SEPA
United States
Environmental Protection
Agency
Office of Research and
Development
Washington DC 20460
EPA/625/R-93/016
February 1994
Guide to Cleaner
Technologies
Alternatives to Chlorinated
Solvents for Cleaning and
Degreasing
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EPA/625/R-93/016
February 1994
GUIDE TO
CLEANER TECHNOLOGIES
ALTERNATIVES TO
CHLORINATED SOLVENTS
FOR CLEANING AND DECREASING
Office of Research and Development
United States Environmental Protection Agency
Cincinnati, Ohio 45268
Printed on Recycled Paper
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NOTICE
This material has been funded wholly or in part by the United States Environmen-
tal Protection Agency under Contract No. 68-CO-0003, Work Assignment 3-49, to
Battelle. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
This Guide to Cleaner Technologies: Alternatives to Chlorinated Solvents for
Cleaning and Degreasing has been subjected to U.S. Environmental Protection
Agency peer review and administrative review and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency.
This document is intended to provide alternatives to chlorinated solvents for
pollution prevention in cleaning and degreasing processes. Site-specific selec-
tion of a technology will vary depending on shop and manufacturing process
applications. It is the responsibility of individual users to make the appropriate
application of these technologies. Compliance with environmental and occu-
pational safety and health laws is the responsibility of each individual business
and is not the focus of this document.
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FOREWORD
Today's rapidly developing and changing technologies and industrial products
and practices frequently carry with them the increased generation of materials
that, if improperly dealt with, can threaten both public health and the environ-
ment. The U.S. Environmental Protection Agency (EPA) is charged by Congress
with protecting the Nation's land, air, and water resources. Under a mandate of
national environmental laws, the agency strives to formulate and implement
actions leading to a compatible balance between human activities and the ability
of natural systems to support and nurture life. These laws direct the U.S. EPA to
perform research to define our environmental problems, measure the impacts,
and search for solutions.
Reducing or eliminating the utilization or generation of hazardous material at the
source or recycling these solvents on site is one of EPA's primary pollution
prevention goals. Economic benefits to industry may also be realized by reduc-
ing disposal costs and lowering the liabilities associated with hazardous waste
disposal.
Publications in the U.S. EPA series, Guides to Pollution Prevention, provide an
overview of several industries and describe options to minimize waste in these
industries. Their focus is on the full range of operations in existing facilities.
Many of the pollution prevention techniques described are relatively easy to
implement in current operations without major process changes.
This Guide to Cleaner Technologies: Alternatives to Chlorinated Solvents for
Cleaning and Degreasing summarizes information collected from U.S. Environ-
mental Protection Agency programs, peer-reviewed journals, industry experts,
vendor data, and other sources. The cleaner technologies are categorized as
commercially available or emerging. Emerging technologies are technologies
that are in various stages of development, and are not immediately available for
purchase and installation. For each technology, the Guide addresses its pollution
prevention benefits, operating features, application, and limitations. Elimination
or reduction in the use of chlorinated cleaning and degreasing solvents is the
main focus of the technologies covered in the Guide.
in
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ACKNOWLEDGMENTS
This Guide was prepared under the direction and coordination of Douglas
Williams of the U.S. Environmental Protection Agency (EPA) Center for Environ-
mental Research Information and Paul Randall of the U.S. EPA Risk Reduction
Engineering Laboratory (RREL), both located in Cincinnati, Ohio. Battefle
compiled and prepared the information used for this Guide.
The following people provided significant assistance in reviewing the guide and
making suggestions: Elliott Berkihiser, Boeing Environmental Affairs Office,
Seattle, Washington; Charles Darvin, U.S. EPA, Organics Control Branch,
Research Triangle Park, North Carolina; Larry Hagner and Bob Pfahl, Motorola,
Inc., Advanced Manufacturing Technology Department, Arlington Heights, Illinois;
Duryodhan Mangaraj, Battelle, Polymer Center, Columbus, Ohio; Kenneth R.
Monroe, Center for Aerosol Technology, Surface Cleaning Technology Consor-
tium, Research Triangle Park, North Carolina; Stephen P. Risotto, Center for
Emissions Control, Washington, D.C.; Johnny Springer and Garry Howell, U.S.
EPA, RREL, Pollution Prevention Research Branch, Cincinnati, Ohio; and Katy
Wolf, Institute for Research and Technical Assistance, Santa Monica, California.
IV
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CONTENTS
Notice ii
Foreword Hi
Acknowledgments iv
Section 1. Overview 1
What Is Cleaner Technology? 1
Why Clean and'Degrease? 1
Solvents and Cleaners 3
Pollution Problem 3
Potential Solutions 4
What's In This Guide? 4
Other Questions Affecting Investment Decisions 4
Who Should Use This Guide? 4
Keywords 5
Summary 5
Reference 5
Section 2. Available Technologies 6
How to Use the Summary Tables 6
Aqueous Cleaners .>» 11
Semi-Aqueous Cleaners 15
Petroleum Hydrocarbons 18
Hydrochlorofluorocarbons (HCFCs) 19
Miscellaneous Organic Solvents 22
Supercritical Fluids 25
Carbon Dioxide Snow 28
Section 3. Emerging Technologies 31
How to Use the Summary Tables 31
Catalytic Wet Oxidation Cleaning 33
Absorbent Media Cleaning 33
Section 4. Pollution Prevention Strategy 35
References 36
Section 5. Cleaner Technology Transfer Considerations 37
Reference 41
Section 6. Information Sources 42
v
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FIGURES
Figure 1. Phase diagram for pure CO2 25
Figure 2. Pressure-density diagram for pure CO2;
temperature in °C; cp = critical point 26
TABLES
Table 1. Properties and Characteristics of Chlorinated Solvents 2
Table 2. Available Technologies for Alternatives to Chlorinated
Solvents for Cleaning and Degreasing: Descriptive Aspects 7
Table 3. Available Technologies for Alternatives to Chlorinated
Solvents for Cleaning and Degreasing: Operational Aspects 9
Table 4. Hydrophilic-Lipophilic Balance Ranges and Applications
of Surfactants 11
Table 5. Physical Properties of CFC-113 and HCFCs 20
Table 6. Properties of Miscellaneous Organic Solvents 22
Table 7. Typical Operating Conditions for Supercritical CO2 Cleaning 27
Table 8. Emerging Technologies for Alternatives to Chlorinated
Solvents for Cleaning and Degreasing: Descriptive Aspects 32
Table 9. Emerging Technologies for Alternatives to Chlorinated
Solvents for Cleaning and Degreasing: Operational Aspects 32
Table 10. Trade Associations and Technology Areas 42
VI
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SECTION 1
OVERVIEW
What Is Cleaner Technology?
A cleaner technology is a source reduction or recycling
method applied to eliminate or significantly reduce
hazardous waste generation. Source reduction in-
cludes product changes and source control. Source
control can be further characterized as input material
changes, technology changes, or improved operating
practices.
Source mduction precedes recycling in the
P&Mtott prevention snovtf emphasize
^^d^m^^^^^n^^^mfmyj -
ding, but, if source redaction technologies
approach to reducing waste generation,
fb&efo®, my#(n&$hwt
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Table 1. Properties* and Characteristics of Chlorinated Solvents
Physical Properties
and Characteristics
Ozone-Depleting Potential (ODP)b
Photochemical Reactivity (RCRA-listed)
Molecular Weight (grams per mole)
Boiling Point (°C)
Density (g/cm3)
Surface Tension (dyne/cm)
Kauri-Butanol Valued
Vapor Pressure (mm Hg)
OSHA PEL 8-hr TWA (ppm)
Flash Point (°C)
CFC-113
CCLFCCIF,
0.8
No
187.4
47.6
1.56
17.3
31
285
1000
None
TCA
CHSCCI3
0.1
No
133.5
72-88
1.34
25.4
124
100
350
None
TCE
CHCICCL,
—
Yes
131.4
86-88
1.46
29.3
130
58
50
None
PERC
CCI2CCIS
—
Yesc
165.9
120-122
1.62
31.3
91
14
25
None
METH
CH2CL
—
—
84.9
40
1.33
N/A
132
350
500'
None
•Applicable at25°C.
bODP relative to CFC-11, which is 1.0.
c PERC is not photochemically reactive, but it is not exempt under the Clean Air Act.
" Value expresses the solvency of the solvent for Kauri rosin; higher values correspond to higher solubility.
• The Occupational Safety and Health Administration (OSHA) has proposed lowering the PEL of METH to 25 ppm or lower (U.S. Department
of Labor, 1991).
• Metal finishing
• Airframe manufacturing
• Automotive manufacturing
• Machine parts manufacturing
• Electronics manufacturing and assembling
• Glass fabrication and finishing
• Repair, overhaul, and equipment maintenance.
Because there is no universal definition of "clean,"
process developers must adopt their own criteria for
judging cleanliness using methods that meet their
individual needs. Underestimating the level of cleanli-
ness required for a particular application may lead to a
loss of product performance or quality, while overesti-
mating may cause time, energy, and materials to be
wasted. As a working definition, "clean" is usually the
level of cleanliness required for any of the following to
occur:
• Mechanical devices function according to design
specifications
• Electronic or electrical devices perform reliably
over their expected service lifetimes
• Organic coatings adhere properly to a substrate
• Product finish meets performance and appear-
ance criteria.
Traditionally, chlorinated hydrocarbon solvents have
been used to remove oils, fats, waxes, and other
organics from surfaces. Chlorinated solvents have
been widely used until recently because they are very
effective cleaners and are safe to workers because
they are nonflammable. The solvents most commonly
used are 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-
113); 1,1,1-trichloroethane (TCA; also called methyl
chloroform, or MCF); trichloroethylene (TCE);
tetrachloroethylene (also called perchloroethylene, or
PERC); and dichloromethane (also called methylene
chloride, or METH). Some properties and characteris-
tics of these solvents are described in Table 1.
Traditionally, three methods have been used for
cleaning and degreasing:
• Vapor degreasing
• Cold cleaning
• Spot cleaning.
In vapor degreasing, a solvent is heated to its boiling
point so that vapor is created which can then contact
parts suspended above the liquid surface. The vapor
condenses on the cooler parts, dissolves the contami-
nants and flushes the liquid mixture back into the hot
liquid. Vapor rising past the parts is condensed by a
cooling jacket that slows the eventual loss of solvent to
the atmosphere. Because the contaminants usually
have higher boiling points than the solvent, the vapor
itself remains relatively pure. The cleaning process is
complete when the parts warm up and vapor no longer
condenses on them. Then the parts are removed and
they quickly dry in air, due to the high vapor pressure of
the solvents.
Process time for vapor degreasing usually is about 10
minutes; however, additional time would be needed for
loading and unloading parts. CFC-113, TCA, TCE, and
PERC are commonly used in vapor degreasing.
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Cold cleaning generally is performed in a tank
containing TCAor CFC-113 at room temperature. The
components to be cleaned are usually agitated me-
chanically or ultrasonically. The primary disadvantage
of cold cleaning compared with vapor degreasing
is that its cleaning performance degrades with use
because the solvent becomes "loaded" with dissolved
contaminants.
Spot cleaning refers to localized cleaning of a work-
piece. A typical method of spot cleaning is to use a lint-
free cloth saturated with solvent. Spot cleaning is
commonly used in repair operations, for example, to
remove solder flux residue after replacing an electronic
component on a circuit board or to remove a small
amount of lubricant on a mechanical device. Methylene
chloride, CFC-113, and TCAare commonly used in
spot cleaning. In spot cleaning, 'excess solvent is
allowed to evaporate from the workpjece. Clean solvent
typically is kept in a closed container to prevent unnec-
essary loss.
Solvents and Cleaners
A solvent could be defined as any substance that can
dissolve another substance. For example, pure water is
a solvent for many polar and ionic compounds. Petro-
leum hydrocarbons are good solvents for many nonpo-
lar organic compounds. In most of the industrial trade
literature the term solvent refers to nonaqueous
substances, whereas the term cleaner refers to sub-
stances that use water. Cleaners are water-based and
generally contain additives that allow them to remove
contaminants. These conventions generally are ad-
hered to in this Guide.
Ct&zmrs dean toy displacing, dissolving,
or chemfcaftystteFing a, c&ni&fnfnajjt.
Cleaning and degreasing can be grouped broadly as
being chemical, electrochemical, or mechanical in
nature. The chemical properties possessed by a
cleaner or solvent determine whether the cleaner or
solvent acts by displacing, dissolving, or in some way
chemically altering the contaminant on a substrate and
hence causing its removal. Cleaners and solvents are
designed to implement one or more of these mecha-
nisms, depending on the nature of the contaminant to
be removed. Details about these chemical mechanisms
are given in Sections 2 and 3 along with general
descriptions of various cleaner and solvent compo-
nents.
Electrochemical methods often are employed prior to
electroplating and consist of applying a current (direct,
reverse, or periodic) through a workpiece. Water
decomposition causes small bubbles of hydrogen
(direct) or oxygen (reverse) to form at the metal surface
and helps to lift away contaminant particles. The metal
itself usually is immersed in an alkaline solution to
increase electrical conductivity and to maximize
cleaning performance.
Mechanical methods control fluid impingement on a
surface and vary considerably with the type of process
equipment being used. Some form of mechanical
energy almost always is used to enhance the chemical
or electrochemical cleaning process. Simple agitation,
air sparging, turbulent flow, spraying, and ultrasonic
action are typical methods used to enhance cleaner
performance. (See U.S. EPA companion publication,
Guide to Cleaner Technologies: Cleaning and Degreas-
ing Process Changes.) The bulk physical properties of
a cleaner or solvent also affect the cleaning process by
determining how a liquid interacts with a surface. For
example, surface tension affects a fluid's ability to
penetrate small spaces such as cracks and holes as
well as getting between the contaminant and substrate
to help displace the contaminant.
Pollution Problem
In the 1970s, it was realized that some chlo-
rofluorocarbons (CFCs) undergo chemical changes in
the upper atmosphere that subsequently lead to the
destruction of stratospheric ozone. It is this "ozone
layer" that filters out much of the sun's harmful ultravio-
let radiation. For this reason, the world community has
since sought to eliminate production and use of CFCs.
According to the Montreal Protocol on Substances That
Deplete the Ozone Layer, signed in 1987 by 45 nations
including the United States, agreements were made to
restrict the production and use of ozone-depleting
chemicals. The Montreal Protocol and its London
Amendments (1990) led to further changes in the U.S.
Clean Air Act, which was amended by President Bush
on November 15, 1990. The Clean Air Act Amendments
(CAAA) established a time frame to eliminate all fully
halogenated CFCs, certain chlorinated hydrocarbons,
and hydrochlorofluorocarbons (HCFCs).
Ctess
must be phased out by
In November 1992, the participating countries voted to
advance the deadline for phasing out ozone layer-
depleting substances (OLDS Class I) to January 1,
1996. The OLDS Class I list includes CFCs and halons,
among which are CFC-113 and TCA, which are the
substances most important to cleaning. Under the
agreement, countries are allowed to seek exemptions
for essential uses for which no technically feasible
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alternatives are available. EPA has petitioned for
mete red-dose inhalers for medical purposes and for 4
other small-use needs. The expected ban on Class II
OLDS, which includes the HCFCs, is between 2020
and 2040 or earlier, as stipulated by the London
Amendments to the Montreal Protocol.
Potential Solutions
Cleaner technologies now exist or are being developed
that would reduce or eliminate the use of CFC-113 and
TCA for many cleaning and degreasing operations.
There are two main strategies in developing cleaner
technologies:
• Alternative cleaning and degreasing sub-
stances that are non-ozone depleting or have
lower ozone depletion potentials; are nonhazard-
ous (measured by Occupational Safety and
Health Act [OSHA] and National Institute of
Safety and Health [NIOSH] criteria); have low
toxicities, low odor, and high flash points; pro-
duce low emissions of volatile organic com-
pounds (VOCs); and are effective for removing
contaminants.
• Process changes that use different technologies
for cleaning or that eliminate the need for clean-
ing.
This Guide is concerned with the first strategy, alterna-
tive cleaning and degreasing substances. A discussion
of process changes is given in the companion U.S.
EPA publication, Guide to Cleaner Technologies:
Cleaning and Degreasing Process Changes. Both
alternative cleaning and degreasing substances and
process changes may have limitations that should be
evaluated carefully by potential users with their specific
applications in mind.
What's In This Guide?
This application guide describes primarily chemical
alternatives to chlorinated solvents that can be used to
reduce waste in cleaning and degreasing operations.
The two main objectives of this application guide are
• To identify commercial and developing cleaning
systems and other technologies that eliminate
the use of ozone-depleting chlorinated solvents
and reduce the use of smog-producing high-VOC
solvents.
• To provide resources for obtaining more detailed
engineering information about these technolo-
gies.
The following questions are addressed:
• What alternative solvents or cleaners are avail-
able or under development that would reduce or
eliminate pollution?
• Under what circumstances might one or more of
these alternative solvents or cleaners be applica-
ble to a given operation?
• What pollution prevention, operating, and cost
benefits could be realized by adopting the new
technology?
