&EPA
AUEQ-TR-1993-0024
EPA/600/R-93/191
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MINIMIZING POLLUTION IN CLEANING AND DECREASING
OPERATIONS
A.B. Tarrer; H.J. Sanjay - Auburn University
S. Garry Howell - U.S. EPA
ENVIRONICS DIRECTORATE
139 Barnes Drive, Suite 2
Tyndall AFB FL 32403-5323
Auburn University
Department of Chemical Engineering
230 Ross Hall
Auburn University AL 36849-5127
US EPA/RREL
26 W Martin Luther King Drive
Cincinnati OH 45268
November 1993
Final Technical Report for Period February 1989 - October 1991
AIR FORCE MATERIEL COMMAND
TYNDALL AIR FORCE BASE, FLORIDA 32403-532^,
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NOTICES
-
-
JOSEPH D. WANDER
Project Officer
_ . » Col, USAF, BSC
Chief, Environica Division
.
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REPORT DOCUMENTATION PAGE
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1. AGENCY USE ONLY (leave blink) 1 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED
1 November 1993 , Final 14 Feb 1989 to 10 Oct 1991
4. TITLE AND SUBTITLE
(U) Minimizing Pollution in Cleaning and
Degreasing Operations
6. AUTHOR(S)
S Garry Howell - U.S. EPA
AR Tarrer and HJ Sanjay - Auburn University
7. PEflfORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
(1) Auburn University ' (continued
Deptartment of Chemical Engineering on reverse)
230 Ross Hall
Auburn University AL 36849-5127
9. SPONSORING/ MONITORING AGENCY NAME(S) AND ADDRESS(ES)
AL/EQS-OL
139 Barnes Dr, Suite 2
Tyndall AFB FL 32403-5323
5. FUNDING NUMBERS
C EPA-CR-816219-01
PE 66206F ;
PR 1900 :
TA 70
WU 61 .
8. PERFORMING ORGANIZATION
REPORT NUMBER
s ••
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
AL/EQ-TR-19 9 3-0024
EPA/600/R-93/191
^heUPava¥i?atTii?y£Sof this report is specified on the reverse of the front cover.
Project Officers: Joseph D Wander - AL/EQS, 904-283-6240, DSN 523-6240
Mary Ann Cur ran - U.S. EPA/RREL, 513-569-7837
. 12a. DISTRIBUTION /AVAILABILITY STATEMENT
Approved for Public Release
Distribution Unlimited
12b. DISTRIBUTION CODE
A
13. ABSTRACT (Maximum 200 words)
The objective of this study was to examine approaches to decreasing rates of loss by
evaporation and extending the useful lifetime of metal-cleaning solvents in service
as means to decrease the generation of pollutant emissions and residues from Air
Force cleaning and degreasing operations. An earlier study correlated properties of
cleaning solvents with cleaning performance. This report includes data from an
experimental study in which the same properties are measured in solvents that had
been removed from service for recovery. Also included is an evaluation of the
operation and maintenance of several degreasers in operation at Tinker AFB, together
with specific suggestions to decrease the rate of evaporative loss. In the test, a
measured volume of spent TCA- was delivered into the sump of a recirculating
filtration system. During recirculation, water content and color intensity
decreased with reasonable consistency, (continued on reverse)
14. SUBJECT TERMS
Solvent recovery, CFC-113, 1,1,1-trichloroethane,
PD-680, filtration, distillation, stabilizers
; 15. NUMBER OF PAGES
50
16. PRICE CODE
17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT
OF REPORT OF THIS PAGE OF ABSTRACT
Urclassified Unclassified Unclassified ; UL
NSN 7ii-0-01-280-5500 Standard .Form 298 (Rev 2-89)
Prescribed by ANSI Std 239-18
1 298-102
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7. (continued) (2) US EPA/RREL
26 W Martin Luther King Drive
Cincinnati OH 45268
(AAV>
and minor obstructions in Sturn lines or f™ J6" «<*•«**»« techniques
coils caused significant increases in.vf °verheatln« °^ evaporation
shows that recovery ^purification LH rfr^^V08868' The study
filtration are practical ont?n«» ^ distillation and -in-situ
metal-cleaning £S degreasing solv!^^'^ the effecti^ lifetime of
Program to monitor «d"SnXin ll^ll 5" USed in conJu"ion with a
Significant refinement of the in-sltu filtriti "^ addltive«-
before implementation can be recommended * Pr°CeSS **" be needed
ii
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PREFACE
This report was prepared by Auburn University, Department of Chemical Engineering,
220 Ross Hall, Auburn University AL 36849-5127, under contract #EPA-CR-816219-01, for
the U.S. Air Force, Armstrong Laboratory Environics Directorate (AL/EQS-OL), 139 Barnes
Drive, Suite 2, Tyndall AFB FL 32403-5323, and the U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory (EPA/RREL), 26 W Martin Luther King Drive,
Cincinnati OH 45268.
This technical report summarizes work done between 14.February 1989 and
10 October 1991. Tin EPA project officer was Mary Ann Curran of RREL; the Air Force
project officers were Surendra B. Joshi of HQ AFESC/RDVS and Dr. Joseph D. Wander of
AL/EQS.
Generous cooperation by Air Force personnel at Warner Robins Air Logistics Center
(WR-ALC) and Tinker Air Force Base (OC-ALC) is gratefully acknowledged.
in
(The reverse of this page is blank)
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EXECUTIVE SUMMARY
A. OBJECTIVE
The objective of this study was to examine approaches to decreasing rates of loss by
evaporation and to extend the useful lifetime of metal-cleaning solvents in service as meams to
decrease the generation of pollutant emissions and residues from Air Force cleaning and
degreasing operations.
