33    RECOVERY AND REUSE OF SPENT ACETONE
VIA A MOBILE SOLVENT RECOVERY UNIT
Mark W. Townsend, Senior Environmental Specialist
Monsanto Company
Addyston, Ohio 45001
BACKGROUND
The Monsanto Chemical Company, an operating division of Monsanto Company, operates a
plastics and resins plant located in Addyston, Ohio. One of the products manufactured at the Port
Plastics facility is a styrene-maleic anhydride copolymer sold under the trade name Scripset®.
The copolymer is produced by a polymerization process with the resulting solids ground into
powder for sale to paper, adhesive, and photoplate manufacturers.
The process equipment requires routine rinsing with technical grade acetone between batches.
Due to the volumes of spent acetone generated and the associated RCRA hazardous waste regulations, the plant sought to recycle and reuse the acetone to reduce the purchase cost of virgin
acetone and the cost of spent acetone disposal.
One of the first options explored was package unit distillation units. The cost of these units
was in the $2O-$30,OOO range in 1989 dollars. Even though the cost of a package unit was not
deemed unreasonable, there were additional costs and concerns that led to elimination of this option. The unit would have required additional manpower to operate and maintain, i.e., at least a
fraction of an operator and mechanic. For plant safety reasons, it was desired to operate this
package unit outside the production building, thus construction of an outbuilding would have
added to the expense of the project. Additionally, there were concerns of package unit reliability.
During this evaluation, tractor-trailer mounted distillation units were discovered. The portable
units were equipped with either thin-film evaporator technology capable of processing 240 to
480 gallons per hour, or pot still (batch) distillation technology capable of rates from 120 to 240
gallons per hour. Both units were constructed of stainless steel.
EQUIPMENT INFORMATION
The thin film evaporator technology allows for rapid heat transfer resulting in high quality reclaimed material. The spent solvent is pumped from its container into the tractor-trailer mounted
process feed tanks. As the feed tanks fill, level controls inside the tank turn off the feed pump to
prevent system overfilling. While being pumped, the material passes through a mass flow meter
that measures density, temperature, incremental and total flow. The spent material then flows to a
control valve and into the evaporator.
The thin film evaporator technology is installed in a horizontal plane to provide for increased
control of residence time and to enable the evaporator to fit into a 48-ft. van trailer, thus allowing
the unit to be portable over the road. The spent material enters the evaporator and is distributed
evenly over the inner circumference, i.e., the heat transfer surface, by the four blades on the
rotor. The spent material spirals along the surface generating a bow wave which creates high turbulence and optimum heat flux. The volatile components are rapidly evaporated and the vapor
flows co-currently through the evaporator until discharged at the outlet. Continuous washing by
the bow waves minimizes fouling of the heat transfer surface where the product or residue is
concentrated.
After passing through the evaporator, the material is condensed. The reclaimed solvent passes
through a bulk water separator tank, through a 1 inch micron filter and returns to the on-site stor-
50th Purdue Industrial Waste Conference Proceedings, 1995, Ann Arbor Press, Inc., Chelsea, Michigan 48118.
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