Pollution Prevention Case Study

Snap-on Tools

Recycling a Rinsewater Stream Using
Ultrafiltration and Ion Exchange
Standard Industrial Classification (SIC) Sheet Metal Fabrication/3444
Process Electrodeposition of water based paints.
Type of Waste Ethylene glycol monobutyl ether (butyl cellusolve)
Strategies Process Modification - Ion Exchange Column Installation
Background Snap-on Tools is a hand tool and tool storage rollaway manufacturer headquartered in Kenosha, Wisconsin. Snap-on employs over 1,300 in its Wisconsin operations and has gross revenues in excess of $900 million.

Snap-on uses an electrocoating paint line with water based coatings. Snap-on Tools uses ultrafiltration to recover process paint from the rinse tanks' effluent. The ultrafiltration process produces concentrated paint for return to the paint bath, and permeate which is recycled to the rinse baths.

The permeate composition is 97% water with 2-3% ethylene glycol monobutyl ether (butyl cellusolve) and a contaminant isopropyl amine present in amounts less than 1%. The recycle loop to the rinse could not be totally closed because the contaminant isopropyl amine would build up in the system and ruin the rinse bath.

To prevent the build up of isopropyl amine, a purge stream was split from the recycle stream and drained to the Publicly-Owned Treatment Works (POTW). In 1989, Snap-on reported sewering over 190,000 pounds of the butyl cellusolve. The local POTW had no difficulty handling the extra strength wastewater loading.
Motivation Snap-on Tools places a substantial value on its image as a good corporate citizen. As a result, Snap-on felt uncomfortable discharging the large amount of butyl cellusolve to the local POTW. The company felt that their disclosure of the discharge in SARA Title III reporting would taint their corporate image.
Changes Implemented Snap-on Tools decided to recover the 190,000 pounds of butyl cellusolve that was lost in the purge of the recycle stream and discharged to the POTW. Snap-on Tools needed a method of removing the contaminant isopropyl amine from the purge stream. Snap-on identified ion exchange as the most attractive means of removing isopropyl amine.

A two stage ion exchange resin system was installed to remove the isopropyl amine from the purge stream. The permeate from the ion exchange system (water and butyl cellusolve) can now returned to the rinse baths. The isopropyl amine that is trapped by the resin is stripped during the regeneration of the resin and is sewered.

The ion exchange system has been very successful in removing the isopropyl amine. Only 3,500 pounds per year of butyl celluslove must now be purged and discharged to the POTW. Snap-on Tools now saves $54,900/year due to butyl cellusolve recovery, and at least $18,000/year on sewer fees.

Problems Encountered It was critical that the ion exchange system be effective in removing isopropyl amine because the build up of the contaminant in the rinsewater could degrade the quality of the electocoating finish. Closing the wastewater loop entirely was contingent on complete removal of isopropyl amine.
Material/Energy Balance Original Process

Feedstock
Butyl cellusolve in rinse water

Waste
Butyl cellusolve in wastewater - 190,000 lbs (1989)

Disposal
Discharged to POTW

Pollution Prevention Approach

Feedstock
Butyl cellusolve in rinse water

Waste
Economics Capital Cost
$150,000 (1989)

Operating/Maintenance Cost
Not available

Payback Period
Payback of 2 years based on total savings of $72,900/year from butyl cellusolve recovery ($54,900/yr.) and sewer fee savings ($18,000/yr.)

Company Address Snap-on Tools Corporation
Kenosha, WI 53141-1410
Contact Person Mr. Hiram J. Buffington, Manager
Environmental Engineering and Industrial Hygiene
Phone: 414/656-5200
Pollution Prevention Resources University of Wisconsin Extension
Solid and Hazardous Waste Education Center
Milwaukee area: 414/475-2845
Remainder of state: 608/262-0385

Pollution Prevention Clearinghouse
Wisconsin Department of Natural Resources
Hazardous Waste Minimization Program
608/264-8852, 608/267-9523 or 608/267-3763
DNR Logo


Bureau of Cooperative Environmental Assistance
Wisconsin Department of Natural Resources
P.O. Box 7921
Madison, WI   53707
608/267-9700

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