Thermodynamic model for predicting thermodynamic properties of inorganic salt-ethyl lactate solution system

Abstract

The invention belongs to the technical field of physicochemical and chemical thermodynamic models, and particularly relates to a thermodynamic model for predicting thermodynamic properties of an inorganic salt-ethyl lactate solution system. According to the method, based on the existence form of salt in a solution, it is assumed that inorganic salt exists in the form of cation-anion-ethyl lactate clusters, and the clusters are constructed and defined through quantitative calculation and serve as new substance components to be introduced into a thermodynamic model. The binary system formed by the new component and ethyl lactate is subjected to gas-liquid equilibrium prediction by using a COSMO-SAC model, and an accurate result can be obtained under the condition that a large amount of experimental data is not needed. According to the method, the research cost and the experiment difficulty are remarkably reduced, the volatility rule of the salt in the ethyl lactate system is disclosed, and a theoretical basis and a calculation tool are provided for separation mechanism research and process design of a salt-containing organic solution system.

Description

Technical Field

[0001] This invention belongs to the field of physical chemistry and chemical engineering thermodynamic modeling technology, specifically relating to a thermodynamic model for predicting the thermodynamic properties of an inorganic salt-ethyl lactate solution system. Background Technology

[0002] Ethyl lactate, as an important green solvent and fine chemical intermediate, is widely used in the preparation of high-purity chemicals, biomass resource utilization, and wet electronic chemical production. In actual production and application processes, ethyl lactate often coexists with inorganic salts, and its gas-liquid equilibrium behavior and thermodynamic properties are of great significance for the design and optimization of separation and purification processes.

[0003] Existing gas-liquid equilibrium predictions are mainly based on empirical correlations or molecular thermodynamic models, such as NRTL, UNIQUAC, and COSMO-SAC. These methods have achieved good results in organic-organic systems, but they have significant shortcomings when dealing with inorganic salt-organic solvent systems. The main problems are: 1. Insufficient handling of salt effects: Traditional models often simplify inorganic salts to electrolyte ions, failing to accurately describe the specific interactions between ions and organic molecules; 2. Lack of volatility prediction capability: Existing models generally assume that inorganic salts do not enter the gas phase, making it difficult to explain the volatility of some inorganic salts or their clusters in organic solvents; 3. Strong experimental dependence: Most methods require a large amount of experimental data for parameter fitting, lacking feasibility in high-purity solvents or under special operating conditions.

[0004] Therefore, there is an urgent need for a new thermodynamic modeling method that can reasonably describe the existence of inorganic salts in ethyl lactate at the molecular level, predict their possible cluster chemical species and their effects on the gas-liquid equilibrium and thermodynamic properties of the system, thereby overcoming the limitations of traditional salt effect theories and models. Summary of the Invention

[0005] 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 inorganic salt-ethyl lactate solution system.

[0006] To achieve the objectives of this invention, the technical solution adopted is as follows:

[0007] The first aspect of this invention provides a method for constructing a thermodynamic model to predict the thermodynamic properties of an inorganic salt-ethyl lactate solution system, comprising the following steps:

[0008] (1) Assuming that the inorganic salt exists in the form of cation-anion-ethyl lactate clusters, the initial configuration of the clusters is constructed by molecular dynamics simulation, the initial configuration is optimized, and the most stable cluster is selected.

[0009] (2) Obtain the surface charge density distribution of the clusters in step (1) and import it into the COSMO-SAC model. Combine it with ethyl lactate to form a binary system and calculate and predict the gas-liquid equilibrium composition of the inorganic salt-ethyl lactate system.

[0010] Preferably, the specific process of calculating and predicting the gas-liquid equilibrium composition of the inorganic salt-ethyl lactate system in step (2) is as follows:

[0011] Based on the COSMO-SAC model, the gas-liquid equilibrium relationship of the binary system composed of clusters and ethyl lactate at 101.325 kPa was predicted, and the mole fractions of the clusters in the liquid and gas phases were obtained, denoted as x. new and y new ;

[0012] mole fraction of inorganic salts in liquid phase x s The calculation is performed using the following formula:

[0013]

[0014] Where n s =n new n 2EL =n 1EL +ɑn new In the formula, n s n is the molar amount of the inorganic salt in the liquid phase. new n is the molar amount of the cluster in the liquid phase. 1EL The molar amount of ethyl lactate in the liquid phase and n when ethyl lactate and clusters are a two-component system are given. 2EL The molar amount of ethyl lactate in the liquid phase when ethyl lactate and inorganic salt are used as a two-component system is α, where α is the number of ethyl lactate groups in the cluster. The molar amount of ethyl lactate in the liquid phase is determined by quantitative calculation and molecular dynamics simulation.

