Transport of uncharged organics in ion-exchange membranes: experimental validation of the solution-diffusion model

The concentration-gradient transport of uncharged organics in ion-exchange membranes (IEMs) and the experimental validation of the solution-diffusion model were investigated. Free interaction energies between organics (paracetamol, theophylline, phenazone) and IEMs were above 0, indicating potential solute resistance against partitioning into the membrane phase. Experiments performed in diffusion cells showed a linear increase in the organics concentration in the receiving solution as a function of time, suggesting a purely diffusion-driven transport. A higher organics transport was observed in anion-EMs (AEMs) than in cation-EMs (CEMs), possibly due to the higher cross-linking and lower affinity to organics of CEMs. A correlation between transport and molecular weight was observed in all IEMs following the trend: paracetamol > theophylline > phenazone. The experimental validation of the solution-diffusion model showed that the model underestimated the solutes transport in IEMs. Monte Carlo analysis indicated that the discrepancy between modeled and measured fluxes could not be eliminated even after considering experimental errors. The method for determining contact angle would influence the modeled fluxes. Moreover, the definition of diffusive hindrance factor may lead to these discrepancies, requiring further investigation. This study contributes to the field of selective organics/inorganics separation in the treatment and resource recovery of organics-rich industrial wastewater.