A thermodynamic model for predicting thermodynamic properties of salt solvent systems

Abstract

The present application belongs to the field of chemical thermodynamics, and particularly relates to a thermodynamic model for predicting the thermodynamic properties of a salt-solvent system. The model first obtains the coordination number n of cations and anions in the salt-solvent system through molecular dynamics simulation, then obtains the initial configuration of the cation-n solvent molecule-anion through configuration optimization, and obtains the most stable structure through quantum chemistry calculation program optimization, and finally obtains the VLE (vapor-liquid equilibrium) data prediction value of the salt-solvent system based on the COSMO-RS theory. The model can obtain the prediction value with high accuracy without experiment, thereby saving a large amount of manpower, material resources and financial resources. Meanwhile, the present application also discloses the phenomenon that the salt in the salt-solvent system is volatile.

Description

Technical Field

[0001] This invention belongs to the field of chemical thermodynamic models, specifically relating to a thermodynamic model for predicting the thermodynamic properties of salt solvent systems. Background Technology

[0002] In industry, extractive distillation is widely used to separate azeotropic or near-boiling point mixtures. During extractive distillation, an additive is added to the original solution to increase the relative volatility between two or more components, thus facilitating the separation of the feedstock. This additive is called the extractant or solvent. Salt-added extractive distillation is a special type of extractive distillation method that involves adding a soluble salt to the extractant or solvent. To enhance the distillation process, fundamental research primarily focuses on obtaining phase equilibrium data during distillation. Therefore, the study of vapor-liquid phase equilibrium (VLE) data for the salt-solvent system in salt-added extractive distillation is of significant industrial importance.

[0003] In existing studies of salt-solvent systems, salt is typically treated as a non-volatile component. Early thermodynamic studies often employed quasi-binary models, treating solvent 1-salt as one component and solvent 2 as another, or solvent 1-salt and solvent 2-salt as separate components. Later researchers considered the dissociation of salt, applying local composition models to the thermodynamics of salt-solvent systems. The electrolyte NRTL equation, UNIQUAC equation, extended UNIFAC equation, and mean sphere approximation theory have all been used in vapor-liquid equilibrium studies of salt-solvent systems. However, all of these studies only considered the influence of salt on other solvents in the system, without addressing the effect of solvents on the added salt.

[0004] The most fundamental salt solvent system is the electrolyte solution system formed by salt and water. Electrolyte solution theory has a long history of development and has formed a relatively complete theoretical framework. The initial theory of strong electrolyte solutions assumed that ions were charged hard spheres, considering only the Coulomb forces between ions and treating water as a continuous medium. Later, the ion hydration theory proposed that water molecules in electrolyte solutions not only exist as a continuous medium but also interact with cations and anions to form hydrated ions; that is, ions do not exist in isolation but form clusters with surrounding water molecules. On the other hand, with the widespread use of computers, computer molecular simulation methods have gradually become a parallel approach to theoretical research. Molecular dynamics simulations of electrolyte solutions show that the introduction of cations and anions disrupts the hydrogen bond structure between water molecules. Radial distribution functions show that both cations and anions first contact with water to form a hydration layer, thus verifying the ion hydration theory. All of the above studies demonstrate that in the microstructure of electrolyte solutions, cations are initially surrounded by water molecules, and anions are surrounding the water molecules.

[0005] Furthermore, the conductor-like screening model (COSMO), proposed by Klamt, is a continuous medium solvation model used to calculate the thermodynamic properties of condensed matter, particularly the liquid phase. Klamt later developed the conductor-like screening model for real solvents (COSMO-RS), which places the solute and solvent on an equal footing in quantum chemistry and statistical mechanics. This model can be widely applied to predicting the thermodynamic properties of matter, and it does not require extensive experimental data, relying solely on quantum chemistry software (TurboChem Gaussian or DMOL3).

[0006] This invention proposes that solvent molecules in salt solvent systems form clusters with anions and cations due to weak interactions, and these clusters then enter the gas phase as a whole during the extractive distillation phase transition, contrary to the assumption in existing studies that salt is completely non-volatile. Therefore, to verify that salt is volatile and to predict the VLE (volatile organic compound) data of salt solvent systems, it is necessary to construct a molecular thermodynamic model that can predict the thermodynamic properties of salt solvent systems. Summary of the Invention

[0007] In view of the problems and shortcomings of the existing technology, the purpose of this invention is to provide a thermodynamic model for predicting the thermodynamic properties of salt solvent systems.

