"Precision Cleaning - The Magazine of Critical Cleaning Technology"
Parts Cleaning

Cleaning With D-Limonenes: A Substitute for Chlorinated Solvents?

by: Tom Toplisek and Ross Gustafson
Pages: 17 - 22; September, 1995

{short description of image} Have you noticed the distinct fragrance of oranges everywhere from the local manufacturing plant to your bathroom? It’s due to the ever-increasing use of d-limonenes as cleaning agents.

Their affinity for grease and oil combined with low or no toxicity make d-limonenes effective alternatives to petroleum-based and chlorinated solvents. Today they are being used in a wide range of industrial, institutional, commercial, medical and residential cleaning applications. Diverse industries such as aerospace, automotive, electronic components, inks, paints and adhesives are all using d-limonenes in their manufacturing processes.

D-limonene is a citrus-based terpene derived from biological sources. Present in both the juice and the peel of oranges, it is a by-product of the citrus processing industry. It is recovered in commercial quantities by distilling orange oil and orange essence and by pressing citrus peel to make cattle feed. Brazil, the U.S. and Mexico are the primary producers of d-limonene.

Not a New Discovery

D-limonenes are not a new discovery; they were first used as cleaning agents nearly 30 years ago. Chlorinated solvents, however, have been the most widely-used cleaning chemicals for the past 25 years because they were inexpensive, effective and their use was unrestricted.

{short description of image} Concerns for worker safety and the environment have since curtailed the use of chlorinated solvents. Some are suspected carcinogens; all are toxic and ozone-depleting. Many European countries banned use of chlorinated solvents from December 31, 1994. The U.S., as we are all aware, will ban many chlorinated solvents, including the widely used 1,1,1-trichloroethane, at the end of this year, except for specific medical research and high technology applications.

Once manufacturers became aware of the problems caused by chlorinated solvents, they began searching for alternative cleaning agents. Many found d-limonenes to be an effective replacement for toxic chlorinated solvents, glycol ether, MEK (methyl ethyl ketone), xylene and chlorofluorocarbons (CFCs).

D-limonenes’ unique affinity for organic contaminants such as petroleum-based greases and oils makes them good cleaning agents. They can be combined with other chemicals to offer specialized cleaning properties such as emulsifying and releasing greases and oils, wetting surfaces, permitting reduction or rinsing with water. Compounds that stabilize foam, increase foam and minimize foam can also be added to d-limonenes.

Growing in Popularity

The versatility of d-limonenes has added to their popularity. Often, companies find that one d-limonene product used in different dilutions can take the place of many separate cleaning agents.

{short description of image} A leading manufacturer of recreational vehicles has replaced 25 different products with a single d-limonene cleaner. The company uses d-limonenes for everything from its chassis shop to windshield installation, paint preparation and janitorial applications.

A nationally-recognized manufacturer of home and office furniture has replaced 1,1,1-trichloroethane vapor degreasers with a water miscible d-limonene system in circulating immersion baths. By doing so, the company has reduced the amount of cleaning chemicals needed and decreased its chemical waste disposal costs. Its use of d-limonene has further reduced the number of rejected parts. In addition, the company uses d-limonene to treat parts prior to its electro-deposition painting process.

D-limonenes are being widely used in the aerospace, shipping and railroad industries. One aerospace company uses d-limonenes to hand-wipe aluminum panels prior to adhesive structural bonding. Another is using d-limonenes to clean fuel and oxygen lines, while others are relying on d-limonenes for cleaning landing gear assemblies and to remove exhaust residue.

In naval and commercial shipping operations, d-limonenes are being used to clean the protective coating applied to protect onboard pipes and equipment prior to repair. Railroads are using them to clean diesel engines and the under carriages of locomotives.

Other uses for d-limonene include electronics cleaning, tar and asphalt removal, asbestos tile removal, graffiti removal and grease trap maintenance. They can also be used as a hand cleaner, floor cleaner, printing press cleaner and carpet stain cleaner. Ski resorts use d-limonene for on-site lift maintenance — its low freezing point (-142F) makes it ideal for cold climate applications.

