Glycerine Removal

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amschind

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I'm new here and working on an odd project that I'll try to lay out as it advances. I greatly appreciate this wonderful source of information! On to my first question:

I haven't found much on glycerine removal. It looks like commercial makers separate the glycerine after the initial steam hydrolysis step, which seems impractical at a small commercial/hobby scale. The one real resource that I've found lists the addition of NaCl to the fully saponified but still hot mixture of a hot process batch as a means of dropping the glycerine and water out of the emulsion. I want to experiment with this, so I thought that I would ask around to see if anyone has thoughts on the amount of salt to be added or a resource on this. I presume that on a small scale, this won't be a 100% efficient process, but since glycerine is desirable (i.e. most home makers just leave it ALL in the finished bar) a reduction rather than complete elimination is preferable anyway.

If nobody has tried this, then I'll try to think of a way to be a little more scientific with this as I presume that there is a curve associated with the amount of salt added and the mount of glycerine extracted with the water. It might be nice to have an extra tool available for those who want to tinker.
 
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If you search for and read the threads here on SMF about “salting out soap” there are some discussions about water and glycerine being separated out during that process. The soap that is left can be used for laundry and the like.
 

DeeAnna

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There is no curve that I'm aware of. Glycerin is highly soluble in water and brine, so adding or subtracting salt has little or no effect on the amount of glycerin removed from the soap.

Adding salt (aka salting-out) is not about controlling the degree of glycerin removal. It's more about controlling the amount of soap that's dissolved in the brine solution.

The degree to which salt causes the soap to precipitate is not only affected by the percent of salt in the brine but also the types of fatty acids that make up the soap. So there's no one "curve" for that either unless you're working with soap made from a pure fatty acid. The results will vary depending on the fatty acid profile of the soap you're working with.
 

amschind

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The degree to which salt causes the soap to precipitate is not only affected by the percent of salt in the brine but also the types of fatty acids that make up the soap. So there's no one "curve" for that eithe
So you're essentially overwhelming the ability of the glycerol/water solution to solvate the soap molecules by adding a more water soluble salt to its point of saturation, thus precipitating the less soluble molecule (the soap)? Presuming that's the case, then it seems like your salt addition needs to be sufficient to produce a saturated brine out of the combination of the initial water, the water formed from the neutralization of the hydroxide ions, and the glycerol. The first two should be pretty simple to calculate, but I'm not sure how much salt can dissolve in glycerol.

Thanks so much for your help!
 
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