[0008] To achieve the objectives of this invention, the technical solution adopted is as follows:

[0009] The first aspect of this invention provides a method for constructing a model to predict the thermodynamic properties of a salt solvent system, comprising the following steps:

[0010] (1) Using molecular dynamics simulation, the radial distribution function of cations and anions and solvent molecules in the salt solvent system is obtained, and the coordination number of cations and anions is calculated; the salt solvent system is composed of ionic compounds and solvents;

[0011] (2) Take the coordination number of the cation and anion determined in step (1) as an integer n, construct the initial configuration of cation-n solvent molecule-anion, optimize the structure and calculate the energy of the initial configuration through quantum chemical calculation program, determine the structure with the lowest energy, and perform geometric optimization of the molecular conformation of the structure to form a COSMO file;

[0012] (3) The COSMO file obtained in step (2) is used to predict the gas-liquid phase data of the two-component system of cation-n solvent molecule-anion and solvent molecule at the corresponding temperature using the COSMO-RS model.

[0013] Based on the above construction method, further, the method for calculating the coordination number of anions and cations in step (1) is as follows: substitute the radial distribution function into equation (1) to calculate the coordination number of anions and cations in the salt solvent system;

[0014]

[0015] In formula (1) g ij (r) represents the radial distribution function, ρ j The number density is represented by r, which represents the distance from the central atom.

[0016] Based on the above construction method, the process of obtaining the radial distribution function in step (1) is as follows: using molecular dynamics simulation, first determine the number of ions and solvent molecules based on salt solvent systems of different concentrations, then construct a model based on the density of the salt solvent system and optimize the energy of the model, and finally perform dynamic calculations to obtain the radial distribution function.

[0017] According to the above construction method, further, the method of optimizing the structure and calculating the energy of the initial configuration by the quantum chemical calculation program in step (2) is as follows: the initial configuration is optimized at the PM6-DH+ level using the MOPAC2016 program, and the energy of the initial configuration is calculated by applying electron density functional theory using Gaussian09 software to determine the structure with the lowest energy.

[0018] Based on the above construction method, further, the specific method for the quantum chemical calculation program in step (2) to perform structural optimization and energy calculation on the initial configuration is as follows: the initial configuration is pre-optimized at the PM6-DH+ level using the MOPAC2016 program, and then the lowest energy configuration is further optimized by applying electron density functional theory with medium basis sets (specific meaning) using Gaussian09 software. Finally, the energy of the lowest energy configuration is accurately calculated by combining electron density functional theory with high-precision basis sets (specific meaning) to determine the lowest energy structure.

[0019] A second aspect of the present invention provides a model for predicting the thermodynamic properties of a salt solvent system constructed by the above method.

[0020] A third aspect of the present invention provides an application of the model described in the second aspect in predicting the thermodynamic properties of salt solvent systems.

[0021] Based on the above application, the application further refers to the application of molecular thermodynamic models in predicting gas-liquid phase data of salt solvent systems.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) This invention provides a thermodynamic model for predicting vapor-liquid phase equilibrium data of a salt solvent system and its construction method. The thermodynamic model can predict the composition of the vapor and liquid phases of the salt solvent system in actual phase change with relatively high accuracy, especially the thermodynamic properties of the salt solvent system at low concentrations, which has guiding significance for process design such as purification of electronic-grade chemicals.

[0024] (2) In existing studies on salt extraction distillation, salt is generally considered to be completely non-volatile. However, this invention reveals that salt is volatile in the salt solvent system of salt extraction distillation. In the salt solvent system, solvent molecules and anions and cations form cluster structures due to weak interactions. Then, during the phase transition, the clusters enter the gas phase as a whole, thus verifying the fact that salt is volatile in the salt solvent system.

[0025] (3) The molecular thermodynamic model provided by the present invention can not only predict the thermodynamic properties of salt solvent systems more accurately, but also saves a lot of human, material and financial resources by not requiring experiments. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the calculation process for constructing the thermodynamic model of this invention.

