Method for determining molecular oxidation activity and oxidation site of asphalt component through quantum chemical simulation

Abstract

The invention belongs to the field of road engineering materials, and relates to a method for determining oxidation activity and oxidation sites of asphalt component molecules through quantum chemistry simulation. Firstly, a molecular model of each component of asphalt is constructed; secondly, calculating front molecular orbits (HOMO, LUMO and an energy gap band) and global softness of molecules through quantum chemistry software, and evaluating the overall oxidation activity of asphalt component molecules; and then, further calculating electrostatic potential, average local ionization energy and a simplified Fujin function of the molecules, and determining local oxidation sites of the asphalt component molecules. The method can effectively compare the molecular oxidation activity of the asphalt component, identify the molecular oxidation sensitive area of the asphalt component, reduce the consumption of experimental resources and reduce the research and development cost of materials, has wide application potential, and is suitable for popularization and application. And theoretical support and practical reference can be provided for asphalt antioxidant design and oxidation reaction prediction of other complex multi-component material systems.

Description

Technical Field

[0001] The present invention belongs to the field of road engineering materials, and relates to a method for determining the oxidation activity and oxidation sites of asphalt component molecules based on a quantum chemical calculation method, specifically a method for determining the oxidation activity and oxidation sites of asphalt component molecules by quantum chemical simulation. Background Art

[0002] Asphalt is a viscous organic material widely used in road engineering, mainly used for paving and maintaining infrastructure such as highways and airport runways. It is composed of a variety of chemical components, mainly including saturated components, aromatic components, colloids and asphaltenes, which correspond to different molecular structures and chemical properties. The content of these components and their interactions determine the overall performance of asphalt. However, asphalt is inevitably affected by environmental factors during its service, especially under the combined effects of oxygen, ultraviolet rays and temperature, it is prone to oxidation and aging, resulting in a decrease in its physical and mechanical properties, cracking, embrittlement and other problems, which affect the service life of the road.

[0003] Asphalt aging is a complex chemical process, which is mainly manifested by the breaking and reorganization of chemical bonds within the molecule, resulting in changes in the molecular structure of asphalt. Studies have shown that the oxidation reaction of asphalt mainly occurs on asphaltene, colloid and aromatic components. Due to the existence of oxidation reaction, the polarity of asphaltene and colloid components increases, and gradually loses their original viscoelasticity, resulting in a significant decrease in the crack resistance and low temperature performance of asphalt.

[0004] At present, the research on asphalt oxidation aging mainly focuses on experimental characterization at the macro and micro levels, such as analyzing the rheological properties, chemical composition and thermal stability of asphalt through dynamic shear rheology test (DSR), infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). However, these methods can only reflect the changes in the macroscopic properties and microscopic properties of asphalt after aging, and it is difficult to deeply reveal the oxidation reaction mechanism at the molecular level. Therefore, developing a method that can predict the oxidation activity of asphalt components at the molecular level is of great significance for understanding the asphalt aging mechanism, delaying the asphalt aging process, and improving the service life of roads.

[0005] Quantum chemical calculation is an advanced method that can simulate molecular structure, electron distribution and its reactivity. In recent years, with the development of computational chemistry, quantum chemical simulation has gradually been applied to the study of asphalt materials to predict and explain the microscopic behavior of asphalt molecules. For example, the frontier molecular orbital energy levels of asphalt components can be calculated by density functional theory (DFT) to evaluate the reactivity of the molecules; the electrostatic potential (ESP) distribution map can be used to determine the sites on the molecular surface that are easily attacked by oxygen or free radicals. However, most of the existing studies only stay at the calculation of a single parameter, lacking a systematic method to comprehensively evaluate the oxidation activity and oxidation sites of asphalt molecules.

