醇、醛和羧酸/水极性体系的分子力场构建及其热力学性质的分子模拟

Thermodynamics data and theory are the basis of unit operations and chemical engineering design. In recent years molecular simulation based on force field method is regarded as a new and promising method to obtain thermodynamic data. Due to apparent polarization of different molecules, the simulation of two-component systems, especially polar molecule/water, is very difficult and the corresponding research is insufficient. The force fields are often built upon the experimental data of pure substance because of hard work. In this case the polarization is not included in such force fields. Therefore the data of the two-component system using these force fields cannot be accurately calculated. In this project we focus on the construction of new force field of the polar molecules, alcohol, aldehyde and carboxylic acid, for predicting the vapor-liquid equilibrium (VLE) and other thermodynamic properties of the polar molecule/water mixtures. The model uses simplified functions and the corresponding parameters are obtained from first principle calculations and experimental data. The polarization problem is handled by two terms, the electrostatic potential and Van der Waals. The electrostatic potential is obtained not from the structure of pure substance but the alcohol, aldehyde or carboxylic acid /water cluster from the QM calculations. Van der Waals parameters are fitted by the experimental data of mixtures. We have done some jobs and obtained good results, including the microscopic structures of acetic acid/water clusters and the simulation of the VLE and other thermodynamic properties of acetic acid/water system. The method in this project is helpful for solving more complicated systems, processes and problems, and is of great theoretical importance and value.

热力学数据和理论是化工单元操作和设计的基础，近年来基于分子力场的分子模拟成为获得它们的一种新选择。二元体系的分子模拟由于显著的极化作用引起力场相容性差等问题，始终是一个难点，研究非常欠缺。分子力场由于构建困难一般都以纯体系实验数据拟合，它们不包含对复杂体系极化作用的描述，无法对二元体系进行准确模拟。本项目拟开发醇、醛和羧酸三类典型极性分子的迁移性好、相容性问题小的力场，适于模拟极性分子/水二元体系的热力学性质。模型采用必要简化，分子内和范德华参数分别以第一性原理和实验数据拟合。特别针对极化作用相关问题，对影响凝聚相性质模拟的关键部分进行处理，即静电项以醇、醛和羧酸与水分子的团簇结构为基础拟合，范德华参数以二元体系实验数据为依据优化。本项目已有良好基础，对醋酸/水体系的微观结构和气液平衡性质进行了探索性研究。本项目方法对多组分多相体系的模拟等提供理论基础，具有重要的科学意义和学术价值。

热力学数据和理论是化工单元设计和操作的基础，通常通过实验获得，但某些困难条件下实验也难以进行，近年来基于分子力场的计算机分子模拟成为获取热力学数据的一种新选择。醇（醛和羧酸）/水二元体系的分子模拟由于极化作用引起力场相容性差等问题，始终是一个难点，研究欠缺。本项目构建了醇（醛和羧酸）/水二元体系的适于模拟其热力学数据的分子力场。为在合理时间内获得模拟结果，力场模型采用了简化形式。其次构建分子力场的关键还在于有足够大的训练集数据，为此通过分子动力学模拟和高精度量子化学计算获得了庞大的随机分子构型训练数据集。力场参数拟合工具采用了ForceBalance（FB）程序，并对FB进行了改写，加入了Towhee的python接口，并针对化学势进行优化拟合参数项。经过大量时间优化参数，最后得到了较为理想的参数，能够对醇（醛和羧酸）/水二元体系的气液平衡热力学数据进行较好描述。本项目最后得到了醇（醛和羧酸）/水二元体系拟合力场参数的基础训练集参数，获得了模拟醇（醛和羧酸）/水二元体系的力场并准确模拟该体系的热力学数据。本项目关键数据为拟合力场参数的庞大训练集数据及醇（醛和羧酸）/水二元体系的实验气液平衡热力学数据。本项目获得的训练集数据，可在今后进一步改进醇（醛和羧酸）/水二元体系分子力场或构建其他形式力场的基础数据；创新的通过化学势优化力场参数方法，可推广至其他分子体系的气液平衡热力学的力场构建；构建的力场能够模拟醇（醛和羧酸）/水二元体系的热力学数据，具有重要科学意义和一定应用价值。