Physical Properties of Bitumen Distillation Fractions and Solvent Effect on Free Radical Content
Creators: Tulegenova, Diana
Publisher: name: University of Alberta Library
Year: 2022

<p>The main target of bitumen upgrading is to reduce its viscosity. One of the pathways to achieve it is visbreaking. It takes place through thermal cracking by a free radical mechanism. The impact of the bulk liquid (solvent) environment on persistent free radical content was evaluated.<br>
Electron Spin Resonance (ESR) spectroscopy was used to generate data on how different solvents affected the free radical content in bitumen by changing the dissociation equilibrium of radical pairs. The solubility of bitumen was checked in 54 different solvents, and only the soluble solvents were evaluated in the study. Depending on the solvent, it was found that the free radical content of the bitumen could be varied over the range 6×10^17 to 1.5×10^18 spins/g.<br>
The g-factor and analyte spin content generated from the quantitative analysis of the ESR spectra were correlated with the solvents’ properties such as the dipole moment, dielectric constant, ionization potential, molecular weight, density, dynamic and kinematic viscosities. The g-factor of dissociated radical pairs was shifted depending on the dipole moment of the solvent. The higher the dipole moment, the more shifted the g-factor is. Surprisingly, the ionization potential of sulfurcontaining, monoaromatic and diaromatic solvents was linearly proportional to the free radical concentration observed in bitumen. Free radical concentration was poorly correlated with the other solvent properties.<br>
Another approach was to interrogate the change of viscosity with respect to distillation temperature, and for this purpose hands-on fractional distillation was applied to obtain liquid oil products from bitumen. While atmospheric distillation did not yield any liquid, vacuum distillation of bitumen was performed five times with an average liquid yield of 25 wt.%. It resulted in about 15 fractions for each of the five distillations with a temperature range of 20°C for each cut. This material was used for further study.<br>
The 15 distillation fractions were characterized by physical properties such as viscosity, density and refractive index. Next, 14 blends were created to compare different bitumen distillation fractions by forming a blend with known ratios. Refractive index and density data demonstrated that properties between the blends are related to weight composition, i.e. knowing the density of two pure distillation fractions, refractive index and density of the blended material can be accurately estimated by only knowing wt.% of each. However, one blend consisting of 70 wt.% of bitumen distillation fraction with a boiling range of 310-330°C and 30 wt.% of 410-430°C repeatedly deviated from that relationship for a reason that could not be determined.<br>
Overall, it was found that the relationship between density and measurement temperature in a blend is linear over the range of 20-60°C, with density decreasing with an increase in temperature at the rate of - 0.0007 g/cm^3/°C. The Refractive index values also decreased with a temperature increase with a slope of the line equal to -0.0004 nD/°C.<br>
The viscosity of the blends was measured, but not evaluated against binary mixing rules. This is recommended as a good starting point for a follow-up study.</p>