(369b) Next Generation Macroporous Polymer Membranes with Low Channeling for Improved Selectivity

Microfiltration (MF) and ultrafiltration (UF) are two pressure-driven membrane technologies with numerous bioprocessing applications such as sterile filtration, protein/nucleic acid steric or affinity capture and virus removal. Depending on the application, membranes used in these applications have a mean pore size rating ranging from 0.01 - 10 µm and a vast majority of these microporous membranes are polymeric. Morphological characteristics of these microporous membranes such as porosity, pore size distribution (PSD) and pore connectivity in the lateral and axial directions are critical because they affect performance (selectivity, capacity, recovery, and fouling propensity)¹. Polymer MF/UF membranes are predominantly synthesized by phase inversion (PI) process. In PI, the temporal and spatial fluctuations in process conditions during the precipitation stage lead to poor control over the morphological structure. The resulting PSD is often log-normal and leads to poor selectivity due to large variation in pore size with subsequent fluid channeling². Channeling is the high velocity fluid flow in the primary flow direction through long and continuous regions in the pore space. It has been a phenomenon of longstanding interest in the field of separations³. Channeling could be detrimental to selectivity because it causes preferential solute transport through selected regions in the pore space which leads to low surface area utilization in adsorptive/affinity-based separations.

In this work, fluid flow and particle filtration behavior through commercial microfiltration and ultrafiltration membranes (PES, PVDF and regenerated cellulose) were studied in-silico to identify and quantify channeling. The regions in the pore space corresponding to velocity outliers (associated with channeling) were identified and connectivity parameters⁴ were calculated in the directions parallel and perpendicular to primary flow direction. Further, the effect of channeling on particle transport was studied as a function of Reynold’s number. To the best of our knowledge, such analysis has not been applied to study the transport characteristics of macoporous polymer membranes. Channels with fast flow had 6 times the pore size of the membrane (PVDF), poor lateral flow connectivity (PES), and preferential transport of fluid and particles through channels were observed. Increasing laminar Reynold’s number flow led to reduced channeling due to flow homogenization and hence increased selectivity.

In-silico filtration experiments and channeling analysis revealed that the flow through microstructures formed by random packing of monodisperse microspheres was more uniform with reduced channeling and improved lateral connectivity. Therefore, membranes with these microstructures, called ‘Fused Microsphere Membranes (FMMs)’ were synthesized, characterized and tested⁵. Experiments showed that a 0.2 µm mean pore size FMM exhibited higher flux (5x), higher selectivity (2x) and increased pore connectivity than 0.2 µm rated commercial membranes. Future work involves tuning the packing fraction and microsphere diameter ratios in bidispersed mixtures to optimize performance. This new class of membranes has the potential to improve filtration performance for solute selective separations in the biotechnology and other industries.

References

(1) Belfort, G. Membrane Filtration with Liquids: A Global Approach with Prior Successes, New Developments and Unresolved Challenges. Angew. Chem. Int. Ed. 2019, 58 (7), 1892–1902. https://doi.org/10.1002/anie.201809548.

(2) Sorci, M.; Woodcock, C. C.; Andersen, D. J.; Behzad, A. R.; Nunes, S.; Plawsky, J.; Belfort, G. “Linking Microstructure of Membranes and Performance.” J. Membr. Sci. 2020, 594, 117419. https://doi.org/10.1016/j.memsci.2019.117419.

(3) Miller, S. F.; King, C. J. AXIAL DISPERSION IN LIQUID FLOW THROUGH PACKED BEDS. 1965.

(4) Siena, M.; Iliev, O.; Prill, T.; Riva, M.; Guadagnini, A. Identification of Channeling in Pore-Scale Flows. Geophys. Res. Lett. 2019, 46 (6), 3270–3278. https://doi.org/10.1029/2018GL081697.

(5) Belfort, G.; Plawsky, J.; Karla, S. Systems and Methods Including Fused Particle Membrane for Filtration. US Provisional Patent Application Number: 63/547,204.