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RE: Acrolein

In a post to P2TECH, Rob Michalowicz (rob.michalowicz@sympatico.ca) asks, in
part: -- 

	> A chemical manufacturer pulls a vacuum on a reactor using a series
	> steam ejectors.  This vented material contains small amounts of
	> along with various fats and oils.  The acrolein is a by-product of
	> reaction.  The steam and vented material are sent to a direct
	> where water contacts the mixture.  Most of the acrolein goes into
	> water....

	> Can anyone suggest a strategy or technology to eliminate the air
	> water discharges of acrolein?  The manufacturer does not know of
any way
	> to change the reaction chemistry to avoid the acrolein by-product.
	> is acrolein treated in air or wastewater?

In reply:

As you've indicated, the problem stems from using the steam ejectors, which
force the acrolein into contact with process water.  While you might be able
to reduce the amount of steam needed per unit mass of acrolein removed,
you'll never eliminate the problem without getting rid of the steam ejector.

Fortunately, and depending on the level of vacuum required, there are other
ways to pull the vacuum than using steam ejectors.  
For instance, there are increasing numbers of dry pumps on the market, that
are roughly similar to compressors or blowers in design (but obviously, in
this case you want it to suck, not blow).  There are also case studies of
using liquid ring pumps, which DO create contact between the vent gases and
the working fluid, that recycle the working fluid.  Rather fortuitously,
there is an article on "dry" vacuum pumps in the latest issue of Chemical
Engineering (Feb 2000, pp 37-41).  The article won't provide much in the way
of design guidance, but does help identify key selection parameters, and
several vendors of appropriate technologies.

This won't eliminate the air emissions, but should get rid of the aqueous
ones, and it may simplify byproduct recovery by giving you a cleaner
acrolein byproduct.

I am also taking the liberty of forwarding your question to the ChemAlliance
list server (http://www.chemalliance.org/Lists/listinfo.htm) to see if any
of our readers can provide additional insights. The list is used primarily
by environmental managers working in the chemical process industries, and is
provided as part of the ChemAlliance compliance assistance center.

Hope this helps.

Scott Butner (butner@battelle.org)
Pacific Northwest National Laboratory
4500 Sandpoint Way NE, Seattle WA  98105
VOICE (206)-528-3290/FAX (206)-528-3552