Method for constructing coal char macromolecular network model based on hrtem and xps

Abstract

The present application provides a kind of coal tar macromolecular network model construction method based on HRTEM and XPS, belongs to chemical molecular reaction kinetics technical field, including S1: processing coal tar macromolecular sample HRTEM image data;S2: determine the element composition and functional group composition of coal tar macromolecular sample;S3: set the basic unit structure of coal tar macromolecular network model, and calculate the proportion of different unit structure;S4: construct the aromatic layer sheet of carbon skeleton unit in coal tar macromolecular network model;S5: set the bridge bond of carbon skeleton unit, finally obtain the complete carbon skeleton unit in coal tar macromolecular network model;S6: revise the edge of carbon skeleton unit, hydrogenation is added to carbon skeleton unit and the coal tar macromolecular network model is optimized.It can finely construct coal tar macromolecular network, restore the real composition of coal tar molecule to the greatest extent, ensure that subsequent calculation structure is more real, suitable for constructing macromolecular network model for coal tar obtained under different coal rank and different working conditions.

Description

Technical Field

[0001] This invention belongs to the field of chemical molecular reaction dynamics technology, specifically relating to a method for constructing a coal char macromolecular network model based on HRTEM and XPS. Background Technology

[0002] Molecular simulation uses computers to model molecular structures and behaviors to obtain physical properties or chemical reaction pathways. Reaction molecular dynamics simulation combines reaction force fields and molecular dynamics, and can handle reaction systems with tens of thousands of atoms. The ReaxFF reaction force field is a highly efficient molecular dynamics calculation method, faster than Gaussian calculations for systems with large atomic numbers. It is suitable for complex hydrocarbon combustion reactions and can analyze continuous chemical reactions under different temperatures and pressures. By constructing appropriate molecular models and selecting suitable reaction force fields, information such as product distribution and trajectories can be obtained.

[0003] For the construction of molecular models of coal char with large molecular weight and complex molecular structure, especially for coal char molecules with a high content of aliphatic structure, the current method of simply stacking graphite sheets and leaving pores is difficult to simulate the real process of coal char reaction. Summary of the Invention

[0004] To overcome the shortcomings of existing methods for constructing coal and char molecular models that are difficult to simulate the real process of coal and char reactions, this invention provides a method for constructing a coal and char macromolecular network model based on HRTEM and XPS, which can accurately construct the coal and char macromolecular network and restore the real composition of coal and char molecules to the greatest extent.

[0005] Glossary: ​​HRTEM: High-resolution transmission electron microscope; XPS: X-ray photoelectron spectroscopy.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for constructing a coal char macromolecular network model based on HRTEM and XPS, comprising the following steps:

[0007] S1: HRTEM image data of processed coal char macromolecular samples

[0008] A portion of the original HRTEM image was cropped using Digital Micrograph software and subjected to a two-dimensional FFT transformation to obtain a frequency domain image. This frequency domain image was then imported into Photoshop software, where a Qia image processing plugin was used for binarization and fringe rendering, and the lengths of the lattice fringes were calculated. Finally, to obtain a clearer image, the frequency domain image was colored according to the fringe lengths. The results are shown in Table 1 below.

[0009] Table 1. Assignment of lattice fringes of different lengths in HRTEM images.

[0010]

[0011] S2: Testing the elemental composition and functional group composition of coal char macromolecular samples.

[0012] S2.1: Conduct industrial and elemental analysis tests on coal char macromolecular samples to determine their main elemental composition.

[0013] S2.2: XPS analysis was performed on the macromolecular samples of coal char, and peak analysis was performed on the C1s spectrum. C=C, CH, CO (including C-OH, C*-OC and C*(O)C=O), C=O (including C=O and C(O)C*=O), and COOH (or COOR) correspond to the peak positions of 284.6 eV, 285.1 eV, 286.1~286.6 eV, 287.6~289.1 eV, and 289.1~289.3 eV on the spectrum, respectively.

[0014] S3: Define the basic unit structure of the coal char macromolecular network model and calculate the proportion of different unit structures.

