Microscopic comparison and experimental verification method for wettability of similar surfactants to coal dust

Abstract

A microscopic comparison and experimental verification method for the wettability of similar surfactants to coal dust, comprising the following steps: S1, collecting an on-site coal sample from a mining area, crushing into powder, and then performing infrared spectrographic analysis and nuclear magnetic resonance spectrographic analysis to obtain information of functional groups and carbon structures of coal molecules; S2, constructing a surfactant-coal electrostatic interaction model, and analyzing an orbital energy difference and an electrostatic potential difference between surfactant molecules and the coal molecules; S3, analyzing the strength and energy of hydrogen bonds between surfactants and water molecules, wherein the strength is determined by bond angles and bond lengths of the hydrogen bonds; S4, constructing a surfactant-coal-water molecule periodic solution model, and performing geometric optimization on the surfactant-coal-water molecule periodic solution model, so that the surfactant-coal-water molecule periodic solution model reaches a stable configuration; S5, performing NPT simulation and NVT simulation on the periodic solution model; and S6, performing experimental verification, so that the problems of long experimental time and high cost and the like of current selection of surfactants can be effectively solved, and a simple and effective thought is provided for the selection of surfactants.

Description

Microscopic comparison and experimental verification of the wettability of similar surfactants on coal dust Technical Field

[0001] The invention belongs to the technical field of coal dust prevention and control, and particularly relates to a microscopic comparison and experimental verification method of the wettability of similar surfactants on coal dust. Background Art

[0002] Due to the hydrophobicity and suspension of coal dust, water mist spraying is not very effective in suppressing dust. The existence of dust suppressants can compensate for this deficiency. However, the selection of dust suppression raw materials is often done through experimentation. When more than 20 or 30 raw materials are involved, the experimentation becomes time-consuming and laborious.

[0003] With the continuous innovation of science and technology, molecular dynamics simulation has become a powerful tool for understanding the structure, properties, and reaction mechanism analysis of substances in various fields such as physics, chemistry, materials science, and biology. It can not only analyze the structure and related properties of adsorbed molecules, but also simulate the dynamic behavior of molecules during the adsorption process. It is an important method for exploring the microscopic level in addition to theoretical and experimental research. Therefore, combining molecular simulation technology, a method for microscopically distinguishing the wettability of similar surfactants on coal dust has been proposed, which is of great significance for the selection of surfactants for spray dust suppression in coal mines.

[0004] Summary of the Invention

[0005] In view of the fact that the selection of surfactants for mining is currently laborious and time-consuming, this paper aims to propose a microscopic comparison and experimental verification method for the wettability of similar surfactants on coal dust, which aims to significantly improve the efficiency of selecting surfactants with excellent wetting effect on coal dust and provide a scientific idea for more effectively reducing coal dust pollution.

[0006] To achieve the above objectives, the present invention proposes a microscopic comparison and experimental verification method of the wettability of similar surfactants on coal dust, comprising the following steps:

[0007] S1: Collect coal samples from the mining area, crush them into powder, and then perform infrared spectroscopy and nuclear magnetic resonance spectroscopy analysis to obtain information on the functional groups and carbon structure of the coal molecules. Then, using ACD / ChemSketchR and Materials Studio molecular design software, construct three-dimensional macromolecular models of the coal sample and at least three similar surfactants, respectively. Similar surfactants refer to those that are both anionic or nonionic surfactants.

[0008] S2: Construct a surfactant-coal electrostatic interaction model, propose the principle of attraction between opposite potentials and competitive adsorption, and analyze the orbital energy difference and electrostatic potential difference between surfactant molecules and coal molecules;

[0009] The surfactant-coal molecule electrostatic interaction model involves density functional theory, using the B3LYP-D3 functional and the 6-311+G** basis set. Multiwfn+VMD is used to visualize the electrostatic potential and orbital energy. The positive and negative electrostatic potential extremes of the surfactant are analyzed. If the surfactant potential is less negative or positive than that of water molecules, the interaction strength between the surfactant and water molecules is greater than the interaction strength between water molecules. Water molecules will adsorb to the surfactant molecule, thereby improving wettability. Therefore, the greater the orbital energy difference and the electrostatic potential extremes, the stronger the surfactant wetting effect, and the better the surfactant's wetting effect on coal dust.

