Effects of crossflow velocity and transmembrane pressure on microfiltration of oil-in-water emulsions

TL;DR

This paper investigates how transmembrane pressure and crossflow velocity influence oil droplet rejection and permeation in microfiltration membranes, using numerical simulations and analytical models to optimize oil-water separation.

Contribution

It provides a numerical and analytical analysis of oil droplet behavior during microfiltration, including phase diagrams and critical pressure expressions for different pore geometries.

Findings

Critical transmembrane pressure matches Young-Laplace predictions without crossflow.

Increasing crossflow velocity deforms oil droplets and raises permeation pressure.

Validated analytical expression for critical pressure across various pore shapes.

Abstract

This study addresses the issue of oil removal from water using hydrophilic porous membranes. The effective separation of oil-in-water dispersions involves high flux of water through the membrane and, at the same time, high rejection rate of the oil phase. The effects of transmembrane pressure and crossflow velocity on rejection of oil droplets and thin oil films by pores of different cross-section are investigated numerically by solving the Navier-Stokes equation. We found that in the absence of crossflow, the critical transmembrane pressure, which is required for the oil droplet entry into a circular pore of a given surface hydrophilicity, agrees well with analytical predictions based on the Young-Laplace equation. With increasing crossflow velocity, the shape of the oil droplet is strongly deformed near the pore entrance and the critical pressure of permeation increases. We determined numerically the phase diagram for the droplet rejection, permeation, and breakup depending of the transmembrane pressure and shear rate. Finally, an analytical expression for the critical pressure in terms of geometric parameters of the pore cross-section is validated via numerical simulations for a continuous oil film on elliptical and rectangular pores.