Thermal Chemistry of Asphaltenes

Asphaltenes are considered bad actors in refinery upgrading processes, because they cause coke and sludge formation, and in catalytic processes because they cause severe catalyst deactivation. It is widely accepted that petroleum is colloidal in nature and that asphaltenes exist in the petroleum in 

As indicated earlier, there is a delicate balance between the concentration of resins and asphaltenes in petroleum fractions. Any interruption in the ratio of asphaltenes resins can cause operational problems because of asphaltene precipitation (coke formation) and plant shutdown. It is therefore crucial, if coke formation is to be minimized, to monitor the ratio of asphaltenes resins during the thermal processing of bitumens and heavy oils. Clarke and Pruden developed a heat transfer analysis technique that can detect the onset of asphaltene precipitation. They showed that precipitated asphaltenes could be re-peptized using polynuclear aromatic compounds such as phenanthrene. It has been demonstrated in the 5000 bbl/d CANMET hydrocracking unit 

During the thermal cracking of vacuum residues, maltenes play an important role in the conversion of asphaltenes. Wiehe has shown that in the hydrocracking of CL VB (Cold Lake Vacuum Bottoms), the presence of maltenes in the resid increases (prolongs) the coke induction period significantly. The results were interpreted based on the efiectiveness of maltenes as hydrogen donors to cap free radicals produced by the thermal cracking of asphaltenes. 

At this stage, a general overview of the chemistry of upgrading is necessary prior to discussing the conversion of bitumen and heavy oil constituents at elevated temperatures. 

It is well documented that the conversion of resid to lighter products, whether or not in the presence of hydrogen and/or a catalyst, is largely thermally driven. The h5q)othetical molecular structure of bitumen and 

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Understanding asphaltene chemistry from the behavior of model compounds is not as straightforward as it may appear. The individual reactions occurring in an extremely complex mixture, a multitude of secondary reactions, and the interference of the products from some of the constituents with those from other constituents of the mixture can make the thermal chemistry of asphaltenes extremely unpredictable (i). 

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