Effect of Solvents on Persistent Free Radical Content in the Absence of Reactions

Abstract

The impact of a solvent environment on persistent free radical concentrations at ambient conditions was studied by electron spin resonance spectrometry. The analyte selected was Canadian oil-sand-derived bitumen due to its high persistent free radical content. The ability of 54 different solvents to produce a homogeneous 5 wt % solution of bitumen was evaluated. The influence of solvents on the free radical content in bitumen was determined exclusively for solvents that were capable of quantitatively dissolving the bitumen. These were compounds in the classes of alkynes, mono-and bicyclic benzene-derivatives, and heteroatom-containing compounds containing nitrogen, oxygen, sulfur, and chlorine. It was found that a shift in the g-factor of bitumen occurred when the solvent was changed. The shift was attributed to the radical−solvent interaction that is affected by the polarity of the solvent and reflected in the solvent dipole moment property. The change in the free radical concentration was independent of changes in g-factor and was not correlated with any of the following solvent properties: molecular weight, dipole moment, dielectric constant, refractive index, density, and viscosity. There was a relationship between the free radical concentration in bitumen and the ionization potential of sulfur-containing and diaromatic hydrocarbon solvents. It was concluded that the bulk liquid properties that affected the electronic environment of the free radical species, resulting in a shift in g-factor, were not related to the bulk liquid properties that affected the dissociation equilibrium and resulted in a change in the free radical concentration.

Intercriteria Analysis to Diagnose the Reasons for Increased Fouling in a Commercial Ebullated Bed Vacuum Residue Hydrocracker

“…This finding suggests that the fouling phenomenon being quite complex is controlled not only by the residual oil colloidal stability, which is affected by the asphaltene content, 46 but also by other factors like, for example, the content of free radicals in the asphaltene fraction. 48 − 50 The increase of the catalyst addition rates contributes to the enhancement of the available catalyst active sites, which with the participation of the hydrogen may saturate the VTB free radicals. It is understandable that this hypothesis needs to be proven by measurement of the free radical content in the hydrocracked vacuum residue, obtained at different catalyst addition rates, and this can be a subject of another study.…”

Persistent Free Radicals in Petroleum

“…In a study by Tannous et al [30], it was also found that at the same level of petroleum dilution the type of solvent affected the free radical concentration. However, this study did not find a relationship between the free radical concentration in the solution with the dipole moment of the solvent.…”

“…Additionally, bulk properties of the solvent such as molecular weight, refractive index, density, and viscosity were not correlated to the free radical concentration of the analyte. Table 3 [30] illustrates the effect of the type of solvent on the persistent free radical concentration. The measurements were all performed at the same concentration of bitumen.…”

Prospect of Controlled Autoxidation to Produce High‐Value Products from the Low‐Value Petroleum Fractions

“…This indicates most of the asphaltenes would be aromatics having side chains and would contain naphthenic‐aromatic rings. It contains persistent free radicals [19] and is being considered the most reactive part of the bitumen. Figure 4 shows the typical free radical contents of the heavier petroleum fractions.…”