Preparação de membranas tubulares porosas empregando caulim e alumina como principais matérias-primas.

Abstract

Ceramic membranes present properties that provide high performance in filtration processes, however, the production cost is still high. Seeking to meet a current demand, this study aimed to develop ceramic masses, containing as main components kaolin and alumina, used in porous ceramics production, aiming its application as tubular membranes. Initially, the raw materials were submitted to the following characterizations: chemical, granulometric and mineralogical. The alumina, before being added to kaolin, was subjected to the milling process, and then three compositions were prepared. The components amount was established considering the mullite stoichiometry. The formulated compositions were homogenized and subjected to heat treatment between 1150 and 1250oC, to define the sintering parameters to be used after a conformation stage. The extrusion process was used to prepare the membranes, therefore, it was necessary to determine the plasticity characteristics of the ceramic masses. Sodium carboxymethylcellulose was added as an additive to improve mass plasticity for extrusion, act as pore forming agent and assist in the forming process of important phases such as mullite. After conformation, heat treatment were performed: drying at 110oC and burning at temperatures 1100, 1200, 1300, 1400 and 1500oC; with the residence time at maximum temperature of 60 minutes. Then, the microstructural, physical, mechanical and flow properties of the membranes were analyzed. The membranes sintering promoted formation of desired crystalline phase, the mullite. The membranes with higher additive amount presented higher flowability obtaining the values of 178,9, 98,5, 44,5 and 1276,8 L/hm2 at temperatures of 1100, 1200, 1300 e 1500oC, respectively. Furthermore, the membranes also presented higher modulus of flexural strength (16,6, 43,2, 68,7, 74,4 e 84,0 MPa) for all analyzed temperatures. These results can be attributed to the CMC contribution that favored the mullite phase formation and also reduced the defects presence in the membranes structure.