Fabricação de fibras ocas a partir de diferentes materiais cerâmicos e aplicação no tratamento de águas oleosas

Abstract

The manufacture and application of ceramic membranes of the hollow fiber type has been highlighted in the literature due to the advantages in relation to the material and geometry. One of the concerns to the widespread use of ceramic membranes is the high cost of the ceramic material and the sintering process. Oily wastewater is produced by several industrial sectors and membrane separation technology has been considered in several studies for oil and water separation, especially in cases where there are emulsions with oil droplets dispersed in water. Spinel is a ceramic material that has interesting characteristics (high melting point, thermal and chemical resistance, low coefficient of thermal expansion) and that can be synthesized through the reaction between alumina (Al2O3) and periclase (MgO) at high temperatures (> 1000°C). Dolomite (CaMg(CO3)2) is an abundant mineral in nature that when decomposed at high temperatures (~900 °C) produces MgO as a by-product. Silicon carbide (SiC) is a hydrophilic ceramic material that can be suggested in the manufacture of hollow fibers and application in the separation of oily wastewater, but it requires sintering at high temperatures (> 2000 °C) and in an inert atmosphere. Spinel hollow fiber type ceramic membranes were successfully prepared by the phase inversion method followed by sintering from different compositions of dolomite and alumina. The membranes produced with 25% by weight of dolomite and 75% by weight of alumina (Fibra-D25), and sintered at 1350°C, showed an asymmetric granulometric distribution with pore sizes ranging from 0.16 to 5.29 µm, porosity 43% and mechanical strength of 54.88 ± 4.25 MPa. Fiber D-25 had a lower cost than fibers produced with pure alumina, due to the use of a smaller amount of alumina in the composition of the ceramic material and contributed with a 49% increase in the mechanical strength of hollow fibers produced with pure alumina, due to spinel formation in its structure. Finally, Fiber D-25 showed an oil rejection rate of 94.5% in soybean oil and water emulsion. In addition to spinel hollow fibers, this work also evaluated the effect of adding silicon (Si) as an additive in the manufacture of silicon carbide hollow fibers, produced by the phase inversion method followed by sintering in an atmosphere with air. The addition of 30% by weight of Si in the SiC ceramic material promoted the bonding of SiC particles and the formation of hollow fibers (HF-SiC70Si30) with mechanical strength (42.25 ± 3.39 MPa) suitable for application after sintering. in air at 1350°C. The HF-SiC70Si30 asymmetric hollow fibers showed a spongy and filamentous structure with average pore sizes of 1.73 and 5.29 µm, respectively. The application of silicon carbide fiber in the separation of oil emulsions showed an oil rejection rate of 98.75%. The cake formation was the main phenomenon responsible for the membrane fouling, and the regeneration of 84% of the membrane flux was verified after cleaning with water under ultrasound irradiation. The silicon carbide fibers were also evaluated in the separation of diesel oil and water emulsions, presenting in this case, rejection rates above 83%. Thus, the use of Si as a sintering aid was favorable in the manufacture of SiC hollow fibers, allowing the sintering of the fibers at temperatures of 1350 °C and application in the separation of oily waters. Finally, the use of alternative materials to alumina, such as dolomite and silicon, is favorable for to produce of hollow fiber membranes with asymmetric pore distribution. These membranes presented adequate morphology and resistance, with oil rejection above 83%.