1
$\begingroup$

I want to remove acetic acid from a mixture of acetic acid and water by aeration. The concentration of acetic acid is 200 ppm (mg/L). The pH of the water is more than 5. I want to reduce the acetic acid concentration by around 80%. I understand that acetic acid can be removed by addition of sulphuric acid to bring down the water pH to around 2 and then boiling the mixture to separate the acetic acid. I however the water quantity I have is very huge, so it is not practically possible to boil the water. The water temperature is more than 60 deg C. Also, I do not want to put lots of sulphuric acid in the water due to various other issues and my practical limit of using sulphuric acid is around 80-100 ppm which lowers the pH to around 3.0. I can also providing aeration to the water at 0.2-0.5 vvm.

I want to know that under these conditions, can acetic acid be removed from the water? Is there any other other method by which we can remove acetic acid by aeration at 60 deg C, by adding not more than 100 ppm of any additive? Is there any other chance that acetic acid would be removed by aeration at 50-70 deg C temperature? If yes how to enhance the efficiency by minimum inputs?

Improve this question
$\endgroup$
8
  • $\begingroup$ Have you ever thought of destroying it by simply adding a few grains of sodium bicarbonate ? The acetic acid will then be transformed it into sodium acetate. $\endgroup$
    – Maurice
    Commented Sep 25, 2020 at 11:35
  • $\begingroup$ Perhaps remaining acetate can be a problem as well. $\endgroup$
    – Poutnik
    Commented Sep 25, 2020 at 12:32
  • $\begingroup$ Not sure how complex a procedure you're willing to put up with, but you might be able to extract with a long-chain amine that is immiscible with water. Tri-n-octylamine has been used for industrial extraction of carboxylic acids. But with a starting concentration of only 200 ppm, any process will be inefficient and it will be very hard to get to nearly pure water. $\endgroup$
    – Andrew
    Commented Sep 25, 2020 at 13:35
  • $\begingroup$ If you employ aeration here and the acetic acid is in a tap water mix (rich in small amounts of transition metals), then O2 will introduce radical oxidizing species to chemically breakdown the acetic acid and other organics present. This is why aeration is effective for processing natural waters (it does more than just add dissolved oxygen). $\endgroup$
    – AJKOER
    Commented Sep 25, 2020 at 16:22
  • $\begingroup$ The presence of sunlight during aeration (in essence, photo-Fenton and photo-Fenton-like reactions) can also create a cyclic reaction system to more effectively purify water. This topic is incorporated in so-called Advanced Oxidation Processes, on which there are hundreds on papers addressing, for example, environmental remediation, for the removal of unwanted organics (like pesticides) in rivers, lakes,....This is the only practical answer for large bodies of waters. $\endgroup$
    – AJKOER
    Commented Sep 25, 2020 at 16:54

2 Answers 2

Reset to default
4
$\begingroup$

Aeration does not seem to be the way to go.

If there are no other ions in the water, electrolysis (Kolbe reaction) would convert the $\ce{HOAc}$ to ethane and carbon dioxide:

$$\ce{2CH3CO2^- -> 2e^- + 2CO2 + H3C-CH3}$$

This process could probably be arranged to be done in a pipe with electrodes on the sides, so that the water was treated as it was used, rather than in a huge tank, where diffusion would slow down the completion of the reaction.

Improve this answer
$\endgroup$
6
  • 1
    $\begingroup$ This is more correctly referred to, in actual practice, as electro-fenton which produces radicals (via the application of electric current) to chemically destroy the unwanted organic. Main problem, any chloride ion presence, could be transformed into chlorine radicals and subsequent creation of very problematic chloro-organics. Unless you are very sure on the complete absence of Cl- here, I would strongly advise against this electrolysis path. $\endgroup$
    – AJKOER
    Commented Sep 25, 2020 at 16:50
  • $\begingroup$ @AJKOER: I wonder if there would be an electrode that could defeat the chloride problem: e.g., a (porous?) silver electrode. Fairly noble, perhaps it would wind up precipitating any chloride ions at the anode, but still permit alkane formation. Or selecting the applied voltage? $\endgroup$
    – James Gaidis
    Commented Sep 26, 2020 at 14:29
  • $\begingroup$ Interesting idea. Try Silver and Activated Carbon for electrodes in water/acetic acid containing some NaCl. Do you see a white precipitate? However, while this may reduce chloride ions, I would not count on a total removal of possible very small amounts of chloro-organics. A source: ncbi.nlm.nih.gov/pmc/articles/PMC5480235 as I apparently can support my comments. $\endgroup$
    – AJKOER
    Commented Sep 26, 2020 at 21:51
  • $\begingroup$ The chlorides are <20 ppm in my water. There are ,however, some sugars (sucrose, glucose and fructose) below 50 ppm. The overall TDS is less than 100. Silver electrode is an interesting idea..but that would be way more costly than I can afford I guess. The water quantity I want to treat is >30 m3/h. Such systems would require very careful design engineering. $\endgroup$
    – Chandrashekhar
    Commented Sep 27, 2020 at 18:32
  • 1
    $\begingroup$ I should have used this as an answer: a strongly basic ion-exchange resin! $\endgroup$
    – James Gaidis
    Commented Sep 28, 2020 at 13:56
3
$\begingroup$

Acetic acid does not form an azeotrop with water and is less volatile than water. So aeration of water would do the opposite - enriching of water by acetic acid due preferred evaporation of water.

Reverse osmosis should help, perhaps after neutralization to be mostly in acetate form.

The question is, if it is worthy the troubles. The cheaper, easier and faster way could be replacing the water.

Improve this answer
$\endgroup$
6
  • $\begingroup$ Given that the water is already on the warm side, I wonder how efficient distillation could be. The goal wouldn't be to boil all the water at once; instead you'd want to use a heat exchanger to reuse as much heat as possible, both from the clean water output stream and the enriched waste stream. $\endgroup$
    – MSalters
    Commented Sep 25, 2020 at 20:12
  • 1
    $\begingroup$ Boiling is very expensive, much cheaper would be water replacement. $\endgroup$
    – Poutnik
    Commented Sep 25, 2020 at 21:22
  • $\begingroup$ Water will boil at 60C at about 150mm Hg pressure or 0.2 bar. That doesn't need any heat input. $\endgroup$
    – alephzero
    Commented Sep 26, 2020 at 0:11
  • 1
    $\begingroup$ @alephzero Evaporation of 1 L would cool down 110 L of water approx by 5 deg C. $\endgroup$
    – Poutnik
    Commented Sep 26, 2020 at 0:16
  • 1
    $\begingroup$ It would help if you described originally all circumstances and relevant info, so advisors would not walk blind in darkness of what is or not acceptable for you. There is generally no magic wand to get rid of unwanted compounds in water. $\endgroup$
    – Poutnik
    Commented Sep 27, 2020 at 18:43

Not the answer you're looking for? Browse other questions tagged or ask your own question.