Asphalt pyrolysis carbon emission behavior simulation method based on molecular dynamics

Abstract

The invention relates to an asphalt high-temperature cracking carbon emission behavior simulation method based on molecular dynamics, belongs to the technical field of road engineering materials, and solves the problem that cracking reaction evolution caused by dynamic temperature change of asphalt in the whole construction process is difficult to reflect due to the fact that a single constant temperature experimental scheme is mostly adopted in existing molecular dynamics simulation. The method comprises the following steps: firstly, constructing a molecular model of four components of asphalt in Materials Studio, then setting a dynamic temperature path from 438K to 343K to carry out molecular dynamics simulation in combination with actual temperature changes of four stages of mixing, transportation, paving and rolling in construction, tracking the fracture conditions of C-C, C-H, C-O and C-S chemical bonds, and calculating the fracture conditions of the C-C, C-H, C-O and C-S chemical bonds. And counting the generation amounts and rates of CO2, CO, CH4 and other carbon-based gaseous compounds in each stage, and finally establishing a quantitative relationship among the construction stage, the temperature path, the chemical bond fracture behavior and the carbon emission characteristics. According to the simulation method provided by the invention, the carbon emission behavior of the asphalt in the whole construction process can be dynamically revealed, and a theoretical basis is provided for green construction.

Description

Technical Field

[0001] This invention is a method for simulating the carbon emission behavior of asphalt at high temperature pyrolysis based on molecular dynamics, belonging to the field of road engineering materials technology. Background Technology

[0002] Asphalt, as a high-performance binder, occupies a core position in global highway infrastructure construction due to its advantages such as high driving comfort, low noise pollution, and ease of maintenance. With the deepening of my country's national strategy of building a strong transportation network, the scale of the highway network continues to expand, and hot-mix asphalt mixtures have become the mainstream material for asphalt pavement construction due to their good workability and road performance. However, hot-mix asphalt mixtures require high-temperature treatment throughout the production and construction process. At high temperatures, asphalt is prone to cracking reactions, releasing large amounts of carbon emissions (such as CO2, CO, CH4, etc.) and harmful substances such as volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs). These emissions are not only a significant contributor to the exacerbation of the global greenhouse effect, but also accumulate over a long period in semi-enclosed construction environments such as long tunnels and urban underground passages due to their difficulty in rapid dispersion, causing serious damage to the respiratory system of construction workers and posing a potential threat to the surrounding soil, water bodies, and ecological environment, thus posing a severe challenge to the construction of green highways.

[0003] The laying of asphalt pavement is not a single heat treatment event, but a continuous dynamic process encompassing four typical stages: mixing, transportation, paving, and compaction. Each stage corresponds to a unique and continuously changing temperature field and physical-mechanical interactions. For example, at the mixing plant, asphalt and aggregate are violently mixed at temperatures typically exceeding 160°C, experiencing the most intense thermal shock. During subsequent transportation, the mixture begins to cool slowly in a relatively static state. By the paving stage, the material is spread out and subjected to a certain degree of shear force, further reducing its temperature. Finally, in the compaction stage, it is compacted at a relatively lower temperature. This dynamic cooling process throughout the construction chain fundamentally determines the kinetic path, reaction rate, and the types and quantities of final emissions from the thermal decomposition of asphalt molecules. Therefore, a scientific understanding and effective control of asphalt carbon emissions must be based on a deep understanding of this complete, multi-stage process.

[0004] Molecular dynamics simulations have become a powerful tool for exploring the material properties of asphalt. Based on Newtonian mechanics, this method calculates the trajectories of atoms and molecules under force fields, revealing the physicochemical behavior of materials at the atomic scale. In recent years, researchers have begun using molecular dynamics simulations to predict many macroscopic properties of asphalt, such as density, glass transition temperature, viscoelasticity, and diffusion coefficient. These studies typically construct molecular models containing components such as asphaltenes, resins, aromatics, and saturates, and conduct simulations at specific equilibrium states or constant temperatures. The comparability between simulation results and experimental data has been successfully verified, laying an important foundation for understanding the complex structure-property relationship of asphalt at the microscopic level. However, these cutting-edge simulations largely focus on the equilibrium physical properties of asphalt, rather than its chemical reaction behavior under non-equilibrium, dynamic thermal loading.