[0015]

[0016] and

[0017]

[0018] In the formula, x new This represents the mole fraction of the cluster in the liquid phase.

[0019] Mole fraction of inorganic salts in the gas phase y s The predicted data is calculated using the following formula:

[0020]

[0021] Similarly, In the formula, This represents the molar amount of inorganic salt in the gas phase. The molar amount of clusters in the gas phase The molar amount of ethyl lactate in the gas phase when ethyl lactate and clusters are a two-component system. The molar amount of inorganic salt in the gas phase when ethyl lactate and inorganic salt are used as a two-component system;

[0022]

[0023] and

[0024]

[0025] In the formula, y new This represents the mole fraction of the cluster in the gas phase.

[0026] Preferably, the specific process of constructing the initial configuration of the cluster through molecular dynamics simulation in step (1) is as follows: using molecular dynamics simulation, the radial distribution functions of cations and anions and ethyl lactate in the inorganic salt-ethyl lactate solution system are obtained, the coordination number of cations and anions is calculated, and thus the initial configuration of the cation-anion-ethyl lactate cluster is constructed.

[0027] More preferably, the radial distribution function is substituted into equation (9) to calculate the coordination number of the anions and cations in the inorganic salt-ethyl lactate system;

[0028]

[0029] Wherein, g ij (r) represents the radial distribution function, ρ j The number density is given by r, where r is the cutoff radius of the first coordination peak.

[0030] Preferably, the specific process of optimizing the initial configuration in step (1) is as follows: structural optimization and energy calculation are performed through quantum chemical calculation program to determine the structure with the lowest energy, and the molecular conformation of the structure is geometrically optimized to select the most stable structure.

[0031] More preferably, the specific method for structural optimization and energy calculation in step (1) using a quantum chemical calculation program is as follows: the initial configuration is optimized using the xTB program and the semi-empirical method GFN2-xTB, the lowest energy configuration is further optimized using the ORCA6.01 program within the B97-3c density functional theory framework, and finally, the geometry is optimized using Gaussian16 software to select the most stable structure.

[0032] Preferably, step (2) involves calculating the surface charge density distribution of the cluster using AmsterdamModeling Suite.

[0033] A second aspect of the present invention provides a thermodynamic model for predicting the thermodynamic properties of an inorganic salt-ethyl lactate solution system constructed by the above method.

[0034] A third aspect of the present invention provides an application of the thermodynamic model described in the second aspect in predicting the thermodynamic properties of an inorganic salt-ethyl lactate solution system.

[0035] Preferably, the application is the use of thermodynamic models in predicting the gas-liquid equilibrium composition of an inorganic salt-ethyl lactate system.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] (1) Based on the actual existing forms of salts in organic solutions, this invention proposes that inorganic salts in ethyl lactate not only exist in simple ionic form, but can also form stable cation-anion-ethyl lactate clusters with solvent molecules. This invention introduces such clusters as new material components into the thermodynamic model to predict the gas-liquid equilibrium properties of the salt-ethyl lactate system.

[0038] (2) The method for constructing the thermodynamic model of this invention does not rely on a large amount of experimental data, and can obtain prediction results with high consistency with experimental results. This method not only significantly reduces research costs and experimental difficulty, but also reveals the volatilization law of inorganic salts in ethyl lactate solution, providing a new theoretical basis and calculation tool for the study of separation mechanism and process optimization design of salt-containing organic systems. Attached Figure Description

[0039] Figure 1 Schematic diagram of the construction and thermodynamic prediction of inorganic salt-ethyl lactate solution clusters;

[0040] Figure 2 Structural optimization results for constructing boxes for LiBr–ethyl lactate solutions using Materials Studio;

[0041] Figure 3 The radial distribution function is given for LiBr–ethyl lactate solutions with a molar fraction of 0.6% at different temperatures.

