Construction method, performance test method and application of gas separation membrane

Abstract

The invention belongs to the technical field of new material development, and particularly relates to a construction method of a gas separation membrane for hydrogen purification, a method for testing the gas separation performance of the gas separation membrane and application of the gas separation membrane. The method comprises the following steps: constructing a molecular model of BILP, carrying out optimization balance processing on the model, and the like. According to the method, the molecular model is scientifically and reasonably constructed, and the core optimization step of alternating circulation of the force field is introduced subsequently, so that macropores in the model are effectively eliminated, and the microstructure is closer to a real material. During performance testing, the combination of a COMPASS force field and PCFF charges is determined, and the reliability and repeatability of a simulation result are remarkably improved. Meanwhile, the BILP material also has excellent mobility, and has good universality in the whole BILP material family.

Description

Technical Field

[0001] This invention belongs to the field of new material development technology, and specifically relates to a method for constructing a benzimidazole-linked polymer membrane (BILP membrane) for predicting the gas separation performance of the membrane, and its application. Background Technology

[0002] With the increasing global demand for clean energy, hydrogen energy is considered an ideal alternative energy source due to its high energy density and zero carbon emissions. Efficient and low-energy separation and purification of hydrogen from industrial by-product gases or reformed gases is a key step in realizing the large-scale application of hydrogen energy. Membrane separation technology, as an energy-saving and easy-to-operate separation method, plays an important role in this process, with its core being the development of membrane materials that combine high permeability and high selectivity.

[0003] Benzimidazole-linked polymers (BILPs) are a new class of microporous polymers with excellent thermal and chemical stability and tunable pore structures, showing great application potential in high-temperature hydrogen separation. However, screening and optimizing BILP materials through traditional experiments is time-consuming, costly, and makes it difficult to understand the structure-property relationship between their structure and properties at the molecular level.

[0004] Molecular simulation technology studies material properties at the atomic scale and is a powerful tool for discovering new materials. However, current molecular simulation studies of BILP have significant limitations: (1) Insufficient model realism: Polymer models constructed by traditional simulation methods often contain excessively large pore sizes, leading to an overestimation of gas permeability and an underestimation of selectivity, resulting in large deviations between predicted results and experimental data. (2) Unclear key structural factors: The topological configuration (e.g., linear, branched) and chain length of polymer chains have a decisive influence on the microstructure and separation performance of the final membrane, but existing research methods lack systematic examination. (3) Force field parameters have not been verified: The choice of molecular force field and atomic charge has a huge impact on simulation results. Existing simulation methods lack optimization and evaluation of force field parameters for the properties of BILP materials, resulting in poor reliability and universality of predictions. (4) Transferability needs to be verified: Existing simulation methods are usually designed for single BILP structures, and their predictive ability for different structural members of the BILP material family lacks systematic verification. Summary of the Invention

[0005] The purpose of this invention is to overcome one or more shortcomings of the existing technology and provide a method for constructing and testing gas separation membranes with high prediction accuracy, good reliability and strong portability. This method has good applications in material screening.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for constructing a gas separation membrane involves building a molecular model of BILP and optimizing and balancing the model.

[0008] When constructing the molecular model of BILP, the Y configuration with a symmetrical branching structure extending radially from the central node is preferred.

[0009] Furthermore, the chain length of the Y configuration is 9-12. Here, chain length refers to the number of repeating units.

[0010] Specifically, the polymer chain model can be built using Materials Studio software.

[0011] Through systematic research, this invention has clarified the optimal Y configuration and established that chain lengths of 9–12 are key structural parameters for constructing realistic, high-performance BILP membrane models, providing clear guidance for the rational construction of molecular models.

[0012] Furthermore, the model is optimized and balanced by alternating heating and annealing cycles between two different molecular force fields until the structural parameters of the model converge, resulting in the balanced BILP model.

[0013] The two different molecular force fields are, in order, the COMPASS force field and the PCFF force field.

[0014] Furthermore, the initially constructed molecular model of BILP was first placed in an initial low-density environment of 0.4-0.6 g / cm³. 3 Energy minimization was performed in the amorphous unit cell, and molecular dynamics simulations were conducted at 600K to increase the system density.

