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My dad has been using naphtha to degrease some animal bones, which based on the MSDS is probably some random jumble of hydrocarbons, mostly heptanes. He's trying to be environmentally friendly so he doesn't want to throw it out once it's saturated, and isn't comfortable trying to distill flammable liquids, so after some experimenting we started using sodium hydroxide to convert most of the dissolved fats into crude soap that separates out and can be discarded. This has worked well, but the naphtha is still accumulating some other impurities, most of which are (I suspect) other fats that are non-saponifiable like cholesterol.

I have a general interest in chemistry, but no formal education in it so I'm running out of ideas and don't have the correct terms to properly google my issue (or to understand most of what I've found). The closest I've come is finding that adding acetic acid causes something to precipitate out, but it hasn't even slightly settled out over 24 hours and when I run the resulting milky-white naphtha through a vacuum filter (10 micron) I don't see any change in clarity.

What are some ways I can try to clean my naphtha, using relatively little specialized labware and equipment?

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    $\begingroup$ You are doing good so far. Placing the naptha in a deep freeze above its freezing point might precipitate more impurities. try a small bottle and see. It might be possible to set up a solar powered [no flame or electricity] molecular still to slowly distill the naptha, [similar to the survival devices to allegedly distill water from the ground] $\endgroup$
    – jimchmst
    Commented Sep 13, 2023 at 2:30
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    $\begingroup$ It would not be environmentally beneficial if you use chemicals or treatments that are more dangerous, or have a larger carbon footprint, than getting more naphtha. Perhaps there is a use for the partially-purified solvent, e.g. cleaning, fuel (yes, that releases CO2), or send it to an efficient commercial solvent recycler. $\endgroup$ Commented Sep 13, 2023 at 4:33
  • $\begingroup$ Throwing my solution in the freezer did the trick, a fair bit of solid settled out to the bottom. I'm going to do some testing to see how much has been removed, but it's looking promising! $\endgroup$
    – ProfWalrus
    Commented Sep 13, 2023 at 13:26

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