Mineral oil is a transparent, colorless, and odorless liquid hydrocarbon mixture that is a byproduct of the process used to create gasoline and other petroleum products. Due to its inert nature and stability, it is used across many industries, including heavy machinery lubrication, cosmetics, and pharmaceuticals.
The Origin Story
Mineral oil originates from petroleum, or crude oil, a complex mixture of hydrocarbons extracted from the Earth’s crust. Production begins in a refinery during the distillation process, which separates crude oil into different fractions based on their boiling points. Mineral oil is obtained from the heavier fractions of this process, as it possesses a high boiling point and low volatility. It is essentially a co-product of the larger operation aimed at producing fuels like gasoline and diesel. The resulting raw oil is then sent for further processing to remove undesirable compounds.
Chemical Structure and Composition
Mineral oil is not a single compound but a mixture of thousands of different hydrocarbon molecules. The primary components are saturated hydrocarbons, which fall into two main families: open-chain alkanes (paraffins) and cyclic saturated hydrocarbons (naphthenes). These saturated molecules are highly stable and non-reactive.
The molecules in mineral oil exhibit a range of carbon chain lengths, typically from C15 to C50. Longer chains result in a thicker, more viscous oil, while shorter chains yield a lighter, thinner product.
From Crude to Clear: The Refining Process
The crude oil fraction must undergo extensive purification to remove harmful substances. The raw material contains alkylated polycyclic aromatic compounds (PACs), sulfur, and nitrogen compounds. These contaminants must be eliminated to transform the opaque base oil into a clear, non-toxic final product.
Modern refining utilizes processes such as vacuum distillation, solvent extraction, and catalytic hydrotreating. Solvent extraction uses specific chemicals to separate and remove aromatic compounds. Catalytic hydrotreating, or hydrogenation, subjects the oil to high temperatures and pressures with a catalyst and hydrogen gas. This process restructures undesirable aromatic and unsaturated molecules into more stable, saturated paraffinic structures, simultaneously removing sulfur and nitrogen.
Different Grades of Mineral Oil
The degree of refinement determines the grade of mineral oil and its appropriate application. International standards regulate purity levels by setting strict limits on the presence of aromatic compounds.
Technical or Industrial Grade mineral oil is less refined and is used for non-contact applications such as machinery lubrication, cooling, and as a solvent. In contrast, Highly Refined or Pharmaceutical Grade mineral oil, often called white oil, must meet stringent purity standards like those set by the United States Pharmacopeia (USP) or the British Pharmacopoeia (BP). These highly purified oils are safe for direct human contact and are used in cosmetics, food-processing equipment, and oral medicines.