Catalytic Hollow Fibre Membrane Micro-reactors for Energy Applications

An asymmetric ceramic hollow fibre is proposed as a substrate for the development of a catalytic hollow fibre microreactor (CHFMR) and a catalytic hollow fibre membrane microreactor (CHFMMR). The ceramic substrate that is prepared using the phase inversion and sintering technique has a finger-like structure and a sponge-like region in the inner region and the outer surface respectively. The finger-like structure consists of thousands of conical microchannels distributed perpendicularly to the lumen of ceramic hollow fibres onto which a catalyst is impregnated using the sol-gel Pechini method to improve a catalytic reaction. To further enhance the catalytic reaction, a membrane has been incorporated on the outer layer of ceramic hollow fibre. This study focuses on the use of palladium (Pd) and palladium/silver (Pd/Ag) membranes to separate hydrogen from reaction zones in the water-gas shift (WGS) reactions and the ethanol steam reforming (ESR) respectively. In the development of CHFMMR, the fabrication of Pd and Pd/Ag membranes is carried out prior to the catalyst impregnation process to avoid the dissolution of catalyst into the plating solution due to the presence of ammonia and ethylenediaminetetraacetic acid (EDTA). The catalytic activity tests show that the CHFMR, that does not have the Pd membrane on its outer surface, improves the carbon monoxide (CO) conversion compared with its fixed-bed counterpart. The presence of conical microchannels is expected to enhance the activities of the catalyst in the substrate. The incorporations of Pd and Pd/Ag membranes on the outer layer of ceramic hollow fibres enable pure hydrogen to be produced in the shell-side for both the WGS reaction and the ESR. The CHFMMR is used to remove one of the products enabling the WGS reaction to favour the formation of product. It also facilitates the small amount of catalyst to be used to produce significant amount of hydrogen in the ESR

Hydrophobic ceramic membrane for membrane distillation: A mini review on preparation, characterization, and applications

Membrane distillation (MD) is one of the emerging separation technologies with extremely high separation factor, especially in desalination application. MD utilizes the hydrophobic membrane which only allows the passage of vapor through the membrane pores. Recent years have witnessed great progress in the development of hydrophobic ceramic membranes for MD applications due to their superior properties over the polymeric counterparts. However, ceramic membranes are hydrophilic in nature; hence, membrane surface modification process is required to acquire hydrophobic properties for MD applications. Direct grafting using silane agents is the most widely used ceramic membrane hydrophobization method. Hence, this mini review provides a complete summary of the research progress on the preparation and characterization of the hydrophobic ceramic membranes through silane agent grafting, as well as their applications in MD. Finally, future research directions have also been addressed

Comparative study of Malaysian and Nigerian kaolin-based ceramic hollow fiber membranes for filtration application

Ceramic membrane has gained increasing interest in water filtration application due to its inherent characteristics. Low-cost clay materials are preferred to fabricate an efficient and cost-effective ceramic membrane. Among the ceramics, kaolin displays better mechanical, thermal, and chemical properties. However, natural properties of kaolin vary from different studies. Hence, cost-effective Nigeria (NK) and Malaysia (MK) kaolins were compared to study the fabrication of kaolin hollow fiber ceramic membrane for filtration application. The effects of kaolin loading concentration (34 and 37 wt. %) and sintering temperature (1200, 1350, 1400, and 1500 °C) on kaolin membrane fabrication were also studied. XRF studies indicated that the hydroxyl silica and alumina compositions were 56.76wt.% and 41.97wt% for NK and 55.21wt.% and 40.33wt% for MK. MK exhibited intense kaolinite peak with a broad range of particle size distribution. The mechanical stability of kaolin ceramic membrane increased with the increase of sintering temperature and kaolin loading concentration. Membrane morphology also varied with MK and NK. Interestingly, 34wt% kaolin at a sintered temperature of 1350 °C produced ceramic membrane with a high water flux. A similar trend was observed in both MK and NK, where the flux of 34wt% MK and NK are 565 and 460 L/m2h, respectively

