Ethanol removal from water by Pervaporation using SBS membranes in both flat and spiral wound module configuration

Introduction Ethanol is considered a green alternative to fossil fuels. Pervaporation (PV) is claimed to be an economical separation technique for ethanol recovery from fermentation broths [2]. In this study, the performance of laboratory-scale symmetric dense membranes [1] was studied. From the first promising results, membranes were scaled-up and pilot scale spiral-wound modules were made by Vladipor, based on composite membranes of SBS, supported on a highly porous support of Fluoroplast F-42. An intermediate layer of PDMS (poly dimethyl siloxane) and PU (poly urethane urea) was used to improve the membrane performance. Experimental The isotropic dense symmetric membranes were prepared by solvent evaporation. The composite membranes were made by casting SBS solution on membrane supports followed by solvent evaporation in air. Morphological analyses (SEM) combined with gas permeation tests allowed the optimization of the defect-free coating and the determination of the effective thickness. The hydrophobicity of these membranes was also valued by contact angle measurements. Pervaporative removal of ethanol from water was investigated by varying operative conditions, such as ethanol concentration and temperature of the feed solution. Pervaporation tests carried out with spiral-wound modules confirmed the trend of the flat lab-scale composite membranes. Results and discussion In gas permeation the SBS/PU combination provided a higher selectivity with a lower flux [3]. This situation was reversed in pervaporation, since PU is more hydrophilic than PDMS and SBS, and it has a different behaviour in dry or wet conditions. In PV, membranes with PDMS as intermediate layer, depending on its hydrophobic character, showed better results than PU ones. From PV tests of both composite membranes it was found an increase in flux and in ethanol selectivity in comparison to SBS isotropic membrane. Following these promising results, the procedure to prepare multilayer membranes was scaled-up for the preparation of spiral-wound modules. In this configuration the best results in terms of ethanol/water selectivity were obtained with a maximum of ? = 8.3 at 3 wt% ethanol and at 30°C (Fig. 1). Also in this case membranes with PDMS as intermediate layer gave better results in terms of selectivity than PU ones. Figure 1. Effect of the temperature on the selectivity at 5 wt% ethanol concentration and a permeate pressure of 6 mbar for all tested membranes. References [1] A. Dobrak, A. Figoli, S. Chovau , F. Galiano, S. Simone, I.F.J. Vankelecom, E. Drioli , B. Van der Bruggen, Performance of PDMS membranes in pervaporation: Effect of silicalite fillers and comparison with SBS membranes, J. Colloid Interface Sci. 346 (2010) 254-264. [2] S.K. Sikdar, J. Burckle, B.K. Dutta, A. Figoli, E. Drioli, Method for fabrication of elastomeric asymmetric membranes from hydrophobic polymers, US Patent 2008/0114087, pub. date: May 15, 2008. [3] F. Bazzarelli, P. Bernardo, F. Tasselli, G. Clarizia, J.C. Jansen, Multilayer composite SBS membranes for pervaporation and gas separation Sep. Purif. Technol. 80/3 (2011) 635-642. Acknowledgement The work leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. NMP3-SL-2009-228631, project DoubleNanoMem.