Characterization of asymmetric hollow fibre membranes with graded-density skins |
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| Affiliation: | 1. R&D Center for Membrane Technology, Department of Chemical Engineering, Chung Yuan University, Chung-Li District, Taoyuan City 32023, Taiwan, ROC;2. Department of Chemical and Materials Engineering, National Ilan University, I-Lan 26047, Taiwan, ROC;3. Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 10607, Taiwan, ROC;1. Department of Chemistry, Faculty of Science, Institut Teknologi Sepuluh Nopember, Sukolilo, Surabaya 60111, Indonesia;2. Advanced Membrane Technology Research Center (AMTEC), Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Darul Ta’zim, Malaysia;3. Department of Energy Engineering, School of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Darul Ta’zim, Malaysia;4. Dow Centre for Sustainable Engineering Innovation, The University of Queensland, QLD 4072, Australia;5. FIM2Lab-Functional Interfacial Materials and Membranes Laboratory, School of Chemical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia;1. Institute of Physical Organic Chemistry, National Academy of Sciences of Belarus, 13 Surganov street, 220072 Minsk, Belarus;2. A. V. Topchiev Institute o f Petrochemical Synthesis, Russian Academy of Sciences, Leninskii pr. 29, Moscow 119991, Russian Federation |
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| Abstract: | Asymmetric hollow fibre membranes can be prepared from polysulphone, polyethersulphone, and polyphenylsulphone by phase inversion from Lewis acid:base complex solvent systems. Formation of a complex from the non-solvent (Lewis acid) and the solvent (Lewis base) permits higher concentrations of non-solvent to be included in the spinning dope than can be added with traditional solvent/non-solvent mixtures. These membranes exhibit gas permeation rates which are a multiple of those obtained with membranes fabricated from traditional solvent/non-solvent mixtures as well as maintenance of selectivity. This enhancement in permeation performance results primarily from the creation of a skin structure with a much thinner effective separating layer than can be obtained from spinning processes utilizing solvent/non-solvent mixtures. However, it is also believed that these membranes possess enhanced free volume which is derived from the kinetics of the sol-to-gel transition. The rapid dissociation of the Lewis acid:base complex by contact with water accelerates the coagulation process, which limits conformational rearrangement. The dissociation of the Lewis acid:base complex into smaller moieties facilitates their removal from the nascent hollow fibre membranes. The acceleration of the coagulation process increases the free volume in the resultant membrane, which is reflected by an increase in the glass transition temperature that disappears upon annealing. This increase is readily seen during the first heat in a DSC scan, and it is believed that this increase is not a result of superheating, which yields the ‘Tg overshoot’ commonly observed in glassy polymers annealed below their glass transition temperatures. |
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