(730b) Influence of Molecular Interactions, Membrane Swelling and Plasticization on Pure and Mixed Fluid Transport in OSN Membranes

The vast majority of industrial chemical synthesis occurs in organic solution. Solute concentration and solvent recovery consume approximately 50% of the energy required to produce chemicals and pose problems that are as relevant as the synthesis process itself. Novel, energy-efficient technologies based on polymer membranes are emerging as a viable alternative to distillation. Despite organic solvent nanofiltration (OSN) could revolutionize the chemical industry, its development is still in its infancy for two reasons: i) the instability of traditional polymer materials in chemically challenging environments, and ii) the lack of fundamental knowledge of elemental transport phenomena in OSN membranes. Most of available transport data refer to composite membranes, where the presence of a fabric backing makes it difficult to provide a fundamental description of solvent and solute sorption and transport in the active layer. The lack of fundamental information has hampered the development of rational methods to design better materials for OSN application.

In this study, the solubility of several pure and mixed organic species in Celazole^®, a commercial polybenzimidazole, has been investigated. Polymer volumetric dilation upon liquid sorption has been investigated as well, using the optical method. The role of polymer-penetrant interactions, membrane degree of swelling, and penetrant clustering on small molecule sorption and transport in Celazole^® has been discussed and several structure-property correlations were identified. Methanol was selected as a model penetrant to run sorption and diffusion experiments in the activity range 0-1. Methanol and other polar lower alcohols cause severe matrix plasticization. We have hypothesized the possible mechanism of Celazole^® plasticization. Specifically, methanol (as well as other polar penetrants) likely break the inter-chain hydrogen bonds in favor of polymer-penetrant hydrogen bonds, according to a mechanism that we could define as competitive hydrogen bonding. The breaking of the original polymeric network would increase, in turn, the distance between polymer chains, thus enhancing their mobility. This picture helps to rationalize mixed methanol-PEG400 sorption data. In contrast, Celazole^® is very stable in non-polar aliphatic and aromatic hydrocarbons.

Finally, the polymer mechanical properties were measured before and after soaking in liquid water and methanol. The results provide further proof that polar liquids severely plasticize Celazole^®.