d-Limonene, Mother Nature’s Solvent
by John L. Thomas, Third Coast Products, Bulverde, TX
d-Limonene is the principal component of the oil extracted from
citrus fruit rinds. When citrus fruits are squeezed and juiced, the
oil is pressed from the rind. This oil is then separated from the
juice and distilled to recover flavor and fragrance compounds. The
bulk of the oil is left behind and collected. This is food grade
After the juice is extracted in a special process, the peels are
sent to a steam extractor. This extracts more of the oil from the
peel. When the steam is condensed, a significant layer of oil
floats to the surface in the condensed water tank. This is
technical grade d-Limonene that is used by most formulators to make
This extraction and distillation process is now done all over the
world to meet the demands of d-Limonene use. Every country that has
abundant crops of citrus fruits also has facilities to extract and
package d-Limonene. Twenty years ago, I started buying the leftover
citrus oils from a juice manufacturer in South Texas near the
citrus orchards. They didn’t need it, so they sold the
technical grade d-Limonene to me at a very reasonable price. I
began selling it as a solvent product, hand cleaner additive,
oilrig cleaner and wastewater treatment compound. Now the world
knows the advantages of d-Limonene, and the prices at the wholesale
level are very high compared to other solvents.
Uses for d-Limonene have expanded dramatically. It is used in
paints, fragrance additives, cooling fluids, downhole oil well
fluid and other specialty products. The largest growth segment has
been in the cleaning products industry. It can now be found in
hundreds of cleaning products in the industrial and institutional
product markets. The worldwide annual production of d-Limonene is
over 150 million pounds and rising fast. Every major manufacturer
has negotiated supply contracts for d-Limonene for years to come.
My company is no exception.
d-Limonene as a straight solvent can replace many undesirable and
dangerous solvents such as mineral spirits, methyl ethyl ketone,
acetone, toluene, xylene and most of the chlorinated solvents. It
makes a great tar and asphalt remover when combined with a special
surfactant that makes rinsing easier. d-Limonene alone is not water
soluble, and upon rinsing even with hot water, the tar turns into a
gooey mess. The fact that it doesn’t mix with water easily
makes it a very good floating degreaser for use in waste water
pumping stations, parts washer tanks, dip tanks and as a paint
thinner. We sell it to the art departments of several colleges for
use as a brush cleaner to replace turpentine that the colleges have
The solvency of solvents is determined by a test called the KB
(Kauri-Butanol) rating test, which is a determination of the rate
at which the solvent dissolves a particular hydrocarbon soil.
d-Limonene has a KB rating of 67 which is almost the same as some
of the chlorinated solvents. Mineral spirits has a KB rating around
55. Butyl Cellosolve has a KB rating around 50, which will give you
an idea about the solvency of d-Limonene. Because it has high
solvency, it can easily dissolve and suspend heavy oils, such as
tar and asphaltic compounds. This same high KB rating allows the
d-Limonene to be distilled and recaptured for reuse with special
equipment. There are some large computer-related industries using
d-Limonene as an electronics cleaner for board washing. They reuse
it as long as possible.
There are a few drawbacks concerning d-Limonene when used as a
straight solvent. The main one is the odor is often too much of a
good thing. When used indoors, the orange citrus odor of technical
grade d-Limonene is overwhelming to some people. If you mist it,
such as when using an air-siphon gun for application, the mist is
flammable. The flash point of technical grade d-Limonene is
115°F. Consequently, it cannot be used to directly replace
1,1,1, tri-chlor, trichloroethylene or other non-flammable solvents
that are popular in the electrical maintenance areas of industry
where they spray clean running electrical equipment and motors.
Some companies, including my own, are mixing d-Limonene with a
flash suppressor. This increases the flash point to over 200°F
and allows it to be used in some applications as an electric motor
cleaner, contact cleaner and dip tank solvent for electrical
equipment. The power must be turned off to do this maintenance, but
the environmental risks are greatly diminished, and it’s
worth the time. d-Limonene does not leave a significant residue,
and it is non-corrosive to metals.
However, it will attack some plastics, rubber, paints and polymers.
This is important information because the seals in high-pressure
pumps on pressure washers can be adversely affected by d-Limonene,
even when the concentration is low in pressure washing detergents.
