Quantum chemistry calculation-based asphalt saturated group molecule judgment method

Abstract

The invention discloses an asphalt saturated group molecule judgment method based on quantum chemistry calculation. Comprising the following steps: establishing an asphalt saturated submolecular model, and optimizing a molecular structure and energy to obtain a stable geometric configuration with lowest energy; on the basis, quantum chemistry calculation is carried out, four parameters, namely, the molecular overall dipole moment, the polar surface area ratio, the HOMO-LUMO energy gap and the molecular polarity index (MPI), obtained through calculation are used as descriptors, and a quantitative index system for judging the asphalt saturation component is established. The judgment method provided by the invention can efficiently and quickly distinguish the saturated component molecules in the asphalt, has relatively high precision and applicability, and provides an effective method for judging the molecules of the saturated component in the asphalt from a nano perspective.

Description

Technical Field

[0001] The present invention relates to a method for judging the molecular weight of asphalt saturated group, and in particular to a method for judging the molecular weight of asphalt saturated group by quantum chemical calculation. Background Art

[0002] Saturated fraction is one of the four components of asphalt. Its nanostructure and characteristics have an important influence on the properties of asphalt such as consistency and anti-aging. In past studies, researchers usually analyzed the saturated fraction of asphalt by experimental means. Although this traditional method can meet the needs of asphalt performance analysis to a certain extent, it still has certain limitations. It is impossible to distinguish the molecules of asphalt saturated fraction at the nanoscopic level, and it is difficult to provide accurate molecular structure information of saturated fraction and explain the reaction mechanism. Summary of the invention

[0003] The purpose of the present invention is to provide a method for determining the molecular weight of asphalt saturated groups based on quantum chemical calculation methods. The method obtains four index parameters of the overall dipole moment, molecular polarity index (MPI), polar surface area ratio and HOMO-LUMO energy gap of the saturated molecules through quantum chemical calculations, determines the distribution range of the molecular weight parameters of asphalt saturated groups, and is used for research related to the classification of asphalt four components. The present invention can efficiently and quickly distinguish the molecular weight of asphalt saturated groups, and solve the problems raised in the above-mentioned background technology.

[0004] To achieve the above object, the present invention provides a method for determining the molecular weight of asphalt saturation group based on quantum chemical calculation method, the method comprising the following steps:

[0005] Step 1: Collect 9 asphalt saturated fractions through existing databases and literature;

[0006] Step 2: Use KingDraw software to identify the molecular structure formula in the literature, and after checking that it is correct, use Chem3D software to convert it into a three-dimensional model;

[0007] Step 3: Using quantum chemistry software Gaussian, the structure was optimized using the B3LYP method and 6-31G (d, p) basis set under density functional theory (DFT) to obtain the lowest energy stable geometric configuration;

[0008] Step 4: Convert the chk file output by Gaussian into an fch file, and import the fch file into the post-processing software multiwfn;

[0009] Step 5: Use Multiwfn software to calculate the overall dipole moment, MPI, polar surface area ratio and HOMO-LUMO energy gap of the nine saturated molecules, and use post-processing software VMD to visualize the HOMO-LUMO energy gap;

[0010] Step 6: Calculate the four index parameters of the other three components of asphalt through the above steps. By examining the index parameters of the saturated fraction, a quantitative index system of the four index distribution of the saturated fraction is obtained, which is used to determine whether the asphalt molecules that have not been tested are saturated components.

[0011] In particular, the saturated molecules collected in step 1 come from asphalt molecules classified based on SARA components in the literature, as well as molecules that are considered as saturated molecules in various crude oil asphalt raw material component determination tests.

[0012] In particular, the dipole moment calculation in step 2 takes the optimized molecular structure, creates a Gaussian input file in the neutral state, calculates the single-point energy of the molecule using the B3LYP method and the 6-311G (2d, p) basis set, converts the obtained chk file into an fch file, and uses the Hirshfeld weight function as the input file of Multiwfn for calculation; MPI is the mean of the absolute values ​​of the molecular surface electrostatic potential; the polar surface area ratio is the ratio of the surface area with an absolute value of electrostatic potential less than 10 kcal / mol to the total surface area of ​​the molecule; the HOMO-LUMO energy gap is the energy level difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1) The determination of saturated components and molecules in asphalt is realized by quantum chemical calculation method, which can calculate the index parameters of saturated components and molecules efficiently and quickly, avoiding the complexity of experimental methods, and has the advantages of safety, time saving and low cost. It provides a new method for the differentiation of asphalt components from a nanoscopic perspective, which is easy to promote and use.

[0015] 2) Applying quantum chemical calculations and molecular simulation methods, the saturation classification method was determined by examining four indicator parameters: the overall molecular dipole moment, MPI, polar surface area ratio, and HOMO-LUMO energy gap, thereby improving the accuracy of classification.

[0016] 3) The three indicators of overall dipole moment, MPI and polar surface area ratio are examined simultaneously, and the molecules are judged based on the polar characteristics of the saturated fraction, which effectively avoids the influence of the overall dipole moment single indicator that may be abnormal due to the symmetry of the molecular structure.

[0017] Beneficial effects of the present invention BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1This is a diagram of the optimized 9 saturation fraction submodels used in the present invention;

[0019] Figure 2 Schematic diagram of the HOMO-LUMO energy gap calculated in the present invention. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work are within the scope of protection of the present invention.