Other Questions Affecting Investment
Decisions
Other questions affecting the decision to choose an
alternative technology include
• Might new pollution problems arise when imple-
menting cleaner technologies?
• Are tighter, more complex process controls
needed?
• Will product quality and operating rates be
affected?
• Will new operating or maintenance skills be
needed?
• What are the overall capital and operating cost
implications?
To the extent possible, these questions are addressed
in this guide. The cleaner technologies described in this
guide are applicable under different sets of product and
operating conditions. If one or more alternative solvents
and cleaners are sufficiently attractive for use as
replacements for chlorinated and high-VOC solvents,
the next step of the user is to obtain detailed engineer-
ing data from vendors of the technology in order
to perform an in-depth evaluation of the technology
potential. Section 6 provides information on trade
associations that may be helpful in obtaining technical
data. Furthermore, the user may benefit greatly by
inquiring among others in related industries who have
already implemented one of the technologies men-
tioned in this guide. Both alternative cleaning solutions
and process changes may have limitations that should
be carefully evaluated by potential users for the specific
applications.
Who Should Use This Guide?
This application guide has been prepared for plant
process and system design engineers and for person-
nel responsible for process improvement and design.
Process change descriptions within this guide allow
engineers to evaluate options so that cleaner technolo-
gies can be considered for existing plants and factored
into the design of new cleaning and degreasing opera-
tions.
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Sufficient information is presented to select one or
more candidate technologies for further analysis and
in-plant testing. The guide does not recommend any
technology over any other. It presents concise summa-
ries of applications and operating information to
support preliminary selection of cleaner technology
options for testing in specific processes. Sufficient
detail is provided to allow identification of possible
technologies for immediate application to eliminate or
reduce waste production.
The keywords given below will help you quickly scan
the available and emerging technologies covered in
this guide.
Keywords
Cleaner Technology
Pollution Prevention
Source Reduction
Source Control
Recycling
Solvent Substitute
Alternative Solvent
CFC Replacement
Cleaning/Degreasing
Metal Cleaning
Defluxing
Aqueous Cleaners
Semi-Aqueous Cleaners
Petroleum Hydrocarbons
Hydrochlorofluorocarbons (HCFCs)
Miscellaneous Organic Solvents
Supercritical Fluids
Carbon Dioxide Snow
Catalytic Wet Oxidation Cleaning
Absorbent Media Cleaning
Summary
The cleaner technologies described in this guide are
divided into two groups based on their maturity:
• Commercially available technologies—Section 2
• Emerging technologies—Section 3.
Pollution Prevention Strategy, Section 4, discusses the
impact of regulations on the potential for cleaner
technologies. The Cleaner Technology Transfer Con-
siderations, Section 5, discusses the various technical,
economic, and regulatory factors that influence the
selection and use of a cleaner technology.
Reference
U.S. Department of Labor, Occupational Safety and
Health Administration (OSHA). 1991. "Occupational
Exposure to Methylene Chloride." 29 CFR Parts
1910,1915, and 1926, Proposed Rule. Federal
Register, 56(216) :57036-57141.
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SECTION 2
AVAILABLE TECHNOLOGIES
How to Use the Summary Tables
Seven available alternatives to chlorinated solvents for
cleaning and degreasing are evaluated in this section:
• Aqueous cleaners
• Semi-aqueous cleaners
• Petroleum hydrocarbons
• Hydrochlorofluorocarbons (HCFCs)
• Miscellaneous organic solvents
• Supercritical fluids
• Carbon dioxide snow.
Tables 2 and 3 summarize descriptive and operational
aspects of these technologies. They contain evalua-
tions or annotations describing each available cleaner
technology and give users a compact indication of the
range of technologies covered to allow preliminary
identification of those technologies that may be appli-
cable to specific situations.
Descriptive Aspects
Table 2 describes each available cleaner technology. It
lists the Pollution Prevention Benefits, Reported
Application, Benefits, and Limitations of each
technology.
Operational Aspects
Table 3 shows the key qualitative operating characteris-
tics for the available materials and technologies. The
rankings are estimated from descriptions and data in
the technical literature and are based on comparisons
to the materials that these alternatives would replace.
Process Complexity is qualitatively ranked as "high,"
"medium," or "low" based on such factors as the
number of process steps involved and the number of
material transfers needed. Process complexity is an
indication of how easily the new technology can be
integrated into existing plant operations. A large
number of process steps or input chemicals, or multiple
operations with complex sequencing, are examples of
characteristics that would lead to a high complexity
rating.
possible candidate cl&aner technologies,
The Required Skill Level of equipment operators also
is ranked as "high," "medium," or "low." Required skill
level is an indication of the level of sophistication and
training required by staff to operate the new technology.
A technology that requires the operator to adjust critical
parameters would be rated as having a high skill
requirement. In some cases, the operator may be
insulated from the process by complex control equip-
ment. In such cases, the operator skill level is low but
the process complexity is high.
Table 3 also lists the Waste Products and Emissions
from the available cleaner technologies. It indicates
tradeoffs in potential pollutants, the waste reduction
potential of each, and compatibility with existing waste
recycling or treatment operations at the plant.
references, w&fom industry and trade
group* to g&t m&
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Table 2. Available Technologies for Alternatives to Chlorinated Solvents for Cleaning and Degreasing: Descriptive Aspects
Operational Benefits
Technology
Type
Pollution Prevention
Benefits
Reported
Application
Limitations
Aqueous
Cleaners
Semi-
Aqueous
Cleaners
Petroleum
Hydrocarbons
Hydrochloro-
fluorocarbons
(HCFCs)
No ozone depletion
potential
May not contain VOCs
Many cleaners
reported to be
biodegradable
Some have low vapor
pressure and so have
low VOC emissions
Terpenes. work well at
low temperatures, so
less heat energy is
required
Some types of clean-
ers allow used solvent
to be separated from
the aqueous rinse for
separate recycling or
disposal
Produce no
wastewater
Recyclable by
distillation
High grades have low
odor and aromatic
hydrocarbon content
(low toxicity)
High grades have re-
duced evaporative loss
Lower emissions of
ozone-depleting
substances than CFCs
Produce no
wastewater
Excellent for removing inorganic
and polar organic contaminants
Used to remove light oils and
residues left by other cleaning
processes
Used to remove heavy oils,
greases, and waxes at elevated
temperatures (>160°F)
High solvency gives cleaners
good ability for removing heavy
grease, waxes, and tar
Most semi-aqueous cleaners can
be used favorably with metals and
most polymers
NMP used as a solvent in paint
removers and in cleaners and
degreasers
Used in applications where water
contact with parts is undesirable
Used on hard-to-clean organic
contaminants, including heavy oil
and grease, tar, and waxes
Low grades used in automobile
repair and related service shops
Used as near drop-in re-
placements for CFC-113 vapor
degreasing
Compatible with most metals
and ceramics, and with many
polymers
Azeotropes with alcohol used in
electronics cleaning
Remove particulates and films
Cleaner performance changes with
concentration and temperature, so
process can be tailored to individual
needs
Cavitate using ultrasonics
Rust inhibitors can be included in
semi-aqueous formulations
Nonalkaline pH; prevents etching of
metals
Low surface tension allows semi-
aqueous cleaners to penetrate small
spaces
Glycol ethers are very polar solvents
that can remove polar and nonpolar
contaminants
NMP used when a water-miscible
solvent is desired
Esters have good solvent properties
for many contaminants and are
soluble in most organic compounds
No water used, so there is less
potential for corrosion of metal parts
Compatible with plastics, most
metals, and some elastomers
Low liquid surface tension permits
cleaning in small spaces
Short-term solution to choosing an
alternative solvent that permits use
of existing equipment
No flash point
Nonflammable and nonexplosive; relatively low
health risks compared to solvents; consult
Material Safety Data Sheet (MSDS) for individual
cleaner
Contaminant and/or spent cleaner may be difficult
to remove from blind holes and crevices
May require more floor space, especially if multi-
stage cleaning is performed in line
Often used at high temperatures (120 to 200°F)
Metal may corrode if part not dried quickly; rust
inhibitor may be used with cleaner and rinsewater
Stress corrosion cracking can occur in some
polymers
NMP is a reproductive toxin that is transmitted
dermally; handling requires protective gloves
Glycol ethers have been found to increase the
rate of miscarriage
Mists of concentrated cleaners (especially
terpenes) are highly flammable; hazard is
overcome by process design or by using as water
emulsions
Limonene-based terpenes emit a strong citrus
odor that may be objectionable
Some semi-aqueous cleaners can cause swelling
and cracking of polymers and elastomers
Some esters evaporate too slowly to be used
without including a rinse and/or dry process
May be aquatic toxins
Flammable or combustible, some have very low
flash points, so process equipment must be
designed to mitigate explosion dangers
Slower drying times than chlorinated solvents
The cost of vapor recovery, if implemented, is
relatively high .
Have some ozone depletion potential and global
warming potential
Incompatible with acrylic, styrene, and ABS
plastic
Users must petition EPA for purchase, per
Section 612 of CAAA
(continued)
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Table 2. (Continued)
Technology
Type
Pollution Prevention
Benefits
Reported
Application
Operational Benefits
Limitations
Miscellaneous
Organic
Solvents
Supercritical
Fluids (SCFs)
oo
Carbon
Dioxide
Snow
Do not contain
halogens, so they do
not contribute to ozone
depletion
Most are considered
biodegradable
Generate no waste-
water when used
undiluted
Nonpolluting when CO2
is used as the super-
critical fluid
Generate no
wastewater
Use natural or
industrial sources of
COj, so no net
production of carbon
No polluting emissions
released
Replaces CFCs and
solvents
Does not generate
wastewater
Uses natural or indus-
trial sources of COZ,
so no net production of
CO2 occurs
Carries contaminants
away in a stream of
inert CO,
Most are used in small batch
operations for spot cleaning
Remove organic contaminants of
moderate molecular weight and
low polarity
Precision clean instrument
bearings, electromechanical
assemblies, direct access storage
devices, optical components,
polymeric containers, porous
metals, ceramics
Low viscosity and high diffusivity
permit cleaning in very small
cracks and pore spaces
Cleans critical surfaces on
delicate fiber optic equipment
Cleans radioactive-contaminated
components
Used in hybrid circuits to remove
submicron particles
Used on the largest, most
expensive telescopes
Removes submicron particles and
light oils from precision
assemblies
Removes light fingerprints from
silicon wafers and mirrors
Prepares surfaces for surface
analysis
Alcohols are polar solvents and are
good for removing a wide range of
inorganic and organic contaminants;
soluble in water and may be used to
accelerate drying
Ketones have good solvent
properties for many polymers and
adhesives; they are soluble in water
and may be useful for certain rapid
drying operations
Vegetable oils are used to remove
printing inks and are compatible with
most elastomers
Lighter alcohols and ketones have
high evaporation rates and therefore
dry quickly
Compatible with metals, ceramics,
and polymers such as Teflon™,
high-density polyethylene, epoxies,
and polyimides
No solvent residue left on parts
May be very useful for cleaning
oxygen equipment
Solvent properties can be altered by
adding a cosolvent
Generates no media waste, thus no
media disposal cost
Does not create thermal shock
Is nonflammable and nontoxic
Noncorrosive
Leaves no detectable residue
Can penetrate narrow spaces
and nonturbulent areas to
dislodge contaminants
Adjustable flake size and intensity
More effective than nitrogen or air
blasting
Can clean hybrid circuits without
disturbing the bonding wire
Most evaporate readily and therefore contribute to
smog
Alcohols and ketones have low flash points and
present a fire hazard
Inhalation of these solvents can present a health
hazard
Some have vapor pressures that are too high to
be used in standard process equipment
MEK and MIBK are on EPA list of 17 substances
targeted for use reduction
Cosolvents used to improve the solvent power of
CO2 may have a pollution potential
Danger of a pressure vessel explosion or line rup-
ture
Cause swelling in acrylates, styrene polymers,
neoprene, polycarbonate, and urethanes
Components sensitive to high pressures and
moderate temperatures should not be cleaned by
SCF methods
Ineffective in removing inorganic and polar
organic contaminants; for example, does not
remove fingerprints
CO2 must be purified
Requires avoidance of long dwell times
Particulates such as sand may be carried by the
gas stream and scratch the surface
Heavier oils may require the addition of chemicals
and heat to be completely removed
-------
Table 3. Available Technologies for Alternatives to Chlorinated Solvents for Cleaning and Degreasing: Operational Aspects
Technology
Type
Aqueous
Cleaners
Process
Complexity
Medium
Required
Skill Level
Medium
Waste Products
and Emissions
• Skimmed oil; filter-
trapped participates
and greases; waste-
water and detergent
Cleaner Cost
per Gallon
$6-10; typical
dilutions range
from 1:3 to 1:9
Energy
Use
Medium — temperature
control, mechanical
control, drying
Optional Post-Cleaning
Operations
• Rinsing— Some cleaners
may leave a residue; to
facilitate removal use DI
water and/or alcohol
• Drying — May be acceler-
ated by blowing with hot air
or nibbing with absorbent
material; automated dryers
are available
References
Gavaskaretal., 1992
Monroe etal., 1993
Munie, 1991
Murphy, 1991
Polhamus, 1991
Ross and Morrison, 1988
U.S. EPA, 1991a, b,c
Weltman and Evanoff,
1992
Semi-
Aqueous
Cleaners
Medium
Petroleum Low
Hydrocarbons
to
Hydrochloro Low
fluorocarbons
(HCFCs)
Medium • Waste terpene con-
taining mostly organic
material and aqueous
part containing mostly
inorganic material;
filters trap particu-
lars, grease, and
non-emulsified oil
Medium • Produce no waste-
water when used
undiluted. VOCs are
emitted; waste solvent
incinerated as fuel or
recycled by distillation
Medium • Still bottoms; contam-
inated solvent; HCFCs
emitted to air unless
closed-loop system is
used
$10-20; typical
dilutions range
from none to 1
$1-3 for kerosene
and mineral spirits;
$7-12 for metal
cleaning formula-
tions; up to $30 for
some specialty and
electronic cleaning
formulations; most
often used without
water
$30-35
Low—mechanical
control, drying
Low—mechanical
control, drying
High—maintain boiling
temperature; run primary
and possibly secondary
condensing systems
Cleaners may leave residue
that is slow to evaporate;
water rinse may be required
Drying may be needed if a
water rinse is used; rinsing
with alcohol will speed
drying
Parts may be dried by
forced air or by some other
method
None
Damall et al., 1976
Hill and Carter, 1993
IPC, 1990
National Toxicology
Program, 1990
U.S. EPA. 1991a, b, c
U.S. EPA, 1993
IPC, 1990
U.S. EPA, 1991a. b
Basu etal., 1991
Finegan and Rusch,
1993
Kitamura et al., 1991
U.S. EPA, 1991 a, b
(continued)
-------
Table 3. (Continued)
Technology Process Required Waste Products
Type Complexity Skill Level and Emissions
Cleaner Cost
per Gallon
Energy
Use
Optional Post-Cleaning
Operations
References
Miscellaneous Low
Organic
Solvents
Supercritical High
Fluids
Low
High
Carbon Medium
Dioxide Snow
Medium
Waste solvents
Contaminants are
condensed in a vessel
CO2 gas may be
vented to the
atmosphere or purified
and reused
Solid coating residue
waste
Airborne particulates
CO2gas
$2-20
Cost of highrpurity
CO2 (about 7*/lb)
is insignificant
compared to
installation cost
Cost of welding
grade CO is about
70/lb
Low—primarily suited
for small scale and local
cleaning
Low—Energy is required
to operate pumps to
perform supercritical
cleaning
Medium—
• Carbon dioxide liquefter
• Refrigeration unit
• Compressed gas sup-
ply to propel blasting
media
• Requires current
between 8 and
14.5 amps
• Requires voltage
between 115 and
230V
Vegetable oil cleaning
requires a secondary
cleaning step
Remove part from pressure
vessel
Requires dry air stream or
chamber to prevent water
condensation while parts are
cold
Burow, 1993
Environmental Program
Office, 1991
Hill and Carter, 1993
U.S. EPA, 1991a. b
Airco Gases, N.D.
Gallagher and Krukonis,
1991
Lira, 1988
Salerno, 1990
Schneider, 1978
U.S. EPA, 1991
Woodwell, 1993
Hoenig, 1990
Layden and WacKow,
1990
Sherman and Whitiock,
1990
Whitiock, 1989
Zito, 1990
-------
The Optional Post-Cleaning Operations column
summarizes additional rinsing, drying, or other opera-
tions that may be needed following cleaning or de-
greasing. These are noted to indicate special
considerations in the application of the cleaner technol-
ogy.
The last column in Table 3 lists References to publica-
tions that will provide further information for each
alternative. These references are given in full at the
end of the respective available technology sections.
The text further describes the pollution prevention
benefits, reported application, operational benefits, and
limitations for each technology. Technologies in earlier
stages of development are summarized to the extent
possible in Section 3, Emerging Technologies.
