Method for designing a mixture of polyamines co2 absorbents guided by density functional theory

Abstract

The application is suitable for the field of CO2 capture, and provides a method for mixed polyamine CO2 absorbent collocation design based on density functional theory, which comprises the following steps: selection of monoamine; structure optimization; transition state calculation; hydrogen bond calculation; data statistics and energy barrier prediction. In the application, at the B3LYP level, the solvent model is considered, the structure optimization and frequency calculation of each part of the proton transfer process in the mixed polyamine solution absorbing CO2 reaction are carried out, the transition state of the reaction is calculated, the free energy of each part of the structure is corrected under a high-precision functional, the energy barrier of the reaction and the microstructure of the pre-transfer complex are obtained conveniently and quickly, the weak interaction analysis and hydrogen bond calculation of the obtained complex structure are carried out to obtain related parameters representing the hydrogen bond strength, it is found through linear fitting that there is an excellent correlation between the hydrogen bond strength and the reaction energy barrier, it is proved that the reaction energy barrier can be predicted from the hydrogen bond strength, and theoretical guidance is provided for the collocation design of mixed polyamine solutions under different requirements.

Description

Technical Field

[0001] This invention belongs to the field of CO2 capture, and in particular relates to a method for designing mixed polyamine CO2 absorbents based on density functional theory, which falls under the category of quantum chemical calculations. Background Technology

[0002] The excessive emission of CO2 has been a global concern, and in recent years, CO2 capture technology has been extensively studied in fields such as thermal power and chemical industry. Among them, post-combustion chemical absorption carbon capture technology has developed rapidly, and organic amine absorbents are currently the most widely used carbon capture materials. Carbon capture systems using monoamine solutions as absorbents have been applied on a certain scale internationally.

[0003] In recent years, numerous demonstration industries and pilot-scale experiments have proven that some monoamines, such as MEA and MDEA, can be used for industrial carbon capture. However, problems such as high desorption energy consumption, high viscosity, and low stability hinder their large-scale industrial application. Extensive experimental research has demonstrated that mixed amines combine the advantages of different amines during the absorption process, offering significant advantages in application. They can simultaneously achieve the goals of fast absorption rate, large absorption capacity, and low regeneration energy consumption.

[0004] However, most current research on mixed amines is limited to experimental studies of specific pairings, making the selection of suitable pairings under specific conditions time-consuming and labor-intensive. Meanwhile, in theoretical calculations, more advanced methods (machine learning, QSAR) focus on designing absorber materials with superior performance, with few reports on the design of mixed amine pairings. Finding usable descriptors can theoretically and quickly determine pairings under specific conditions. However, few studies describe differences in reaction energy barriers from microscopic parameters to guide pairing.

[0005] Therefore, finding the parameters that can affect the reaction energy barrier from a microscopic perspective has become one of the urgent problems to be solved. In view of the above situation, it is imperative to develop a method based on density functional theory to guide the design of mixed polyamine CO2 absorbent combinations in order to overcome the shortcomings in current practical applications. Summary of the Invention

[0006] The purpose of this invention is to provide a method for designing mixed polyamine CO2 absorbents based on density functional theory. Based on density functional theory, starting from the hydrogen bond strength, the energy barrier of mixed amines can be predicted more accurately. Combined with actual needs, mixed polyamines can be reasonably matched, which greatly reduces the manpower, material resources and financial resources spent on the screening of mixed polyamine combinations, and reduces time costs.

[0007] The present invention is implemented as follows: a method for designing mixed polyamine CO2 absorbents based on density functional theory includes the following steps:

[0008] Step 1: Selection of Monoamines

[0009] Based on the requirements, amines with different advantages are selected as research objects, and their molecular monomers and unstable intermediate products after CO2 absorption are optimized.

[0010] Step 2, Structural Optimization

[0011] Based on the implicit solvation model and combined with the proton transfer direction, the complex structure before and after proton transfer was established and optimized, and frequency analysis was performed.

