Particle Separation and Fractionation by Microfiltration

Particle separation and fractionation by microfiltration Promotor: Prof. Dr. Ir. R.M. Boom Hoogleraar Levensmiddelenproceskunde, Wageningen Universiteit Copromotoren: Dr. Ir. C.G.P.H. Schroën Universitair docent, sectie Proceskunde, Wageningen Universiteit Dr. Ir. R.G.M. van der Sman Universitair docent, sectie Proceskunde, Wageningen Universiteit Promotiecommissie: Prof. Dr. Ir. J.A.M. Kuipers Universiteit Twente Prof. Dr. Ir. M. Wessling Universiteit Twente Dr. Ir. A. van der Padt Royal Friesland Foods Prof. Dr. M.A. Cohen Stuart Wageningen Universiteit Janneke Kromkamp Particle separation and fractionation by microfiltration Scheiding en fractionering van deeltjes middels microfiltratie Proefschrift Ter verkrijging van de graad van doctor op gezag van de rector magnificus van Wageningen Universiteit, Prof.dr. M.J. Kropff, in het openbaar te verdedigen op dinsdag 6 september 2005 des namiddags te vier uur in de Aula. Particle separation and fractionation by microfiltration Janneke Kromkamp Thesis Wageningen University, The Netherlands, 2005 - with Dutch summary ISBN: 90-8504-239-9 Contents 1 Introduction 1 1.1 Membrane filtration 2 1.2 Microfiltration 2 1.3 Mass transport 5 1.4 Shear-induced diffusion 7 1.5 Research aim and outline 9 2 Lattice Boltzmann simulation of 2D and 3D non-Brownian suspensions in Couette flow 13 2.1 Introduction 14 2.2 Computer simulation method 15 2.2.1 Simulation of the fluid 15 2.2.2 Fluid-particle interactions 17 2.2.3 Accuracy of particle representation and particle-particle interactions 18 2.3 Single and pair particles in Couette flow 20 2.3.1 Wall effects on a single particle 20 2.3.2 Two colliding particles in shear flow 21 2.4 2D and 3D multiparticle suspensions in Couette flow 23 2.4.1 Wall effects 23 2.4.2 Viscosity 25 2.4.3 Shear-induced diffusion 27 2.5 Conclusions 33 2.6 Lubrication force in a 2D suspension 34 2.7 Analytical model for shear-induced diffusion 36 2.7.1 The collision frequency of the particle in 3D 36 2.7.2 The collision frequency of a particle in 2D 38 2.7.3 The displacement of the particle in a collision 38 2.7.4 The self-diffusion tensor 40 3 Shear-induced self-diffusion and microstructure in non-Brownian suspensions at non-zero Reynolds numbers 41 3.1 Introduction 42 3.2 Computer simulation method 45 3.3 Effects of hydrodynamics and inertia in particle suspensions 48 3.4 Shear-induced diffusion at non-zero Reynolds numbers 55 3.5 Shear-induced changes in microstructure 61 3.6 Conclusions 63 3.7 Lubrication force in a 2D suspension 65 4 Shear-induced self-diffusion in bidisperse suspensions 69 4.1 Introduction 70 4.2 Computer simulation method 73 4.3 Rheology and microstructure of bidisperse particle suspensions at non- zero Reynolds numbers 76 4.4 Shear-induced self-diffusion in bidisperse suspensions 79 4.5 Conclusions 86 5 Shear-induced diffusion model for microfiltration of polydisperse suspensions 89 5.1 Introduction 90 5.2 Shear-induced migration model for polydisperse suspensions 91 5.3 Materials and methods 92 5.4 Results and discussion 92 5.4.1 Predicted steady-state fluxes 92 5.4.2 Experimental results 95 5.5 Conclusions 96 6 Effects of particle size segregation on crossflow microfiltration performance: control mechanism for concentration polarisation and particle fractionation 99 6.1 Introduction 100 6.2 Shear-induced diffusion in polydisperse suspensions 101 6.2.1 Particle back-transport as determined by shear-induced migration 101 6.2.2 Shear-induced particle segregation in channel flow 102 6.3 Materials and methods 103 6.3.1 CSLM experiments 103 6.3.2 Fractionation of milk fat globules 105 6.4 Results 106 6.4.1 Kinetics of particle deposition 106 6.4.2 Shear-induced diffusive particle behaviour 107 6.4.3 Fractionation of milk fat globules 112 6.5 Conclusions 114 7 Differential analysis of particle deposition layers from micellar casein and milk fat globule suspensions 117 7.1 Introduction 118 7.2 Materials and methods 120 7.2.1 Preparation of colloidal suspensions 120 7.2.2 Viscosity of micellar casein suspensions 121 7.2.3 Dead-end filtration 122 7.2.4 Analysis of cake properties 122 7.3 Results 124 7.3.1 Latex suspensions 124 7.3.2 Micellar casein suspensions 126 7.3.3 Milk fat globule suspensions 129 7.4 Conclusions 131 8 A suspension flow model for hydrodynamics and concentration polarisation in crossflow microfiltration 137 8.1 Introduction 138 8.2 Computer simulation method 140 8.2.1 Suspension flow model 140 8.2.2 Lattice Boltzmann method for hydrodynamics and convection- diffusion 141 8.2.3 Initial and boundary conditions 144 8.3 Results 147 8.3.1 Simulation of microfiltration with the suspension flow model 147 8.3.2 Effect of transmembrane pressure on flux and cake layer formation 147 8.3.3 Position-dependence of flux and cake layer thickness 150 8.3.4 Microfiltration in systems with different geometries 152 8.4 Conclusions 155 9 References 161 Summary 169 Samenvatting 173 Nawoord 177 Curriculum vitae 181 List of publications 183 