Gas separation membrane model construction method, performance test simulation method and electronic equipment

Abstract

The invention relates to a method for constructing a gas separation membrane model, a performance test simulation method and electronic equipment. The method for constructing the gas separation membrane model comprises the following steps: constructing a polyethyleneimine (PEI) monomer model and carrying out structure optimization; extending the PEI single-chain model into a PEI single-chain model, and performing energy minimization; performing molecular dynamics simulation under an NVT ensemble and an NPT ensemble on the PEI single-chain model; constructing a simulation box and randomly inserting a plurality of PEI single-chain models to obtain an initial system, carrying out molecular dynamics simulation on the initial system under an NVT ensemble, then carrying out molecular dynamics simulation under an NPT ensemble for multiple rounds on the initial system, and carrying out fusion annealing simulation on the simulation and the simulation to obtain a PEI gas separation membrane model; and carrying out statistics on the potential energy and density change trends along with time at the end stage of the initial system molecular dynamics simulation, and when the potential energy and density change trends along with time converge, confirming that the PEI gas separation membrane model reaches balance.

Description

Technical Field

[0001] The present application relates to the technical field of gas separation membranes, and in particular to a method for constructing a gas separation membrane model, a performance test simulation method, and an electronic device. Background Art

[0002] In recent years, the concentration of carbon dioxide (CO2) in the atmosphere has increased from 280 ppm before industrialization to about 400 ppm, and is expected to exceed 750 ppm by the end of the 21st century. This trend poses a major threat to the global climate system. In order to address the problem of CO2 emissions, carbon dioxide capture and storage (CCS) technology is recognized as one of the most direct and efficient emission reduction strategies. Existing CO2 capture technologies mainly include chemical solvent absorption, physical solvent absorption and membrane separation. Among them, membrane separation technology has become a research hotspot in recent years due to its advantages such as high efficiency, energy saving and environmental friendliness.

[0003] Among the many membrane materials, solid membranes with amines and polyamine materials as adsorbents have gradually become a strong candidate to replace aqueous amine solutions. These materials have shown good CO2 capture performance due to their adjustable pore structure, excellent thermal stability and high chemical selectivity. However, at low CO2 concentrations, although these materials show high selectivity and adsorption capacity, their performance is still inferior to that of specifically designed CO2 capture materials, such as polyethyleneimine (PEI).

[0004] PEI is widely used in the field of CO2 capture due to its low volatility and high main chain amine density. By combining PEI with a variety of supporting materials, efficient CO2 adsorbents can be prepared. However, the adsorption process of PEI has the common problem that the outer layer reacts preferentially with CO2 and the internal pore utilization is insufficient. The mainstream view is that this is because the "ion gelation" phenomenon generated by the reaction of CO2 and PEI hinders the diffusion path of CO2, thereby limiting its further mass transfer efficiency. Therefore, a deep understanding of the interaction mechanism between CO2 molecular diffusion and PEI network structure is of key significance to the optimization of this technology. However, in related technologies, the time and cost of experimentally preparing PEI gas separation membranes and conducting tests are high, and it is difficult to understand the PEI gas separation membrane and the gas adsorption process from the internal atomic and molecular level. Summary of the invention

[0005] The purpose of this application is to provide a method for constructing a gas separation membrane model, a performance test simulation method and an electronic device, aiming to construct a PEI gas separation membrane model based on a molecular dynamics simulation method and simulate its adsorption process of gas molecules to help understand the PEI gas separation membrane model structure and its interaction mechanism with gas molecules.

[0006] In order to achieve the above-mentioned object, the first aspect of the present application provides a method for constructing a gas separation membrane model, the method comprising: Construct a polyethyleneimine PEI monomer model and optimize its structure based on density functional theory; The structurally optimized PEI monomer model was extended to a PEI single chain model, and the energy of the PEI single chain model was minimized; The energy-minimized PEI single-chain model was subjected to molecular dynamics simulations under the NVT ensemble and the NPT ensemble to enable the PEI single-chain model to reach pre-equilibrium; A simulation box is constructed and multiple PEI single-chain models that have reached pre-equilibrium are randomly inserted to obtain an initial system, a molecular dynamics simulation is performed on the initial system under the NVT ensemble, and then multiple rounds of molecular dynamics simulations are performed on the initial system under the NPT ensemble and the size of the simulation box is expanded after the simulation is completed, and a melt annealing simulation is performed between two adjacent molecular dynamics simulations under the NPT ensemble to finally obtain a PEI gas separation membrane model; The time variation trends of potential energy and density at the end stage of the initial system molecular dynamics simulation are statistically analyzed. When the time variation trends of potential energy and density converge, it is confirmed that the PEI gas separation membrane model has reached equilibrium.

[0007] Optionally, the molecular dynamics simulation of the initial system is performed under the NVT ensemble, and then multiple rounds of molecular dynamics simulation of the initial system are performed under the NPT ensemble and the size of the simulation box is expanded after the simulation is completed, and a melt annealing simulation is performed between two adjacent molecular dynamics simulations under the NPT ensemble, including: In the NVT ensemble, the temperature was set to 600 K, and a 2 ns molecular dynamics simulation was performed on the initial system; In the NVT ensemble, the temperature was set to 300 K, and a 2 ns molecular dynamics simulation was performed on the initial system; In the NPT ensemble, set the temperature to 300 K and the pressure to 0.2P max , a 2 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was expanded after the simulation was completed. max is the maximum pressure parameter; Performing a melt annealing simulation on the initial system, wherein the melt annealing simulation includes a melting simulation in which the temperature is increased from 300 K to 600 K and the simulation duration is 2 ns, and an annealing simulation in which the temperature is decreased from 600 K to 300 K and the simulation duration is 2 ns; In the NPT ensemble, set the temperature to 300 K and the pressure to 0.6P max , a 2 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was enlarged after the completion of this simulation; Repeating the melt annealing simulation on the initial system; In the NPT ensemble, set the temperature to 300 K and the pressure to P max , a 2 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was enlarged after the completion of this simulation; Repeating the melt annealing simulation on the initial system; In the NPT ensemble, the temperature was set to 300 K, the pressure was set to 1 bar, a 20 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was expanded after the simulation was completed.

