What Dissolves Oil?

Petroleum contains different kinds of oil, such as fuel oil and lubricants, and many other oils come from vegetable matter, such as olive oil, palm oil, and canola oil. None of these oils mix with water at room temperature, but they dissolve in some organic solvents such as benzene or gasoline. Even water can dissolve oil under the right conditions of temperature and pressure.

Some molecules exhibit an electrostatic property called polarity. One end of their molecules has a positive charge and the other end has a negative charge. In general, polar substances dissolve in polar solvents, such as water. However, oils do not have polarity, so they dissolve in nonpolar solvents.

Gasoline contains many different nonpolar substances, such as hexane, heptane and octane. Gasoline effectively dissolves oils and even grease. Hexane, isolated from other gasoline components, serves as a solvent for vegetable oils, such as peanut oil and soybean oil.

The carbon tetrachloride molecule consists of four chlorine atom united with a single carbon atom. Chlorine often forms polar compounds. However, in carbon tetrachloride, the carbon atom is at the center of the molecule, while the chlorine atoms position themselves in such a way that no side of the carbon tetrachloride molecule is more electronegative than any of its other sides. As a result, carbon tetrachloride acts like a nonpolar molecule and dissolves oils.

Some organic solvents, such as acetone and diethyl ether, contain electronegative oxygen as part of their molecular composition. However, the single oxygen atom of acetone is attached to the central carbon of a three-carbon chain, and the single oxygen atom in diethyl ether occupies the center of a chain with two carbon atoms on either side. Because of the central position of oxygen, neither acetone nor diethyl ether is a polar substance, and both dissolve oils effectively. Acetone serves as an ingredient in commercial preparations designed to remove excess oil from oily skin.

Benzene, a component of petroleum, has the chemical formula C6H6. Its six carbon atoms form a ring. Since carbon-hydrogen bonds have no polarity, benzene is a nonpolar compound that effectively dissolves oils. It serves as a solvent to extract oil from shale. Other organic solvents, such as diethyl ether and acetone, serve the same purpose.

Under normal conditions, water does not dissolve oil. However, the properties of water change when subjected to high temperatures and pressures. When water reaches a temperature of 374 degrees C and a pressure of 218 atmospheres, it becomes supercritical water, according to Yokohama University. Under these extreme conditions, oil dissolves in water. Supercritical water serves as a solvent for refining heavy oils.