Sandwich nanofiber membrane with high thermal conductivity boundary for high-flux membrane distillation

High heat loss represents the main constraint against hypersaline brine desalination by membrane distillation (MD) technology. The non-recyclable heat loss is mainly caused by temperature polarization and heat conduction. Typical strategies for this problem often require additional energy consumption, and the losses may outweigh the gains. In the MD process, heat loss mainly occurs in three regions, including the membrane region (heat conduction), the feed boundary layers (temperature polarization), and permeate boundary layers (temperature polarization). Theoretically, an ideal MD membrane should have a low thermal conductivity in the membrane and high thermal conductivity in the boundary layers. In this study, a sandwich structure nanofibrous membrane (abbreviated as CP-PP-CP) was designed using electrospinning technology for hypersaline brine desalination through direct contact membrane distillation (DCMD). The PDMS/PH (Polydimethylsiloxane/Poly (vinylidene fluoride-co-hexafluompropylene)) nanofibrous membrane with low thermal conductivity and high durability was selected as the substrate. The carbon nanotube (CNT) nanofiber layers with high thermal conductivity were used to reduce the temperature polarization of the boundary. The results showed that the water flux of the CP-PP-CP nanofibrous membrane was 1.3 times that of the PDMS/PH nanofiber substrate. Furthermore, the high-flux mechanism of the CP-PP-CP nanofibrous membrane was investigated. Finally, the effects of flow rate, temperature and salinity on the CP-PP-CP nanofibrous membrane were discussed.