Polyamide⊥TpPa-PVDF membranes for aliphatic-aromatic solvent separations

To achieve net-zero emissions, the petrochemical industry requires energy-efficient processes for solvent recovery, and traditional distillation technologies may not be adequate. Membrane separations with 2D COFs (covalent organic frameworks) have shown potential due to their tunable pore sizes and modifiable properties. However, the large pores of the COFs have provided challenges in fabricating 2D COF membranes for solvent separation. Recent research has been focused on improving the selectivities and permeation fluxes for solvent mixtures, and to achieve long-term operation, the membranes must have high chemical and mechanical stabilities. To address the issue of large pores, our research group cross-linked the Tp (2,4,6-triformylphloroglucinol) and Pa (p-phenylenediamine) monomers of the COF with TMC (trimesoyl chloride), a monomer used traditionally for reverse osmosis interfacial polymerization, which resulted in COF(TpPa) with TMC cross-linking and small pore sizes for solvent separation. Polyamide⊥TpPa-PVDF membranes were fabricated for the first time with this method, and the TMC cross-linked COF membrane successfully rejected salts and separated aromatic/alkane solvents; a toluene/benzene mixture showed a higher separation factor than methanol/isopropanol. Use of the 2D materials for reverse osmosis at 20 bar enhanced the potential of the energy-efficient membranes for use in future petrochemical industrial applications.