Chemical Characterization of Fatty Acid Structures and Molecular Dynamics Simulation on the Effects of Different...

In molecular dynamics investigations of rejuvenated bitumen (RB), overestimation or misjudgment of intermolecular interactions between bio-oil rejuvenators and asphaltenes, as well as ambiguous mechanistic interpretations at the molecular scale, can be triggered by the adoption of molecular models that fail to reflect the actual chemical composition of bio-oil rejuvenators. Multiple chemical characterization experiments were performed herein to identify the fatty acid forms (FAF) of three distinct bio-oils employed for the preparation of bio-oil RB. Ten molecular dynamics models of RB were established via a controlled variable approach. The influences of bio-oil dosage, FAF, and fatty acid unsaturation (FAU) on some thermodynamic properties of RB were systematically investigated. Combined characterization and simulation results suggest that free fatty acids (FFA) were identified as the primary constituent of tall oil fatty acids, whereas the other two bio-oils were composed of triglycerides. Following bitumen aging, the self-aggregation degrees of asphaltenes and resins were elevated by 23.92% and 59.81%, respectively. The self-aggregation behavior of asphaltenes and resins in aged bitumen (AB) could be effectively alleviated by optimized dosages of rejuvenators, particularly FFA-based rejuvenators. This study further supports that FFA-based rejuvenators showed better compatibility with AB, more effectively enhanced the flow performance of AB, and yielded a more pronounced attenuation of π-π stacking interactions. In comparison with FAU, FAF was found to play a more dominant governing role in regulating the molecular-scale thermodynamic properties of bio-oil RB. This study developed a testing and analytical framework for defining FAF in rejuvenators and elucidated the differential effects and dominant roles of FAF and FAU on the thermodynamic properties.