[0010] S3: Analyze the strength and energy of hydrogen bonds between surfactants and water molecules, where the strength is determined by the bond angle and bond length of the hydrogen bonds formed; calculate the average values ​​of the bond length, bond angle, and hydrogen bond energy of the hydrogen bonds formed between surfactants and water molecules. The greater the strength of the hydrogen bonds formed between surfactants and water molecules, the smaller the energy, the stronger the adsorption effect of water molecules, and the better the wetting effect on coal dust;

[0011] S4: Construct a surfactant-coal-water molecular periodic solution model, assign it a charge through the COMPASSII force field, and then optimize its geometry to achieve a stable configuration;

[0012] S5: Perform NPT simulation on the geometrically optimized periodic solution model until the densities of coal molecules, surfactants, and water molecules are consistent with the experimental conditions. Then, perform NVT simulation to observe the movement of water molecules in different surfactant systems and calculate the number of hydrogen bonds formed between various surfactants and water molecules in equilibrium, as well as the interaction energy between surfactants and water molecules.

[0013] The interaction energy is calculated as follows:

[0014] Eint (surfactant-water) is the interaction energy between surfactant and water in the system; E int(coal-surfactant) is the interaction energy between coal and surfactant in the system; E total is the total energy of the system; E coal 、E water and Esurfactant are the energies of coal, water and surfactant respectively; E coal+water Ecoal+surfactant, Esurfactant+water represent the total energy of the two components in the system, respectively. The total energy of these two components is obtained by removing the third component from the system and performing energy calculation, i.e., E coal+water =E total-E surfactant , E coal+surfactant =E total -E water , E surfactant+water =E total -E coal ;

[0015] The number of hydrogen bonds and interaction energy between various surfactants and water molecules are statistically analyzed. The more hydrogen bonds formed between surfactants and water molecules, the stronger the interaction between them and water molecules.

[0016] S6: Select multiple concentration gradients within the concentration range of 0.01-0.14% to prepare various surfactant solutions, and define the surfactant concentration when the surface tension reaches the minimum value as the optimal usage concentration of the surfactant; pour the weighed coal dust into a beaker containing the surfactant solution at the optimal usage concentration according to the ratio of 0.5g coal powder: 250mL of surfactant solution at the optimal usage concentration, and record the time required from the coal dust contacting the liquid surface until it completely sinks into the liquid surface. The shorter the time, the stronger the wettability to the coal; in this way, it is verified that the wetting performance under the experimental conditions is consistent with the results obtained in step S2 through the microscopic judgment method from two angles: the orbital energy difference and electrostatic potential difference under quantum mechanics, and the number of hydrogen bonds and interaction energy under molecular dynamics in steps S3-S5.

[0017] As a preferred embodiment of the above scheme, in step S2, in the process of constructing the surfactant-coal electrostatic interaction model, one coal molecule and 50 water molecules; one surfactant molecule and 50 water molecules; one surfactant molecule and one coal molecule are selected.

[0018] More preferably, in step S4, the surfactant-coal-water molecule periodic solution model constructed includes 10 coal molecules, 25 surfactant molecules and 2000 water molecules.

[0019] It is further preferred that, in step S4, the surfactant-coal-water molecule periodic solution model must first undergo geometry optimization-annealing treatment to make the system energy reach the lowest point and be in a stable state; during the geometry optimization process, different molecular charges are assigned by setting the COMPASSII force field, and the net charge of the system is 0.

[0020] More preferably, in step S5, after the periodic solution model is constructed, a force field and a charge are first assigned to it, and a 500ps NPT simulation is performed to reach a density equilibrium state, ensuring that the density of the coal molecules, surfactants, and water molecules has an error of less than 10% from the actual coal sample density, and the density of the water molecules is 1000kg / m 3After the density of the periodic solution model is balanced, NVT simulation is performed to simulate the motion trajectories of different molecules in a confined space. The simulation time is 1000 ps and the step size is 1 fs until the system energy is balanced.

[0021] More preferably, in step S1, the coal sample collected on site is crushed into powder by a ball mill.

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

[0023] (1) Judging the quality of surfactants in improving the wettability of solutions to coal dust from two independent microscopic perspectives, namely, the orbital energy difference and electrostatic potential difference in quantum mechanics and the number of hydrogen bonds and interaction energy in molecular dynamics, is more reliable than judging from a single perspective.

