Mechanism of pore wetting in membrane distillation with alcohol vs. surfactant
Mechanism of pore wetting in membrane distillation with alcohol vs. surfactant
复制标题
DOI：
10.1016/j.memsci.2018.04.045
复制
发表时间：
2018-08
影响因子：
9.5
通讯作者：
Zhangxin Wang;Yuanmiaoliang Chen;Xiangming Sun;R. Duddu;Shihong Lin
中科院分区：
文献类型：
--
作者：
Zhangxin Wang;Yuanmiaoliang Chen;Xiangming Sun;R. Duddu;Shihong Lin
在使用疏水性膜的膜蒸馏(MD)中，孔润湿是一个独特而重要的技术挑战，可能导致过程失败。虽然众所周知，低表面张力和水可混溶的液体(如醇)和两亲性分子(如表面活性剂)都是有效的润湿剂，但这些湿润剂诱导孔隙润湿的详细机制尚不清楚。特别是，表面吸附在表面活性剂诱导的润湿中的作用仍有待阐明。这项研究为理解这两种不同润湿剂引起的孔隙润湿机理提供了基本的见解。利用最近发展起来的基于单频跨膜阻抗的润湿监测技术，对润湿前沿的传播动力学进行了实验研究。我们证明了乙醇诱导的润湿是瞬时的，而表面活性剂诱导的润湿是动态的，其动力学速率取决于几个关键因素。我们还发展了一个基于准平衡吸附假设的理论模型，成功地解释了实验观察到的表面活性剂诱导润湿的重要特征。实验结果表明，表面活性剂的润湿动力学强烈依赖于料液中的水蒸气通量和表面活性剂的体积浓度，而与跨膜水压差无关。我们的研究结果还表明，虽然表面活性剂的存在促进了润湿，但表面活性剂在孔表面的吸附实际上阻止了孔的润湿，而不是通过使表面亲水而促进了孔的润湿。
Pore wetting is a unique and important technical challenge that can lead to process failure in membrane distillation (MD) using hydrophobic membranes. While it is well known that both low-surface-tension and water miscible liquids, such as alcohols, and amphiphilic molecules, such as surfactants, are effective wetting agents, the detailed mechanisms for these agents to induce pore wetting remain unclear. In particular, the role of surface adsorption in surfactant-induced wetting remains to be elucidated. This study provides fundamental insights to understanding the mechanism of pore wetting induced by these two different wetting agents. Using a recently developed wetting monitoring technique based on single-frequency transmembrane impedance, we experimentally probe the kinetics of wetting frontier propagation. We demonstrate that ethanol-induced wetting is instantaneous whereas surfactant-induced wetting is dynamic with its kinetic rate dependent on several critical factors. We also develop a theoretical model, based on the assumption of quasi-equilibrium adsorption, to successfully explain the important features experimentally observed in surfactant-induced wetting. Specifically, it was found that the kinetics of surfactant-induced wetting strongly depends on the vapor flux and the bulk concentration of surfactants in the feed solution, but surprisingly not on the transmembrane hydraulic pressure difference. The results from our study also suggest that while the presence of surfactants promotes wetting, adsorption of surfactants onto pore surface actually deters pore wetting instead of promoting it by rendering the surface hydrophilic.