[0015] Furthermore, the model is treated by alternating heating-annealing cycles between two different molecular force fields as follows:

[0016] S1.1: Utilize COMPASS force field and charge to perform multiple heating-annealing cycles;

[0017] S1.2: Switch to the PCFF force field and execute the heating-annealing cycle multiple times again;

[0018] S1.3: Repeat the heating-annealing cycle between COMPASS and PCFF force fields until the density and porosity structural parameters of the model converge;

[0019] S1.4: Set the atomic charge of the BILP model to the charge corresponding to the PCFF force field, and execute the heating-annealing cycle again to obtain the final equilibrium model;

[0020] The heating-annealing cycle in steps S1.1 and S1.2 is preferably performed 6-7 times; specifically, it can be performed as follows:

[0021] step Simulation Synthesis Temperature T (K) Pressure P (bar) Duration (ps) 1 NPT 600 1 50 2 NPT 300 1 50 3 NPT 600 1 50 4 NPT 300 1 50 5 NPT 600 10 50 6 NPT 300 10 50 7 NPT 600 50 50 8 NPT 300 50 50 9 NPT 600 100 50 10 NPT 300 100 50 11 NPT 600 1 50 12 NPT 300 1 50 13 NPT 600 1 50 14 NPT 300 1 50

[0022] If you are performing 6 heating-annealing cycles, follow steps 1-12 in the table above. If you are performing 7 heating-annealing cycles, follow steps 1-14.

[0023] The above-described process of alternating heating-annealing cycles between two different molecular force fields can be achieved using Materials Studio software. Simply follow the key parameters and steps provided in this invention.

[0024] The present invention further provides a performance testing method for the gas separation membrane obtained by the construction method. Based on the model of the constructed gas separation membrane, the solubility coefficient and diffusion coefficient of the gas to be separated in the gas separation membrane are calculated by molecular simulation, and the permeability and separation selectivity of the gas are obtained.

[0025] Among them, the adsorption isotherm and solubility coefficient of the gas to be separated were calculated using the giant canonical Monte Carlo simulation (GCMC) within the target temperature and pressure range.

[0026] Equilibrium molecular dynamics simulations were performed under the NVT ensemble. By analyzing the relationship between the mean square displacement of gas molecules and time, the diffusion coefficient was calculated using Einstein's formula.

[0027] In calculating the gas solubility coefficient and diffusion coefficient, the Lennard-Jones interaction between the gas separation membrane and gas molecules is described throughout the process using the COMPASS force field; the atomic charge is represented by the charge parameters of the PCFF force field. The optimized selection of the force field and charge parameters described above in this invention maximizes the prediction accuracy.

[0028] According to the dissolution-diffusion mechanism, the permeability (P) of a gas can be obtained by multiplying its solubility coefficient (S) and diffusion coefficient (D) (P = D × S). The separation selectivity (α) is the ratio of the permeabilities of the two gases (α = P). i / P j ).

[0029] The test method can be used to test the separation performance of the gas separation membrane for H2 and CO2 systems, H2 and N2 systems, and H2 and CH4 systems.

[0030] This invention utilizes the gas separation membrane obtained by the described construction method for performance testing, which can be used to screen high-performance hydrogen separation membrane materials. Specifically, it can predict the gas separation performance of various candidate BILP materials, and based on the predicted permeability and selectivity indicators, select candidate materials with excellent overall performance to guide experimental synthesis.

[0031] In general, this invention constructs BILP polymers with Y-configuration chain lengths of 9-12 and improves the equilibrium simulation method by using two molecular force fields in alternating cycles. Based on the equilibrium model, the solubility coefficient and diffusion coefficient of the gas are calculated using giant canonical Monte Carlo (GCMC) and molecular dynamics simulation (MD). Finally, the permeability and separation selectivity of the gas are predicted based on the dissolution-diffusion mechanism.

[0032] This invention overcomes the shortcomings of traditional simulation methods, such as poor prediction accuracy and low universality, by alternating and cycling force fields and selecting appropriate force field / charge parameters. This method can accurately predict the H2 separation selectivity of BILP membranes, and the results are in high agreement with experimental values. This method can serve as a powerful screening tool, significantly accelerating the development of high-performance hydrogen separation membrane materials.