[0015] S3.1: Based on the HRTEM image fitting results, the aromatic ring structures on the coal char macromolecular network are defined. The 1×1 structure is defined as benzene, naphthalene, anthracene, and phenanthrene, while the 2×2, 3×3, 4×4, and other n×n structures are defined as parallelograms with sides consisting of n benzene rings, according to the parallelogram structure hypothesis of Daniel Van Niekerk and Jonathan P Mathews.

[0016] S3.2: Based on the HRTEM image fitting results, determine the structure with the most six-membered rings and the structure with the fewest six-membered rings. Based on the ratio between the structure with the most six-membered rings and the structure with the fewest six-membered rings, simplify the ratio values ​​of each type of structure.

[0017] Step S3.2 is divided into the following three cases:

[0018] Case 1: The structure with the most six-membered rings and the structure with the fewest six-membered rings are the same type. In this case, when calculating the proportion, this structure is represented as 1 for easier modeling later.

[0019] Case 2: The structure with the most six-membered rings has a higher content than other structures. In this case, the structure with the fewest six-membered rings is assigned the value 1.

[0020] Case 3: The structure with the most six-membered rings is not necessarily the most or least abundant. When calculating the proportion, this structure is set to 1, and structures with a proportion value less than 0.5 are discarded.

[0021] S4: Constructing aromatic lamellae of carbon skeleton units in a coal char macromolecular network model

[0022] S4.1: Using Material Studio software, insert a graphite unit and import the graphite.msi graphite model. Use makep1 to eliminate symmetry to obtain a single-layer graphene structural unit;

[0023] S4.2: Based on the calculation results of the unit structure ratio in step S3.2, determine the size of the side length of the graphene structural unit. It should be based on the content of the structure with more six-membered rings and its side length, and added to a multiple of the side length of the structure with more content, which is the size of the side length of the graphene structural unit.

[0024] In step S4.2, the dimensions of graphene need to be analyzed based on the composition of different structural proportions. When the condition is case 1, the side length of the graphene structural unit is at least A1 + 2A2 + 3A3 + ... + nA n It consists of six six-membered rings, where A1, A2, A3 and A n The values ​​represent the proportions of 1×1, 2×2, 3×3, and n×n structures, respectively; when condition 2 is met, the side length of the graphene structural unit is determined by m·C. M +m'·C' m It consists of six six-membered rings, where m and m' are the number of six-membered rings on the side lengths of the two most abundant structures, respectively, and C M C' m The sum of the proportions of the two structures with the highest content; when the condition is case 3, the number of six-membered rings on the edge of graphene should be the sum of the products of the number of six-membered rings on the edge of each structure and the proportion value, i.e., ∑(iA i ), where i is the number of six-membered rings on the side length of the structure; A i This is the proportional value of the structure.

[0025] S4.3: Construct a supercell from graphene structural units with known side lengths.

[0026] S4.4: The supercell is divided to obtain aromatic sheets. The number of supercells for each graphene structural unit is the proportion of that structure. First, the structure with the most six-membered rings is divided, and the carbon-carbon bonds connected to this structure are deleted. Then, the structures are divided in descending order of proportion, and the bonds connecting the structures are deleted. For structures with a proportion greater than 1, incomplete six-membered rings at the edges are not included. For structures with a proportion less than 1, the edge regions are divided, and incomplete six-membered rings are considered complete and included.

[0027] S5: Setting bridge bonds for carbon skeleton units

[0028] S5.1: Calculate the relative content of each structure based on the XPS peak fitting results. Here, C=C is assumed to be an aromatic ring structure, and CH, CO, C=O, and COOH (or COOR) are assumed to be aliphatic structures, i.e., carbon-hydrogen bonds, carbon-oxygen bonds, carbonyl groups, and carboxyl groups. The number of carbon atoms in the carbon skeleton unit is obtained by summing the proportions of aromatic ring structures and the content of C=C structures, thus determining the number of carbon atoms in each type of aliphatic structure. The ratio of the number of carbon atoms in the aliphatic structure to the proportion of the aromatic ring structure is the average number of carbon atoms on the bridging bond, i.e., this number of carbon atoms connects the aromatic layers in step S4.

[0029] In step S5.1, using the results of the XPS C 1s spectrum, the number of carbon atoms in the carbon skeleton unit is obtained by the ratio of the sum of the proportion values ​​of aromatic ring structures to the relative content of C=C structures. This number is then multiplied by the relative content of various aliphatic structures to obtain the number of carbon atoms in each aliphatic structure.