[0006] During the aging process of asphalt, free radical reaction is one of the main driving forces of oxidation. Free radicals react with certain active sites in the asphalt molecules, resulting in the destruction or reorganization of the molecular structure. Therefore, judging the oxidation activity of the molecule and the local oxidation site is crucial to understanding and controlling the aging process of asphalt. As a tool to quantify the local reactivity of molecules, the Fukui function can effectively characterize the active sites attacked by free radicals in the molecule. In addition, global softness is a parameter used to quantify the overall reactivity of a molecule, reflecting the sensitivity of the molecular electronic structure to external influences. By combining global softness and local Fukui function, the oxidation reaction behavior of the molecule can be more comprehensively evaluated. Summary of the invention

[0007] The present invention is based on quantum chemical simulation technology and provides a calculation method based on quantum chemical simulation, which is used to accurately predict the oxidation activity of the four-component molecules of asphalt and determine the specific oxidation sites of their oxidation reactions. It overcomes the difficulty that ordinary experimental means cannot accurately evaluate the oxidation active sites of asphalt components and helps to analyze the oxidation mechanism. By constructing a molecular model of the four components of asphalt, calculating its frontier molecular orbital, global softness, electrostatic potential distribution, average local ionization energy and reduced Fukui function, the oxidation activity of the molecules and their local oxidation sites are systematically analyzed. This method can not only reveal the oxidation mechanism of asphalt component molecules, but also can be used to predict the aging behavior of different asphalt materials in actual use. It can effectively evaluate the molecular-level oxidation behavior of asphalt components and provide a theoretical basis and practical reference for the design and modification of asphalt materials.

[0008] The technical solution of the present invention is as follows:

[0009] The method for determining the oxidation activity and oxidation sites of asphalt component molecules by quantum chemical simulation includes the following steps:

[0010] (1) Construction of a four-component molecular model of asphalt

[0011] Asphalt is composed of four components: saturated fraction, aromatic fraction, colloid and asphaltenes. Different components have different molecular structures and chemical properties. First, molecular models of these four components are constructed by molecular simulation software, including verifying the density, surface energy, glass transition temperature and other parameters of the molecular model to ensure that the constructed molecular model can accurately represent the component structure of the actual asphalt. For saturated fraction, the model is mainly composed of saturated hydrocarbon compounds; aromatic fraction is represented by aromatic hydrocarbon molecules; colloid model is usually a medium molecular weight compound with some polar functional groups; asphaltenes are composed of large molecular weight compounds with more polar functional groups. Model construction can be achieved by simulating the chemical structure of common asphalt components or using the common asphalt component distribution data in experiments. This step provides the basis for subsequent quantum chemical calculations.

[0012] (2) Determination of the overall oxidative activity of the molecule

[0013] The frontier molecular orbitals (HOMO, LUMO, energy gap band) and global softness of the four asphalt component molecules were calculated using quantum chemical calculation software to determine the overall oxidation activity of each asphalt component molecule; specifically, as follows:

[0014] After the molecular model is constructed, quantum chemical software (such as Gaussian) is used to perform quantum chemical calculations on the various components of asphalt, including frontier molecular orbital calculations and conceptual density functional calculations. By determining the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) of each molecule, the reactivity of the molecule to external substances (such as oxygen molecules or free radicals) can be evaluated. The energy level difference of the frontier molecular orbital (i.e., the HOMO-LUMO energy gap) is calculated. The smaller the energy gap, the easier it is for the molecule to undergo oxidation reactions. This parameter is usually used to characterize the overall chemical reactivity of the molecule and can reflect the difficulty of the molecule to participate in the oxidation reaction. In addition, by calculating the global softness, the overall reaction tendency of the asphalt molecule when facing oxygen can be evaluated. The larger the global softness value, the stronger the reactivity of the molecule to external attacks, indicating that its oxidation activity is higher. The energy gap band and the global softness parameter can be used to compare the overall reactivity differences of different asphalt components in oxidation reactions.

[0015] (3) Determination of local oxidation active sites

[0016] The electrostatic potential, average local ionization energy and reduced Fukui function (radical attack index) of the four component molecules of asphalt were calculated to determine the local oxidation site of each component molecule.