[0042] Figure 4 Let be the radial distribution function of LiBr–ethyl lactate solutions of different concentrations; where Figure 4 a represents the Li-O content of LiBr–ethyl lactate solutions of different concentrations. EL Radial distribution function of (lithium ions and double-bonded oxygen atoms in ethyl lactate molecules); Figure 4 b is the radial distribution function of Br--Hw (chloride ions and hydroxyl hydrogen atoms in ethyl lactate molecules) in LiBr-ethyl lactate solutions of different concentrations;

[0043] Figure 5 The graph shows the y-x of LiBr–ethyl lactate solution at 452.15 K. The horizontal axis represents the molar content of inorganic salts in the ethyl lactate solution, and the vertical axis represents the molar content of inorganic salts in the gas phase. The red balls correspond to the experimental values ​​of LiBr, and the red lines represent the predicted values. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer and more explicit, the invention is further described in detail below through embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0045] Example 1

[0046] A thermodynamic model for predicting the thermodynamic properties of an inorganic salt-ethyl lactate solution system is constructed, and its calculation flowchart is shown below. Figure 1 As shown, the specific method includes the following steps:

[0047] (1) Taking the lithium chloride (LiBr) – ethyl lactate system as an example, molecular dynamics simulations of the lithium bromide – ethyl lactate solution were first performed using Materials Studio software. The concentrations of LiBr were determined based on different molar fractions of lithium bromide (0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%). + ,Br - The volume of the box is calculated based on the density of the solution, along with the number of ethyl lactate molecules. Figure 2 A solution model was constructed for energy optimization and molecular dynamics calculations to obtain the radial distribution function (RDF). Figure 3 The radial distribution function is given for LiBr–ethyl lactate solutions with a molar fraction of 0.6% at different temperatures. Figure 4 Let be the radial distribution function of LiBr–ethyl lactate solutions of different concentrations; where Figure 4 a represents the Li-O content of LiBr–ethyl lactate solutions of different concentrations. EL Radial distribution function of (lithium ions and double-bonded oxygen atoms in ethyl lactate molecules); Figure 4 b is the radial distribution function of Br--Hw (chloride ions and hydroxyl hydrogen atoms in ethyl lactate molecules) in LiBr-ethyl lactate solutions of different concentrations.

[0048] The coordination number was calculated using the radial distribution function and formula (9). The coordination number results of the anions and cations in lithium bromide-ethyl lactate solutions with different initial concentrations are shown in Table 1.

[0049]

[0050] Among them, g ij (r) represents the radial distribution function, ρj The number density is given by r, where r is the cutoff radius of the first coordination peak.

[0051] Table 1. Coordination numbers of anions and cations in lithium bromide-ethyl lactate solutions with different initial concentrations.

[0052]

[0053] Table 1 shows that the initial concentration of lithium chloride has a limited effect on the coordination number.

[0054] Figure 3 The radial distribution function shows that in LiBr–ethyl lactate solutions at 298.15 K and 452.15 K, the metal cations react with the oxygen atoms in the ethyl lactate (Li–O). EL ), anions and hydroxyl hydrogen atoms in ethyl lactate molecules (Br–H) OH The radial distribution function of the interaction between cations and anions (Li–Br). Li–O EL The peak appears first, followed by Br–H. OH The presence of peaks in the radial distribution function and the Li–Br peak indicates that solvation occurs prior to the interaction between cation and anion pairs. Notably, while the position of the radial distribution function peak remains largely unchanged with increasing temperature, its intensity decreases, suggesting that while solvation and association by ions are weakened at high temperatures, they still occur.

[0055] Figure 4 The distribution of ethyl lactate around ions in a LiBr–ethyl lactate solution is shown, where 4a and 4b represent different concentrations of Li–O. EL and Br–H OH RDF. (via) Figure 4 As can be seen from a and 4b, with the increase of concentration, Li–O EL and Br–H OH The peak positions and magnitudes of the RDF values ​​remained unchanged. Therefore, the change in ion coordination number determined by the radial distribution function was not significant. This indicates that within a certain mass fraction range, the esterification between ions and ethyl lactate molecules in the solution tends to saturate. Even increasing the molar fraction of salt does not significantly increase the number of ester molecules in the esterification shell (i.e., the coordination number). This is because the number of ester molecules that each ion can attract is limited, and once the arrangement of ester molecules around the ion reaches a stable state, the esterification shell will not change significantly even with an increase in salt concentration. Therefore, within a certain concentration range, the ion coordination environment of the salt solution is relatively stable.

