分子动力学模拟计算超临界CO2的溶解度参数

采用分子动力学模拟方法，计算了超临界CO2和超临界CO2-乙醇体系的溶解度参数，并分析了体系内粒子间距离的径向分布函数。结果表明，超临界CO2的溶解度参数随温度的升高而减小，随压力的增大而增大，且随体系密度的增大而线性增大；添加乙醇可明显提高超临界CO2的溶解度参数，且随着乙醇浓度的增加，在相同条件下的溶解度参数也增大。乙醇分子可与CO2分子形成分子间氢键而提高CO2的极性，从而提高体系的溶解度参数；超临界CO2-乙醇体系中，分子间，特别是乙醇分子间存在聚集现象。当体系压力较低时，增大压力，可大幅度减弱乙醇分子间的聚集程度，使体系的溶解度参数迅速增大；但继续增大压力到一定程度时，乙醇分子间的聚集程度达到定值，即乙醇已均匀分散在CO2中，溶解度参数随压力的变化趋于平缓。

Calculation of Solubility Parameters of Supercritical CO2 by Molecular Dynamics Simulation

The solubility parameters of supercritical CO2 and supercritical CO2-ethanol system were calculated by molecular dynamics simulation. The radial distribution function of the systems was analyzed. The results indicated that the solubility parameter of supercritical CO2 decreased with the increase of temperature, increased with the increase of pressure, and increased linearly with the density of the system. Addition of ethanol could significantly improve the solubility parameter of supercritical CO2, and the solubility parameter increased with the increase of ethanol concentration under the same condition. It is found that the intermolecular hydrogen bonds were formed between ethanol and CO2, thereby the polarity and the solubility parameter of supercritical CO2 increased. There was intermolecular aggregation in supercritical CO2-ethanol system, especially, in ethanol molecules. When the pressure was lower, aggregation of the ethanol molecules would be significantly weakened with the increase of pressure. However, when the pressure increased to a certain extent, aggregation of the ethanol molecules tended to be smooth, meaning that the ethanol molecules were evenly dispersed in CO2, and the solubility parameter gently increased with the increase of pressure.