Aqueous Cleaners
\ t
Pollution Prevention Benefits
The primary pollution prevention benefit of aqueous
cleaners is that they are non-ozone depleting and may
not contain VOCs. Aqueous cleaners that are nonhaz-
ardous initially remain so unless they become contami-
nated with hazardous materials during cleaning
operations. In some cases, spent cleaner can
be treated to remove contaminants, which may allow
them to be discharged to sewers, provided that the
effluents meet local discharge requirements.
How Do They Work?
Aqueous cleaners are mixtures of water, detergents,
and other additives that promote the removal of organic
and inorganic contaminants from hard surfaces. Each
component of an aqueous cleaner performs a distinct
function and affects the way the contaminant is re-
moved from a substrate.
Surfactants, or "surface action agents," provide
detergency by lowering surface and interfacial tensions
of the water so that the cleaner can penetrate small
spaces better, get below the contaminant, and help lift
it from a substrate. Surfactants may be cationic,
anionic, or nonionic in nature. These terms refer to the
aqueous phase properties of their hydrophilic portions
(see below). The anionic and nonionic types most often
are used in immersion cleaning; nonionic surfactants
have lower foam-producing characteristics and are
preferred in applications where agitation is used.
Nontonte surfactants arepmfofredtn
Surfactants are characterized empirically by their
hydrophilic-lipophilic balance (HLB), which describes a
relationship between their water-soluble (hydrophilic)
and oil-soluble (lipophilic) portions. Oil-soluble surfac-
tants have low HLB values and highly water-soluble
surfactants have high HLB values. Typical HLB ranges
and applications of surfactants are shown in Table 4.
Table 4. Hydrophilic-Lipophilic Balance Ranges and
Applications of Surfactants
HLB Value
Application
3.5-6
7-9
8-18
13-15
15-18
Water-in-oil emulsifier
Wetting agent
Oil-in-water emulsion
Detergent
Solubilizer
Source: Ross and Morrison, 1988.
In the category of anionic surfactants, sulfosuccinates
are commonly used as wetting agents, whereas long-
chain su If o nates, fatty alcohol sulfates, and alkali soaps
are used as emulsifiers. Among the nonionic surfac-
tants, ethoxylated alkylphenols are used as wetting
agents and emulsifiers, while glycol ethers
(Cellosolves™) and ethylene oxide condensates of
alkylphenols are used as emulsifiers (Ross and
Morrison, 1988).
In addition to HLB, Monroe et al. (1993) describe the
utility of surfactant chain length ethylene oxide/propy-
lene oxide content, cloud point, and critical micelle
concentration in selecting surfactants for aqueous
cleaning. Another important surfactant selection factor
is emulsion stability, which depends on a complex
interaction of properties such as droplet size, interfacial
viscosity, repulsion terms, and internal volume (Ross
and Morrison, 1988).
in
w&ter.
Oil-in-water emulsifiers cause water-immiscible con-
taminants, such as oil or grease, to become dispersed
in the water. This kind of emulsification can be accom-
plished by surfactants with moderate to high HLB
values. Many kinds of surfactants are used as emulsifi-
ers in aqueous cleaners; however, users should be
aware that some are hazardous and should note OSHA
or NIOSH exposure limits on the Material Safety Data
Sheet (MSDS) provided with the product. Examples of
hazardous components found in some aqueous
cleaners are 2-butoxyethanol (or ethylene glycol butyl
ether; CAS#11 1-76-2), 2-ethoxyethanol (or ethylene
glycol ethyl ether; CAS#1 10-80-5), and dipropylene
glycol methyl ether (CAS#34590-94-8). Oil-in-water
emulsifiers are most useful when a small amount of
11
-------
contaminant is present so that the cleaner does not
become "loaded" too quickly. Oil-in-water emulsifiers
are undesirable in situations where a large amount of
oil is to be removed. In cleaning situations where the oil
content is high, a better methodology is to rely on the
oil's natural immiscibility with water and allow separa-
tion^ occur so that the lighter fractions can be
skimmed off the top and the heavier fractions can be
removed by filtration. The volume of waste generated is
greatly reduced using this kind of phase separation
technique, and the lifetime of the cleaner is thereby
extended.
affect cleaning performance, the cleaner may require
maintenance to restore its chemical balance.
Chemicals added to help maintain the dispersion of
contaminant particles in the cleaning medium are
known as deflocculants. Deflocculants may be anionic
or nonionic surfactants, or they may be inorganic salts
such alkali phosphates. Because many emulsions
remain stable only at elevated temperatures and under
alkaline conditions, separation of the oily fraction from
the aqueous cleaner often can be induced in emulsion-
type aqueous cleaners by lowering the temperature
and, sometimes, by acidifying the bath. Individual
manufacturers can provide information on their specific
oil separation techniques.
Sapofiiffers formsGaps.
Saponifiers are compounds that react chemically with
oils containing fatty acids to form soaps. Vegetable oils
and animal fats (triglycerides) are examples of sub-
stances that can be saponified by alkalis. It is common
for some contaminants in a particular kind of "soil" to be
saponifiable, whereas others are not. For example,
thickeners added to a base oil to form grease may be
saponifiable, whereas the base oil may not. Neverthe-
less, the grease is more readily removed by this kind of
chemical action. Coupled with saponifiers, surfactants
can act as wetting agents to help remove contaminants
from the surface.
The organic amines comprise an important class of
saponifiers. Organic amines can react with many
common hydrocarbon contaminants, including the
saponifiable portion of solder flux rosin (Munie, 1991).
However, users should be aware that the organic
amines are hazardous and also should note OSHA or
NIOSH exposure limits on the MSDS provided with the
product. Examples of organic amines found in some
aqueous cleaners are ethanolamine (CAS#141-43-5),
diethanolamine (CAS#11 1-42-2), and triethanolamine
(CAS#102-71-6). The organic amines range in volatility
according to molecular weight and will volatilize
(evaporate) overtime when the cleaner is used at high
temperatures. As the loss of these compounds will
atkatittity,
Alkalinity is a property of aqueous media which
describes its ability to neutralize acid. Alkalinity is not a
factor of pH alone but also is a measure of a solution's
ability to duffer itself against acid. Buffering capacity
provides stability, so that the chemical environment of
the cleaner is not subject to abrupt pH and other
chemical changes. Alkalinity also promotes detergency.
Aqueous cleaners range in alkalinity from mild alkaline
(pH 8 to 10) to high alkaline (pH 12 and higher). Mild
alkaline conditions prevent etching of most metals,
which have solubility minima in the range of pH 8 to 11 .
Two important cases where mild alkaline cleaners
should be used are aluminum and magnesium, which
are readily etched above pH 11. Mild alkalinity often is
maintained by soluble silicates, carbonates, berates,
and citrates.
In some cases, high alkalinity is desired to remove
metal oxides and hydroxides from a surface to provide
a fresh surface. Highly alkaline (caustic) cleaners are
used to prepare metal surfaces prior to plating. Typi-
cally, very high pH (>12) is achieved by adding strong
bases such as sodium hydroxide (lye) or potassium
hydroxide. Highly alkaline cleaners often are used to
remove heavy grease and oil from corrosion-resistant
steels. The hydroxide ions attack the saponifiable part
(e.g., the thickeners) of the grease and oil.
S&questettng ag&m$ assist cleaning in
fmrtf water, Otter additfv&s @ftfiafic&
draping p&ffomanee in various way$.
Sequestering agents prevent the mineral content of
hard waters (mostly waters rendered hard by calcium
and magnesium ions) from forming insoluble products
with the cleaner. The use of sequestering agents
permits the cleaner to attack only the contaminant and
ensures that lower cleaner concentrations are needed.
Common chelating agents, such as sodium EDTA,
NTA, and ODA, typically are used to sequester cations.
In all aqueous cleaners, the alkalis, deflocculants, and
sequestering agents are referred to as builders. Other
additives may be included to enhance overall cleaning
performance, for example, anti-foaming agents and
corrosion Inhibitors. Corrosion inhibitors work either
by passivating the surface through adsorption of a
molecular species onto it that will react with oxygen
before the metal can oxidize, or by forming a protective
barrier over the surface that excludes oxygen.
12
-------
Operating Features
Aqueous cleaning and degreasing can be performed
for a wide variety of applications, including those that
once were considered the domain of vapor degreasing
or cold solvent cleaning. However, some ferrous metals
may exhibit flash rusting in aqueous environments;
therefore, such parts should be tested prior to full-scale
use.
The oteaner chosen depends both on
cwtf«mals#f type antftfje fype &fpr$css$
equfctmnt Jo be its&d,
Many kinds of aqueous cleaning products are avail-
able. Thus, some investigation is required to find
cleaners that are most effective against the contami-
nants typically encountered and to find cleaners that
give the best performance with the process equipment
that will be used. Whereas solvents depend largely on
their ability to dissolve organic contaminants on a
molecular level, aqueous cleaners utilize a combination
of physical and chemical properties to remove macro-
scopic amounts of organic contaminants from a sub-
strate. Aqueous cleaning is more effective at higher
temperatures, and normally is performed above 120°F
using suitable immersion, spray, or ultrasonic washing
equipment. For this reason, good engineering practices
and process controls tend to be more important in
aqueous cleaning than in traditional solvent cleaning to
achieve optimum and consistent results.
When switching from solvent cleaning to aqueous
cleaning, users must be aware that parts usually need
to be rinsed and will remain wet for some time unless
action is taken to speed up the drying process. Three
common methods for drying parts are evaporation,
displacement, and mechanical removal (Polhamus,
1991).
T&cfmigms $xtet to speed up ovaporafim.
Evaporation of rinsewater under ambient conditions is
slow, depends on temperature and humidity, and
creates an opportunity for dust to settle onto the part. A
heat lamp can speed the process but is dependent on
orientation and still exposes the parts to air contact.
Parts can be dried in small batches in a vacuum oven.
Evaporation is improved by the technique of hot air
recirculation, in which heated air is recirculated within a
large chamber; makeup air is continuously introduced
to replenish moist air which is slowly exhausted.
Another method, called evaporative drying, passes dry
air or inert gas (to lessen the tendency for oxidation)
through a chamber to provide laminar flow past the wet
parts.
water,
Displacement methods include capillary or slow-pull
drying. With this method, a hot part is extracted slowly
from equally hot deionized water. The surface tension
of the water in effect peels the water off the part;
whatever water is left readily vaporizes. Another
displacement technique, common to metalworking,
uses oil to displace water from the part. The oil also
acts as a rust inhibitor by forming a protective barrier
between the part surface and the air. However, if the
cleaning objective is to produce a residue-free surface,
this latter option would be inappropriate.
Afec/rantcaf removal Mcktdtts btewmgand
Mechanical removal techniques also are commonly
used. Air knives blow water off the part with high-
pressure air. Centrifugal drying spins the water off.
Aqueous cleaners are available in the form of concen-
trated liquids and as powders. The concentrated liquids
cost between $6 and $1 0 per gallon, when purchased
in drum-size quantities. They are diluted 1 :3 to 1 :10
with water for most applications. The cost of powders is
equivalent when prepared to the same final concentra-
tions.
The cleaner's longevity also must be considered when
evaluating cost. Filtering to remove particulates and
skimming to remove oil will extend a cleaner's lifetime.
Other benefits of these actions include more uniform
cleaning performance and reduced disposal costs,
because the oily wastes collected can be disposed of
separately.
e&nt&mnants remwetfby aqueous
ete&ners ftomths wa&tewater fa tower
Waste disposal costs can be kept low by discharging
the bulk of the used cleaner to a sewer. In choosing an
aqueous cleaner, it must be determined whether
rinsewater can be discharged to a local sewer. If
municipal or other restrictions are in effect, the cost of
performing all required pretreatments must be consid-
ered and included in estimates of an operating budget.
It is necessary to treat the cleaner prior to disposal, if
dissolved metals can be precipitated or absorbed onto
a substrate using a number of developed technologies.
Suspended solids can be removed by small-pore filters
(10 urn or less). Emulsified oil can be separated from
the aqueous cleaner by means of coalescing equip-
ment or advanced membrane ultrafiltration techniques.
13
-------
Cleaning system equipment manufacturers should be
consulted to determine the best approach.
Application
Aqueous cleaners have been used for a long time by
metal finishers, and new products are continually being
developed for an expanding market. Primary deter-
gents are used to process buffed metals at tempera-
tures of at least 120°F. Alkaline detergent cleaners are
used to remove light oils and residues (including
solvents or other types of cleaners) left by manufac-
turing processes, shop dirt, and light scale. Alkaline
cleaners are used at elevated temperatures, ranging
from 120 to 200°F (Murphy, 1991). Field evaluations of
aqueous cleaners are available from U.S. EPA's Waste
Reduction Innovative Technology Evaluation (WRITE)
Program. For example, see Gavaskar et al. (1992).
Weltman and Evanoff (1992) discuss performance,
materials compatibility, and regeneration of aqueous
cleaners.
Benefits
The ability of aqueous cleaners to remove most
contaminants has been demonstrated in numerous
tests. Aqueous cleaners are capable of removing
inorganic contaminants, particulates, and films. They
also exhibit considerable flexibility in application
because their performance is strongly affected by
formulation, dilution, and temperature. The formulation
that gives the best results can be found through some
investigation, and the user can select the dilution factor
and temperature that give the best results.
Limitations
Health and Safety. Health risks associated with
aqueous cleaners are relatively low. However, as noted
earlier, some aqueous cleaners contain organic sub-
stances that may be hazardous. Because aqueous
cleaners are nonflammable, there is no risk of fire.
Material Safety Data Sheets (MSDSs) for individual
products should be consulted before use.
Compatibility with Materials. Metal corrosion may
occur if parts cannot be dried quickly enough. A rust
inhibitor may be used along with the cleaner to help
prevent rust. Stress corrosion cracking can occur in
some polymers as a result of contact with alkaline
solutions. Consult with cleaner manufacturers to obtain
recommended formulations and procedures.
Water Tolerance. The most important factor in aque-
ous cleaning is whether the product and/or process can
tolerate water. Compatibility of the product/process with
water must be carefully investigated.
References
Gavaskar, A. R., R. F. Olfenbuttel, and J. A. Jones.
1992. An Automated Aqueous Rotary Washer for
the Metal Finishing Industry. EPA/600/SR-92/188,
U.S. Environmental Protection Agency Project
Summary.
Monroe, K. R., E. A. Hill, and K. D. Carter, Jr. 1993.
"Surfactant Parameter Effects on Cleaning Effi-
ciency." In: Proceedings of the 1993 International
CFC and Halon Alternatives Conference. The
Alliance for Responsible CFC Policy, Washington,
D.C. pp. 405-414.
Munie, G. C. 1991. "Aqueous Defluxing: Materials,
Processes, and Equipment." In: L. Hymes (Ed.),
Cleaning Printed Wire Assemblies in Today's
Environment. Van Nostrand Reinhold, New York,
New York. pp. 120-150.
Murphy, M. (Ed.). 1991. Metal Finishing Guidebook and
Directory, Vol. 89, No. 1a. Metals and Plastics
Publications, Inc., Hackensack, New Jersey.
pp. 106-121.
Polhamus, R. L. 1991. "Precision Cleaning of Metal
Parts without Solvents." Metal Finishing, September,
pp. 45-47.
Ross, S., and Morrison, I. D. 1988. "The HLB Scale."
Colloidal Systems and Interfaces. John Wiley &
Sons, New York, New York. p. 274.
U.S. Environmental Protection Agency. 1991 a. Aque-
ous and Semi-Aqueous Alternatives for CFC-113
and Methyl Chloroform Cleaning of Printed Circuit
Board Assemblies. E PA/401 /1 -91 /016. Prepared by
the Industrial Cooperative for Ozone Layer Protec-
tion Technical Committee and U.S. EPA, Washing-
ton, D.C.
U.S. Environmental Protection Agency. 1991b. Elimi-
nating CFC-113 and Methyl Chloroform in Precision
Cleaning Operations. EPA/401/1-91/018. Prepared
by the Industrial Cooperative for Ozone Layer
Protection Technical Committee and U.S. EPA,
Washington, D.C.
U.S. Environmental Protection Agency. 1991c. Aque-
ous and Semi-Aqueous Alternatives for CFC-113
and Methyl Chloroform in Metal Cleaning. EPA/400/
1-91/019, Washington, D.C.
Weltman, H. J., and S. P. Evanoff. 1992. "Replacement
of Halogenated Solvent Degreasing with Regener-
able Aqueous Cleaners." 46th Purdue Industrial
Waste Conference Proceedings. Lewis Publishers,
Inc., Ann Arbor, Michigan, pp. 851-871.
14
-------
Semi-Aqueous Cleaners
Pollution Prevention Benefits
The primary pollution prevention benefit of semi-
aqueous cleaners is that they are non-ozone-depleting.
However, they may be partly or completely composed
of VOCs. In addition, their use commands substantially
more concern about aquatic toxicity and human
exposure than does the use of aqueous cleaners. Most
semi-aqueous cleaners are reported to be biodegrad-
able. One benefit of semi-aqueous cleaners is that
distillation and membrane filtration technologies are
being developed that will permit recycling and reuse of
the products.