[0027] Figure 2 Lithium chloride solutions of different concentrations + -Ow (radial distribution function of lithium ions and oxygen atoms in water molecules);

[0028] Figure 3 Cl in lithium chloride solutions of different concentrations - -Hw (radial distribution function of chloride ions and hydrogen atoms in water molecules);

[0029] Figure 4 The graph shows the y-x values ​​of lithium chloride, sodium chloride, and potassium chloride solutions at 100℃. The horizontal axis represents the molar content of the three electrolytes in the liquid phase, and the vertical axis represents the molar content of the three electrolytes in the gas phase. ○ corresponds to the experimental value of lithium chloride, the solid black line corresponds to the predicted value of lithium chloride, ▽ corresponds to the experimental value of sodium chloride, the dashed black line corresponds to the predicted value of sodium chloride, ◇ corresponds to the experimental value of potassium chloride, and the dotted black line corresponds to the predicted value of potassium chloride.

[0030] Figure 5 Na+ in sodium chloride solutions of different concentrations + -Ow (radial distribution function of sodium ions and oxygen atoms in water molecules);

[0031] Figure 6 Cl in sodium chloride solutions of different concentrations - -Hw (radial distribution function of chloride ions and hydrogen atoms in water molecules);

[0032] Figure 7 Kc for potassium chloride solutions of different concentrations + -Ow (radial distribution function of potassium ions and oxygen atoms in water molecules);

[0033] Figure 8 Cl in potassium chloride solutions of different concentrations - -Hw (radial distribution function of chloride ions and hydrogen atoms in water molecules);

[0034] Figure 9 The radial distribution function is given for a lithium chloride electrolyte solution with a molar fraction of 4.51%, where the black dotted line corresponds to Na. + -Ow (radial distribution function of sodium ions and oxygen atoms in water molecules), with the black underline representing Cl. - -Hw (radial distribution function of chloride ions and hydrogen atoms in water molecules), the black solid line represents Li + -Cl - The radial distribution function;

[0035] Figure 10 The radial distribution function is given for a sodium chloride electrolyte solution with a molar fraction of 3.31%, where the black dotted line corresponds to Na. + -Ow (radial distribution function of sodium ions and oxygen atoms in water molecules), with the black underline representing Cl. - -Hw (radial distribution function of chloride ions and hydrogen atoms in water molecules), the black solid line represents Na + -Cl - The radial distribution function;

[0036] Figure 11 The radial distribution function is given for a potassium chloride electrolyte solution with a molar fraction of 2.62%, where the black dotted line corresponds to Na. + -Ow (radial distribution function of sodium ions and oxygen atoms in water molecules), with the black underline representing Cl. - -Hw (radial distribution function of chloride ions and hydrogen atoms in water molecules), the black solid line represents K. + -Cl - The radial distribution function. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0038] Example 1

[0039] A thermodynamic model for predicting the thermodynamic properties of salt solvent systems is constructed, and its calculation flowchart is shown below. Figure 1 As shown, the specific method includes the following steps:

[0040] (1) In this embodiment, a lithium chloride (LiCl) and water (H2O) system was selected, and molecular dynamics simulations were performed using Materials Studio. First, the number of ions and water molecules was determined based on different initial molar fractions of LiCl aqueous solutions (lithium chloride molar fractions of 2.19%, 3.33%, 4.51%, 5.72%, 6.98%, 8.27%, and 9.60%, respectively). The box volume was determined based on the solution density to create the box. Energy optimization was performed on the constructed solution model, and then kinetic calculations were conducted to obtain the radial distribution function. The radial distribution functions corresponding to different initial concentrations of lithium chloride solutions are shown in [reference needed]. Figure 2 , Figure 3 . Figure 2 The graph shows the radial distribution function of Li-Ow (lithium ions and oxygen atoms in water molecules) in lithium chloride solutions with different initial molar fractions. Figure 3 The radial distribution function of Cl-Hw (chloride ions and hydrogen atoms in water molecules) in lithium chloride solutions with different initial molar fractions is shown.

[0041] Substitute the radial distribution function obtained in step (1) into equation (1) to calculate the coordination number of the anions and cations in the lithium chloride solution.

[0042]

[0043] In formula (1) g ij (r) represents the radial distribution function, ρ j The number density is represented; the coordination numbers of anions and cations in lithium chloride solutions with different initial concentrations are shown in Table 1:

[0044] Table 1. Coordination numbers of anions and cations in lithium chloride solutions with different initial mole fractions.