It takes a while to damage them, but we have proven that it is a
significant cause of pump failure. We do not include it in our
pressure washing products that go through a pump system.
d-Limonene As A Cleaning Compound
Now that the world has turned to organic natural solvents such as
d-Limonene, a whole new formulation industry is emerging. In the
past fifty years, we have grown accustomed to using solvents like
butyl, mineral spirits and other less than desirable ones to add to
our detergents to make them into water-soluble solvents. Butyl
Cellosolve (ethylene glycol monobutyl ether) has been the all-time
leader in this field. Most of the degreasers on the shelves at the
local supermarket contain butyl. The popular ones are Fantastik
™, 409 ™, Windex ™, Simple Green ™ and many
more. They are all great products and have been for many years. In
my opinion, butyl is still the best solvent additive, and I use it
in many products also. It will stay in solution easily and will not
cause damage to spraying systems.
However, the times are changing, so now we see products containing
d-Limonene, soy oil solvent, corn oil solvents, pine tree terpene
solvents and the like. The difficult part about using natural
solvents is their resistance to solubility in water. As
manufacturers of degreasers, we have had to spend many hours in the
lab developing ways to make a nice, clear liquid degreaser with a
percentage of d-Limonene in it. The same surfactant system we use
for butyl will not work for d-Limonene. It turns the whole liquid
product into a milky-looking mess, so most of the leading
manufacturers have developed ways to make the product stable and
work as well or better than the “good old” butyl
Another challenge for us when using d-Limonene as an additive in
detergents is its suppression of the foaming ability of “foam
making” surfactants. We must keep the total concentration of
d-Limonene under ten percent and add more surfactants to keep the
foam levels up to customers’ expectations.
How d-Limonene Works in Detergents
Ok, here comes the technical part that everyone should know about
how solvents such as d-Limonene actually work in a detergent
system. Modern detergents do not use soap as a part of the cleaning
system. Soap is comprised of tallow or tall oil mixed with alkaline
material and water. The resulting soap is fine for taking baths but
is terrible for cleaning hard surfaces. It combines with the
calcium and magnesium found in most unsoftened water to form lime
soap (bathtub ring) and is difficult to rinse off of newly cleaned
We now use surfactants in different amounts and blends to replace
soap. Surfactant is a term referring to these “surface active
agents.” They are synthetically produced and do not contain
soaps at all. There are actually hundreds of different surfactants
to choose from as a formulator. Many hours are spent in the lab to
pick the correct combination of surfactants to put in detergents.
Surfactants are combined with other alkaline ingredients, rinse
agents, water softeners (such as phosphates) and sequestrants to
control the calcium and magnesium in water. The surfactants are the
ingredients that actually penetrate the dirt and put it in
suspension. They also surround the oils in the dirt like little
spheres and don’t allow them to reform or stick to the
surface again. This is called solubilization. The surfactant
molecules line up in a certain way to form micelles. These micelles
are the controlling force in a detergent system and get utilized in
the cleaning process. The more surfactant in the product, the more
micelles are available for cleaning. Some companies scrimp on the
surfactants because they are expensive. Instead, they pay the price
of ineffective products that just don’t dilute well with
water or work effectively.
Solvents are added to this detergent system to attack the barrier
of hydrocarbons such as oils, grease, tar, asphalt, fuels, etc.
Surfactants do what they can to put them in suspension for rinsing,
but they just can’t get them all off. Alkaline ingredients
work to emulsify them, but only a limited amount can be put in the
product because of the adverse effects of high pH on some surfaces.
To solve this dilemma, a solvent is added to take up the slack and
help the surfactants do their job. Butyl works great as a booster,
but some states think it causes health problems. (The jury is still
out on that one.) Terpenes, such as d-Limonene and other natural
solvents, do help in these degreasing products. There are no known
health-related problems except for people allergic to citrus
Applications and Techniques for d-Limonene Products
Products containing more than fifty percent of d-Limonene fall into
the straight solvent category. These are used for removing wax,
inks, tar, asphalt, gum, adhesives and other hydrocarbon soils. For
the best results, it is recommended that the product be applied
undiluted with a low-pressure pre-spray applicator of some kind
that is solvent resistant. It is also used in dip tanks or parts
washers in this concentration. Some companies also offer d-Limonene
at ninety percent mixed with a surfactant and gelling agent. The
resulting product is thick but still sprayable. It clings to
vertical surfaces and does not run off. The solvent dissolves the
oils, and the surfactant removes the dirt, clay and salt particles.