[0008] Optionally, P max = 50000 bar.

[0009] Optionally, the statistical initial system molecular dynamics simulation of the potential energy and density over time at the end stage, when the potential energy and density over time trends converge, confirming that the PEI gas separation membrane model has reached equilibrium, includes: The potential energy variation with time graph and the density variation with time graph of the molecular dynamics simulation process under the NPT ensemble in the last stage of the initial system are statistically analyzed. When the potential energy variation with time graph and the density variation with time graph respectively judge that the potential energy and density variation with time trends converge, it is confirmed that the PEI gas separation membrane model has reached equilibrium.

[0010] Optionally, the energy minimization of the PEI single-chain model comprises: The steepest descent algorithm was used to minimize the energy of the PEI single chain model for 5000 steps.

[0011] Optionally, the energy-minimized PEI single chain model is subjected to molecular dynamics simulations under the NVT ensemble and the NPT ensemble, including: In the NVT ensemble, the temperature was set to 300 K, and molecular dynamics simulations were performed on the energy-minimized PEI single-chain model; In the NPT ensemble, the temperature was set to 300 K and the pressure was set to 1 bar, and a molecular dynamics simulation was performed on the energy-minimized PEI single chain model.

[0012] The second aspect of the present application provides a gas separation membrane performance test simulation method, the method comprising: Constructing a PEI gas separation membrane model using the method described in any one of claims 1 to 6; Create a new simulation box and randomly insert multiple gas molecule models to obtain a gas box, and pre-balance the gas box; The gas box was combined with the PEI gas separation membrane model, and a 1 nm vacuum layer was left between the gas box and the PEI gas separation membrane model to obtain a combined model; Setting a periodic boundary condition in the direction of the region where the gas molecule model in the combined model is located relative to the PEI gas separation membrane model, and setting a blocking wall in the combined model for blocking the gas molecule model from moving in a direction away from the direction to pass through the periodic boundary of the combined model; Fixing multiple carbon atoms at one end of each PEI single chain model in the PEI gas separation membrane model; The binding model was energy minimized, and then molecular dynamics simulations were performed on the binding model under NVT ensemble and NPT ensemble.

[0013] Optionally, the method further comprises: Adding a constant force on the gas molecule model to make the gas molecule model move toward the PEI gas separation membrane model; Molecular dynamics simulations of the binding model with a constant force added to the gas molecule model were performed under the NVT ensemble.

[0014] Optionally, the method further comprises: The distances between all gas molecule models and the PEI gas separation membrane model at different times were counted, and it was determined that the gas molecule models with a distance less than 0.5 nm were adsorbed by the PEI gas separation membrane model; A graph showing the change in the number of gas molecule models adsorbed by the PEI gas separation membrane model over time is plotted, and the adsorption performance of the PEI gas separation membrane model on the gas molecule model is analyzed based on the graph.

[0015] A third aspect of the present application provides an electronic device, including: a memory having a computer program stored thereon; A processor is used to execute the computer program in the memory to implement the steps of the method described in any one of the first aspect and the second aspect above.

[0016] Through the above technical scheme, the polyethyleneimine PEI monomer model is constructed and then extended to a PEI single chain model, and then multiple PEI single chain models are inserted into the simulation box. Through molecular dynamics simulation and melt annealing simulation under the NVT ensemble and NPT ensemble, the pressing process of the PEI single chain can be simulated, and then multiple PEI single chain models can be pressed into a membrane, and when it is confirmed that the potential energy and density at the end of the simulation construction process converge with time, it is confirmed that the obtained PEI gas separation membrane model reaches equilibrium and can be used for further research. Since the PEI monomer model and the PEI single chain model are optimized by energy minimization structure, and simulated by the NVT ensemble and the NPT ensemble, the PEI gas separation membrane model finally constructed can be more in line with the actual situation, which is convenient for understanding the structure of the PEI gas separation membrane, so as to help understand the structural basis and principle of its adsorption of gas molecules. Afterwards, by simulating the free diffusion of gas molecules and non-equilibrium simulation, the adsorption process of the constructed PEI gas separation membrane model on gas molecule models such as CO2 can be tested, and then the specific adsorption performance of the PEI gas separation membrane on gas molecules can be understood, and the corresponding reasons can be analyzed.

[0017] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present application but do not constitute a limitation to the present application. In the accompanying drawings: Figure 1 The present invention is a flow chart showing a method for constructing a gas separation membrane model according to an exemplary embodiment.

[0019] Figure 2 is a simplified flow chart of a method for constructing a gas separation membrane model according to an exemplary embodiment.

[0020] Figure 3A is a graph showing the change of potential energy over time at the end stage of a molecular dynamics simulation under an NPT ensemble according to an exemplary embodiment.

[0021] Figure 3B is a graph showing density variation over time at the end stage of a molecular dynamics simulation in an NPT ensemble according to an exemplary embodiment.

[0022] Figure 4 The present invention is a flow chart of a gas separation membrane performance test simulation method according to an exemplary embodiment.

[0023] Figure 5 is another flow chart of a gas separation membrane performance test simulation method according to an exemplary embodiment.

[0024] Figure 6 is a diagram of an initial structure before gas adsorption simulation according to an exemplary embodiment.

[0025] Figure 7 is a schematic diagram showing a result of a free diffusion simulation according to an exemplary embodiment.

[0026] Figure 8 is a schematic diagram showing a result of a non-equilibrium simulation according to an exemplary embodiment.

[0027] Fig. 9 is a schematic diagram of pores of a gas separation membrane according to an exemplary embodiment.

[0028] Fig.10 The figure is a graph showing the change in the amount of gas adsorbed by a gas separation membrane during a simulation according to an exemplary embodiment.

[0029] Fig.11 It is a block diagram of an electronic device according to an exemplary embodiment. DETAILED DESCRIPTION

[0030] The specific implementation of the present application is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present application, and is not used to limit the present application.