[0005] While molecular dynamics simulations possess the ability to reveal dynamic processes, existing technologies have key limitations in simulating carbon emissions from high-temperature asphalt pyrolysis. They fail to effectively correlate simulation conditions with real-world multi-stage construction conditions. Current simulations often employ a single constant-temperature experimental scheme, only approximating the instantaneous state during the mixing stage, and cannot reproduce the dynamic evolution of pyrolysis reactions accompanying natural temperature changes throughout the entire hot-mix asphalt pavement construction process. Specifically, existing simulation scenarios are disconnected from actual engineering practices, failing to construct a system that continuously reflects temperature changes at each stage of mixing, transportation, paving, and compaction, making it difficult to answer key engineering questions. Furthermore, there are gaps in the analysis of pyrolysis mechanisms; due to the static nature of the simulations, it is impossible to track the temperature dependence of the sequence of chemical bond breaking, the evolution of intermediate products, and the generation of small molecule gases under dynamic cooling, leading to a fragmented understanding of carbon emission behavior.

[0006] Therefore, this invention proposes a molecular dynamics-based method for simulating the carbon emission behavior of asphalt at high temperatures, addressing the shortcomings of existing technologies that cannot correlate multiple construction stages. This method constructs a dynamic temperature change simulation scheme corresponding to the temperature histories of each stage—mixing, transportation, paving, and compaction—to reproduce the complete evolution of asphalt from high-temperature cracking to low-temperature reaction within a molecular dynamics framework. This invention extends simulation research from static equilibrium to dynamic non-equilibrium states, enabling phased analysis and quantitative assessment of carbon emission behavior throughout the entire construction process, which is of significant value in promoting the development of green construction technologies and environmentally friendly materials. Summary of the Invention

[0007] (1) Technical issues

[0008] The purpose of this invention is to provide a molecular dynamics-based method for simulating the carbon emission behavior of asphalt at high temperatures, which solves the problems of current simulations that mostly use a single constant temperature scheme, which can only approximate the instantaneous state of a certain moment in the mixing stage and cannot reproduce the dynamic evolution of the cracking reaction accompanied by natural temperature changes throughout the construction process of hot-mix asphalt pavement.

[0009] (2) Technical solution

[0010] To address the core problem that existing molecular dynamics simulation methods cannot correlate the multi-stage dynamic process of asphalt pavement construction and are unable to reveal the evolution of carbon emission behavior, this invention proposes a technical solution based on the fundamental principles of molecular dynamics and combined with the temperature characteristics of each stage of construction—mixing, transportation, paving, and compaction—that can dynamically simulate the high-temperature cracking carbon emission behavior of asphalt. The technical solution is as follows: First, based on the determination results of the four components of asphalt, a microscopic molecular model is constructed using Materials Studio software, and the model is optimized and verified using an isothermal-isobaric ensemble (NPT). Then, in Materials Studio, a canonical ensemble (NVT) is used to set dynamic temperature paths corresponding to each construction stage for simulation. By outputting atomic trajectories at high frequency, the breaking dynamics of key chemical bonds are tracked and reaction intermediates are identified. Finally, based on the Analysis module of Materials Studio, the trajectories are divided and the generation patterns of gaseous products at each stage are statistically analyzed to establish a quantitative relationship of "construction stage - temperature path - chemical bond breaking dynamics - carbon emission characteristics." This dynamically reveals the high-temperature cracking mechanism and carbon emission behavior of each stage of the entire asphalt construction process at the atomic scale, providing a theoretical basis for the design and process optimization of low-emission asphalt materials.

[0011] (3) Beneficial effects

[0012] With the continuous advancement of highway infrastructure construction in my country, the problem of high-temperature carbon emissions generated during the production and construction of hot-mix asphalt mixtures is becoming increasingly prominent. Especially in semi-enclosed construction environments such as long tunnels and urban underground passages, the volatile organic compounds, polycyclic aromatic hydrocarbons, and harmful gases such as CO and CH4 produced by asphalt cracking under high temperatures are difficult to disperse quickly, exacerbating the greenhouse effect and posing a serious threat to the respiratory system of construction workers and the surrounding ecological environment. This invention provides a molecular dynamics-based simulation method for the carbon emission behavior of asphalt at high temperatures, capable of simulating the dynamics of carbon emissions from asphalt throughout the entire construction process. By constructing molecular models of the four major components of asphalt and combining them with temperature changes in four stages of asphalt construction, the method dynamically tracks the cracking reaction and the generation pathways of carbon emissions. This has significant theoretical and practical value for guiding the molecular design of low-emission asphalt materials, optimizing construction process parameters, and promoting the construction of green highways. Detailed Implementation

[0013] This invention provides a method for simulating the carbon emission behavior of asphalt at high temperature pyrolysis based on molecular dynamics, and the specific implementation steps are as follows:

[0014] (1) Based on the "Four-component determination method of petroleum asphalt (NB / SH / T0509-2010)", the mass ratio of saturated components, aromatic components, resins and asphaltene in the matrix asphalt was determined by solvent precipitation and chromatographic separation, providing a basis for the proportion of asphalt components for molecular model construction.

