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I have been able fractionate palm oil and extract palm stearin using the following method:

  1. Melt the palm oil (over 80 °C)
  2. Keep the melted oil at 33.5 °C for 24 hours (using an immersion circulated water bath)
    • At this point I was able observe crystals being formed. I assume they were palm stearin crystals.
  3. Centrifuge to separate the crystals to obtain palm stearin.
    • I was able fractionate almost 30 % crystals by weight.

However the same process did not really hold true while processing the shea butter to fractionate shea stearin. After Step 2, it was still in liquid form and there was no visible crystal formation. I'm further considering seeding (with crystals) or playing with the time and temperature variations.

How can I modify my approach to promote stearin crystal formation in shea butter?

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  • $\begingroup$ As I’m planning to use food grade shea butter, I’m looking for ways to dry fractionate it. $\endgroup$
    – zetaprime
    Feb 11, 2019 at 10:44

2 Answers 2

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Shea butter is a complex combination of esters:

enter image description here

(Wikipedia). The overall ratio of oleic to stearic acids is about 2/1, but statistically, there will a little of the high melting stearic, more of the 2 stearic to 1 oleic; much more of the 2 oleic to 1 stearic, and a lot of all oleic ester. The melting point of shea butter is low (body temperature) and so if it does not precipitate out the tristearin even at room temperature, you will have to do something different.

A fractional crystallization involving higher temperatures would use a poor solvent for the tristearin (mp ~ 72C), like ethanol. The oleic esters will be more soluble. Make a 20-30% solution in hot ethanol (be careful!!) and let it cool. Experimenting with similar alcohols (propyl, isopropyl, and perhaps with a bit of water added (~5-10%) could give better results.

Oiling out is a common problem in trying to crystallize organic compounds.

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  • $\begingroup$ Considering ethanol boils at 78C and the tristerain melting at 72C. I would guess the “hot ethanol” temperature would be between 72C and 78C? Or should I get a temperature lower than 72C? $\endgroup$
    – zetaprime
    Feb 16, 2019 at 8:14
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    $\begingroup$ Tristearin is dissolved in (or mixed with) the other components of shea butter at room temp. If you add 20-30% shea butter to ethanol at RT, it will probably not all go into solution, the tristearin least of all. Warm the mixture until it is all dissolved (~clear), then let it cool, or cool it in a refrigerator or freezer. If it oils out, more ethanol, or a different alcohol will be needed to keep the oleic esters in solution so the solid tristearin can crystallize out. To get solid tristearin, the final cool temp will have to be below 72C. Way below! $\endgroup$
    – James Gaidis
    Feb 16, 2019 at 14:13
  • $\begingroup$ I’ve tried 30% shea butter and it oiled out. I’ll be trying 15%. Btw the ethanol I’m using is 96.2% pure. Hope that’s good. $\endgroup$
    – zetaprime
    Feb 17, 2019 at 13:23
  • $\begingroup$ Sounds like you are a good experimentalist. Keep trying. $\endgroup$
    – James Gaidis
    Feb 17, 2019 at 14:18
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The industrial processes uses acetone for shea fractionation. The crude oil is degummed first by a water degumming process and then fractionation is carried out using acetone as a solvent for separating oleic fractions.

Palm oil melts at approx. 36 °C. And you provided the temperature for crystallization as 33.5 °C. Decrease the temperature. Shea butter melts between 32 °C and 37 °C. I would recommend decreasing temperature and slow agitation at a temperature below 20 °C if possible. If you cannot agitate, try it at 30 °C.

If it solidifies at 30 °C, try at 32 °C.

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