Abstract:

An analytical method for separation and identification of the saturated hydrocarbons in diesels at molecular level by comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOF MS)was established. The saturated hydrocarbons were pre-separated from diesel samples by solid phase extraction before GC×GC-TOF MS analysis. More than 1000 individual compounds (including paraffins, naphthenes and olefins) in coker diesel were tentatively identified based on NIST library search, mass spectrum resolution, boiling point distribution law and separation characteristics. Normal paraffins showed great regularity and could be identified easily through the relative position with pristane and phytane. The cyclic alkanes arranged above paraffins with the increasing number of rings. The normal alkyl cyclohexanes and cyclopentanes were well distinguished due to the difference of their polarity. Normal α -olefins which were often neglected in the past were also identified. With the support of the above-introduced identification, the distribution by structural type and carbon number were presented using peak area normalization. This analytical method was successfully used to investigate the molecular composition of saturated fractions in different diesel samples. All the results indicated that the molecular compositions of saturates in catalytic cracking diesel and coker diesel were significantly different because of the processing mechanism. This method provided technical support for the characterization of saturated hydrocarbons in diesels and the investigation of processing mechanism.

Key words: comprehensive two-dimensional gas chromatography (GC×, diesel, GC), molecular composition, saturated hydrocarbons, time-of-flight mass spectrometry (TOF MS)