Enhanced separation of tetrafluoropropanol from water via carbon nanotubes membranes: insights from molecular dynamics simulations

Fluorinated alcohols exhibit promising prospects in chemical industry because of their special structure and many exciting properties, in which tetrafluoropropanol (TFP) is extensive applied in synthesis of pesticides, dyestuffs, variety of solvents and detergents. However, the presence of TFP in water garners increasing attention globally because of their intrinsic potential to threat ecosystems and human health. Carbon nanotubes (CNTs) membranes are burgeoning candidates for TFP-water separation owing to well-endowed extraordinary structural and transport properties. However, a grand challenge lies in the rational design of CNTs for improving separation performance. Herein, molecular dynamics (MD) simulations were performed to investigate the effects of various parameters on the separation of TFP-water mixtures including feed temperature, CNTs pore diameters, and fluorine functionalization position. It was found that TFP was pre-selected in CNTs ranging from 9.48 to 18.98 Å due to preferential adsorption and diffusion mechanism. Excellent separation factor of 16 was achieved by (7,7) CNTs and the mass fraction of TFP was purified from 75% to 97.51%. Fluorine modified CNTs separated TFP and water by preferentially permeating water due to hydrogen bonding interaction. Simulation results showed that CNTs modified at both the entrance and interior had better separation performance than CNT modified only at one of these positions. The 100wt% water content in permeate was achieved by (11,11) CNTs modified with fluorine at the entrance and interior. These findings provide valuable insights for designing potential candidates for fluorinated alcohol-water azeotropic mixtures membrane separation, and promise extensive application aspects for the reclamation of fluorinated alcohol.