Porous Organic Cage Membranes for Biofuel Purification via Pervaporation: A Molecular Simulation Study

Porous organic cages (POCs) have attracted tremendous attention and have been widely used in membrane separation. In this study, four POCs (CC3, CC5, CC17, and CC19) are investigated as pervaporation (PV) membranes for biofuel (represented by ethanol/water mixtures) purification using molecular simulations. All four POCs show good adsorption selectivity for ethanol extraction from ethanol/water mixtures (x_e = 10 wt %), and CC3 presents the best ethanol adsorption selectivity due to its hydrophobicity and a strong affinity for ethanol. In terms of PV separation, due to the strong interaction of ethanol, CC19 exhibits an excellent separation factor of 1217.65 and also a comparable flux of 16.69 kg·μm/m²·h at 60 °C. Benefitting from the large aperture and hydrophobic characteristics, the CC5 membrane shows high ethanol selectivity without compromising solvent flux. The separation factor is up to 22.67 with a flux of 311.03 kg·μm/m²·h. The PV performance is mainly governed by solvent–membrane interactions as well as solvent diffusion in the membrane. This study microscopically elucidates ethanol/water mixture adsorption in POC membranes and predicts the performance for PV separation, and CC19 and CC5 membranes are proposed to be useful for high-performance separation.