[0030] S5.2: Adjust the number of carbon atoms in each bridging bond according to the distance between each aromatic layer to ensure spatial rationality. Modify it again according to the number of oxygen-containing ring functional groups. Finally, a complete carbon skeleton unit in the coal char macromolecular network model is obtained.

[0031] S6: Optimization Model

[0032] S6.1: Adjust the number of supercells according to the calculation requirements. After determining the final number, remove unsaturated carbon atoms at the edge positions of the carbon framework units. Finally, add hydrogen to the carbon framework units and use the Forcite module to optimize the coal char macromolecular network model.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. Coal char molecules obtained under different coal ranks and operating conditions have different structures, and the aromatic and aliphatic structures have different effects on the reactivity of coal char. The modeling method provided by this invention can accurately construct the macromolecular network of coal char, restore the true composition of coal char molecules to the greatest extent, and ensure that the subsequent calculation structure is more realistic. It is applicable to constructing macromolecular network models of coal char obtained under different coal ranks and operating conditions, and provides a good foundation for exploring the reaction mechanism of coal char.

[0035] 2. The modeling method provided by this invention can explore the influence of various reaction factors on coal char reactions. Constructing a single-layer coal char molecular network structure can explore the role of functional groups or defect sites in the reaction; constructing a multi-layer coal char molecular network can explore the influence of diffusion in pore structure on the reaction. Attached Figure Description

[0036] Figure 1This is a flowchart of the method for constructing a coal char macromolecular network model based on HRTEM and XPS according to the present invention;

[0037] Figure 2 The electron microscopy processing diagrams of this invention are as follows: (a) original image; (b) frequency domain image; (c) binarization; (d) skeletonization; (e) image colorization;

[0038] Figure 3 This is the XPS C 1s spectrum of the present invention;

[0039] Figure 4 The aromatic layer in the carbon skeleton unit of the present invention;

[0040] Figure 5 The carbon framework in the supercell of this invention;

[0041] Figure 6 This is the modified edge structure coal char macromolecular network model of the present invention;

[0042] Figure 7 This is the optimized coal char macromolecular network model of the present invention. Detailed Implementation

[0043] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0045] Example 1

[0046] This embodiment applies a coal char macromolecular network model constructed based on HRTEM and XPS to the CO2 gasification reaction process of rapid pyrolysis semi-coke of Naomohu (NMH) coal, in order to explore the reactivity of different types of carbon atoms and improve accuracy.

[0047] The method for constructing a coal char macromolecular network model based on HRTEM and XPS specifically includes the following steps:

[0048] Step 1: Process the HRTEM image data of coal char molecules.

[0049] A portion of the original image was cropped using Digital Micrograph software and subjected to a two-dimensional FFT transformation to obtain a frequency domain image. This image was then imported into Photoshop software, where a Qia image processing plugin was used for binarization and fringe rendering, and the lengths of the lattice fringes were calculated. Finally, to obtain a clearer image, it was colored according to the fringe lengths. The results are as follows: Figure 2 As shown, the relative contents of the 1×1, 2×2, 3×3, and 4×4 structures were 61%, 21%, 14%, and 4%, respectively.

[0050] Step 2: Test the elemental composition and functional group composition of the coal char molecular sample.

[0051] 2.1 Industrial analysis and elemental analysis were performed on the samples to determine that the main elements of coal char are carbon, hydrogen, and oxygen, and these elements account for 98.8% of the total elements (C, H, O, N).

[0052] 2.2. X-ray photoelectron spectroscopy (XPS) was performed on the sample, and the C1s spectrum was analyzed by peak separation. The results are as follows: Figure 3 As shown, the relative contents of the CH, CO, C=O, and COOH (COOR) structures are 83%, 11%, 5%, 0%, and 1%, respectively.

[0053] Step 3: Set the basic unit structure and determine the proportions of different unit structures.

[0054] According to the HRTEM fitting results, the 1×1 and 2×2 structures are predominant in the coal coke. Since the 4×4 structure content is less than 5%, it is ignored, and the 3×3 structure is considered the least abundant. For this rapid pyrolysis semi-coke, the ratio of 1×1, 2×2, and 3×3 structures is 3:2:1.

