膜蒸馏结晶的热质耦合跨膜传递机理和结晶过程调控方法

Membrane crystallization has shown the great potentials in seawater desalination and preparation of functional molecules due to the advantages of crystal control and induction over the traditional methods. In this study, 1) to well understand the transport phenomena across the membrane, the transmembrane heat and mass transfer is correlated with the non-equilibrium phase transformation and the migrating molecules’ interactions with microscopic textures of membrane matrix. The establishing model, experimentally verified with the membrane crystallization of a millimeter-scale droplet, expects to well predict the membrane distillation behaviors. With aid of the computational fluid dynamics simulation to circumvent the precise measurement of local flow fields, the crystallization thermodynamics and heterogeneous kinetics for crystal nucleation and growth are correlated with the video imaging online measurements of membrane crystallization; 2) as the crystal precipitation on the membrane deteriorates the membrane fouling, the centrifugal membrane crystallization is proposed to alleviate the membrane fouling. A meso-scale model of liquid-solid two phase flow, incorporated with population balance model of crystal size determination, is developed to evaluate the crystal separation and evolution. The simulation, verified with corresponding experiments of centrifugal membrane crystallization, will reveal to control the crystal size distribution in varied operation conditions; 3) the integrated LNG cold energy and waste heat recovery in seawater desalination, together with preparation of paracetamol in ethanol solution, are used as representative systems for flowsheet simulation to show the feature of process intensification for integrating membrane distillation, crystallization and centrifugation. With using the exergy analysis to illustrate the improved energy utilization, the membrane crystallization will be a promising method for industrial crystallization of featured crystals.

膜结晶在结晶调控和诱导分子空间取向等方面比传统结晶具有明显优势，已在海水淡化和功能分子制备与分离等领域显示出巨大的应用潜力。针对膜结晶跨膜传递的复杂性和易膜污染的问题，本申请拟开展如下研究：1)在精确描述微尺度结构对物质输运的影响和非平衡相变特征的基础上，结合微液滴膜结晶实验，研究跨膜微观分子运动与对流输运协同作用下的膜蒸馏跨膜热质耦合传递机理，进而模拟获得难以通过实验直接测定的瞬时局部流场性质，并通过可视化在线检测典型体系的膜结晶实验，关联膜微观结构与膜面非均相结晶的热力学和动力学关系；2)采用旋转膜结晶实验和模拟计算相结合的方法，建立基于粒数衡算模型的多场耦合两相流模型，研究解决膜结晶易污染的问题，获得结晶调控方法；3)基于上述工作，针对典型膜结晶体系建立膜结晶过程模拟方法，结合(火用)分析，揭示旋转膜结晶技术的过程强化作用。本项目的预期成果，将丰富膜结晶理论，并为其工业应用夯实基础。

膜结晶在结晶调控和诱导分子空间取向等方面比传统结晶具有明显优势，已在海水淡化和功能分子制备与分离等领域显示出巨大的应用潜力。首先本研究采用分子动力学模拟的方法研究并发现了膜面官能团对结晶取向存在诱导作用；进而建立了更准确的膜蒸馏模型及热质耦合CFD模拟方法，针对膜结晶跨膜传递的复杂性和易膜污染的问题，本项目通过实验和模拟量化分析了料液浓度对传质阻力的影响，获得膜渗透通量随盐度增加而降低的普遍化定量关系，由此可通过调节膜蒸馏操作条件避免膜面局部过饱和，从而有效抑制膜结垢，实现膜蒸馏的可持续操作；然而当前CFD模拟计算工作量较大而难以在实际大型结晶系统实施，本项目采用了成核功作为结晶可能性的量化判据，进一步采用“双因素响应面方法”建立了临界雷诺数与操作温度的经验关联式，通过揭示膜结晶条件下操作温度和操作流速间的关系，有效预测了膜面结晶的过程条件；为进一步提高MD中能源利用率、降低综合能耗，本项目开发了一种集成半导体热泵的多级膜组件，通过优化设计新型高效的集成多级热泵膜蒸溜系统，实现MD能耗在现有基础上再降低50%；为实现膜结晶的高效、可持续操作，重点解决晶体颗粒的膜面分离的关键问题，本项目研究采用类似超重力分离过程的旋转膜结晶（RMDC）过程，通过一步优化CFD计算模型考察多相分离现象，深入分析RMDC的热质分离特性，开拓MD在生物医药和功能食品领域的浓缩结晶过程应用。