Single-layer membranes for organic solvent nanofiltration: a molecular dynamics simulation and comparative experimental study

Organic solvents are widely used in pharmaceutical and chemical industries. Their separation and recovery account for a large part of energy consumption and capital cost in many industrial processes. MoS₂ membranes with varying pore sizes (0.6 nm pore with S atoms, 0.7 nm pore with Mo atoms, 1.3 nm pore with S atoms, 1.4 nm pore with Mo atoms) were investigated as organic solvent nanofiltration (OSN) membranes using molecular simulation in this study. The fluxes of five polar solvents (methanol, ethanol, propanol, acetonitrile and acetone) and a nonpolar solvent (n-hexane) were predicted. Although the 0.6 nm S pore has a smaller pore size, it has a better flux for some organic solvents than the 0.7 nm Mo pore. This selective behavior of molybdenum disulfide was confirmed by calculating the potential of mean force (PMF) of each solvent molecule. The PMFs show that polar solvents face a higher energy barrier through the pore, and greater resistance needs to be overcome. After testing the permeability of solvent by experiment and simulation, the flux changes of different solvents have the same trend in experiment and simulation. The solvent permeability was slightly affected in the presence of solute (acetaminophen), and MoS₂ membranes with small pores demonstrated 100% rejection rate for acetaminophen. This study confirmed that pore chemistry and pore size play important roles in OSN, and MoS₂ is a promising OSN membrane for the recovery of organic solvents.

Both simulated and experimental results demonstrated a good correlation between solvent permeances and solvent properties for the single-layer MoS₂ membrane.