Letters: March 2023 | AIChE

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Letters: March 2023


Reviewing Word Choice in the Liquid-Liquid Extraction Article

Dear Editor,

I was enjoying the December 2022 article, “Optimal Mixing for Agitated Extraction Columns,” until I came across this clinker on page 42: “Since acetic acid has a higher boiling point than water (i.e., high heat of vaporization), its recovery from water by distillation requires too much energy…” This prompted a few thoughts:

  • A higher boiling point of a compound does not equate to a high heat of vaporization. Acetic acid does have a higher boiling point than water (244°F vs. 212°F), but the heat of vaporization is much less (173 Btu/lb vs. 1,000 Btu/lb).
  • A well-designed distillation column, with appropriate heat recovery, can be fairly efficient. And, it is often the best choice when high throughput is needed.
  • There’s no mention of the initial concentration of acetic acid in the fermentation broth. That’s probably the key determinant in the economics of the recovery process, as well as the allowable concentration of organic (both residual acetic acid and ethyl acetate) in the treated water stream.
  • The capacity of the extraction column, in m3/m2-hr, is given, but it’s not clear if this refers to the feed, water, solvent, or solvent+product...

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