How Do They Work?
Semi-aqueous cleaners comprise a group of cleaning
solutions that are composed of natural or synthetic
organic solvents, surfactants, corrosion inhibitors, and
other additives. The term semi-aqueous refers to the
use of water in some part of the cleaning process, such
as washing, rinsing, or both. Semi-aqueous cleaners
are designed to be used in process equipment much
like that used with aqueous cleaners. The commonly
used semi-aqueous cleaners include water-immiscible
types (terpenes, high-molecular-weight esters, petro-
leum hydrocarbons, and glycol ethers) and water-
miscible types (low-molecular-weight alcohols, ketones,
esters, and organic amines). Petroleum hydrocarbons
are the next Available Technology to be discussed in
this Guide. Alcohols and ketones are discussed in
Available Technologies under Miscellaneous Organic
Solvents. One water-miscible solvent, W-methyl-
2-pyrrolidone (NMP), commonly is used for large-scale
cleaning and paint removing and so is included in this
discussion of semi-aqueous cleaners.
qu$n$yar$ u$od in semi-aqueous ct&m-
efs,
Terpenes are natural hydrocarbons used in semi-
aqueous cleaners. There are many kinds of terpenes.
Among them, d-limonene and a- and B-pinene are
listed most frequently in commercial semi-aqueous
cleaners. Terpene alcohols and para-menthadienes
also are used. Terpenes are derived from plant sources
such as citrus (orange, grapefruit, and lemon) and pine
oils. Although terpenes are not miscible in water, they
do form emulsions with water that are stabilized by
surfactants and other additives.
In cleaning applications, terpenes may be used undi-
luted or diluted with water. Dilution reduces cleaning
performance but, on the other hand, decreases usage,
reduces expense, and lowers vapor pressure which
decreases vapor emissions. Diluted terpene semi-
aqueous cleaners may produce acceptable results with
less difficult contaminants.
Terpenes have relatively low flash points (about 115 to
120°F) and so it is unsafe practice to heat them above
about 90°F, except when used in an inert atmosphere
or when diluted to a safe concentration with water as
recommended by the product manufacturer. Some
commercial formulations of terpene-based cleaners
and degreasers contain higher-molecular-weight
hydrocarbons which lower the volatility of the terpene-
hydrocarbon mixture and increase the flash point.
tfiffioutt c&ntafmnartis,
in
Esters have good solvent properties for many contami-
nants and are soluble in most organic compounds.
High-molecular-weight esters have limited solubility in
water, whereas low-molecular-weight esters are soluble
in water. The types of high-molecular-weight esters
most often used in cleaning and degreasing include
aliphatic mono-esters (primarily alkyl acetates) and
dibasic acid esters. Dibasic acid esters are made by
reacting alcohols, such as methyl-, ethyl-, propyl-, or
butyl alcohol, with dicarboxilic acids, such as glutaric
acid, adipic acid, and succinic acid. High-molecular-
weight esters may be used either cold or heated to
improve cleaning performance.
Among the low-molecular-weight esters, (LJ ethyl
lactate is reported to have good cleaning, health, and
safety properties (Hill and Carter, 1993). Ethyl lactate is
an ethyl ester of (LJ lactic acid. It is a VOC, with
moderate flash point (126°F). Additional information on
ethyl lactate is given in the Available Technology
section, "Miscellaneous Organic Solvents." Other
esters that currently are being studied for cleaning and
degreasing solvents are the small cyclic esters such as
ethylene carbonate and propylene carbonate.
Giyc&t eftiers hav&
but are a heaMh risk*
Glycol ethers also have good solvent properties for
common contaminants. They form emulsions with
water that can be separated for recycling. Health
concerns relating to the use of both the ethyl- and
propyl- series glycol ethers are now being examined in
the wake of reports that they cause an increased rate
of miscarriage among women.
15
-------
NMP has sotv&ot properties, is
with
be usetf coidt of heated,
W-methyl-2-pyrrolidone, or NMP, has been used in
the chemical and petrochemical industries as a solvent
for extraction and as a formulating agent for coatings,
paint removers, and cleaners. NMP has high solvency
for a number of contaminants. It normally is used
undiluted, but it can be mixed with water. NMP is
completely miscible with water and organic compounds
such as esters, ethers, alcohols, ketones, aromatic and
chlorinated hydrocarbons, and vegetable oils. NMP can
be used cold or heated because of its high flash point
(about 199°F).
Operating Features
Semi-aqueous cleaners are designed to be water-
rinsable or non-water-rinsable. After washing in a
water-rinsable type, cleaned parts may be rinsed in
water to remove residue. If a non-water-rinsable type is
used, cleaned parts may be rinsed in alcohol, such as
isopropyl alcohol, or other organic solvent, or the
residue may be allowed to remain on the parts. If
rinsing is the desired option, it is common practice to
rinse in a secondary tank to capture dragout cleaner.
Several tecbnotogtes aiow s&mi*aque&us
Knowing the ft&$h point ts important wttert
water to be recycled or discharged for
If the semi-aqueous cleaner is diluted with water to
form an emulsion, the cleaner can be coalesced into its
aqueous and nonaqueous components by gravity
separation or by advanced membrane separation
techniques. These techniques permit used cleaner to
be recycled back into the wash tank or discharged for
treatment and disposal. Vacuum distillation can be
used to purify single-component solvents. Reclaimed
rinsewater also can be reused or discharged.
Proper use of these cleaners is required to reap their
full pollution prevention benefits. Good engineering
design is essential so that air emissions can be kept
low. For example:
• The cleaning bath should be operated at the
minimum temperature where acceptable cleaning
performance is obtained.
• Low-vapor-pressure cleaning agents should be
used.
• Dragout should be minimized by the use of air
knives.
• The air exhaust rate should be maintained at a
minimum level.
Terpene semi-aqueous cleaners normally are used at
ambient temperature or heated to no higher than 90°F.
However, many high-molecular-weight esters have
flash points in excess of 200°F. Also, the glycol ethers
generally have flash points above 200°F and can be
heated for improved solvency.
NMP has been used for removing cured paint and
hence is a substitute for methylene chloride. NMP is
better suited for immersion tanks than other application
methods, because elevated temperatures are required
to enhance its chemical activity. Usually, NMP immer-
sion cleaning or paint removing is done at 155°F in an
open tank, or up to 180°F if a mineral oil seal is
present.
heavy grease, tar, and waxes r andean
In general, the semi-aqueous cleaners have excellent
solvency for a number of difficult^ontaminants, such as
heavy grease, tar, and waxes. The cleaners have low
surface tension, which decreases their contact angles
and allows them to penetrate small spaces such as
crevices, blind holes, and below-surface-mounted
electronic components.
As with aqueous cleaners, rinsing is necessary to avoid
leaving a residue on the cleaned parts. If water rinsing
is performed, the parts must be dried. The methods of
drying cited for aqueous cleaners apply here as well. If
rinsing is done by a volatile organic solvent, such as
isopropyl alcohol, then drying will be accelerated.
Semi-aqueous cleaners are widely available. Terpenes,
esters, and glycol ethers are typically priced from $10
to $20 per gallon, when purchased in drum-size
quantities. The cost of NMP is higher, about $25 to $30
per gallon, when purchased by the drum.
More waste streams must be managed with semi-
aqueous cleaners than with either solvent cleaning or
aqueous cleaning. Each waste stream can increase
costs.
Application
Semi-aqueous hydrocarbon cleaners first gained
acceptance in the metal cleaning industry, where they
were known as emulsion cleaners. Semi-aqueous
cleaners currently are gaining wider appeal in all types
of industries where parts are cleaned, such as metal
fabrication, electronics, and precision parts manu-
16
-------
facturing. The performance of some of these cleaners
has been validated in government tests, for example,
the Phase 2 Standards for Electronic Components
issued by The Institute for Interconnecting and Packag-
ing Electronic Circuits (IPC, 1990).
Benefits
Semi-aqueous cleaners may have certain advantages
over aqueous cleaners; for example, semi-aqueous
cleaners
• May be more aggressive in removing heavy
organic contaminants.
• May have lower corrosion potential with water-
sensitive metals.
• Penetrate small spaces more easily because
they have lower surface tensions.
Limitations
Health and Safety. Mists of concentrated semi-
aqueous cleaners can be ignited at room temperature.
Terpenes are a special concern because they have the
flash points as low as 115°F. The low flash point
restricts safe operating temperatures to no more than
90°F in some cases . Washing equipment should be
designed to avoid creating mists, such as by spraying
or agitating below the fluid surface or by using ultra-
sonic action. Also, equipment used with low-flash point
cleaners should have overtemperature protection.
feefttife further res&arch
The health effects associated with using semi-aqueous
cleaners have not been fully explored. Limited testing
of d-limonene has yielded positive carcinogenicity
results in male rats (National Toxicology Program,
1990). Also, the terpenes in general, and cMimonene in
particular, are highly photochemically reactive (Darnall
et al., 1976), so it is desirable to minimize losses.
Another concern with terpenes is that their strong odors
may become objectionable to workers, thus requiring
additional ventilation in areas where they are used.
The reproductive health problems associated with
glycol ethers are a cause for serious concern. Whether
glycol ethers can be used safely will have to be estab-
lished by further testing. U.S. EPA's Office of Pollution
Prevention and Toxics (OPPT) recently published a
report stating that NMP could present a significant risk
of reproductive and developmental harm to humans
(U.S. EPA, 1993). The route of entry is dermal, so it is
believed that protective gloves may be sufficient in
preventing harmful exposure. OPPT is currently
working with NMP product manufacturers to resolve the
issues of worker health and safety.
Although semi-aqueous cleaners are biodegradable,
the capacity of treatment facilities to treat wastewater
must be understood. For example, the residence time
of a waste stream in older industrial wastewater
treatment facilities may be too short to effect complete
degradation. In such cases, an add-on treatment
system should be considered. An industrial plant may
consider purchasing a batch-type or continuous-flow
fixed-film or other type biological reactor to process
rinsewater from semi-aqueous cleaning. This kind of
add-on treatment system may be essential if wastewa-
ter otherwise would be discharged directly to a publicly
owned treatment works (POTW).
aM p/as$?s & notrnvoforfrnfttett,
Compatibility with Materials. Semi-aqueous cleaners
are noncorrosive to most metals and generally are safe
to use with most plastics. Terpenes generally are not
recommended for cleaning polystyrene, PVC, polycar-
bonate, low-density polyethylene, and polymethylpen-
tene; nor are they compatible with the elastomers
natural rubber, silicone, and neoprene. NMP dissolves
or degrades ABS, Kynar™, Lexan™, and PVC and it
causes swelling in Buna-N, Neoprene, and Viton™.
Glycol ethers seem to degrade polystyrene and cause
swelling in the elastomers Buna-N and sificone rubber.
References
Darnall, K. R., A. C. Lloyd, A. M. Winer, and J. N. Pitts,
Jr. 1976. "Reactivity Scale for Atmospheric
Hydrocarbons Based on Reaction with Hydroxyl
Radical." Environ. Sci. Technol., 70:692.
Hill, E. A., and K. D. Carter, Jr. 1993. "An Alternative to
Chlorinated Solvents for Cleaning Metal Parts." In:
Proceedings of the 1993 International CFC and
Halon Alternatives Conference. The Alliance for
Responsible CFC Policy, Washington, D.C. pp. 465-
471.
IPC (The Institute for Interconnecting and Packaging
Electronic Circuits). 1990. Cleaning and Cleanliness
Testing Program: Phase 1 & 2 Cleaning Alterna-
tives. A joint industry/military/EPA program to
evaluate alternatives to chlorofluorocarbons (CFCs)
for printed board assembly cleaning. IPC,
Lincolnwood, Illinois.
National Toxicology Program. 1990. Toxicology and
Carcinogenesis Studies of d-Limonene (CAS NO.
17
-------
5989-27-5) in F344/N Rats and B6CF, Mice (Ga-
vage Studies). Technical Report Series No. 347,
U.S. Department of Health and Human Services,
Public Health Service, National Institutes of Health.
U.S. Environmental Protection Agency. 1991 a. Aque-
ous and Semi-Aqueous Alternatives for CFC-113
and Methyl Chloroform Cleaning of Printed Circuit
Board Assemblies. EPA/401/1-91/016. Prepared by
the Industrial Cooperative for Ozone Layer Protec-
tion Technical Committee and U.S. EPA, Washing-
ton, D.C.
U.S. Environmental Protection Agency. 1991b. Elimi-
nating CFC-113 and Methyl Chloroform in Precision
Cleaning Operations. EPA/401/1-91/018. Prepared
by the Industrial Cooperative for Ozone Layer
Protection Technical Committee and U.S. EPA,
Washington, D.C.
U.S. Environmental Protection Agency. 1991 c. Aque-
ous and Semi-Aqueous Alternatives for CFC-113
and Methyl Chloroform in Metal Cleaning. EPA/400/
1-91/019, Washington, D.C
U.S. Environmental Protection Agency. 1993. Lifecycle
Analysis and Pollution Prevention Assessment for
N-Methylpyrrolidone (NMP) in Paint Stripping. Final
Assessment, Public RM2 Administrative Record
Document. Office of Pollution Prevention and
Toxics, Washington, D.C.
Petroleum Hydrocarbons
Pollution Prevention Benefits
The primary pollution prevention benefits of petroleum
hydrocarbon solvents are that they produce no waste-
water and they are recyclable by distillation. Paraffinic
grades have very low odor and aromatic content and
low evaporative loss rates. However, planned recovery
of VOCs is an important part of pollution prevention if
these solvents are to be used.
How Do They Work?
Petroleum hydrocarbons are available in two grades,
the basic petroleum distillates and the specialty grade
of synthetic paraffinic hydrocarbons. Products of the
petroleum distillate grade include mineral spirits,
kerosene, white spirits, naphtha, Stoddard Solvent, and
PD-680 (military designation; types I, II, and III). These
are technologically less advanced, as they contain
components that have a broad range of boiling points
and may include trace amounts of benzene derivatives
and other aromatics. Petroleum distillates were avail-
able many years before chlorinated solvents attained
their popularity.
More recently, improved separation and synthesis
techniques have led to the production of the specialty
grade of paraffinic hydrocarbons. Paraffins are straight-
chain, branched, or cyclic alkanes; they are aliphatic as
opposed to aromatic (i.e., derived from benzene and
naphthalene). The number of carbons in the paraffin
solvent typically ranges from 10 to 14. Compared to
petroleum distillates, the paraffinic hydrocarbons have
very low aromatic content, narrower boiling ranges, and
higher solvency, and they are more expensive.
/a&e #te Hash potrtf ofpetroleum toy&$car-
bons.
Hydrocarbon solvents work by dissolving organic soils.
Some solvents that have flash points as low as 105°F
must be used at ambient temperature to avoid a fire
hazard. Many high-grade hydrocarbon solvents have
flash points above 140°F. Higher flash points are
achieved using higher-molecular-weight compounds.
Some formulations contain nonpetroleum additives
such as high-molecular-weight esters to improve
solvency and raise the flash point.
When the cleaning lifetime of a hydrocarbon solvent
expires, the entire bath must be replaced. Used
hydrocarbon solvents commonly are blended with other
fuels and incinerated in cement kilns.
Petroleum hydrocarbons typically are used when water
contact with the parts is undesirable. Cleaning with
petroleum distillates lends itself to simple, inexpensive,
one-step cleaning in situations where a high level of
cleanliness is not essential.
Operating Features
Petroleum hydrocarbons have high solvencies for
many "hard-to-clean" organic soils, including heavy oil
and grease, tar, arid waxes. In addition, they have low
liquid surface tensions (-22 to 28 dynes/cm), which
allows them to penetrate and clean small spaces.
Mineral spirits cost around $3 per gallon, and paraffinic
hydrocarbons for metal cleaning cost from $7 to $10
per gallon, when purchased in drum-size quantities.
Specialty-grade paraffinic hydrocarbons for electronic
cleaning may cost up to $30 per gallon.
Because hydrocarbon cleaners have slower drying
times than chlorinated solvents, parts may be dried by
forced air or by oven drying. Restrictions on VOC
emissions may apply in some areas. If so, the cost of
18
-------
vapor recovery also must be considered when evaluat-
ing the cost of using these solvents.
Application
Petroleum distillates have had a long history of use,
particularly in automobile repair and related service
areas. Specialty-grade paraffinic hydrocarbons have
become widely available only recently, but are reported
to be used for a broad range of metal cleaning and
electronics defluxing purposes. They currently are
undergoing rapid development for specialized cleaning
operations. The performance of some of these solvents
has been validated in government tests, for example,
the Phase 2 Standards for Electronic Components
issued by The Institute for Interconnecting and Packag-
ing Electronic Circuits (IPC, 1990).
Benefits
No water is used with hydrocarbon cleaners, so there is
no potential for water corrosion or for water to become
trapped in cavities. Some precision cleaning operations
are most effective with hydrocarbon cleaners.
