Morphologies of ceramic hollow fibre membranes prepared from suspensions of Al 2 O 3 , NMP (Nmethyl-2-pyrrolidone) and polyethersulfone (PESf) using a dry-wet spinning/sintering process have been studied experimentally. The results indicate that two types of membrane morphologies, i.e. fingerlike and sponge-like structures can be expected. It is believed that finger-like void formation in asymmetric ceramic membranes is initiated by hydrodynamically unstable viscous fingering developed when a less viscous fluid (non-solvent) is in contact with a higher viscosity fluid (ceramic suspension containing invertible polymer binder). Finger-like void growth occurs only below a critical suspension viscosity, above which a sponge-like structure is observed over the entire hollow fibre cross section.The effects of the air-gap, viscosity and non-solvent concentration on fibre morphology have been studied and it has been determined that viscosity is the dominating factor for ceramic systems.
In this study, a new controlled sintering process has been proposed to improve the water permeation of asymmetric alumina hollow fibre membranes. In this process, polymer binder (PESf) in precursor fibres is purposely pre-treated in static air at selected temperatures (400-600 °C) to have it partially removed, prior to be converted into carbon in a second sintering step (1450 °C) under an oxygen free environment. During the second sintering step, proper bounding between ceramic particles takes place, while the growth of ceramic grains is effectively suppressed due to the presence of carbon. The carbon in the voids formed by particle packing also acts as a pore structure "stabiliser" and can be removed easily via subsequent thermal treatment in static air at 800 °C. Compared to the membranes with the same asymmetric structure and sintered in static air only (i.e. normal sintering), the membranes sintered using the new controlled sintering process shows water permeation flux is approximately 13 times higher, together with comparable mechanical strength. Moreover, this original concept of using the polymer binder to design the pore structure of ceramic membranes can be transferred to other inorganic materials.
This article describes development of a catalytic hollow fibre membrane micro-reactor (CHFMMR) for high purity H 2 production. Asymmetric Al 2 O 3 hollow fibres produced by a phase-inversion and sintering technique were employed as a single substrate for both coating of the Pd membrane and impregnation of the 30%CuO/CeO 2 catalyst. The Pd membrane was first deposited onto the outer layer of Al 2 O 3 hollow fibre using the electroless plating (ELP) technique, followed by impregnation of the 30%CuO/CeO 2 catalyst into the inner finger-like structure of the substrate using the sol-gel Pechini method. Performance of the proposed reactor was carried out using water gas shift (WGS) reaction as a sample reaction. A comparative study of conversion obtained in the WGS reaction as a function of the reaction temperature (from 200 o C to 500 o C) in a fixed-bed reactor, a catalytic hollow fibre micro-reactor (CHFMR) and the CHFMMR using different flow rates of a sweep gas (from 45 to 70ml/min) was performed, concluding that the conversion is the highest in the CHFMMR. It is important to highlight that, at 500ºC and a sweep gas flow rate of
A novel inorganic hollow fiber membrane reactor (iHFMR) has been developed and applied to the catalytic dehydrogenation of propane to propene. Alumina hollow fiber substrates, prepared by a phase inversion/sintering method, possess a unique asymmetric structure that can be characterized by a very porous inner surface from which finger-like voids extend across $80% of the fiber cross-section with the remaining 20% consisting of a denser sponge-like outer layer. In contrast to other existing Pd/Ag composite membranes, where an intermediate c-Al 2 O 3 layer is often used to bridge the Pd/ Ag layer and the substrate, the Pd/Ag composite membrane prepared in this study was achieved by coating the Pd/Ag layer directly onto the outer surface of the asymmetric substrate. After depositing submicron-sized Pt (0.5 wt %)/c-alumina catalysts in the finger-like voids of the substrates, a highly compact multifunctional iHFMR was developed. Propane conversion as high as 42% was achieved at the initial stage of the reaction at 723 K. In addition, the space-time yields of the iHFMR were $60 times higher than that of a fixed bed reactor, demonstrating advantages of using iHFMR for dehydrogenation reactions. V
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