Development of hydrophobic metakaolin hollow fibre membrane for membrane distillation application

Metakaolin hollow fibre membranes (MHFM) was prepared by a combined phase inversion and sintering method for direct contact membrane distillation (DCMD) application. Four hydrophobic metakaolin hollow fibre membranes (h-MHFM) sintered at different temperatures (1200ºC to 1500ºC) were successfully prepared by grafting 1H,1H,2H,2H-perfluorodecyltriethoxysilane on the MHFM. Prior to the grafting process, the MHFM was hydrolysed with a mixture of ethanol and water with the ratio of 1:2 for 24 hours. The effectiveness of the hydrophobization on each MHFM was assessed using contact angle measurement, scanning electron microscopy (SEM) and three-point bending test. It was found that the increasing sintering temperature improved the mechanical strength from 117.6 MPa to 182.3 MPa. Further increment in mechanical strength was also observed after the modification with fluoroalkylsilane (FAS). The contact angle of the membrane was enhanced up to 120˚ after modification. In general, the membrane prepared at low sintering temperature of 1200°C exhibited the highest DCMD performance with the water vapor flux of 17.5 kg/m2h due to the sufficient pore size for the vapor to pass through the membrane structure

Preparation of high performance SPEEK/Cloisite 15A nanocomposite membrane via advanced membrane formulation method

Sulfonated poly (ether ether ketone) (SPEEK)/Cloisite 15A® nanocomposite membranes were prepared via solution intercalation method. For better dispersion of nanoclay in the polymer matrix, the solution intercalation method was modified and a compatibilizer was introduced. The state of nanoclay dispersion was determined by FESEM. The effect of the solution formulation preparation method and compatibilizer on the performance properties such as proton conductivity and methanol permeability of all membranes was studied. FESEM analysis confirmed that SPEEK/Cloisite 15A® nanocomposite membrane prepared via modified solution intercalation method and in the presence of compatibilizer was the best membrane in terms of its morphological structure. Due to its well nanoclay distribution in polymer matrix, this kind of membrane exhibited the highest selectivity owing to its high proton conductivity and low methanol permeability. SPEEK/Cloisite 15A® with compatibilizer prepared via modified solution intercalation method was found to be the best membrane

Removal of As(III) and As(V) from water using green, silica-based ceramic hollow fibre membranes via direct contact membrane distillation

Arsenite [As(III)] and arsenate [As(V)] removal by direct contact membrane distillation (DCMD) using novel hydrophobic green, silica-based ceramic hollow fibre membranes derived from agricultural rice husk was investigated in this work. The green ceramic hollow fibre membranes were prepared from amorphous (ASHFM) and crystalline (CSHFM) silica-based rice husk ash and modified to be hydrophobic via immersion fluoroalkylsilane (FAS) grafting of 1H,1H,2H,2H-perfluorodecyltriethoxysilane. Superhydrophobic contact angle values up to 157° and 161° were obtained for ASHFM and CSHFM, respectively. Remarkably, the membrane surface morphology mimicked a look-alike lotus-leaf structure with decrement in pore size after grafting via the silane agent for both membranes. The effect of arsenic pH (3–11), arsenic concentration (1–1000 ppm) and feed temperature (50–80 °C) were studied and it was found that feed temperature had a significant effect on the permeate flux. The hydrophobic CSHFM, with a flux of 50.4 kg m−2 h−1 for As(III) and 51.3 kg m−2 h−1 for As(V), was found to be the best of the tested membranes. In fact, this membrane can reject arsenic to the maximum contaminant level (MCL) limit of 10 ppb under any conditions, and no swelling mechanism of the membranes was observed after testing for 4 hours