[0056] (2) Combining the principle of neutrality of substances and the relationship between Li+ and Br+ - Given a coordination number of 6 and considering the solvent effect of the ions, Li+–6EL–Br is chosen. -As a representative cluster, 500 initial configurations were generated using the genmer program. This program can construct a set of initial structures covering different spatial arrangements by randomly perturbing the atomic positions and adjusting the coordinate bond angles, effectively avoiding the problem that the optimization results are limited to local minima due to the single initial configuration.

[0057] Based on the initial configuration, the clusters were optimized using the xTB program and the semi-empirical method GFN2-xTB, which accurately reflects the basic characteristics of the coordination bonds. After the initial optimization, the 100 lowest-energy clusters were selected according to energy ranking for the next optimization step, eliminating redundant structures with higher energy and poor stability. This approach ensures the accuracy of subsequent calculations while reducing the cost of high-level theoretical calculations.

[0058] Subsequently, these clusters were optimized using the ORCA 6.01 program within the B97-3c level density functional theory (DFT) framework, including DFT-D3 dispersion correction and short-range basis correction. After B97-3c level DFT optimization, the five lowest-energy clusters were selected based on their energy levels. These clusters were considered the most likely composite structures, as their lowest energy indicates the strongest thermodynamic stability under current theoretical conditions, making them the core targets for subsequent fine-tuning. Finally, the five lowest-energy clusters were selected as the most likely composite structures, and geometric optimization was performed using Gaussian16 software with the M062x function and def2-tzVP basis set to select the most likely and stable clusters. The surface charge density distribution of the clusters was calculated using the Amsterdam Modeling Suite, generating COSMO files.

[0059] (3) Import the COSMO file into the COSMO-SAC model to form a binary system with ethyl lactate. Predict VLE (vapor-liquid equilibrium) data at the boiling point to obtain Li+–6EL–Br in the liquid and gas phases. - Cluster content (x) new y new ), and then calculate the LiBr content (x) in the liquid phase and gas phase. s y s );

[0060] The molar fraction of lithium bromide in the liquid phase, x s The following formula can be used for calculation:

[0061]

[0062] Where n s =n new n 2EL =n 1EL +ɑn new In the formula, ns n new n 1EL n 2EL , respectively, represent the molar amount of inorganic salt in the liquid phase, the molar amount of cluster, the molar amount of ethyl lactate when ethyl lactate and cluster are two-component systems, and the molar amount of ethyl lactate when ethyl lactate and inorganic salt are two-component systems, where α is the number of ethyl lactate in the cluster, determined through quantitative calculations and molecular dynamics simulations.

[0063]

[0064] and

[0065]

[0066] mole fraction y of inorganic salts in the gas phase s The predicted data can be calculated using the following formula:

[0067]

[0068] Similarly, In the formula, These represent the molar amounts of inorganic salts in the gas phase, the molar amounts of clusters, the molar amounts of ethyl lactate in a two-component system consisting of ethyl lactate and clusters, and the molar amounts of inorganic salts in a two-component system consisting of ethyl lactate and inorganic salts, respectively.

[0069]

[0070] and

[0071]

[0072] The predicted values ​​are obtained through the above calculations, and the predicted value curve is shown below. Figure 5 The red solid line in the curve; see Table 2 for specific values.

[0073] To verify the accuracy of the thermodynamic model predictions in this embodiment, an experiment was conducted. A LiBr–ethyl lactate solution with a LiBr molar fraction of 0.10%–0.60% was prepared, and the vapor reflux was collected after distillation. The Li+ content (c) in the vapor phase was analyzed by ICP-OES, and the LiBr content (y) in the vapor phase was calculated. s ).

[0074] Preparation of LiBr–ethyl lactate solution: Prepare 0.5 mol of LiBr–ethyl lactate solutions with different mole fractions. The mole fraction of inorganic salts in the liquid phase can be calculated using formula (10):

[0075]

[0076] Where, n s and 0.5-n s These are the molar amounts of inorganic salt and ethyl lactate, respectively.

[0077] The content of metal ions in the gas phase, as measured by ICP-OES, is represented by c:

[0078]

[0079] In the formula, This represents the mass of the metal ions in the gas phase. Let be the mass of ethyl lactate in the gas phase. For an inorganic salt ethyl lactate solution, if the mole fraction of the inorganic salt in the gas phase is equal to the mole fraction of the metal ions, then the mole fraction of the inorganic salt in the gas phase can be calculated using the following formula:

[0080]

[0081] The experimental values ​​were obtained through the above calculations, and the experimental value curve is shown in the figure. Figure 5 The specific values ​​of the red dots in the curve are shown in Table 2.

