A pollution prevention fact sheet about Terpene Cleaners used for industrial cleaning.
What would you do with 15 million pounds of orange peels? How about 50 million pounds of pine chips? Would you:
Terpenes are plant-derived hydrocarbons. They have been used for years in a variety of applications including fragrances, food additives, even insecticides, but in the last few years (with the phase-out of CFCs and trichloroethane), more interest has been focused on terpene cleaners. The most common ingredient in terpene cleaners is D-limonene, a derivative of orange peels. Alpha and beta pinene (Pine-Sol) are derived from wood turpentine and are also commonly used as cleaners. The majority of literature on terpene cleaners deals with D-limonene-based products and, in fact, the terms "terpene" and "D-limonene" are often used interchangeably.
Terpenes are extracted by pressing and distillation of the feed stock. The first run at distillation produces a 95% pure terpene, commonly used in 'gross' cleaning applications. Re-distillation and other purification techniques, results in a higher purity product, commonly used for fine cleaning applications. Terpenes can be used in a water/terpene emulsion, in a terpene/hydrocarbon blend or 'straight'. Though there are considerable differences between terpene formulas, there are also some common characteristics to be discussed.
Terpenes have very high solvency and clean very well, often better than chlorinated solvents. Greases, oils, fluxes and adhesives are easily removed using terpenes and blends have been developed which remove resins, paints and carbon deposits. As with most cleaning chemicals, straight terpenes are stronger than the water/terpene blends.
Terpenes are non-reactive with metals and most types of plastics. Strong terpene solutions can swell or degrade some types of plastic and rubber, so experimentation is recommended.
Terpenes have really caught on for cleaning electronic assemblies and printed circuit boards. If properly rinsed, terpenes are compatible with painting and plating operations and are now commonly used in machine shops and engine rebuilding operations, especially in solvent sinks. High purity terpene solutions are popular for cleaning precision parts and high voltage electrical parts.
Because of terpenes' low volatility, a rinse and/or dry step may be necessary. Experts debate whether unrinsed terpenes leave residues. The answer is -- some do, some don't. High purity terpenes don't leave a residue but do take longer to dry than chlorinated solvents. Low purity terpenes also dry slowly, but the impurities will remain as a residue. At 80/20, a terpene/water mix may turn to a paste, so if you are making a 10% terpene/water mix, make sure to add the terpene to the water instead of the other way around. Also be aware that terpene cleaners or terpene rinse water may attack PVC plumbing in your cleaning equipment.
Terpenes are flammable so spraying is not recommended, except in specially designed equipment. Terpenes are not highly volatile, but they are VOCs and may be regulated under the new Clean Air Act. Some salesmen are quick to point out that terpenes are "generally recognized as safe" by the FDA and that they are found in a myriad of products, from food additives to toothpaste. Unfortunately, toothpaste is not often used for industrial cleaning. Yes, terpenes are safer to use than many solvents, but to compare a terpene food additive to a terpene paint stripper is not only misleading, it is reckless. Terpene cleaners are mildly neurotoxic. They are known to cause respiratory distress and/or irritation and that "pleasant citrus fragrance" can very quickly become nauseating. There is a controversy about the carcinogenicity of D-Limonene. One preliminary study linked D-limonene to testicular cancer in male rats. Another study indicates that those results do not apply to humans. Who knows? The good news is that detection limits (by smell) are orders of magnitude below the recommended exposure limits so, for safety, try to use terpenes in a manner that minimizes odor. And wear your gloves.
With any cleaning chemical, recyclability is dependent on the ability to separate the soils and oils from the cleaning solution. Pick any two, terpene, oil or water and you can separate them economically. Put all three together and you've got a mess. That's one reason vendors who have been in the business the longest are moving away from terpene/water emulsions and toward straight terpene blends. Straight terpene cleaners are more expensive to purchase, but can be vacuum distilled and reclaimed. Terpene/water emulsions on the other hand are cheaper to purchase, but reclamation of the cleaner is not economically feasible. Thus, after oil concentrations render the cleaner ineffective, the whole bath must be disposed of. Terpenes actually dissolve oils, so separation by oil skimming is not possible. Separation by filtration has not been feasible because of the similarity of terpenes to oil.
Terpenes are biodegradable, perhaps too biodegradable. Terpenes are often discharged to sewers, but the biological and chemical oxygen demands (BOD/COD) are exceptionally high, possibly leading to sewer surcharges. Don't wait for a surprise. Check with your local waste water authority BEFORE purchasing a terpene-based cleaning system. Even better, design a closed-loop system that doesn't require disposal. Terpenes also have a very high BTU value as a fuel source, so incineration as waste oil is an option. Watch for metals and other contaminants which may exceed discharge or incineration limits.
Terpene cleaners are reasonably priced but costs are closely tied to bath concentrations and recyclability. Bath concentrations vary widely, from 5% to 100%, and water is cheap. But using and reclaiming a straight terpene cleaner may be cheaper than using and disposing of a terpene/water mix. Reclamation will reduce both purchase costs and sewer charges. Evaporative losses of terpenes are minimal due to their low volatility.
At Motorola's portable radio plant in Plantation, they've been cleaning circuit board assemblies with terpenes for about three years. Says Tony Suppelsa, Sr., a project engineer with Motorola, "It started back in 1989. We were looking for a way to get away from cleaning with CFC-113. We evaluated a number of cleaning chemicals including terpenes. The terpenes worked OK, but weren't necessarily the best at that time. But we found one company that made a machine to clean PC boards using terpenes, while the rest of the equipment industry was still tripping over itself. I loaded up some PC boards on a plane and flew to their test facility to do some test cleaning. When I got back, we ran accelerated life tests on the boards and they performed beautifully. They were actually cleaner than with the CFC-113. We put in an order for the equipment, installed it, and it ran without a glitch!" The equipment consists of a special terpene spray chamber (with a fire suppression system), an air knife (to reduce dragout), 2 recirculating spray rinses, a hot de-ionized water rinse and a dryer.
In step 2 of the project, Motorola began to recycle rinse water from the system. "We were using about 5 gallons per minute and the water and sewer bill just skyrocketed. So we installed a system that skims off the terpene from the rinse water, and now we reuse the water. That brought our water consumption down to about 80 gallons per day, mostly used to make-up for evaporation, and no discharge of pollutants." With these 2 steps, Motorola reduced the cost of cleaning PC boards by 85%.
Step 3 according to Tony: "A lot of Motorola facilities are using terpene cleaning as a stepping stone towards the ultimate goal: no-clean. Little by little, products are showing up that don't require cleaning; for example we now use no-clean fluxes. We're applying these new products to more and more processes. Now that's the ultimate answer."
Fact Sheets available in the Industiral Cleaning series:
Pollution Prevention Program
c/o the State of Florida Department of Environmental Protection
2600 Blair Stone Road
Tallahassee, FL 32399-2400 or
call 904-488-0300 (fax 904-921-8061), or
- in the Jacksonville area, call 904-448-4300
- in the Tampa area, call 813-744-6100.
Last Updated: October 18, 1995