[0055] Step 4: Construct aromatic lamellae of carbon skeleton units in the coal char molecular network model.

[0056] 4.1 Using Material Studio software, insert a graphite unit and import graphite.msi. Use `make p1` to eliminate symmetry and obtain a single-layer graphene structural unit;

[0057] 4.2. Based on the calculation results of the basic unit ratio, determine the size of the graphene. The aromatic layer structure ratio of this fast pyrolysis semi-coke satisfies condition 1. Therefore, a graphene structure with a side length of 10 six-membered rings should be constructed.

[0058] 4.3 Construct a supercell from a graphene structure with 10 six-membered rings on each side.

[0059] 4.4. Divide the supercell into segments, with the number of segments for each structure being a proportional value for that structure. First, divide into 3×3 structures, then divide into 1×1 and 2×2 structures. For example... Figure 4 As shown.

[0060] Step 5: Set the bridging bonds for the carbon skeleton units.

[0061] 5.1 Based on the XPS peak fitting structure, calculate the relative content of each structure. The ratio of C=C, CH, CO, and COOH is 83:11:5:1. The content of oxygen-containing functional groups (CO and COOH (COOR)) is too low, and since this model is designed to explore the oxidation pathway of carbon atoms, these oxygen-containing functional groups can be classified into the CH structure, meaning the ratio of aromatic to aliphatic structures is 83:17. Calculations show that each bridging bond contains an average of 3 carbon atoms.

[0062] 5.2. Adjust the number of carbon atoms in each bridging bond according to the distance between each aromatic layer to ensure spatial rationality. The adjustment result is as follows: Figure 5 As shown.

[0063] Step Six: Optimize the Model

[0064] 6.1. The number of unit cells can be adjusted according to calculation needs. After determining the final size, unsaturated carbon atoms at the edge positions are removed. For example... Figure 6 As shown. Finally, hydrogen was added to the carbon skeleton, and the model was optimized using the Forcite module to further refine the model. The results are as follows. Figure 7 As shown.

[0065] The final model can be placed into a CO2 system for simulation calculations to obtain the product distribution and then analyze the activity of various carbon atoms.

[0066] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for constructing a coal char macromolecular network model based on HRTEM and XPS, characterized in that, include: S1: HRTEM image data of processed coal char macromolecular samples; S2: Perform industrial and elemental analysis tests on coal char macromolecular samples to determine their elemental composition; perform XPS tests on coal char macromolecular samples to determine their functional group composition. S3: Based on the HRTEM image fitting results, set the basic unit structure of the coal char macromolecular network model and calculate the proportion of different unit structures; S4: Construct aromatic lamellae of carbon skeleton units in the coal char macromolecular network model; S5: Based on the distance between each aromatic layer, bridge bonds are set for the carbon skeleton unit to finally obtain the complete carbon skeleton unit in the coal char macromolecular network model. S6: Correct the edges of carbon skeleton units, add hydrogen to carbon skeleton units, and optimize the coal char macromolecular network model; The method for setting the basic unit structure of the coal char macromolecular network model in step S3 is as follows: define the aromatic ring structure on the coal char macromolecular network, define the 1×1 structure as benzene, naphthalene, anthracene, phenanthrene, and define the 2×2, 3×3, 4×4...n×n structure as a parallelogram whose side length is composed of n benzene rings. The calculation method for calculating the proportion of different unit structures in step S3 is as follows: determine the structure with the most six-membered rings and the structure with the fewest six-membered rings, and simplify the proportion values ​​of each type of structure based on the proportional relationship between the structure with the most six-membered rings and the structure with the fewest six-membered rings.

2. The method for constructing a coal char macromolecular network model based on HRTEM and XPS according to claim 1, characterized in that, When calculating proportions, there are three cases: Case 1: When the structure with the most six-membered rings and the structure with the fewest six-membered rings are the same type, classify the structure as 1; Case 2: When the content of the structure with the most six-membered rings is greater than that of other structures, the structure with the fewest six-membered rings is assigned as 1; Case 3: When the structure with the most six-membered rings is not the most or the least abundant, set the content of that structure to 1 and discard structures with a proportion value less than 0.

5.

