Tracing the Compositional Changes of Asphaltenes after Hydroconversion and Thermal Cracking Processes by High-Resolution Mass Spectrometry

Abstract

With heavy crude oil refining on the rise, upgrading strategies are fundamental to yield high-value products. Hydroconversion and thermal cracking are well-established and widely used upgrading processes for heavy oils' distillation cuts and residues. Recognizing molecular changes in these fractions after upgrading, particularly of asphaltenic compounds, is fundamental to understand and optimize the processes. In this work, we follow compositional changes in the asphaltene fraction of a Colombian heavy crude, after hydroconversion and thermal cracking, using high-resolution mass spectrometry. The liquid products from the upgrading processes were fractionated into maltenes and residual asphaltenes, with yields between 33% and 38% in maltenes from the original asphaltene feedstock. Contoured plots of double bond equivalents versus carbon number and van Krevelen diagrams show maltenic fractions exhibiting lower aromaticity, smaller molecular size, fewer heteroatomic species, and higher content of alkyl side chains than the starting asphaltenic material. Residual asphaltenes, on the other hand, consist of compounds with lower H/C ratios and reduced content of alkyl groups than the feedstock. In addition, structural information about the feedstock, such as archipelago or island structures, can be derived from the plots. This information is useful to establish trends between compound class reactivity and the suitability to produce valuable maltenic compounds through upgrading technologies.

Investigation of Island/ Single Core and Archipelago/ Multicore Enriched Asphaltenes and Their Solubility Fractions by Thermal Analysis Coupled to High Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…This type of thermal degradation might give rise to mono-heteroatomic compound classes. Similar trends were previously observed by investigating the compositional changes of asphaltenes during thermal cracking and hydroconversion by direct infusion APPI-FT-ICR MS [34]. The maltene fraction obtained by cracking was shown to contain only 9 major compound classes, while the parent asphaltenes consisted of 21 classes [34].…”

Investigation of Island/Single-Core- and Archipelago/Multicore-Enriched Asphaltenes and Their Solubility Fractions by Thermal Analysis Coupled with High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…(2) From 300 to 350 °C, pyrolysis of asphaltenes starts by thermal decomposition of C-C-and C-S-bonds [58], releasing smaller structural elements in the gas phase. Archipelago-type structures are preferably cracked at alkyl linkers between two smaller core structures [10,34]. Islandtype structural motifs, however, are known to cleave off alkyl side chains during thermal treatment [34,[59][60][61] resulting in lowly alkylated, highly aromatic cores clustering at the aromatic limit [62][63][64] as well as aliphatic compounds.…”

“…After thermal cracking, the newly formed maltene fraction has been found to consist of alkylated 1-5-ring aromatics, alkanes, and alkenes, as well as naphthenes. [31][32][33][34][35][36] These observations are supported by Savage et al (1985Savage et al ( /1988, who investigated structural building blocks of pyrolyzed asphaltenes with gas chromatography (GC)-MS [37,38]. Furthermore, Strausz and co-workers provided detailed compositional and structural information on asphaltene pyrolysis products by applying gas chromatographic (GC and GC-MS) as well as spectroscopic techniques.…”

Investigation of Island/ Single Core and Archipelago/ Multicore Enriched Asphaltenes and Their Solubility Fractions by Thermal Analysis Coupled to High Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…Islandtype structural motifs, however, are known to cleave off alkyl side chains during thermal treatment [34,[59][60][61] resulting in lowly alkylated, highly aromatic cores clustering at the aromatic limit [62][63][64] as well as aliphatic compounds. If the aromatic core of island-type asphaltenes is still evaporable, it is detected during the pyrolysis phase, otherwise, (3) extremely highly aromatic cores (high boiling point) tend to form coke and remain as residue [34,59,60]. Furthermore, highly stable aggregates may survive high temperatures during the pyrolysis phase and form coke instead of thermally decompose into smaller fragments [65].…”