Quantitative Evidence for Bridged Structures in Asphaltenes by Thin Film Pyrolysis

• Published in: Energy & fuels 2011-08, Vol.25 (8), p.3581-3589
• Main Authors: Karimi, Arash, Qian, Kuangnan, Olmstead, William N, Freund, Howard, Yung, Cathleen, Gray, Murray R
• Format: Article
• Language: English
• Subjects: Asphaltenes; Condensing; Fossil Fuels; Gas streams; Liquids; Paraffins; Pyrolysis; Recovery; Simulation; Thin films
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef200518g

Thin film pyrolysis was used to thermally crack asphaltene molecules into their constituent building blocks at 500 °C. By using a thin film of liquid of ca. 20 μm, the cracked products were rapidly released into a much colder sweep gas stream to quench the reactions and minimize further decomposition. The liquid products were condensed and collected, with over 91% material balance on the recovery of gas, liquid, and coke product. Simulated distillation of the condensed liquid products showed a wide range of compounds with boiling points up to more than 700 °C produced in various stages of the reaction. Less than 1% of the original mass of the asphaltenes was released in the form of light gases such as methane and ethane. The liquid components boiling below 538 °C comprised 15–20% of the initial asphaltenes, and contained a wide range of chemical structures including paraffins, olefins, naphthenes, aromatics, thiophenes and sulfides, and nitrogen-containing compounds, identified by gas chromatography–field ionization–time-of-flight mass spectrometry. The ring groups were substituted with a range of alkyl side chains. Asphaltenes from a range of different crude oils gave similar results. The recovery of the building blocks was limited by the reaction conditions, because rereaction of the heavy products generated more light fragments. 13C NMR spectroscopy of the feed and products of thermal cracking of C7 asphaltenes showed a 10–26% increase in the aromatic or double-bonded carbon contents of the products compared to the feed, consistent with yields of toluene-insoluble coke in the range of 50%. The diverse components in the cracked products, with paraffins accounting for a small fraction of the total mass, are consistent with a significant concentration of complex structures attached by bridges in the asphaltene fraction.