Catalytic surface modification of alumina membrane for oxygen separation

Two types of alumina ceramic membrane in hollow fibre shape was used in this study. Both alumina hollow fibres (AHF) were sintered at different temperatures; (a) 1350oC and (b) 1450oC. In order to improve the catalytic activity of the alumina membrane for oxygen separation purposes, surface modification of the membranes was carried out using La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) perovskite catalyst. LSCF was synthesised using simple Pechini sol-gel method. The evaporation time and temperature of the LSCF-sol were varied to obtain various viscosity of catalytic sol. From XRD analysis, pure LSCF perovskite structure formed at temperature at 850oC. The morphological of unmodified and surface-modified alumina hollow fibre membranes (AHF) were studied using FESEM. The effect of LSCF catalytic sol viscosity was studied and it was found that as the viscosity of the sol increases, the amount of catalyst deposited on the alumina hollow fibre were increased. Besides, the amount of catalyst deposited on 1350 AHF was found to be higher than 1450 AHF. This result is supported by the result of pore distribution data whereby 1350 AHF was observed to be more porous than 1450 AHF, with porosity percentage of 40.38% and 28.80%, respectively. Although higher viscosity of catalytic sol could lead to a high amount of catalyst deposited on the AHF substrate, there is a tendency for micro-cracks to develop. Thus, the viscosity of the catalytic sol is important to control in order to have higher oxygen permeation flux

Development of high-performance anode/electrolyte/cathode micro-tubular solid oxide fuel cell via phase inversion-based co-extrusion/ co-sintering technique

A complete set of triple-layer (anode/electrolyte/cathode) hollow fiber for high temperature micro-tubular solid oxide fuel cell (MT-SOFC) consisting of nickel oxide (NiO) – yttria-stabilized zirconia (YSZ)/YSZ/lanthanum strontium manganite (LSM) – YSZ has been successfully fabricated in this study. A simplified fabrication technique of phase inversion-based co-extrusion/co-sintering has yielded a perfectly bounded sandwich structure with free-delamination and defect layers. The effect of co-sintering temperatures (1300 °C–1450 °C) on the morphologies, elemental distributions, electrolyte gas-tightness, mechanical strength, electrochemical performance and the impedance spectra test are well-inspected. The increase of co-sintering temperature has significant effects on the anode finger-like micro-channels shrinkage where the voids become very sharp-thin structure; and developing a thin gas-tight electrolyte layer. Whereas, rapid co-sintering rate (10 °C min -­¹) and large particle size of 3–5 μm (micron) of YSZ has hindered the formation of fully dense cathode layer resulting from higher co-sintering temperature. Correspondingly, with only 0.1116 Ωcm2 value of area-specific resistance (ASR), a maximum power density has increased from 0.34 W cm ­² to 0.75 W cm ­² with 1.05 V OCV at 700 °C when the co-sintering temperature ranging from 1400 °C to 1450 °C; which comparable with single-layer counterpart

High strength and antifouling metakaolin-based ceramic membrane for juice clarification

Key lime, watermelon, and kiwifruit juices were successfully clarified by using a novel high strength and antifouling metakaolinbased ceramic membranes prepared via combination of phase inversion and sintering technique. The fabricated membrane was characterized by utilizing scanning electron microscopy (SEM) analysis, three-point bending strength, juice permeation, and fouling behavior analysis. In this work, the fouling behavior of the membrane was studied using Darcy’s law for cross-flow filtration system. Analysis of the fouling mechanism revealed that the membranes’ fouling was most influenced by the cake filtration mechanism and can be solved easily by applying high operating pressure. Membranes prepared at a sintering temperature of 1300 °C were found to be optimum membranes for juice clarification as it possessed excellent mechanical strength (176.8 MPa) and pure water flux of 273 L/m2 h at 500 kPa. Interestingly, it was also found that the membrane could endure high operating pressure up to 700 kPa, which consequently solved the fouling issue. Thereby, the precious juice properties, such as total suspended solid (TSS), pH, acidity, and density for all juices, were found to be almost unaffected