Heavy oil resources in the world are extremely abundant, and viscosity is currently the main reference index for heavy oil classification. However, the diversification of practical issues in heavy oil exploitation, and the refinement of processing and utilization urgently require the support of heavy oil classification with more reference indexes. In this study, the macroscopic properties of typical heavy oils in China were analyzed, and the semi-quantitative analysis of the molecular composition of different heavy oils was completed based on high-resolution mass spectrometry. The results show that heavy oils with similar viscosities can exhibit huge differences in macroscopic properties and chemical composition. According to the evaluation of the chemical composition and macroscopic properties of typical Chinese heavy oils, 12 types of compounds belonging to saturates, aromatics, resins, and asphaltenes (SARA) were identified, establishing a connection between the macroscopic fractions and molecular compositions of heavy oils. By summarizing the comparative results, a new classification criterion for heavy oils was established, focusing on the main parameters of H/C ratio and total acid number (TAN), with sulfur content as a supplementary indicator. H/C is the embodiment of the degree of molecular condensation in the macroscopic properties, reflecting the structural characteristics of the main molecules of the heavy oil. Chinese heavy oil is generally characterized by high TAN, which corresponds to the composition of petroleum acids, and it is also an important reference index for the exploitation and processing of heavy oils. Most Chinese heavy oils have a very low sulfur content, but the presence of sulfur compounds in high-sulfur heavy oils can lead to significant differences in the distribution of compound types among the SARA. This new classification method for heavy oil combines the characteristics of chemical composition of heavy oils, which is expected to provide valuable support for the extraction and processing of heavy oil.

Electrospray ionization (ESI) coupled with high-resolution mass spectrometry (HRMS) is rapidly developing into a powerful tool for the molecular characterization of petroleum fractions. However, the occurrence of ion–molecule aggregates seriously affects the interpretation of the mass spectrometry results. Ion–molecule aggregates are not inherent compounds in petroleum but they are produced during the analysis of petroleum samples by high-resolution mass spectrometry. Also, the classes of aggregates are the same as many compounds in petroleum. Therefore, the removal of these species is crucial, and their analysis from methods of dissociation and mechanism points of view is essential for this purpose. In this study, aggregates of a vacuum gas oil fraction were analyzed and the types were defined. The compositions of the aggregates were characterized by changing operating conditions. Several factors affecting the aggregates were evaluated by a parameter of dissociation efficiency. By establishing the operating methods, the residual content of the aggregates can be controlled by less than 1% of the total ions. The results are instructive for the molecular characterization of petroleum fractions by using mass spectrometry with ESI ionization.

Polyglycolic acid (PGA) is a biologically friendly material with a wide range of applications. The production of dimethyl oxalate using coal-based syngas and the hydrogenation of dimethyl oxalate can produce the polymerization raw material of PGA, glycolide, which requires a methyl glycolate polymerization and depolymerization process. The intermediate products of the production process were analyzed using gas chromatogram-mass spectrometry (GC-MS) and Orbitrap mass spectrometry (Orbitrap MS), which revealed the presence of cyclic and linear PGAs with different capped ends. The impurities present in the oligomer were mostly methyl-capped PGA and were retained in the subsequent depolymerization process to glycolide, solvent washing can be used to remove this part of the impurity and ultimately obtain a refined glycolide product. Furthermore, it is proposed that the use of the specialized Kendrick Mass Defect (KMD) to plot and analyze PGA compounds obtained using mass spectrometry can enable the direct classification of PGAs without the need for exact molecular formula assignment.