[0024] (2) By collecting coal samples on site and constructing an accurate coal molecular model, the determination of the wettability of coal by surfactants is most suitable for this type of coal, with the characteristics of strong pertinence and high accuracy;

[0025] (3) This method makes judgments from two microscopic perspectives, quantum mechanics and molecular dynamics, and then combines them with laboratory verification. The conclusions of the three are completely consistent. In the subsequent practical application process, only one of quantum mechanics and molecular dynamics is needed to select surfactants at the microscopic level. This can effectively solve the current problems of long experimental time and high cost for selecting surfactants, and provide a simple and effective judgment method for the selection of surfactants, which has the advantages of short time, no cost and pre-selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a schematic flow diagram of the present invention;

[0027] Figure 2 is a three-dimensional macromolecular model diagram of coal sample, SDBS, RPT and SDS;

[0028] Figure 3 shows the surface tension and sedimentation time diagram of the macroscopic wettability of coal samples by SDBS, RPT and SDS. DETAILED DESCRIPTION

[0029] To describe the present invention, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0030] A microscopic comparison and experimental verification method for the wettability of similar surfactants on coal dust includes the following steps:

[0031] S1: Collect a coal sample from the mining area and crush it into a powder, preferably using a ball mill. Then, perform infrared spectroscopy and nuclear magnetic resonance spectroscopy to obtain information about the functional groups and carbon structure of the coal molecules. Using ACD / ChemSketch and Materials Studio molecular design software, construct 3D macromolecular models of the coal sample and at least three similar surfactants, which are either anionic or nonionic surfactants. Three anionic surfactants are used for demonstration purposes: SDBS, RPT, and SDS, as shown in Figure 2.

[0032] S2: Construct a surfactant-coal electrostatic interaction model, propose the principle of attraction between opposite potentials and competitive adsorption, and analyze the orbital energy difference and electrostatic potential difference between surfactant molecules and coal molecules.

[0033] The surfactant-coal molecule electrostatic interaction model involves density functional theory. The B3LYP-D3 functional is selected, and the basis set is 6-311+G**. The electrostatic potential and orbital energy are visualized through Multiwfn+VMD. The positive and negative electrostatic potential extremes of the surfactant are analyzed. If the negative or positive value of the surfactant potential is smaller than that of water molecules, the interaction strength between the surfactant and water molecules is greater than the interaction strength between water molecules. The water molecules will be adsorbed on the surfactant molecule attachment, thereby improving the wettability. Therefore, the greater the orbital energy difference and the electrostatic potential extreme value, the stronger the surfactant wetting effect, and the better the wetting effect of the surfactant on coal dust.

[0034] Preferably, in step S2, in the process of constructing the surfactant-coal electrostatic interaction model, one coal molecule and 50 water molecules; one surfactant molecule and 50 water molecules; one surfactant molecule and one coal molecule are selected.

[0035] The order of electrostatic potential extreme value and orbital energy difference is RPT, SDBS and SDS. It is preliminarily judged that RPT surfactant has the best wetting effect on coal dust, while SDS has the worst. The results are shown in Table 1.

[0036] Table 1 Electrostatic potential energy and molecular orbital energy of surfactant-water-coal molecules

[0037] S3: Analyze the strength and energy of hydrogen bonds between surfactants and water molecules. The strength is determined by the bond angle and length of the hydrogen bonds. The average values ​​of the bond length, angle, and energy of hydrogen bonds between surfactants and water molecules are calculated. The stronger the hydrogen bond strength and the smaller the energy, the stronger the adsorption of water molecules and the better the wetting effect on coal dust. The results are shown in Table 2. The hydrogen bond strength between RPT and water molecules is the strongest and the energy is the smallest (negative), resulting in the strongest adsorption of water molecules and the best wetting effect on coal dust.

[0038] Table 2 Average data of hydrogen bonds formed between three surfactants and water molecules

[0039] S4: Construct a surfactant-coal-water molecular periodic solution model, give it a charge through the COMPASSII force field, and then optimize its geometry to achieve a stable configuration.

[0040] Preferably, in step S4, the surfactant-coal-water molecule periodic solution model constructed includes 10 coal molecules, 25 surfactant molecules and 2000 water molecules.

[0041] Ideally, in step S4, the surfactant-coal-water molecular periodic solution model must first undergo geometry optimization-annealing treatment to make the system energy reach the lowest point and be in a stable state; during the geometry optimization process, different molecular charges are assigned by setting the COMPASSII force field, and the net charge of the system is 0.

[0042] S5: Perform NPT simulation on the geometrically optimized periodic solution model until the densities of coal molecules, surfactants, and water molecules are consistent with the experimental conditions. Then, perform NVT simulation to observe the movement of water molecules in different surfactant systems and calculate the number of hydrogen bonds formed with water molecules in the equilibrium state of various surfactants and the interaction energy between surfactants and water molecules.

