**Membrane Distillation: Principle, Advances, Limitations and Future Prospects in Food Industry**

Pelin Onsekizoglu *Trakya University Department of Food Engineering, Edirne Turkey* 

### **1. Introduction**

232 Distillation – Advances from Modeling to Applications

Schilling, S., T. Alber, S. Toepfl, S. Neidhart, D. Knorr, A. Schieber and R. Carle (2007).

Sharma, S. K., S. J. Mulvaney and S. S. H. Rizvi (2000). *Food Process Engineering - Theory and* 

Taiwo, K. A., M. N. Eshtiaghi, B. I. O. Ade-Omowaye and D. Knorr (2003). Osmotic

Toepfl, S. (2006). Pulsed Electric Fields (PEF) for Permeabilization of Cell Membranes in

Toepfl, S. and V. Heinz (2011). Pulsed Electric Field Assisted Extraction - A Case Study.

Toepfl, S., V. Heinz and D. Knorr (2007). High intensity pulsed electric fields applied for food preservation. *Chemical Engineering and Processing* Vol.46, No.6, pp. 537-546. Torreggiani, D. (1993). Osmotic dehydration in fruit and vegetable processing. *Food Research* 

Tsong, T. Y. (1991). Electroporation of cell membranes. *Biophysical Journal* Vol.60, No.2, pp.

Vauck, W. R. A. and H. A. Mueller (2000). *Grundoperationen Chemischer Verfahrenstechnik*.

Wilhelm, C., M. Winterhalter, U. Zimmermann and R. Benz (1993). Kinetics of pore size

Yin, Y. and G. He (2008). A fast high-intensity pulsed electric fields (PEF)-assisted extraction

Zhang, Q., G. V. Barbosa-Cánovas and B. G. Swanson (1995). Engineering Aspects of Pulsed Electric Field Pasteurization. *Joumal of Food Engineering* Vol.25, pp. 261-281. Zimmermann, U., G. Pilwat, F. Beckers and F. Riemann (1976). Effects of external electrical

during irreversible electrical breakdown of lipid bilayer membranes. *Biophysical* 

of dissoluble calcium from bone. *Separation and Purification Technology* Vol.61, No.2,

fields on cell membranes. *Bioelectrochemistry and Bioenergetics* Vol.3, No.1, pp. 58-83.

M. Balasubramaniamet al, Blackwell Publishing Ltd. : pp. 190-200.

*Laboratory Experiments*. Canada, John Wiley & Sons.

Stuttgart, Deutscher Verlag für Grundstoffindustrie. Weaver, J. C. (2000). Electroporation of Cells and Tissues. No.28, pp. 24-33.

*Science & Technology* Vol.38, No.6, pp. 693-707.

No.1, pp. 127-134.

Berlin. PhD.

297-306.

pp. 148-152.

*International* Vol.26, pp. 59-68.

*Journal* Vol.64, No.1, pp. 121-128.

Effects of pulsed electric field treatment of apple mash on juice yield and quality attributes of apple juices. *Innovative Food Science & Emerging Technologies* Vol.8,

dehydration of strawberry halves: influence of osmotic agents and pretreatment methods on mass transfer and product characteristics. *International Journal of Food* 

Food- and Bioprocessing - Applications, Process and Equipment Design and Cost Analysis. Fakultät III - Prozesswissenschaften der Technischen Universität Berlin.

*Nonthermal processing Technologies for Food*. H. Q. Zhang, G. V. Barbosa-Cánovas, V.

Membrane separation processes have become one of the emerging technologies in the last few decades especially in the separation technology field. They offer a number of advantages over conventional separation methods in a wide variety of applications such as distillation and evaporation. Membrane processes can be easily scaled up due to their compact and modular design; they are able to transfer specific components selectively; they are energy efficient systems operating under moderate temperature conditions ensuring gentle product treatment.

Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), pervaporation and electrodialysis are conventional membrane processes that have already gained wide acceptance in food processing (Bazinet et al., 2009; Couto et al., 2011; Gomes et al., 2011; Mello et al., 2010; Quoc et al., 2011; Santana et al., 2011). Membrane distillation (MD) is an emerging thermally driven membrane process in which a hydrophobic microporous membrane separates a heated feed solution and a cooled receiving phase. The temperature difference across the membrane results a water vapour pressure gradient, causing water vapour transfer through the pores from high vapour pressure side to the low one. Some of the key advantages of membrane distillation processes over conventional separation technologies are: relatively lower energy costs as compared to distillation, reverse osmosis, and pervaporation; a considerable rejection of dissolved, non-volatile species; much lower membrane fouling as compared with microfiltration, ultrafiltration, and reverse osmosis; reduced vapour space as compared to conventional distillation; lower operating pressure than pressure-driven membrane processes and lower operating temperature as compared with conventional evaporation (Bazinet et al., 2009; Couto et al., 2011; Gomes et al., 2011; Lawson & Lloyd, 1996b; Mello et al., 2010; Quoc et al., 2011; Santana et al., 2011).

Dewatering aqueous solutions is one of the key unit operations encountered in food processing, particularly in the processing of beverages, fruit juice, milk, whey, vegetable extracts, etc. The initial soluble solid contents are increased by concentration process, reducing the volume with consequent reduction of transport, storage and packaging costs. In addition, the concentrates are more resistant to microbial and chemical deterioration as a result of water activity reduction.

Membrane Distillation: Principle, Advances,

Fig. 1. Schematic representation of MD configurations

Limitations and Future Prospects in Food Industry 235

Today, multistage vacuum evaporation is the predominant method used for liquid concentration in food industry. The main drawbacks of this system are high energy consumption and heat induced deterioration of sensory (color changes, off-flavor formation) and nutritional characteristics (Ibarz et al., 2011; Kadakal et al., 2002; Simsek et al., 2007; Toribio & Lozano, 1986; Varming et al., 2004). Recently, technological advances related to the development of new membrane processes including membrane distillation have been proved to overcome this limitation (Bagger-Jorgensen et al., 2011; Cassano & Drioli, 2007; Hongvaleerat et al., 2008; Kozak et al., 2009; Onsekizoglu et al., 2010b; Valdes et al., 2009).

This chapter will cover the process features, theoretical aspects and the relevant mathematics related to water transport mechanism in membrane distillation. The most basic concepts of osmotic distillation, a membrane distillation variant operating at lower temperature will be also discussed. The suggestions for membrane selection taking into account the membrane material and module configuration together with contact angle and membrane wettability will be presented in detail. The process parameters affecting the transmembrane flux and the most promising applications for enhancement of flux will be highlighted. Applications in food industry and long term performance of membrane distillation systems will be evaluated. The possibility of integrating membrane distillation with other existing processes and suggestions for future work will be presented.