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

[0034] This invention scientifically and rationally constructs a molecular model, and then effectively eliminates macropores in the model by introducing a core optimization step of alternating force fields, making the microstructure closer to that of real materials. During performance testing, the combination of the COMPASS force field and PCFF charge was determined to most accurately reproduce the adsorption and diffusion behavior of BILP materials, significantly improving the reliability and repeatability of the simulation results. The invention's prediction of gas separation selectivity highly matches experimental values, solving the core problem of large prediction bias in traditional methods and significantly improving prediction accuracy. Furthermore, this invention exhibits excellent transferability; when applied to BILP-5 and BILP-15, the predicted structural parameters and separation performance are also highly consistent with experimental data, demonstrating the method's good universality and transferability across the entire BILP material family. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the overall method flow for constructing a molecular simulation design model, performing performance testing, and screening polymers with high-performance H2 in this invention.

[0036] Figure 2 This is a schematic diagram of the Y-configuration used in the embodiments of the present invention. Figure 2 a), and schematic diagrams of the state before and after model equilibrium ( Figure 2 b);

[0037] Figure 3 The graph shows the variation of solubility parameters of the BILP-101 model under different chain length configurations according to the present invention.

[0038] Figure 4 This is a comparison diagram of the structural parameters of the BILP-101 model under different chain length Y-shaped configurations of the present invention;

[0039] Figure 5 This is a comparison graph showing the performance of the gas separation membrane obtained by the construction method of this invention with experimental values;

[0040] Figure 6 This invention illustrates the effect of the force field on the gas separation performance of the constructed BILP-101 model.

[0041] Figure 7 This invention relates to the effect of gas charge change on the gas separation performance of the BILP-101 model.

[0042] Figure 8 This invention relates to the effect of polymer charge change on the gas separation performance of the BILP-101 model.

[0043] Figure 9 This is a comparison chart of the simulation performance and experimental values ​​of the BILP-5 and BILP-15 models constructed in this invention. Detailed Implementation

[0044] The technical solution of the present invention is illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0045] Taking BILP-101 as an example, the implementation process of the present invention will be described in detail.

[0046] Example 1: Construction of the BILP-101 Model

[0047] (I) Initial Model Construction

[0048] Using Materials Studio software, models with different degrees of polymerization and configurations were constructed based on the monomer structure of BILP-101, totaling approximately 200 monomers with L, Y, and X configurations. The molecular chains were end-capped with aldehyde groups and placed in an initial density of 0.5 g / cm³. 3 In the cubic amorphous unit cell.

[0049] (II) Optimizing Balance

[0050] Energy minimization and initial compression: The steepest descent method and the conjugate gradient method were used to minimize the energy of the system. Subsequently, molecular dynamics simulations were performed at 600 K and NPT ensemble for 50 ps to initially compress the system.

[0051] First-stage annealing: A COMPASS force field is used to perform a heating annealing cycle at 300-600K, with the pressure also varying simultaneously. The specific steps can be followed as shown in Table 1 below:

[0052] Table 1

[0053] step Simulation Synthesis Temperature T (K) Pressure P (bar) Duration (ps) 1 NPT 600 1 50 2 NPT 300 1 50 3 NPT 600 1 50 4 NPT 300 1 50 5 NPT 600 10 50 6 NPT 300 10 50 7 NPT 600 50 50 8 NPT 300 50 50 9 NPT 600 100 50 10 NPT 300 100 50 11 NPT 600 1 50 12 NPT 300 1 50

[0054] Force field alternation cycle: Switch the force field from COMPASS to PCFF and repeat the heating-annealing cycle in Table 1. Then, switch the force field back to COMPASS and repeat the cycle in Table 1 again. Repeat this cycle and monitor the model density until the density change between two consecutive force field alternation cycles is less than 0.5%.

