THE CONCEPT OF ASPHALTENES REVISITED

Petroleum asphaltenes are defined as material insoluble in pentane or heptane and the nature of the molecular species that constitute asphal tenes has been a well researched subject over the past three decades. These investigations have led to a general consensus of the majority o f researchers that asphaltenes contain condensed aromatic systems carr ying alkyl, cycloalkyl, and heteroatom substituents. A variety of mole cular models has been developed which have been used to explain the be havior of asphaltenes in feedstocks during recovery and processing ope rations. However, an alternate concept introduced the idea that asphal tenes can be defined as a complex mixture of organic compounds of vary ing molecular weight and polarity. This allows asphaltenes to be descr ibed more fully in terms of their behavior during processes and proper ties in products, such as asphalt. Thus, the concept can be used to ex plain, even predict, the incompatibility of asphaltenes with the other petroleum constituents as well as the deposition of asphaltic materia l on reservoir rock and the occurrence of sediments during refinery op erations.