Limitations
Health and Safety. Petroleum hydrocarbons are
flammable or combustible, and some have very low
flash points, as low as 105°F. Process equipment,
including drying ovens, must be designed to mitigate
explosion dangers. The toxicity level of hydrocarbon
solvents is considered low: 8-hour PELs for Stoddard
solvent and VM & P naphthas are 100 ppm and
400 ppm, respectively. Values for synthetic petroleum
hydrocarbons have not been determined yet, but they
are expected to be higher than the values for petroleum
distillates. Products with high flash points evaporate
more slowly than low-flash point solvents.
Residues may remain on the parts long after they are
cleaned. Petroleum distillates contain compounds with
different molecular weights, and hence a range of
evaporation rates. In addition, some specialty solvents
are blends of paraffinic hydrocarbons and other organic
solvents. In either case, the less volatile components
may be left on the parts after the bulk liquid has
evaporated. Furthermore, contaminated solvents will
tend to leave a residue, so they should be repjaced
when slow drying or residue becomes a problem. If
residues are unacceptable, a second level of cleaning
may be needed. Follow-up cleaning may include
rinsing in a clean or more volatile organic solvent or
aqueous cleaning.
Hydrocarbons are VOCs, and hence they are photo-
chemical smog producers. Restrictions against their
use may be realized in the future. Businesses choosing
this alternative must consider the expenses of possible
requirements for recovering VOCs from exhaust
equipment.
Compatibility with Materials. Hydrocarbon cleaners
are compatible with most metals and plastics, and with
some elastomers.
References
IPC (The Institute for Interconnecting and Packaging
Electronic Circuits). 1990. Cleaning and Cleanliness
Testing Program: Phase 1 & 2 Cleaning Alterna-
tives. A joint industry/military/EPA program to
evaluate alternatives to chlorofluorocarbons (CFCs)
for printed board assembly cleaning. IPC,
Lincolnwood, Illinois.
U.S. Environmental Protection Agency. 1991 a. Elimi-
nating CFC-113 and Methyl Chloroform in Precision
Cleaning Operations. EPA/401/1-91/018. Prepared
by the Industrial Cooperative for Ozone Layer
Protection Technical Committee and U.S. EPA,
Washington, D.C.
U.S. Environmental Protection Agency. 1991 b. Aque-
ous and Semi-Aqueous Alternatives for CFC-113
and Methyl Chloroform in Metal Cleaning. EPA/400/
1-91/019, Washington, D.C.
Hydrochlorofluorocarbons (HCFCs)
Pollution Prevention Benefits
Hydrochlorofluorocarbons, or HCFCs, were developed
to lower emissions of ozone-depleting substances that
are used in cleaning, foam-blowing agents, and
refrigerants. Although HCFCs accomplish the goal of
reducing emissions, they have some Ozone Depletion
Potential—about 0.15 for HCFC-141b and 0.033 for
HCFC-225cb—relative to CFC-113, which is 1.0.
Therefore, HCFC-141b depletes ozone at a rate about
6 or 7 times less than that of CFC-113, but about equal
to that of TCA (see Table 5). The ozone depletion rate
for HCFC-225cb is about 30 times lower than that of
CFC-113.
How Do They Work?
HCFCs are designed to be near replacements to CFC-
113 for vapor degreasing. However, the properties of
the HCFCs differ somewhat from those of CFC-113, so
that vapor degreasing equipment that was designed for
CFC-113 would have to be retrofitted to accommodate
HCFCs.
19
-------
Table 5. Physical Properties* of CFC-113 and HCFCs
Compound
CFC-113
HCFC-141b
HCFC-225ca
HCFC-225cb
Molecular Weight
Boiling Point (°C)
Freezing Point (°C)
Liquid Density (cm3)
Liquid Viscosity (cps)
Liquid Surface Tension (dyne/cm)
Heat of Vaporization (cal/g)
Kauri-Butanol Value
Flash Point
Relative Evaporation Rate
(Ether=100)
Azeotropic Composition
with Alcohol (wt%)
Methanol
Boiling Point (CC)
Ethanol
Boiling Point (°C)
OOP
187.38
47.6
-35
1.57
0.68
17.3
34
31
None
123
93.6/6.4
39
96.2/3.8
44.5
0.8
116.95
31.7
-103
1.24
N/A
19.3
51
56
None
120
96.0/3.9"
29.4
No data
0.15
202.94
51.1
-112
1.55
0.58
15.8
33
34
None
101
94.7/5.3
45.5
97.3/2.7
50.0
0.025
202.94
56.1
-116
1.56
0.60
16.7
33
30
None
84
93.3/6.7
47.2
95.6/4.4
53.8
0.033
• Properly measurements at 25°C.
b 0.1% Nitromethane added.
Sources: Basu et al., 1991; Kilamura et al., 1991.
Two basic chemistries of HCFCs are being used for
vapor degreasing: HCFC-141b (CCI2FCH3) which is in
the ethane series, and HCFC-225 which is in the
propane series. Actually, HCFC-225 is a mixture of
isomers HCFC-225ca (CF3CF2CHCI2) and 225cb
(CCIF2CF2CHCIF). The physical properties of these
HCFCs are compared to the properties of CFC-113 in
Table 5. The table shows that the boiling temperature
of HCFC-141b is lower than that of CFC-113. However,
the heat of vaporization of HCFC-141b is greater, so
that the evaporation rates for both compounds are
similar. The table also shows that the boiling tempera-
tures of HCFC-225ca and -cb are higher than that of
CFC-113, and that all three compounds have similar
heats of vaporization. The surface tension, density, and
Kauri-Butanol values of the HCFCs are comparable to
those of CFC-113, which indicates that similar cleaning
performance is expected.
Both HCFC-141b and 225ca, -cb can be used in pure
form or as azeotropes with methanol; HCFC-225ca, -cb
also can be used in azeotrope form with ethanol.
Azeotropes are liquid mixtures that produce a vapor of
the same chemical composition. Boiling temperatures
for azeotropes are compared with boiling temperatures
for CFC-113 in Table 5. Alcohols provide improved
solvency for ionic and polar contaminants, such as
solder flux. Nitromethane sometimes is added in small
amounts to stabilize the alcohol component.
Operating Features
It is important to realize that HCFCs are being devel-
oped for interim use only. The London Amendments to
the Montreal Protocol call for a ban of HCFCs between
2020 and 2040. The main reason for choosing this
technology is to enable an existing CFC-113 vapor
degreasing system to continue in use until a long-term
alternative is found. The long-term alternative could be
a completely enclosed vapor degreaser or a non-HCFC
technology discussed in this Guide.
HCFC-141b currently costs approximately $3.00 to
$3.50/lb, or about $30.00 to $35.00/gallon. Because
production of HCFC-225 mixtures is under develop-
ment, prices were not available.
Application
HCFCs had no commercial solvent use prior to pas-
sage of the Clean Air Act Amendments (CAAA) of
1990. HCFCs now are used in vapor degreasers for the
same applications as CFC-113. HCFCs have similar
performance characteristics to CFC-113. However, like
the CFCs, the HCFCs will be phased out of use. It is
unknown at this time whether regulations will permit
use of HCFCs until at least the year 2020, as expected.
Benefits
HCFCs provide a short-term solution to choosing an
alternative solvent and allow use of existing equipment.
Limitations
Health and Safety. Because HCFCs have lower boiling
points than CFC-113, HCFC solvent vapors may be
lost too quickly in older degreasers, and these vapors
20
-------
may be a health risk. Some emission control features
may have to be added, such as extending freeboard
height, adding secondary condensers, or completely
enclosing the system (Guide to Cleaner Technologies:
Cleaning and Degreasing Process Changes, 1993).
Toxicity testing of HCFC has been ongoing by the
industry consortium — Program for Alternative Fluoro-
carbon Toxicity Testing (PAFT). Results of their findings
were recently reported (Finegan and Rusch, 1993) and
are summarized below.
The toxicology program studied the effects of HCFC-
141 b on rats, showing that, at an exposure level of
20,000 ppm, an increase in cholesterol, reduced
fertility, and reduced body weight were the predominate
effects. No effects were seen with pup viability or
survival.
Metabolism studies showed that HCFC-141b has a low
activity rate and can be metabolized to 11-dichloro-1-
fluoroethanol. HCFC-141b in the gas phase was active
in the CHO cell chromosome aberration assay up to
exposure levels of 10% but inactive in all the other
assays.
The chronic inhalation toxicity study at exposure levels
of up to 20,000 ppm found no effects on survival,
hematology, clinical observations, serum chemistries,
urinalysis, or organ weights. An increased incidence of
benign Leydig cell tumors and related hyperplasia in
male rats in the mid- and high-level exposure groups
did not result in any life shortening effects, as survival
rates were excellent in all groups.
The program showed HCFC-225ca to have slight liver
effects at 650 ppm, whereas all levels of exposure (50,
500,5,000 ppm) in the 4-week inhalation study showed
hepatotoxic effects and peroxisome induction. At the
500 and 5,000 ppm levels there was indication of
cytochrome P450 induction. A 14-day comparative
effect study in rats, hamsters, and guinea pigs run at 5,
50, and 500 ppm showed minimal effects in rodents at
5 ppm, consisting of hepatotoxicity, induction of peroxi-
some, and cytochrome P450 activity. Guinea pigs
showed minimal effects at 500 ppm.
A marmoset study at an exposure level of 1,000 ppm is
showing similar signs of peroxisome induction, marked
reduction in triglycerides, a reduction in cholesterol,
and discolored livers. The cause of the one death is
unknown. HCFC-225ca was not active in the chromo-
some aberration assay.
The same program conducted on HCFC-225cb using
levels 10 times higher than those for the HCFC-225ca
study showed results, for the most part, parallel to
those for HCFC-225ca. The no-adverse-effect level
was 500 ppm for rodents and 5,000 ppm for guinea
pigs. Pharmacokinetics work indicated a blood half-life
of 11 minutes.
The marmoset study indicates a mild reduction in
triglycerides at its exposure level of 5,000 ppm but so
far no evidence of peroxisome induction or induction of
cytochrome P450. The genetics program and results
are similar to those for HCFC-225ca.
HCFCs have no flash point and are nonflammable. Like
TCA, however, HCFC-141b will bum if the oxygen
content is sufficiently high.
Compatibility with Materials. HCFC cleaners are
compatible with most metals and ceramics and with
many polymers. They are incompatible with acrylic,
styrene, and ABS plastic.
HCFCs probably have been developed to their full
extent Except for HCFC-141b and HCFC-225, all other
HCFCs that are suitable as cleaning and degreasing
solvents have turned out to be toxic.
References
Basu, R. S., P. B. Logsdon, and E. M. Kenny-
McDermott. 1991. "Precision Cleaning in Aerospace
Industry with HCFC Based Blend—A Status Up-
date." In: Proceedings of the 1991 International CFC
and Halon Alternatives Conference. The Alliance for
Responsible CFC Policy, Baltimore, Maryland.
pp. 188-199.
Finegan, C. E., and G. M. Rusch. 1993. "Update:
Program for Alternative Fluorocarbon Toxicity
Testing." In: Proceedings of the 1993 International
CFC and Halon Alternatives Conference. The
Alliance for Responsible CFC Policy, Washington,
D.C. pp. 895-904.
Kitamura, K., K. Ohnishi, S. Morikawa, and M. Yamabe.
1991. "HCFC-225 as a Promising Substitute for
Drop-in Replacement of CFC-113." In: Proceedings
of the 1991 International CFC and Halon Alterna-
tives Conference. The Alliance for Responsible CFC
Policy, Baltimore, Maryland, pp. 209-215.
U.S. Environmental Protection Agency. 1991 a. Elimi-
nating CFC-113 and Methyl Chloroform in Precision
Cleaning Operations. EPA/401/1-91/018. Prepared
by the Industrial Cooperative for Ozone Layer
Protection Technical Committee and U.S. EPA,
Washington, D.C.
21
-------
U.S. Environmental Protection Agency. 1991b. Aque-
ous and Semi-Aqueous Alternatives for CFC-113
and Methyl Chloroform in Metal Cleaning. EPA/400/
1-91/019, Washington, D.C.
Miscellaneous Organic Solvents
Pollution Prevention Benefits
The miscellaneous organic solvents do not contain
halogens; therefore, they do not contribute to ozone
depletion. However, all of these compounds are VOCs
and evaporate readily, thereby contributing to smog
formation. The solvents discussed in this section
normally are used in small quantities for niche applica-
tions.
How Do They Work?
This group covers a wide range of solvents that may be
beneficial as a replacement technology, particularly on
a small scale, such as bench-top or spot cleaning.
Types of miscellaneous organic solvents that are
commonly used are shown in Table 6.
Alcohols are polar solvents and have good solubility for
a wide range of inorganic and organic soils. The lighter
alcohols are soluble in water and may be useful in
drying operations.
Ketones have good solvent properties for many poly-
mers and adhesives. Lighter ketones, such as acetone,
are soluble in water and may be useful for certain rapid
drying operations. Heavier ketones, such as
acetophenone, are nearly insoluble in water. Ketones
generally evaporate completely without leaving a
residue. Some ketones such as methyl ethyl ketone
(MEK) and methyl isobutyl ketone (MIBK) once were
widely used. However, they now are considered HAPs
and thus are not favorable solvent substitutes.
Esters and ethers also have good solvent properties.
Low-molecular-weight compounds dry readily without
leaving a residue.
Table 6. Properties of Miscellaneous Organic Solvents
Compound
Alcohols
ethanol
n-propanol
isopropanol
n-butyl alcohol
furfuryl alcohol
benzyl alcohol
cyclohexanol
Ketones
acetone
acetophenone
Esters
n-butyl acetate
(L)ethyl lactate
Ether
anisole
Linear Methyl Siloxanos
2-Si chain
3-Si chain
4-Si chain
Vegetable Oils
peanut oil
soybean oil
Molecular
Weight
46.07
60.11
60.11
74.12
98.10
108.15
100.2
58.08
120.16
116.16
118.13
108.15
162
236
310
—
Boiling
Point (°C)
78.5
97.4
82.4
117
171
205.3
161
56.2
202.6
125
154
155
100
149
192
443 (ignition
temperature)
445 (ignition
temperature)
Melting
Point (°C)
-117
-127
-90
-89
-14
-15
25
-95
20.5
-77
NA
-37.5
-68
-86
-76
-5
-10
Density
g/cm3
0.789
0.803
0.786
, 0.81
1.130
1.042
0.96
0.790
1.028
0.883
1.031
0.996
0.76
0.82
0.85
0.917to
0.921
0.91 6 to
0.922
Solubility
in Water
Soluble
Soluble
Soluble
9%
Soluble
4%
4%
Soluble
Slight
<1%
Soluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
22
-------
A new class of organic solvents are the volatile methyl
siloxanes. Their molecular structure is either linear or
cyclic. The linear type, which was recently introduced
commercially (Burow, 1993), has the general formula
(CH3)3SiO-[SiO(CH3)2]n-Si(CH3)3, where 0
-------
alcohol and ether. Toxicity test data show its LD50
(orally in rats) to be 3700 mg/kg (Budavari, 1989).
Volatile methyl siloxanes have been found to remove
contaminants in precision metal working, optics, and
electronics processing (Burow, 1993). They remove
cutting fluids, greases, and silicone fluids. They have
low odor and evaporate in the range of butyl acetate,
without leaving a residue. They can be used in cleaning
equipment designed for use with isopropyl alcohol.
Limitations
Limitations of some of these cleaners is that some
have vapor pressures that are too high to be used in
standard process equipment, whereas others evapo-
rate too slowly to be used without including a rinse and/
or dry process.
Health and Safety. Most of the organic solvents men-
tioned in Table 6 have low flash points and present a
fire hazard. Inhalation of these solvents can present a
health hazard. It is not known whether the more volatile
solvents will be able to meet VOC emission restrictions
in highly regulated areas of the country. Users should
consult MSDS literature for safe handling practices.
The lighter alcohols, such as ethanol and propanol,
have flash points below room temperature so they are
potential fire hazards unless precautions are taken to
mitigate the possibility of igniting their vapors. A/-butyl
alcohol has a flash point of 36 to 38°C or 97 to 100°F
(closed cup), which is considered flammable.
W-butyl alcohol may cause irritation of mucous mem-
branes, dermatitis, headache, dizziness, and drowsi-
ness (Budavari, 1989). Furfuryl alcohol is relatively
toxic (OSHA permissible exposure limit is 40 mg/m3).
Also, furfuryl alcohol is an irritant to eyes and skin;
exposure to its vapor should be avoided.
A/-butyl acetate is irritating to eyes and skin and it may
cause conjunctivitis. Also, it is a narcotic in high con-
centrations (Budavari, 1989). W-butyl acetate has a
flash point of 22°C, or 72°F (closed cup), so it is a
potential fire hazard unless precautions are taken to
prevent igniting its vapor.
Acetone is quite volatile, evaporates quickly, and is a
highly flammable liquid. Its flash point is -18°C, or 0°F
(closed cup) making it a fire safety hazard unless strict
fire prevention measures are taken. Acetophenone has
a flash point of 105°C or 221 °F (closed cup).
