Pollution Prevention and Control Technologies for Plating
Section 5 - Substitute Technologies
5.3 CHLORINATED SOLVENTS USE REDUCTION/ELIMINATION
Chlorinated solvents have been used extensively in the metal working
and metal finishing industry for degreasing and cleaning. The
most commonly used degreasing solvents include: 1,1,1-trichloroethane
(or TCA), trichloroethylene (or TCE), perchloroethylene (or PERC),
chlorofluorocarbons, (or solvent 113) and methylene chloride.
These solvents are used in a variety of methods, but most frequently
in vapor degreasers, immersion or spray operations, and hand wiping.
Solvent use has declined during recent years and especially since
1990, due to regulations restricting the use of ozone-depleting
substances, voluntary actions by industry under EPA's 33/50 Program
(Industrial Toxics Project) (ref. 203), rising costs for the purchase
of solvents and the disposal of solvent wastes, and concerns over
the health effects of solvents. However, as late as 1989, an estimated
73,000 U.S. firms (includes all types of industry) still used
vapor degreasing with TCA (ref. 79).
Solvent use among the respondents to the Users Survey is summarized
in Exhibit 5-1. Column 1 indicates the shop code number (PS 001
to PS 318). Column 2 shows the type of solvent used. Column 3
indicates the percentage of the shop's work that is job shop-type.
Where 100% is shown, that business is entirely a job shop. Where
0% is shown, that business is entirely a captive shop. Where a
different percentage is shown, that shop does both job and captive-type
work. Column 4 indicates the year that the business commenced
plating operations. Column 5 indicates the year that solvent use
was eliminated. Where no year is shown in column 5, the solvent
process was still in use at the time of the survey. Columns 6
and 7 indicate the quantity of solvent (in gallons or pounds)
that is currently used or was used in cases where the applications
were eliminated. Column 8 indicates the type of application (vapor
degreasing, cold dip, spray or hand wipe). The last column indicates
the most sophisticated method that is used (or was used in the
case of eliminated applications) for controlling solvent emissions.
The following abbreviations are used (shown in increasing levels
NONE no controls
FREEBOARD increased freeboard degreaser
ROLLTOP automatic rolltop for degreaser
LIFTSPEED controls to limit vertical speed of degreaser hoist
REFRIGER refrigeration zone to supplement conventional cooling coils
Exhibit 5-2 shows that among respondents to the Users Survey,
the number of solvent users has changed since 1980. In Exhibit
5-2, the shops are divided into three groups: (1) those in existence
in 1980; (2) those established from 1981 to 1985 (inclusive);
and (3) those established from 1986 to 1993 (inclusive). For the
older shops, the number of solvent users remained approximately
the same from 1980 to 1985 and then declined substantially from
1986 to 1993. In 1980, 53% of the shops used solvent and by 1993
only 39% used solvent. Therefore, 26% of the solvent users in
1980 have eliminated its use. For shops established from 1981
to 1985, the frequency of solvent use was below that of the older
shops in 1985 and then from 1986 to 1993, the percentage declined
similarly to the declining use rate of the older shops. Thirty-one
percent of the shops established from 1981 to 1985 that originally
used solvent have eliminated its use. The most recently established
shops (1986 to 1993) presently have approximately the same percentage
of solvent use as the shops established in 1981 to 1985.
Exhibit 5-2 indicates that shop age had only a small bearing on
the frequency of solvent use. This is somewhat surprising since
older shops are often thought of as being less likely to change
their operational procedures and processes.
Exhibit 5-3 shows that the quantity of solvent use per application
has also declined during the time period 1980 to 1993 and that
this decline has been restricted to the time period of 1986 to
1993. A solvent application is defined as the use of a given type
solvent by a given shop. Therefore, shops can have more than one
solvent application. Combined with the fact that there are fewer
applications, overall solvent use has declined significantly,
probably by 50 percent or more from 1986 to 1993. All of the solvent
use data are contained in the database and users are encouraged
to utilize the database and draw their own conclusions.
Solvent use reduction has been achieved by survey respondents
by improving the designs of vapor degreasers and the operating
practices used with these units and by substituting aqueous and
semi-aqueous cleaners for solvent degreasing. The most frequent
vapor degreaser design and operating changes made by survey respondents
focus on reducing solvent emissions, and include: increasing freeboard,
adding a rolltop, controlling hoist speed and adding a refrigeration
zone (see Exhibit 5-1). Of the 90 vapor degreasing applications
in use in 1993, at least 75 percent were equipped with one or
more of these design and operational changes. Various substitutions
for solvent have been made by the survey respondents and these
are discussed later in this section.
Although the numerical survey data provide insight to the changes
regarding solvent use in the metal finishing industry, the comments
submitted by respondents give an even clearer picture. The remainder
of this subsection is devoted to their comments.