[0012] Step 3: Transition state calculation

[0013] The transition state of the proton transfer process is calculated at the same computational level to obtain the electronic energy barrier. The solute free energy in the solvent is corrected under high-precision functional theory to obtain the free energy barrier.

[0014] Step 4: Hydrogen bond calculation

[0015] Using a wavefunction analysis program, based on the structure and wavefunction file of the pre-transfer complex obtained in step 1, the interaction strength and hydrogen bond strength parameters are calculated.

[0016] Step 5: Data Statistics and Energy Barrier Prediction

[0017] Linear fitting of the energy barrier data and hydrogen bond strength parameters revealed an excellent correlation, proving that hydrogen bond strength can be used to predict the reaction energy barrier.

[0018] Further technical solutions include the following steps: In steps 1 and 2, structural optimization employs B3LYP functionals combined with ma-def2-TZVP to calculate the basis set and DFT-D3 dispersion correction. Frequency calculations are performed on the optimized structure to detect the presence of imaginary frequencies. If imaginary frequencies are present, re-optimization is required. Due to the presence of significant weak interactions and anions in the system, dispersion functions need to be introduced into the basis set. The complex configuration is constructed using Gaussview 5.0, while structural optimization, frequency analysis, and subsequent single-point energy calculations are performed using ORCA 5.0.3 software. The implicit solvation model uses SMD to simulate the system in a solvent environment.

[0019] A further technical solution involves calculating the transition state using the NEB-TS method in step 3. The verification method for the correctness of the transition state is that the frequency analysis result has one and only one imaginary frequency, and the direction of the imaginary frequency vibration connects the reactants and products. The electronic energy barrier E is obtained through the transition state calculation. b Characterizing the reaction rate, E b Calculations are performed using Formula 1:

[0020] E b =E TS -EIS (1)

[0021] Among them, E TS E is the transition state energy. IS Energy of reactants;

[0022] The free energy barrier G is obtained through transition state calculation. b G represents the ease with which a reaction occurs. b Calculations are performed using Formula 2:

[0023] G b =G TS -G IS (2)

[0024] Among them, G TS For the transition state free energy, G IS The free energy of the reactants;

[0025] Under solvation conditions, the free energy of the solute needs to be corrected. Specifically, the corrected free energy G in the liquid phase after structure optimization in step 1 is first obtained. co Then, the gas-phase single-point energy of the structure was obtained at the PWPB95 D3 def2-TZVPP level, and the single-point energies in the liquid and gas phases of the structure were obtained at the wB97M-V def2-TZVP level, respectively. The corrected free energy G was calculated using Equation 3.

[0026] G = (E -gas-1 +G co )+(E -sol -E -gas-2 +1.89 (3)

[0027] Among them, E -gas-1 It is the single-point energy of the gas phase at the PWPB95 level, E -sol and E -gas-2 These are the liquid phase single-point energy and gas phase single-point energy at the wB97M-V level, respectively, and the difference between them is the solute's dissolution free energy.

[0028] A further technical solution involves using the Independent gradient model based on Hirshfeld partition (IGMH) method to analyze the complex interactions in step 4, and the Atmos in Molecules (AIM) method to calculate hydrogen bond strength. The analysis software used is the Multiwfn wavefunction analysis program, and the visualization software is VMD. All of these analytical methods use the XXX.molden file. It is necessary to convert the XXX.gbw file containing wavefunction information to the XXX.molden file. Specifically, this is done by entering the command `orca_2mkl XXX-molden` in the file's location.

[0029] In a further technical solution, in step 4, the electron density and energy density parameters of the NH…N type hydrogen bond at the (3, -1) point obtained by AIM analysis represent the hydrogen bond strength; where the (3, -1) point corresponds to the second-order saddle point of the real space function, the function has a positive curvature in one direction and a negative curvature in the other two directions. For the electron density function, it usually appears between two interacting atoms and is also called the bond critical point (BCP).

[0030] In a further technical solution, in step 5, for mixed diamines, the parameters of a single hydrogen bond are used for fitting, and the results are used to predict the reaction energy barriers of other mixed diamines; for mixed triamines, the elementary reaction involves two proton transfers, and the parameters of a weaker hydrogen bond are used for fitting, and the results are used to predict the reaction energy barriers of other mixed triamines and tetraamines.

