Conductive heating vacuum membrane distillation for brine desalination: Study on operational conditions, temperature polarization and energy consumption

Abstract

Membrane distillation (MD) has gained significant attention for treating hypersaline brine. However, conventional MD is still constrained by technical issues such as temperature polarization (TP) caused by the feed being continuous heated. Herein, through the use of a thermal conducting layer, this study introduced a conductive heating vacuum membrane distillation (CH-VMD) system capable of transmitting external heat directly to the membrane-water interface without preheating the feed. The influence of operational conditions on distillate flux and salt rejection was investigated. In both CH-VMD and conventional VMD systems, the temperature profile at the membrane-water interface were examined and compared. In addition, we analyzed the TP differences between the two systems under different operational conditions. In CH-VMD system, with a 35 g/L NaCl feed solution, thermal conducting layer temperature of 60 °C, a flow velocity of 3.1 cm/s, and 90 kPa vacuum level, the distillate flux reached 9.8 L/m2·h and the salt rejection achieved 99.9%. The temperature polarization coefficient was greater than unity, resulting in a thermal efficiency as high as 83.2%. Heat conduction increased the temperature of the membrane-water interface, which is critical for optimizing MD performance in terms of overcoming TP, enhancing distillate flux and salt rejection, and lowering energy consumption.