B. BACKGROUND
In an earlier study, several properties of cleaning solvents were measured at intervals
during usage and correlated with the cleaning ability of the solvent. The purpose of that
exercise was to extend the lifetime of the solvent by developing quantitative measures of the
extent of contamination or of expenditure of metal-protecting additives. Application of the
endpoints identified would actually remove the solvents from service before their cleaning
capability had been exhausted. Of these tests, the acid acceptance value (AAV)--which
measures the amount of acid inhibitor remaining—was the most reliable. Field experience has
shown that replacement of the inhibitors can restore usability to partially contaminated 1,1,1-
trichloroethane (TCA).
C. SCOPE
This report includes data from an experimental study in which the same properties
identified in the previous study -v?r? measured on solvents that had been removed from
service for recovery. The used solvents were pumped from a sump through a mechanical
filter for a period of time corresponding to five complete passages through the filter, and the
evolution of the properties was followed as a function of the extent of treatment. A second
section contains an evaluation of the operation and maintenance of several degreasers in
operation at Tinker AFB, together with specific suggestions to decrease the rate of
evaporative loss from these units.
D. METHODOLOGY
No new methods were used in this study. Water content was measured by a Karl
Fischer method (ASTM 1364-90). AAV was measured by addition of an aliquot of acid and
back-titration with alkali (ASTM D-2942). Visible transmittance was measured with a direct-
reading UV—visible spectrometer, .electrical conductivity with a conductivity meter, and
viscosity with a falling-ball viscometer. Nonvolatile matter (NVM) was measured
gravimetrically, either by evaporating the solvent over a steam bath or by filtering and
evaporating the adhering solvent. The survey of the degreasers was performed by Jim C.
Johnston of Dow Chemical Company, U.S.A.
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E. TEST DESCRIPTION
A measured volume of spent TCA was delivered into the sump of the recirculating
filtration system. Small samples were withdrawn for analysis and the solvent was circulated
through a pair of filters in tandem and back into the sump. Sampling was repeated at
intervals corresponding to the time required to pump the entire volume of solvent through the
filters for five cycles. The evaluation of the degreasers was a walk-through inspection that
included no quantitative measurements.
F. RESULTS
During recirculation through the filter, water content and color intensity (from
transmittance measurements) decreased with reasonable consistency, while AAV remained
essentially constant. There is some inconsistency and scatter in the data, but the trends are
consistent. (At the end of the treatment, the inhibitors are preserved and the general condition
of the solvent is improved enough for preliminary cleaning.) Slight deviations from best
operating techniques and minor obstructions in return lines or overheating of evaporation coils
cause significant increases in the rate of evaporative loss from average-to-good degreasing
operations.
G. CONCLUSIONS
Recovery by purification and distillation and in-situ filtration are practical options to
extend the effective working lifetime of metal-cleaning and degreasing solvents when used in
conjunction with a program to monitor levels of protective additives and maintain additive
protection above critical thresholds. Significant refinement of the in-situ filtration process
will be needed before implementation can be recommended. Refinement of operating
technique and aggressive maintenance policies can decrease the rate of loss of solvent from
degreasing baths.
H. RECOMMENDATIONS
The following recommendations are offered: (1) Refine and expand in-situ
purification technology and implement as a field test, (2) Retrain degreaser operators at
regular intervals, and (3) Conduct unscheduled evaluations of operating technique on the line
and of maintenance status of the degreasing baths.
VI
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TABLE OF CONTENTS
Section Page
INTRODUCTION
A. PROJECT OBJECTIVES
B. BACKGROUND
C. SCOPE
II DECREASING SOLVENTS ............. ................... . 3
A. PHYSICAL CHANGES ............................... 3
B. CHEMICAL CHANGES ............. .................. 3
STABILIZER ANALYSIS
A. ANALYSIS METHODS
1. Water Content ................................. 5
2. Acid Acceptance Value (AAV) ..................... 5
3. Visible Absorbance .............................. 5
4. Nonvolatile Matter (NVM) ......................... '. 7
5. Electrical Conductivity ............................ 7
6. Viscosity ..................................... 7
IV BATH REJUVENATION BY FILTRATION ...................... 8
A. FILTRATION OF 1,1,1-TRICHLOROETHANE .............. 8
1. Water Content ........ .......................... 8
2. Acid Acceptance Value (AAV) ...................... 12
3. Visible Absorbance .............................. 12
4. Nonvolatile Matter (NVM) ......................... 12
5. Conductivity ................................... 12
B. FILTRATION OF FREONR 113 (CFC-113) . . . ............... 17
V STABILIZER REPLENISHMENT ............................. 18
A. DISTILLATION ........... ....................... 18
B. ULTRAFILTRATION ............................... . . 18
vn
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TABLE OF CONTENTS (CONCLUDED)
