Compositional characterization of neutral fractions in <300 °C distillates of six shale oils using extrography followed by GC-TOF/MS analysis

The neutral fractions of <300 °C fractions of six Chinese shale oils obtained from different locations of Huadian, Wangqing, Fushun, Longkou, Maoming and Yaojie were eluted to six sub-fractions using extrography method. The compositions of sub-fractions were determined using gas chromatography-time of flight mass spectrometer (GC-TOF/MS). The results showed that F1 sub-fractions contained aliphatic hydrocarbons, such as alkanes, alkenes and cycloalkanes. In addition, HD F1 sub-fraction had the highest content of aliphatic hydrocarbons. The F2 sub-fractions contained aromatic hydrocarbons with 1-4-ring. Furthermore, a small amount of heteroatom compounds with aromatic rings (such as, dibenzofurans and carbazols) were also detected. The F3 sub-fractions contained aliphatic ketones and aliphatic nitriles ranging from C7-C25 and C9-C24, respectively. The F4 sub-fractions contained aliphatic ketones. However, the aliphatic ketones in F3 sub-fractions were 4-, 5-, 6-, 7- and 9-ketones, whereas those in F4 sub-fractions were all 2-ketones. The F5 sub-fractions contained nine kinds of compounds. Moreover, 2,5-hexanedione was dominant in all the samples except for MM F5 sub-fraction, whereas only two compounds were detected in MM F5 sub-fraction. Moreover, the F6 sub-fractions with less than 1 wt% in neutral fractions contained the unresolved complex matter (UCM), which cannot be eluted through gas chromatography (GC). Compared with the distribution of compounds in sub-fractions, the compounds of different samples consisted of similar species and slightly different contents. It indicates that the formation of compounds in the neutral fraction follows the same reaction pathways during kerogen pyrolysis.