Mineral oil or liquid petroleum is a by-product in the distillation of petroleum to produce gasoline and other petroleum based products from crude oil. It is a transparent, colorless oil composed mainly of alkanes (typically 15 to 40 carbons) and cyclic paraffins, related to petroleum jelly (also known as “white petrolatum”). It has a density of around 0.8 g/cm3. Mineral oil is a substance of relatively low value, and it is produced in very large quantities. Mineral oil is available in light and heavy grades, and can often be found in drug stores.
In the late 1800s, the term “mineral oil” or “rock oil” was first used to describe the petroleum hydrocarbons and associated products that were produced from wells that tapped underground reservoirs. The term differentiated petroleum hydrocarbons produced from underground sources from other common oil sources at the time, such as palm oil or whale oil. In today’s petroleum exploration and production (E&P) business, the phrase “mineral oil” is most often used in legal documents to define and encompass all of the liquid hydrocarbon and gaseous products produced from wells drilled into underground petroleum-bearing reservoirs.
There are three basic classes of refined mineral oils:
- paraffinic oils, based on n-alkanes
- naphthenic oils, based on cycloalkanes
- aromatic oils, based on aromatic hydrocarbons (not to be confused with essential oils)
Due to its low price and ubiquitous supply, mineral oil has been pressed into service in a wide variety of capacities. Most of these exploit its properties as a low-toxicity, non-reactive general purpose lubricant and coolant, or for electrical properties.
Medicine – external uses
Mineral oil with added fragrance is marketed as baby oil in the US, UK and Canada. While baby oil is primarily marketed as a generic skin ointment, other applications exist in common use. It is often used on infant “diaper rashes” to ease the inflammation. Similarly, it may alleviate mild eczema, particularly when the use of corticosteroid creams is not desirable. Mineral or baby oil can also be employed in small quantities (2–3 drops daily) to clean inside ears. Over a couple of weeks, the mineral oil softens dried or hardened earwax so that a gentle flush of water can remove the debris. In the case of a damaged or perforated eardrum, however, mineral oil should not be used, as oil in the middle ear can lead to ear infections. It is also a recommended way of removing an insect from the ear of a human. A few drops can drown the insect, which can then be easily removed.
Mineral oil is used as a suspending and levigating agent in sulphur-based ointments.
Medicine – internal uses
Mineral oil is taken orally as a lubricative laxative, and is often prescribed to ease the pain of bowel movements for those who suffer fromhemorrhoids and constipation.
Certain mineral oils are used in livestock vaccines, as an adjuvant to stimulate a cell-mediated immune response to the vaccinating agent. In the poultry industry, plain mineral oil can also be swabbed onto the feet of chickens infected with scaly mites on the shank, toes, and webs. Mineral oil suffocates these tiny parasites. In beekeeping, food grade mineral oil saturated paper napkins placed in hives are used as a treatment for tracheal and other mites.
Mineral oil is a common ingredient in baby lotions, cold creams, ointments and cosmetics. It is a lightweight inexpensive oil that is odorless and tasteless. It can be used on eyelashes to prevent brittleness and breaking and, in cold cream, is also used to remove creme makeup and temporary tattoos. One of the common concerns regarding the use of mineral oil is its presence on several lists of comedogenic substances. These comedogenic lists were developed many years ago yet remain frequently quoted in the dermatologic literature.
Mechanical, electrical and industrial
Mineral oil is used in a variety of industrial/mechanical capacities as a non-conductive coolant in electric components as it does not conduct electricity or thermal fluid, while simultaneously functioning to displace air and water. Some examples are in transformers where it is known astransformer oil, and in high voltage switchgear where mineral oil as an insulator and as a coolant to disperse switching arcs. The dielectric constant of mineral oil ranges from 2.3 at 50 degrees Celsius to 2.3 at 200 degrees Celsius.
Electric space heaters sometimes use it as a heat transfer oil. Because it is non-compressible, mineral oil is used as a hydraulic fluid in hydraulic machinery and vehicles. Mineral Oil is also used as a lubricant. Light mineral oil is also used in textile industries and used as a jutebatching oil. An often cited limitation of mineral oil is that it is poorly biodegradable; in some applications, vegetable oils such as cottonseed oilor rapeseed oil may be used instead.
