Utilização de alumina e dolomita na fabricação de membranas cerâmicas do tipo fibra oca

Abstract

The membrane separation process has received great attention for the purification of different fluids in several applications. Due to the advantages of ceramic inorganic membranes (greater chemical, thermal and mechanical resistances) compared to polymeric membranes, several studies have been proposed for the production of ceramic membranes. One of the main challenges for the widespread use of ceramic membranes are related to the high cost of the ceramic material. In this context, the main objective of this study was to produce hollow fiber membranes by the phase inversion method followed by sintering using different ceramic materials. The morphology of the fabricated membrane depends directly on the composition of the prepared ceramic suspension and the applied extrusion parameters. Thus, two solvents (dimethylsulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP)) were evaluated for preparing the ceramic suspension with pure alumina of 1 μm. The use of DMSO as a solvent provided a higher density of filaments in the membrane structure when compared to NMP. The possibility of adding alumina with higher particle size (D50 = 4 μm) in the ceramic suspension with thin alumina (1 μm) was also evaluated in order to reduce the membrane cost. Addition of 20wt% of thick alumina (D50 = 4 μm) reproduced the structure of the fibre that was produced only with thin alumina and increased in 18.32% the water permeability through the fiber. The fiber produced with thin alumina was then applied as a ceramic support for the production of composite membranes formed by an inner layer of alumina and an outer layer of polyethersulfone (PESf). The influence of the polymeric solution concentration on the structures of the composite membranes was evaluated. It was suggested the application of a polymeric layer in the concentration of 125 g/L in order to guarantee a uniform and selective layer on the fiber. In addition, we evaluated the production of hollow fiber membranes using only dolomite and a mixture of dolomite and alumina in the composition of the ceramic material. The fibers produced using only dolomite presented macroporous structures due to the greater particle size (D50 = 25,4 μm) of the used ceramic material. The sintering process of dolomite fibers at 400 °C, which still have polymer in the interstices of the ceramic material, presented satisfactory mechanical strength (4,22±0,23 MPa) and were suggested for separations involving aqueous solutions. The sintering of the dolomite fibers at 1350 °C completely eliminates the polymer, but promotes the sintering of the material and thus guarantees a satisfactory mechanical resistance (5,55 ±0,78 MPa). However, the sintering of dolomite material at 1350 °C results in doloma, which is a water-soluble material. The water solubility of the dolomite fiber sintered at 1350 °C was confirmed by ion chromatography that detected magnesium and calcium at the concentrations of 0,056 e 2,714 ppm, respectively, after contact of the fiber with water for 56 h. Thus, the dolomite fiber sintered at 1350 °C was suggested for applications as ceramic support for formation of composite membranes involving gas separations. Membranes produced with different proportions of dolomite in fine alumina (75%, 50% and 25%, wt% of dolomite) in the composition of the ceramic material resulted in the formation of magnesium aluminate (spinel) in the membrane structures when these were subjected to high temperatures. The initial compositions of the ceramic material formed by alumina and dolomite have generated, at different sintering temperatures, different structures in the membranes that can be adapted, depending on the required application.