3 replies to this topic

[pamjacinto]

Hi!

What is the best way to recover ethanol from continuous fermentation? (Reactor used is fluidized bed bioreactor)
The effluent per hour is as follows:

component weight (kg)
Glucose 68.57
Xylose 708.57
Ethanol 2537.126201
Lactic Acid 457.139856
Acetic Acid 447.38
CO2 2,426.82
Yeast extract 553.80
KCl 413.13
KH₂PO₄ 221.52
tetracycline 1.11
water 109,089.11

Those that are italicized are components of the fermentation broth. The major components of the effluent are those in bold.
What can I do to separate those?
How do I recover ethanol? If I use distillation to recover ethanol from water, would it be practical? knowing that almost 94% of the effluent is water?
Is there any better way to recover ethanol from the given effluent?

Thank you for your answers.

[kkala]

Without having experience, distillation seems a good way. Most of ethanol is produced by distillation, see http://en.wikipedia....ki/Ethanol_fuel. I assume that CO2 is removed while it is produced, water goes to the bottom, ethanol to the top of the column. Of course ethanol comes out as 96.5% (v/v) azeotropic mixture with water, further process is required if more purity is needed.
Have a look at "All things ethanol" Forum just "below" here. It may be useful.

Edited by kkala, 20 March 2011 - 02:45 PM.

[riven]

Multistage distillation is used to get the ethanol to around 90 wt% ethanol with the remainer being water. A typical setup is

• Fist distillation column with a side stripper on the reboiler
• Rectification cdistillation coumn going from 40 wt% ethanol to near the azeotrope and any other remaining components other than ethanol water out the bottom
• Molecular sieve for fuel grade ethanol purification. Acids and solids are definately not allowed in the sieves typically used by the ethanol industry

The solids and other pruities will typically goes out the bottom of the first column At this stage the stream is pure so can be purified to fuel grade using molecular sieves. My data mainly reflects fuel ethanol and not food ethanol.

References (there are many more and many more are better; happy hunting)
Use google: Energy efficiency at its best - Bioethanol plant of Lantmännen Agroetanol
Process engineering economics of bioethanol production. Galbe et al. (2007)
http://www.usda.gov/...rgy/aer-814.pdf (there should be a new version)

Distillation (and molecular sieve for fuel grade) is the state of the art. However due to the high water concentration, it consumes a lot of energy. A rule of thumb is that 50% of the steam energy used in an ethanol plant is used solely for the purificatino of ethanol. Another overview of possibilities for purification

Separation technologies for the recovery and dehydration of alcohols from fermentation broths. Vane et al. (2008)

[katmar]

I don't know of any commercial installation, but a hydrophobic membrane process could be used with the ethanol depleted stream being recycled to the fermentation vessel. The distribution, and therefore potential accumulation, of the other organics could be a problem.