Tubular microporous alumina structure for demulsifying vegetable oil/water emulsions and concentrating macromolecular suspensions

A microstructure composed of alumina-silica (mullite, 3Al(2)O(3)center dot 2SiO(2)) was molded into tubes to be used in a microfiltration process for separating water/vegetable oil emulsions and to concentrate macromolecular suspensions. The microporous tubes were produced by the precipitation method using raw material supplied by Rhodia do Brasil Ltda, and sintered at a final temperature of 1450 degrees C. The microporous medium was characterized by mercury porosimetry and by scanning electron microscopy (SEM). Most of the samples showed average pore sizes ranging from 0.3 to 20 mu m, which the literature indicates as appropriate for the demulsification of macroemulsions. The microfiltering performance of the tubes was evaluated using emulsified mixtures of water and vegetable oil (sunflower and soybean) and macromolecular mixtures of xanthan and guar gum suspensions (molecular weight of 10(6) Da), under transmembrane pressures of 1.5-5.0 bar and a turbulent crossflow regime (Re> 10.000). The process was then repeated and the tubes' performance compared with that of a commercial membrane of German origin with a nominal pore size of 0.4 mu m. The quality of the permeate, from the standpoint of carbon retention in the mixtures, was evaluated based on measurements of the total organic carbon (TOC) and the pH. In the case of mixtures in suspension, the microporous tubes exhibited better carbon retention than the membrane. In the case of the emulsified mixtures, carbon retention exceeded 90%, and the demulsifying process achieved results compatible with those reported in the literature. (C) 2005 Elsevier B.V. All rights reserved.