[0031] The present invention provides a method for designing mixed polyamine CO2 absorbents based on density functional theory. Starting from the perspective of hydrogen bonds, it uses density functional theory combined with wavefunction analysis for calculations. The reactants and products of the proton transfer reaction are calculated, along with the reaction transition state. By extracting the wavefunction information of the reactants, weak interaction analysis and topological analysis of the reactant structure are performed using Multiwfn software. The obtained hydrogen bond strength parameters are fitted with energy barrier data to obtain a fitting formula. This formula can be used to predict the reaction energy barrier from the hydrogen bond strength.

[0032] This invention innovatively proposes a method for predicting the proton transfer reaction energy barrier from the perspective of hydrogen bond strength in the field of amine solution research and development, providing a theoretical basis for the design of mixed amine solutions in experiments and engineering. The advantages of this method are: accurate and reliable calculation results and prediction effects, which can reduce the time and manpower costs consumed in the experimental screening process. Attached Figure Description

[0033] Figure 1The five monoamine molecular structures and proton transfer reaction molecular formulas (in MEAH) selected in Example 1 of this invention are... + COO - (Taking the dominant proton transfer system as an example);

[0034] Figure 2 These are the electronic energy barrier and free energy barrier of the proton reaction in Example 1 of this invention;

[0035] Figure 3 This is a visualization of the IGMH weak interaction analysis of the reactants in Example 1 of this invention (using MEAH). + COO - (Taking the dominant proton transfer system as an example);

[0036] Figure 4 This is a visualization of the (3, -1) distribution of the reactants obtained from AIM analysis in Example 1 of this invention (using MEAH). + COO - (Taking the dominant proton transfer system as an example);

[0037] Figure 5 This is a linear fitting diagram of the electronic energy barrier and hydrogen bond strength parameters in Embodiment 1 of the present invention;

[0038] Figure 6 This is a flowchart of a method for designing mixed polyamine CO2 absorbents based on density functional theory, provided in an embodiment of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0040] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0041] Example 1

[0042] like Figure 1-6 As shown, a method for designing mixed polyamine CO2 absorbents based on density functional theory, as provided in an embodiment of the present invention, includes the following steps:

[0043] 1. Five typical amines—MEA (primary amine), PZ (piperazine), DEA (secondary amine), DEEA (tertiary amine), and AMP (sterically hindered amine)—were selected, and MEAH was constructed using Gaussview 5.0. + COO - -MEA、MEAH + COO - -PZ、MEAH+ COO - -DEA, MEAH + COO - -DEEA、MEAH + COO - -AMP, PZH + COO - -MEA、PZH + COO - -PZ、PZH + COO - -DEA、PZH + COO - -DEEA、PZH + COO - The initial structures of 20 mixed diamines, including AMP, were established, and the product structures were derived based on the optimized initial structures and proton transfer directions. Monoamine structures and reaction diagrams are attached. Figure 1 .

[0044] 2. After building the model, perform structural optimization and frequency calculations. The calculation parameters are set as follows:

[0045] ! B3LYP D3 ma-def2-TZVP(-f RIJCOSX tightopt numfreq tightSCF

[0046] %cpcm

[0047] smd true

[0048] SMD solvent "water"

[0049] end

[0050] *xyz 0 1

[0051] 3. The calculations are performed using ORCA 5.0.3 software, with the server language being Linux.

[0052] 4. After checking that the optimized reactant and product structures have no imaginary frequencies, the structure information files were extracted as inputis.xyz and inputfs.xyz, respectively. Transition state search calculations were performed at the same computational level, with the NEB-TS parameters set as follows:

[0053] ! NEB-TS

[0054] %NEB NEB_END_XYZFILE"inputfs.xyz"END

[0055] *xyzfile 0 1 inputis.xyz

[0056] 5. Check the correctness of the transition state. There is one and only one imaginary frequency. Ensure that the imaginary frequency value is large and that the direction of the imaginary frequency vibration is the direction of proton transfer.

