(573e) Effect of Filler Surface Properties on Ethanol Dehydration By Mixed-Matrix-Membranes Pervaporation

Pervaporation (PV) is an attractive membrane operation for dehydrating organic solvents due to its low energy demand and applicability in heat sensitive compounds. In PV process, separation parameters are independent of thermodynamic limitations like azeotropes, and can operate at much lower energy footprint than conventional distillation processes. Going beyond the single phase polymeric membranes, two phase mixed matrix membrane (MMM) comprising a filler phase embedded into continuous polymer matrix has been introduced to overcome the permeability-selectivity trade off. Since research and development in tailoring fillers for specific separation requirements has seen increased activity as high performing membrane selectivity becomes a function of filler content. In such fillers, when embedded in polymer matrix, surface properties or hydrophilicity plays an important role on polymer interaction and species transport. With hydrophilic filler, the water contact angle becomes smaller than the pure hydrophilic membrane. Conversely, hydrophobic fillers water contact angles are usually increased. However, while much effort has been devoted to MMMs in practice, modeling on pervaporative dehydration process was limited to only mass transfer prediction models with attempts failing to integrate and evaluate filler surface properties. In this study, fillers with tunable hydrophilicity is produced by systematic pyrolysis of lignin in a fluidized bed reactor (FBR). Three fillers were produced with contact angle 70⁰, 110⁰, 135⁰ and embedded in a hydrophilic Polyvinyl alcohol (PVA) matrix. Pervaporative dehydration of ethanol-water (5-15 wt%, with the azeotrope point) is studied for experimental data and a semi-empirical solution-diffusion transport model is developed to describe the mass transport in the MMM membranes. Maxwell equation for relative permeability is explored to evaluate maximum and minimum change of filler permeability (P_f) with filler volume fraction. Furthermore, equilibrium sorption of the fillers is measured to normalize any permeation by the filler. The model fillers with only variable surface characteristics i.e. hydrophilicity is utilized to develop a mass transfer model for species permeability with contact angle as model parameter. Evaluation of such models is essential for novel filler design and scaled up pervaporation application with MMM. This study is also insightful for understanding and modelling filler-polymer interaction for similar transport mechanisms specially gas separations.