Section Page
VI MINIMIZING POLLUTION BY MORE-EFFICIENT OPERATION ..... 20
A. AUDIT OF DECREASING BATHS AT TINKER AFB
FOR PILOT STUDY 20
B. SURVEY OF TINKER AFB DEGREASERS 30
1. Cooper Open-Top Degreaser N-37 30
2. Open-Top Degreaser U-45 31
3. Delta Open-Top Degreaser HA-49.4 31
4. Ramaco Open-Top W-65 32
5. Phillips Open-Top R-3 5 32
6. Ramaco Open-Top Degreaser N-58 . . 33
VII CONCLUSIONS AND RECOMMENDATIONS 34
REFERENCES 35
via
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LIST OF FIGURES
Figure Title Page
1 1,1,1-Trichloroethane Calibration Chart ! 6
2 Filtration Scheme for Reclaiming Solvents 9
3 Water Content of 1,1,1-Trichloroethane for Various •
Cycle Times (Set #.1) 10
4 Water Content of 1,1,1-Trichloroethane for Various
Cycle Times (Set #2) 11
5 Variation of Acid Acceptance Value With Cycle Times (Set #1) 13
6 Variation of Acid Acceptance Value With Cycle Times (Set #2) 14
7 Variation in Transmittance With Cycle Time (Set #1) 15
8 Variation in Transmittance With Cycle Time (Set #2) 16
IX
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LIST OF TABLES
Table - Title Page
1 COMMONLY USED DECREASING SOLVENTS 2
2 TYPICAL INHIBITORS/STABILIZERS AND THEIR FUNCTIONS . 4
3 SOLVENT CONSUMPTION REDUCED BY 40 PERCENT . . . .... 21
4 SOLVENT AND DOLLAR SAVINGS FOR
40-PERCENT SOLVENT REDUCTION 22
5 WASTE REDUCTION ; 23
6 SAVINGS IN WASTE REDUCTION . , | 24
7 TOTAL ANNUAL SOLVENT AND DOLLAR
SAVINGS (20 PERCENT SLUDGE) '. 25
8 WASTE REDUCTION 26
9 SAVINGS IN WASTE REDUCTION I. ... 27
10 TOTAL ANNUAL SOLVENT AND DOLLAR
SAVINGS (5 PERCENT SLUDGE) 28
11 HALOGENATED SOLVENTS USAGE INFORMATION 29
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SECTION I
INTRODUCTION
A. PROJECT OBJECTIVES
Large volumes of chlorinated solvents are used in cleaning and degreasing U.S. Air Force
aircraft and engine parts. The objective of this project is to investigate methods to minimize loss
of solvents through evaporation and extend the useful lifetime of metal-cleaning solvents in use at
overhaul and maintenance operations.
B. BACKGROUND
Overhaul and maintenance operations operated by the U.S. Air Force use large volumes of
solvents for cleaning and degreasing of aircraft and engine parts, gyroscopes, guidance systems,
and electronic components. A major portion of these solvents are chlorinated compounds such as
1,1,1-trichloroethane, methylene chloride, or perchloroethylene. During normal use, some of
these materials evaporate into the atmosphere, and are thought to contribute to stratospheric ozone
depletion. As grease and dirt build up in cleaning baths, a point is reached at which the solvent
must be discarded, resulting in the loss of the value of the solvent, plus the added cost of
disposal. As part of the implementation of its waste minimization program, the U.S. Air Force is
trying to find the most efficient, safe, and economical methods to extend the useful life of (or
recycle) cleaning solvents, particularly TCA. Other less widely used solvents considered for
recycling are methylene chloride, perchloroethylene, and PD-680 (a petroleum fraction similar to
the well known Stoddard solvent). Properties of some common cleaning solvents are given in
Table 1.
C. SCOPE
Auburn University, in cooperation with major solvent manufacturers, developed a research
program to determine which physical and chemical properties were most important for
maximizing the useful life of the solvents. The target was to develop fairly simple; methods for
determining these properties so that users could get the longest useful life from their cleaning
baths. After testing has shown that the the solvent is no longer usable, two options are offered:
(1) critical additives may be replenished, or (2) the solvent may be recycled by distillation,
filtration, or other means.
The first sections of this report concentrate on the TCA recycling technology developed at
Auburn University by Professor A.R. Tarrer (Reference 1). Subsequent sections will address
other solvents and their potential for recycling.
Efficient operation of degreaser baths can also reduce solvent usage and minimize
emissions. An expert from Dow Chemical Co. was asked to audit degreasing operations at
Tinker AFB, Oklahoma, and recommend changes that would accomplish these goals.
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TABLE 1. COMMONLY USED DECREASING SOLVENTS
Hydrocarbons6
Mineral Spirits
Aromatic Naphtha
Stodclard Solvent
Toluene
Xylene
Alcohol
2-Propanol
(Isopropyl Alcohol)
Ketones
Boiling Range
°C °F
116-135
200-350
155-210
111
135-143
82
240-275
392-660
310-410
231
275-289
180
Flash Point8
°C °F
10
65
<38
4
85
21
50
150
<100
40
185
70
Uses'
D, S
D, S
D, S
D, S
D, S
D, S
Acetone 55-57 131-135 -20
Methyl Ethyl Ketone (MEK) 80 176 -4
Halogenated Solvents
Methylene Chloride
Perchloroethylene (perc)
1,1,1-Trichloroethane (TCA)e
Trichloroethylene (TCE)
Trichlorotrifluoroethane
(CFC-113)f 48 118
40
121
74
87
104
250
165
188
NFd
NF
NF
NF
-4
25
NF
D, S
D, S
D, S, V
D, S,V
D.S.V
D, S, V
D, S,V
Typical range
b With the exception of toluene and xylene, these solvents are petroleum fractions having a range of molecular weights,
and consequently a boiling range, rather than discrete boiling points. Xylene, when used as a solvent, is usually a mixture of
ortlw, meta, and para isomers, each having a discrete boiling point.
c D = dip, S = spray or brush, V = vapor
d NF = Non Flammable
* Also called methyl chloroform
f Also available as binary azeotropes with ethanol, 2-propanol, acetone, and methylene chloride. Several ternary
azeotropes are also available.
