(447e) Highly Selective and Stable Organic Solvent Nanofiltration Membranes Based on Inter-Crosslinked Spirocyclic Composite Polymers

Organic solvent nanofiltration (OSN) and organic solvent reverse osmosis (OSRO) are promising alternatives to reduce the energy burden of thermally-based separation processes. While highly permeable membranes for organic solvent separation have been reported, highly selective performance remains difficult to achieve due to the chemically challenging operating conditions. Additionally, the long-term stability of OSN-OSRO membranes remains a relatively unexplored issue.

In this work, we fabricate thin film composite membranes based on carboxylated polymer of intrinsic microporosity and triptycene-isatin porous polymer networks (PPNs). Inter-crosslinking between carboxy-PIM and PPN was achieved in the active layer upon thermal treatment at temperatures as low as 200°C. The resulting membranes lack solubility in most organic solvents and show a defect free structure, with an active layer 300 nm thick. Remarkably, their OSN performance with styrene oligomers in toluene exceeds that of several state-of-the-art materials.

To investigate their long-term stability, membranes were exposed to liquid toluene for six months before running a second OSN test. Noteworthy, aged inter-crosslinked membranes exhibited larger permeance and similar selectivity relative to freshly cast samples, pointing out an exceptional long-term stability. Non-crosslinked membranes, fabricated as control samples, however, lost significant selectivity. The origin of this behavior was investigated. We show that unique chemical interactions between the active layer and the porous support contribute in part to the observed short- and long-term performance, highlighting the opportunity to engineer the interface between the support active layer to improve membrane performance and stability.