[0055] Charge setting and final equilibrium: The charges of all atoms in the BILP-101 polymer are set to the charges corresponding to the PCFF force field. Under the COMPASS force field, a final complete heating-annealing cycle is performed (i.e., steps 1 and 2 in Table 1) to obtain the final equilibrium model.

[0056] (III) Results and Analysis

[0057] like Figure 3 As shown, the solubility coefficient of the Y configuration gradually stabilizes with increasing chain length, indicating that the Y configuration is reasonable.

[0058] N2 adsorption was performed at 77 K liquid nitrogen temperature, and the specific surface area and average pore size of BILP-101 powder were measured. Under the same conditions, simulation calculations were performed to determine the specific surface area and average pore size of the constructed model, where the kinetic diameter of the probe molecule was set to [value missing].

[0059] The specific surface area and average pore size of the measured BILP-101 powder were 87 μm. 2 / g and

[0060] from Figure 4 It can be seen that, by comparing the simulated values ​​with the experimental values, the simulated results are most consistent with the experimental values ​​when the chain length is 9 to 12.

[0061] Example 2: Validation and Comparison of the BILP-101 Model

[0062] Model Construction: Using Materials Studio software, a model was constructed based on the monomer structure of BILP-101, with Y-9 as the single chain, totaling approximately 200 monomers. Aldehyde groups were used to cap the ends of the molecular chains, and the model was placed in an initial density of 0.5 g / cm³. 3 The BILP-101 model was constructed within a cubic amorphous unit cell and balanced using the optimization balancing method described in Example 1.

[0063] Performance testing and calculation:

[0064] Adsorption and solubility coefficients: GCMC simulations were performed using the Sorption module. Conditions: 300K, 0-10 bar, 10 steps each for equilibrium and production steps. 7 MC loop.

[0065] Diffusion coefficient: NVT-EMD simulation was performed using the Forcite module for a duration of 2 ns. The mean square displacements of gas molecules (H2, CO2, N2, CH4) were recorded.

[0066] Permeability and Selectivity: Calculating the permeability P of H2 and CO2 / N2 / CH4 H2 and P CO2 / P N2 / P CH4 And calculate the corresponding selectivity.

[0067] When calculating the gas solubility coefficient and diffusion coefficient, the Lennard-Jones interaction between the gas separation membrane and gas molecules is described throughout the calculation using the COMPASS force field; the atomic charge is represented by the charge parameters of the PCFF force field.

[0068] Results and Analysis: This embodiment systematically evaluated the comparison between simulated values ​​and experimental values ​​(actual measurements were performed under the same conditions as the simulation) for different systems and at different temperatures.

[0069] according to Figure 5 The results show the selectivity of different systems under the conditions of 373K and 1 bar. Compared with experimental values The very close proximity indicates a strong consistency between the different gas mixtures.

[0070] Figure 5 In b, under 1 bar conditions, when applied to the H2 / CO2 system, the temperature-dependent simulation selectivity of the constructed model is discussed. With experimental data It is also highly relevant.

[0071] from Figure 5 It can be seen that the simulation results of BILP-101 selectivity obtained by using the method of the present invention correspond well with the experimental values ​​at different temperatures and systems; the gas separation membrane model constructed by the present invention has very good prediction accuracy.

[0072] If other conditions remain unchanged, but the non-equilibrium molecular dynamics (NEMD) method is used instead of the performance testing method of this invention for prediction, the prediction accuracy of the method is far inferior to that of this invention.

[0073] For example, under conditions of 423K and 1 bar, the H2 permeability predicted by the method of this invention for the BILP-101 membrane is 1514.07 GPU. Although this value is higher than the experimental value of 184.80 GPU, the accuracy of the prediction by this invention is significantly improved compared to the prediction result of 6914.10 GPU by the NEMD method.

[0074] For the BILP-101 membrane, using the NEMD method, the H2 / CO2 selectivity (simulated value) at 298K and 1 bar is 11.11, with a relative error of 9.8% compared to the experimental value of 10.12, which is much higher than the error of 10.32 (simulated value) of the present invention.

[0075] For the BILP-5 membrane, at 298K and 1 bar, the H2 permeability predicted by this invention is 502.20 GPU, which is higher than the experimental value of 348.80 GPU, but significantly better than the prediction result of 2171.86 GPU by the NEMD method.

