1. Membrane Technology Group, Faculty of Science and Technology, University of Twente, Postbus 217, 7500 AE Enschede, The Netherlands, Department of Engineering Chemistry and Inorganic Chemistry, University of Cantabria, Avenida Los Castros, s/n, 39005 Santander, Spain, and Department of Chemical Engineering, Fachhochschule Münster, University of Applied Sciences, Stegewaldstrasse 39, 48565 Steinfurt, Germany