[0045] Initial molar fraction of lithium chloride (%) 2.19 3.33 4.51 5.72 6.98 8.27 9.60 <![CDATA[Li + Coordination number]]> 4.28 4.19 4.06 4.03 3.98 3.95 3.90 <![CDATA[Cl - Coordination number]]> 6.35 6.33 6.29 6.25 6.23 6.21 6.13

[0046] As can be seen from Table 1, the initial concentration of lithium chloride solution has a certain influence on the coordination number of anions and cations, but the influence is not significant.

[0047] (2) Considering the coordination numbers of lithium ions and chloride ions, and also taking into account the situation where lithium ions and chloride ions share water molecules, a coordination number of 5, which is relatively close to the coordination numbers of the anions and cations, was selected. 500 Li ions were then generated using the Genmer program. + -5H2O-Cl - Initial configurations were pre-optimized at the PM6-DH+ level using the MOPAC2016 program. Then, density functional theory (DFT) was applied using Gaussian09 software, combined with an intermediate basis set (B3LYP / 6-311G). *The ten lowest energy configurations were further optimized, and finally the energies of these configurations were accurately calculated using DFT combined with high-precision basis sets (B3LYP / ma-TZVP) to select the most stable molecular configuration. The most stable configuration was then used to generate a cosmo file in cosmotherm.

[0048] (3) Predicting Li in cosmotherm software + -5H2O-Cl - VLE data of the H2O two-component system at 100℃; Li in the gas phase was obtained. + -5H2O-Cl - The content of LiCl is then used to calculate the predicted value of LiCl content in the gas phase. The predicted value curve for this embodiment is shown in [reference needed]. Figure 4 , Figure 4 The horizontal axis represents the mole fraction of lithium chloride in the liquid phase, and the vertical axis represents the mole fraction of lithium chloride in the gas phase. ○ represents the experimental value of lithium chloride, and the black solid line represents the predicted value of lithium chloride.

[0049] To verify the accuracy of the thermodynamic model predictions in this embodiment, LiCl aqueous solutions with lithium chloride molar fractions of 2.19%, 3.33%, 4.51%, 5.72%, 6.98%, 8.27%, and 9.60% were prepared. After distillation, the reflux liquid was collected and analyzed for Li content using inductively coupled plasma optical emission spectrometry (ICP-OES). + The content is then obtained, and the LiCl content in the gas phase is obtained. The specific values ​​are shown in Table 2, and the specific values ​​are compared with the predicted values ​​obtained in step (3) of this embodiment.

[0050] Table 2. Experimental and predicted values ​​of LiCl content in the gas phase at different concentrations.

[0051] Initial mole fraction of LiCl (%) 2.19 3.33 4.51 5.72 6.98 8.27 9.60 <![CDATA[Experimental value (×10 -6 / ppm)]]> 15.57 23.88 37.89 47.76 62.03 76.31 92.14 <![CDATA[Predicted value (×10 -6 / ppm)]]> 14.19 24.95 37.75 54.13 74.47 102.97 147.87

[0052] from Figure 4 As shown in Table 2, the prediction results of the ion solution distillation predictive molecular thermodynamic model constructed in this invention have high accuracy in the low concentration range (i.e., the molar fraction of lithium chloride in the liquid phase is less than 0.06), while the prediction results in the high concentration range (i.e., the molar fraction of lithium chloride in the liquid phase is 0.06-0.1) deviate from the experimental results. Simultaneously, the microstructure of the electrolyte solution also changes to some extent. This is because at higher ion concentrations, associated ion pairs form in the electrolyte solution, rather than only Li... + -5H2O-Cl - .

[0053] Example 2

[0054] A thermodynamic model for predicting the thermodynamic properties of salt solvent systems is constructed, and its calculation flowchart is shown below. Figure 1 As shown, the specific method includes the following steps:

[0055] (1) In this embodiment, a sodium chloride (NaCl) and water (H2O) system was selected, and molecular dynamics simulations were performed using Materials Studio. First, the number of ions and water molecules was determined based on different initial molar fractions of NaCl aqueous solutions (1.6%, 2.44%, 3.31%, 4.22%, 5.16%, 6.14%, 7.16%). The box volume was determined based on the solution density to create the box. Energy optimization was performed on the constructed solution model, and then dynamic calculations were conducted to obtain the radial distribution function. The radial distribution functions corresponding to different initial molar fractions of sodium chloride solutions are shown in [reference needed]. Figure 5 and Figure 6 , Figure 5 The plot shows the radial distribution function of Na-Ow (sodium ions and oxygen atoms in water molecules) in sodium chloride solutions with different initial mole fractions. Figure 6 The radial distribution function of Cl-Hw (chloride ions and hydrogen atoms in water molecules) in sodium chloride solutions with different initial molar fractions is shown.

