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

Abstract

a b s t r a c tThis 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 on 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.

Oil droplet behavior at a pore entrance in the presence of crossflow: Implications for microfiltration of oil–water dispersions

“…More recently, Darvishzadeh and Priezjev [47] studied numerically the entry dynamics of nonwetting oil droplets into circular pores as a function of the transmembrane pressure and crossflow velocity. It was demonstrated that in the presence of crossflow above the membrane surface, the oil droplets can be either rejected by the membrane, permeate into a pore, or breakup at the pore entrance.…”

The critical pressure for microfiltration of oil-in-water emulsions using slotted-pore membranes

“…1. The numerical methodology for the problem of an oil droplet at a slotted pore is very similar to the numerical setup used in our previous papers, where the permeation, rejection and breakup of an oil droplet at a circular pore was investigated for a number of material parameters and various operating conditions [17,18]. In particular, we performed test simulations to determine the appropriate domain size and grid resolution necessary to accurately capture the effects of interface curvature and flow around the droplet.…”

“…In the absence of crossflow, a simple model for the critical pressure of permeation of an oil droplet into a circular pore was validated via detailed numerical simulations [17] and experimental measurements [16]. As an aside, an analytical expression for the critical permeation pressure in the case of a continuous oil film above a membrane surface with a pore of arbitrary crosssection was obtained and validated for rectangular and elliptical pores [17]. It was later shown that in the presence of crossflow along the membrane surface, the critical pressure increases due to the drag force generated by the shear flow around an oil droplet, and, at sufficiently high shear rates, the droplet above the pore breaks up into two segments [17][18][19].…”

“…As an aside, an analytical expression for the critical permeation pressure in the case of a continuous oil film above a membrane surface with a pore of arbitrary crosssection was obtained and validated for rectangular and elliptical pores [17]. It was later shown that in the presence of crossflow along the membrane surface, the critical pressure increases due to the drag force generated by the shear flow around an oil droplet, and, at sufficiently high shear rates, the droplet above the pore breaks up into two segments [17][18][19]. The results of numerical simulations have demonstrated that the breakup capillary number and the increase in critical pressure due to crossflow are nearly independent of the contact angle but depend strongly on the oil-to-water viscosity ratio, surface tension, and drop-to-pore size ratio [18].…”

Mechanics and stability of vesicles and droplets in confined spaces

“…A number of experimental and theoretical studies [18,19,22,25,50] have focused on evaluating the maximum pressure drop [critical permeation pressure (CPP)] for a vesicle to go through (i.e., enter and exit) a pore. The distinction between pore entry pressure (EP) and CPP is however not explicit in these studies and the effects of pore throat geometry (rather than opening) and adhesion are often neglected.…”