The role of skin layer defects in organic solvent reverse osmosis membranes

The fractionation of complex liquid hydrocarbon mixtures is an important and emerging area of membrane science. Polymeric asymmetric hollow fiber membranes have the potential to be used for this purpose, especially if the size and number of defects in the membrane skin layer can be precisely engineered. Here, we fabricated various “defect-engineered” Torlon hollow fiber membranes by modifying hollow fiber spinning conditions and spin dopes to study the role of skin layer defects in the organic solvent reverse osmosis (OSRO) membranes. The quality of the membranes was investigated using several sets of pure gas permeation experiments, which provided input data for a permeation resistance model that estimates the pore size and surface porosity of the asymmetric hollow fiber membrane. We develop and experimentally validate a resistance permeation model for solvent permeation and utilize the surface properties derived from the gas permeation experiments to estimate the relative permeation rates of solvents in a mixture. The approach outlined here highlights the interconnection between gas permeation analysis and OSRO separation performance using Torlon hollow fiber membranes as an exemplar test case. The solvent permeation model is then utilized to provide quantitative insight on the differences between OSRO and organic solvent nanofiltration (OSN), and highlight the important transition region between these two modalities.