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SECTION II
DECREASING SOLVENTS
A. PHYSICAL CHANGES
Vapor degreasing is a common industrial process in which the parts to be cleaned are
suspended in the vapor space above a boiling bath of solvent. The most common solvents for
such operations are TCA and perc. The vapors are much heavier than air, so that a properly
designed and operated bath (see Reference 2) will confine most of the vapors in the "head
space" and lose very little to the atmosphere. During operation, solvents in a vapor degreaser
undergo both chemical and physical changes. In addition, the liquid in the boiling sump
starts to build up solids such as metal chips, dirt, or paint particles. Oils and greases are in
solution in the liquid phase, and may build up sufficiently to increase viscosity and seriously
impair heat transfer; in electrically heated baths, heater sheath temperatures may increase and
cause failure. As the concentration of lighter oils increases, they will appear in the vapors,
and will leave a noticeable residue on the "cleaned" parts. A chemical analysis aimed only at
the composition of the solvent itself may show that it is still usable, but its efficiency is
severely impaired by dissolved material. At least part of this efficiency may be restored by
some physical methods described in a later section.
B. CHEMICAL CHANGES :
Partially chlorinated solvents tend to decompose after prolonged heating. This is
manifested by chlorine breaking off the hydrocarbon backbone, forming hydrogen chloride
(HC1). The HC1 then combines with any water present to form hydrochloric acid, which
causes corrosion of metals. (Fluorine, as in CFC-113, is more tightly bound, and less likely
to be released). The HC1 itself promotes further dechlorination; this is inhibited by additives
called acid acceptors, which are designed to combine with or neutralize HC1. Table, 2 lists
some commonly used inhibitors (see Reference 3 for a review of inhibitor patents).
Many halogenated solvents are relatively resistant to attack by oxygen until a chlorine
is abstracted. Removal of the chlorine (or fluorine) and an adjacent hydrogen leaves a double
bond, which is susceptible to oxidation, particularly in the presence of metals such as copper
or vanadium. Perchloroethylene and trichloroethylene have these double bonds already in
place, and are more suceptible to oxidation. Another class of stabilizers called oxidation
inhibitors or antioxidants may be added to retard this mode of decomposition.
The interaction between acid and metal can cause etching or corrosion of a metal
surface. Conversely, as stated above, some metals promote oxidation, requiring some means
of protecting the solvent from the metal. Metal stabilizers accomplish this by forming a
protective film on metal surfaces that retards attack by acids, while deactivating the catalytic
properties of the surface.
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The concentration of these stabilizers in halogenated solvents is critical, particularly
the ratio of metal stabilizer to acid acceptor. While other stabilizers decompose chemically,
or react with acids and become depleted,, metal stabilizers are intentionally chosen to be
somewhat volatile to maintain some presence in the vapor phase. An almost monomolecular
layer is formed on the metal surfaces so that, as the parts are withdrawn, adherent stabilizer is
consumed.
TABLE 2 .
TYPICAL INHIBITORS/STABILIZERS AND THEIR FUNCTIONS
Function Compound and Formula _
Acid Acceptor*"1" Butylene Oxide (1,2-Epoxybutane)
CHjCHjCHCH,
V
Acid Acceptor* Epichlorohydrin (l,2-Epoxy-3-chloropropane)
CICHjCHCHj
Acid Acceptor* Butoxymethyloxirane (l,2-Epoxy-3-butoxypropane)
C4H9OC2CH2CHCH2 \
V
Metal Stabilizer*10 1,4-Dioxane (1,4-Dioxacyclohexane)
CH2CH,
Antioxidant lonol™-11, BHT (2,6-Di-r-butyl-p-cresol)
2,6-(C4H9)j-4-CH3C6H2OH
Antioxidantb Nitromethane
* Flammable and classed as possible carcinogens.
b Donahue et al. (Reference 1) misinterpreted mass spectral data and mistakenly identified
nitromethane and a-butylenc o:dc!e (1,2-epoxybutane) as W-methoxymethanamine (CH3ONHCH3) and
formaldehyde dimethylhydrazone (H2C=NN(CHJ)2), respectively, during analytical characterization of the
additives present in TCA. .
c Fatty acid amines are sometimes used; these give some rust inhibition after parts are exposed to air.
4 Trademark Shell Oil Company. lonol or BHT is illustrative of a broad classi of phenolic
antioxidants; it may not be suitable for all types of degreasing baths.
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SECTION in
STABILIZER ANALYSIS
Visual inspection alone is unreliable as a means of determining the condition of degreasing
solvents. A bath which is perfectly clear could be deficient in inhibitor, and one which is
badly discolored can still be well stabilized. The most reliable method of determining the
levels and types of stabilizers in halogenated solvents is by gas chromatography/mass
spectrometry (GC/MS); however, the expense involved makes it impractical for most users.
Dr. Tarrer has suggested several reliable methods of analyzing for stabilizers and for
estimating the remaining useful life of a degreasing bath; when in doubt, one should use two
or more of them. The acid acceptance value (AAV) is the most important parameter, as it is
an accepted measure of stabilizer content (References 4 and 5). Viscosity is affected by dirt
and grease buildup, and might be the second most important analysis, although conductivity is
considered by some to be at least as important. Some operators of degreasers concur with Dr.
Tarrer in principle but consider his criteria for judging bath condition overly conservative.
They state that using his measurement methods, but lowering the standards, allows them to
extend useful life of the solvent while still getting efficient cleaning.
A. ANALYSIS METHODS
1. Water Content
The presence of water is detrimental in two respects: first, it promotes
corrosion at metal interfaces; second, it promotes hydrolysis of the halogen-carbon bond,
releasing free HC1, which immediately combines with water to form hydrochloric acid and
become even more corrosive. The accepted standard test for water content of volatile
solvents is ASTM 1364-90, a Karl Fischer-type analysis.
