The current state-of-the-art in analysis techniques for petroleum fractions has progressed substantially during the last decade. This has helped to further improve the lumping procedures and modeling approaches of these complex systems. Recent advances in gas chromatography (GC), GC-field ionization mass spectrometry (GC-FIMS), and comprehensive gas chromatography (GC × GC) have made it possible to determine the compositions of fractions with up to 45 carbon atoms and in some cases up to C80. The combination of MS techniques with other selective detectors and reversed-phase column combinations has made it possible to quantify even traces of heteroatomic compounds in these complex hydrocarbon matrices. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), in some cases combined with GC × GC for the lighter part, has pushed the characterization of larger macromolecules in particular asphaltenes. Matrix-assisted laser desorption/ionization (MALDI) is also used widely for this purpose but has the disadvantage that quantification is not obvious. The development of more detailed characterization techniques has not remained unnoticed in the petrochemical society, and more recently in the petrochemical kinetic modeling society. More detailed characterization of petrochemical fractions has made the implementation of detailed kinetic models for simulation and optimization possible including more and more molecular detail. Additionally, advances in photo-ionization mass spectrometry (PI-MS) have allowed the detection of reactive intermediates and direct kinetic measurements in time-resolved experiments. It can only be expected that this trend will continue and that the application field will move from now primarily petrochemistry, (from catalytic cracking, over hydrotreating and hydrocracking, to pyrolysis, combustion, and steam cracking) to larger-scale chemical recycling and biomass conversion processes.
The inherent complexity of petroleum fractions makes molecular reconstruction an essential element to make use of advanced kinetic models in the petrochemical industry, in particular when sulfur compounds need to be accounted for. Therefore, we have developed a method based on Shannon entropy maximization that can reconstruct the molecular composition of vacuum gas oils and atmospheric gas oils including sulfur compounds even if only a limited amount of global information is provided. Unique in this work is the fact that the results of the reconstruction are compared with analytically determined compositions obtained using comprehensive 2D gas chromatography coupled to a flame ionization detector and a selective sulfur chemiluminescence detector next to the global properties such as boiling point curves and densities. The reconstructed carbon number distribution for global groups (n-paraffins, isoparaffins, naphthenes, and aromatics) and distribution of the sulfur compounds show a good agreement with the analytical data with a maximum standard deviation of 1% or less. Essential is the fact that the molecular library that is used to represent the feedstocks is based on a sufficiently large database of extensively characterized feedstocks. Acquiring the detailed molecular composition of the sulfur-containing compounds could only be done accurately if next to classical commercial indices such as boiling points of a distillation curve, the specific density, and the PINA mass fractions, the total amount of sulfur and that of aromatic sulfur were specified.
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