[0031] Molecular dynamics (MD) simulation, as an effective tool for analyzing the behavior of materials at the nanoscale, can provide important theoretical support for the CO2 capture process of PEI. MD simulation provides a new perspective for analyzing the microscopic adsorption mechanism of PEI and its performance optimization.

[0032] Figure 1 is a flow chart of a method for constructing a gas separation membrane model according to an exemplary embodiment. Figure 1 , the method comprising: S101, constructing a polyethyleneimine PEI monomer model, and optimizing the structure of the PEI monomer model based on density functional theory.

[0033] S102, extending the structurally optimized PEI monomer model into a PEI single chain model, and performing energy minimization on the PEI single chain model.

[0034] S103, performing molecular dynamics simulations under NVT ensemble and NPT ensemble on the energy-minimized PEI single-chain model to enable the PEI single-chain model to reach pre-equilibrium.

[0035] S104, construct a simulation box and randomly insert multiple PEI single chain models that have reached pre-equilibrium to obtain an initial system, perform molecular dynamics simulation on the initial system under the NVT ensemble, then perform multiple rounds of molecular dynamics simulation on the initial system under the NPT ensemble and expand the size of the simulation box after the simulation is completed, perform melt annealing simulation between two adjacent molecular dynamics simulations under the NPT ensemble, and finally obtain a PEI gas separation membrane model.

[0036] S105, statistically analyzing the time-varying trends of potential energy and density at the end stage of the initial system molecular dynamics simulation, and when the time-varying trends of potential energy and density converge, confirming that the PEI gas separation membrane model has reached equilibrium.

[0037] In step S101, the Gaussview software can be used to draw a monomer model of polyethyleneimine PEI, such as a monomer model of PEI monomer molecule ethyleneimine. For example, the construction of the polyethyleneimine PEI monomer model can be achieved by constructing the atoms of the monomer model and establishing corresponding connection relationships. After the PEI monomer model is constructed, the structure is optimized based on energy minimization. The opt operation in the Gaussian software can be used to optimize the structure of the PEI monomer model. When optimizing the PEI monomer model, the density functional theory (DFT) method can be used to optimize the structure of the PEI monomer model at the microscopic level to improve the accuracy. When setting the parameters, select Optimization in the Job Type; select DFT, B3LYP, 6-31g (d, p) in the Method, and set the correct charge (Charge) and spin multiplicity (Spin).

[0038] After step S101 is completed, step S102 can be executed. In step S102, using the above example, the code can be used to copy and extend the PEI monomer to generate a single-chain structure, and the PEI single-chain model is obtained as shown in Figure 2 In the initial configuration shown, the number of repeating units of the PEI single chain model, that is, the chain length, can be 50.

[0039] After obtaining the PEI single-chain model, the energy minimization simulation calculation can be performed on it using Gromacs software to optimize its structure and make its structure more stable. For example, the steepest descent algorithm can be used to minimize the energy of the PEI single-chain model for 5000 steps. In order to make the PEI single-chain model more in line with the actual situation, after step S102 is completed, step S103 can be entered to continue pre-balancing the PEI single-chain model, and molecular dynamics simulation of the PEI single-chain model is performed under the NVT ensemble and the NPT ensemble to achieve pre-equilibrium.

[0040] Optionally, in step S103, a molecular dynamics simulation is performed on the energy-minimized PEI single-chain model under the NVT ensemble and the NPT ensemble, including: S1031, in the NVT ensemble, the temperature was set to 300 K, and the energy-minimized PEI single chain model was subjected to molecular dynamics simulation.

[0041] S1032, under the NPT ensemble, set the temperature to 300 K and the pressure to 1 bar, and perform molecular dynamics simulation on the energy-minimized PEI single chain model.

[0042] The molecular dynamics simulation as described in step S1031 and step S1032 can be performed on the energy minimized PEI single chain model by molecular dynamics simulation calculation software such as Gromacs software. The simulated PEI single chain configuration is closer to the actual situation, thereby making subsequent modeling and simulation more realistic and accurate.

[0043] After step S103 is completed, step S104 is executed. In step S104, a simulation box can be newly created in molecular dynamics simulation software such as Gromacs. The simulation box is a cubic space in the software, which serves as the spatial range for molecular dynamics simulation, like a virtual container. In a possible implementation, the size of the simulation box is 12 nm×12 nm×12 nm, and has periodic boundary conditions.

[0044] After constructing the simulation box, multiple pre-equilibrium PEI single-chain models are randomly inserted into the box. Using the above example, 30 pre-equilibrium PEI single-chain models can be inserted, and the minimum distance between the PEI single-chain model and the simulation box can be set to 1 nm.

[0045] After the initial system is established, molecular dynamics simulation and melt annealing simulation can be performed on the initial system under NVT ensemble and NPT ensemble. The process of pressing multiple PEI single chains into films under high pressure conditions can be simulated through step-by-step simulation equilibrium. For example, the 12-step film formation method can be selected to perform molecular dynamics simulation on the initial system to obtain a PEI gas separation membrane model.

[0046] Optionally, in step S104, a molecular dynamics simulation is performed on the initial system under the NVT ensemble, and then multiple rounds of molecular dynamics simulations are performed on the initial system under the NPT ensemble, and after the simulation is completed, the size of the simulation box is expanded, and a melt annealing simulation is performed between two adjacent molecular dynamics simulations under the NPT ensemble, including: S1041, in the NVT ensemble, the temperature was set to 600 K, and a 2 ns molecular dynamics simulation was performed on the initial system.

[0047] S1042, in the NVT ensemble, the temperature was set to 300 K, and a 2 ns molecular dynamics simulation was performed on the initial system.

[0048] S1043, in the NPT ensemble, set the temperature to 300 K and the pressure to 0.2P max , a 2 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was expanded after the simulation was completed. max is the maximum pressure parameter.

[0049] S1044, performing a melt annealing simulation on the initial system, wherein the melt annealing simulation includes a melt simulation of heating from 300 K to 600 K with a simulation duration of 2 ns, and an annealing simulation of cooling from 600 K to 300 K with a simulation duration of 2 ns.

[0050] S1045, in the NPT ensemble, set the temperature to 300 K and the pressure to 0.6P max , a 2 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was expanded after the simulation was completed.

