Carbon isotope analyses of n-alkanes released from rapid pyrolysis of oil asphaltenes in a closed system

RationaleCarbon isotope analysis of n-alkanes produced by the pyrolysis of oil asphaltenes is a useful tool for characterizing and correlating oil sources. Low-temperature (320-350 degrees C) pyrolysis lasting 2-3days is usually employed in such studies. Establishing a rapid pyrolysis method is necessary to reduce the time taken for the pretreatment process in isotope analyses. MethodsOne asphaltene sample was pyrolyzed in sealed ampoules for different durations (60-120s) at 610 degrees C. The C-13 values of the pyrolysates were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The molecular characteristics and isotopic signatures of the pyrolysates were investigated for the different pyrolysis durations and compared with results obtained using the normal pyrolysis method, to determine the optimum time interval. Several asphaltene samples derived from various sources were analyzed using this method. ResultsThe asphaltene pyrolysates of each sample were similar to those obtained by the flash pyrolysis method on similar samples. However, the molecular characteristics of the pyrolysates obtained over durations longer than 90s showed intensified secondary reactions. The carbon isotopic signatures of individual compounds obtained at pyrolysis durations less than 90s were consistent with those obtained from typical low-temperature pyrolysis. Several asphaltene samples from various sources released n-alkanes with distinct carbon isotopic signatures. ConclusionsThis easy-to-use pyrolysis method, combined with a subsequent purification procedure, can be used to rapidly obtain clean n-alkanes from oil asphaltenes. Carbon isotopic signatures of n-alkanes released from oil asphaltenes from different sources demonstrate the potential application of this method in oil-oil' and oil-source' correlations. Copyright (c) 2016 John Wiley & Sons, Ltd.