Sixty-eight percent of the respondents that are presently using
solvent identified that its elimination is a pressing environmental
problem. These shops are at various stages in the process of elimination.
Some shops indicated that they are just beginning to evaluate
solvent substitution alternatives (PS 156, PS 165, PS 184) and
other shops indicated that they have made progress and are continuing
to work toward elimination (PS 124, PS 166, PS 176, PS 178, PS
181, PS 191). Only 11.7 percent of the solvent users gave an indication
that they plan to continue the use of solvent. These shops gave
a range of reasons why solvent use is necessary. These reasons
- Solvent use is necessary to meet aerospace requirements (PS
- Unsuccessful at attempts to clean zinc die castings without
solvent (PS 089).
- Solvent is needed to remove polishing or buffing compounds
(PS 098, PS 170, PS 171, PS 191, PS 205).
- No single answer for replacing solvent degreasing (PS 049).
- Some non-solvent products work well, but there is always a
problem with long drying times for parts.
- Have replaced TCA vapor degreasing with alkaline cleaning,
but can't replace acetone used to strip maskant (PS 166).
- Substitutes are too expensive (PS 217).
- Citrus cleaners did not work (PS 248).
- Tried six different safety solvents (citric based). None were
satisfactory due to residue or unacceptable evaporation time (PS
A number of problems with solvent substitution were cited by survey
respondents. These include the following comments from both successful
and unsuccessful substitution efforts:
- Alkaline cleaners increase the amount of waste treatment performed
and/or the labor for these efforts (PS 114).
- More difficult to remove masking wax without solvent (PS 108).
- Citric acid based emulsion cleaner leaves a residue that inhibits
good plating and causes poor adhesion (PS 109, PS 271).
- "Orange-Peel Cleaners" caused skin rashes on employees
and excessive foaming in the waste treatment system (PS 021).
- Caused oil fouling of ion exchange resins (PS 130).
- Increased labor for degreasing and/or bath maintenance (PS
130, PS 262).
- Created a new wastestream (e.g., oily waste, spent cleaner)
in some cases that is more difficult to deal with than solvent
waste (PS 153, PS 171).
- Solvent substitutes simply do not perform as well as solvents
(PS 163).Substitutes are too expensive (PS 217).
- Citrus smell of substitute cleaners is objectionable.
- Many substitutes contain chelating agents or surfactants that
interfere with metal hydroxide precipitation (PS 296).
- PS 021 indicated that they had a Òdifficult transitionÓ
that took approximately 24 months and Òa lot of patience.Ó
Their efforts included trials with terpene cleaners, Òterpene-like
cleaners and non-ionic surfactant packages,Ó and finally
they settled on a mildly alkaline aqueous cleaner with a non-ionic
surfactant. They also use barium carbonate for post cleaning but
eventually switched to pumice. These changes combined with "enough
(cleaning) time" and "elbow grease" have resulted
in "few cleaning problems."
Only two shops specifically indicated that there were no production
related problems associated with the substitution for solvent
degreasers (PS 153, PS 190).
Some respondents provided information with regard to successful
substitute degreasers that they use in place of chlorinated solvents.
The following responses were given:
- Aqueous cleaner with glycol ether (PS 064).
- Aqueous cleaner (PS 124, PS 166, PS 187, PS 292, PS 268).
- Citri-Solv product and Safety Clean (PS 105).
- Mildly alkaline, biodegradable aqueous cleaner with a non-ionic
surfactant (PS 021).
- Global 6 (PS 169).
- Aqueous, citric, terpene cleaners (PS 174).
- Emulsion cleaner (PS 181).
- Alkaline power washer (PS 079, PS 197).
- Alkaline non-etch ultrasonic clean, Enthone NS-35 (PS 221).
- Increased concentration of existing cleaner (PS 253, PS 295),
e.g., PS 295 eliminated solvent use (80,030 gal/yr CFC 113 and
TCA) by increasing cleaner concentration from 10 oz/gal to 12
- Converted degreasers to soak cleaners and use 7-9 oz/gal Midstate
4310, 140 - 180 oF, alkalinity ratio 0.40 minimum, soil load 10%
maximum (PS 273).
- Water soluble solvents (PS 276).
A number of miscellaneous methods were employed to reduce solvent
use; these include:
- Use safety solvent cans with hand wipe operation (PS 069,
- Use low vapor pressure solvent blend in place of MEK for hand
- Increase level of training and reviewed good operating practices
in safety meetings (PS 191).
- Increased use of hand wiping and decreased use of vapor degreaser
- Added inspection of degreaser to regular monthly procedures
- Working with customer on the cleanliness of parts (PS 248).
- Increased agitation in cleaning bath.
- Subcontract the 5% of workload that requires solvent degreasing.
- Install solvent recovery stills (PS 124, PS 149).
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