(498b) Investigating Mixed Solvent Effects on Organic Solvent Nanofiltration Using Tppa-1 Covalent Organic Framework Membranes

Currently, 10-15% of the world’s energy is consumed by chemical separations, and more than 80% of that energy is used to purify organic liquids. Organic solvent nanofiltration (OSN) presents an energy and cost saving alternative to current separation technologies, such as distillation and evaporation. Polymeric membranes with graphene oxide fillers have been developed for OSN processes that show enhanced anti-swelling, chemical stability, and selectivity. However, these composite membranes lack high permeability. Covalent Organic Frameworks (COFs) were discovered in 2005 that are highly crystalline, chemically and thermally stable, and tunable in size and charge. COFs, especially 2D COFs, possess narrow pore-size distribution and controlled porous structures. As such, together with their resistance to swelling, 2D COFs inherently possess desirable properties as membrane materials for complex liquid separations, such as organic solvent nanofiltration (OSN). However, molecular interactions in OSN often dictate final membrane performance, resulting in a discrepancy between designed and apparent COF properties. Understanding and resolving this discrepancy is critical in utilizing COF membranes as a viable alternative to energy-intensive separations. To minimize the common issues of irreproducibility in newly designed and synthesized COF, a commercially available COF, TpPa-1, is used as a COF platform in this study. TpPa-1 is well studied and shows remarkable stability under harsh conditions but has not been reported for OSN applications. Effects of solvent interaction and COF chemistry are carefully examined on apparent TpPa-1 pore size and, consequently, on the permeability of COF membranes for neat and mixed solvents, and selectivity of a targeted solute. Using a molecular dynamics model, experimental data are compared and corroborated with predicted single and mixed solvent diffusivity using the Einstein relation. Findings from this study will provide a refined link for future COF design, synthesis, and desired COF membrane performance.