2. Acid Acceptance Value (AAV)
The AAV is a measure of the concentration of acid acceptor in the solvent. It
is easily determined by a simple titration as outlined in ASTM D-2942. Figure 1 is a
calibration chart for AAVs with Dr. Tarrer's recommended minimum (Reference 2) for
1,1,1-trichloroethane before it must be redistilled or discarded.
3. Visible Absorbance
A spectrophotometer for absorbance testing can be bought for about $2000;
these instruments do not require extensive operator training.
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4. Nonvolatile Matter (NVM) :
While the accepted method is ASTM D-2109^85, evaporating solvent from a
weighed sample over a steam bath will give good enough results for most users. The residue
is oil, grease, soils, etc., which build up and impair cleaning efficiency.
5. Electrical Conductivity
Halogenated solvents are good insulators, and water containing ionic materials
such as acids or salts will raise the conductivity measurably. Conductivity meters cost from
$750 to $1500, and are as easily operated as spectre-photometers.
6. Viscosity
Many types of viscometers are available; a simple falling ball type can be
bought from laboratory supply houses for about $150.
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SECTION IV
BATH REJUVENATION BY FILTRATION
As a degreasing or cleaning bath is used, and dissolved oil and grease, dirt, metal particles,
and water accumulate, some steps must be taken to return it to a usable condition. Some of
the tests run above might indicate that there is some useful life left, and that less drastic
methods than discarding or distillation might suffice to extend it. An investigation of
alternative rejuvenation methods was made by Professor Tarrer at Auburn University1. He
demonstrated that one approach is to carefully filter the solvent and monitor changes in
properties by several of the methods noted above. An experimental filtration setup is
illustrated in Figure 2. The solvent was pumped from a stirred tank through a series of three
filters, the first being a bag that removed very coarse (25-micrometer) particles, then through
1.0- land 0.5-micrometer filters. Pumping was continued until the tank's contents were passed
through the filters approximately five times; a single cycle was about 10 minutes. Samples
were taken after each cycle to monitor the condition of the solvent. Filters were cleaned
when the differential pressure across them reached 15 psi. Some test results from these
filtration experiments are given below.
A. FILTRATION OF 1,1,1-TRICHLOROETHANE
1. Water Content
As stated before, the presence of water is deleterious to the solvent and to parts
being cleaned. If the starting content was above about 0.5 percent, repeated filtration cycles
actually reduced it as illustrated in Figures 3 and 4. In Runs 1, 2, and 5 in Figure 3, in which
the initial concentrations were less than 0.5 percent, water content remained almost unchanged
despite the number of passes through the filtration system. The reason for this is unclear, but
may possibly be due to the fact that water solubility in TCA is about 500-600 ppm (0.05-0.06
percent), and above this level, as in Runs 9 and 10, and all the runs in Figure 4, the water
exists; as a dispersion. At higher water contents, filtration would cause some coalescence of
droplets, causing them to float to the surface of the feed tank and evaporate. Whatever the
mechanism, filtration done in this manner does remove some of the water.
1 Performed as part of an Interagency Agreement between E.P.A. and the U.S.Air Force, which provided
most of the funding. Dr. Joseph D. Wander of AFCESA/RAVS (now AL/EQS) was the Air Force project
officer, and Mary Ann Curran of the Risk Reduction Engineering Laboratory was the EPA project officer on
contract no. EPA-CR-816219-01.
8
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CIRCULATE FOR FIVE CYCLE TIMES
BAG
FILTER
ONE-
MICRO-
METER
FILTER
0.5-
MICRO-
METER
FILTER
F8LTRATION SYSTEM
Figure 2. Filtration Scheme for Reclaiming Solvents
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ooooo RUN
RUN
RUN
66666 RUN
RUN
0.00
T r
2 3
NUMBER OF CYCLES
Figure 3. Water Content of 1,1,1-Trichloroethane for Various Cycle Times (Set #1)
10 '
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2.00
Q££££> RUN
RUN
RUN
RUN
RUN
0.00
-r
234
NUMBER OF CYCLES
Figure 4. Water Content of 1,1,1-Trichloroethane for Various Cycle Times (Set #2)
11 .
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V ' ' ,
2. Acid Acceptance Value (AAV)
The presence of acid acceptors (as measured by AAV) was not affected by
' filtration, as shown in Figures 5 and 6. Five passes through the system left the AAV almost
unchanged at three times the minimum value. This is in contrast to distillation or adsorption
on carbon, both of which decrease AAV.
3. Visible Absorbance
New TCA is water-white and crystal-clear, and its clarity is decreased by either
dissolved materials or suspended particles. A portable spectrophotometer was used to
measure the light (580 nm) absorbed or scattered by the solvent samples; this is reported as
percent transmittance in Figures 7 and 8. Although water droplets would always be expected
to haive some effect on the light transmitted (or absorbed), the presence of water-soluble or
wettable impurities can affect absorbance; however, the lack of correlation between Figs. 7
and 8 and Figs. 3 and 4, suggests that other factors could combine to increase absorbance.
Dissolved colored waxes, oils, and grease as well as suspended particles of dirt, etc., also
lower light transmission. Absorbance measurements should always be used in tandem with at
least one other test, because a clear, clean-looking solvent could be completely devoid of acid
acceptors or other stabilizers.
4. Nonvolatile Matter (NVM)
Weighed samples of contaminated solvent were evaporated under vacuum
(unspecified) at 105 ± 5oC. The NVM remained almost constant during all the runs.
Measuring the solids content by filtering the samples, then drying the filter paper at 60°C
gave higher values than the NVM. This was attributed to volatilization of lighter oils in the
vacuum oven. Evaporating the samples on a steam table (the preferred method) would
probably give higher results than the filter paper method, particularly if dissolved solids were
present.
