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RE: Cleaning of polymerization reactors

	Chris Montovino (cmontovino@pprc.org) asks:

	> Does anyone have experience with cleaning polymerization reactor
vessles from adhesive manufacturing?  

	No.  But I understand it's a sticky problem.

	Sorry, couldn't resist.

	Actually, there are a couple of potential solutions that have been
written up in various case studies.  They include:

	* insure that the reactor vessel can be more easily cleaned.  This
is largely a design-time strategy but some of the options can be done
retro-fit.  They include:

		- lined reactor internals (e.g., teflon or other engineering
fluoropolymer) can significantly reduce adhesion to the surface; this will
reduce the amount of residual material in the vessel, and reduce the amount
of solvent/cleaning fluid required to clean the vessel).  There are vendors
out there who will retro-fit linings to vessels.

		- as an alternative, sometimes you can accomplish much the
same by having a smoother vessel surface.  This is very reactor and polymer
specific, but you can do some cheap evaluation of this option by using
sample coupons of the reactor material polished to different levels, and
conduct extraction tests in a lab. 

		- careful consideration of vessel intrusions or other
surface irregularities -- thermocouple and sampling ports, access ports,
etc.  If it is possible to reduce the number or size of void/dead spaces on
the vessel surface, you can reduce cleaning time/solvent needs.

	* look at the process control situation.  Is residual material
that's being cleaned simply adhering to the vessel walls because it's
sticky, or is it scorched on?  from the original inquiry, I'd be surprised
if the vessel wall material isn't being cooked on somehow, perhaps during
initiation of polymerization.  Often, even in exothermic systems, the vessel
is heated to initiate reactions, and that's leading to scorching, you might
want to look at options for more carefully controlling that initiation step
-- ie., better instrumentation, lower steam pressure in the vessel jacket or
heating coils, a draw-stream heat exchanger to increase surface area, etc.
I haven't heard of this being done, but it might even be possible to
initiate the reaction by direct steam injection, since it's aqueous

	I am sure there are other solutions, but these are the ones that
come to mind off the top.  Have to leave some for others (Mr. Bilkovich, are
you listening today?  I bet you know more solutions....).

	Hope this helps.

Scott Butner (rs_butner@pnl.gov)
Senior Research Scientist, Environmental Technology Division
Pacific Northwest National Laboratory
4000 NE 41st Street, Seattle, WA  98105