(646d) Torlon® Hollow Fiber Membranes for Organic Solvent Reverse Osmosis Separation of Complex Aromatic Hydrocarbon Mixtures

Defect-free polyamide-imide (Torlon^®) hollow fiber membranes were fabricated with the aim of investigating the potential for polymer-based organic solvent reverse osmosis (OSRO) separations of complex aromatic hydrocarbon mixtures. The quality of the membranes was assessed by gas permeation, and the membranes used in this study were found to be essentially defect-free (i.e., the permselectivity of the fibers closely matched the permselectivity of dense films).Low molecular weight cut offs (MWCO) of ~180 g mol^-1 were obtained using a complex mixture of aromatic hydrocarbons relevant to separations downstream of naphtha crackers. Beyond characterizing the membranes, we also demonstrate bulk OSRO-type separations of 80/20 (mol%) mixtures of toluene and 1,3,5-triisopropylbenzene (TIPB, 204 g mol^-1) where TIPB was used as a probe molecule of large aromatic hydrocarbons. At an upstream pressure of 70-80 bar (more than 50 bar over the osmotic pressure for this system), we find that the solvent concentration is approximately 98.5-99.0 mol% and that the TIPB rejection coefficient is approximately 90% (separation factor of ~25) in the permeate. These purities and rejections approach 100% as the concentration of the TIPB decreases. Complex mixture of alkyl aromatics were also investigated, and we observe that solvent molecules with molecular weights larger than 185 g mol^-1 have rejection coefficients in excess of 90%. We observe low solvent (toluene) permeances of approximately 0.01 L/m²-h-bar, which we find is consistent with the low driving forces in OSRO separations and the general low permeability of Torlon^®. However, the ability to reject solutes as small at 185 g mol^-1 using commercial polymers, commercially-inspired spinning techniques, and without the need of post-fabrication crosslinking suggests that these membranes have the potential to enable challenging solvent-solute or even solvent-solvent separations found in the hydrocarbon processing industry. This work provides a detailed benchmark for OSRO-type separations using polymeric hollow fiber membranes.