3. The method for constructing a coal char macromolecular network model based on HRTEM and XPS according to claim 2, characterized in that, Step S4 includes: S4.1: Using Material Studio software, insert a graphite unit, import the graphite.msi graphite model, and use makep1 to eliminate symmetry to obtain a single-layer graphene structure unit; S4.2: Determine the side length of the graphene structural unit based on the calculation results of the proportions of different unit structures; S4.3: Construct a supercell from graphene structural units with determined side lengths; S4.4: The supercell is divided to obtain aromatic sheets, and the number of supercells for each graphene structural unit is the proportion of that structure.

4. The method for constructing a coal char macromolecular network model based on HRTEM and XPS according to claim 3, characterized in that, The method for determining the size of the graphene structural unit in step S4.2 is as follows: based on the content of the structure with the most six-membered rings and its side length, add it to the side length of the structure with the most content, which is the size of the side length of the graphene structural unit.

5. The method for constructing a coal char macromolecular network model based on HRTEM and XPS according to claim 4, characterized in that, When condition 1 is met, the side length of the graphene structural unit is at least... It consists of six six-membered rings, among which , , and The values ​​represent the proportions of 1×1, 2×2, 3×3, and n×n structures, respectively; when condition 2 is met, the side length of the graphene structural unit is... It consists of six six-membered rings, among which , These represent the number of six-membered rings on the side lengths of the two structures with the highest content, respectively. , It is the sum of the proportions of the two structures with the highest content; when the condition is case 3, the side length of the graphene structural unit is changed from... It consists of six six-membered rings, that is, the sum of the products of the number of six-membered rings on each structural side length and the proportional value, where, The number of six-membered rings along the side length of the structure; This is the proportional value of the structure.

6. The method for constructing a coal char macromolecular network model based on HRTEM and XPS according to claim 3, characterized in that, The method for dividing the supercell in step S4.4 is as follows: First, divide the structure with the most six-membered rings and delete the carbon-carbon bonds connected to the structure; then divide it in order of decreasing ratio value and delete the bonds connected between the structures; for structures with a ratio value greater than 1, incomplete six-membered rings at the edge are not divided into the structure; while for structures with a ratio value less than 1, the edge region is divided and incomplete six-membered rings are considered complete and included in the structure.

7. The method for constructing a coal char macromolecular network model based on HRTEM and XPS according to claim 3, characterized in that, Step S5 includes: S5.1: Based on the XPS peak fitting results, calculate the relative content of each structure. Here, C=C is assumed to be an aromatic ring structure, and CH, CO, C=O, and COOH / COOR are assumed to be aliphatic structures, namely carbon-hydrogen bonds, carbon-oxygen bonds, carbon groups, and carboxyl groups. By summing the proportions of aromatic ring structures and the content of C=C structures, the number of carbon atoms in the carbon skeleton unit is obtained, and then the number of carbon atoms in each type of aliphatic structure is obtained. The ratio of the number of carbon atoms in the aliphatic structure to the proportion of the aromatic ring structure is the average number of carbon atoms on the bridging bond, that is, this number of carbon atoms connects each aromatic layer in step S4. S5.2: Adjust the number of carbon atoms in each bridging bond according to the distance between each aromatic layer to ensure spatial rationality. Modify again according to the number of oxygen-containing ring functional groups to finally obtain a complete carbon skeleton unit.

8. The method for constructing a coal char macromolecular network model based on HRTEM and XPS according to claim 7, characterized in that, In step S5.1, the specific method for obtaining the number of carbon atoms in various aliphatic structures is as follows: using the results of XPS C 1s spectra, the number of carbon atoms in the carbon skeleton unit is obtained by the ratio of the sum of the proportion values ​​of aromatic ring structures to the relative content of C=C structures, and then multiplied by the relative content of various aliphatic structures to obtain the number of carbon atoms in various aliphatic structures.

9. The method for constructing a coal char macromolecular network model based on HRTEM and XPS according to claim 7, characterized in that, Step S6 specifically involves: adjusting the number of supercells according to the calculation requirements, determining the final number, removing unsaturated carbon atoms from the edge positions of the carbon framework units, adding hydrogen to the carbon framework units, and using the Forcite module to optimize the coal char macromolecular network model.

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