Alumina Hollow Fiber Membranes Research Articles

Hydrophobic alumina hollow fiber membranes for sucrose concentration by vacuum membrane distillation

Hydrophobic alumina hollow fiber membranes were first used for sucrose concentration in a vacuum membrane distillation (VMD) system. The alumina hollow fiber membranes were prepared using the combined phase inversion and sintering method and then grafted with FAS to impart hydrophobicity. The as-prepared hydrophobic alumina hollow fiber membrane had a high mechanical strength of 191 MPa, a high water contact angle of 140° and a high liquid entry pressure of water of 5.0 bar. Fifty-two hydrophobic alumina hollow fibers were packed into a shell-and-tube module. To evaluate the sucrose concentration performance of the prepared membrane module, the effects of various parameters on the permeate flux, such as the feed flow rate, temperature, vacuum pressure and concentration, were investigated in the VMD system. In the batch sucrose concentration tests, an 8 L 10°Brix sucrose solution was successfully concentrated to 50°Brix by removing 6.4 L of water using the VMD system. At a feed flow rate of 5 L/min and temperature of 70 °C, the permeate flux remained as high as 35.1 and 19.0 kg/m2 h when the sucrose solution was concentrated to 10°Brix and 50°Brix. Furthermore, the permeate flux could be recovered in a new concentration cycle after the membrane module was washed with pure water. The results revealed that the hydrophobic alumina hollow fiber membranes are promising and feasible for concentration processes in a VMD system.

Morphological design of alumina hollow fiber membranes for desalination by air gap membrane distillation

Alumina hollow fiber membranes were prepared by the phase inversion technique under different spinning conditions in order to induce various types of structural morphologies. In the membrane fabrication process, the studied parameters were the polymer concentration in the inorganic suspension and its flow rate, the gap distance, the bore liquid, the outer coagulant composition and their flow rates. After sintering, the hollow fibers were chemically modified by grafting (1H,1H,2H,2H-perfluorodecyltriethoxysilane) rendering them hydrophobic for their use in membrane distillation (MD) process. The effects of the membrane morphology on the obtained MD membrane characteristics and on air gap membrane distillation (AGMD) desalination performance were studied in order to figure out the most promising structure for MD. The suitability of alumina hollow fibers for AGMD was confirmed by various membrane characterization techniques. In general, the membranes prepared with lower polymer concentration in the inorganic suspension exhibited higher AGMD performance (i.e. higher permeate flux with a smaller flux reduction factor and a good salt rejection factor). Among all prepared hollow fiber membranes prepared in this study, the one with the largest micro-channel structure exhibited the best AGMD performance, even better than all hydrophobic ceramic membranes used so far in desalination by AGMD and DCMD.

Preparation of Alumina Hollow Fiber Membrane with Controlled Pore Structure for Contactor Process

The alumina hollow fiber membranes were prepared by spinning and then sintering method. The dope solution was fabricated by using 1-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), dimethylacetamide (DMAc), and triethylphosphite (TEP) as solvents, which have different interaction rate with non-solvent. SEM analysis showed that the alumina hollow fiber membranes have different pore structure. In particular, the hollow fiber membranes prepared with DMSO, DMAc and NMP had finger structures. In contrast, when it was made with TEP, the membrane had a sponge structure. The gas permeability and the contact angle of each hollow fiber membranes were measured. The fabricated hollow fiber membranes were applied to the membrane contact process for the carbon dioxide absorption. The hollow fiber membranes prepared with TEP is had the highest carbon dioxide absorption characteristics. A higher carbon dioxide absorption activity of hollow fiber membranes prepared with TEP was suggested to be due to its gas permeability and hydrophobicity. In conclusion, it was confirmed that the higher gas permeation due to pore structure of the membrane had a favorable effect on the absorption performance.

Effect of hydrophobic modification on carbon dioxide absorption using porous alumina (Al2O3) hollow fiber membrane contactor

Porous alumina (Al2O3) hollow fiber membranes were successfully prepared using phase inversion spinning and sintering technique. Hydrophilic surface of porous Al2O3 hollow fiber membrane was modified with a fluoroalkylsilane (FAS) solution that was used as hydrophobic agent for treating the surface of Al2O3 hollow fiber membranes. The unmodified and modified porous Al2O3 membranes were characterized using scanning electron microscopy, mercury porosimetry, gas permeation testing equipment, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and the contact angle analyzer. The hydrophobicity of the porous Al2O3 hollow fiber membrane increased with increasing FAS coating time. The effect of the FAS coating on the CO2 absorption performance was also investigated. As a result, the CO2 absorption flux decreased with increasing FAS coating time. In particular, these experiments revealed that 2h coating was sufficient to obtain an optimal hydrophobic protection against the wetting process of the Al2O3 hollow fiber membrane pores. In addition, the best performance for CO2 absorption flux was achieved with the Al2O3 hollow fiber membrane modified for 2h coating. The maximum CO2 absorption flux of surface modified Al2O3 hollow fiber membrane was 6.022×10−3mol/m2s with a liquid flow rate of 50ml/min at room temperature. Finally, a 50-hours-long stability test demonstrates that the modified porous Al2O3 hollow fiber membranes are stable and promising for membrane contactors.