[0051] S1046, repeat the melt annealing simulation on the initial system.

[0052] S1047, in the NPT ensemble, set the temperature to 300 K and the pressure to P max , a 2 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was expanded after the simulation was completed.

[0053] S1048, repeat the melt annealing simulation on the initial system.

[0054] S1049, in the NPT ensemble, set the temperature to 300 K, set the pressure to 1 bar, perform a 20 ns molecular dynamics simulation on the initial system and expand the size of the simulation box after the simulation is completed.

[0055] Specifically, steps S1041 to S1049 can all be implemented using molecular dynamics simulation software such as Gromacs, and can be performed in the order of steps S1041 to S1049. After the molecular dynamics simulation under the NPT ensemble, the size of the simulation box will become smaller due to the pressure. To facilitate subsequent simulations, the size of the simulation box can be expanded after the NPT ensemble simulation. For example, after the first three molecular dynamics simulations under the NPT ensemble, the simulation box can be expanded to the original size such as the aforementioned 12 nm×12 nm×12 nm. After the last molecular dynamics simulation under the NPT ensemble, the size of the simulation box can be expanded to the required size according to subsequent needs. For example, in order to test the adsorption performance of the constructed PEI gas separation membrane model on the gas, the size of the simulation box can be expanded to the same or corresponding size as the gas box of the gas. For example, when the size of the gas box is 5 nm×5 nm×5 nm, the simulation box can be expanded to 5 nm×5 nm×A nm to facilitate alignment with the gas box. A is determined according to actual conditions, for example, it can be 18 or 24, etc. Expanding the size of the simulation box is also convenient for subsequent statistical data such as potential energy. After the size of the simulation box is enlarged, the multiple PEI single chain models as a whole, i.e., the PEI gas separation membrane model, are placed in the center of the simulation box. Continuing with the above example, in the simulation process, in order to improve the simulation accuracy, the long-range interaction particle network Ewald (PME) method can be used for processing, the van der Waals interaction is processed using the cut-off method, and the distance cutoff value is set to 1.2 nm. A V-rescale thermostat is used to control the system temperature to 300 K, and a Berendsen barostat is used to control the pressure. In a possible embodiment, P max =50000 bar.

[0056] Through two rounds of molecular dynamics simulations under the NVT ensemble, the PEI molecules are allowed to move and interact under constant temperature and volume conditions, which can further make the initial system reach a relatively balanced state. Subsequently, molecular dynamics simulations under the NPT ensemble are carried out, and melt annealing simulations are carried out between two adjacent molecular dynamics simulations under the NPT ensemble. Through multiple such alternating processes, the PEI single chain can continuously adjust its structure, eliminate local stress and defects in the system, and thus obtain a more stable and ordered structure. Through multiple rounds of molecular dynamics simulations under the NPT ensemble, high pressure is first used for compression, and finally low pressure is used for slow compression, and finally a PEI gas separation membrane model close to the real structure is obtained.

[0057] In a possible implementation, the Lennard-Jones (LJ) potential was smoothly shifted to zero between 0.9 nm and 1.2 nm during the simulation to reduce cutoff noise. The pressure was maintained at 1 bar using a semiisotropic Parrinello-Rahman barostat with a coupling constant of 4 ps and a compressibility of 4.5 × 10 in all three directions. -5 bar -1 Periodic boundary conditions are applied in all three directions. The time step is 10 fs and the neighbor list is updated every 10 steps.

[0058] After step S104 is completed, the process proceeds to step S105. In step S105, in order to confirm whether the obtained PEI gas separation membrane model has reached equilibrium, the data of the potential energy and density variation over time at the end of the molecular dynamics simulation can be statistically analyzed and judged accordingly.

[0059] The end stage of the initial system molecular dynamics simulation can be the molecular dynamics simulation under the NPT ensemble in the last stage in step S104, such as step S1049, or the last ten percent of the entire molecular dynamics simulation process. By statistically analyzing the trend of potential energy and density over time in the end stage, when the trend converges, it can be considered that equilibrium is reached, and the obtained PEI gas separation membrane model can be used for further research such as subsequent performance test simulation. In the molecular dynamics simulation process, the long-range interaction particle network Ewald (PME) method can be used for processing, and the van der Waals effect is processed using the cut-off method, and the distance cutoff value is set to 1.2 nm. A V-rescale thermostat is used to control the system temperature to 300K, and a Berendsen barostat is used to control the pressure.

[0060] Optionally, in step S105, the potential energy and density variation trends over time at the end stage of the initial system molecular dynamics simulation are statistically analyzed, and when the potential energy and density variation trends over time converge, it is confirmed that the PEI gas separation membrane model has reached equilibrium, including: The potential energy variation with time graph and the density variation with time graph of the molecular dynamics simulation process under the NPT ensemble in the last stage of the initial system are statistically analyzed. When the potential energy variation with time graph and the density variation with time graph respectively judge that the potential energy and density variation with time trends converge, it is confirmed that the PEI gas separation membrane model has reached equilibrium.

[0061] Specifically, the potential energy variation over time and density variation over time of the PEI gas separation membrane model in step S1049 can be statistically analyzed. For details, see Figure 3A and Figure 3B, it can be observed that if there is an obvious convergence trend between the two figures, it can be determined that the PEI gas separation membrane model has reached equilibrium. In addition, a curve fitting can be performed based on the data of potential energy and density versus time to obtain a smooth fitting curve, and then a judgment can be made based on the slope of the fitting curve. If the slope converges, for example, its absolute value is less than a threshold, it can be determined that the trend of potential energy and density changing over time converges.

[0062] Figure 2 is a simplified flow chart of a method for constructing a gas separation membrane model according to an exemplary embodiment. Figure 2 It is shown in Figure 1 The key steps of the method flow shown and the corresponding system configuration. Figure 2 The initial configuration is a system formed by multiple PEI single chain models. After EM (energy minimization), NVT (molecular dynamics simulation under NVT ensemble), NPT (molecular dynamics simulation under NPT ensemble), melt annealing simulation and finally NPT (molecular dynamics simulation under NPT ensemble), the final conformation is obtained as follows Figure 2 As shown, the system configuration in the process can also be seen Figure 2 .

