微波场对汽液相平衡及传质过程的作用机理研究

The distillation/reactive distillation technology intensified by microwave irradiation has the vast reservoir of potential application in the field of chemical separation, due to the special effects of the microwave irradiation on the role of substance. The process of vapor-liquid phase equilibria and mass transfer in the microwave field is the key issue. In this project, intends to adopt the Monte Carlo method based on the priciples of statistical thermodynamics and nonequilibrium molecular dynamics method, introducing the effect of electromagnetic field on the molecular polarization rotation, the theoretical models for the effects of microwave field on vapor-liquid equilibria and mass transfer are constructed by using molecular simulation method. The experiments of vapor-liquid phase equilibrium and distillation separation in the microwave field are executed respectively to validate the two models. Further, the influences of the difference degree of the relative volatility and dielectric properties and the power density of microwave irradiation on the vapor-liquid equilibria and mass transfer are systematically investigated to analysis the effects law and strengthening mechanism. Consequently, the basic theory system in describing the role of microwave field on the vapor-liquid equilibria and mass transfer are build. This project will help to deepen the understanding of the mechanism of the effect of microwave field on molecular, enrich and extend the application field of microwave strengthening technology, which has theoretical value and practical significance on the application of distillation/reactive distillation processes intensified by microwave irradiation.

微波场对物质作用的特殊效应，使微波强化精馏及反应精馏技术在化工分离领域中蕴藏着巨大的潜在应用价值，如何揭示微波场对汽液相平衡及传质过程的作用机理是亟待解决的关键理论问题。本项目采用基于统计热力学原理的Monte Carlo方法和非平衡态分子动力学方法，通过引入电磁场对分子的极化转动作用，运用分子模拟的手段分别构建微波场作用下汽液相平衡和气液传质过程的理论模型并进行求解，设计相应的微波辐射汽液相平衡及气液传质效率测试实验完成模型验证，进而利用模型系统地研究体系相对挥发度差异、介电性质差异和微波场强密度的变化对于微波场作用下汽液相平衡及气液相传质过程的影响规律及强化机理，从而构建出描述微波场作用下汽液相平衡及传质过程的基本理论体系。本项目研究有助于深化微波场对分子作用机理的认识，丰富和扩展微波强化技术的应用领域，为微波强化精馏以及反应精馏技术的应用提供理论依据和指导。

本项目针对乙醇/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。进一步提出了“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。实验方面进行了微波对二元体系相对挥发度影响的研究。测定了不同微波功率下，环己烷-异丙醇、环己烷-乙醇和乙醇-异丙醇三种不同体系处于非平衡稳态时，体系的相对挥发度。通过与常规加热方法对比，结果发现微波作用下，环己烷-异丙醇体系中环己烷的相对挥发度有所降低；乙醇-异丙醇和环己烷-乙醇体系的相对挥发度没有发生明显变化。分析其主要原因在于体系中各物质的介电性质、蒸发焓、沸点序列以及分子间作用力的不同。微波仅对介电性质相差较大的极性-非极性二元体系的相对挥发度有影响，且当极性组分的沸点比非极性组分高时，微波可以大大加速极性分子的传质过程，降低非极性物质的相对挥发度。体系中极性分子间作用力越弱，微波作用下体系的相对挥发度变化越明显。