# Influence of Module Design and Concentration Polarization on Pore Size Determination for Nanofiltration Membranes

## TL;DR

This paper explores how membrane module design and concentration polarization affect pore size determination in nanofiltration membranes.

## Contribution

The study introduces a method to reliably determine true retention rates by optimizing channel design and reducing concentration polarization effects.

## Key findings

- Optimized channel design enables more accurate determination of true retention rates without concentration polarization.
- Observed and intrinsic retention rates are nearly identical when mass transfer coefficients are considered.
- Lower cross-flow rates improve lab-scale applicability while maintaining accuracy.

## Abstract

Nanofiltration is an important part of pressure-driven membrane separation processes. A comprehensive understanding of the interplay between module hydrodynamics, concentration polarization, and solute rejection is essential for predicting NF performance and for scaling up processes. For two different membrane modules, the characterization and determination of concentration polarization as well as pore-size determination according to the Donnan steric pore model are described. The results show that an optimized channel design allows for a more reliable determination of true retention rates without concentration polarization. Differences between observed retention rates and intrinsic retention rates considering mass transfer coefficients can be neglected. These results are obtained at significantly lower cross-flow rates, allowing for better applicability at the lab scale.