Solvents - The Alternatives

Minor edits: 5/18/99, with 2003 Addendum

Bob Carter
Waste Reduction Resource Center
P. O. Box 29569
RALEIGH NC 27699-1639

Due to the rapid change in technology, new cleaners, new processes and experiences gained from their use, some of the material in this report may be out of date. Except for the Waste Reduction Resource Center (WRRC) contact information, this report has not been updated since 1996. For specific information on alternatives to an existing process or a new cleaning application, contact WRRC at:

A special thanks is due to all who provided constructive criticisms of this report. Hopefully it will be more useful to readers because of their interest. Vic Young, Phil Morse, and Gary Hunt of the Center and Stephen Evanoff, General Dynamics, Dallas, TX, and many others provided valuable input. The person due the greatest thanks is Ann Hoke of the Center whose patience and tolerance through many rewrites made it all possible.

The Waste Reduction Resource Center is an EPA Region IV/TVA supported activity charged with providing information clearing house, waste reduction training, and audit support to State Technical Assistance Programs, local governments, and other requestors, public and private, in the Southeast. Waste reduction information and support is provided to requestors outside Region IV on a noninterference basis with priority given to other EPA Regions, DOD, and other governmental programs state and federal. The Center has provided assistance to over 6000 requestors since opening for operation, April 1, 1989. The Center shares the offices and a technical resource library and uses the extensive technical expertise of the staff of the North Carolina Office of Waste Reduction.

"Crunch" time has come and passed for most solvent users. If the excise tax didn't do it, accelerated phase out of the chlorinated ozone depleters and the Clean Air Act did. All users of solvents, whatever the application, need to look for safe and effective alternatives. What ever the motivation - cost, safety, regulatory - the time to change is now.

In June 1992, President Bush unilaterally directed the production phase out date for chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform be moved from 2000 - 2005 to December 31, 1995. In November 1992, the Montreal Protocol Nations agreed to the earlier phase out date, if changed one day, to January 1, 1996. This change came about due in part to new NASA measurement data showing accelerated ozone depletion over North America far in excess of original predictions.

The Clean Air Act will further reduce economical options available as regulations are promulgated to control emissions for the photo chemical reactors, green house gas contributors, carcinogens, and other chemicals with toxic or hazardous characteristics. In communities classified as "non-attainment" areas for ozone, particulates, or carbon and nitrogen gases, limits will be extremely restrictive on volatile organic compound (VOC) emissions. Product labeling requirements will provide strong motivation to producers to make material substitutions. New labeling requirements were published in the February 1993, Federal Register with new requirements beginning in May 1993. NESHAPS for high VOC compounds have since been promulgated for various industrial applications.

While many have already changed, this report attempts to summarize existing technologies, equipment and cleaners to help those who have not changed to take a realistic look at alternatives. Options, not solutions, will be presented. Products identified as available are presented as just that. The Center does not, and will not, recommend a specific alternate cleaner, equipment or treatment methodology as the "best" approach. The tables represent a cross section of products available and identifies where additional information can be obtained. You must identify the best, or as is often the case, best combination of cleaners and equipment that meet your specific needs.

There is no "drop-in" replacement for chlorinated solvents in any cleaning application. Switching to aqueous or semi-aqueous cleaners and processes generally requires additional equipment, multiple cleaning and rinsing steps, and drying depending on the cleaning level currently being attained in vapor degreasers and other solvent based cleaning processes. The customer's cleaning specifications may limit alternatives available or dictate the final configuration of the cleaning process. What follows cleaning - plating, coating, heat treating, anodizing, etc. - also dictates the specifications for "clean". While many techniques and technologies exist to measure cleanliness, these are not addressed in this pamphlet. Information can be obtained from the Center if needed.

There are many variables that must be considered when choosing the best cleaning process for your application. The soils to be removed, the substrate to be cleaned, safety to workers, disposal of spent cleaners (treatability), recyclability, production rate and, as stated, before, what follows cleaning. Different cleaners work better for different applications. The key is to optimize the cleaning process for your application.

Soils: There are three general classifications of soils - organics (rosins, glycols, oils, greases, waxes), water soluble inorganic salts (chlorides, sulfates, etc.) and insoluble particles (dirt, dust, metal fines, etc.). Parts that have passed through multiple processes grinding, machining, forming, heat treating, etc., will have soil combinations to remove.

Acid and alkaline cleaners may attack metal substrates. Strong alkaline cleaners will etch aluminum, aluminum alloys, and zinc. Strong acids will etch steel. Strong oxidizing acids (nitric and chromic) will corrode copper. Suppliers typically add inhibitors, or prescribe contact time and temperatures, to control or reduce the effect of these characteristics.