[0063] Through the above technical solution, a polyethyleneimine PEI monomer model is constructed and then extended to a PEI single-chain model, and then multiple PEI single-chain models are inserted into the simulation box. Through molecular dynamics simulation and melt annealing simulation under the NVT ensemble and NPT ensemble, the pressing process of the PEI single chain can be simulated, and then multiple PEI single-chain models are pressed into a membrane, and when it is confirmed that the potential energy and density at the end of the simulation construction process converge over time, it is confirmed that the obtained PEI gas separation membrane model reaches equilibrium and can be used for further research. Since the PEI monomer model and the PEI single-chain model are optimized by energy minimization structure, and simulated by the NVT ensemble and the NPT ensemble, the PEI gas separation membrane model finally constructed can be more in line with the actual situation, which is convenient for understanding the structure of the PEI gas separation membrane, so as to help understand the structural basis and principle of its adsorption of gas molecules.

[0064] Figure 4 is a flow chart of a gas separation membrane performance test simulation method according to an exemplary embodiment. Figure 4 As shown, the method includes: S401, constructing a PEI gas separation membrane model using a method for constructing a gas separation membrane model.

[0065] S402, creating a new simulation box and randomly inserting multiple gas molecule models to obtain a gas box, and pre-balancing the gas box.

[0066] S403, combining the gas box and the PEI gas separation membrane model, and leaving a 1 nm vacuum layer between the gas box and the PEI gas separation membrane model to obtain a combined model.

[0067] S404, setting periodic boundary conditions in the direction of the region where the gas molecule model in the combined model is located relative to the PEI gas separation membrane model, and setting a blocking wall in the combined model for blocking the gas molecule model from moving in a direction away from the direction to pass through the periodic boundary of the combined model.

[0068] S405, fixing a plurality of carbon atoms at one end of each PEI single chain model in the PEI gas separation membrane model.

[0069] S406, energy minimization is performed on the binding model, and then molecular dynamics simulations are performed on the binding model under the NVT ensemble and the NPT ensemble.

[0070] In step S401, the following method may be used: Figure 1 The method for constructing a gas separation membrane model is used to construct a PEI gas separation membrane model. For details, please refer to the description of step S101 to step S105, which will not be repeated here.

[0071] After step S401 is completed, step S402 may be executed. In step S402, a simulation box may be newly created using software such as Gromacs. The type of the simulation box may be the same as the type of the simulation box in step S104. The size of the newly created simulation box may be 5 nm×5 nm×5 nm. Multiple gas molecule models may be randomly inserted into the newly created simulation box. For example, 50 CO2 molecule models and 50 N2 molecule models may be randomly inserted to obtain a gas box. The gas box is pre-balanced. For example, the pre-balance may be to minimize the energy of the gas box. By inserting different molecules of the same mole, it is convenient to compare the adsorption performance.

[0072] After step S402 is completed, step S403 can be executed. In step S403, the gas box is combined with the constructed PEI gas separation membrane model. Specifically, the gas box can be aligned with the simulation box of the PEI gas separation membrane model in the Gromacs software, for example, the two boxes are placed in the Z-axis direction in the molecular dynamics calculation software, and the center line of the two boxes is parallel or approximately parallel to the Z-axis. When aligned, a vacuum layer is left between the gas box and the PEI gas separation membrane model, and the distance can be 1 nm. Then the two boxes can be eliminated, and a new large simulation box can be created to include the gas molecule model and the PEI gas separation membrane model, and the gas molecule model and the PEI gas separation membrane model can be included in it, and a new system, that is, a combined model, is formed as a whole, which serves as the object and simulation space of subsequent molecular dynamics simulation.

[0073] After step S403 is executed, step S404 can be executed. In step S404, a periodic boundary condition is set in the direction of the gas molecule model in the combined model relative to the PEI gas separation membrane model, so as to facilitate the subsequent simulation of the gas molecule model passing through the PEI gas separation membrane model along this direction. For example, the periodic boundary condition in the Z-axis direction can be set using Gromacs software. Since the gas molecule model will move in all directions during the subsequent simulation, the gas will be blocked by the boundary of the simulation box in the X-axis and Y-axis directions, but in the Z-axis direction, due to the periodic boundary condition, the gas may move away from the PEI gas separation membrane model and pass through the periodic boundary of the simulation box in the Z-axis direction to reach the other side of the PEI gas separation membrane model, affecting the simulation test. Therefore, in the combined model, a blocking wall is set along the direction in which the gas molecule model deviates from the PEI gas separation membrane model, for example, along the Z-axis away from the PEI gas separation membrane model. To block the gas molecule model from passing through the simulation box of the combined model along this direction. The blocking wall can be set using materials such as graphene, and when using Gromacs software, an air wall can also be used for blocking.

[0074] After step S404 is completed, step S405 can be executed. In step S405, due to the interaction in the simulation process, the PEI gas separation membrane model will have a large positional displacement due to the action of force, so the position of the PEI gas separation membrane model needs to be fixed. At the same time, in order to retain the flexibility of the PEI single-chain model, so that the PEI gas separation membrane model has the ability to deform, and simulate the real situation, only a few carbon atoms of the PEI single-chain model are fixed, so a few carbon atoms at either end of each PEI single-chain model in the PEI gas separation membrane model can be selected for fixing, for example, in the Gromacs software, the 5 carbon atoms at the front end of the PEI single-chain model set in the software are fixed.

[0075] After step S405 is completed, step S406 can be executed. In step S406, the energy of the binding model set in step S405 is minimized to optimize its structure, and the molecular dynamics simulation of the energy-minimized binding model is performed under the NVT ensemble and the NPT ensemble to simulate the interaction between the test gas molecule model and the PEI gas separation membrane model under the condition of free diffusion. For example, Gromacs can be used for simulation, and the simulation conditions are set to a temperature of 300 K and a pressure of 1 bar. During the simulation process, the gas molecule model moves in all directions. When moving toward the PEI gas separation membrane model, the gas molecule model may penetrate the PEI gas separation membrane model, or it may be captured by the PEI gas separation membrane model to complete the adsorption of the gas molecule model. In other directions, the gas molecule model will be blocked by the simulation box boundary or the blocking wall, thereby forcing the gas molecule model to change the direction of movement and make the gas molecule model move toward the PEI gas separation membrane model as much as possible.