Since it does not absorb atmospheric moisture, mineral oil is useful as a protective coating or bath for water-sensitive materials. Alkali metalslike lithium are often submerged in mineral oil for storage or transportation.
Mineral oil is also often used as a coating on metal tools and weapons, knives in particular, as a way to inhibit oxidation. The Japanese swordsNihonto, for example, are traditionally coated in Choji oil which consists of 99% mineral oil and 1% oil of cloves. The use of oil of cloves is sometimes explained as a means of differentiating sword oil from cooking oil to prevent accidental ingestion, but may also be purely aesthetic.
Mineral oil can be used as a leather conditioner as well, though most shoe polishes use naphtha, lanolin, turpentine and Carnauba wax instead.
It can also be used as a wood preservative. A light coating of mineral oil, rubbed into well-sanded wood, provides an easy-to-apply and relatively durable finish, without the odor or drying time (or toxicity) of varnish or urethane.
Mineral oil’s ability to prevent water absorption, combined with its lack of flavor and odor, make it a popular preservative for wooden cutting boards, salad bowls and utensils. Rubbing a small amount of mineral oil into a wooden kitchen item periodically will prevent absorption of food odors and ease cleaning, as well as maintain the integrity of the wood, which is otherwise subjected to repeated wetting and drying in the course of use. The oil fills small surface cracks that may otherwise harbor bacteria.
It is occasionally used in the food industry, particularly for candy. In this application, it is typically used for the glossy effect it produces, and to prevent the candy pieces from adhering to each other. It has been discouraged for use in children’s foods, though it is still found in many candies, including the popular movie theater treat Swedish Fish.
It can be used as a release agent for baking pans and trays, but food oils like vegetable oil are a more popular choice.
Mineral oil can be used to clean heavier oil stains by diluting and liquefying the other oils, rendering the oils more accessible to detergents. Likewise, it can be employed to “de-gum,” to remove adhesive residue left by price tags or adhesive tape. It can be used as a cleaner and solvent for inks in fine art printmaking as well as in oil painting, though turpentine is more often used.
Mineral oil is also used in some guitar string cleaners, since it can help mobilize dirt and oil without contributing to the oxidization of the metal strings.
Mineral oil can leave a residue, which is undesirable in some applications.
Mineral oil is the main fuel used by professional firespinners and firebreathers. It is chosen for its high flashpoint and low burning temperature. As a firebreathing fuel it is ideal because it will not tend to burn as a liquid, due to the high flashpoint, thus preventing blowback.
Mineral oil’s ubiquity has led to its use in some niche applications as well.
- It is used to make lava lamps.
- Mineral oil is used to darken soapstone countertops for aesthetic purposes.
- It is commonly used to create a “wear” effect on new clay poker chips, which can otherwise only be accomplished through prolonged use. The chips are either placed in mineral oil (and left there for a short period of time), or the oil is applied to each chip individually, then rubbed clean. This removes any chalky residue leftover from manufacture, and also improves the look and “feel” of the chips.
- It has a high refractive index, so it is sometimes used in oil immersion microscopes.
- It is the principal fuel in some types of gel-type scented candles.
- It is an effective pesticide, particularly for edible plants. It is effective against a wide range of insects and all stages of insect development.
- Mineral oil has been used to immerse computers in order to absorb heat and cool the system in some custom-built projects.
- Mineral oil is used in some household cleaners but has been proven to have no real cleaning benefits.
- It is sometimes used as a personal lubricant (although it is not safe for use with latex condoms), and as an alternative to plant or herbal oils for massage.
- It can be used in some model trains as a substitute for the “smoke fluid” or “smoke oil” that simulates steam coming from a steam engine.
- It can be used in basement floor drain traps to float on top of the water slowing its evaporation thereby keeping sewer gas from entering the house for a longer period of time
- Mineral oil can be used as a dust suppressant.
- In microbiology, mineral oil may be added atop agar stab growth media to create an anaerobic environment.