Journal of the European Ceramic Society 25 (2005) 1895–1903 Preparation and characterization of tubular ceramic membranes for treatment of oil emulsions J.M. Benito, A. Conesa, F. Rubio, M.A. Rodr´ ıguez ∗ InstitutodeCer´ amicayVidrio(CSIC),28049Cantoblanco,Madrid,Spain Received 20 January 2004; received in revised form 31 May 2004; accepted 4 June 2004 Available online 17 August 2004 Abstract Multilayer membranes for the treatment of oily waters have been prepared from ceramic materials. Alumina and cordierite supports have been prepared as well as -Al 2 O 3 intermediate layers. -Al 2 O 3 top layers with very high porosities were prepared by the sol–gel method and a detailed study has been performed because of the importance of this layer in the filtration process. A structural study by means of nitrogen adsorption–desorption, nitrogen permeability and scanning electron microscopy has been carried out on unsupported and supported top layers membranes. The effect of the sol concentration and calcination temperature on the structure of the membrane was studied to get an appropriate pore size and porosity. Also, the necessary amount of PVA as binder/plastizier to get defect-free membranes was investigated. Top-layer membranes in tubular configuration with an average pore diameter around 4nm and porosities of 72% have been obtained. © 2004 Elsevier Ltd. All rights reserved. Keywords: Membranes; Al 2 O 3 ; Sol–gel process; Permeability 1. Introduction There is much current interest in the application of membranes in separation procedures because of their application in the treatment of big amounts of wastewaters, and in places where the available space is small. In the last years, the volume of research and development of ceramic membranes has undergone a big advance, 1 because of their applications in filtration environments where polymeric membranes suffer changes in their structure. These are sep- arations in chemically aggressive environments and at high temperatures, in applications requiring a long life-time (low fouling rate), a good mechanical strength and cost-effective production. Ceramic membranes with high permeability can only be obtained in an asymmetric configuration, which consists in a multilayer system with a macroporous support (with ∗ Corresponding author. Tel.: +34 917355840; fax: +34 917355843. E-mailaddress: mar@icv.csic.es (M.A. Rodr´ ıguez). the largest pore diameter), which provides the mechanical strength to the system, an intermediate layer, whose roles are to reduce any inherent defects of the support and to prevent the infiltration of the top layer material into the pores of the support, and the top layer, which is the true membrane of the system. In this layer is necessary a comprehensive control of the pore size. 2,3 Alumina, silica, titania or zirconia are considered as the main ceramic materials for the formation of the asymmetric structures. 4,5 The main synthesis route for the preparation of top lay- ers is the modification of intermediate layers using a sol–gel method. 4,6 The advantages of sol–gel derived films include a lower densification temperature, a narrow pore size distri- bution with nanometer pore-scale, a high degree of chemical homogeneity and the possible production of multicomponent films. 7,8 Different techniques of characterization are used cur- rently in the structural study of ceramic membranes. 4,9 Meth- ods such as mercury porosimetry and nitrogen adsorption 0955-2219/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2004.06.016