[0056] Then, calculate the coordination number of anions and cations in the sodium chloride solution according to formula (1). The coordination number results of anions and cations in sodium chloride solutions with different initial concentrations are shown in Table 3.

[0057]

[0058] In formula (1) g ij (r) represents the radial distribution function, ρ j Represents number density.

[0059] Table 3. Coordination numbers of anions and cations in sodium chloride solutions with different initial concentrations.

[0060] Initial mole fraction of sodium chloride (%) 1.60 2.44 3.31 4.22 5.16 6.14 7.16 <![CDATA[Na + Coordination number]]> 5.40 5.38 5.36 5.21 5.18 5.11 5.06 <![CDATA[Cl - Coordination number]]> 6.32 6.28 6.25 6.23 6.19 6.12 6.07

[0061] As can be seen from Table 3, the initial concentration of sodium chloride solution has a certain influence on the coordination number of anions and cations, but the influence is not significant.

[0062] (2) Considering the coordination numbers of sodium and chloride ions, and also taking into account the situation where sodium and chloride ions share water molecules, a coordination number of 6 was chosen. Using the genmer program, 500 Na+ ions were generated. + -6H2O-Cl -Initial configurations were pre-optimized at the PM6-DH+ level using the MOPAC2016 program. Then, the ten lowest-energy configurations were further optimized using Gaussian09 software with electron density functional theory (DFT) and intermediate basis sets. Finally, the energies of these configurations were accurately calculated using DFT combined with high-precision basis sets to select the most stable molecular configuration. The most stable configuration was then used to generate a cosmo file in cosmotherm.

[0063] (3) Predicting Na in cosmotherm software + -6H2O-Cl - VLE data for the H2O binary system at 100℃; Na in the gas phase was obtained. + -6H2O-Cl - The content of NaCl in the gas phase is then used to calculate the predicted value of NaCl content. The predicted value curve can be found in [reference needed]. Figure 4 , Figure 4 The horizontal axis represents the molar content of sodium chloride in the liquid phase, the vertical axis represents the molar content of sodium chloride in the gas phase, ▽ represents the experimental value of sodium chloride, and the black line represents the predicted value of sodium chloride.

[0064] To verify the accuracy of the thermodynamic model predictions in this embodiment, NaCl aqueous solutions with sodium chloride molar fractions of 1.60%, 2.44%, 3.31%, 4.22%, 5.16%, 6.14%, and 7.16% were prepared. After distillation, the reflux liquid was collected and analyzed for Na+ content using inductively coupled plasma optical emission spectrometry (ICP-OES). + The content of NaCl in the gas phase is obtained by measuring the content of NaCl in the gas phase. The specific values ​​are shown in Table 4, and the specific values ​​are compared with the predicted values ​​obtained in step (3) in Table 4.

[0065] Table 4. Experimental and predicted values ​​of NaCl content in the gas phase at different concentrations.

[0066] Initial mole fraction of NaCl (%) 1.60 2.44 3.31 4.22 5.16 6.14 7.16 <![CDATA[Experimental value (×10 -6 / ppm)]]> 3.53 5.70 9.01 12.78 16.30 20.06 23.70 <![CDATA[Predicted value (×10 -6 / ppm)]]> 3.22 5.31 9.01 12.05 17.02 24.41 34.20

[0067] from Figure 4 As can be seen from Table 4, the prediction results of the ion solution distillation predictive molecular thermodynamic model constructed in this invention have high accuracy in the low concentration range (i.e., the molar content of lithium chloride in the liquid phase is less than 0.06), while the prediction results in the high concentration range (i.e., the molar content of lithium chloride in the liquid phase is 0.06-0.1) deviate from the experimental results.