Aqueous and semi-aqueous cleaners fall into several categories. Suppliers classify their products as biodegradable, safe, non-hazardous, and use other subjective qualifiers. Determine the validity of these claims for yourself. If not, you can be presented with surprises you would prefer not having to solve.

The Air Force found that "biodegradability" ranged from hundreds of parts per million (ppm) to hundreds of thousand (ppm) of biological oxygen demand (BOD). Chemical oxygen demand (COD) tests had parallel variability. Suppliers can provide this information to you. Don't let sudden increases in sewer use charges be your motivation to check. Trading one problem for a different one may not be the solution you are seeking.

When choosing the cleaners and affiliated equipment to meet your needs, there are many factors that must be considered. Production rates, customer requirements, cost and floor space are common to all. Material screening must include health hazards, treatability, either in a publically owned or onsite treatment plant, and equivalent cleaning performance. Corrosion potential and impact on down stream processes, while corrective with additives in cleaning tanks or post-clean rinse tanks, must be considered when choosing the right process. If discharging to a municipal sewer system, keep your Publically Owned Treatment Works informed of any change anticipated in the volume, strength, or potential toxicity of your waste.

There are many blends being marketed. One "aqueous" cleaner contains alcohol, an alkaline detergent, surfactants, saponifiers and water with or without glycol ethers. The relative concentration of each will determine what problem or combination of problems such as flammability, treatability, health effects, etc., you must deal with in your design. Closed cycle systems have been designed to over come problems such as flammability, treatability, VOCs, etc., associated with exotic cleaners. As a general rule, if you use two barrels of chlorinated solvents per month, it may be cost effective to consider closed systems using terpenes, alcohols or blends.

Note: If switching to terpenes or hydrocarbons, alcohols or other materials with potentially low flash points or contain toxic or hazardous additives, OSHA and Fire Code Standards must also be met. While vendors can formulate or design to offset or control potential work place hazards, be sure you switch to a product that meets all your work place requirements, not just equivalent cleaning.

Test! If tests are conducted at a supplier's laboratory, be certain that all variables are incorporated into the series of tests, such as:

• Cleaner concentration, temperature, immersion time
• Parts movement speeds (production rate)
• Solution contact with parts/agitation (type and rate)
• Solution replacement rates
• Tank and pump dimensions (depth of solution, agitation, etc.)
• Nozzle spacing, pressures, and flow rate

If you test a supplier's product, use the supplier's (prequalified) expertise to assist you.

Terpenes: Terpenes are chemical compounds extracted from plants such as the bark of trees or citrus fruit skins. They have been used in household cleaners, pharmaceuticals, deodorizers, and other commercial products. While having excellent solvency characteristics, there are factors, including safety, that must be considered. In general, terpenes cannot be sprayed in an open tank. The vapor has a relatively low flashpoint. This generally limits open tank liquid heating to 100o F or less. Terpenes are not as easily recycled as aqueous cleaners. Odor may be a work place detractant. BODs and CODs need to be checked and verified. Water chemistry, keeping the right balance between the cleaner and additives, can be a problem accentuated by evaporative losses. At least one manufacturer has developed a "closed" system that minimizes safety problems. The same manufacturer can incorporate a vacuum distillation or membrane filtration unit to reuse the terpene based cleaner. An alcohol or mineral spirits rinse system is required for some applications.

Hydrocarbons, usually combined with a surfactant and rust inhibitor, are effective in removing soils such as cutting oils, coolants, greases and waxes. These compounds can be effectively recycled. Disposal options generally involve incineration. Most have low flash points that must be considered and planned for in equipment selection.

For other applications such as replacing methyl ethyl ketone or methylene chloride in special cleaning applications (wiping, paint gun cleaning, etc.), many have turned to combinations of N-methyl pyrolidone (NMP), dibasic esters (DBE), and other less hazardous materials coming available. Any alternative should be thoroughly tested and evaluated for health and environmental impact before switching. No attempt has been made to separately identify alternative wiping compounds. Many new ones are being marketed. This information is available on request.

Aqueous cleaners range from pure water to exotic combinations of water, detergents, saponifiers, surfactants, corrosion inhibitors and other special additives. When combined with heat, pressure, agitation, filtration, etc., an effective combination can be found for most cleaning applications.

Alkaline type cleaners have reemerged as safe, effective substitute compounds for chlorinated solvents in many applications. As with other families of cleaners, there is no one drop-in replacement for all uses. The large suppliers generally will be able to formulate cleaners to meet your needs. These additives take into consideration the soils and subsequent production process. Additives generally perform the following:

• Penetrate soils to wet surface
• Emulsify (dissolve) solids in to solution (can be filtered out or rinsed off)
• Neutralize (raise Ph of acid soils, lower Ph of alkalines)
• Saponify (change insoluble fats and fatty acids into water soluble soaps)
• Oxidize (loosen rust and stains for easy removal)
• Precipitate (convert soils to heavier form for removal as sludge)
• Coagulation (to assist in removal of suspended soils by filtration)
• Flotation (cause soils to migrate to surface for skimming).