: 5. Conductivity
Electrical conductivity tests made after every pass through the filtration system
showed very little variation; however, comparison to virgin solvent indicated contamination
by some conductive material. The small amount of water dissolved in the TCA (the literature
values are 500-600 ppm) could carry minute amounts of HC1 or salts, which would raise the
conductivity well above the 10'10 mhos/cm of the new material. Filtration, as stated
previously, will not remove dissolved materials, so little or no effect on conductivity would be
expected.
12
-------
0.25 -
0.20 -
0.05 -
0.00
RUN
QAOOP RUN
RUN
RUN
***** RUN
1
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5
9
10
Acid Acceptance Value below which solvent condition is unacceptable.
I I l
234
NUMBER OF CYCLES
Figure 5. Variation of Acid Acceptance Value With Cycle Times (Set #1)
13
-------
0.25 -
0.20 -
0.05 -
0.00
' RUN
RUN
RUN
OOQOORUN
fetfci* RUN
I 3
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7
8
Acid Acceptance Value below which solvent condition is unacceptable.
~T
1
T~ 1 1 T
2345
NUMBER OF CYCLES
Figure 6. Variation of Acid Acceptance Value With Cycle Times (Set #2)
14
-------
100,00 -
0.00
i ' i 4 4 T
NUMBER OF CYCLES
Figure 7. Variation in Transmittance With Cycle Time (Set #1)
15
-------
120.00 -
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on
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T i 1
234
NUMBER OF CYCLES
Figure 8. Variation in Transmittance With Cycle Time (Set #2)
16
-------
B. FILTRATION OF FREONR 113 (CFC-113)
Used CFC-113 (trichlorotrifluoroethane) was reclaimed by filtration at Warner Robins
ALC. The samples taken had high water and solids contents, both of which were reduced by
filtration. Water content was reduced by about 90 percent, to very nearly the solubility level
of water in CFC-113, which is 0.009 percent.
Solids were almost completely removed, indicating that most of it was particles larger
than 0.05 micrometer. Since CFC-113 is primarily used for cleaning delicate precision parts,
base personnel thought that the filtered solvent would be usable for preliminary cleaning, if
followed by a rinse with virgin solvent.
17
-------
SECTION V
STABILIZER REPLENISHMENT
If the AAV or GC/MS analysis indicates that solvent is deficient in stabilizer(s), but still
acceptable as a cleaner, there are two options that can be used to restabilize it. The first,
easiest, and safest is to buy new solvent containing higher than usual levels of stabilizer.
This is added to the old bath in quantities sufficient to raise the stabilizer to a safe level. The
second option, which requires more skill and training, is to buy stabilizers (often including
acid acceptor, metal stabilizer, and antioxidant) and add them as needed. Careful analysis is
required to determine the amount to be added, and safety precautions must be strictly
observed, as the chemicals used (see Table 2 for some examples) are flammable, toxic, and
possibly carcinogenic. For these reasons, only those knowledgable in and adept at handling
chemicals should attempt to make up their own stabilizer packages.
A. DISTILLATION
If, after filtration, the level of dissolved oils and grease is too high, one of the best
options for reclaiming solvents of all types is distillation. Properly done, distillation can
yield the base solvent in almost virgin condition. Petroleum solvents, such as Stoddard
solvent, or PD-680, might require vacuum to lower their boiling points, but are otherwise
unaffected by the process. TCA, TCE, and perc all boil at 250°F or below, and may easily
be handled in either steam or electrically heated stills at atmospheric pressure. The major
disadvantage of distilling halogenated solvents is that the stabilizers could be partially retained
in the still bottoms, while the condensate, or overhead, might be understabilized. It is
therefore advisable to analyze redistilled solvents to confirm stabilizer levels.
r
Many stills have been installed, tried a few times, and abandoned because of their
presumed difficulty of operation. These could quite likely be reactivated with more thorough
operator training and retrofitting with modern automatic control systems. An 'excellent
example of solvent recovery is in operation at Warner Robins ALC, where distillation has
been sucesssfully carried out since 1982 (see Reference 7). In 1987, an estimated $800,000
was saved on CFC-113 alone. (Personnel at the base found that redistilled TCA has retained
acid acceptors, but as a precaution, blend the recycled TCA with virgin solvent for safe use.
In addition, the base keeps some 1,2-butylene oxide on hand for addition to the reclaimed
solvent.)
B. ULTRAFILTRATION
Conventional filtration will normally remove particles of 0.5 micrometer diameter and
larger. When particles smaller than 1 micrometer are to be removed, polymeric membranes
may be used instead of the solid media of ordinary filters. Some newer membranes are
resistant to many solvents, and are capable of retaining molecules larger than 150-200 daltons
(molecular weight), which means that Stoddard solvent (ca 150-160 daltons) or TCA (133.4
18
-------
daltons) would pass through, but dissolved oils and greases would be retained. The higher-
molecular-weight inhibitors such as butoxymethyloxirane (130.2 daltons, see Table 2) would
also pass through the membrane. Membrane filters should always be preceded by a
conventional filter to minimize fouling. Development of these solvent-resistant membranes,
as well as those resistant to acids and bases, is continuing, and membrane separations are
expected to replace distillation in many instances.
19
-------
SECTION VI I
MINIMIZING POLLUTION BY MORE EFFICIENT OPERATION
The period between rejuvenation or recycling solvents can be greatly increased by more
careful operation of degreasing operations. Szabo and Nutter investigated the technical and
economic feasibility of several methods of reducing solvent usage and ambient vapor
concentrations near a TCA vapor degreaser at Wright-Patterson Air Force Base (Reference 8).