[0076] Figure 5 is another flow chart of a gas separation membrane performance test simulation method according to an exemplary embodiment. Figure 5 As shown, the method includes: S501, constructing a PEI gas separation membrane model using a method for constructing a gas separation membrane model.

[0077] S502, creating a new simulation box and randomly inserting multiple gas molecule models to obtain a gas box, and pre-balancing the gas box.

[0078] S503, combining the gas box and the PEI gas separation membrane model, and leaving a 1 nm vacuum layer between the gas box and the PEI gas separation membrane model to obtain a combined model.

[0079] S504, setting periodic boundary conditions in the direction of the region where the gas molecule model in the combined model is located relative to the PEI gas separation membrane model, and setting a blocking wall in the combined model for blocking the gas molecule model from moving in a direction away from the direction to pass through the periodic boundary of the combined model.

[0080] S505, fixing a plurality of carbon atoms at one end of each PEI single chain model in the PEI gas separation membrane model.

[0081] S506, energy minimization is performed on the binding model, and then molecular dynamics simulations are performed on the binding model under the NVT ensemble and the NPT ensemble.

[0082] S507, adding a constant force to the gas molecule model to make the gas molecule model move toward the PEI gas separation membrane model.

[0083] S508, performing molecular dynamics simulation on the binding model with constant force added to the gas molecule model under the NVT ensemble.

[0084] Steps S501 to S506 can refer to steps S401 to S406. This process is used to simulate the adsorption process of gas molecules by the PEI gas separation membrane in the gas free diffusion stage. Steps S507 to S508 are non-equilibrium simulation stages, which are used to simulate the adsorption process of gas molecules by the PEI gas separation membrane under the action of a constant force on the gas molecules.

[0085] In step S501 to step S506, the gas molecule model freely diffuses and moves in multiple directions, and some molecules will not move toward the PEI gas separation membrane model. In order to make more gas molecule models move toward the PEI gas separation membrane model and speed up the adsorption simulation test process, on the basis of the aforementioned free diffusion simulation, a non-equilibrium simulation is performed for a certain period of time to speed up the process of interaction between the gas molecule model and the PEI gas separation membrane model. After step S506 is completed, step S507 is executed. In step S507, a constant force is added to the gas molecule model to make the gas molecule model move toward the PEI gas separation membrane model and can contact the PEI gas separation membrane model more quickly.

[0086] Using the previous example, the pull option in Gromacs provides a single-direction traction, pull-coord1-rate is set to 0.002, that is, the pulling rate is set to 0.002 nm / ps, and pull-coord1-k is set to 1000, that is, the pulling constant is 1000 kJ / (mol·nm²). In this way, a constant force can be applied in the Z-axis direction, which can make the gas molecule model move along the Z-axis toward the PEI gas separation membrane model. The constant force value is small and will not affect the interaction process between the gas molecule model and the PEI gas separation membrane model.

[0087] After step S507 is completed, the process proceeds to step S508. In step S508, molecular dynamics simulation is performed under the NVT ensemble. Gromacs software can be used to set the temperature parameter to 300 K to simulate the movement of the gas molecule model under the action of a constant force.

[0088] After the test simulation is completed, the results can be analyzed. Figure 4 or Figure 5The gas separation membrane performance test simulation method shown may also include: taking snapshots of key moments of the simulation process using VMD software to obtain the interaction details between the separation membrane and the gas molecule model. Specifically, the simulation process can be visualized using the VMD software, and PEI, CO2, and N2 in the simulation snapshots are colored with different colors to distinguish them. The display of molecules in VMD is optimized using the script vmdscene.dat, which is used to render high-resolution images. First, Tachyon needs to be selected as the renderer in VMD, and then the script is used: -aasmpls 100 -mediumashade -trans vmd -res 1024 742 -format BMP -oFigure.bmp.

[0089] See also Figures 6 to 8 , Figure 6 The initial structure of the binding model constructed in step S503 before the gas adsorption simulation is shown, and it can be found that the CO2 molecules and the N2 molecules are located on one side of the PEI gas separation membrane model; Figure 7 The result of free diffusion simulation in step S506 is shown. At this time, it can be found that more CO2 molecules are adsorbed by the PEI gas separation membrane model; Figure 8 The result of the non-equilibrium simulation in step S508 is shown. It can be found that under the action of the constant force, most of the N2 molecules penetrate the PEI gas separation membrane model, while more CO2 molecules are adsorbed by the PEI gas separation membrane model, indicating that the PEI gas separation membrane model has a good selective adsorption for CO2 molecules.

[0090] In addition, you can also use Multiwfn to graphically display the holes and free areas in the molecular dynamics simulation system. Use 1.8 times the atomic van der Waals radius as the full width at half maximum (FWHM) of the Gaussian function and set the grid for calculation. Use the three side lengths of the unit cell as the three side lengths of the grid data calculation range, and use a grid point spacing of 0.25 angstroms. Export the grid data as the free_smooth.cub file in the current directory. Load it after starting VMD, enter pbc box and color Display Background white in the console to display the box border and change it to a white background. The image should look like this: Fig. 9 The colored areas in the figure are the holes in the system.

[0091] Alternatively, if Figure 4 or Figure 5 The gas separation membrane performance test simulation method shown may also include: The distances between all gas molecule models and the PEI gas separation membrane model at different times are counted, and it is determined that the gas molecule models whose distance is less than 0.5 nm are adsorbed by the PEI gas separation membrane model; A graph showing the change in the number of gas molecule models adsorbed by the PEI gas separation membrane model over time is plotted, and the adsorption performance of the PEI gas separation membrane model on the gas molecule model is analyzed based on the graph.