[0076] The above data fully demonstrate that the method of the present invention has higher accuracy and reliability in both the prediction of gas permeability and separation selectivity.

[0077] Example 3: The Influence of Force Field and Charge Parameters on the Prediction Accuracy of Performance Test Results

[0078] This embodiment systematically evaluates the impact of different combinations of force fields and charges on the prediction results of H2 / CO2 separation performance in the performance testing method.

[0079] Based on the same BILP-101 model and optimized equilibrium process (same as Example 1), the polymer configuration was fixed, and only the force field and charge values ​​were changed. When calculating the gas solubility coefficient and diffusion coefficient, force fields including COMPASS, PCFF, and GAFF were used throughout to describe the Lennard-Jones interaction between the gas separation membrane and gas molecules; atomic charges were calculated using the charge parameters of the COMPASS or PCFF force fields.

[0080] For specific combinations, please refer to Table 2 below and... Figures 6-8 .

[0081] Table 2

[0082]

[0083] Table 2 and Figures 6-8 In this context, LJ represents the force field, q represents the electric charge, and C and P are abbreviations for COMPASS and PCFF, respectively.

[0084] Results and Analysis:

[0085] Combination Figure 6According to Table 2, when using the COMPASS force field (LJ) in combination with PCFF charge (q), the simulated H2 / CO2 selectivity at 298 K and 1 bar is 10.32, which is closest to the experimental value of 10.12. However, when using the PCFF force field, GAFF force field, and COMPASS force field combined with other charges, the simulated values ​​are either much lower than the experimental values ​​or significantly higher. Figure 6 As can be seen from b, using PCFF or GAFF force fields alone will severely underestimate the diffusion coefficient of H2, resulting in a predicted selectivity that is much lower than the experimental value.

[0086] Figure 7 This invention relates to the effect of gas charge change on the gas separation performance of the BILP-101 model, wherein the polymer charge remains unchanged and is kept consistent with the force field, only the gas charge is transformed. Figure 8 This invention relates to the effect of polymer charge change on the gas separation performance of the BILP-101 model, wherein the gas is selected with PCFF charge to eliminate the influence of gas charge.

[0087] from Figure 7 (b) and Figure 8 As can be seen in (b), under the same force field, changing the charge of the polymer itself has a negligible effect on the amount of CO2 adsorbed (see details). Figure 8 b), while changing the charge of CO2 gas has a significant impact on its adsorption behavior (see details). Figure 7 b). By further calculation and comparison of solubility and diffusion coefficient ( Figure 7 b) It was found that when the CO2 charge changes from C(q) to P(q), the CO2 solubility decreases while the H2 solubility remains unchanged, leading to an increase in H2 / CO2 adsorption selectivity, which further increases the selectivity. Figure 8 In step b, changes in polymer charge have relatively little impact on CO2 adsorption performance; therefore, the adsorption performance is more significantly affected by the gas charge. However, regarding selectivity, from... Figure 7 It can also be seen that when the PCFF-derived charge (P(q)) is substituted into the COMPASS framework, the selectivity is significantly improved to 14.73. Figure 7 a).

[0088] It is evident that the combination of the COMPASS force field and the PCFF charge is the key parameter for achieving high-precision prediction in this method.

[0089] Example 4: Method Transferability Verification

[0090] Y-9 and Y-12 models were constructed for BILP-5 and BILP-15 respectively, and the same optimization balancing process and performance calculation process as in Example 1 and Example 2 were performed.

[0091] Figure 9 The figure shows a comparison between the simulation performance and experimental values ​​of the BILP-5 and BILP-15 models constructed in this invention. The experimental values ​​of the specific surface area of ​​both models were obtained under nitrogen adsorption conditions at 77K. The simulation performance was obtained under the same conditions by analyzing the pore structure using probe molecules, with the probe molecule size being the molecular dynamics diameter of one N2.