1 Introduction 2 CHAPTER 1 1.1 Membrane filtration In the field of separation processes, two groups can be distinguished, techniques to separate phases and techniques to separate components [1, 2]. Phase separation techniques take advantage of differences in particle size (sieving, filtration) or density (sedimentation, centrifugation). Component separation techniques are based on differences in vapour pressure (distillation, stripping), freezing point (crystallization), charge (ion exchange, electrolysis), affinity (absorption, extraction), or chemical nature (leaching, complexa- tion). Membrane filtration is a separation technique in which the flow through a membrane is used to separate different components from each other. In pressure-driven membrane filtration processes, such as microfiltration, ultrafiltration, nanofiltration and reverse osmosis, these components are present in a fluid and their separation is driven by a pressure gradient over the membrane. These processes can be classified based on the separation property of the process and on the membrane pore size (Table 1). Consequently, some belong to the group of phase separation techniques and others to the group of component separation techniques. Table 1.1: Pressure-driven membrane filtration processes Process Separation property Membrane Operating pore size pressure Microfiltration size 0.05 - 5 µm ≤ 3 bar Ultrafiltration size 2 nm - 0.05 µm 1-10bar Nanofiltration size and/or affinity 0.5-2nm 5-40bar and/or charge Reverse osmosis affinity and/or charge - ∗ 10 - 100 bar ∗ subject of debate; often considered not to have pores In general, advantageous aspects of pressure-driven membrane filtration processes are their high selectivity and the possibilities for operation without a phase change. Further they are operated at ambient temperatures, without the need for additives and with relatively low energy consumption. Besides that, membrane filtration processes offer the advantages of continuous and automatic operation, modular construction and simple in- tegration in existing production processes, as well as relatively low capital and running costs. 1.2 Microfiltration Microfiltration (MF) is one of the pressure-driven membrane filtration processes. As stated in table 1.1, MF membranes are size-selective, have relatively large pores and are operated at pressures below 3 bar. In general, the size of the particles that are retained during MF ranges from 0.02 to 20 µm. Some of the particles in the feed solution may be small compared to the membrane pores and are consequently able to pass the membrane. In this case, not only a fluid- particle but also a size-selective particle-particle separation may be accomplished (see INTRODUCTION 3 Figure 1.1: Schematic representation of “dead-ended flow” (left) and “cross-flow” (right) MF. e.g. Chapter 6). MF is one of the oldest membrane filtration processes. In 1929 the process was first commercialised by Sartorius Werke GmbH in Gottingen, Germany as a bacteriological assay to rapidly determine the safety of drinking water. Application on an industrial scale started in the late sixties. An important factor for the industrial application was the devel- opment of cross-flow membrane filtration systems. In such a system, the feed suspension flow is directed parallel or tangential to the membrane with inlet and outlet ports (Figure 1.1). Compared to “dead-ended flow” or “impact flow” with a perpendicular direction of the feed suspension flow to the membrane, a “cross-flow” flow pattern results in much higher permeation fluxes. This is due to re-entrainment of polarised and deposited particles by wall shear stresses along the membrane. Control over this re-entrainment process is of key importance for process operation as is discussed in Chapters 5-8 for the applications under study in this thesis. Nowadays MF has a broad application range in industries such as the biotechnological, food, electronic and automobile industry. The applications are diverse, but to mention afew: • biotechnological applications: bacterial, yeast and mammalian cell harvesting; clarification of antibiotics and virus containing solutions; sterilisation of solutions containing antibiotics, valuable biological molecules and DNA, and tissue culture media; • food applications: wine, juice and beer clarification, sterilisation, protein separation in milk; • medical applications: blood oxygenators, plasma separation from blood; • water treatment: production of ultrapure water, oil-water separations, wastewater treatment. This thesis is targeted at future membrane separation processes for dairy applications. 4 CHAPTER 1 Figure 1.2: Components in milk: size indication and membrane processes [3]. MF=microfiltration UF=ultrafiltration NF=nanofiltration RO=reverse osmosis. Milk consists of a wide variety of constituents with different functionalities. The function- ality of these constituents could be used more effectively if they were available separately.

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