Ultrafiltration modeling of non-ionic microgels

TL;DR

This paper develops a macroscopic ultrafiltration model for non-ionic microgels, emphasizing the importance of concentration-dependent transport coefficients and particle permeability in predicting filtration performance.

Contribution

It introduces a novel filtration model incorporating recent semi-analytic expressions for diffusion and viscosity of permeable microgel dispersions, validated against simulations and experiments.

Findings

Proper transport coefficients are crucial for accurate predictions.

Microgel permeability significantly enhances permeate flux.

Model analysis of CP layer and flux under various conditions.

Abstract

Membrane ultrafiltration (UF) is a pressure driven process allowing for the separation and enrichment of protein solutions and dispersions of nanosized microgel particles. The permeate flux and the near-membrane concentration-polarization (CP) layer in this process is determined by advective-diffusive dispersion transport and the interplay of applied and osmotic transmembrane pressure contributions. The UF performance is thus strongly dependent on the membrane properties, the hydrodynamic structure of the Brownian particles, their direct and hydrodynamic interactions, and the boundary conditions. We present a macroscopic description of cross-flow UF of non-ionic microgels modeled as solvent-permeable spheres. Our filtration model involves recently derived semi-analytic expressions for the concentration-dependent collective diffusion coefficient and viscosity of permeable particle dispersions [Riest et al., Soft Matter, 2015, 11, 2821]. These expressions have been well tested against computer simulation and experimental results. We analyze the CP layer properties and the permeate flux at different operating conditions and discuss various filtration process efficiency and cost indicators. Our results show that the proper specification of the concentration-dependent transport coefficients is important for reliable filtration process predictions. We also show that the solvent permeability of microgels is an essential ingredient to the UF modeling. The particle permeability lowers the particle concentration at the membrane surface, thus increasing the permeate flux.