[0092] By counting the distances between all gas molecule models and the PEI gas separation membrane model at different times, using the distance formula Calculate the distance between all gas molecule models and the separation membrane, where x1, y1, and z1 are the coordinates of the atoms in the gas molecule model, and x2, y2, and z2 are the coordinates of the atoms on the PEI gas separation membrane model. d < 0.5 nm is marked as contact, which means that the gas molecule model is considered to be adsorbed by the PEI gas separation membrane model. The corresponding distance d is calculated by traversing the coordinates of each atom in the gas molecule and each atom on the PEI gas separation membrane model. If there is a distance d less than 0.5 nm, the gas molecule is considered to be in contact with the PEI gas separation membrane model. Then a graph showing the change in the number of gas molecule models adsorbed by the PEI gas separation membrane model over time can be plotted, such as Fig.10 The changes in the number of CO2 and N2 molecules adsorbed by the PEI gas separation membrane model during the simulation process are shown.

[0093] The change diagram can be used to analyze the adsorption performance of the PEI gas separation membrane model to the gas molecule model, see Fig.10 , it can be clearly seen from the number of contacts at different time periods that in the free diffusion stage (0-10 ns), the PEI gas separation membrane has a stronger adsorption effect on CO2; in the non-equilibrium simulation stage, in the early stage of the simulation (10-27 ns), most of the N2 gas molecular models penetrated the PEI gas separation membrane due to the force; and most of the CO2 gas molecular models will remain in the membrane due to the selective adsorption of polyethyleneimine. After 40 ns simulation, the PEI gas separation membrane captured 39 CO2 gas molecular models and 6 N2 molecules. It can be found that the PEI gas separation membrane has excellent selective adsorption capacity for CO2 gas molecular models.

[0094] After the PEI gas separation membrane model is constructed through the above technical scheme, the PEI gas separation membrane model is combined with the gas box to obtain a combined model, and then periodic boundary conditions and barrier walls are set, and the PEI gas separation membrane model is fixed by fixing the carbon atoms of the PEI single chain model. Molecular dynamics simulation is performed under the NVT ensemble and the NPT ensemble to simulate the adsorption effect of the PEI gas separation membrane model on gas molecules under the condition of free diffusion of gas molecules. Then, in order to accelerate the adsorption process, a constant force is applied to the gas molecule model to accelerate the interaction process between the gas molecule model and the PEI gas separation membrane model during the non-equilibrium simulation process, and the adsorption results of the PEI gas separation membrane model on the gas molecule model are obtained. After obtaining the results, the simulation process and structure can be analyzed by visualization and other methods. In this way, there is no need to analyze through experiments, which saves costs, and the molecular dynamics simulation process can be understood from a microscopic perspective, which helps to understand the adsorption capacity of the PEI gas separation membrane model on gas molecules and the corresponding principles, which is of great significance for further studying the adsorption of gas molecules such as CO2 by the PEI gas separation membrane.

[0095] Fig.11 FIG. 1 is a block diagram of an electronic device according to an exemplary embodiment. Fig.11 As shown, the electronic device 700 may include: a processor 701 , a memory 702 . The electronic device 700 may also include one or more of a multimedia component 703 , an input / output (I / O) interface 704 , and a communication component 705 .

[0096] The processor 701 is used to control the overall operation of the electronic device 700 to complete all or part of the steps in the above-mentioned method for constructing a gas separation membrane model and the gas separation membrane performance test simulation method. The memory 702 is used to store various types of data to support the operation of the electronic device 700, and these data may include, for example, instructions for any application or method used to operate on the electronic device 700, and application-related data, such as contact data, sent and received messages, pictures, audio, video, etc. The memory 702 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (Static Random Access Memory, referred to as SRAM), electrically erasable programmable read-only memory (Electrically Erasable Programmable Read-Only Memory, referred to as EEPROM), erasable programmable read-only memory (Erasable Programmable Read-Only Memory, referred to as EPROM), programmable read-only memory (Programmable Read-Only Memory, referred to as PROM), read-only memory (Read-Only Memory, referred to as ROM), magnetic memory, flash memory, magnetic disk or optical disk. The multimedia component 703 may include a screen and an audio component. The screen may be, for example, a touch screen, and the audio component is used to output and / or input audio signals. For example, the audio component may include a microphone, which is used to receive external audio signals. The received audio signal may be further stored in the memory 702 or sent through the communication component 705. The audio component also includes at least one speaker for outputting audio signals. The I / O interface 704 provides an interface between the processor 701 and other interface modules, and the above-mentioned other interface modules may be keyboards, mice, buttons, etc. These buttons may be virtual buttons or physical buttons. The communication component 705 is used for wired or wireless communication between the electronic device 700 and other devices. Wireless communication, such as Wi-Fi, Bluetooth, Near Field Communication (NFC), 2G, 3G, 4G, NB-IOT, eMTC, or other 5G, etc., or a combination of one or more of them, is not limited here. Therefore, the corresponding communication component 705 may include: Wi-Fi module, Bluetooth module, NFC module, etc.

[0097] In an exemplary embodiment, the electronic device 700 can be implemented by one or more application specific integrated circuits (ASIC), digital signal processors (DSP), digital signal processing devices (DSPD), programmable logic devices (PLD), field programmable gate arrays (FPGA), controllers, microcontrollers, microprocessors or other electronic components to execute the above-mentioned method for constructing a gas separation membrane model and the gas separation membrane performance test simulation method.

[0098] In another exemplary embodiment, a computer-readable storage medium including program instructions is also provided, and when the program instructions are executed by a processor, the steps of the method for constructing a gas separation membrane model and the method for simulating the performance test of a gas separation membrane are implemented. For example, the computer-readable storage medium may be the memory 702 including the program instructions, and the program instructions may be executed by the processor 701 of the electronic device 700 to complete the method for constructing a gas separation membrane model and the method for simulating the performance test of a gas separation membrane.

[0099] The preferred embodiments of the present application are described in detail above in conjunction with the accompanying drawings; however, the present application is not limited to the specific details in the above embodiments. Within the technical concept of the present application, a variety of simple modifications can be made to the technical solution of the present application, and these simple modifications all fall within the protection scope of the present application.