Their recommendations resulted in $25,200 per year savings in solvent costs, indicating a
payback period of 0.6 year. In addition, almost 4000 gallons of TCA were prevented from
entering the atmosphere anually.
A similar survey of the various degreasing operations at Tinker ALC was made by a
representative of Dow Chemical Co., a major solvent supplier; following those
recommendations should save about $68,000 per year. While the comments made referred to
specific units at Tinker, they are applicable to many operations. An edited version of the
Dow survey is given below.
A. AUDIT OF DEGREASING BATHS AT TINKER AFB FOR PILOT STUDY
(Note: This section was authored by Jim C. Johnston of Dow Chemical Company,
U.S.A., who conducted the audit at Tinker AFB during July 1990. Data given are unchanged;
editorial changes were made by Dr. J.D. Wander of Tyndall AFB.)
In this section, each degreasing bath at Tinker AFB is reviewed on its own merit. The
second portion of this section estimates solvent savings that could be realized by Tinker if
they install steam condensate return pumps, adjust to proper heat balance, use the stop-and-go
technique, slow the hoist speed to 2-4 linear feet per minute, and take action on other
suggestions made by Dow (Section B following). With these improvements, they could
decrease their solvent consumption by not less than 40-60 percent. The calculations are based
on a 40-percent solvent reduction (Tables 3 and 4). For the waste solvent of 20-percent
contamination (assumed), a projected concentration of 60 percent was calculated for
perchloroethylene and 50 percent for 1,1,1-trichloroethane (Tables 5 and 6). For estimation
purposes, waste reduction for 5-wt% contamination are also included (Tables 8 and 9), since
Tinker AFB appears to be giving to their reclaimer waste that contains less than 5-wt%
contamination.
Tinker AFB can achieve a solvent savings of 6,012 gallons plus waste reduction
savings of 2,912 gallons; the corresponding annual dollar savings will slightly exceed
$50,000. A solvent reduction of 59.4 percent or greater is achievable (see Table 7).
As Tinker appears to be sending out waste at less than 5 wt%, then even greater
savings may be available (see Tables 8 and 9). Table 10 summarizes the solvent and dollar
savings that could be realized.
20
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TABLE 7. TOTAL ANNUAL SOLVENT AND DOLLAR SAVINGS
(20 PERCENT SLUDGE).
Solvent Savings
Waste Savings
TOTAL
TOTAL SOLVENT SAVINGS
(Sludge @ 20%)
Cost $
Gals. Savings
6,012
2.912
8,924
$36,708
$14.117
$50,825
Reduce by 40% to:
Reclaim Reduce Another 30%:
Total Reduction of:
9,016 Gals/Yr Total Solvent
-2.912 Gals/Yr
6,104 Gals/Yr
8.924 Gals = 59.4%
15,028 Gals
TOTAL DOLLAR SAVINGS
Solvent Saving from 40% Reduction: $36,708
Projected Waste Savings:
Subtotal
$14.117
$50,825
Solvent Reclaimed Value:
Total
$17.721
$68,546
Dollar Savings:
$68.546 = 74.7%
$91,766
25
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(5 PERCENT SLUDGE).
TOTAL SOLVENT SAVINGS
(Sludge @ 5%)
Cost/
Gals. f$^ Savings ($)
Solvent Savings 6,012 36,708
Waste Savings 4.212 19.620
TOTAL 10,224 56,328
Solvent Consumption Reduced by 40%: 9,016 Gals/Yr
Reclaim Solvent from Waste: -4.212 Gals/Yr
Gals. Needed for the Coming Year: 4,804 Gals/Yr
Total Solvent Reduction = 10.224 Gals. = 68%
15,028 Gals.
TOTAL DOLLAR SAVINGS
Solvent Savings from 40% Reduction: $36,708
Projected Waste Savings: +19.620
SUBTOTAL: $56,328
Solvent Reclaim Value: +25.983
$82,311
Dollar Savings = $82.311 = 89.7%
$91,766
28
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29
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B. SURVEY OF TINKER AFB DEGREASERS
i - |
1. Cooper Open-Top Degreaser N-37 f
i * •
Solvent: Perchloroethylene ; :
Suggestions:
a. Use a steam condensate return pump to return the steam condensate
instead of using the steam pressure to return the condensate to the boiler. The use of
excessive steam pressure results in boiling the solvent faster, but not hotter. This results in
higher solvent emission loss in the range of 7-15 percent.
b. If this machine is to be used in this area continuously, door strips or
welder strips should be hung in the doorway or around the degreaser to reduce the drafts.
c. The cold trap was iced up. It would help to raise the temperature of the
refrigeration unit to 0° or 20°F. This would decrease the volume of water condensing into the
degreaser. •
d. The water separator was nonfunctional. It contained approximately 3
inches of water which needed to be expelled immediately. This can be accomplished by
restricting the solvent flow back into the degreaser by installing a needle valve in the exit
line. By use of the needle valve, the solvent flow can be reduced to raise the solvent level to
a quarter or half-inch below the center line of the water drain outlet. The water drain spigot
would be left open all the time so the water could be drained constantly into a 5-gallon open
container. By law (the Clean Water Act), you cannot allow any of the water to fall on the
ground or contaminate the ground water. The other way the water from the top of the water
separator can be removed is to siphon the water layer off daily.
e. Lower the hoist speed to 2 linear feet per minute. Holding your hoist
speed in the range of 2 to 8 linear feet per minute can decrease solvent losses by 7-27
percent. The lower the speed, the lower the solvent emissions.
f. Make sure your cooling water is coming in at the bottom of your
condensing coils. This prevents condensation of water. To get the desired effect, the cooling
water must exit from the top of the coil.
g. Keep degreaser covered when idling or not in operation. This unit was
covered properly while in the idling mode.
h. Have operators use the stop-and-go technique. This technique can
decrease solvent consumption by 12-27 percent
30
-------
i. Use a smaller work basket, so it takes up only 50 percent of the
freeboard area. This will decrease the plunger effect and greatly lessen solvent loss due to
plunging, chimney, and drag-out effects. Using a properly sized workload basket can
contribute to a savings of solvent from 10-20 percent.
