Journal of Membrane Science 349 (2010) 225–230 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci The use of factorial design for modeling membrane distillation Pelin Onsekizoglu a,∗ , K. Savas Bahceci b , Jale Acar a a Department of Food Engineering, Hacettepe University, 06532 Beytepe, Ankara, Turkey b Department of Food Engineering, Hitit University, Corum, Turkey article info Article history: Received 27 August 2009 Received in revised form 26 October 2009 Accepted 22 November 2009 Available online 27 November 2009 Keywords: Osmotic distillation Membrane distillation Factorial design Osmotic agent Temperature abstract A two-level factorial experimental design was used to investigate the influence of the main operating parameters on evaporation flux and soluble solid content of apple juice during concentration through osmotic distillation (OD) and membrane distillation (MD) processes. The factorial models have been obtained from experimental design to study all interactions among the considered parameters (osmotic agent concentration (0–65% CaCl 2 ), flow rate (10–30 L/h) and temperature difference between feed and osmotic agent (10–30 ◦ C)) and validated statistically by analysis of variance (ANOVA). For both responses, the osmotic agent concentration was the most influential factor. The magnitude of the main influence of CaCl 2 concentration was followed by the temperature difference and flow rate, respectively. The anal- ysis of the experimental responses revealed that CaCl 2 concentration and temperature difference had significant interactive effects on evaporation flux. All interactions between the studied parameters were significant in the case of soluble solid content at the 99% confidence level. Although the interaction terms have significant effects, their levels were only a small amount compared to linear effects. The predicted responses were compared with the experimental ones. In general, the predicted values were in reason- able agreement with the experimental data, further confirming the very good prediction ability of the models. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Fruit juices are beverages of high nutritional value since they contain high levels of minerals, vitamins and other beneficial components for human health. In order to obtain chemical and microbiological stability as well as reducing the transport, pack- aging and storage costs, fruit juices are generally concentrated. During the concentration process, the water should be removed selectively in order to obtain a product with an appearance and taste as close as possible to the original juice. However, multi-stage vacuum evaporation processes are generally used for concentra- tion, resulting significant loss of aroma compounds, irreversible alteration of nutritional value and color changes due to high oper- ation temperatures [1]. One of the solutions to this problem is the use of alternative processes that avoid high temperatures of operation, such as the membrane processes. Membrane distillation (MD) and osmotic distillation (OD) are well known methodolo- gies having great potential as concentration processes carried out at atmospheric pressure and temperatures near the ambient tem- perature [2–4]. Both operations involve microporous hydrophobic membranes that are in contact with fruit juices at different tem- ∗ Corresponding author. Tel.: +90 312 297 71 20; fax: +90 312 297 21 23. E-mail address: pelins@hacettepe.edu.tr (P. Onsekizoglu). peratures and/or compositions. In both processes, a microporous hydrophobic membrane is in contact with feed solution on one side. The driving force for the water transport through the gas phase immobilized within the pores is a water vapor pressure difference related with the water activity differences between the juice and an osmotic agent, in the case of the OD process, or by a temperature difference for the MD process [5,6]. Response surface methodology (RSM), a collection of statisti- cal and mathematical techniques, is a useful tool for development, improvement, and optimization of processes. It is used to exam- ine the relationship between one or more response variables and a set of quantitative experimental variables or factors. Meanwhile, use of RSM has gained prominence in food process design and optimization owing to the ease of operation, reliability and repro- ducibility of the model parameters. Nowadays, factorial designs have proved their usefulness, and are widely used in the statis- tical planning of experiments to obtain empirical models relating process response to process factors. Khayet et al. [7] studied RSM in direct contact membrane distillation using salt (NaCl) aqueous solutions and investigated the operating factors, namely, the stir- ring rate, feed temperature, and solute concentration. However, the effects of main process parameters involved in OD and MD dur- ing concentration of fruit juices need to be carried out in detail. The objective of this work is to evaluate the effects of temperature difference between the feed and permeate side of the membrane, concentration of the osmotic agent (CaCl 2 solution) and flow rate 0376-7388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2009.11.049