[0017] ① Electrostatic potential: Electrostatic potential is used to describe the charge distribution on the molecular surface, helping to determine which areas of the molecule are likely to react with charged particles or oxygen molecules. Areas where positive charges are concentrated are usually prone to electron acceptance reactions, i.e. oxidation reactions. By calculating and drawing the electrostatic potential distribution map of the molecule, the most likely location on the molecular surface to become an oxidation site can be intuitively displayed.

[0018] ② Average local ionization energy: The average local ionization energy reflects the ease with which a molecule loses electrons in a specific area. The lower the average local ionization energy, the more susceptible it is to attack by oxygen. Therefore, by calculating the average local ionization energy of a molecule, we can further accurately locate the local area in the molecule where oxidation reactions are most likely to occur.

[0019] ③ Simplified Fukui function: The Fukui function is used to quantify the reactivity of a molecule when attacked by free radicals or electrophilic reagents. The present invention pays special attention to the free radical attack index. The area with a larger free radical attack index is more susceptible to attack by oxygen free radicals. By calculating the simplified Fukui function (free radical attack index) in the molecule, the active sites in the asphalt molecule that are easily attacked by oxygen free radicals can be accurately predicted.

[0020] By combining the electrostatic potential, average local ionization energy and reduced Fukui function (radical attack index), the oxidation reaction tendency of the local site of each asphalt component molecule can be comprehensively analyzed, and ultimately the molecular site where oxidation reaction is most likely to occur can be determined.

[0021] (4) Based on the above calculation results, the oxidation activity and oxidation sites of asphalt component molecules are analyzed.

[0022] The beneficial effects of the present invention are:

[0023] The present invention systematically predicts the oxidation activity and local oxidation sites of the four-component molecules of asphalt through quantum chemical simulation methods, providing a fast and accurate analysis tool. It overcomes the difficulty that ordinary experimental means cannot accurately evaluate the oxidation active sites of asphalt components, and helps to analyze the oxidation mechanism. Compared with the traditional method that relies on a large amount of experimental test data, the present invention can accurately identify the oxidation activity and oxidation sensitive areas of asphalt components at the molecular level, thereby providing strong support for antioxidant design. At the same time, the present invention greatly reduces the investment in experimental resources, reduces experimental costs and time. The oxidation site information obtained by calculation can effectively guide the research and development of new anti-aging asphalt materials, thereby significantly improving the service life and durability of roads. In addition, the present invention has good adaptability and can be promoted and applied to other complex multi-component material systems, providing a new solution for material aging research and optimization. Therefore, the present invention has significant advantages in improving material performance, optimizing material design and reducing research and development costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 are the four-component molecules of asphalt in the embodiment, wherein a is an asphaltene molecule, b is an aromatic molecule, c is a colloid molecule, and d is a saturated molecule.

[0025] Figure 2 These are the HOMO, LUMO orbital diagrams and HOMO-LUMO gap of the four components of asphalt in the embodiment, wherein a, b, c, and d are the HOMO, LUMO orbital diagrams and HOMO-LUMO gap of asphaltene molecules, aromatic molecules, colloidal molecules, and saturated molecules, respectively.

[0026] Figure 3 It is the global softness of the four components of asphalt in the embodiment.

[0027] Figure 4 is the electrostatic potential diagram of asphaltene molecules in the examples.

[0028] Figure 5 It is the electrostatic potential diagram of the aromatic molecules in the examples.

[0029] Figure 6 is the electrostatic potential diagram of the colloidal molecules in the example.

[0030] Figure 7 is the average local ionization energy diagram of asphaltene molecules in the examples.

[0031] Figure 8 is the average local ionization energy diagram of the aromatic molecules in the examples.

[0032] Fig. 9 is the average local ionization energy diagram of the colloidal molecules in the embodiment.

[0033] Fig.10 is a graph of the free radical attack index of asphaltene molecules in the examples.

[0034] Fig.11 Graph showing the free radical attack index of the aromatic molecules in the examples.