[0015] (2) Based on the content and chemical structure characteristics of the four components of asphalt, representative molecules of each component were screened. The Amorphous Cell module of Materials Studio software was used to construct an initial amorphous molecular system containing the four components of asphalt in proportion. The energy minimization geometry optimization of the system was performed by the Forcite module. Under the conditions of 298K and 1 standard atmosphere, the energy and density of the system were balanced by isothermal and isobaric ensemble molecular dynamics optimization. When the error with the measured density of asphalt was less than 3%, the constructed model was confirmed to be reasonable and could be used for subsequent simulation analysis.

[0016] (3) Use the Forcite module to perform molecular dynamics simulation on the optimized asphalt micro molecular model in step (2) using the regular ensemble, and set the dynamic temperature path corresponding to each stage of the construction process, including simulating the temperature of the mixing stage rising from 298K to 438K, simulating the temperature of the transportation stage falling from 438K to 423K, simulating the temperature of the paving stage falling from 423K to 413K, and simulating the temperature of the rolling stage falling from 413K to 343K.

[0017] (4) A trajectory file is output every 1 picosecond throughout the simulation process. The file records the spatial coordinates of all atoms, system energy and temperature at that moment. It focuses on tracking the breaking of CC, CH, CO and CS chemical bonds, and counts the number and rate of breaking of different chemical bonds. By analyzing the atomic trajectory data, the free radicals and unstable intermediate products generated during the asphalt cracking process are identified, and the carbon emission behavior mechanism during the high-temperature cracking process is further revealed.

[0018] (5) After the simulation is completed, the complete molecular trajectory data recorded during the simulation is divided into four construction stages: mixing, transportation, paving and compaction, according to the preset temperature range and heat preservation time. Using the Analysis module of Materials Studio, the generation quantity, rate and accumulation of CO2, CO, CH4 and carbon-based gaseous compounds in each stage are statistically analyzed. A quantitative correspondence between “construction stage-temperature path-chemical bond breaking dynamics-carbon emission characteristics” is established through data analysis, further revealing the carbon emission behavior mode of asphalt high temperature cracking during asphalt construction, and proposing a simulation method for carbon emission behavior of asphalt high temperature cracking based on molecular dynamics.

Claims

1. A method for simulating carbon emission behavior of asphalt high-temperature pyrolysis based on molecular dynamics, characterized in that... The specific steps of this method are as follows: (1) Based on the "Four-component determination method of petroleum asphalt (NB / SH / T0509-2010)", the mass ratio of saturated components, aromatic components, resins and asphaltene in the matrix asphalt was determined by solvent precipitation and chromatographic separation, providing a basis for the proportion of asphalt components for molecular model construction. (2) Based on the content and chemical structure characteristics of the four components of asphalt, representative molecules of each component were screened. The Amorphous Cell module of MaterialsStudio software was used to construct an initial amorphous molecular system containing the four components of asphalt in proportion. The energy minimization geometry optimization of the system was performed by the Forcite module. Under the conditions of 298K and 1 standard atmosphere, the energy and density of the system were balanced by isothermal and isobaric ensemble molecular dynamics optimization. When the error with the measured density of asphalt was less than 3%, the constructed model was confirmed to be reasonable and could be used for subsequent simulation analysis. (3) Use the Forcite module to perform molecular dynamics simulation on the optimized asphalt micro molecular model in step (2) using the regular ensemble, and set the dynamic temperature path corresponding to each stage of the construction process, including simulating the temperature of the mixing stage rising from 298K to 438K, simulating the temperature of the transportation stage falling from 438K to 423K, simulating the temperature of the paving stage falling from 423K to 413K, and simulating the temperature of the rolling stage falling from 413K to 343K. (4) A trajectory file is output every 1 picosecond throughout the simulation process. The file records the spatial coordinates of all atoms, system energy and temperature at that moment. It focuses on tracking the breaking of CC, CH, CO and CS chemical bonds, and counts the number and rate of breaking of different chemical bonds. By analyzing the atomic trajectory data, the free radicals and unstable intermediate products generated during the asphalt cracking process are identified, and the carbon emission behavior mechanism during the high-temperature cracking process is further revealed. (5) After the simulation is completed, the complete molecular trajectory data recorded during the simulation is divided into four construction stages: mixing, transportation, paving and compaction, according to the preset temperature range and heat preservation time. Using the Analysis module of Materials Studio, the generation quantity, rate and accumulation of CO2, CO, CH4 and carbon-based gaseous compounds in each stage are statistically analyzed. A quantitative correspondence between "construction stage - temperature path - chemical bond breaking dynamics - carbon emission characteristics" is established through data analysis, further revealing the carbon emission behavior mode of asphalt high temperature cracking during asphalt construction, and proposing a simulation method for carbon emission behavior of asphalt high temperature cracking based on molecular dynamics.