A review on thermally stable membranes for water treatment: Material, fabrication, and application

Membrane separation is an environmentally friendly process with low energy consumption and high separation efficiency. Energy can be retrenched by in-situ treating high temperature aqueous streams without heat exchange. Unfortunately, dealing with such streams, most commercial organic membranes are restricted by low thermal stability. Therefore, scientists turned to thermally stable polymers and inorganic materials. Numerous materials have been studied to develop thermally stable membranes for separating high temperature aqueous streams. However, difficulties were faced in elevating the flux of inorganic membranes and balancing the structure rigidity and flux of polymer membranes. This review aims at collecting the researches focusing on applications of thermal stable materials in treating high temperature streams, as well as the accompanied challenges. Firstly, the effect of temperature on the structure and performance of membranes are interpreted by mathematic models. Sequentially, the structure change of membranes at elevated temperature are discussed in terms of movement of polymer chains. Classified discussion is held according to the components of thermal stable membranes. The key points discussed include fabrication process, relationship between structure and performance in practical applications. The objective of this review is to summarize the recent developments and challenges in thermally stable membranes for water treatment, offer some advice for designing new materials and modifying existent materials, and emphasize the significance for researches in this area. The future direction for fully exploiting the potential of thermally stable membranes for water treatment is also presented.