[0021] A method for determining the molecular weight of asphalt saturation group based on quantum chemical calculation method, comprising the following steps:

[0022] Step 1: Collect 9 asphalt saturated molecular molecules from literature and databases as research objects, identify the molecular structure formula in the literature through KingDraw software or other online software, and convert it into a three-dimensional model using Chem3D software after checking that it is correct (such as Figure 1 shown);

[0023] Step 2: Using quantum chemistry software Gaussian, the structure was optimized using the B3LYP method and 6-31G (d, p) basis set under density functional theory (DFT) to obtain the lowest energy stable geometric configuration;

[0024] Step 3: Convert the chk file output by Gaussian into an fch file and import it into the post-processing software Multiwfn;

[0025] Step 4: Use Multiwfn to calculate MPI, polar surface area ratio and HOMO-LUMO energy gap, organize the data and use post-processing software VMD to generate HOMO-LUMO energy gap diagram (such as Figure 2 As shown), it is convenient for intuitive inspection;

[0026] Step 5: Take the optimized molecular structure, create the Gaussian input file in the neutral state, calculate the single point energy of the molecule using the B3LYP method and the 6-311G (2d, p) basis set, and convert the obtained chk file into an fch file;

[0027] Step 6: Import the fch file obtained from the single point energy calculation into Multiwfn, and calculate the overall dipole moment of the molecule under the conditions of a higher basis set;

[0028] Step 7: Collect 21 asphaltene molecules, 22 colloid molecules, and 13 aromatic molecules, and calculate the four index parameters using the same steps as above;

[0029] Step 8: Count the distribution range of the parameters of the four groups and four indicators, and use the distribution results of the four indicators of the saturation group as a quantitative indicator system to determine whether the unknown molecule belongs to the saturation group. If the four indicators of the molecule to be tested are all within this range, it can be considered that the molecule belongs to the saturation group.

[0030] Table 1 shows the comparison of the index parameters of the four components. It can be seen from Table 1 that the overall dipole moment and MPI of the saturated component are smaller than those of the other three components, the polar surface area is 0, and the HOMO-LUMO energy gap is higher than that of the other three components, which is consistent with the conclusions obtained from the experiment. This shows that the indexes obtained by quantum chemical calculation are more accurate and can be used to determine whether the unknown asphalt molecules can be attributed to the saturated component.

[0031] Table 1 Comparison of the four parameters of the saturated molecular overall dipole moment, MPI, polar surface area ratio and HOMO-LUMO energy gap with the other three components

[0032]

[0033] Except for the saturated fraction, the polar surface area percentages of the other three components are not 0, so the specific values ​​are omitted in the table.

[0034] In this example, the saturated molecule in the literature and database is collected more comprehensively. By calculating the four indicators of the molecule to be divided and comparing them with the ranges obtained by the nine saturated molecule, it can be more reliably judged whether the molecule to be tested is a saturated molecule. The calculation has the advantages of accuracy, high efficiency and low cost, and can be effectively applied to the judgment of asphalt saturated grouping molecules.

Claims

1. A method for determining the molecular weight of asphalt saturation group based on quantum chemical calculation, characterized in that: The steps include: Step 1: Collect 9 saturation molecular weights from literature and databases; Step 2: Use KingDraw software to identify the molecular structure formula in the literature, and after checking that it is correct, use Chem3D software to convert it into a three-dimensional model; Step 3: Using Gaussian software, the structure was optimized using the B3LYP method and 6-31G (d, p) basis set under density functional theory (DFT) to obtain the lowest energy stable geometric configuration; Step 4: Convert the chk file output by Gaussian into an fch file, and import the fch file into the post-processing multiwfn software; Step 5: Use Multiwfn software to calculate the overall dipole moment, MPI, polar surface area ratio and HOMO-LUMO energy gap of the nine saturated molecules, and use post-processing software VMD to visualize the HOMO-LUMO energy gap; Step 6: Calculate the four index parameters of the other three components of asphalt through the above steps. By examining the index parameters of the saturated fraction, a quantitative index system of the four index distribution of the saturated fraction is obtained, which is used to determine whether the asphalt molecules that have not been tested are saturated components.

2. A method for distinguishing four components of asphalt based on quantum chemical calculation according to claim 1, characterized in that: The saturated molecules collected in step 1 come from asphalt molecules classified based on SARA components in the literature, as well as molecules considered as saturated molecules in various crude oil asphalt raw material component determination tests.

3. A method for distinguishing four components of asphalt based on quantum chemical calculation according to claim 1, characterized in that: The dipole moment calculation in step 2 takes the optimized molecular structure, creates a Gaussian input file in the neutral state, calculates the single-point energy of the molecule using the B3LYP method and the 6-311G (2d, p) basis set, converts the obtained chk file into an fch file, and uses the Hirshfeld weight function as the input file of Multiwfn for calculation; MPI is the mean of the absolute values ​​of the molecular surface electrostatic potential; the polar surface area ratio is the ratio of the surface area with an absolute value of electrostatic potential less than 10 kcal / mol to the total surface area of ​​the molecule; the HOMO-LUMO energy gap is the energy level difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital.

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