This kind of product is a real labor saver when pre-spraying trucks
or cleaning refineries, construction machinery and other areas that
get oily and dirty. Non-viscous degreasers tend to run off onto the
ground or evaporate before they do their job. Less product is
actually used when it is gelled and can stick to the surface.
Products containing from twenty to fifty percent d-Limonene are
usually hand cleaners, printing press cleaners and other heavy-duty
cleaners that are not required to foam or be used as a detergent.
This category also includes automotive type cleaners such as brake
cleaner, engine degreaser, automatic parts washer solvent and floor
cleaners. They rinse well because of the amount of surfactants in
the formulas, and there is usually over thirty percent of water in
them. A product containing an alkaline detergent and thirty percent
of d-Limonene makes one of the best degreasers for cleaning
concrete driveways, mechanics shops and even commercial kitchens.
D-Limonene is very effective on baked on oils like soy.
Products containing less than twenty percent of d-Limonene make up
over eight percent of the products on the market categorized as
detergents. With five percent of d-Limonene, alcohol and
surfactant, a very good glass and mirror cleaner is produced. At
ten percent, it makes a great wheel wash, floor cleaner, equipment
cleaner, upholstery cleaner and multi-use degreaser for spray and
wipe cleaning on almost any surface.
Remember, d-Limonene at higher concentrations can affect pump seals
and rubber parts. Use equipment to apply it that has viton seals or
some other resistant-type material. An ordinary plastic garden-type
pump up sprayer will last about ten minutes if you put d-Limonene
in it. Flo-Jet™ pumps should be ordered with special
diaphragms installed in the pump. The regular off-the-shelf ones
will not last.
Safety and Environmental Concerns
d-Limonene is definitely a preferred solvent when it comes to
safety and the environment. As a naturally occurring solvent, it
biodegrades quickly; is much less toxic than mineral spirits and
the chlorinated solvents; and is non-caustic and non-reactive to
metals. The EPA has classified it as a non-toxic chemical in TSCA.
It is not a SARA Title III compound, and it is not regulated by the
Clean Air Act. Some states, such as California, have regulated
d-Limonene as a VOC, but this status is currently being
investigated in most states. At this time, it does not fall into
that category like other solvents.
d-Limonene is a slight skin and eye irritant, and the mist can be
aggravating to the lungs. These are temporary problems, and there
is no known long-term effect on humans. It is classified as
non-carcinogenic and non-mutagenic.
Overall, d-Limonene is the premier natural solvent in use at this
time. I have investigated other ones, such as soy oil solvent. Soy
oil solvent has good characteristics such as having high KB rating,
and being non-flammable and non-odorous. However, this solvent has
drawbacks. It is slow reacting, oily and has a limited supply.
Terpenes from pine trees work as well as d-Limonene, but the odor
is terrible. If its distillers ever eliminate the odor, these
terpenes will be a good choice for a natural solvent. The supply is
almost unlimited — there are a lot of pine trees in the
world, and it is a renewable resource, just like citrus trees.
Shopping for d-Limonene Products
Contract cleaners should always ask for a copy of the Material
Safety Data Sheet (MSDS) on any d-Limonene product. Some
manufacturers have used less expensive hydrocarbon-based diluents
to extend the natural solvent. They work fine, but there are some
companies who can experience problems with the EPA when any
hydrocarbons are used for cleaning at their facilities. The
resulting run-off is the culprit. If it ends up in a waste stream
that is monitored, the fines are high. The MSDS should clue you in
to these undesirable solvents in the formula. Choose one that just
uses d-Limonene to be safe and ask about the percentage of
d-Limonene in the product. It’s your right to know.
The author, John L. Thomas, has been in the specialty chemical and
pressure washing equipment industry for thirty years. His company,
Third Coast Products in Bulverde, TX, is a nationally recognized
wholesale supplier of detergents and solvents to pressure washer
and chemical product distributors. He also has owned a Texas-based
retail division with sales reps covering much of the state since
1980. Mr. Thomas is a consultant to the pressure washer and