[0068] Example 3

[0069] A thermodynamic model for predicting the thermodynamic properties of salt solvent systems is constructed, and its calculation flowchart is shown below. Figure 1 As shown, the specific method includes the following steps:

[0070] (1) In this embodiment, a potassium chloride (KCl) and water (H2O) system was selected, and molecular dynamics simulations were performed using Materials Studio. First, the number of ions and water molecules was determined based on different initial molar fractions of KCl aqueous solutions (1.26%, 1.92%, 2.62%, 3.33%, 4.09%, 4.88%, 5.70%). The box volume was determined based on the solution density to create the box. Energy optimization was performed on the constructed solution model, and then kinetic calculations were conducted to obtain the radial distribution function. The radial distribution functions corresponding to different initial molar fractions of potassium chloride solutions are shown in [reference needed]. Figure 7 and Figure 8 , Figure 7 For potassium chloride solutions with different initial mole fractions, K + Radial distribution function plot of -Ow (potassium ions and oxygen atoms in water molecules) Figure 8 The radial distribution function of Cl-Hw (chloride ions and hydrogen atoms in water molecules) in potassium chloride solutions with different initial molar fractions is shown.

[0071] Then, calculate the coordination number of anions and cations in the potassium chloride solution according to formula (1). The coordination number results of anions and cations in potassium chloride solutions with different initial concentrations are shown in Table 5.

[0072]

[0073] In formula (1) g ij (r) represents the radial distribution function, ρ j Represents number density.

[0074] Table 5. Coordination numbers of anions and cations in potassium chloride solutions with different initial concentrations.

[0075] Initial mole fraction of KCl (%) 1.26 1.92 2.62 3.33 4.09 4.88 5.70 <![CDATA[K + Coordination number]]> 6.32 6.22 6.20 6.19 6.13 6.07 5.91 <![CDATA[Cl - Coordination number]]> 6.48 6.43 6.36 6.34 6.31 6.28 6.11

[0076] As can be seen from Table 5, the initial concentration of potassium chloride solution has a certain influence on the coordination number of anions and cations, but the influence is not significant.

[0077] (2) Considering the coordination number of potassium and chloride ions, and also taking into account the situation where potassium and chloride ions share water molecules, a coordination number of 6 was selected. 500 K+ molecules were then generated using the genmer program. + -6H2O-Cl -Initial configurations were pre-optimized at the PM6-DH+ level using the MOPAC2016 program. Then, the ten lowest-energy configurations were further optimized using Gaussian09 software with electron density functional theory (DFT) and intermediate basis sets. Finally, the energies of these configurations were accurately calculated using DFT combined with high-precision basis sets to select the most stable molecular configuration. The most stable configuration was then used to generate a cosmo file in cosmotherm.

[0078] (3) Predicting K in cosmotherm software + -6H2O-Cl - VLE data for the H2O binary system at 100℃; Na in the gas phase was obtained. + -6H2O-Cl - The content of NaCl in the gas phase is then used to calculate the predicted value of NaCl content. The predicted value curve can be found in [reference needed]. Figure 4 , Figure 4 The ◇ in the center corresponds to the experimental value of potassium chloride, and the black dotted line corresponds to the predicted value of potassium chloride.

[0079] To verify the accuracy of the thermodynamic model predictions in this embodiment, KCl aqueous solutions with potassium chloride molar fractions of 1.26%, 1.92%, 2.62%, 3.33%, 4.09%, 4.88%, and 5.70% were prepared. After distillation, the reflux liquid was collected and analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the potassium content. + The KCl content in the gas phase is obtained by measuring the KCl content. The specific values ​​are shown in Table 6, and the specific values ​​are compared with the predicted values ​​obtained in step (3) in Table 6.

[0080] Table 6. Experimental and predicted values ​​of KCl content in the gas phase at different concentrations.

[0081] Initial mole fraction of KCl (%) 1.26 1.92 2.62 3.33 4.09 4.88 5.70 <![CDATA[Experimental value (×10 -6 / ppm)]]> 2.19 3.20 4.75 6.27 8.11 9.77 11.52 <![CDATA[Predicted value (×10 -6 / ppm)]]> 1.85 2.95 4.35 5.80 7.57 10.02 12.58

[0082] from Figure 4 As can be seen from Table 6, the prediction results of the ion solution distillation predictive molecular thermodynamic model constructed in this invention have high accuracy in the low concentration range (i.e., the molar content of lithium chloride in the liquid phase is less than 0.06), while the prediction results in the high concentration range (i.e., the molar content of lithium chloride in the liquid phase is 0.06-0.1) deviate from the experimental results.