[0100] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not further describe various possible combinations.

[0101] In addition, the various implementation modes of the present application may be arbitrarily combined, and as long as they do not violate the concept of the present application, they should also be regarded as the contents recorded in the present application.

Claims

1. A method for constructing a gas separation membrane model, characterized in that: The method comprises: Construct a polyethyleneimine PEI monomer model and optimize its structure based on density functional theory; The structurally optimized PEI monomer model was extended to a PEI single chain model, and the energy of the PEI single chain model was minimized; The energy-minimized PEI single-chain model was subjected to molecular dynamics simulations under the NVT ensemble and the NPT ensemble to enable the PEI single-chain model to reach pre-equilibrium; A simulation box is constructed and multiple PEI single-chain models that have reached pre-equilibrium are randomly inserted to obtain an initial system, a molecular dynamics simulation is performed on the initial system under the NVT ensemble, and then multiple rounds of molecular dynamics simulations are performed on the initial system under the NPT ensemble and the size of the simulation box is expanded after the simulation is completed, and a melt annealing simulation is performed between two adjacent molecular dynamics simulations under the NPT ensemble to finally obtain a PEI gas separation membrane model; The time variation trends of potential energy and density at the end stage of the initial system molecular dynamics simulation are statistically analyzed. When the time variation trends of potential energy and density converge, it is confirmed that the PEI gas separation membrane model has reached equilibrium.

2. The method according to claim 1, characterized in that The method comprises: performing molecular dynamics simulation on the initial system under the NVT ensemble, and then performing multiple rounds of molecular dynamics simulation on the initial system under the NPT ensemble, and expanding the size of the simulation box after the simulation is completed, and performing melt annealing simulation between two adjacent molecular dynamics simulations under the NPT ensemble, including: In the NVT ensemble, the temperature was set to 600 K, and a 2 ns molecular dynamics simulation was performed on the initial system; In the NVT ensemble, the temperature was set to 300 K, and a 2 ns molecular dynamics simulation was performed on the initial system; In the NPT ensemble, set the temperature to 300 K and the pressure to 0.2P max , a 2 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was expanded after the simulation was completed. max is the maximum pressure parameter; Performing a melt annealing simulation on the initial system, wherein the melt annealing simulation includes a melting simulation in which the temperature is increased from 300 K to 600 K and the simulation duration is 2 ns, and an annealing simulation in which the temperature is decreased from 600 K to 300 K and the simulation duration is 2 ns; In the NPT ensemble, set the temperature to 300 K and the pressure to 0.6P max , a 2 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was enlarged after the completion of this simulation; Repeating the melt annealing simulation on the initial system; In the NPT ensemble, set the temperature to 300 K and the pressure to P max , a 2 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was enlarged after the completion of this simulation; Repeating the melt annealing simulation on the initial system; In the NPT ensemble, the temperature was set to 300 K, the pressure was set to 1 bar, a 20 ns molecular dynamics simulation was performed on the initial system and the size of the simulation box was expanded after the simulation was completed.

3. The method according to claim 2, characterized in that P max = 50000 bar。 4. The method according to claim 1, characterized in that: The potential energy and density variation trends over time of the final stage of the statistical initial system molecular dynamics simulation, when the potential energy and density variation trends over time converge, confirming that the PEI gas separation membrane model has reached equilibrium, includes: The potential energy variation with time graph and the density variation with time graph of the molecular dynamics simulation process under the NPT ensemble in the last stage of the initial system are statistically analyzed. When the potential energy variation with time graph and the density variation with time graph respectively judge that the potential energy and density variation with time trends converge, it is confirmed that the PEI gas separation membrane model has reached equilibrium.

5. The method according to claim 1, characterized in that: The energy minimization of the PEI single chain model comprises: The steepest descent algorithm was used to minimize the energy of the PEI single chain model for 5000 steps.

6. The method according to claim 1, characterized in that The energy-minimized PEI single-chain model was subjected to molecular dynamics simulations under the NVT ensemble and the NPT ensemble, including: In the NVT ensemble, the temperature was set to 300 K, and molecular dynamics simulations were performed on the energy-minimized PEI single-chain model; In the NPT ensemble, the temperature was set to 300 K and the pressure was set to 1 bar, and a molecular dynamics simulation was performed on the energy-minimized PEI single chain model.

7. A gas separation membrane performance test simulation method, characterized in that: The method comprises: Constructing a PEI gas separation membrane model using the method described in any one of claims 1 to 6; Create a new simulation box and randomly insert multiple gas molecule models to obtain a gas box, and pre-balance the gas box; The gas box was combined with the PEI gas separation membrane model, and a 1 nm vacuum layer was left between the gas box and the PEI gas separation membrane model to obtain a combined model; Setting a periodic boundary condition in the direction of the region where the gas molecule model in the combined model is located relative to the PEI gas separation membrane model, and setting a blocking wall in the combined model for blocking the gas molecule model from moving in a direction away from the direction to pass through the periodic boundary of the combined model; Fixing multiple carbon atoms at one end of each PEI single chain model in the PEI gas separation membrane model; The binding model was energy minimized, and then molecular dynamics simulations were performed on the binding model under NVT ensemble and NPT ensemble.

8. The method according to claim 7, characterized in that The method further comprises: Adding a constant force on the gas molecule model to make the gas molecule model move toward the PEI gas separation membrane model; Molecular dynamics simulations of the binding model with a constant force added to the gas molecule model were performed under the NVT ensemble.

9. The method according to claim 8, characterized in that The method further comprises: The distances between all gas molecule models and the PEI gas separation membrane model at different times are counted, and it is determined that the gas molecule models whose distance is less than 0.5 nm are adsorbed by the PEI gas separation membrane model; A graph showing the change in the number of gas molecule models adsorbed by the PEI gas separation membrane model over time is plotted, and the adsorption performance of the PEI gas separation membrane model on the gas molecule model is analyzed based on the graph.

10. An electronic device, characterized in that: include: a memory having a computer program stored thereon; A processor, configured to execute the computer program in the memory to implement the steps of the method according to any one of claims 1 to 9.

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