[0043] The interaction energy is calculated as follows:

[0044] Eint (surfactant-water) is the interaction energy between surfactant and water in the system; E int(coal-surfactant) is the interaction energy between coal and surfactant in the system; E total is the total energy of the system; E coal 、E water and Esurfactant are the energies of coal, water and surfactant respectively; E coal+waterEcoal+surfactant, Esurfactant+water represent the total energy of the two components in the system, respectively. The total energy of these two components is obtained by removing the third component from the system and performing energy calculation, i.e., E coal+water =E total -E surfactant (Energy of coal and water in the system = total energy of the system - energy of surfactant in the system),

[0045] E coal+surfactant =E total -E water (Energy of coal and surfactant in the system = total energy of the system - energy of water in the system),

[0046] E surfactant+water =E total -E coal (Energy of water and surfactant in the system = total energy of the system - energy of coal in the system);

[0047] The number of hydrogen bonds and interaction energy between various surfactants and water molecules were statistically analyzed. The more hydrogen bonds formed between the surfactant and water molecules, the greater the interaction energy between the surfactant and the water molecules, the better the adsorption effect on water molecules during the dynamic adsorption process, and the stronger the wettability.

[0048] Preferably, in step S5, after the periodic solution model is constructed, its force field and charge are first assigned to it. It is necessary to first undergo a 500ps NPT simulation to reach a density equilibrium state, ensuring that the density of coal molecules, surfactants, and water molecules has an error of less than 10% with the actual coal sample density, and the density of water molecules is 1000kg / m 3 After the density of the periodic solution model is balanced, NVT simulation is performed to simulate the motion trajectories of different molecules in a confined space. The simulation time is 1000 ps and the step size is 1 fs until the system energy is balanced.

[0049] The statistical table of the number of hydrogen bonds and interaction energy between the three surfactants and water molecules is shown in Table 3. RPT forms the largest number of hydrogen bonds with water molecules and has the largest interaction energy with water molecules. It has the best adsorption effect on water molecules during the dynamic adsorption process and exhibits the strongest wettability.

[0050] Table 3 The number of hydrogen bonds and interaction energy between three surfactants and water molecules

[0051] S6: Select multiple concentration gradients within the concentration range of 0.01-0.14% to prepare various surfactant solutions, and define the surfactant concentration when the surface tension reaches the minimum value as the optimal usage concentration of the surfactant; pour the weighed coal dust into a beaker containing the surfactant solution at the optimal usage concentration according to the ratio of 0.5g coal powder: 250mL of surfactant solution at the optimal usage concentration, and record the time required from the coal dust contacting the liquid surface until it completely sinks into the liquid surface. The shorter the time, the stronger the wettability to the coal; in this way, it is verified that the wetting performance under the experimental conditions is consistent with the results obtained in step S2 through the microscopic judgment method from two angles: the orbital energy difference and electrostatic potential difference under quantum mechanics, and the number of hydrogen bonds and interaction energy under molecular dynamics in steps S3-S5.

[0052] The experimental results of the three surfactants are shown in Figure 3. RPT has the best wetting performance under the experimental conditions.

