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Recovery of painting solvents from air stream
Your assistance in the following problem would be appreciated!
A manufacturer paints parts and the solvent used in the paint
formulation, n-butyl acetate, gets into the exhaust air (13,000 CFM) in
trace amounts (500 ppm). The air is passed over activated carbon to
remove the n-butyl acetate. The activated carbon is then re-activated
using low pressure steam. The steam is condensed and most of the
n-butyl acetate is decanted as a separate phase from the water and
re-used. However, the n-butyl acetate is slightly soluble in the water
and some remains in the water along with decomposition products - acetic
acid and n-butanol. The BOD of this wastewater is 10,000 mg/L and it
needs to be reduced before discharge.
I have several questions:
1) Does the acetic acid contribute to the BOD?
2) Is there a better way to approach solvent recovery from dilute air
3) What would be the advantages/disadvantages of using nitrogen to
re-activate the activated carbon?
4) What is the best treatment technology for this wastewater containing
n-butyl acetate, acetic acid, n-butanol?
5) Steam stripping has been suggested, but doesn't the steam have to be
re-condensed, getting the problem of dilute organics in a wastewater
stream once again? Can the organics be recovered from a steam stripper?
6) How about oxidation with peroxide and UV? What is the removal
Rob Michalowicz, P.Eng.
Chem Process & Environment Inc.