To separate oil from water, add a solution of soluble ionic salt to the solution. Distillation, which involves boiling and condensing the water, is another option, as well as partially freezing the oil and water combination and discarding one-fourth to one-third of the unfrozen water.
Changing the state of the water to either a gas or a solid is a means to cleanly remove all of the oil from the water. Boiling the mixture eliminates the water by turning it into a gas. Boiling affects the water and not the oil because oil has a lower vapor pressure than water.
Likewise, freezing the mixture pushes any oil molecules out of the water when the water molecules bond more closely with one another, eliminating any space for stray oil molecules. After it is frozen, the frozen water can be separated from the still-liquid oil, which has a lower freezing point.
To remove the water from the oil, add a soluble ionic salt such as Epsom salts to the mixture. Adding the salt to the oil makes it less soluble and coagulates any stray oil molecules in the water section, allowing for easy removal.
Oil spills are one example of when the separation of oil and water is necessary. This typically involves separation through membrane-based filtration systems. Shortcomings of these devices include loss of effectiveness over time and the inability to separate all types of oil and water mixtures. Due to their pumping nature, these systems are also energy intensive.