Claims

1. A microscopic comparison and experimental verification method for the wettability of coal dust by homologous surfactants, characterized in that, Including the following steps: S1: Collect on-site coal samples from the mining area, crush them into powder, and conduct infrared spectroscopy and nuclear magnetic resonance spectroscopy analysis to obtain information on the functional groups and carbon structures of coal molecules. Then, combined with ACD / ChemSketch and Materials Studio molecular design software, construct three-dimensional macromolecular models of the coal sample and at least three types of surfactants of the same kind. Surfactants of the same kind refer to either anionic surfactants or non-ionic surfactants. S2: Construct a surfactant-coal electrostatic interaction model, propose the criterion of combining attractive interaction of opposite electric potentials and competitive adsorption, and analyze the orbital energy difference and electrostatic potential difference between surfactant molecules and coal molecules. The density functional theory is involved in the surfactant-coal molecular electrostatic interaction model. Select the B3LYP-D3 functional and the 6-311+G** basis set. Visualize the electrostatic potential and orbital energy through Multiwfn+VMD. Analyze the extreme values of the positive and negative electrostatic potentials of the surfactant. If the negative or positive value of the surfactant potential is less than that of water molecules, the interaction strength between the surfactant and water molecules is greater than the interaction strength between water molecules, and water molecules will adsorb near the surfactant molecules, thus improving the wettability. Therefore, the greater the orbital energy difference and the extreme value of the electrostatic potential, the stronger the wetting effect of the surfactant, and the better the wetting effect of the surfactant on coal dust. S4: Analyze the strength and energy of the hydrogen bonds between the surfactant and water molecules. The determination of the strength is the bond angle and bond length of the hydrogen bonds formed. Statistically analyze the average values of the bond length, bond angle, and hydrogen bond energy of the hydrogen bonds formed between the surfactant and water molecules. The greater the strength of the hydrogen bonds formed between the surfactant and water molecules and the smaller the energy, the stronger the adsorption effect of water molecules and the better the wetting effect on coal dust. S5: Construct a surfactant-coal-water periodic solution model, endow it with charges through the COMPASSII force field, and perform geometric optimization to make it reach a stable configuration. S6: Conduct NPT simulation on the geometrically optimized periodic solution model until the densities of coal molecules, surfactants, and water molecules are consistent with the experimental conditions, and then conduct NVT simulation to observe the movement of water molecules in different surfactant systems Calculate the number of hydrogen bonds formed between the surfactant and water molecules and the interaction energy between the surfactant and water molecules at the equilibrium state of various surfactants. The calculation formula for the interaction energy is as follows: Eint(surfactant-water) is the interaction energy between surfactant and water in the system; E int(coal-surfactant) is the interaction energy between coal and surfactant in the system; E total is the total energy of the system; E coal 、E water and E surfactant are the energies of coal, water and surfactant respectively; E coal+water 、E coal+surfactant 、E surfactant+water represent the total energies of two components of coal and water, coal and surfactant, surfactant and water in the system respectively. The total energies of these two components are obtained by removing the third component from the system for energy calculation, that is, E coal+water = E total - E surfactant , E coal+surfactant = E total - E water , E surfactant+water = E total - E coal ; Statistically analyze the number of hydrogen bonds and the interaction energy between various surfactants and water molecules. The more hydrogen bonds formed between the surfactant and water molecules and the greater the interaction energy between the surfactant and water molecules, the better the adsorption effect on water molecules and the stronger the wettability shown during the dynamic adsorption process. S6: Select multiple concentration gradients within the range of 0.01 - 0.14% to prepare various surfactant solutions, and define the surfactant concentration when the surface tension reaches the minimum value as the optimal usage concentration of the surfactant; according to the ratio of 0.5 g of pulverized coal to 250 mL of the surfactant solution with the optimal usage concentration, pour the weighed coal dust into a beaker containing the surfactant solution with the optimal usage concentration, and record the time required from when the coal dust contacts the liquid surface until it completely sinks into the liquid surface. The shorter the time, the stronger the wettability of the coal; verify that under the experimental conditions, the wetting performance is consistent with the results obtained from the microscopic judgment methods from two perspectives of the orbital energy difference and electrostatic potential difference under quantum mechanics and the number of hydrogen bonds and interaction energy under molecular dynamics in steps S3 - S5, which show the superiority and inferiority of the surfactant's wettability to coal dust.

2. The microscopic comparison and experimental verification method of the wettability of coal dust by surfactants of the same kind according to claim 1, characterized in that: In step S2, during the process of constructing the surfactant - coal electrostatic interaction model, select 1 coal molecule and 50 water molecules; 1 surfactant molecule and 50 water molecules; 1 surfactant molecule and 1 coal molecule.

3. The microscopic comparison and experimental verification method for the wettability of coal dust by the same type of surfactant according to claim 1, characterized in that: In step S4, the constructed surfactant - coal - water molecule periodic solution model contains 10 coal molecules, 25 surfactant molecules, and 2000 water molecules.

4. The microscopic comparison and experimental verification method for the wettability of coal dust by surfactants of the same type according to claim 1, characterized in that: In step S4, the surfactant - coal - water molecule periodic solution model needs to undergo geometric optimization - annealing treatment first to make the system energy reach the lowest point and be in a stable state; During the geometric optimization process, different molecular charges are assigned by setting the COMPASSII force field, and the net charge of the system is 0.

5. The microscopic comparison and experimental verification method for the wettability of coal dust by surfactants of the same kind according to claim 1, characterized in that: In step S5, after the periodic solution model is constructed, a force field and charges are first assigned to it. It is necessary to first perform an NPT simulation for 500 ps to reach the density equilibrium state, ensuring that the density error of coal molecules, surfactants, and water molecules from the actual coal sample density is less than 10%. The density of water molecules is 1000 kg / m 3 ; after the density of the periodic solution model reaches equilibrium, an NVT simulation is then carried out to simulate the movement trajectories of different molecules within a restricted space. At this time, the simulation time is 1000 ps and the time step is 1 fs until the system energy reaches equilibrium.

6. The microscopic comparison and experimental verification method for the wettability of coal dust by surfactants of the same kind according to claim 1, characterized in that: In step S1, the coal sample collected on site is pulverized into powder by a ball mill.

Images