[0092] from Figure 9 As can be seen, the simulated specific surface area of ​​BILP-15 is 35.7 m². 2 / g, slightly higher than the experimental value of 24.2m 2 / g; while the simulated value for BILP-5 is 14.4m. 2 / g, compared to the experimental value of 17.8m 2 The / g is slightly lower. These minor differences stem from the fundamental differences between the computational and experimental methods, but the errors are all within one order of magnitude. The comparison of the specific surface area between the simulation and the experiment shows a high degree of agreement, and the optimized pore size distribution is more reasonable, with a reduction in the number of macropores.

[0093] Figure 9 Figure b shows the deviations between the simulated predicted H2 / CO2 selectivity of BILP-5 and BILP-15 and the experimental values ​​in the literature. Specifically, under the conditions of 298K and 1 bar, the simulated value for BILP-5 is 15.71, and the experimental value is 16.2, showing a high degree of agreement; the simulated value for BILP-15 is 5.91, and the experimental value is 6.24, also showing a high degree of agreement. The selectivity data for BILP-5 and BILP-15 show that the error between the simulated values ​​and the literature values ​​is only within 3-5%, which fully verifies the transferability of the simulation method.

[0094] It is evident that the method of this invention exhibits excellent transferability and predictive reliability among BILP materials with different chemical structures.

[0095] In summary, this invention provides an accurate, reliable, and universal molecular simulation method that effectively solves the problem of predicting the gas separation performance of BILP membrane materials and provides a powerful technical tool for the efficient development of new materials.

Claims

1. A method for constructing a gas separation membrane, characterized in that, A molecular model of BILP was constructed, and the model was optimized and balanced.

2. The method for constructing the gas separation membrane as described in claim 1, characterized in that, When constructing the molecular model of BILP, a Y configuration with a symmetrical branching structure extending radially from the central node was adopted.

3. The method for constructing the gas separation membrane as described in claim 2, characterized in that, The chain length of the Y configuration is 9-12.

4. The method for constructing the gas separation membrane as described in claim 1, characterized in that, The optimization and equilibration process for the model involves alternating heating and annealing cycles between two different molecular force fields until the structural parameters of the model converge, resulting in the equilibrium BILP model.

5. The method for constructing the gas separation membrane as described in claim 4, characterized in that, The two different molecular force fields are, in order, the COMPASS force field and the PCFF force field.

6. The method for constructing the gas separation membrane as described in claim 4, characterized in that, First, the initially constructed molecular model of BILP was placed in an initial low-density atmosphere (0.4-0.6 g / cm³). 3 Energy minimization was performed in the amorphous unit cell, and molecular dynamics simulations were conducted at 600 K to increase the system density.

7. The method for constructing the gas separation membrane as described in claim 4, characterized in that, The model was treated by alternating heating-annealing cycles between two different molecular force fields as follows: S1.1: Utilize COMPASS force field and charge to perform multiple heating-annealing cycles; S1.2: Switch to the PCFF force field and execute the heating-annealing cycle multiple times again; S1.3: Repeat the heating-annealing cycle between COMPASS and PCFF force fields until the density and porosity structural parameters of the model converge; S1.4: Set the atomic charge of the BILP model to the charge corresponding to the PCFF force field, and execute the heating-annealing cycle again to obtain the final equilibrium model; The heating-annealing cycle in steps S1.1 and S1.2 is performed 6-7 times.

8. A method for testing the performance of a gas separation membrane obtained by any of the construction methods described in claims 1-7, characterized in that, Based on the constructed gas separation membrane model, the solubility coefficient and diffusion coefficient of the gas to be separated in the gas separation membrane are calculated by molecular simulation, and the gas permeability and separation selectivity are obtained. When calculating the gas solubility coefficient and diffusion coefficient, the Lennard-Jones interaction between the gas separation membrane and gas molecules is described throughout the process using the COMPASS force field; the atomic charge is represented by the charge parameters of the PCFF force field.

9. The performance testing method for the gas separation membrane as described in claim 8, characterized in that, The test method can be used to test the separation performance of the gas separation membrane for H2 and CO2 systems, H2 and N2 systems, and H2 and CH4 systems.

10. The gas separation membrane obtained by any of the construction methods described in claims 1-7 is subjected to performance testing to screen high-performance hydrogen separation membrane materials.

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