基于GEMC方法从分子层次分析汽液相平衡

发布时间：2018-04-26 22:40

本文选题：Gibbs系综蒙特卡罗 + 共沸　；参考：《天津大学》2015年硕士论文

【摘要】：近十年,Monte Carlo统计方法在物理化学领域的应用已经成为化工界的研究热点之一,其中GEMC方法被普遍应用于求解分子热力学等相关问题,且已被证明在模拟计算流体相平衡方面效果明显优于其他模拟方法。共沸物作为一种表现出特殊相行为的混合物,其形成原因和特殊结构至今未有合理详细的报道,这极大地限制了该混合物在工业工程中的分离设计。本文研究中将采用GEMC方法结合相应力场TaPPE-UA对共沸物相平衡进行计算并评价了方法的适用性,同时对共沸物的特殊结构及共沸现象的形成原因进行了详细探究,提出了模型假设和重要推论。除了共沸体系外,本研究还使用GEMC方法对相对挥发度较小的二元醇体系的汽液相平衡的模拟计算进行方法评价,并对混合物平衡液相的微观结构和氢键缔合进行了简要探究,总结了相应规律。本文首先选定了乙醇/苯这一典型的共沸物作为目标研究体系,使用GEMC方法和TraPPE-UA力场对该共沸物的相平衡进行了计算,经与实验数据和Wilson状态方程计算结果比较发现,该方法能很好地描述乙醇/苯共沸物的相平衡行为。之后又提出了“共沸团簇”的假设模型,通过两相径向分布函数分析对假设进行了初步验证,相关结果可以为理解共沸物的形成及其特点提供理论支撑。此外,由共沸物液相的团簇分布分析可知,乙醇/苯共沸物的形成与体系中形成的大量环状结构有关,由此提出了环状结构是本体系表现共沸行为的必要条件这一推论。本文还对乙二醇/1,2-丁二醇、乙二醇/1,3-丙二醇和乙二醇/1,4-丁二醇这三个二元醇体系的相平衡进行了GEMC方法模拟,结果表明使用OPLS-AA力场下的乙二醇/1,2-丁二醇体系和TraPPE-UA力场下的另两体系计算的汽液相平衡数据与实验结果(或Wilson方程计算结果)相比良好。通过对以上三个体系平衡液相的径向分布函数分析可知,混合物分子间的相互作用强弱顺序是:乙二醇/1,2-丁二醇乙二醇/1,3-丙二醇乙二醇/1,4-丁二醇。另一方面,通过对乙二醇/1,3-丙二醇和乙二醇/1,4-丁二醇体系氢键缔合分布的分析,得出乙二醇和1,4-丁二醇异种分子缔合比例较小,因此从氢键角度揭示了其在相同条件下可能较易从中分离出乙二醇的原因。
[Abstract]:In recent ten years, the application of Monte Carlo statistical method in the field of physical chemistry has become one of the research hotspots in the chemical industry, in which the GEMC method has been widely used to solve the related problems such as molecular thermodynamics. It has been proved that it is better than other simulation methods in simulating and calculating fluid phase equilibrium. Azeotrope, as a mixture with special phase behavior, has not been reported in detail due to its formation and special structure, which greatly limits the separation design of the mixture in industrial engineering. In this paper, the GEMC method combined with the corresponding force field TaPPE-UA is used to calculate the phase equilibrium of the azeotrope and the applicability of the method is evaluated. At the same time, the special structure of the azeotrope and the reasons for the formation of the azeotropic phenomenon are discussed in detail. The model hypothesis and important corollary are proposed. In addition to the azeotropic system, the GEMC method was used to evaluate the vapor-liquid equilibrium of the diol system with low relative volatility, and the microstructure and hydrogen bond association of the equilibrium liquid phase of the mixture were studied briefly. The corresponding laws are summarized. In this paper, a typical azeotrope, ethanol / benzene, is first selected as the target research system. The phase equilibrium of the azeotropic compound is calculated by using GEMC method and TraPPE-UA force field. The results are compared with experimental data and Wilson equation of state. This method can well describe the phase equilibrium behavior of ethanol / benzene azeotrope. The hypothesis model of "azeotropic cluster" is proposed, and the hypothesis is preliminarily verified by two-phase radial distribution function analysis. The relevant results can provide theoretical support for understanding the formation and characteristics of azeotrope. In addition, the cluster distribution of azeotropic liquid phase shows that the formation of ethanol / benzene azeotrope is related to the formation of a large number of ring structures in the system, and it is concluded that the ring structure is a necessary condition for the azeotropic behavior of the system. In this paper, the phase equilibrium of three binary alcohols, ethylene glycol / 2-butanediol, ethylene glycol / 1-butanediol and ethylene glycol / 1-butanediol, has been simulated by GEMC method. The results show that the vapor-liquid equilibrium data calculated by using the ethylene glycol / 1 / 1-butanediol system under OPLS-AA force field and the other two systems under TraPPE-UA force field are better than the experimental results (or Wilson equation calculation results). By analyzing the radial distribution function of the equilibrium liquid phase of the above three systems, it can be seen that the order of the intermolecular interaction of the mixture is: ethylene glycol / 1o _ 2-butanediol / _ 3- propanediol / _ 4-butanediol. On the other hand, based on the analysis of hydrogen bonding association distribution of ethylene glycol / / 1 / 1 / 1-butanediol and ethylene glycol / 1 / 1-butanediol system, it is concluded that the ratio of dissimilar molecular association between ethylene glycol and 1-butanediol is relatively small. Therefore, the reason why ethylene glycol may be easily separated from the hydrogen bond under the same conditions is revealed.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ013.1

【相似文献】