Gypsum scaling mechanisms on hydrophobic membranes and its mitigation strategies in membrane distillation
Gypsum scaling mechanisms on hydrophobic membranes and its mitigation strategies in membrane distillation
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疏水膜上的石膏结垢机制及其在膜蒸馏中的缓解策略
DOI：
10.1016/j.memsci.2022.120297
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发表时间：
2022
影响因子：
9.5
通讯作者：
Yuelian Peng
中科院分区：
文献类型：
--
作者：
Songchen Xie;Zhixia Li;Ngie Hing Wong;Jaka Sunarso;Dunshang Jin;Lixin Yin;Yuelian Peng
矿物质结垢是使用膜蒸馏（MD）技术处理高盐废水的重大障碍之一。更深入地了解结垢机理有助于解决矿物结垢问题。这项工作研究了直接接触膜蒸馏（DCMD）工艺中使用的三种具有不同表面孔径和疏水特性的多孔膜，即PTFE-0.22、PTFE-0.10和PVDF-0.22。我们选择石膏作为结垢实验中的模型污染物，并重点研究其对膜结垢的均质和异质成核效应。结垢膜的形貌分析表明，均匀成核可能是结垢的主要原因。此外，膜孔内的石膏结晶是导致通量显着下降和物理清洗效率低（PTFE-0.22）的主要原因。当膜（PTFE-0.10和PVDF-0.22）的表面孔径减小时，可以减轻孔内石膏的结晶。这种现象主要是由均相成核引发的。尽管如此，PVDF-0.22 的表面结垢仍然很严重，因为它的疏水性太低，无法抑制膜上的异质成核。然而，具有小表面孔径和高疏水性的PTFE-0.10可以同时减轻两次成核的影响。通过物理清洗可以轻松去除沉积在膜表面的石膏晶体，并实现90%以上的通量恢复效率。因此，减小表面孔径和增加表面疏水性应该是制备MD用防垢疏水膜的两个主要策略。
Mineral scaling is one of the significant obstacles in hypersaline wastewater treatment using membrane distillation (MD) technology. A deeper understanding of the scaling mechanism can help to solve mineral scaling problems. This work investigated three porous membranes with different surface pore sizes and hydrophobic properties, i.e., PTFE-0.22, PTFE-0.10, and PVDF-0.22, used in the direct-contact membrane distillation (DCMD) process. We selected gypsum as a model contaminant in the scaling experiment and focused on its homogeneous and heterogeneous nucleation effects on membrane scaling. The morphology analysis of the scaled membrane revealed that homogeneous nucleation might be the main reason for scaling. In addition, gypsum crystallization in the membrane pores was the main reason for the significant flux decline and low physical cleaning efficiency (PTFE-0.22). When the surface pore size of the membrane (PTFE-0.10 and PVDF-0.22) was reduced, gypsum crystalization in the pores could be alleviated. Such phenomenon was mainly initiated by homogeneous nucleation. Nonetheless, the surface scaling was still severe for PVDF-0.22 because its hydrophobicity was too low to inhibit the heterogeneous nucleation on the membrane. However, PTFE-0.10 with a small surface pore size and high hydrophobicity could simultaneously alleviate the effect of two nucleations. We could easily remove the gypsum crystals deposited on the membrane surface by physical cleaning and achieve more than 90% flux recovery efficiency. Therefore, reducing the surface pore size and increasing the surface hydrophobicity should be two main strategies in preparing the anti-scaling hydrophobic membrane used in MD.