[0082] Table 2. Experimental and predicted values ​​of LiBr content in the gas phase at different concentrations.

[0083]

[0084] from Figure 5 As can be seen from Table 2, the thermodynamic model constructed in this invention for predicting the thermodynamic properties of the inorganic salt-ethyl lactate solution system has high prediction accuracy in the low concentration range (mole fraction <0.004), but some deviation occurs in the high concentration range. This is due to the occurrence of ion pair association effect.

Claims

1. A method for constructing a thermodynamic model for predicting thermodynamic properties of inorganic salt-ethyl lactate solution systems, characterized by, Comprise the following steps: (1) Assuming that inorganic salt exists in the form of cation-anion-ethyl lactate cluster, an initial configuration of the cluster is constructed by molecular dynamics simulation, the initial configuration is optimized, and the most stable cluster is selected; (2) Obtain the surface charge density distribution of the cluster in step (1) and import it into the COSMO-SAC model, form a binary system with ethyl lactate, and calculate and predict the vapor-liquid equilibrium composition of the inorganic salt-ethyl lactate system.

2. The thermodynamic model building method of claim 1, wherein, The specific process of step (2) for calculating and predicting the vapor-liquid equilibrium composition of the inorganic salt-ethyl lactate system is: Based on COSMO-SAC model, the gas-liquid equilibrium relationship of the binary system of cluster and ethyl lactate was predicted at 101.325 kPa, and the mole fraction of cluster in liquid phase and gas phase was obtained, respectively denoted as x new and y new ; Mole fraction x of inorganic salt in the liquid phase s The calculation is made by the following formula: wherein n s = n new , n 2EL = n 1EL + a n new , in the formula, n s is the molar mass of the inorganic salt in the liquid phase, n new is the molar mass of the cluster in the liquid phase, n 1EL is the molar mass of ethyl lactate in the liquid phase when ethyl lactate and the cluster are a two-component system, n 2EL is the molar mass of ethyl lactate in the liquid phase when ethyl lactate and the inorganic salt are a two-component system, and a is the number of ethyl lactate in the cluster, which is determined by a quantitative calculation and a molecular dynamics simulation; And wherein x new is the molar fraction of the clusters in the liquid phase; Mole fraction of inorganic salt in the gas phase, y s The predicted data is calculated from the following equation: The same applies to the following examples. wherein, is the molar amount of the inorganic salt in the gas phase, is the molar amount of the cluster in the gas phase, is the molar amount of the ethyl lactate in the gas phase when ethyl lactate and the cluster are the two-component system, is the molar amount of the inorganic salt in the gas phase when ethyl lactate and the inorganic salt are the two-component system. And where y new is the mole fraction of the clusters in the gas phase.

3. The thermodynamic model building method of claim 1, wherein, The specific process of step (1) for constructing the initial configuration of the cluster by molecular dynamics simulation is: radial distribution functions of anions, cations and ethyl lactate in the inorganic salt-ethyl lactate solution system are obtained by molecular dynamics simulation, coordination numbers of anions and cations are calculated, and the initial configuration of the cation-anion-ethyl lactate cluster is constructed.

4. The thermodynamic model building method of claim 3, wherein, The specific process of step (1) for optimizing the initial configuration is: structure optimization and energy calculation are performed by quantum chemistry calculation program, the structure with the lowest energy is determined, the molecular conformation of the structure is geometrically optimized, and the most stable structure is selected.

5. The thermodynamic model building method of claim 4, wherein, The specific method of step (1) for structure optimization and energy calculation by quantum chemistry calculation program is: the initial configuration is optimized by xTB program and semi-empirical method GFN2-xTB, the energy minimum configuration is further optimized by ORCA 6.01 program under the framework of B97-3c level density functional theory, and finally Gaussian16 software is used for geometric optimization to select the most stable structure.

6. The thermodynamic model building method of claim 5, wherein, The surface charge density distribution of the cluster is obtained by Amsterdam Modeling Suite in step (2).

7. A thermodynamic model for predicting the thermodynamic properties of the inorganic salt-ethyl lactate solution system constructed by the method of any one of claims 1-6.

8. The use of the thermodynamic model of claim 7 in predicting the thermodynamic properties of the inorganic salt-ethyl lactate solution system.

9. Use according to claim 8, characterized in that, The application is the application of the thermodynamic model in predicting the vapor-liquid equilibrium composition of the inorganic salt-ethyl lactate system.

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