Study On The Mixing Mechanism Of Sawdust Bio-oil And Asphalt Based On Molecular Simulation

Bio-asphalt as an environmentally friendly asphalt material has received widespread attention in recent years in the field of road engineering.The technology involves the use of liquid bio-oil as a modifier or additive to miscible with asphalt,thereby modifying or replacing asphalt.At present,the mechanism of interaction between bio-oil and asphalt is not clear,which limits the further development of bio-asphalt technology.In this thesis,sawdust is selected as the research object,to carry out research on the preparation process of bio-oil,the average bio-oil molecular model and the interaction mechanism between bio-oil and asphalt,which is of great significance to improve the bio-oil model construction method and explain the microscopic mechanism of bio-oil and asphalt miscibility,and can provide some theoretical basis for the application of bio-asphalt in road engineering.Poplar sawdust were selected as the biomass raw material,the sawdust and solvent were put into the reactor in a certain ratio,the mixture of bio-oil and sawdust residue was extracted under different experimental conditions,then the mix was treated by reduced pressure rotary distillation to obtain sawdust bio-oil.Using the oil yield as the response value,single-factor and orthogonal tests were designed to investigate the effects of process parameters（reaction solvent type,material-to-liquid ratio,reaction time,reaction temperature and additive dosage）on the oil yield and to obtain the optimum process parameters for the preparation of bio-oil.The results showed that the optimum oil yield of 49.62%could be achieved when the mass ratio of sawdust to solvent was 1:10,the reaction time was 100 min,the reaction temperature was 290℃and the amount of Na OH was 24%.The sawdust bio-oil was characterized by microscopic measures such as ¹³C-NMR and XPS,the structural parameters of bio-oil were calculated based on the characterization data,and the average molecular structure model was drawn with the aid of Chem Office software.The model was further optimized in terms of configuration and energy using Gaussian software,and the FITR and NMR spectra of the molecular model of the bio-oil were calculated.By comparing with the experimental spectra,the optimal model was selected,the accuracy and rationality of the model was verified.The results show that the overall cross-linked structure of the sawdust bio-oil is mainly composed of benzene,naphthalene,ether bond,methylene and carboxyl groups,and the molecular formula of the average molecular structure model is C₅₀H₇₄O₁₉.Material Studio software was used to construct matrix asphalt model,bio-oil model,and bio-asphalt model.The models were then optimized and validated to find the lowest energy conformation;molecular dynamics simulations of the relaxation structure were carried out to analyze the interaction mechanism between sawdust bio-oil and asphalt using solubility parameters interaction energy,free volume fraction,radial distribution function and radius of gyration as indicators.It was found that:the solubility parameters of bio-oil and bitumen are close to each other,so they have good compatibility;bio-oil only physically modifies asphalt and physically adsorbs with the lighter components of asphalt,but this adsorption does not affect the polarity of asphalt molecules and does not change the colloidal structure of asphalt;In bio-asphalt,there is less free volume distribution near the bio-oil molecules and this microstructure contributes to the stability of the bio-asphalt;asphalt and bio-oil are both amorphous substances,and bio-oil will not have a significant aggregation effect with the asphalt components;The bio-asphalt model has similar radius of gyration for each component compared to the matrix asphalt model,indicating that the viscosity of the asphalt does not change significantly with the addition of bio-oil.