Inhalation of acetone may cause headache, fatigue,
excitement, bronchial irritation, and in large amounts,
narcosis (Budavari, 1989). Prolonged breathing of
acetone may cause erythema.
The flash points of the volatile methyl siloxanes are in
the flammable and combustible ranges: -1°C (30°F) for
n=Q, 34°C (94°F) for n=1, and 57°C (135°F) for n=2
compounds.
The volatile methyl siloxanes are reported to have low
oral and dermal toxicities, and are non-irritating to the
skin and respiratory tract (Burow, 1993). They are mild
eye irritants.
Compatibility with Materials. In general, solvents are
safe to use with most metals, but some can cause
swelling and cracking of polymers and elastomers.
Ketones also are incompatible with many structural
polymers. Esters, on the other hand, seem compatible
with most polymers.
Ethyl lactate hydrolyzes to form lactic acid upon
exposure to4 water, including contact with moist air. The
acidity could have a negative impact on cleaning metal
parts. In one set of tests, a sample of lactic acid aged
6 months at room temperature without nitrogen purge
showed 0.10% acidity by Wration (Hill and Carter,
1993). Therefore, precautions are needed to minimize
the contact of lactic acid with moist air.
References
Budavari, S. (Ed.). 1989. The Merck Index: An Encyclo-
pedia of Chemicals, Drugs, and Biologicals. Merck &
Co., Inc., Rahway, New Jersey.
Burow, R. F. 1993. "Volatile Methyl Siloxanes (VMS) as
Replacements for CFCs and Methyl Chloroform in
Precision and Electronics Cleaning." In: Proceed-
ings of the 1993 International CFC and Halon
Alternatives Conference. The Alliance for Respon-
sible CFC Policy, Washington, D.C. pp. 654-661.
Environmental Program Office, City of Irvine, California.
1991. Brochure.
Hill, E. A., and K. D. Carter, Jr. 1993. "An Alternative to
Chlorinated Solvents for Cleaning Metal Parts." In:
Proceedings of the 1993 International CFC and
Halon Alternatives Conference. The Alliance for
Responsible CFC Policy, Washington, D.C. pp. 465-
471.
U.S. Environmental Protection Agency. 1991 a. Elimi-
nating CFC-113 and Methyl Chloroform in Precision
Cleaning Operations. EPA/401/1-91/018. Prepared
by the Industrial Cooperative for Ozone Layer
Protection Technical Committee and U.S. EPA,
Washington, D.C.
24
-------
U.S. Environmental Protection Agency. 1991b. Aque-
ous and Semi-Aqueous Alternatives for CFC-113
and Methyl Chloroform in Metal Cleaning. EPA/400/
1-91/019, Washington, D.C.
Supercritical Fluids
Pollution Prevention Benefits
The main advantage of using carbon dioxide (CO2) as
a supercritical fluid (SCF) is that CO2 is nonpolluting.
CO2 is derived from the atmosphere and is not created
for use as a solvent. Furthermore, the small quantity of
CO2 released would have an insignificant effect on
global warming. On the other hand, cosolvents, which
may be used to improve the solvent power of CO2, may
have pollution potential and should be investigated
before use. Energy is required to operate the pumps
and temperature control equipment that are needed in
supercritical cleaning equipment.
How Do They Work?
CO2 compressed above its critical pressure (73.7 bars,
or 1077 psi) becomes a critical fluid, and if also heated
above its critical temperature (31 .1°C, or 88.0°F), it
becomes a supercritical fluid. Typically, however, the
term supercritical (SC) is applied to any region in phase
space that is above either the critical temperature (To)
or the critical pressure (Pc). Critical and supercritical
fluids are excellent solvents for dissolving many
medium-molecular-weight, nonpolar or slightly polar
organic compounds.
$Cft$toavG{fi&r&$Qt¥ent power ike tfensw
Figure 1 is a phase diagram for CO2 that shows its
stable phase boundaries, including the supercritical
region. The solvent power of supercritical fluids in-
creases as the density of the fluid increases. The
density of SC CO2 can be made nearly liquid-like at
moderate pressures. The shaded region in Figure 2
shows the pressure-temperature (P-7) region that is
most useful for cleaning. Fluid densities range from
approximately 0.2 to 0.8 g/cm3. Figure 2 shows how the
fluid density may be varied to achieve a broad range of
solvating ability. It may be said that supercritical fluids
can be "tailored" to achieve a desired solvent capability.
1
0.
,000
,000
,000
,000
,000
600
400
200
100
60
40
20
10
6.0
4.0
2.0
1.0
0.6
0.4
0.2
0.1
Solid Region
-
,.
/
f
1
|
4
1
Y
I
A
;
£
"?
c§
^
&
-160 -120
i
?
5
m
>
V
V
Liquid Region
/
'
&
<•
&
*»*
"• Triple Point
A
$
_>
^
S
_^
^m
\
\
Vapor Region
Superheated)
F
^—
Criti
upen
luidF
^BB
cal P
:ritic
iegio
M
.
ll
n
• •
• •
-80 -40 0 40 80 120 160 20
Source: Airco Gases
Figure 1. Phase diagram for pure CO2.
Temperature (°F)
25
-------
Temperature (°C)
500 -
400 -
300 -
^ 150 -
|
$ 100 -
Q_
74 -
3D -
10 -
.25
I
.50
Source: Schneider, 1978
.75
Density (g/mL)
1.0
1.25
Figure 2. Pressure-density diagram for pure CO2; temperature in °C; cp = critical point.
Other factors that affect the cleaning abilities of SCFs
are their gas-like low viscosity and high diffusivity,
which enable them to penetrate into small confined
spaces, such as cracks and blind holes. In the P-T
region of interest (shaded area in Figure 2) viscosities
are about twice those of the gas at atmospheric
pressure and at the same temperature, whereas
diffusivrties are about 30 times smaller (Lira, 1988).
However once CO2 molecules have solvated contami-
nant molecules, the kinematic properties of the fluid
may change, especially near the SCF/contaminant
interface. With this change, the solvated contaminant
species may be difficult to remove. In practice, some
sort of mixing mechanism or flow control usually is built
into the extraction vessel.
A typical SCF cleaning system consists of the following
components:
• CO2 source (compressed gas cylinder)
• Chiller to condense CO2 gas to liquid
Pressure pump to elevate CO2 liquid pressure
Hot water bath to elevate line temperature to that
of the cleaning chamber
Cleaning chamber where parts are cleaned
Pressure reduction valve at fluid exit port
Separator vessel to collect contaminants
Air flow meter to monitor CO2 usage.
awaysotubie contemftmnts.
Samples to be cleaned are placed in the cleaning
chamber, which also is called an extraction vessel or
autoclave. The process is started by drawing CQ2 from
the gas cylinder, then pressurizing and heating the CO2
to the same P- 7" conditions as in the extraction vessel.
Heat tape may be wound around all critical fluid
transfer lines, and temperatures should be monitored at
various points by thermocouples. SC CO2 flows
through the cleaning chamber where it dissolves and
carries away soluble substances. After extraction, the
26
-------
CO2 and dissolved contaminants pass through a
pressure reduction valve where pressure is dropped
below Pc, and then they enter the separator vessel. As
CO2 returns to the gaseous state, its solvent power
decreases substantially and contaminants drop out of
solution and remain in the separator vessel. The CO2
continues to flow out of the separator vessel through a
flow meter and to the atmosphere.
As a rule of thumb, to achieve good solvency at
moderate temperature, the fluid pressure should be 2
or more times the critical pressure of the fluid. Typical
operating conditions for SCF cleaning equipment are
listed in Table 7.
Table 7. Typical Operating Conditions for Supercritical CO2
Cleaning
Parameter
Pressure (gauge)
Temperature
SC CO2 Density
SC CO2 Flow Rate
Time
Scientific Units
100-300 bars
40-85°C
0.5-0.8 g/cm3
1-5kg/hr
0.5-3 hours
; Engineering Units
>. 1 ,450-4,350 psi
100-185°F
30-50 Ib/ft3
2-11 Ib/hr
0.5-3 hours
Operating Features
SCF cleaning exploits the marked improvement of the
solvent power of CO2 or other substances after they
undergo a phase transition from a gas or liquid phase
to become supercritical fluids. Supercritical CO2 has
been used very successfully to remove organic soils of
moderate molecular weight and low polarity. Supercriti-
cal CO2 does not give good results for soils that are
ionic or polar in nature, such as fingerprints.
SCF cleaning is probably best reserved for removing
small amounts of soil from parts that require a high
degree of cleanliness. For example, precision cleaning
operations have been performed successfully on the
following devices: gyroscope parts, accelerometers,
thermal switches, nuclear valve seals, electro-
mechanical assemblies, polymeric containers, optical
components, porous metals, and ceramics (Gallagher
and Krukonis, 1991; Woodwell, 1993). The cleaning
technology is available commercially.
Capital costs for installing SCF equipment are high, at
least $1OOK for small-capacity equipment. The cost of
the autoclave increases considerably with size. Small
vessels may be only 1 liter in volume and are relatively
inexpensive. Large vessels—30 liters, for example—
are many times more expensive for the same pressure
rating. If large parts are to be cleaned, it may be more
cost effective to purchase lower-pressure-rated equip-
ment and operate the SCF system for longer times at
lower pressure. The expense of supplying CO2 to the
system, however, is quite small, about 7 cents per
pound.
Application
Supercritical fluids have been used in organic chemical
analysis equipment and in the food and flavor indus-
tries. SCFs have been used to clean and degrease
precision parts in the defense industry since the mid-
1980s.
Supercritical fluids have been used to remove machine
coolants on aluminum and stainless steel substrates
(Salerno, 1990). The cleaning process, performed at
35°C, 138 bars for 15 to 30 minutes, yielded a residual
0.65% of the coolants on the substrates. The solubility
of the coolants ranged from about 1 to 5% under these
conditions.
Benefits
Low viscosity and high diffusivity permit SCFs to clean
within very small cracks and pore spaces. The solvent
power of SCFs is pressure-dependent, making it
possible to extract different soils selectively and
precipitate them into collection vessels for analysis.
Limitations
Health and Safety. The only major safety concern is
the danger of a pressure vessel or line rupture. How-
ever, the pressures used in SCF cleaning are well
within the strength limits of most standard autoclave
equipment.
Compatibility with Materials. SCFs are compatible
with metals, ceramics, and polymers such as Teflon™,
high-density polyethylene, epoxies, and polyimides.
SCFs cause swelling in acrylates, styrene polymers,
neoprene, polycarbonate, and urethanes (Gallagher
and Krukonis, 1991). Components that are sensitive to
high pressures and temperatures should not be
cleaned by SCF methods. Process developments in
the future probably will make SCF cleaning more
aggressive toward removing cross-linked polymeric
materials and displacing particulates.
Cleaning Efficacy. The major deficiencies of SCF
cleaning are that SCFs are not effective in removing
inorganic and polar organic soils, nor do they remove
loose scale or other particulates. For these reasons,
the soil must be well characterized to ensure its
solubility in SCF before an investment is made in this
technology.
27
-------
It also is not known whether the process can remove a
complex mixture of contaminants. Therefore, a detailed
analysis of the contaminants must be done before the
likelihood of success can be determined.
References
Airco Gases. N.D. 474 Mountain Avenue, Murray Hill,
New Jersey 07947.
Gallagher, P. M., and V.J. Krukonis. 1991. "Precision
Parts Cleaning with Supercritical Carbon Dioxide."
Proceedings of the 1991 International CFC and
Halon Alternatives Conference. The Alliance for
Responsible CFC Policy, Baltimore, Maryland.
pp. 262-271.
Lira, C. T. 1988. "Physical Chemistry of Supercritical
Fluids: A Tutorial." In: B. A. Charpentier and M. R.
Sevenarrts (Eds.), Supercritical Fluid Extraction and
Chromatography. American Chemical Society,
Symposium Series No. 366. pp. 1-25.
Salerno, R. F. 1990. "High Pressure Supercritical
Carbon Dioxide Efficiency in Removing Hydrocar-
bon Machine Coolants from Metal Coupons and
Components Parts." In: Solvent Substitution—A
Proceedings/Compendium of Papers. DE-AC07-
76ID01570, U.S. Department of Energy, Office of
Technology Development, Environmental Restora-
tion and Waste Management; and U.S. Air Force,
Engineering and Services Center, pp. 101-110.
Schneider, G. M. 1978. "Physicochemical Principles of
Extraction with Supercritical Gases." Angew. Chem.
Int. Ed. Engl., 17:716-727.
U.S. Environmental Protection Agency. 1991. Eliminat-
ing CFC-113 and Methyl Chloroform in Precision
Cleaning Operations. EPA/401/1-91/018. Prepared
by the Industrial Cooperative for Ozone Layer
Protection Technical Committee and U.S. EPA,
Washington, D.C.
Woodwell, R. 1993. Personal communication from
Robert Woodwell of Honeywell Space Systems
Group to Bruce Sass of Battelle. September 21.
Carbon Dioxide Snow
Pollution Prevention Benefits
Chilled CO2 is a nontoxic, inert gas that replaces
solvent use to eliminate ozone-depleting substances.
Because the CO2 is recycled, there is no need for
disposal, nor is any wastewater produced. It generates
no hazardous emissions.
How Does It Work?
Gaseous or liquid CO2 is drawn from a room-tempera-
ture gas cylinder or high-pressure dewar and expanded
through a nozzle to produce fine CO2 particles and CO2
gas. These particles are dry ice snowflakes and are
propelled by the gas stream.
The CO2 gas or liquid is expanded through a special
nozzle to form a jet. For example, when liquid CO2 at
750 psi is throttled through a nozzle and expanded into
a volume at 1 atm pressure, it undergoes a phase
change to the solid state. The shape and size of the
snowflakes depend on the configuration of the nozzle
and the conditions in which the flake formed in the gas
stream. The snowflakes can be individual crystals or
collective groupings of crystallites.
Cleaning action is performed when the snow particles
impact a contaminated surface, dislodge adherent
contaminant particles, and carry them away in the gas
stream. The process is effective in removing very small
(submicron) particles, where fluid drag normally
restricts the performance of liquid phase cleaning. The
CO2 snow cleaning process also is believed to attach
hydrocarbon film by dissolving hydrocarbon molecules
in a temporal liquid CO2 phase at the film-substrate
interface (Whrtlock, 1989). The dissolved film is then
carried away by subsequent flow of snow and gas.
Operating Features
A complete system includes a CO2 purifier, a pneu-
matic actuated head, and a microprocessor-based
timing circuit. Several models of manual spray booths
are available that provide a nitrogen-purged, heated,
and monitored environment for CO2 spraying that cost
$10K to $15K. One commercial purifier is available in a
17 x 14 x 24 1/2 inch stainless steel cabinet. It weighs
135 Ib and requires an energy supply of 6 A, 115 VAC,
and 60 Hz.
Another commercially available purifier is capable of
purifying CO2 to a water content of less than 20 ppb by
weight. In laboratory analyses of CO2 before and after
purification, the hydrocarbon content of 1800 ppb by
weight was reduced to 3 ppb hydrocarbon; CO2 with
140 ppb by weight halocarbons was purified to 1 ppb
wt halocarbons. The purifier works on a 25% duty
cycle, allowing use for 1 minute to every 3 minutes of
recovery time. The snow gun consumes 0.6 Ib of CO2
per minute when used continuously.
If the dust or dirt particles removed by CO2 snow
cleaning are a hazard, they can be collected by an
electrically charged curtain (Hoenig, 1990).
28
-------
Application
Benefits
CO2 snow gently removes particles smaller than 10
microns in diameter down to 0.1 micron that are difficult
to remove using high-velocity liquid nitrogen. It is used
to remove light oils and fingerprints from mirrors,
lenses, and other delicate surfaces, and from precision
assemblies, without scratching the surface.
CO2 snow can clean hybrid circuitry and integrated
circuits without disturbing the bonding wires. This
unique ability cannot be duplicated by any other
cleaning mechanism. In the disc drive industry, CO2
snow is used to remove particles from discs without
damage to the operation (Hoenig, 1990).
The process is used to remove paste fluxes in solder-
ing. If the grease cannot be removed with CO2 snow
alone, a combination of C02 snow and ethyl alcohol is
effective, followed by CO2 snow alone to remove the
impurities from the alcohol (Hoenig, 1990).
CO2 is used to remove hydrocarbons and silicone
grease stains from silicon wafers. Wafers artificially
contaminated with a finger print, a nose print, and a
thin silicone grease film were found to have surface
hydrocarbon levels 25 to 30% lower after CO2 snow
cleaning than the original wafer surfaces (Sherman and
Whitlock, 1990).
QO? mow Meaning is &xtmm&iy effective.
Layden and Wadlow (1990) report a reduction of zinc
orthosilicate concentration on a silicon wafer of more
than 99.9% after cleaning by high-velocity CO2 snow.
Whitlock (1989) reports removal of greater than 99.9%
for particles ranging from 0.1 to 0.5 micron diameter.
