8.: Asphaltenes

Unlike that of waxes, asphaltene deposition is primarily driven by pressure changes.

Asphaltenes are the heaviest and most polar components in crude oil, but there is no universally accepted definition of what an asphaltene molecule is—the two most commonly used definitions are that it is the oil fraction that is insoluble in either pentane or heptane. There is no single asphaltene structure, but asphaltenes generally comprise a core of polyaromatic rings associated with a number of alkyl side chains.

Asphaltene behavior is somewhat complex, but these molecules might be partly dissolved in the crude oil and partly in a colloidal state in the oil, stabilized primarily by resin molecules that are adsorbed on the asphaltene surface. If this adsorption equilibrium is disturbed, for example, by the addition of a paraffinic solvent, the asphaltene particles will become destabilized and might then undergo an aggregation process to form larger particles.