工业废水零排放新技术-多组分体系低共熔点冷冻结晶的探索性研究

Recently, eutectic freezing crystallization (EFC), which is characterized by high selectivity (producing high purity product in one process step), low energy consumption, and relatively mild process conditions, attracted more and more attention in terms of industrial wastewater treatment and desalination. A major limitation to improving the control of eutectic freezing crystallization process lies in the lack understanding of crystallization behavior of target components during multi-component eutectic freezing crystallization process. The current project deals with the impact regularity and mechanism of different components and ice crystals on the nucleation and crystal growth behavior of target components during multi-component eutectic freezing crystallization process, which has not been proposed in publications. Impact regularity of the two factors on the nucleation and crystal growth process of target component is investigated through monitoring of kinetic behavior of both freezing crystallization and eutectic freezing crystallization process using new on-line monitoring technologies, respectively. On this basis, molecular dynamics simulations are performed to illustrate the impact mechanism of the two factors on the nucleation and crystal growth process of target component. The results can improve the process development of eutectic freezing crystallization, producing high quality salt and pure water with low energy consumption, as well as the design of an economical and intensified equipment.

近年来，低共熔点冷冻结晶技术以其高效、低能耗和操作条件温和等优点在工业废水处理和海水淡化方面受到了广泛关注。多组分体系低共熔点冷冻结晶过程中目标组分的成核和生长行为受溶液中的其它组分和析出的冰的双重影响，决定过程效率和能耗。本项目拟考察多组分体系低共熔点冷冻结晶过程溶液中其它组分及析出的冰对目标组分晶体成核和生长的影响及其机理，国内外尚未见类似报道。研究采用新型在线监测技术对多组体系的冷冻结晶和低共熔点冷冻结晶过程动力学行为进行平行观测，并结合计算机分子模拟技术从微观上研究其它组分及析出的冰的耦合作用对目标组分溶质表面扩散以及晶体成核和生长的影响及其机理。研究结果将揭示多组分体系低共熔点冷冻结晶过程各目标组分的晶体成核和生长行为，为相关结晶过程的工艺开发和结晶器设计提供理论依据，在保证最终结晶产品质量的同时优化操作条件以降低过程能耗。

淡水资源短缺和污染是我国现阶段国民经济和社会发展面临的严峻问题。低共熔点冷冻结晶作为一种新型结晶技术，可同时实现废水中无机物的回收以及水的循环利用。由于实际工业废水组分较多，晶体成核和生长行为复杂，结晶过程控制不当易导致晶体粒径较小、分布不均和多种组分晶体同时析出的混晶等问题，并由此造成过程效率下降和能耗增加。为辨析多组分体系溶液中其它组分及析出的冰的耦合作用对目标组分晶体成核和生长的影响及其机理，本项目以硫酸铵-氯化铵-水体系为研究对象，分别考察了多组分体系的热力学特性及低共熔点冷冻结晶过程溶液中其它组分及析出的冰对目标组分晶体成核和生长的影响及其机理。所取得的重要结果包括：（1）分别采用静态法和动态法测量了硫酸铵和氯化铵体系在水中的溶解度，并考察了不同杂质存在下的硫酸铵及氯化铵体系的溶解度及变化规律；（2）采用在线监测技术分别考察了硫酸铵和氯化铵体系在不同杂质存在下的成核动力学行为。结果表明，杂质的存在会抑制两种组分在水溶液中的成核，但成核级数均较低，符合瞬间成核机理。该成核速率级数也说明溶液体系中的成核为三维异相成核或二次成核；（3）采用在线监测技术分别测量了两种组分在水溶液中的浓度变化规律，利用PBE方程对两种组分的晶体生长动力学行为进行了研究，为结晶过程的最优化控制提供了实验依据；（4）考察了操作温度、过饱和度、晶种添加量和添加温度等对最终产品质量（晶型、纯度及粒度分布）的影响，获取了最优化结晶工艺条件；本项目共发表论文6篇，其中包括一篇Chemical Engineering Science，两篇Fluid Phase Equilibria，一篇Journal of Crystal Growth和一篇RSC Advances，培养博士生1名，硕士生3名。