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Editor's Choice : High Hydrogen Permeance Silica Membranes Prepared by a Chemical Vapor Deposition Method
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Abstract: H2 permselective silica hybrid membranes were successfully prepared by using a counter diffusion chemical vapor deposition (CVD) method. Hexyltrimethoxysilane (HTMOS), phenyltrimethoxysilane (PhTMOS) or diphenyldimethoxysilane (DPhDMOS) were used as silica precursors. The oxidants were O3 or O2. These reactants were provided at the opposite side of the γ-alumina substrates, and the deposition occurred in the pores of the substrates. The HTMOS/O3 derived membrane deposited at 450°C showed the highest H2 permselectivity. The H2 permeace was 2.1×10-6 mol m-2 s-1 Pa-1 with the H2/SF6 permeance ratio of 5.9×106. H2 permeances through the HTMOS derived membranes increased with increasing the deposition temperatures. While the H2 permeance through the PhTMOS and DPhDMOS derived membranes decreased with increasing the deposition temperatures. The PhTMOS derived membrane prepared at 150°C showed the H2 permeance of 1.7×10-6 mol m-2 s-1 Pa-1 with the H2/SF6 permeance ratio of 13. The PhTMOS membrane prepared at 320°C showed the highest H2/SF6 permeance ratio of 1.8×104among the PhTMOS derived membranes. However, the H2/SF6 permeance ratio through the DPhDMOS membranes showed the different trend. Higher H2/SF6 permeance ratio was found through the DPhDMOS derived membranes deposited at 180°C and 360°C. The maximum H2/SF6 permeance ratio was 4.2×104 through the DPhDMOS membrane deposited at 180°C. The decomposition properties of organic groups on silica surface are investigated by using hydrolysis powders derived from the each silica precursor. The HTMOS powders showed O3 stability after the high temperature treatment. Thus, high H2 permselective membranes were prepared by the HTMOS at 450 °C. Keywords: Silica hybrid membrane, counter diffusion CVD method, H2permselective membrane, pore size control, silica precursors. Download Full Article |
Editor's Choice : Ion Exchange Membranes for Electrodialysis: A Comprehensive Review of Recent Advances
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Abstract: Electrodialysis related processes are effectively applied in desalination of sea and brackish water, waste water treatment, chemical process industry, and food and pharmaceutical industry. In this process, fundamental component is the ion exchange membrane (IEM), which allows the selective transport of ions. The evolvement of an IEM not only makes the process cleaner and energy-efficient but also recovers useful effluents that are now going to wastes. However ion-exchange membranes with better selectivity, less electrical resistance, good chemical, mechanical and thermal stability are appropriate for these processes. For the development of new IEMs, a lot of tactics have been applied in the last two decades. The intention of this paper is to briefly review synthetic aspects in the development of new ion-exchange membranes and their applications for electrodialysis related processes. Keywords: Electrodialysis, ion exchange membrane, anion exchange membrane, cation exchange membrane, bipolar membrane.Download Full Article |
Editor’s Choice : Investigation of Membrane-Based Total Heat Exchangers with Different Structures and Materials
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Abstract: Membrane-based total heat exchangers are devices to recover both sensible heat and latent heat from the exhaust air. The performances of exchangers assembled with different structures and membranes vary dramatically. To investigate performances, five modules are fabricated for comparison. A test rig is built to measure the performance of these total heat exchangers. The heat and moisture transfer in the cores are studied simultaneously. These cores can be divided into two categories: with different structures and with different membranes. For the first category, parallel-plates, plate-fins and cross-corrugated structures are used. For the second category, three kinds of membranes, i.e. one-step hand-made CA membrane, hydrophobic-hydrophilic composite membrane and machine-made CA membrane are used. The heat and mass transfer coefficients, sensible cooling and latent effectiveness are obtained through experimental measurements. The experimental results show that the cross-corrugated ducts can enhance heat and mass transfer effectively. And the one-step hand-made CA membrane has the lowest resistance in heat and moisture transfer. Keywords: Total heat exchanger, core structure, membrane materials, energy recovery, comparison.Download Full Article |
Editor’s Choice : Preparation and Characterization of Superhydrophobic Modification of Polyvinylidene Fluoride Membrane by Dip-Coating
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Abstract: The superhydrophobicity polyvinylidene fluoride (PVDF) membranes were modified via reducing surface energy by dip-coating perfluoroalkyl methacrylic copolymer (Zonyl 8740) onto the membranes prepared on mat glass. The chemical component of the unmodified and modified PVDF membranes surface was investigated by ATR-FTIR. Morphology and hydrophobicity of the unmodified and modified PVDF membranes were examined by scanning electronic microscopy and water contact angle, respectively. The effects of concentration of Zonyl 8740, coating time, conditions of heat treatment on hydrophobic capability of PVDF membranes were investigated. The results showed that the water contact angle increased from 141˚ to 151˚ by the dip-coating modification, therefore getting superhydrophobic PVDF membrane. Moreover, the porosity and the morphology of modified PVDF membrane were unchanged by the dip-coating modification. This results suggested that the hydrophobicty stability of the modified PVDF membrane was also good. Keywords: Polyvinylidene fluoride, Superhydrophobic, Coating modification, Perfluoroalkyl methacrylic copolymer, Membrane preparation. Download Full Article |
Editor’s Choice : Preparation and Performance of Catalytic Hollow Fibre Membranes for Hydrogenation Reduction of Nitrites in Water
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Abstract: Porous Al2O3 hollow fiber membranes have been fabricated via a phase inversion – sintering technique. Pd-loaded carbon nanotubes(CNTs) are formed inside the hollow fibre wall by the catalytic decomposition of methane over Fe particles, followed by impregnation and reduction with hydrogen to form catalytic hollow fibre membranes. Hydrophobic modification of the hollow fibres is conducted by gas permeable polymeric coating. The resultant hollow fibre membranes exhibit highly catalytic activity to the hydrogenation reduction of nitrites in aqueous solution. Hollow fibre membrane reactors are assembled for nitrite hydrogenation by pumping nitrite solution into the tube side and introducing hydrogen countercurrently to the shell side of the reactor. The nitrite removal in the hollow fibre membrane reactors increases with the operation temperature and the hydrogen feed concentration at lower hydrogen partial pressures, but less influenced by the hydrogen feed concentration when it is higher than 50%. A higher nitrite concentration favors the nitrite hydrogenation reaction but lowers the nitrite removal efficiency. Keywords: Hollow fibre,catalytic membrane reactor,nitrite removal,hydrogenation reduction.Download Full Article |