(17e) Partitioning, Immobilization, and Acylation of Resorcinol in Perfluorosulfonic Acid Polymer Membranes

Perfluorosulfonic acid (PSA) polymers are presently used as solid acid catalysts for the industrial production of bisphenol A and are of growing interest for biofuels synthesis and renewable energy development. Alteration of polymer morphology during solvent uptake is known to influence the catalytic activity of these materials. Experimental difficulties associated with separating the time scales of species diffusion, polymer structure relaxation, and complex reaction kinetics have prevented identification of the intrinsic reactivity and optimum morphology of active sites within the solid catalysts. In this work, we demonstrate how resorcinol may be immobilized within PSA polymer membranes to form cage structures that diffusionally constrain quinone products that result from acylation with acid anhydrides in the gas phase. The use of ppb-level concentrations of anhydrides in an inert gas carrier permits us to quantify how changes to the partitioning of imbibed resorcinol concentration in the heterogeneous (lipophilic, hydrophilic, and transitional) bulk phases of PSA can have a significant influence on their intrinsic catalytic activity, independent of diffusion effects. More specifically, we have determined that the less accessible, less hydrophilic reactive sites within the membrane yield the highest conversion rates. Solvent extraction is used to contrast the UV/VIS extinction coefficients of products and reactants in the PSA membranes versus the solution phase and to quantify diffusion and reaction kinetics. Continuity calculations that couple the Berens-Hopfenberg model for non-Fickian diffusion through polymers with Fickian transport through heterogeneous media are used to assess resorcinol partitioning among the various PSA phases.