Preparation and characterization of self-cleaning alumina hollow fiber membrane using the phase inversion and sintering technique

Asymmetric alumina hollow fiber membranes were prepared using the phase inversion technique followed by the sintering process at high temperatures. The ceramic suspensions were formulated by mixing alumina powder with polyethersulfone (PESf), polyethylene glycol-30-dipolyhydroxystearate and N-methyl-2-pyrrolidone (NMP) as the polymer binder, dispersant and solvent, respectively. The objectives of this study were (i) to investigate the effects of spinning parameters, namely, ceramic loading, ceramic to polymer binder ratio, different internal coagulant temperatures and air gap variation on asymmetric structure formation and (ii) to study the self-cleaning properties of alumina hollow fiber membranes. The ceramic hollow fiber membrane was characterized in terms of its viscosity, structural morphology and mechanical strength using a scanning electron microscope (SEM). The results showed that the finger-like structures in alumina hollow fiber membranes could be formed but their patterns were influenced by the ceramic suspension and spinning parameters. Variations in their morphology resulted in significant effects on the mechanical properties and permeability of ceramic hollow fiber membranes. A CuO/CeO2 catalyst was deposited onto the alumina membrane support with the catalyst distribution determined by SEM/EDX. Self-cleaning properties were examined by comparing normal cleaning and self-cleaning properties with irradiation of UV for protein rejection. The result of self-cleaning by UV showed higher bovine serum albumin (BSA) permeation due to super-hydrophilicity of the CuO/CeO2 catalyst.

Preparation of Ceramic Hollow Fiber Membrane Using Phase Inversion and Sintering Technique

Alumina hollow fiber membrane with asymmetric structure has been developed using phase inversion technique followed by sintering process. The formation of asymmetric alumina hollow fiber was influenced by a phenomenon known as hydrodynamically unstable viscous fingering. A desired morphology of the ceramic hollow fiber membrane, that consists of 52 % of finger-like and the rest is sponge-like structure, is tailored by controlled parameters during membrane fabrication process. The result shows that the ratio of alumina/PESf should be reduced to 6. At this ratio, the finger-like structure can be easily formed with inner and outer diameters were 1.11 mm and 2.05 mm respectively. From the given thickness, approximately 243 µm of finger-like length can be developed originating from the lumen of hollow fiber.

SiC nanofiber reinforced porous ceramic hollow fiber membranes

Brittleness is the main obstacle for commercial implementation of ceramic hollow fiber membranes. Here we report the reinforcement of porous alumina hollow fiber membranes by using commercial SiC nanofibers. The SiC reinforced alumina hollow fiber membranes were produced by the polymer-assisted phase inversion method and subsequent removal of the polymer and sintering at high temperatures. The effects of the amounts of SiC nanofibers (2.5–10.0 wt%) on the mechanical strength, microstructure and water flux of the hollow fiber membranes were investigated. The results showed that without addition of SiC nanofibers, the maximum bending strength was about 154 MPa for the porous alumina hollow fiber sintered at 1510 °C. However, the maximum bending strength of the reinforced membrane reached 218 MPa, in which 5 wt% SiC was incorporated and sintered at 1450 °C; in other words, a 40% improvement in bending strength was achieved. After being sintered at 1450 °C, the 5% SiC reinforced membrane exhibits a porosity of 41.7% and a peak pore size of 1.35 μm whereas the pure alumina membrane has a porosity of 37.5% and a peak pore size of 1.25 μm; the former shows a water permeability of 7.99 L m−2 h−1 kPa−1, which is 3.3 times higher than that of the latter. Therefore, the ceramic nanofiber reinforcement is promising for the development of high-performance ceramic hollow fiber membranes for practical applications.

Preparation of Highly Permeable Al<sub>2</sub>O<sub>3</sub> Hollow Fiber Membrane via Phase Inversion Method with Ethanol as External Coagulant

Highly permeable porous alumina (Al2O3) hollow fiber membranes have been developed by a combined phase inversion and sintering technique. Ethanol substituting for water was used as the external coagulant in order to prepare Al2O3 hollow fiber membranes with low trans-membrane resistance. The prepared Al2O3 membranes show a special asymmetric structure with an outer skin layer, highly porous inner surface and sub-layer composed of long and large finger-like pores. The influences of sintering temperature on the average pore size, N2 permeability and bending strength were investigated. Results show that Al2O3 hollow fiber membranes with higher permeability can be prepared using ethanol as the external coagulant. The prepared Al2O3 hollow fiber membranes show a N2 permeability of 871.5 m3·m-2·h-1·bar-1 and a bending strength of 91.4 MPa when sintered at 1550°C for 5h.

Preparation and characterization of alumina hollow fiber membranes

With the rapid development of membrane technology in water treatment, there is a growing demand for membrane products with high performance. The inorganic hollow fiber membranes are of great interest due to their high resistance to abrasion, chemical/thermal degradation, and higher surface area/volume ratio therefore they can be utilized in the fields of water treatment. In this study, the alumina (Al2O3) hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The organic binder solution (dope) containing suspended Al2O3 powders was spun to a hollow fiber precursor, which was then sintered at elevated temperatures in order to obtain the Al2O3 hollow fiber membrane. The dope solution consisted of polyethersulfone (PES), Nmethyl-2-pyrrolidone (NMP) and polyvinylpyrrolidone (PVP), which were used as polymer binder, solvent and additive, respectively. The prepared Al2O3 hollow fiber membranes were characterized by a scanning electron microscope (SEM) and thermal gravimetric analysis (TG). The effects of the sintering temperature and Al2O3/PES ratios on the morphological structure, pure water flux, pore size and porosity of the membranes were also investigated extensively. The results showed that the pure water flux, maximum pore size and porosity of the prepared membranes decreased with the increase in Al2O3/PES ratios and sintering temperature. When the Al2O3/PES ratio reached 9, the pure water flux and maximum pore size were at 2547 L/m2·h and 1.4 μm, respectively. Under 1600dgC of sintering temperature, the pure water flux and maximum pore size reached 2398 L/(m2·h) and 2.3 μm, respectively. The results showed that the alumina hollow fiber membranes we prepared were suitable for the microfiltration process. The morphology investigation also revealed that the prepared Al2O3 hollow fiber membrane retained its’asymmetric structure even after the sintering process.