Characterization of Asphaltene Building Blocks by Cracking under Favorable Hydrogenation Conditions

The chemical building blocks that comprise petroleum asphaltene molecules were determined by thermal cracking of samples under conditions that minimized alterations to aromatic and cycloalkyl groups. Favorable hydrogenation conditions that used tetralin as a hydrogen-donor solvent and an iron-based catalyst allowed asphaltenes derived from different crude oils to yield approximately 50–60 wt % distillates (<538 °C fraction), with coke yields below 10 wt %, and reach conversions of the vacuum residue fraction between 65 and 75 wt %. Products in a wide range of boiling points, from naphtha to heavy material in the vacuum residue range, were observed by simulated distillation. Quantitative recovery of the cracked products, with mass balances above 96%, and characterization of the distillate fraction by gas chromatography–field ionization–time-of-flight high-resolution mass spectrometry (GC–FI–TOF HR MS) provided information on the abundance of building blocks, including saturates, 1–3-ring aromatics, 4+-ring aromatics, and nitrogen- and sulfide-containing molecules. Samples of asphaltenes from different geological basins exhibited a remarkable similarity in the yields of building blocks, with paraffins and 1–3-ring aromatics as the most abundant species. The diversity of molecules identified in the distillate products from the cracking of asphaltenes suggests a high degree of heterogeneity and complexity of asphaltene molecules, built up by smaller fragments attached to each other by bridges. The sum of material remaining in the vacuum residue fraction and the yield of coke were in the range of 35–45% and represent the maximum amount of large aromatic clusters present in asphaltenes that could not be converted to distillates or gases under the cracking conditions used in this study

Determination of Structural Building Blocks in Heavy Petroleum Systems by Collision-Induced Dissociation Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Collision-induced dissociation Fourier Transform ion cyclotron resonance mass spectrometry (CID-FTICR MS) was developed to determine structural building blocks in heavy petroleum systems. Model compounds with both single core and multicore configurations were synthesized to study the fragmentation pattern and response factors in the CID reactions. Dealkylation is found to be the most prevalent reaction pathway in the CID. Single core molecules exhibit primarily molecular weight reduction with no change in the total unsaturation of the molecule (or <i>Z</i>-number as in chemical formula C<i>_c</i>H_{2<i>c</i>+<i>Z</i>}N_<i>n</i>S<i>_s</i>O_<i>o</i>VNi). On the other hand, molecules containing more than one aromatic core will decompose into the constituting single cores and consequently exhibit both molecular weight reduction and change in <i>Z</i>-numbers. Biaryl linkage, C₁ linkage, and aromatic sulfide linkage cannot be broken down by CID with lab collision energy up to 50 eV while C₂+ alkyl linkages can be easily broken. Naphthenic ring-openings were observed in CID, leading to formation of olefinic structures. Heavy petroleum systems, such as vacuum resid (VR) fractions, were characterized by the CID technology. Both single-core and multicore structures were found in VR. The latter is more prevalent in higher aromatic ring classes