What are Mineral Oils?
Any oil refinery product that is liquid at room temperature, such as gasoline, kerosene, diesel, fuel oil, or lubricating oil, could be described as a mineral oil.
Usually, however, the term "mineral oils" (sometimes referred to as "paraffin oils" or "liquid paraffin" ) is reserved for highly refined by-products of fuel production.
Highly Refined Mineral Oils
There is no agreed specification of what a mineral oil is. In general, highly refined pharmaceutical and food grade mineral oils are colorless, odorless, and flavorless.
They consist of a mixture of higher alkanes - a mixture of straight chained, branched, and cyclic alkanes. Alkylated aromatics may also be present.
Alkanes are rather unreactive chemically, hence mineral oils are also rather unreactive chemically.
How Many Carbon Atoms?
Mineral oils are composed of hydrocarbons with fifteen carbon atoms upwards. As greater proportions of higher molecular mass hydrocarbons are added to the mineral oil mixture, the melting point of the oil increases until it becomes waxy at room temperature. At this stage, it is no longer an oil.
Melting and Boiling Points of Straight-Chain Alkanes at 1 Atmosphere Pressure
| Formula | Name | m.pt/°C | b.pt/°C |
|---|---|---|---|
| C15H32 | n-pentadecane | 9.9 | 271 |
| C16H34 | n-hexadecane | 18 | 287 |
| C17H36 | n-heptadecane | 21 | 302 |
| C18H38 | n-octadecane | 28 | 316 |
| C19H40 | n-nonadecane | 32 | 330 |
| C20H42 | n-icosane | 36.7 | 342.7 |
| C25H52 | n-pentacosane | 54 | 401.9 |
| C30H62 | n-triacontane | 65.8 | 449.7 |
| C35H72 | n-pentatriacontane | 75 | 490 |
| C40H82 | n-tetracontane | 81.5 | 522 |
| C50H102 | n-pentacontane | 91 | 575 |
Properties and Uses
Inexpensive Hydrocarbons: Mineral oils are not expensive to produce and are widely used in applications appropriate to their properties.
Grades: Different grades of mineral oil are available - these differ in their viscosity (runniness). Increasing the average chain length of the alkanes in mineral oil makes it more viscous (less runny). Comments here refer to highly refined, pharmaceutical and food grade mineral oils.
No Rancidity: Mineral oils have similar physical properties to oils sourced from plants or animals. While plant and animal oils contain oxygen in addition to carbon and hydrogen and can become rancid, mineral oils are hydrocarbons and do not go rancid.
Laxative: Mineral oil cannot be digested by humans. It is sometimes used as a lubricant laxative to ease bowel movements in cases of constipation in humans and animals.
Skin Products: Pharmaceutical grade mineral oil is used in a wide variety of skin products including baby lotions, cosmetics, ointments, and cold creams.
Blackheads and Acne: Although claims have been made in popular publications that skin preparations based on mineral oil block pores and cause blackheads and acne, recent scientific research suggests otherwise. (See Georgios N Stamatas, Mineral Oil in Skin Care: Safety Profile, International Journal of Cosmetic Science, Dec 2015.)
"mineral oil and vegetable oils used in skin care products form a protective layer on the skin, enhancing moisture retention, while allowing the skin to breathe without obstructing the pores."
Domestic Products: Food grade mineral oil is used in a wide variety of household roles, such as rust prevention coatings, preserving food preparation surfaces made of wood, and lubrication of kitchen equipment such as food processing machines.
Carcinogenic Behavior
Mineral oils, untreated or mildly treated, are classed as Group 1 carcinogens by The International Agency for Research on Cancer (IARC). Highly refined mineral oils are classed as Group 3 carcinogens.
IARC Carcinogen Groups
| Group | Definition |
|---|---|
| 1 | Carcinogenic to humans. |
| 2A | Probably carcinogenic to humans. |
| 2B | Possibly carcinogenic to humans. |
| 3 | Not classifiable as to its carcinogenicity to humans. |
| 4 | Probably not carcinogenic to humans. |