A pollution prevention fact sheet on Hydrocarbon Based Cleaners for industrial cleaning.
For years folks have cleaned parts using a variety of different hydrocarbon solvents, such as mineral spirits, stoddard solvent, naphtha, kerosene, diesel fuel, even gasoline. Like dissolves like and the soils to be removed from parts are often hydrocarbon based. Greases, oils, waxes, all can be removed with hydrocarbon fluids. But there are associated health and safety concerns, especially flammability and worker exposure.
Enter the "Tri-chlor brothers," TCA and TCE. These chlorinated brethren were heralded as the new 'safety solvents', low in toxicity and high in flash point. Right off it was known that trichloroethylene (TCE) was a superior cleaner, and it took the market. But after a few years, studies revealed that TCE was not as benign as previously thought. Long-term health effects included liver and kidney damage and an increased risk of cancer. Industry soon started switching to trichloroethane (TCA), the less toxic (and less effective) alternative. Now with concerns about the ozone layer, Class I Ozone Depleters (including TCA) are being phased out of production. Time to return to the days of TCE? Not really. Besides the safety concerns, TCE is also a Volatile Organic Compound (VOC), making it a major contributor to ground level ozone or 'smog'. And because TCE is classified as a Hazardous Air Pollutant, the new Clean Air Act will severely restrict emissions of TCE, making it much more costly to use. Add to this the reporting requirements under RCRA and SARA Title III, and you will see that stepping backwards to TCE is not a good idea. By the way, the same arguments can be made against methylene chloride and perchloroethylene. It's time to look for alternatives to chlorinated solvents and one alternative is...(drum roll please!) ... hydrocarbons.
Actually, hydrocarbon cleaners have come a long way since mineral spirits and gasoline. New formulas have been developed with improved solvency, lower vapor pressure and higher flash points. These cleaners usually consist of long-chain aliphatic hydrocarbons. Aliphatic esters are often added to raise the flash point and improve solvency.
Like still dissolves like. Hydrocarbons will clean oils and greases (both hydrocarbon and silicone based), waxes, fluxes and inks. Carbonaceous soils are tough and require heat or ultrasonics to enhance cleaning. Hydrocarbons are not very effective against salts, fingerprints or resinous soils, but aliphatic esters may work on un-cured resins. Most hydrocarbon cleaners have low surface tension which improves cleaning of intricate parts.
Hydrocarbon cleaners are non-reactive with metals but may swell or degrade certain types of plastics and rubber. Be sure to check for compatibility with your specific parts.
Though vehicle maintenance shops are still probably the largest users, hydrocarbon solvents are also commonly used in precision cleaning, electronics and high voltage electrical applications. Hydrocarbon cleaners are seldom used in painting or plating operations.
When left on a part, hydrocarbon cleaners will dry, but much more slowly than common chlorinated solvents. Cleaners with higher flash points dry more slowly, so there is a trade-off between fast drying and safety. Residue is usually not a problem unless the cleaner is contaminated. If fast drying is necessary, try forced air drying (ambient or heated) or vacuum drying. Or try rinsing with a volatile rinse agent such as alcohol. Since no water is introduced in hydrocarbon cleaning, rust is not a problem, but some of the cleaners carry an obnoxious odor.
Hydrocarbon vapors are mildly neurotoxic, but many of the new cleaners available have low vapor pressure which minimizes exposure. Assuming you don't drink them, the major hazard associated with the use of hydrocarbon solvents (and the aforementioned alcohol rinse) is flammability. Choose a cleaner with a high (>140F) flash point. This will increase worker safety, reduce regulatory requirements and may allow you to add heat to the process, if necessary, to increase cleaning efficiency or decrease drying time. All hydrocarbons are volatile organic compounds (VOCs) and thus may be subject to regulation under the new Clean Air Act Amendments.
Hydrocarbon cleaners are usually circulated through a filter which removes insoluble particles. Filtration will not remove dissolved oils from a hydrocarbon solution. Thus, oils will build up in the solution and eventually render it ineffective. The cleaner will then need to be disposed of or, preferably, recycled using vacuum distillation. To reduce the frequency of recycling/replacement, use dirty solution in a pre-wash step to remove heavy soil deposits.
Hydrocarbon cleaners have a high BTU value, so users commonly send them out with waste oil for incineration. Pay close attention to your processes to assure that the cleaning solution is not contaminated with heavy metals or halogens (i.e. chlorinated solvents). Contamination means that the whole bath must be disposed of as a hazardous waste; incineration is no longer an option.
This new breed of hydrocarbon cleaners is more expensive per gallon than the old workhorse solvents like stoddard, mineral spirits or tri-chlor. But because of the lower volatility, losses due to evaporation are significantly reduced. And if the cleaner is recycled, both purchase and disposal costs are reduced, making hydrocarbon cleaners an economically attractive option.
There are a number of similarities between hydrocarbon cleaners and the cleaners we discussed in the terpene fact sheet. The obvious question is: "Why not mix the two?" A number of manufacturers have done just that. The resulting terpene/hydrocarbon blends combine the higher solvency of terpenes with the higher flash point of a long chain hydrocarbon. This combination of traits is very attractive for many cleaning applications.
Hi-Stat Manufacturing in Sarasota manufactures high quality temperature sensors for the automotive industry. After manufacturing, the sensors are tested for accuracy in a heated silicone oil bath. Electrical leads are soldered to some of the sensors. Initially Hi-Stat cleaned the sensors using Freon 113, later switching to 1,1,1,-trichloroethane. With the phase-out of these substances scheduled, they considered taking the backwards step to trichloroethylene. "We needed a solvent to remove flux as well as silicone oils", says Hi-Stat Engineer Chuck Griffiths, "and the sensors can't tolerate being wet for very long, so we steered clear of semi-aqueous systems. We tested quite a few substances and finally found a hydrocarbon cleaner that was the best at quickly removing the soils we've got, and was better for the environment."
"We use an old vapor degreaser as a batch dip tank. The tank is equipped with ultrasonics, but we found that we don't really need it. After cleaning, the solvent is blown from the parts with an air knife. There is very little evaporation and the batch is dry to touch in about 45 seconds. This cleaner is one of the more expensive hydrocarbon cleaners, and (per pound) costs a lot more than 1,1,1, or Freon used to cost. But it is still cost justified because we don't use anywhere near as much." What's the down-side? Chuck replies, "The only negative is that some people don't like the odor; but the cleaner we use may be one of the more objectionable ones. Others (hydrocarbons) don't clean flux as well and dry slower, so there is a trade off."
Fact Sheets available in the Industrial Cleaning series:
Last Updated: October 17, 1995