In addition to their versatility, d-limonenes have a high K-B (Kauri-Butanol) value. K-B is an ASTM test method which measures solvency. It demonstrates how much dirt a compound can hold relative to its own weight.

D-limonenes can hold two to 2.5 times their own weight in greases and oils before becoming ineffective as cleaning agents. Mineral spirits, on the other hand, have a K-B value of 20-40 and can only hold one half their weight in dirt. Therefore, manufacturers can use far less d-limonene and achieve comparable cleaning results.

Regulating D-Limonenes

From a regulatory standpoint, d-limonene offers several important benefits. The FDA lists d-limonene as GRAS ("generally regarded as safe"). D-limonene is not listed on California’s Prop 65 toxic substance list. The National Toxicology Program (NTP), International Agency for Research on Cancer (IARC) and OSHA do not list it as carcinogenic to humans. It does not contain lead, cadmium, mercury or hexavalent chromium or come in contact with these chemicals since it is a citrus-derived essential oil produced by steam distillation. It does not contain and is not manufactured with any of the Class I or Class II ozone-depleting substances under the U.S. Clean Air Act of 1990.

D-limonenes are non-toxic as defined by the Toxic Substance Control Act (TSCA). This makes them especially popular with manufacturers concerned about workplace safety. Many U.S. companies are taking a pro-active approach by substituting d-limonenes for chlorinated solvents before the ban on their use takes effect.

In certain cleaning applications, d-limonenes are not classified as a hazardous waste. This means companies that use them for grease and oil removal can generate waste streams that are not hazardous. The benefits here are considerable. Not only does the company offer a safer workplace, but it also reduces the expenses and liability involved with disposing hazardous materials.

Although they are an organic substance, d-limonenes are readily biodegradable. Their chemical structure enables them to rapidly break down into water and carbon dioxide. In addition, d-limonenes are a renewable resource; more citrus products are produced every year.

Drawbacks to Using D-Limonenes

Despite their many advantages, d-limonenes have their drawbacks. They are slower to dry than comparable chlorinated solvents. This means manufacturers may need to make changes in their production processes to compensate for the slower drying times. These can include slowing the line speed or increasing the amount of the area used for the drying process. Another approach is to add blowers of either hot or cold air or to increase temperatures across wet surfaces.

D-limonenes are not a direct substitute for vapor degreasers, although they can be used effectively in circulating tanks, sprays and ultrasonic baths. D-limonenes have a strong, characteristic orange fragrance and some may find this objectionable in poorly-ventilated areas.

D-limonenes’ growing popularity has affected demand and, therefore, prices. Weather, unstable markets and volatile political conditions in South America have caused prices to fluctuate wildly. Droughts and unseasonably wet weather have resulted in fruit with thinner peels. Since much d-limonene comes from the peels, less was produced.

While d-limonenes are a renewable resource, there is a finite supply of citrus fruit. Annual production of d-limonenes and orange terpenes worldwide is approximately 36 million gallons. Only 10 percent of this is available to companies that produce d-limonene cleaners and degreasers. Also, since d-limonenes are a citrus by-product, supplies depend on another production stream (foods and food additives).

Cost also deters some manufacturers from relying solely on d-limonenes. The cost per gallon for d-limonene cleaners is higher than the cost for a similar quantity of mineral spirits. However, since less d-limonene is needed to clean a given area or number of parts, the total cost for cleaning is usually comparable.

On balance, d-limonenes offer more positives than negatives. They are an effective cleaning agent. They are versatile and can be used for multiple applications throughout a wide spectrum of industries. They are non-toxic to both people and the environment. They are able to hold twice their weight in grease and oil before becoming ineffective. While their cost per gallon is higher than mineral spirits, less d-limonene is needed for comparable cleaning tasks. Companies looking to increase workplace safety, purchase fewer cleaning products and use a biodegradable cleaning agent would do well to consider using d-limonenes in their manufacturing processes.

About the Authors

Tom Toplisek holds a B.S. in economics and an M.B.A. An industry veteran, Toplisek is a member of the Society of Manufacturing Engineers, the Society of Plastics Engineers and the Rocky Mountain Society of Coating Technologies. Ross Gustafson holds a B.A. and an M.S. in chemistry and has worked with terpenes for the past six years.

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