In the field of optics, CO2 snow is used to clean the
light-scattering particles and debris from the mirrors of
the world's largest and most expensive telescopes.
CO2 snow also is used to clean surfaces exposed to
contaminants in air prior to surface analysis. The
process was found to work better than solvents to
clean vacuum components. Because the aerosol could
penetrate narrow spaces, no disassembly was re-
quired, greatly shortening the time required for clean-
ing. Furthermore, CO2 cleaning is effective on some
plastic parts that cannot be cleaned by solvents
(Layden and Wadlow, 1990).
Some of the major beneficial aspects of CO2 snow
include
• CO2 snow performs ultrapure cleaning of light oils
down to submicron size on the most delicate,
sensitive materials ranging from bonding wires to
precision mirrors in telescopes.
• The CO2 snow crystals generated by the snow
gun are extremely gentle.
• The CO2 snowflakes are adjustable to a wide
range of size and intensity.
• The process does not create thermal shock, is
nonflammable and nontoxic, and causes no
apparent chemical reactions.
• Cleaning by CO2 snow is noncorrosive and
leaves no residue.
• CO2 snow does not crack glass or other ceram-
ics.
• No media separation system is needed, nor is
there a media disposal cost.
• CO2 snow can penetrate the nonturbulent area to
dislodge contaminants and can be used on
components without disassembly that otherwise
must be disassembled because the aerosol
penetrates narrow spaces.
Limitations
Potential hazards and limitations of CO2 snow include
• Heavier oils, alone or mixed with light oils, may
require chemical precleaning and/or heating to
be completely removed.
• The CO2 must be purified because of its ten-
dency to dissolve contaminants from the walls of
tanks in which it is stored. Purification equipment
adds expense to the CO2 snow cleaning system.
• When surfaces are excessively chilled by long
dwell times, airborne impurities may condense
and settle on the clean surface (Zito, 1990).
• CO2 snow has low Mohs hardness and will not
scratch most metals and glasses. However, hard
particulates such as sand that may be present on
a surface potentially could cause scratching
when they are carried by the gas stream.
References
Hoenig, S. A. 1990. "Dry Ice Snow as a Cleaning Media
for Hybrids and Integrated Circuits." Hybrid Circuit
Technology, December, p. 34.
Layden, L, and D. Wadlow. 1990. "High Velocity
Carbon Dioxide Snow for Cleaning Vacuum System
Surfaces." Journal of Vacuum Science Technology,
A8(5):3881-3883.
29
-------
Sherman, R., and W. Whitlock. 1990. 'The Removal of the Fine Particle Society, Boston, Massachusetts,
Hydrocarbons and Silicone Grease Stains from Silicon August 22.
Wafers." Journal of Vacuum Science Technology,
B9(3):563-567. Zito, R. R. 1990. "Cleaning Large Optics with CO2
Snow." SPIE Advanced Technology Optical Telescopes
Whitlock, W. 1989. "Dry Surface Cleaning with CO2 IV, 7236:952-971.
Snow." Paper presented at the 20th Annual Meeting of
30
-------
SECTION 3
EMERGING TECHNOLOGIES
How to Use The Summary Tables
Two emerging alternatives to chlorinated solvents for
cleaning and degreasing are evaluated in this section:
• Catalytic wet oxidation cleaning
• Absorbent media cleaning.
Tables 8 and 9 summarize descriptive and operational
aspects of these technologies. The tables contain
evaluations or annotations describing each emerging
cleaner technology and give a compact indication of
the range of technologies that may be applicable to
specific situations. Readers are invited to refer to the
summary tables throughout this discussion to compare
and contrast technologies.
Descriptive Aspects
Table 8 describes each emerging cleaner technology. It
lists the Pollution Prevention Benefits, Application,
Benefits, and Limitations of each emerging cleaner
technology.
Operational Aspects
Table 9 shows the key operating characteristics for the
emerging technologies. The technical qualitative
rankings are estimated based on the descriptions and
data in the literature.
In Table 8, Process Complexity is qualitatively ranked
as "high," "medium," or "low" based on such factors as
the number of process steps involved and the number
of material transfers needed. Process Complexity is
an indication of how easily the technology can be
integrated into existing plant operations. A large
number of process steps or input chemicals, or multiple
operations with complex sequencing, are examples of
characteristics that would lead to a high complexity
rating.
The Required Skill Level of equipment operators also
is ranked as "high," "medium," or "low." Required Skill
Level is an indication of the level of sophistication and
training required by staff to operate the new technology.
A technology that requires the operator to adjust critical
parameters would be rated as having a high skill
requirement. In some cases, the operator may be
insulated from the process by complex control equip-
ment. In such cases, the operator skill level is low, but
the maintenance skill level is high.
Table 9 also lists the Waste Products and Emissions
from the emerging cleaner technologies. It indicates
tradeoffs in potential pollutants, the waste reduction
potential of each, and compatibility with existing waste
recycling or treatment operations at the plant.
candidates,
The Capital Cost column provides a preliminary
measure of process economics. It is a qualitative
estimate of the initial cost impact of the engineering,
procurement, and installation of the process and
support equipment compared to continuing to use
chlorinated solvents. Due to the diversity of cost data
and the wide variation in plant needs and conditions, it
is not possible to give specific cost comparisons. Cost
analysis must be plant-specific to adequately address
factors such as the type and age of existing equipment,
space availability, throughput, product type, customer
specifications, and cost of capital. Where possible,
sources of cost data are referenced in the discussions
of each cleaner technology.
The Energy Use column provides data on energy use
for a specific technology.
Operations Needed After Cleaning summarizes
additional inspection, hand cleaning, or other opera-
tions that may be needed after use of the clean alterna-
tive solvent. These are noted to indicate special
31
-------
Table 8. Emerging Technologies for Alternatives to Chlorinated Solvents for Cleaning and Degreasing: Descriptive Aspects
Technology Type
Pollution
Prevention Benefits
Application
Benefits
Limitations
Catalytic Wet
Oxidation Cleaning
Absorbent Media
Cleaning
Only CO and water
produced
No water involved in
cleaning
Replaces solvents
Media biodegradable
and/or can be recycled
Oxidizable organic soils
Degrease low alloy steel prior to
heat treatment
Clean fingerprints from mylar
Sop up oil
Degrease aluminum and other
sensitive parts
Can be used to clean wet parts
Wipes are made of recyclable, potentially
redaimable materials
Wipes can be incinerated
Starch applicators can be reused indefinitely
Sewered starch is useful as a feedstock for .
municipal processing plants
Spent wipers and starch have BTU value
May damage/corrode some
substrates
Plant air or a shop vacuum needed in
most cases
Not useful on complex surfaces or
detailed parts
ro
Table 9. Emerging Technologies for Alternatives to Chlorinated Solvents for Cleaning and Degreasing: Operational Aspects
Technology Process Required Waste Products
Type Complexity Skill Level and Emissions
Catalytic Wet Medium Medium CO2, water
Oxidation Cleaning
Absorbent Media Low Low Spent media
Cleaning
Capital
Cost
No commercial system
to date
Low material cost and
low operating cost
Energy
Use
• Low
• Low for air filtration or
vacuum system
Operations Needed
After Cleaning
• Drying to remove water
• Sweeping or vacuuming
may be required
References
Dhooge, 1990
Doscher, 1991
Doschsretal., 1990
-------
considerations in the application of the cleaner technol-
ogy.
The last column in Table 9 cites References to publica-
tions that will provide further information for each
emerging technology. The citations are given as full
references at the end of the respective Emerging
Technology sections.
The text further describes pollution prevention benefits,
application, product benefits, and limitations known for
.each technology. More highly developed technologies
are summarized in Section 2, Available Technologies.
Catalytic Wet Oxidation Cleaning
Catalytic wet oxidation is a proposed method for
chemically oxidizing, or "burning," organic contami-
nants within an aqueous medium. Oxygen-rich air
pumped into an aqueous solution can be used to gasify
organics that adhere to a substrate, thereby converting
them to more easily degradable chemical intermedi-
ates. The concept was developed for the destruction of
organic wastes (Dhooge, 1990), but may be applicable
to substrate cleaning as well. In principle, the final
waste products are CO2 and water. The process
consumes little energy.
Oxidation in the presence of water is the source of the
term wet oxidation. This technology can be used to
treat waste streams high in organic matter. Wet oxida-
tion works most effectively on materials that contain
substantial amounts of water and cannot be easily
combusted under conventional burning conditions.
A catalyst^typically iron (lll)/iron (II) salts that dissolve
in solution—and one of several homogeneous (aque-
ous phase) cocatalysts are used to increase the rate of
the wet oxidation reaction. Typical cocatalysts could be
chosen from the platinum (IV), ruthenium (III), rhodium
(III), nickel (II), cobalt (II), palladium (II), or vanadium
(V) complex.
The process works by forming water-soluble intermedi-
ates as organic materials are broken down into smaller
molecular species. Sometimes polymerization occurs,
as in the formation of gums in petroleum oils. High
temperatures (250 to 300°C) may be required to obtain
nearly complete conversion of organic matter with the
wet oxidation technology.
Reference
Dhooge, P. M. 1990. Method lor Treating Organic
Waste Material and an Oxidation Catalyst/Cocat-
alyst Composition Useful Therefor. U.S. Patent No.
4,925,540. May 15.
Absorbent Media Cleaning
Absorbent media can be used to remove grease and oil
in situations where aqueous or semi-aqueous treat-
ments cannot be used, as in degreasing water-sensi-
tive materials or where lack of floor space makes
rinsing impractical. Two types of absorbent media have
been introduced to replace VOC-exempt solvents. The
first involves wiping with oil-absorbent wipers contain-
ing polypropylene fibers. The second makes use of a
variety of particulate absorbents, such as natural
silicates, wheat starch, and dry cellulose pulp (Doscher,
1991).
The effectiveness of wipers depends on the surface
size and viscosity of the grease or oil. Cheesecloth and
specially produced wipers of fine texture have been
used to remove fingerprints from mylar. Wipers of
larger fiber dimension and rougher surface texture are
used to sop up oil used during shop equipment mainte-
nance and are effective on large, exposed surfaces. As
part complexity increases and part size decreases,
wipers containing thinner, finer fibers are required.
Absorbent me&ta demers now are macte
The new generation of wipers are made of recycled
materials such as polypropylene. Because the fibers
are not woven or coated, excess lint or shedding may
occur. To combat this problem, a ventilation system
should be designed to capture fugitive dusts. Spent
wipers should be disposed of by recycling, incinerating,
or landfilling, provided that they were not used to
absorb toxic materials. Recycling is seen as the most
desirable option, but in lieu of a cost-effective method
for removing oil and grease from the fibers, incinerating
or landfilling the wipers are the only currently available
options. Because polypropylene has high BTU value,
incineration may be the better alternative.
of natural materi&ts,
Loose, paniculate absorbents are reported to be even
more effective than wipers for removing grease and oil
because of their greater surface area and better
impingement. They may also have a greater affinity for
oil (Doscher, 1991). The term particulate absorbent
comprises such materials as siliceous materials and
33
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organic cellulose-based materials. The three commonly
used siliceous materials, talc, kaolin, and diatoma-
ceous earth, visibly scratch aluminum surfaces and are
unacceptable unless abrasive surface preparation is
required. Of the organic absorbents tested, wheat
starch performed best in terms of ease of use and
results (Doscher, 1991).
Sfc&ti waste cm b& used fa v&r&ts wsty$,
successive wipings, replacing the wiper each time,
achieved 96% clean panels (Doscher, 1991).
Starch cleaning involves dipping a foam-backed nylon
bristle paint pad in the loose starch and using standard
wipe techniques. The process waste, i.e., the oil-
soaked starch aggregate, is vacuumed or swept away
and can be sewered in many cases, depending on the
toxicology and wastewater characteristics of the oil.
When sewered, the starch itself is useful as a feed-
stock for municipal processing plants. If the process
grease or oil cannot be sewered, the process waste
has BTU value for incineration. The nylon bristle pad
can be reused many times. Thus, the waste volume
and handling requirements for starch are minimal.
In a test to compare cleaning of sesame oil with the
solvent MEK to starch cleaning of the same oil, starch
applied in one wiping cycle (5 up-and-down scrubs) got
the panels 99% clean. Using fresh MEK in three
Absorbent cleaning has in the past been regarded as a
"last resort" substitution method. With starch, however,
the material cost; shop time; and safety, health, and
environmental considerations outweigh the disadvan-
tages for cleaning flat, exposed surfaces. Adust
collection unit or vacuum table must be provided to
prevent excess material from becoming airborne. When
the surface is not too complex and dust collection is
feasible, starch cleaning is a process improvement.
The effectiveness of starch in a fluidized bed dry-
cleaning system is described by Doscher and others
(1990).
References
Doscher, P. A. 1991 . Grease and Oil Removal Using
Absorbent Media. Paper presented at the Second
Annual International Workshop on Solvent Substitu-
tion. Phoenix, Arizona. December 10-13.
Doscher, P. A., N. E. Larson, D. D. McCain, and M. J.
Cooper. 1990. "Fluidized Bed Dry Cleaning as a
Replacement for Vapor Degreasing." Proceedings of
the 22nd International SAMPE Technical Confer-
ence. pp. 895-904.
34
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SECTION 4
POLLUTION PREVENTION STRATEGY
The main federal environmental regulations influencing
the application of new cleaning technologies are the
Clean Air Act Amendments (CAAA), the Resource
Conservation and Recovery Act (RCRA), the Right to
Know provisions of the Superfund Amendment and
Reauthorization Act (SARA), and the- emphasis on
eliminating pollution at the source in the Pollution
Prevention Act of 1990. Solvent cleaners also increase
the potential workplace exposures to volatile organic
compounds (VOCs) regulated under the Occupational
Safety and Health Act (OSHA). There are a wide
variety of state and local limits on VOC, hazardous,
and aqueous wastes that also are of concern.
RCRA regulations make processes ibai
$®wm ^tm^ftt #My«m #
-------
recommends that occupational exposure to carcin-
ogens be limited to the lowest feasible concentration.
OSHA regulations for workplace emissions are also
becoming increasingly stringent.
Title III of the CAAA requires adoption of Maximum
Achievable Control Technologies (MACT) for control of
189 hazardous air pollutants (HAPs). Cleaning pro-
cesses using solvents are considered major sources of
HAPs and are subject to MACT standards. Vapor
degreasing is the single largest use for solvents,
followed by dry cleaning (clothes cleaning) and cold
cleaning (liquid solvent cleaning). Based on 1987 U.S.
EPA estimates, approximately 25,000 to 35,000 batch
vapor degreasers and 2,000 to 3,000 continuous
cleaners were used in the United States.
The P&tfatiafl Prevention Aat establishes
The Pollution Prevention Act establishes pollution
prevention as the preferred method for pollutant
management. The processes described in this docu-
ment provide promising alternatives to conventional
processes for potential users, i.e., the metal-finishing,
dry-cleaning, electronics, and any other industry
that uses cleaning processes. Under programs such as
the U.S. EPA's 33/50 Program, industries are encour-
aged to reduce pollutants voluntarily in anticipation of
future regulations, which are expected to become
increasingly stringent. The CAAA of 1990 allows the
U.S. EPA to grant a 6-year compliance extension on
the MACT compliance date to any existing source of air
toxics that reduces emissions voluntarily by 90% (95%
for particulates) below 1987 levels before January 1 ,
1994.
MACT standards will be issued by the U.S. EPA for
new and existing sources, using the best controlled
similar sources as a measure. MACT can include
control equipment, process changes, material substitu-
tions, equipment design modifications, work practices,
or operational practices. All sources in a source cat-
egory or subcategory will have to implement MACT.
Unless the owner of the source is eligible for the 6-year
extension (for 90% reduction), all industrial sources are
expected to be in compliance within 3 years of promul-
gation of the MACT standards. A 5-year compliance
extension also may be granted for prior installation of
Best Available Control Technology (BACT) or Lowest
Achievable Emissions Rate (LAER).
VnftfGMA, MAGT$tertiafd$
exp&ctect for hziog&rtated solvent £t&amr&
Under Title III of the CAAA, the U.S. EPA on July 16,
1992 (Federal Register, 1992) added halogenated
solvent cleaners as an area source category. Thus,
halogenated solvent cleaners are considered a major
source category emitting at least 1 0 tons/year of any
one air toxic or 25 tons/year of any combination of air
toxics. Therefore, MACT standards can be expected to
be promulgated for these cleaners. Vapor degreasing
constitutes the single largest use of solvents in the
United States, and therefore is an important area
targeted for pollution prevention.
References
Federal Register. 1992. "The Clean Air Act Amend-
ments, Title III." Federal Register, 57(137). July 16.
U.S. Environmental Protection Agency. 1991. The33/
50 Program: Forging an Alliance for Pollution
Prevention (2nd ed.). Special Projects Office, Office
of Toxic Substances, Washington, D.C. July.
U.S. Environmental Protection Agency. 1992. EPA's 33/
50 Program Second Progress Report. TS-792A,
Office of Pollution Prevention and Toxics. February.
