Particle migration leads to deposition-free fractionation

• Shear-induced diffusion leads to fractionation of different sized droplets.
• Membrane pores five times larger than the particle can be used for fractionation.
• Concentrated emulsions up to 50% can be fractionated with high selectivities.
• Zero permeation of large and enhanced permeation of small droplets.
• The membrane fractionation process operates at industrial fluxes without fouling.

In membrane filtration, the pore size of the membrane determines the size of ‘particles’ that should be rejected, leading to accumulation of particles on the membrane surface and changed particle retention in time. A process without accumulation and thereby constant retention as function of time would be well suited for fractionation of components close in size.In this research, emulsions consisting of small droplets (∼2.0 µm) and large droplets (∼5.5 µm), with total concentrations between 10% and 47%, were fractionated. The cross-flow module consisted of a closed channel to allow particles to migrate, followed by a membrane area with 20 µm pores where emulsion fractions could be removed. Under appropriate process conditions, the permeate consisted of only small droplets, at concentrations higher than in the original emulsion, leading to very high selectivities. Especially at high concentrations, known to cause severe fouling in regular membrane filtration, these effects were occurring as a result of shear-induced diffusion of the droplets. If only small particles are targeted, the module can be operated at fluxes of 40 L/(m²/h); if fractionation is targeted the fluxes can be considerably higher. These fluxes are comparable to current operational fluxes, but here cross-flow velocity and trans-membrane pressure are much lower (corresponding to fluxes of 1–4 m3/(m²/h/bar)) with stable retention and flux as function of time.