[0057] 6. Under the premise of ensuring correctness, all three optimization results are corrected through free energy, and the implementation process using formula 3) above is as follows:

[0058] Read the free energy correction from the input.out file

[0059] (1) Gas phase single-point energy under high-precision functional PWPB95

[0060] ! PWPB95 D3 def2-TZVPP! def2 / J def2-TZVPP / C RIJCOSX tightSCF

[0061] *XYZ 0 1

[0062] (2) Gas phase free energy under high-precision functional wB97M-V

[0063] ! wB97M-V def2-TZVP def2 / J RIJCOSX strongSCF

[0064] *XYZ 0 1

[0065] (3) Liquid phase free energy under high-precision functional wB97M-V

[0066] ! wB97M-V def2-TZVP def2 / J RIJCOSX strongSCF

[0067] %cpcm

[0068] smd true

[0069] SMD solvent "water"

[0070] end

[0071] *xyz 0 1

[0072] 7. Calculate the electron energy barrier and free energy barrier using the above formulas (1) and (2), and the results are as follows: Figure 2 .

[0073] 8. At the location containing the initial structure wavefunction file before the transition, input orca_2mkl input-molden to obtain the .molden file containing wavefunction information.

[0074] 9. Open the .molden file with Multiwfn and perform IGMH analysis using function 20-11-3 to obtain the weak interactions of the complex. After the calculation, input 6 to get the percentage of atomic pair interactions, and input 3 to obtain the .cube file. Combine this with VMD visualization of the interactions, as shown below. Figure 3 MEAH + COO - Take the dominant proton transfer system as an example.

[0075] 10. Open the .molden file with Multiwfn and perform AIM topology analysis using function 2. Enter 2-2-3-8-0 sequentially, adjust the angle to obtain the point number (3, -1) representing the NH…N type hydrogen bond, and enter 6-number to obtain the electron density value ρ at that point. BCP and energy density E (r) As shown in Table 1 below:

[0076] Table 1. AIM analysis results of reactants

[0077]

[0078]

[0079] 11. The obtained electronic energy barrier value and the parameters obtained from topological analysis are linearly fitted as shown in the attached figure. Figure 5 The correlation coefficients squared were 0.88 and 0.85, respectively, indicating a good fit. The fitting formula can be used to predict the reaction energy barrier of the mixed diamine absorbent.

[0080] The above embodiments of the present invention provide a method for designing mixed polyamine CO2 absorbents based on density functional theory. Starting from the perspective of hydrogen bonds, density functional theory combined with wavefunction analysis is used for calculations. The reactants and products of the proton transfer reaction are calculated, and the reaction transition state is also calculated. By extracting the wavefunction information of the reactants, weak interaction analysis and topological analysis of the reactant structure are performed using Multiwfn software. The obtained hydrogen bond strength parameters are fitted with energy barrier data to obtain a fitting formula. This formula can be used to predict the reaction energy barrier from the hydrogen bond strength.

[0081] This invention innovatively proposes a method for predicting the proton transfer reaction energy barrier from the perspective of hydrogen bond strength in the field of amine solution research and development, providing a theoretical basis for the design of mixed amine solutions in experiments and engineering. The advantages of this method are: accurate and reliable calculation results and prediction effects, which can reduce the time and manpower costs consumed in the experimental screening process.

