Pervaporation for Drying and Dewatering Wladyslaw Kaminski and Joanna Marszalek Faculty of Process and Environmental Engineering, Technical University of Lodz, Lodz, Poland Dewatering denotes moisture removal from materials and it is a more general term than drying. In dehydration and drying tech- nology, a growing role of modern techniques used either separately or in hybrid solutions is observed. Membrane techniques find many industrial applications in this field. Based on available literature, examples of dehydration on membranes, important from the view- point of energy saving, environmental protection, and recoverable energy sources, are presented in this study. Special attention is given to the process of pervaporation as the most modern and promising technique for azeotropic mixture separation to be used in dehy- dration of solvents, including alcohols, and removal of volatile organic compounds from sewage, concentration of aromas, and separation of multicomponent systems. Keywords Alcohols; Hybrid technologies; Phase separation; Solvents INTRODUCTION Dewatering denotes moisture removal from materials. The process may, though not necessarily, be accompanied by a change of the state of moisture. In the case of a chan- ging state, transfer from liquid to vapor phase, i.e., evapor- ation, or from solid to vapor phase, sublimation can take place. The method of drying can also be moisture removal using osmotic or sorption forces, when an additional material receives moisture bound to material. Between the auxiliary and processed material the state of physico- chemical equilibrium is set up that determines the possible degree of drying. In these cases, moisture transfer in the material with or without phase change can be described by the diffusion equation. [1,2] Dewatering is the process in which classical drying is combined with other unit operations leading to moisture removal from material. [3,4] Membrane separation is an example of the group of methods for moisture removal without phase change. This transformation, however, can occur in the discussed processes, of which an example is pervaporation. As follows from the literature analysis, membrane processes driven by the difference of pressure, concentration, temperature, or chemical potential have found applications mainly in food and pharmaceutical industries and in biotechnology, where they constitute the stage of preliminary concentration (dewatering) preceding final operations. Interest in the membrane processes follows from their following advantages: [5]  a possibility for selective separation of chemical compounds at relatively low costs  minimization of thermal degradation  a possibility for raw material recirculation with a small amount of waste products generated  moderate energy consumption. A possibility for low energy consumption, processing of solutions with low and very low concentrations at high cost-efficiency of the process, gives membrane techniques a privileged position. Kaminski [1] presented numerous examples of processes that in recent years have gained spe- cial importance in ecology, technology, and power engin- eering. [6] This is also confirmed by a number of studies published in scientific and technical journals of world renown. [7] Membrane processes can be analyzed from the view- points of technology, ecology, energy saving, novel tech- nologies, higher product quality, etc. The membrane processes are the modern methods for separation, purifi- cation, and concentration of mixtures that are alternative and competitive to classical methods that find increasing industrial applications. [8] These processes can be used at the stage of preliminary processing, as a method to carry out the main material transformation, and on the final pro- cessing stage, e.g., sewage treatment. A special place in this group of methods is occupied by dewatering of solutions and mixtures. PERVAPORATION Water removal by means of membrane techniques has great practical importance because of high heat of water evaporation. Table 1 gives heat of evaporation of selected Correspondence: Wladyslaw Kaminski, Faculty of Process and Environmental Engineering, Technical University of Lodz, Wolczanska 215, 90-924 Lodz, Poland; E-mail: kaminski@wipos. p.lodz.pl Drying Technology, 24: 835–847, 2006 Copyright # 2006 Taylor & Francis Group, LLC ISSN: 0737-3937 print/1532-2300 online DOI: 10.1080/07373930600733994 835