[0035] Fig.12 Graph showing the free radical attack index of the colloidal molecules in the embodiment.

[0036] Fig.13 is the oxidation site determined on the asphaltene molecule in the examples.

[0037] Fig.14 is the oxidation site determined by the aromatic molecules in the examples.

[0038] Fig.15 is the oxidation site determined by the colloidal molecule in the example. DETAILED DESCRIPTION

[0039] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0040] A method for determining the oxidation activity and oxidation sites of four-component asphalt molecules by quantum chemical simulation, comprising the following steps:

[0041] (1) Constructing a four-component model of asphalt. The four components of asphalt include asphaltenes, aromatic components, colloids and saturated components. Solvent extraction and silica gel chromatography are used to separate the four components of asphalt. Fourier transform infrared spectroscopy, gel permeation chromatography and elemental analysis are performed on each component to determine the functional group distribution, molecular weight range and distribution and elemental composition of the four components. In this way, a molecular model of the four components of asphalt is established and the model is verified using molecular dynamics software to ensure that the simulation results, such as viscosity and diffusion coefficient, are consistent with the actual data. The four-component model of asphalt used in this example is as follows: Figure 1 shown.

[0042] (2) Use quantum chemistry software to establish the four-component molecules of asphalt, and perform geometry optimization and vibration analysis. After using quantum chemistry software (Gaussian is used in this example) to model the molecular model constructed in the previous step, since the initial molecular structure usually comes from experimental data or a guessed model, it may not meet the requirements of quantum chemistry calculations, so geometry optimization is still required. Through the geometry optimization process, the molecule tends to the global or local minimum potential energy point, that is, the stable state of the molecular system. The non-optimized structure may be in a high-energy or unstable configuration and cannot truly reflect the chemical properties of the actual molecule. Vibration analysis is to obtain the frequency and thermodynamic information related to molecular motion by calculating the vibration mode of the molecule after the geometry optimization is completed. Vibration analysis can determine whether the optimized geometry is the minimum point (corresponding to the real stable structure) or the saddle point of the potential energy surface, so as to verify whether the geometry optimization is successful. In this example, the geometry optimization and vibration analysis functionals and basis sets are set to b3lyp / 6-31g(d)em=gd3bj.

[0043] (3) Perform high-precision single-point energy calculations on the results of geometry optimization and vibration analysis in the previous step. In geometry optimization, a lower calculation accuracy is usually used to reduce the calculation cost. Although the optimized structure is reasonable under low accuracy, the corresponding total energy may not be accurate enough, so high-precision single-point energy calculations are still required. The main purpose of high-precision single-point energy calculations is to obtain a more accurate total energy of the system through calculations at a higher theoretical level and a larger basis set based on the optimized structure. Its role is reflected in correcting errors, improving the calculation accuracy of reaction energy and activation energy, improving the description of weak interactions, and reducing the overall calculation cost. In this example, the high-precision single-point energy calculation uses M062X / 6-311G**em=gd3.

