Product purity and particle size distribution are important factors determining the functionality and the value of products in the chemical, pharmaceutical and food industry. Many feed streams in the food industry (e.g. milk) consist of suspended micro particles, such as proteins, fat droplets, and possibly bacteria [1]. For micro particles with approximately the same charge, separation on size is the method of choice, which could be realized by membrane filtration.
Aim of the research
The aim of this research was to obtain more insight in membrane processes for the fractionation of micro sized particles (0.1 - 10 μm) with small size differences, and with special attention for microsieve technology as an alternative for conventional membranes. Because of their high fluxes, flow phenomena are very relevant for microsieves. The effects of microsieve design and process conditions (transmembrane pressure, cross flow velocity) on particle deposition were investigated. Flows were studied on pore/particle scale and on the scale of a microsieve pore field with Computational Fluid Dynamics (CFD). These CFD simulations were performed with the lattice Boltzmann (LB) method [2, 3]. Concentration polarization and module design were studied with a continuum approach for particle suspensions in LB [4]. A simulation method for suspension flow with discrete particles is currently being developed [5]. Besides computer simulations, experimental validation was performed. The effects of process conditions and feed composition on fractionation were studied for polymer membranes and microsieves. As a model, we worked with polystyrene latex particle suspensions in milliQ water. Particle deposition on polymer membranes and polymer microsieves was investigated in-line with Confocal Scanning Laser Microscopy (CSLM) [6].
Results
Some results are depicted in the following figures:
CFD simulation of flow through a microsieve and the effect of the support structure.
Bi-disperse suspension flow with Lattice Boltzmann sub-grid particle method.
CSLM images of particle deposition on silicon and polymer microsieves during fractionation.
CFD simulation of flow through a microsieve and the effect of the support structure.
Bi-disperse suspension flow with Lattice Boltzmann sub-grid particle method.
CSLM image of particle deposition on a silicon microsieve during fractionation.
CSLM image of particle deposition on a polymer microsieve during fractionation.
Publications
[1] Membrane fractionation of milk: state of the art and challenges. G. Brans, C.G.P.H. Schroën, R.G.M. van der Sman, R.M. Boom (2004) J. Membrane Sci. 243 263. [2] Evaluation of microsieve membrane design. G. Brans, J. Kromkamp, N. Pek, J. Gielen, J. Heck, C.J.M. van Rijn, R.G.M van der Sman, C.G.P.H. Schroën, R.M. Boom, Accepted J. Membrane Sci. [3] Optimization of the membrane and pore design for micro-machined membranes. G. Brans, R.G.M. van der Sman, C.G.P.H. Schroën, A. van der Padt, R.M. Boom, Accepted J. Membrane Sci. [4] A suspension flow model for hydrodynamics and concentration polarization in crossflow microfiltration, J. Kromkamp, A. Bastiaans, J. Swarts, G. Brans, R.G.M van der Sman, R.M. Boom (2005) J. Membrane Sci. 253, 67. [5] 3D Lattice Boltzmann sub-grid particle method for suspension flow. G. Brans, R.G.M. van der Sman, R.M. Boom, In preparation. [6] Transmission and fractionation of micro-sized particle suspensions. G. Brans, A. van Dinther, B. Odum, C.G.P.H. Schroën, R.M. Boom, In preparation
