of fire.

yes what ron said.. just to add: it does work perfectly to remove emulsions from the typical mimosa extraction. You can just throw a bunch of salt right on top and many times the emulsion will immediately settle.

as for iodized salt.. iodized salt means NaCl with a small amount of other iodine-containing salts (like potassium iodate, sodium iodate, etc). Ive read a bit around and it seems the quantity of these iodine containing salts are super super small, like 0.01%. They should be water soluble, so they shouldnt migrate to your solvent. But then again, if you read the wiki for potassium iodate, it says that pure potassium iodate is an oxidant. Though I doubt in the quantity mentioned, it would do anything problematic (though im no chemist), I guess if you can, better avoid adding any of these unknown factors to an extraction. Im very sure anybody can find pure non-iodized salt, just go to natural food stores, they always have non-iodized salts, or even ordering online I bet you can find too.

Thanks 69ron for the speedy and informative response. And endlessness, I bow down before your dedication to research and to your resources. I am writing my own tek, and just want to make sure that I don't make any noob errors in the chemistry explanations, and, of course, wanted to know out of sheer insatiable curiosity!!

If anyone has anything to add or has any elaborations, it will be much appreciated!!

Cheers,

JBArk