[0044] (4) Determine the overall oxidation activity of asphalt molecules. The high-precision single-point energy calculation results are processed by Multiwfn and visualized by VMD to draw HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) diagrams, calculate energy bands (i.e., HOMO-LUMO energy gaps), and calculate global softness. By determining the HOMO and LUMO orbitals of each molecule, the reactivity of the molecule to external substances (such as oxygen molecules or free radicals) can be evaluated. The energy level difference of the frontier molecular orbitals (i.e., HOMO-LUMO energy gap) is calculated. The smaller the energy gap, the easier it is for the molecule to undergo oxidation reactions. This parameter is usually used to characterize the overall chemical reactivity of the molecule and can reflect the difficulty of the molecule to participate in oxidation reactions. In addition, by calculating the global softness, the overall reaction tendency of the asphalt molecules when facing oxygen can be evaluated. The larger the global softness value, the stronger the reactivity of the molecule to external attacks, indicating that its oxidation activity is higher. The energy gap band and global softness parameters can be used to compare the overall reactivity differences of different asphalt components in oxidation reactions. The HOMO, LUMO orbital diagrams and HOMO-LUMO gap of the four components of asphalt are shown in Figure 2. Figure 2 The calculation results of the global softness of the four components of asphalt are shown in Figure 3 In this example, the HOMO-LUMO gaps of asphaltene molecules, aromatic molecules, colloidal molecules, and saturated molecules are 4.23 eV, 5.07 eV, 5.45 eV, and 10.73 eV, respectively; the global softness is 5.862168 Hartree -1 、4.679733Hartree -1 4.469572Hartree -1 , 2.378593Hartree -1 . The results show that the HOMO-LUMO gap of asphaltene molecules is the smallest and the global softness is the largest, so the overall oxidation activity of asphaltene molecules is the highest; the HOMO-LUMO gap of saturated molecules is the largest and the global softness is the smallest, so the overall oxidation activity of saturated molecules is the lowest and it is difficult to react with oxygen or free radicals; the HOMO-LUMO gap and global softness of aromatic and gum molecules are between asphaltene and saturated molecules, so the overall oxidation activity of aromatic and gum molecules is less than that of asphaltene but greater than that of saturated molecules, and the overall oxidation activity of aromatic molecules is slightly greater than that of gum molecules. From the above results, the overall oxidation activity of the four components of asphalt is arranged from high to low as asphaltene, aromatic, gum, and saturated.

[0045] (5) Determine the local oxidation active sites through electrostatic potential. The high-precision single-point energy calculation results are processed by Multiwfn and visualized by VMD to draw the electrostatic potential map. Electrostatic potential is used to describe the charge distribution on the molecular surface and help determine which areas of the molecule are prone to react with charged particles or oxygen molecules. Areas where positive charges are concentrated are usually prone to electron acceptance reactions, that is, oxidation reactions. By calculating and drawing the electrostatic potential distribution map of the molecule, the position on the molecular surface that is most likely to become an oxidation site can be intuitively displayed. Since the overall oxidation activity of the saturated fraction is relatively low, the electrostatic potential maps are only drawn for asphaltene, aromatic fraction, and colloid molecules. The results are as follows: Figure 4 , Figure 5 , Figure 6 As shown. Figure 4 As shown in the figure, the top three extreme points of the maximum and minimum values ​​of the electrostatic potential of asphaltene molecules are marked respectively. It can be seen that the larger values ​​of the electrostatic potential are all located near the heteroatoms, among which the electrostatic potential near the two hydroxyls is the largest, indicating that the oxidation activity is the greatest here, and the electrostatic potential near the nitrogen atom is also large. The point with the maximum absolute value of the electrostatic potential is the reaction site with the greatest oxidation activity. The most likely oxidation site of the asphaltene molecule determined by the electrostatic potential is the benzene hydroxyl group. Figure 5 As shown in the figure, the electrostatic potential values ​​of the methyl group near the aromatic carbon of the aromatic benzene ring, near the sulfur atom, and at the end of a branch chain are relatively large, among which the electrostatic potential near the sulfur atom is the largest, indicating that the sulfur atom has the highest oxidation activity and is a potential oxidation site. Figure 6 As shown, the electrostatic potential near the aromatic carbon and hydroxyl groups of the colloidal molecules is relatively large, among which the electrostatic potential at the hydroxyl group is the largest and the oxidation activity is the highest.

[0046] (6) Determine the local oxidation active sites by averaging the local ionization energy. The high-precision single-point energy calculation results are processed by Multiwfn and visualized by VMD to draw the average local ionization energy diagram. The average local ionization energy reflects the ease with which a molecule loses electrons in a specific area. The lower the average local ionization energy, the more susceptible it is to attack by oxygen. Therefore, by calculating the average local ionization energy of a molecule, the local area in the molecule that is most susceptible to oxidation reactions can be further accurately located. The average local ionization energy diagram of asphaltene, aromatic components, and colloid molecules is shown in Figure 1. Figure 7 , Figure 8 , Fig. 9 As shown in Figure 2, it is observed that the average local ionization energy of sulfur atoms in asphaltene molecules, aromatic molecules and colloid molecules is the smallest, and the oxidation activity is the highest, which is the most easily oxidized potential reaction site.

