Investigating Change of Polydispersity and Rheology of Crude Oil and Bitumen Due to Asphaltene Oxidation

Abstract

This paper examines the effect of oxidation of asphaltene molecules on the overall polydispersity and rheology of a bituminous matrix. The research hypothesis is that oxidation of asphaltene molecules increases bitumen polydispersity; it is further hypothesized that increased polydispersity leads to reduction in crossover modulus and viscosity of the bituminous matrix. To test this hypothesis, laboratory experiments combined with molecular dynamics simulations were used to examine the properties of bitumen samples containing different concentrations of oxidized asphaltenes. To prepare samples, asphaltene was initially solvent-extracted from the bitumen sample; a portion of the extracted asphaltenes was then oxidized using an ozone treatment oven. The oxidized portion and nonoxidized portion were then blended and added back to the original bitumen sample via solvent blending to ensure uniform distribution. Rheological characterization of bitumen samples containing oxidized asphaltene showed that viscosity measured at shear rates above 1 s–1 decreases as the concentration of oxidized asphaltenes increases. Our molecular level analysis showed that aggregation of asphaltene molecules increases with the increase in concentration of oxidized asphaltene, which in turn increases the polydispersity in the bitumen matrix. Polydispersity is inversely related to crossover modulus, so an increase in polydispersity is expected to reduce the crossover modulus. The latter was confirmed by our rheometry results showing a significant reduction in crossover modulus when the content of oxidized asphaltene molecules increased. The outcome of this study shows that oxidation of asphaltene molecules alone leads to formation of nanoaggregates of asphaltene that easily move against each other reducing bitumen viscosity at high shear rates. The latter reduction effect may be masked in the field when asphaltene oxidation is accompanied by the loss of volatiles, aromatization, and carbonation as aging progresses. The study highlights the role of oxidized asphaltene molecules in the flow behavior of bitumen; this, in turn, helps refineries and blending terminals tune viscous flow and bitumen rheology by controlling the extent of asphaltene oxidation and subsequent aggregation.

Inherently Functionalized Carbon from Lipid and Protein-Rich Biomass to Reduce Ultraviolet-Induced Damages in Bituminous Materials

“…To facilitate comparing studied scenarios, the sum of the two indexes was calculated at each aging interval and referred to as the chemical aging index (CAI), following the method used by other researchers. 28 − 30 The asphalt sample without biochar showed a CAI of 22% after 50 h and 40% after 200 h of aging ( Table 7 ). Among all asphalt samples with biochar, the sample containing algal biochar (100–0 scenario) had the lowest CAI value of 17% after 50 h and 26% after 200 h of aging.…”

“…It should be noted that the crossover values (frequencies at which storage modulus and loss modulus are equal) are reported to be reliable measures to track changes in the polydispersity of bitumen. 28 Considering that progressive aging leads to significant changes in polydispersity as asphaltene molecules forms nanoaggregates, 29 , 30 crossover values are deemed appropriate to not only track the evolution of bitumen during aging but also rejuvenation. 31 Provided the crossover frequency and corresponding crossover moduli are measured at the same temperature for all bitumen specimens in comparison, the crossover values can properly detect and compare the extent of aging and in this study extent of delay in aging.…”

“…At the crossover point, the elastic modulus ( G ′) and viscous modulus ( G ″) are equal. It should be noted that the crossover values (frequencies at which storage modulus and loss modulus are equal) are reported to be reliable measures to track changes in the polydispersity of bitumen . Considering that progressive aging leads to significant changes in polydispersity as asphaltene molecules forms nanoaggregates, , crossover values are deemed appropriate to not only track the evolution of bitumen during aging but also rejuvenation .…”

A Role for Newly Developed Sorbents in Remediating Large‐Scale Oil Spills: Reviewing Recent Advances and Beyond

“…[88] Emulsions significantly change the properties and characteristics of spilled oil. [89][90][91][92][93] Stable emulsions contain 60-85% water, thereby expanding the spill's volume by three to five times the original volume of spilled oils. [94] Oxidation alters oil mixtures by creating new compounds and rearranging the distribution of residual compounds.…”

Effect of ultrasound irradiation on asphaltene aggregation and implications to rheological behavior of bitumen

“…It appears from the literature that the viscosity reduction pertains to (1) asphaltene re-dissolution [18] , [38] , (2) conversion of asphaltene molecules by dehydrogenation [27] , or (3) conversion of asphaltenes to lighter aromatics [39] , [40] . At any rate, controlling the solubility of asphaltene under ultrasound irradiation, could provide significant insights on the reduction of bitumen viscosity.…”