Low temperature recovery of acetone–butanol–ethanol (ABE) fermentation products via microwave induced membrane distillation on carbon nanotube immobilized membranes
Acetone, butanol and ethanol (ABE) mixture separation from dilute aqueous fermentation products is an important process for the biofuel industry. Here, we present a novel approach for ABE recovery using microwave induced membrane distillation (MD). Carbon nanotubes (CNTs) and octadecyl amide (ODA) functionalized CNTs were immobilized on membrane surfaces and were used in sweep gas MD separation of ABE. The ABE flux, separation factor and mass transfer coefficient obtained with CNT and CNT-ODA immobilized membranes were remarkably higher than those of the commercial pristine membrane under various experimental conditions. The ABE flux enhancement reached as high as 105, 100 and 375% for the CNIM and 63, 62 and 175% for CNIM-ODA respectively. The ABE flux obtained was nearly ten times higher than that reported previously for pervaporation. The mass transfer coefficient also increased significantly along with a lower activation energy for the modified membranes. Mechanistically speaking, the immobilization of carbon nanotubes on the active membrane layer led to preferential sorption of ABE leading to enhanced separation. This phenomenon has been validated by the reduction of contact angles for the aqueous ABE mixtures on the CNT and CNT-ODA immobilized membranes indicating enhanced interaction of ABE on the membrane surface.