Diesel is classified as a solvent. A solvent is a substance, typically a liquid, capable of dissolving another substance (the solute). Diesel fuel is a petroleum-based product used primarily to power compression-ignition engines. Due to its chemical composition, this common fuel also possesses strong solvent properties.
Understanding Diesel’s Nonpolar Nature
The reason diesel functions as a solvent lies in its molecular structure. Diesel is a complex mixture of hydrocarbons, which are molecules composed solely of hydrogen and carbon atoms. These chains typically range from 10 to 22 carbon atoms, making diesel a heavier fraction of crude oil distillation than gasoline.
This molecular makeup results in a substance that is overwhelmingly nonpolar. In chemistry, the rule of solubility is “like dissolves like.” Polar solvents, such as water, dissolve polar substances. Conversely, nonpolar solvents like diesel effectively dissolve other nonpolar substances.
The long hydrocarbon chains in diesel lack the electrical charge separation found in polar molecules. When diesel contacts another nonpolar substance, the weak intermolecular forces are easily overcome, allowing the molecules to mix freely and dissolve heavy oils and greases.
Practical Dissolving Capabilities
Diesel’s nonpolar nature allows it to break down a wide array of other nonpolar materials. It is highly effective at dissolving heavy oils, various types of grease, and crude petroleum residues. This property sometimes leads to its use as an inexpensive, though hazardous, cleaning agent.
Diesel can readily dissolve substances like tar and bitumen, the heavy hydrocarbon binding agents used in asphalt. Because bitumen is also a nonpolar hydrocarbon, the solvent action of diesel is efficient, which is why it is sometimes used to clean asphalt from equipment and truck beds. Its capabilities also extend to waxes, which are also long-chain hydrocarbons, and certain types of plastics and rubber compounds.
The dissolving action is a physical process where the diesel molecules surround and separate the molecules of the target material. This makes diesel useful in applications like cleaning tanks, engines, and refinery equipment where heavy, oily residues accumulate. Its effectiveness is tied to its classification as a hydrocarbon solvent.
Health Consequences of Skin Contact
The powerful dissolving action that makes diesel an effective degreaser also poses significant risks to human health, particularly upon skin contact. The outermost layer of human skin is protected by a natural barrier composed primarily of lipids, known as sebum. When diesel touches the skin, its nonpolar solvent nature immediately strips away these protective natural oils.
This degreasing action is known as defatting, and it quickly compromises the skin’s natural defense mechanism. Immediate consequences include irritation, redness, and excessive dryness. Repeated or prolonged exposure can lead to contact dermatitis (eczema), characterized by inflammation and cracking of the skin.
A compromised skin barrier also increases the risk of chemical absorption into the body. Toxic components within the diesel fuel, such as aromatic hydrocarbons, can pass easily through the damaged skin and enter the bloodstream. Furthermore, diesel releases volatile organic compounds (VOCs) that can be inhaled, leading to symptoms like dizziness, headache, and nausea.