Atomistic Prediction of the Effects of Structural Differences in Bio-Oil Fatty Acids on Thermodynamic Properties and Rejuvenation Behavior of Aged Bitumen

Bio-oil is derived from a diverse range of feedstocks with significant differences in fatty acid form (FAF) and unsaturation (FAU), driven by its inherent compositional diversity. However, existing studies often show deviations in the selection of molecular models for bio-oil rejuvenators, resulting in an overestimation of certain interactions in rejuvenated bitumen (RB) models. This study aims to elucidate the differences in FAF and FAU among bio-oil rejuvenators and to investigate the polarity and thermodynamic properties of bio-oils with different FAF and FAU, thereby facilitating the prediction of their effects on the performance recovery of RB. Different chemical tests were employed to elucidate the chemical structure, molecular structure, and chemical composition of the four bio-oils. Combined with density functional theory calculations and molecular dynamics simulations, the polarity of four representative fatty acid molecules and the thermodynamic properties of six rejuvenator models with varying FAF and FAU combinations were investigated. The results demonstrated that tall oil fatty acid consisted of free fatty acids (FFAs), while soybean oil, palm oil, and rapeseed oil were composed of triglycerides rather than other esters. The overall influence of FAF on the intrinsic properties of bio-oils was more pronounced than that of the FAU. After oleic acid and palmitic acid were esterified into triolein and tripalmitin, respectively, their molecular polarity index increased by 41.6% and 31.3%, respectively. FFA-based rejuvenators were predicted to outperform triglyceride-based ones in enhancing the compatibility, fluidity, and diffusivity of RB, and rejuvenators with high FAU were anticipated to be more conducive to enhancing the low-temperature performance and diffusivity of RB. The findings from this study established an analytical system for clarifying fatty acid molecular models in bio-oil rejuvenators, offering theoretical support for predicting the polarity and thermodynamic properties of RB with varying bio-oil.