[0082] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for designing mixed polyamine CO2 absorbents based on density functional theory, characterized in that, Includes the following steps: Step 1: Selection of Monoamines Based on the requirements, amines with different advantages are selected as research objects, and their molecular monomers and unstable intermediate products after CO2 absorption are optimized. Step 2, Structural Optimization Based on the implicit solvation model and combined with the proton transfer direction, the complex structure before and after proton transfer was established and optimized, and frequency analysis was performed. Step 3: Transition state calculation The transition state of the proton transfer process is calculated at the same computational level to obtain the electronic energy barrier. The solute free energy in the solvent is corrected under high-precision functional theory to obtain the free energy barrier. Step 4: Hydrogen bond calculation Using a wavefunction analysis program, based on the structure and wavefunction file of the pre-transfer complex obtained in step 1, the interaction strength and hydrogen bond strength parameters are calculated. Step 5: Data Statistics and Energy Barrier Prediction Linear fitting of energy barrier data and hydrogen bond strength parameters revealed an excellent correlation, proving that hydrogen bond strength can be used to predict reaction energy barriers. In step 3, the transition state is calculated using the NEB-TS method. The verification method for whether the transition state is correct is: the frequency analysis result has one and only one imaginary frequency, and the direction of the imaginary frequency vibration is connected to the reactant and the product. The electronic energy barrier was obtained through transition state calculations. E b Characterizing reaction rate, E b Calculations are performed using Formula 1: （1） in, E TS The transition state energy, E IS Energy of reactants; The free energy barrier is obtained through transition state calculation. G b Characterizing the ease with which a reaction occurs, G b Calculations are performed using Formula 2: （2） in, G TS For the transition state free energy, G IS The free energy of the reactants; Under solvation conditions, the free energy of the solute needs to be corrected. Specifically, the corrected free energy in the liquid phase after structure optimization in step 1 is obtained first. G co Then, the gas-phase single-point energy of the structure was obtained at the PWPB95 D3 def2-TZVPP level, and the single-point energies in the liquid and gas phases of the structure were obtained at the wB97M-V def2-TZVP level, respectively. The corrected free energy G was calculated using Equation 3. （3） in, E -gas-1 This is the gas-phase single-point energy at the PWPB95 level. E -sol and E -gas-2 These are the liquid phase single-point energy and gas phase single-point energy at the wB97M-V level, respectively, and the difference between them is the solute's dissolution free energy.

2. The method for designing mixed polyamine CO2 absorbents based on density functional theory as described in claim 1, characterized in that, In steps 1 and 2, the structure optimization uses B3LYP functionals combined with ma-def2-TZVP to calculate the basis set and DFT-D3 dispersion correction, and performs frequency calculations on the optimized structure to detect whether there are imaginary frequencies. If imaginary frequencies are present, the structure needs to be re-optimized. Since there are obvious weak interactions and anions in the system, the basis set needs to introduce a dispersion function. The complex configuration was constructed using Gaussview 5.0, and structural optimization, frequency analysis, and subsequent single-point energy calculations were performed using ORCA 5.0.3 software. The implicit solvation model uses SMD to simulate a system in a solvent environment.

3. The method for designing mixed polyamine CO2 absorbents based on density functional theory as described in claim 1, characterized in that, In step 4, the interaction of the complex was analyzed using the Independent gradient model based on Hirshfeldpartition method, the hydrogen bond strength was calculated using the Atmos in Molecules method, the analysis software was Multiwfn wavefunction analysis program, and the visualization software was VMD. The above analysis methods all use the XXX.molden file. It is necessary to convert the XXX.gbw file containing wavefunction information into the XXX.molden file. The specific operation is to enter the command orca_2mkl XXX -molden in the file location.

4. The method for designing mixed polyamine CO2 absorbents based on density functional theory as described in claim 3, characterized in that, In step 4, the electron density and energy density values ​​of the NH…N type hydrogen bonds obtained by AIM analysis represent the hydrogen bond strength. The point (3, -1) corresponds to the second-order saddle point of the real space function. The function has positive curvature in one direction and negative curvature in the other two directions. For the electron density function, it usually appears between two interacting atoms and is also called the bond critical point.

5. The method for designing mixed polyamine CO2 absorbents based on density functional theory as described in claim 1, characterized in that, In step 5, for mixed diamines, the parameters of the unique hydrogen bond are fitted, and the results are used to predict the reaction energy barriers of other mixed diamines. For mixed triamines, the elementary reaction involves two proton transfers. We use parameters with weaker hydrogen bonds to fit the reaction and use the results to predict the reaction energy barriers of other mixed triamines and tetraamines.

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