2. Open-Top Degreaser U-45
Solvent: Perchloroethylene
This machine was expelling abnormally high vapor fumes which appeared to be
the result of situations described below. These suggestions were made:
a. Heat balance: Excessive heat input. Degreaser should operate on 45-
50 psi. See item a on degreaser N-37 regarding installing steam condensate return pump.
b.. It appeared that there was also a water flow problem through the
condensing coils and water jacket. Possibility of Penn Control valve not properly adjusted or
malfunctioning. The exit water was so hot that you could not hold your hand on the pipe.
Entrance water should be between 50°-60°F. and exit water between 90°-100°F. Probably
good reason for having a water chiller and a closed-loop cooling system.
c. The condensation troughs were backed up, which could be a result of
over-heating, partial plugging of the drain lines from the degreaser or water separator, a valve
partially closed in the solvent return line, or a combination of these possibilities.
d. It would also be a good idea when you need to replace the condensing
coils to use at least 1/2 - 5/8 inch diameter coils for better vapor control.
e. Refer to item e, degreaser N-37 (Hoist speed).
f. Refer to item h, degreaser N-37 (Stop-and-Go technique).
3. Delta Open-Top Degreaser HA-49.4
Solvent: Perchloroethylene
Suggestions:
a. Heat balance overheating: see item a, degreaser N-37. Steam pressure
should be about 45-50 psi.
b. Coil trap was frosted: refer to item c, degreaser N-37.
31
-------
c. Water separator nonfunctional: check to see if water drain spigot is
open and if solvent level is within 1/4 to 1/2 inch of the center line of the spigot. Refer to
item d, degreaser N-37.
d. Check Hoist speed. Refer to item e, degreaser N-37.
e. Condensing water: refer to item f, degreaser N-37.
f. See item i, degreaser N-37 (basket size).
g. Stop-and-Go technique: refer to item h, degreaser N-37.
h. Keep degreaser covered: refer to item g, degreaser N-37.
4. Ramaco Open-too W-65
Solvent: 1,1,1-Trichloroethane.
Suggestions:
a. Incorporate a water chiller to give year-around water at 50°F. This will
give you a closed loop. The closed loop will alleviate your internal water recycle problem.
b. Install a steam condensate return pump: refer to item a, degreaser N-37.
c. Water separator nonfunctional: refer to item d, degreaser N-37.
d. Hoist speed: refer to item e, degreaser N-37.
e. Change water inlet to bottom of condensing coil. Refer to item f,
degreaser N-37.
f. Keep degreaser covered when idling or not in operation. The unit was
properly covered at time of inspection.
g. Stop-and-Go technique: refer to item h, degreaser N-37.
5. Phillips Open-Top R-35
Solvent: 1,1,1-Trichloroethane
Suggestions:
32
-------
a. Unit was being overheated. Use steam condensate return pump (refer to
item a, degreaser N-37) so that the steam pressure can be reduced to 3-4 psi or lower steam
' pressure. ;
b. Water separator was not functioning: refer to item d, degreaser N-37.
c. There is a problem with solvent backup in the condensation trough.
Refer to item c, degreaser U-45.
d. Water was noted floating in the condensation trough. This could be due
to a water leak in the condensing coil or the result of water picked up from the atmosphere
separating in the trough because the trough is not emptying properly.
e. Again, good candidate for a water chiller to prevent having to use
excess steam pressure. Refer to item b, degreaser U-45.
f. Check to see that inlet cooling water is coming in at bottom of
condensing coil. Refer to item f, degreaser N-37.
g. The plastic cover was in place, but had numerous holes in the top.
«
h. Check the hoist speed. It should not be greater than 2-3 linear feet per
minute. Refer to item e, degreaser N-37.
i. Have operators use Stop-and-Go technique. Refer to item h,
degreaser N-37.
6. Ramaco Open Top Degreaser N-58
Solvent: 1,1,1-Trichloroethane
This machine was in good condition but needed the following adjustments to
reduce solvent emission:
a. Install steam condensate return system. Refer to item a, degreaser N-37.
This unit can normally operate on 1 to 1-1/2 psi.
b. Use a water chiller: refer to item a, degreaser W-65.
c. Hoist speed: refer to item e, degreaser N-37.
d. Water separator was nonfunctional: refer to item d, degreaser N-37!
This machine had its top in place at time of inspection.
33 ;
-------
SECTION VH
CONCLUSIONS AND RECOMMENDATIONS
Recovery by purification and distillation and in-situ filtration are practical options to
extend the effective working lifetime of metal-cleaning and degreasing solvents when used in
conjunction with a program to monitor levels of protective additives and maintain additive
protection above critical thresholds. Refinement of operating technique and aggressive
maintenance policies can decrease the rate of loss of solvent from degreasing baths.
Refinement of in-situ purification technology and implementation as a field test is
recommended. As part of a quality control program, degreaser operators should be retrained
at regular intervals, with unscheduled evaluations of operating technique on the line and of
maintenance status of the degreasing baths performed. '
34
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REFERENCES
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