As previously stated, the additives can create concurrent or post cleaning problems. Special handling, health, safety, treatment, and disposal must be considered in a process design and cleaner selection. Some additives, such as certain glycol ethers and esters, have unanswered health and safety questions. Review Material Safety Data Sheets (MSDS) and demand full answers, particularly the BOD and COD of solutions with additives. As stated previously, many suppliers can formulate to meet your needs to reduce bad side effects such as corrosion, etching, flammability, health effects, treatability, etc.

Mechanical cleaning and stripping has not been addressed in this report. Information on processes including use of sand, plastic beads, glass beads, steel shot, aluminum oxide, walnut shells, supercritical CO2, frozen CO2 cereal, baking soda, sponges, xenon lamp, laser stripping, etc. To clean various substrates, information is available on request.

Cleaning equipment ranges from "A to Z". Many suppliers will custom design for your process. Despite disclaimers, vapor degreasers and other solvent cleaning processes can be modified to do the job. Large units can be converted to multiple tanks, modified to incorporate spray rinsing, ultrasonics, mechanical agitation, filtration, air knives, etc., to do the job. This may be the most cost effective approach to take. Many companies will quote on retrofitting existing equipment and/or providing new equipment. Some companies have designed retrofit packages to use terpenes or NMP in their existing degreasers as a substitute for CFCs in vapor degreasing.

If you have the in-house capability to modify your units, consider it. Check with the original manufacturer; they may have modification plans and kits. If not, several companies have been identified that specialize in existing equipment modification.

As stated in the beginning, this report attempts to provide information on the considerations and options available when changing from solvent cleaning to aqueous or semi-aqueous cleaning. Others have made the transition effectively with the attendant benefits of cost savings, risk reduction, and a better work environment. You can do it also.

Some of the references available through the Center are listed in Table 1. These and other more current reports will be made available to you on request.

Equipment and vendor information was extracted from product literature available in the Center. It is a representative list, not a complete list of products on the market. Others are coming available or are already available but not known to the Center. We do not recommend any product or supplier. Only you can choose the product(s) and supplier(s) that meet your special set of needs and criteria. The "Potential Problem" column is there to alert you to the possibility of a characteristic of the cleaner that you may have to consider. As stated before, vendors can formulate or design to over come bad characteristics and make cost effective use of their product an alternative.

Free, nonregulatory technical assistance is available through various State and Federal programs. Information on these programs is available through the Center. If you are in our service area, do not hesitate to call.

