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DIY ion exchange? Purifying glycerol, removing salt/lye/h2o

  1. Dec 1, 2014 #1
    My challenge is to provide a low-tech (DIY) way to purify the glycerol produced from soapmaking or biodiesel production. Simple distillation is out because the boiling point for glycerol is above its smoke point. Vacuum distillation and electrolysis do not count as low-tech. :)

    The input mixture is a mixture of glycerol, water, sodium hydroxide, and sodium chloride.

    The desired output is concentrated (>80%, preferably 100%) glycerol in water.

    Someone suggested a gelatin-and-salt bridge to some distilled water, but I'm not sure how that would work. Any suggestions or pointers to tech that might solve this are welcome.
     
  2. jcsd
  3. Dec 1, 2014 #2

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    "Low-tech, DIY?" You mean, "cheap." You might try setting a five gallon bucket out for the next week long cold spell, pour off liquid when it's half-frozen, and see if you're looking at: 1) pure water ice plus concentrated glycerin, salt, and lye; or, 2) a glassy mixture of glycerin plus a mostly aqueous solution of salt and lye; or, 3) a waste of time. I'm suspecting 1) is the case, but it at least concentrates solutes, and can be repeated to the point that either the salts drop out, or the glycerin freezes out and leaves a salt solution. You might get lucky and 2) will let you get rid of the salt and lye without losing too much glycerin.

    You could also dry the feed solution with silica gel if the pH isn't too high (knock it down with HCl if need be), and be able to dry/recycle the silica gel. Getting rid of salt is still a problem.

    I've got vague recollections from grad school of the organickers recrystallizing glycerin from ethanol by adding ether to a cold solution (this is to get crystalline samples for m.p. determinations), but I guarantee nothing. Too expensive, anyway. Might serve for knocking salts out once you get into the high glycerin concentrations.
     
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