[0047] (7) Determine the local oxidation active site by the free radical attack index. The free radical attack index diagram is drawn by combining Gaussian with Multiwfn and VMD. The area with a larger free radical attack index is more susceptible to attack by oxygen free radicals. By calculating the free radical attack index in the molecule, the active sites in the asphalt molecule that are easily attacked by oxygen free radicals can be accurately predicted.

[0048] Asphaltene, aromatic components, and free radical attack index of colloid molecules are shown in the figure below. Fig.10 , Fig.11 , Fig.12 As shown. Fig.10 As shown in Figure 2, the free radical attack index at the sulfur atom of the asphaltene molecule is the largest, and the oxidation activity is the greatest. Fig.11 As shown in the figure, the free radical attack index at the aromatic carbon opposite to the sulfur-containing branch chain of the aromatic molecule is the largest, which is a potential oxidation site. Fig.12 As shown, the free radical attack index is the largest at the sulfur atom of the colloidal molecule, and the oxidation activity is the greatest.

[0049] (8) Combine the electrostatic potential, average local ionization energy, and free radical attack index of the asphalt molecule to determine the reaction site of the asphalt molecule. The reaction sites determined by the electrostatic potential, average local ionization energy, and free radical attack index are summarized and sorted out. The oxidation sites determined by asphaltene, aromatic components, and colloid molecules are as follows: Fig.13 , Fig.14 , Fig.15 As shown. The numbers in the figure represent the ranking, such as 1 represents the maximum absolute value of the electrostatic potential minimum (+1 represents the maximum electrostatic potential maximum) or the minimum average local ionization energy or the maximum free radical attack index. The maximum absolute value of the electrostatic potential, the minimum average local ionization energy, and the maximum free radical attack index are taken as the most likely potential oxidation sites (red circles in the figure), which are the places with the highest oxidation activity. Fig.13 It can be seen that the reaction sites determined by asphaltene molecules are the benzene hydroxyl group and two sulfur atoms. Fig.14 It can be seen that the oxidation reaction sites determined by the aromatic molecules are the branched sulfur atom and the aromatic carbon opposite to the branch. Fig.15 It can be seen that the oxidation reaction sites determined by the colloidal molecules are the benzene hydroxyl group and the sulfur atom.

Claims

1. A method for determining the oxidation activity and oxidation sites of asphalt component molecules based on quantum chemical simulation, characterized in that: The method comprises the following steps: (1) Construct a four-component molecular model of asphalt; (2) using quantum chemical calculation software to calculate the frontier molecular orbitals and global softness of the four asphalt component molecules to determine the overall oxidation activity of each asphalt component molecule; (3) Calculate the electrostatic potential, average local ionization energy and reduced Fukui function of the four component molecules of asphalt to determine the local oxidation site of each component molecule; (4) Based on the above calculation results, the oxidation activity and oxidation sites of asphalt component molecules are analyzed.

2. A method for determining the oxidation activity and oxidation sites of asphalt component molecules based on quantum chemical simulation according to claim 1, characterized in that: The four-component molecular model of asphalt constructed in step (1) includes: a saturated component model representing saturated hydrocarbon molecules, an aromatic component model representing aromatic hydrocarbon molecules, a colloid model with some polar functional groups, and an asphaltene model with more polar functional groups.

3. The method for determining the oxidation activity and oxidation sites of asphalt component molecules based on quantum chemical simulation according to claim 1, characterized in that: The frontier molecular orbitals in step (2) include the highest occupied molecular orbital HOMO, the lowest unoccupied molecular orbital LUMO and the energy gap band.

4. The method for determining the oxidation activity and oxidation sites of asphalt component molecules based on quantum chemical simulation according to claim 1, characterized in that: The simplified Fukui function used in step (3) is the free radical attack index.

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