White oil, also known as mineral oil, liquid paraffin, and liquid petrolatum, is a transparent, colorless, and odorless oil that is derived from petroleum. It has a variety of uses and applications, from cosmetics to laxatives to machine lubricants. But what exactly makes up this versatile oil? Here we’ll take a closer look at the composition and ingredients of white oil.
The Origins and Production of White Oil
White oil starts off as crude oil that is drilled or pumped up from underground reservoirs. This crude oil contains a complex mixture of hydrocarbon chains of varying lengths and structures. It is transported to an oil refinery where it undergoes a refining process called fractional distillation. This involves heating the crude oil to high temperatures so that the different hydrocarbons boil off at different temperatures, allowing them to be separated and collected as fractions.
One of the fractions collected is the naphthenic distillate fraction. It has hydrocarbon chains ranging from 15 to 30 carbons long. This fraction undergoes further processing and purification to produce white mineral oil. The oil is treated to remove aromatics and impurities. It is then hydrotreated to convert remaining unsaturated hydrocarbons to saturated hydrocarbons through reactions with hydrogen gas. The oil also undergoes a solvent extraction process to further remove any residual aromatics and impurities. Finally, it is dewaxed by cooling it down and filtering out any waxes that crystallize during cooling. The resulting product is a purified mixture of liquid hydrocarbons known as white mineral oil.
The Chemical Composition
White mineral oil consists of saturated hydrocarbons, which are hydrocarbon chains containing only single bonds between carbon atoms. This gives white oil its stability, inertness, and lubricating properties. The hydrocarbons present in white oil typically range from 15 to 40 carbon atoms long. They include:
- Paraffins – straight chain alkanes like pentadecane (C15H32) and triacontane (C30H62)
- Isoparaffins – branched chain alkanes like pristane (C19H40)
- Naphthenes – saturated cyclic hydrocarbons like cyclohexane (C6H12)
These hydrocarbons make up around 98-100% of white mineral oil by weight. The specific composition can vary based on the crude oil source and refining process. Most white mineral oil consists primarily of naphthenic hydrocarbons with smaller amounts of paraffinic hydrocarbons. In addition to hydrocarbons, white oil may contain trace amounts of:
- Aromatic hydrocarbons like benzene – less than 0.5%
- Sulfur compounds – less than 50 ppm
- Nitrogen compounds – less than 5 ppm
- Metals like nickel and iron – less than 1 ppm
These impurities and additives are tightly controlled to meet pharmaceutical and cosmetic grade specifications.
Grades of White Oil
While all white oils share a similar hydrocarbon composition, they can vary in viscosity and purity. Based on these properties, white oils are assigned grades with different designations and specifications:
| Grade | Typical Viscosity | Key Characteristics |
|---|---|---|
| Heavy white oil | 33 – 37 cSt at 40°C | Highest viscosity; used for ointments and lubricants |
| Medium white oil | 22 – 27 cSt at 40°C | Medium viscosity; multi-purpose grade |
| Light white oil | 18 – 22 cSt at 40°C | Low viscosity; used in cosmetics and food |
| Pharmaceutical white oil | 20 – 25 cSt at 40°C | High purity; meets USP specifications |
Heavier white oils have higher average molecular weights and longer hydrocarbon chains, leading to higher viscosity. Lighter grades have more short-chain hydrocarbons, giving lower viscosity. Pharmaceutical grades have extra purification processing to remove more impurities and require toxicological testing.
Examples of Hydrocarbons in White Oil
Here are some examples of specific hydrocarbons that can be found in white mineral oil, along with their chemical structures:
n-Nonadecane (C19H40)
n-Nonadecane is a 19-carbon straight-chain alkane (paraffin) that is commonly present in white mineral oil. It has a melting point of 32°C.
Pristane (C19H40)
Pristane is a branched 19-carbon isoparaffin that is typically found in white oil. It has a higher viscosity compared to straight-chain alkanes of the same carbon number.
Cyclohexane (C6H12)
Cyclohexane is a 6-carbon naphthenic cycloalkane commonly present in white oil. Naphthenes impart viscosity index improver properties to white oil.
Butylcyclohexane (C10H20)
Butylcyclohexane is a more complex 10-carbon cycloalkane that can be found in white mineral oil. The presence of side-chains adds to the viscosity of the oil.
Properties and Applications
The unique properties of the hydrocarbon composition give white mineral oil a range of useful characteristics and applications:
Low Viscosity and Density
White oil has a lower viscosity and density compared to crude oil and many other petroleum products. This allows it to flow and spread easily.
Chemical Stability
The lack of reactive functional groups gives white oil excellent chemical stability. It does not readily oxidize or degrade, even when exposed to air, light, or moderate heat.
Low Volatility
The long hydrocarbon chains have low vapor pressure, so white oil does not easily evaporate. This allows it to retain its lubricating properties.
High Hydrophobicity
The nonpolar hydrocarbon chains cannot form hydrogen bonds with water, making white oil highly hydrophobic. This gives it moisture resistant properties.
Biocompatibility and Low Toxicity
Well-purified white oil has low systemic toxicity in humans, allowing it to be used in pharmaceutical and cosmetic products. The lack of reactivity makes it inert and non-irritating when applied topically.
These properties make white mineral oil suitable for uses like:
- Baby oils and adult skin care oils
- Hair and scalp conditioners
- Makeup and lip products
- Ointments and cold creams
- Laxatives and lubricating laxatives
- Textile scouring
- Cutting oils and lubricants
- Pesticides and insecticides
- Vaccine adjuvants
Safety and Regulatory Status
White mineral oil is considered safe for its intended uses when manufactured to the acceptable purity standards. Some key points regarding its safety include:
- It is minimally irritating and non-sensitizing when applied to skin.
- It has low acute oral toxicity, with an LD50 above 5 g/kg in rats.
- It is not considered a human carcinogen by IARC.
- Well-refined white oils show low potential for accumulation in the body.
- It is generally recognized as safe (GRAS) by the FDA for use in food up to concentrations of 10 ppm.
- It meets the requirements for direct and indirect food additive use per FDA 21 CFR 172.878 and 178.3620(a).
- It is approved for pharmaceutical use by the FDA when meeting USP specifications.
Despite the relative safety of pharmaceutical-grade white mineral oil, there have been rare cases of lipid pneumonia and pulmonary granulomas associated with inhalation or aspiration of mineral oil into the lungs. It also reduces absorption of fat-soluble vitamins like vitamin K from the gut. Due to these concerns, consumption is not recommended outside of occasional laxative use.
Overall, highly refined white mineral oils are considered non-hazardous under OSHA Hazard Communication Standard criteria. They are not classified as dangerous goods for transportation. Under EU regulations, the substance is registered and authorized for use in cosmetic products.
Conclusion
In summary, white mineral oil is primarily composed of saturated hydrocarbons known as paraffins, isoparaffins, and naphthenes. These include 15 to 40 carbon straight-chain alkanes, branched alkanes, and cycloalkanes. Trace impurities may include small amounts of aromatics, olefins, and sulfur or nitrogen compounds. Different viscosity grades are produced ranging from light to heavy. The purified mixture of nonpolar liquid hydrocarbons gives white oil a variety of useful properties, like chemical stability, low volatility, and biocompatibility. This allows it to be widely used in pharmaceuticals, cosmetics, food processing, and industrial lubricants when meeting the proper regulatory purity standards. While generally considered safe, care should be taken to avoid inhalation or contamination issues with lower grade technical white oils.