Fluorination And Polyaniline Modified Fiber Membrane For Membrane Distillation And Its Application In Seawater Desalination

The lack of freshwater resources has become a global environmental issue.In the face of the vast seawater resources,seawater desalination is one of the best way to provide sustainable freshwater resources.As a low-temperature,low-pressure,and low capital cost membrane-based process,membrane distillation?MD?is a promising seawater desalination technology,especially when low-grade thermal energy is available.However,some bottlenecks hinder the development of this technique,such as the low-flux,the wetting,and the fouling of separation membranes.Herein,we devoloped a superhydrophobic membrane for direct contact membrane distillation?DCMD?and systematically investigated the performance on the water flux,anti-fouling and anti-wetting.In this study,we developed a superhydrophobic fluorination and polyaniline modified nanofibrous membrane via the successive processes,including the electrospinning,the aniline polymerization,and the low surface energy modification.The purpose of aniline polymerization is to construct a rough fiber surface for amplifying the wettability of the membrane.Superhydrophobic PVDF nanofibrous membrane produced the rough surface,the high porosity and the adequate mechanical strength.The measured membrane pore size is about 0.6?m,contact angle up to 155°.In the DCMD experiments,the water flux and conductivity of the superhydrophobic F/Si-PANi@PVDF nanofibrous membrane at different temperature and membrane thickness were analyzed.The results showed that with the increase of temperature difference,the water flux increased significantly,but the salt rejection decreased.With the increase of membrane thickness,the heat loss of the membrane decreased,but the resistance of steam through the film increased.It is considered that the temperature in this experiment should be maintained between 40°C and 50°C,and the membrane thickness should be between 80?m and 120?m.The experiment further analyzed the resistance of the superhydrophobic F/Si-PANi@PVDF nanofibrous membrane to organic contaminants such as dyes,surfactants and humic acids.The results showed that the modified F/Si-PANi@PVDF membrane had better anti-pollution performance.We conducted a continuous 50-hour running test and the membrane flux remained at 25 L·m^-2·h^-1or more,demonstrating that the membrane has good stability.Comparing the modified F/Si-PANi@PVDF membrane with commercial PVDF membrane,the results proved that the membrane we prepared had better performance.Finally,we expanded the methods of membrane preparation and the application of superhydrophobic F/Si-PANi@PVDF membranes to provide more possibilities for direct contact membrane distillation in membrane selection and application.We also conducted economic analysis and prospects for direct contact membrane distillation in seawater desalination.