Oxidation Behavior and Kinetics of Light, Medium, and Heavy Crude Oils Characterized by Thermogravimetry Coupled with Fourier Transform Infrared Spectroscopy

The oxidation behavior of three crude oils was characterized by thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR) to investigate the oxidation mechanism of crude oils. The results indicated that the entire oxidation process can be divided into three main reaction intervals: low-temperature oxidation (LTO) interval (<400 °C), coking process (400–500 °C), and high-temperature oxidation (HTO) interval (500–650 °C). For the LTO interval, oxygen addition reactions to produce hydroperoxides were believed to be dominant at the early stage, while the isomerization and decomposition reactions of hydroperoxides became more significant at the later stage. For light and medium oils, the isomerization and decomposition reactions that release H₂O started at about 200 °C and the isomerization and decomposition reactions that release CO₂ and CO started at about 300 °C. However, no CO₂ and CO were detected in the LTO interval of the heavy oil, which means that the reaction pathways of the heavy oil might be a little bit different from those of the light and medium crude oils in LTO intervals. Evaporation played an important role during the entire LTO interval. In the coking process, the coke formation by the oxidative cracking of the LTO residue is believed to be the main reaction with the release of gaseous products of CO₂ (and CO), H₂O, and hydrocarbons. In the HTO interval, the combustion of coke was considered as the only one significant reaction. For the LTO and coking process, the activation energies increased with the decrease of the American Petroleum Institute (API) gravity of crude oils. However, for the HTO stage, the activation energies were similar (100–125 kJ/mol) for different crude oils

Oxidation Behavior and Kinetics of Eight C₂₀–C₅₄ <i>n</i>‑Alkanes by High Pressure Differential Scanning Calorimetry (HP-DSC)

In this study, the oxidation behavior and kinetics of linear alkanes (C₂₀H₄₂, C₂₄H₅₀, C₃₀H₆₂, C₃₂H₆₆, C₃₆H₇₄, C₃₈H₇₈, C₅₀H₁₀₂, and C₅₄H₁₁₀) were investigated by high pressure differential scanning calorimetry (HP-DSC). It turned out that only the exothermic peak of low-temperature oxidation (LTO) was observed during the oxidation process of these linear alkanes, which is different from the oxidation behavior of the crude oil. For the crude oil, two exothermic peaks were observed: LTO and high-temperature oxidation (HTO). This means that the linear alkanes barely contributed in the HTO reaction of crude oils. In addition, the exothermic peaks in the oxidation process of all these linear alkanes overlapped each other. They showed almost the same oxidation behavior in terms of the temperature range of reaction as well as the onset and peak temperatures. It seems that the oxidation behavior of the tested linear alkanes was independent of their carbon number. It was also found that increasing pressure resulted in an increase of the heat release. The kinetics parameters of the oxidation reaction were estimated using three “model-free methods” known as Friedman, Ozawa–Flynn–Wall (OFW), and ASTM E698. The results showed that the activation energy of the LTO process of each linear alkane can be regarded as a constant average value in the range of conversion degree from 0.2 to 0.8, and all the tested linear alkanes had similar activation energy values of 80–120 kJ/mol calculated by the Friedman method and 90–110 kJ/mol calculated by the OFW method. The OFW method showed a lower error than the Friedman method when being applied to the DSC data. The values of activation energy estimated using the ASTM E698 method were 100.41, 95.61, 93.62, 100.55, and 92.47 90–110 kJ/mol for C₂₀H₄₂, C₂₄H₅₀, C₃₀H₆₂, C₃₈H₇₈, and C₅₄H₁₁₀, respectively, which are also in the same range of the values of the activation energy obtained by the Friedman and OFW methods. Similar activation energy values of different linear alkanes partly explained why they showed almost the same oxidation behavior

Hybrid Nanostructures of Hyperbranched Polyester Loaded with Gd(III) and Dy(III) Ions

Hyperbranched polymers are successful nanoscale functional platforms for loading metal ions and creating promising nanomaterials for medicine. This work presents the synthesis of metal–polymer nanostructures based on a second generation hyperbranched polyester with eight terminal benzoylthiocarbamate (BTC) groups loaded with Gd(III) or Dy(III) ions. Their structure (Fourier transform infrared spectroscopy) and morphology (transmission electron microscopy), photophysical (ultraviolet–visible and luminescence spectroscopy), thermophysical, magnetic activity, relaxivity, and aggregation properties (nanoparticle tracking analysis) were studied. The formation of the metal–polymer complex is carried out by chelation of lanthanide ions −CO and −CS groups of the BTC fragment of polyester. Coordination units with composition Ln(III)-3BTC (Ln = Dy, Gd) were localized on the branched polymer platform. The load is three lanthanide ions per branched polyester polybenzoylthiocarbamate macromolecule. Logarithms of stability constants of complexes and composition of coordination polyhedron have been determined. The dysprosium complex is in a paramagnetic state with antiferromagnetic correlations, and the gadolinium complex is in a paramagnetic state. The relaxivity of the Dy(III) and Gd(III) complexes increased by 2.5 and 3 times, respectively, compared to their nitrates. An important achievement is the identification of rare-earth metal (REM)-controlled morphology and self-organization for Dy(III) and Gd(III) complexes with branched polyester polybenzoylthiocarbamate in solution and on the surface. Spherical nanostructures for the dysprosium complex and nanorods for the gadolinium complex were observed. Synthesized REM-loaded nanostructures with polyester polybenzoylthiocarbamates have low hemotoxicity and can be applied in biomedicine