chemical engineering research and design 88 (2010) 653–660 Contents lists available at ScienceDirect Chemical Engineering Research and Design journal homepage: www.elsevier.com/locate/cherd Microfiltration of whole milk with silicon microsieves: Effect of process variables Edmundo Brito-de la Fuente a,∗ , Beatriz Torrestiana-Sánchez b , Egon Martínez-González a , José M. Mainou-Sierra a a Kabi Innovation Centre, Fresenius-Kabi Deutschland, Else-Kröner Strasse 1, D-61352 Bad Homburg, v.d.H., Germany b Food Research & Development Unit, Technological Institute of Veracruz, M.A. Quevedo 2779, Veracruz, Ver., 91808, Mexico abstract The impact of high-frequency cross-flow back-pulsing on microsieves permeation performance during the micro- filtration of whole milk is described in this work. Silicon nitride microsieves (0.8 m rectangular) combined with a dynamic permeate cross-flow back-pulsing technique to control fouling were used. Results showed that the transmembrane pressure (TMP pos ) and the back-pulsing frequency were the process variables that most influenced microsieves performance. Permeation rates in the range of 5000 up to 27,000 L h -1 m -2 which are one order of mag- nitude higher than those reported for skim milk microfiltration were obtained depending on the process conditions selected. It was concluded that higher permeation rates are obtained when the back-pulse pressure, i.e., the negative TMP is set equal to the positive TMP, both at 150mBar and the back-pulsing frequency at 15Hz. © 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Microfiltration; Microsieves; Milk; Cold sterilization; Membrane engineering 1. Introduction Processes based upon conventional and/or traditional micro- filtration membranes are quite often compromised by their poor performance and high operational cost. However, lat- est developments in membrane manufacturing process, based upon the use of photolithographic techniques from the semi- conductor industry (van Rijn, 2004; Brans et al., 2006) and more recently on phase separation micromolding (Gironès et al., 2006a), have resulted in the production of membranes charac- terized by their low flow resistance, high chemical and thermal stability and an extremely narrow pore size distribution. Thanks to their well-structured and constant morphology as well as their unique highly controlled constant porosity and their extremely thin selective layer, permeation fluxes orders of magnitude higher than those obtained with typical micro- filtration membranes can be achieved with microsieves (van Rijn, 2004). On the fouling and polarization concentration side, micro- filtration processes using microsieves can perform better by combining different strategies like high-frequency back- ∗ Corresponding author. Tel.: +49 6172 686 7421; fax: +49 6172 686 7969. E-mail address: edmundo.brito@fresenius-kabi.com (E. Brito-de la Fuente). Received 11 May 2009; Received in revised form 23 August 2009; Accepted 28 September 2009 pulsing and/or back-flushing also known as back-washing, in addition to the classical cross-flow operational mode. Back- pulsing and back-flushing produce a transient flow reversal lifting accumulated deposits of the membrane (i.e., polar- ization concentration). The fundamental difference between these two antifouling and anti-polarization concentration strategies are the forces and time used to generate the back- flow conditions (Koh et al., 2008). We believe that the use of microsieves in combination with in situ fouling and polariza- tion concentration control possibilities in modern processing equipment will lead to a better rational design of products and processes based upon microfiltration. Thus, the aim of this work is to perform a process variable study on whole milk microfiltration using silicon nitride microsieves in combination with high-frequency back- pulsing. The effects of different hydrodynamic conditions on microfiltration performance using 0.8 m rectangular slit microsieves are reported in this work. The main focus is to study the role of transmembrane pressure, cross-flow velocity and permeate back-pulsing on microsieves performance. The intended purposes of studying this microfiltration operation 0263-8762/$ – see front matter © 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.cherd.2009.09.014