[0083] The radial distribution functions of the lithium chloride electrolyte solution with a molar fraction of 4.51% in Example 1, the sodium chloride electrolyte solution with a molar fraction of 3.31% in Example 2, and the potassium chloride electrolyte solution with a molar fraction of 2.62% in Example 3 were calculated to be as follows: Figure 9 , Figure 10 and Figure 11 .from Figure 9 , Figure 10 and Figure 11 As can be seen, the microstructure of sodium chloride, lithium chloride, and potassium chloride solutions consists of cations that first come into contact with water, while anions are present outside the water.

[0084] The above examples and results demonstrate that the predictive molecular thermodynamic model established in this invention can effectively predict the thermodynamic properties of salt solvent systems at low concentrations, providing guidance for process design in areas such as the purification of electronic-grade chemicals. It also shows that solvent molecules and cations / anions in salt solvent systems form clusters due to weak interactions, and these clusters then enter the gas phase as a whole during phase transitions, thus verifying that salt in salt solvent systems is volatile, rather than completely non-volatile. On the other hand, while accurate VLE data can be obtained experimentally, it consumes significant human and material resources, and phase equilibrium experiments under many extreme conditions cannot be performed. This invention provides a method that saves considerable resources while accurately predicting the thermodynamic properties of salt solvent systems, which is precisely its significance.

[0085] The above embodiments are specific implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any other combination, change, modification, substitution, or simplification that does not exceed the design concept of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for constructing a molecular thermodynamic model for predicting the thermodynamic properties of a salt solvent system, characterized in that, Includes the following steps: (1) Using molecular dynamics simulation, the radial distribution function of cations and anions and solvent molecules in the salt solvent system is obtained, and the coordination number of cations and anions is calculated. (2) Take the coordination number of the cation and anion determined in step (1) as an integer n, construct the initial configuration of cation-n solvent molecule-anion, optimize the structure and calculate the energy of the initial configuration through quantum chemical calculation program, determine the structure with the lowest energy, and perform geometric optimization of the molecular conformation of the structure to form a COSMO file; (3) The COSMO file obtained in step (2) is used to predict the gas-liquid phase data of the two-component system of cation-n solvent molecule-anion and solvent molecule at the corresponding temperature using the COSMO-RS model; The method for optimizing the structure and calculating the energy of the initial configuration in step (2) is as follows: the initial configuration is optimized at the PM6-DH+ level using the MOPAC2016 program, and the energy of the initial configuration is calculated using the Gaussian09 software with electron density functional theory to determine the structure with the lowest energy.

2. The construction method according to claim 1, characterized in that, The method for calculating the coordination number of anions and cations in step (1) is as follows: Substitute the radial distribution function into equation (1) to calculate the coordination number of anions and cations in the salt solvent system; g in formula (1) ij (r) denotes the radial distribution function, p j denotes the number density, r denotes the distance from the central atom.

3. The construction method according to claim 2, characterized in that, The process of obtaining the radial distribution function in step (1) is as follows: using molecular dynamics simulation, first determine the number of ions and solvent molecules based on salt solvent systems of different concentrations, then construct a solution model based on the density of the salt solvent system and perform energy optimization on the solution model, and finally perform dynamic calculations to obtain the radial distribution function.

4. The construction method according to claim 1, characterized in that, The specific method for the quantum chemical calculation program in step (2) to perform structural optimization and energy calculation on the initial configuration is as follows: the initial configuration is pre-optimized at the PM6-DH+ level using the MOPAC2016 program, and then the lowest energy configuration is further optimized by applying electron density functional theory with medium basis sets using Gaussian09 software. Finally, the energy of the lowest energy configuration is accurately calculated using electron density functional theory with high-precision basis sets to determine the lowest energy structure.

5. A molecular thermodynamic model for predicting the thermodynamic properties of a salt solvent system constructed using the method described in any one of claims 1-4.

6. The application of the molecular thermodynamic model of claim 5 in predicting the thermodynamic properties of salt solvent systems.

7. The application according to claim 6, characterized in that, The application described is the use of molecular thermodynamic models to predict gas-liquid phase data in salt solvent systems.

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