Microwave Induced Membrane Distillation for Enhanced Ethanol-Water Separation on a Carbon Nanotube Immobilized Membrane

This article demonstrates the enhanced organic separation via microwave-induced sweep gas membrane distillation from its aqueous mixture. Microwave heated ethanol-water mixtures were separated on polytetrafluoroethylene (PTFE) and carbon nanotube immobilized membranes (CNIM). The membrane performances in terms of ethanol vapor flux and separation factors were evaluated and compared between microwave-induced membrane distillation (MIMD) and MD using conventional heating. The combination of CNIM and microwave heating was most effective where the ethanol flux reached up to 11.3 L/m² h and separation factor was 13.7, which were 46% and 102% higher than that by conventional MD. The mass transfer coefficient in CNIM-MIMD was also 81% higher than what was achieved by conventional MD. While the plain PTFE membrane was not as effective as CNIM, MIMD on PTFE also showed significant enhancement over conventional MD. Performance improvements in MIMD were due to nonthermal effects such as localized superheating and break down of hydrogen-bonded ethanol-water clusters. Moreover, MIMD required less energy to operate than conventional MD under similar conditions. The lower energy consumption along with higher flux and separation factor in MIMD represents a major advancement in the state of the art in solvent separation by MD.