[gundog48]

I hope you'll bear with me, I'm a distiller, not a chemist and am trying to muddle my way through!

I'm trying to follow an old process for rum production. It involves taking a portion of the dunder (liquid left in the still after distillation) and/or a part of the tails (late distillate) and adding a base such as NaOH or CaOH. The process causes the base to form salts with the carboxylic acids in the liquid which are fermentation co-products. The acids will largely consist of acetic, butyric, lactic and several others.

The aim is to be left with something close to a powder, or at the very least, a high concentration of these salts. Once these salts have formed after the base addition, are they likely to precipitate out due to the high alkalinity? I think I can add ethanol to push them out of solution, but it may require a great deal of it in a large volume. Other than that, I know I could evaporate the liquid, but this would be extremely time and energy intensive.

In an ideal world, I would precipitate the salts, decant the liquid and then finish off with evaporation at a low temperature. Is this likely to be an achievable goal? I'd love to know how you would go about it.

[chenbeier]

In an ideal world, I would precipitate the salts, decant the liquid and then finish off with evaporation at a low temperature. Is this likely to be an achievable goal? I'd love to know how you would go about it.

This would be the best way. Or you have possibility to filter it.

[gundog48]

In an ideal world, I would precipitate the salts, decant the liquid and then finish off with evaporation at a low temperature. Is this likely to be an achievable goal? I'd love to know how you would go about it.

This would be the best way. Or you have possibility to filter it.

Would the salts precipitate on their own after the base addition, or would I need to do some extra processing to make that happen? I do have some filtration equipment, what kind of pore size do you think I would be looking at?

[OrganicDan96]

the resulting salts would probably be quite water soluble (apart from calcium salts, but calcium hydroxide is poorly soluble anyway so maybe not the best base to use) addition of ethanol should push them out of solution.

[Enthalpy]

But how much of the carboxylic acids is allowed to remain? For instance butyric acid stinks. Precipitating most of it as a useful product is one thing, eliminating it from the useful product is a different goal, possibly more difficult.

Will you distil again after the acids are eliminated or made non-volatile?

[gundog48]

the resulting salts would probably be quite water soluble (apart from calcium salts, but calcium hydroxide is poorly soluble anyway so maybe not the best base to use) addition of ethanol should push them out of solution.

Interesting about the solubility of the calcium salts. In the literature they tend to refer to the result as 'lime salts' which suggests CaOH is preferred, but this may be simply because it would have been on hand as it is used extensively in sugar processing. Perhaps I'll try it with calcium hydroxide and see what the result is. If I do it with just the tails of the distillate, I'll be working with a clear liquid so I can monitor the results better.

If I wanted to work with sodium hydroxide and add ethanol, would you have any idea what concentration would be needed to push them out?

But how much of the carboxylic acids is allowed to remain? For instance butyric acid stinks. Precipitating most of it as a useful product is one thing, eliminating it from the useful product is a different goal, possibly more difficult.

Will you distil again after the acids are eliminated or made non-volatile?

I'm actually doing the opposite and attempting to concentrate the carboxylic acids. Roughly, the process is to concentrate the acids by removing them from waste streams (dunder, tails) by locking them up as salts and disposing of the liquid. The next step is to add the salts to ethanol, then add sulphuric acid. This will free the carboxylic acids. This will be refluxed for an extended period, and in the presence of an overabundance of ethanol and with the sulphuric acid acting as a catalyst, should induce esterification, after some time, refluxing will be stopped and the distillate would be collected.

What you should end up with are concentrated (mostly) ethyl esters which reflect the esters found in rum. This 'concentrate' was historically used to allow for cheaper shipping to Europe, where it could be added to a locally produced neutral spirit, or used as a food additive.

What you're describing is a process sometimes used in neutral spirit production. Where esters and volatile acids are undesirable, distillers may add a base to lock those acids up as salts and distil their product, leaving the salts behind for disposal. I'm trying to achieve the exact opposite!