36
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SECTION 5
CLEANER TECHNOLOGY TRANSFER CONSIDERATIONS
Since the 1970s it has been realized that some chlorof-
luorocarbons (CFCs) undergo chemical changes in the
upper atmosphere that subsequently lead to the
destruction of the ozone layer. The world community
has since sought to eliminate production and use of
CFCs. According to the Montreal Protocol, agreements
were made to restrict the production and use of ozone-
depleting chemicals. The Montreal Protocol and later
amendments led to changes in the U.S. Clean Air Act,
which was amended by President Bush on November
15, 1990. The Clean Air Act Amendments (CAAA)
established a time frame to eliminate all fully haloge-
nated CFCs, certain chlorinated hydrocarbons, and
hydrochlorofluorocarbons (HCFCs).
rtu&tbe pfraseof ottf by 189&
In November 1992, the participating countries voted to
advance the deadline for phasing out ozone layer-
depleting substances (OLDS Class I) to January 1 ,
1996. The OLDS Class I list includes CFCs and halons,
among which are CFC-113 and TCA, which are the
substances most important to cleaning. The expected
ban on Class II OLDS, which includes the HCFCs, is
between 2020 and 2040 or earlier, as stipulated by the
London Amendments to the Montreal Protocol.
Newaqu&ous andsem+aqueous wasb&fs
m mm <$&&# e&mpmtf to &>tmn~
ttonat aqueous ctemng processes.
Some users may want to retain vapor degreasing
rather than convert to aqueous or semi-aqueous
cleaning. Industries have been reluctant to eliminate
vapor degreasing completely because of its advantage
with certain types of parts or simply because of tradi-
tion and ease of operation. Some users in this group
may consider completely enclosed vapor degreasing
(see Guide to Cleaner Technologies: Cleaning and
Degreasing Process Changes) or HCFC vapor de-
greasing solvents (see Available Technologies) as a
temporary solution. Because perfect "drop-in" replace-
ments do not exist, some process modification will be
needed to obtain results that are similar to those
achievable with the former vapor degreasing process.
In addition, users who want to purchase HCFC sol-
vents for major use areas, such as vapor degreasing in
electronics and metal finishing industries, must petition
EPA, per Section 612 of the CAAA.
If users are ready to switch to a liquid cleaning ap-
proach, many options already are available. Aqueous,
semi-aqueous, and solvent cleaning technologies have
advanced in recent years in terms of both the type of
cleaning chemicals used and the type of equipment
used. (See the discussion of cleaning equipment in
Guide to Cleaner Technologies: Cleaning and Degreas-
ing Process Changes).
databases em ass&f tts&rs m choosing a
Reluctance to switch over to a new cleaning technology
may stem from concern over cleaning performance, as
well as from uncertainty in choosing an alternative from
the large number of cleaning technologies and prod-
ucts now available. Users may be intimidated by the list
of options and wonder how to begin selecting an
alternative. Although trade journals provide technical
literature on alternative cleaning technologies, the
subject may not be presented in a systematic form that
facilitates making detailed comparisons among all the
different attributes. To assist in making knowledgeable
decisions, several online and offline computer data-
bases are available that provide information searching
in various ways. These databases are discussed in the
following paragraphs: The Alternative Technologies
Transfer Information Clearinghouse (ATTIC), the
Pollution Prevention Information Exchange System
(PIES), the Solvent Alternatives Guide (SAGE), the
Solvent Alternative Utilization Handbook, and the
NCMS Solvent Database.
ATTtC is a fottHn-on& mfyv&rk,
The ATTIC network is maintained by the Technical
Support Branch of EPA's Risk Reduction Engineering
37
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Laboratory (RREL). This network has four online
databases that can be searched by external users.
• The ATTIC database contains abstracts and
bibliographic citations to technical reports,
bulletins, and other publications produced by
EPA, other federal and state agencies, and
industry dealing with technologies for treatment
of hazardous wastes. Performance and cost
data, quality assurance information, and a
contact name and phone number are given for
the technologies.
• The Risk Reduction Engineering Laboratory
(RREL) Treatability Database provides informa-
tion about contaminants physiochemical proper-
ties, environmental data, treatment technologies,
contaminant concentration, media or matrix,
performance, and quality assurance.
• The Technical Assistance Directory lists experts
from government, universities, and consulting
firms who can provide guidance on technical
issues or policy questions.
• A Calendar of Events list provides information on
conferences, seminars, and workshops on
treatment of hazardous wastes. International as
well as U.S. events are covered.
There is no charge for the ATTIC service. It is available
via modem over standard telephone lines. The phone
number for the ATTIC modem contact is (301) 670-
3808 (300-2400 baud), and the modem settings are no
parity, 8 data bits, 1 stop bit, and full duplex. The user's
manual also is available from EPA.
PI&& fiaks fc severeefate&ases.
PIES is a bulletin board system that links to several
databases and provides messaging capabilities and
forums on various topics related to pollution prevention.
Through its link to the United Nation's International
Cleaner Production Information Clearinghouse, it
provides a communication link with international users.
PIES is part of the Pollution Prevention Information
Center (PPIC), which is supported by EPA's Office of
Environmental Engineering and Technology Demon-
stration and Office of Pollution Prevention and Toxics.
PIES contains information about the following topics:
• Current events and recent publications relating to
pollution prevention
• Summaries of federal, state, and corporate
pollution prevention programs
• Case studies and general publications.
Searches can be performed by keywords related to
specific contaminants, pollution prevention technolo-
gies, or industries. The phone number for dial-up
access is (703) 506-1025; qualified state and local
officials can obtain a toll-free number by calling the
PPIC at (703) 821-4800. Modem settings are
2400 baud, no parity, 8 data bits, 1 stop bit, and full
duplex.
SAGE has a question-and-answer format that lets the
user input basic cleaning parameters about the parts to
be cleaned and about the desired process outcome
(Monroe and Hill, 1993). The user-provided information
is then applied, internally, to the SAGE database, which
derives recommendations for chemical and process
alternatives. Based on the information given, the
alternatives are assigned a relative score that allows
them to be compared. A brief summary of each recom-
mendation can be presented on the screen. Other
information, such as a representative MSDS and case
studies, also is included.
SAGE is available through the Control Technology
Center (CTC) of the U.S. EPAAir and Energy Engi-
neering Research Laboratory (AEERL). A system
operator at the CTC can be reached by calling
(919) 541-0800. The SAGE software can be trans-
ferred on an electronic bulletin board system in a file
named SAGE.ZIP. The bulletin board can be reached
at (919) 541-5742 (9600 baud, no parity, 8 data bits, 1
stop bit).
An 0rtl{ft& Solvent UtffteatiQn Handbook
The U.S. Department of Energy (DOE) has supported a
solvent alternative Utilization study through the Idaho
National Engineering Laboratory. As a result, a pro-
gram was established to develop an online electronic
Solvent Utilization Handbook. The handbook helps
users accomplish the following tasks:
• Identify solvents that are not restricted for use at
DOE Defense Programs, U.S. Department of
Defense (DoD) facilities, and private business.
• Evaluate their cleaning performance needs.
• Identify potential problems, such as corrosivity,
flammability (flash point), and hazardous material
content (OSHA and NIOSH exposure limits).
• Evaluate potential concerns for air emissions.
• Decide whether solvent recovery and recycling
are feasible.
• Determine whether the solvents are biodegrad-
able.
The information provided in this database is based on
results of actual experiments that included 16 different
contaminants on 26 metal alloys. The database is
38
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accessible through Internet or by using a telephone
modem. Further information can be obtained from the
Idaho National Engineering Laboratory by calling
(208) 526-7834.
The National Center for Manufacturing Sciences
(NCMS) is developing an electronic Solvent Database
that provides information on environmental fate, health
and safety data, regulatory status, chemical and
physical properties, and product suppliers. The data-
base includes more than 320 pure solvents and trade
name mixtures. A relational search capability enables
users to identify potential alternative solvents by
specifying search criteria. For example, solvent alterna-
tives can be selected by minimum flash point or by a
particular regulatory issue. Product performance data
are not included in the current version.
The NCMS Solvent Database will be a stand-alone
application that runs on the DOS platform. It will be
distributed on floppy disks. The cost of the software
has not been released. For further information contact
Mike Wixom, Project Manager, Environmentally Con-
scious Manufacturing, NCMS; telephone (313) 995-
4910.
Because there is no universal definition of "clean,"
process developers must adopt their own criteria for
judging cleanliness using methods that meet their
individual needs. Underestimating the level of cleanli-
ness required for a particular application may lead to a
loss of product performance or quality, while overesti-
mating may cause time, energy, and materials to be
wasted. As a working definition, "clean" usually is the
level of cleanliness required for any of the following to
occur:
• Mechanical devices function according to design
specifications
• Electronic or electrical devices perform reliably
over their expected service lifetimes
• Organic coatings adhere properly to a substrate
• Product finish meets performance and appear-
ance criteria.
must be tek&n Mo accoy/rf wben choosing
Before selecting an alternative solvent, process devel-
opers must consider the following aspects about the
parts to be cleaned:
• Material composition — is the part sensitive to
water or solvents?
Coating type — will the coating become dam-
aged? — should it be removed?
Part size — a concern for cleaning equipment
configuration
Part shape — complex shape may require engi-
neering modifications to ensure thorough clean-
ing and drying
Value of the part — determines how much invest-
ment should be made in an alternative process
Stability of the part— will an aggressive cleaning
process damage the part?
Type of contaminants present — potential for
aqueous, semi-aqueous, or other types of
cleaning
Rate of production — determines speed and
capacity of the alternative process
Postcleaning steps — how clean must the part
be? — must it be dry immediately?
tfedsfon in choosing m %lt&mativ$ ctean*
In addition, considerations must be made for
process changes that do not directly impact the
cleaning process:
• Operational costs — cleaner/solvent; particulate
filters, heating, ultrasonics, tap water, water
deionization, drying, and other energy costs
• Investment costs — cost of the cleaning unit;
accessories; electrical, water, steam, and drain-
age connections
• Labor requirements — regular labor compared to
current requirements, special training
• Hazardous material usage — fire protection, air
ventilation, waste collection and shipment
• Waste stream handling — used solvent, skimmed
oil/grease, solvent vapor emission/capturing,
wastewater pretreatment
• Process sensitivity— cleaner/solvent testing/
maintenance, requirement to add chemicals to
restore balance, filter changes.
to assist in selecting a daamr technology,
An approach to selecting a cleaning system that will
perform the necessary cleaning functions and one that
can be supported by industry is to conduct a multiple-
attribute evaluation based on the attributes listed
above. The evaluation should compare attributes of the
current cleaning system (the baseline) with those of
alternative technologies. A simple numerical scheme
can be easily developed. For example, scores between
1 and 10 would be assigned to each attribute and their
sum would then rank the technology. The highest
scoring technology would be the best alternative. If the
score should fall below that of the baseline, then the
39
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need to change technologies should be reevaluated.
The attributes can be weighted evenly or they can be
weighted to emphasize issues of particular concern.
For example, if removal of an adhesive is a critical
concern, then a cleaner that is capable of attaining this
goal should be prioritized. As another example, if a
plant has no industrial wastewater treatment facility and
must discharge wastewater directly to a POTW, then a
process that either does not produce wastewater, or
one that could produce wastewater that meets the
discharge criteria of the POTW would be an important
attribute which should be weighted accordingly. This
methodology can include quantitative and qualitative
attributes, both of which are important in making
process engineering and waste minimization decisions.
fM festing&fttm new t&stmatogy cm b&
dene to evaluate fts effectiveness,
In addition to querying electronic databases and
reading technical literature, it is a good idea to consult
with industry partners who face similar choices and
may have had to make critical decisions. Another
approach is to discuss the possibility of testing a
cleaning system on site or at a vendor's location. Many
vendors have test units at their manufacturing loca-
tions, where typical parts can be cleaned to evaluate
the effectiveness of the technology.
Vendors can ftelp fa f/re $etecti0nprQce$s>
When evaluating the effectiveness of a new cleaning
technology, the user often must evaluate how clean the
part is after washing. Evaluating the cleanliness of the
workpiece can involve anything from simple visual
observation to sophisticated surface analysis depend-
ing on the requirements of the application. For ex-
ample, many metal finishing industries use a relatively
simple test called the water-break test to evaluate a
clean surface. The test involves dipping the cleaned
workpiece or a cleaned test panel into a beaker of
water and pulling it out. If the water film forms a con-
tinuous layer on the workpiece surface that can be
sustained for about a minute, the surface is considered
clean enough for further product finishing steps such as
electroplating. Evaluating the cleanliness of an irregu-
larly shaped part with crevices or blind holes may be
more difficult.
Alternative cfe&fiing technologies frave
enough fiexMity to overcome many
performance problems,
If cleaning effectiveness of an alternative cleaning
system should fall below expectations, equipment
vendors or contractors often can bring about improve-
ments by making design or process modifications. For
example, in spray cleaning, changing the angle of the
spray nozzles can sometimes improve the cleaning
effectiveness dramatically. Parts holders also can be
custom designed for a particular application to maxi-
mize cleaning performance. Similarly, optimization of
process parameters can improve performance. Pro-
cess parameters include bath temperature, run time,
solution filtration, and the chemical balance of the
cleaner or solvent.
If aqueous cleaning seems like a desirable option, then
keep the following features and limitations in mind:
• Aqueous cleaning is more effective at higher
temperatures, and normally is performed above
120°F using suitable immersion, spray, or
ultrasonic washing equipment. For this reason,
good engineering practices and process controls
tend to be more important in aqueous cleaning
than in traditional solvent cleaning to achieve
optimum and consistent results.
• In cleaning situations where the oil content is
high, a useful methodology is to rely on the oil's
natural immiscibility in water and allow separa-
tion to occur so that the lighter fractions can be
skimmed off the top and the heavier fractions can
be removed by filtration. The volume of waste
generated is greatly reduced using this kind of
phase separation technique, and the lifetime of
the cleaner is thereby extended.
• An important factor in choosing aqueous clean-
ing is whether the product and/or process can
tolerate water. Compatibility of the product/
process with water must be carefully investi-
gated. For example, some ferrous metals may
exhibit flash rusting in aqueous environments;
therefore, such parts should be tested prior
to full-scale use.
Similarly, if semi-aqueous and solvent alternatives
seem desirable, then consider the following features
and limitations:
• Semi-aqueous cleaners may be more aggressive
in removing heavy organic contaminants.
• They may have lower corrosion potential with
water-sensitive metals.
• Semi-aqueous cleaners penetrate small spaces
more easily than aqueous cleaners because they
have lower surface tensions.
• No water is used with hydrocarbon cleaners, so
there is no potential for water corrosion or for
water to become trapped in cavities.
• One benefit of semi-aqueous cleaners and
hydrocarbon solvents is that distillation and
membrane filtration technologies are being
developed that will permit recycling and reuse of
the products.
40
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• A wide range of organic solvents is available that applications. In addition, the emerging technologies
may be beneficial as a replacement technology, discussed in Section 3, and those yet to be devel-
particularly on a small scale, such as bench-top oped, may find a role in alternative cleaning methods.
or spot cleaning.
• Most semi-aqueous cleaners are reported to be Reference
biodegradable.
• One must be more concerned about aquatic Monroe, K. R., and E. A. Hill. 1993. "SAGE (Solvent
toxicity and human exposure than one is with the Alternatives G,uidg): Computer Assisted Guidance
use of aqueous cleaners. for Solvent Replacement." In: Proceedings of the
1993 International CFC and Halon Alternatives
Finally, advanced technologies such as supercritical Conference. The Alliance for Responsible
CO2 and CO2 snow cleaning may be suitable in niche CFC Policy, Washington, D.C. pp. 431-439.
41
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SECTION 6
INFORMATION SOURCES
Table 10 shows the trade associations and the technology areas they cover. Readers are invited to contact these
trade associations and request their assistance in identifying one or more companies that could provide the
desired technological capabilities.
Table 10. Trade Associations and Technology Are
Trade Association or
Technology Group
Technology Areas Covered
Contact
Association for Finishing Processes of the
Society of Manufacturing Engineers
Industry Cooperative for Ozone Layer
Protection (ICOLP)
Institute for Interconnecting and Packaging
Electronic Circuits (IPC)
National Association of Metal Finishers
Society of Automotive Engineers
Industrial finishing operations
Alternative substances for ozone layer
protection
Electronic assemblies, defluxing
operations
Industrial finishing operations
Process engineering and finishing
operations
P.O. Box 930
One SME Drive
Dearborn, Ml 48121
(313)271-1500
1440 New York Avenue, NW
Suite 300
Washington, D.C. 20005
(202)737-1419
7380 North Lincoln Avenue
Lincolnwood, IL 60646
(708) 677-2850
111 East Wacker Drive
Chicago, IL 60601
(312)644-6610
400 Commonwealth Drive
Warrendale, PA 15096
(412)776-4841
42
•&VS. GOVERNMENT PRINTING OFFICE: 1996 - 75M0M1M*
-------
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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