1. "1991, U.N.E.P. Solvents, Coatings, and Adhesives Technical Options Report", U.N.E. P., December 1991.
2. "Alternatives For CFC-113 And Methyl Chloroform In Metal Cleaning", I.C.O.L.P., 1991.
3. "Surface Preparation Via Chemical Applications", Joseph V. Otrhalek, P.E., and Dr. Stanley M. Sokalski, Detrex Chemical Industries, Inc. Undated report provided by Detrex Corporation.
4. "A Emulsion Cleaning Feasibility Study", Peter H. Wu, Shawn Vierthaler, Rick Bruce, Boeing Commercial Airplane Group, Wichita, KS. Presented at "Solvents Alternatives" DOE/USAF Conference, Phoenix, AZ, November 1990.
5. "Emulsion Cleaning (Immersion and Spray)", Process Specification Boeing Commercial Airplane Group, 7/26/91, Seattle, Washington.
6. "Aqueous Clean Does Work", Steven M. Nourie, American Metal Wash, Inc. Paper presented at the 1991 International Conference on CFC Alternatives, Baltimore, MD, December 3-5, 1991.
7. "A New Semi-Aqueous Alternative To 1,1,1-Trichloroethane In Metal Cleaning", Felipe A. Donate and James G. Papajesk, The Dow Chemical Company. Paper presented at the 1991 International Conference on CFC Alternatives, Baltimore, MD, December 3-5, 1991.
8. "New Metal Cleaning Alternatives", Gary L. Horton, Dupont Corporation. Paper presented at the 1991 International Conference on CFC Alternatives, Baltimore, MD, December 3-5, 1991.
9. "Use of Advanced Hydrocarbon Fluids for Precision and Metal Cleaning", Peter G. Miasek and James L. Schreiner, Exxon Chemical Company. Paper presented at the 1990 International Conference on CFC and Halon Alternatives, Baltimore, MD, 27-29 November 1990.
10. "General Dynamics Program to Eliminate Halogenated Solvents" Stephen P. Evanoff, P.E., and Henry J. Weltman, General Dynamics Corporation, Fort Worth. Paper presented at the 1990 International Conference on CFC and Halon Alternatives, Baltimore, MD, 27-29 November 1990.
11. "Replacement of Halogenated Solvent Degreasing With Regenerable Aqueous Cleaners", 46th Annual Purdue Industrial Waste Conference Proceedings, Lewis Publishers, Inc., Chelsea, MI, 1992, p. 851 - 871.
12. "Aqueous Degreasing, A Viable Alternative To Vapor Degreasing" J. T. Snyder, Martin Marietta Astronautics Group. Proceedings of the Annual Hazardous Waste Minimization Symposium, Costa Mesa, CA, Spring 1990.
13. Alternate Cleaning Technology, Phase I Summary, Ratheon Corporation. Alternate Cleaning Technology Committee, handout at the 1991 International Conference on CFC Alternatives.
14. "Advances In Halogen-Free Cleaning Using Semi-Aqueous Processes", Michale E. Hayes, Ph.D., Petroferm, Inc. Paper presented at the 1990 International Conference on CFC and Halon Alternatives, Baltimore, MD, 27-29 November 1990.
15. "Solvent Substitution and Equipment Modifications For Vapor Degreasing", Van T. Nguyen, Nora A. Zirpa, and Deborah K. Shaver, ICF Technology, Inc., 1988 study presented at "New Realties Conference" Santa Clara, CA, Feb. 1989.
16. "Industrial Trials of The Perflurocarbon Isopropyl Alcohol Cleaning System", Bryan Baxter, British Aerospace Dynamics, LTD. Paper presented at the 1990 International Conference on CFC and Halon Alternatives, Baltimore, MD, 27-29 November 1990.
17. "Semi-Aqueous Cleaning Technology: An Effective, Environmentally Safe Alternative To CFCs", Owen W. Blake, E.I. duPont deNemours & Co., Inc. Paper presented at Singapore - U.S. Seminar on CFC's, Singapore, Sept. 17-19, 1990.
18. "The Development of Analytical Techniques for Quantitatively Comparing The Performance of Alternative Metal Cleaning Products", Joanna M. Farella, Gary E. Mitchel, and Laura A. Bonadies, The Dow Chemical Company. Paper presented at the 1991 International Conference on CFC Alternatives, Baltimore, MD, December 3-5, 1991.
19. "Hybrid Assembly Cleaning with Non-Halogenated Solvents" Urmi Ray, Iris Artaki, Roland Ellis, Jr, and Gary S. Heyer, AT&T Bell Laboratories. Paper presented at the 1991 International Conference on CFC Alternatives, Baltimore, MD, December 3-5, 1991.
20. "Replacement of Chlorinated Solvents for In-Line Pre-Plate Metal Cleaning With Environmentally Sound Alternatives", William O. Gillum & Anna M. Jackson, AT& T Bell Laboratories. Paper presented at the 1991 International Conference on CFC Alternatives, Baltimore, MD, December 3-5, 1991.
21. "Closed Loop Water Cleaning", Frank Grano and Bryan Neumann, Printed Circuit Assembly, August 1990.
22. "Particle Removal Using Ultrasonic Cleaning", Ismail Kashkoush and Ahmed Busnaina, Clarkson University, and Frederick Kern, Jr. and Robert Konesh, IBM General Technology Division. Paper presented at the 1990 Conference of the Institute of Environmental Sciences.
23. "Water - Alcohol Cleaning: It's Economics and Performance", Steven D. Glass, Electronic Controls Design, Inc. Paper presented at the 1990 International Conference on CFC and Halon Alternatives, Baltimore, MD, 27-29 November 1990.
24. "Evaluation of Possible Methods For Determining Non-volatile Residue in Aqueous Precision Cleaning", Many Contributors, NASA. Study report published by Kennedy Space Center, FL, 1990.
25. "Innovations in Chemical/Process Solutions to Metal Cleaning", Jonathan Harmon, Envirosolv, Inc. Paper presented at the 1991 International Conference on CFC Alternatives, Baltimore, MD, December 3-5, 1991.
26. "Impingement: The Key to Effective Aqueous Cleaning", Steve Temple, Ransohoff. Paper presented at the 1991 International Conference on CFC Alternatives, Baltimore, MD, December 3-5, 1991.
27. Cleaning Hand Book, Published by Grace Metal Working Fluids, W. R. Grace Co., Lexington, MA. Undated.
28. The Polychem Environmental Alternative Chemical and Equipment Book, Published by U. S. Polychemical Corp., Spring Valley, NY. Undated.
29. Guide To Powder Coating Pretreatment, Published by Fremont Industries, Inc., Shakopee, MN. Undated.

Continued