I have no experience distilling, though I understand the basics about it. When two liquids with different boiling points are mixed, you can sometimes separate them by boiling away one of the liquids, leaving the other behind. Sometimes multiple iterations of this process can enhance the process. If the important substance is the one that boils first, the gas form can be collected and condensed back to liquid. This is usually done with liquors and other alcohol products, but in principle should be possible with many substances.

I have been reading up on fermentation with Clostridium acetobutylicum bacteria. Some strains produce acetone, butanol, and ethanol in a 3-6-1 ratio. From my reading, it's not entirely certain what yields could be expected, but I would imagine these are low, and that what's left over in a fermentation vat is still mostly water. Plus, I suppose, some sediment and biological contaminants that won't filter out entirely.

Acetone's boiling point 58° according to Wikipedia, far below the boiling point of water, even significantly below the boiling point of ethanol. Can this be distilled out (first) to some reasonably high purity?

Would it then be simply a matter of raising the temperature to next remove the ethanol, and after that the water (both mostly waste products to be discarded responsibly)? Would the butanol be left in the vat afterward at some reasonable level of purity (contaminants aside)?

I am interested in both the acetone and butanol, and would like to be able to make modest quantities of both, but if I had to take one or the other the butanol is the more important of the two.


1 Answer 1


Though distillation can separate chemicals to some extent, water, alcohols and acetone form azeotropes, making complete separation by distillation impossible.

An azeotrope, or constant heating point mixture, has the same proportion of chemicals in the vapor as in the liquid. For example, when an ethanol/water mixture is ~95.6% alcohol, the ratio of the two in the distillate stays the same. To get purer ethanol, with less water, requires another method, such as use of a desiccant, e.g., anhydrous $\ce{CaO}$.

The Wikipedia article to which you're referring mentions the issue under Improvement attempts. Could you make some relatively impure acetone and butanol, as a demonstration? Certainly! Would it be economically feasible? "ABE fermentation became generally non-profitable, compared to the production... from petroleum." It would cost less to buy them than to ferment and distill. Acetone, for example, can be found for ~US$6/L.

BTW, it's interesting to read how Weizmann further developed that process to help the Allies make acetone during WWII.

  • $\begingroup$ The whole point of the exercise would be to not have to buy it. And I don't have any petroleum. Is there any way to know at what percentages this particular mixture maxes out? 95.6% ethanol is useful for several things for instance (though I think it can take several passes through the still before you get it that high?). 95% butanol might serve its purpose, if it could be separated as well as that. $\endgroup$
    – John O
    Jan 22 at 18:45
  • $\begingroup$ The mix probably has several azeotropes look them up in a handbook. With a decent column acetone and 95 ethanol possibly could be distilled out. Freeze out water from the butyl compounds. possibly a sodium sulfate dehydrant and distillation could recover butanol . It sounds like a chemical engineering bad dream if not a nightmare, but I agree profit is not everything. Get a book on organic laboratory techniques and read it! Check out simple and fractional distillation. $\endgroup$
    – jimchmst
    Jan 22 at 22:38

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