Synthesis of buckypaper supported ionic liquid membrane for pervaporation process
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Date
2016-02-01
Authors
Ong Yit Thai
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Abstract
Supported liquid membrane (SLM) is one of the liquid membrane configurations that employ a liquid phase substances as membrane and immobilized in a porous supporting membrane. Recently, the idea of using SLM in pervaporation process has attracted a great deal of research attention. However the use of SLM in pervaporation has always suffered from instability problem which is mainly due to the displacement of liquid membrane. In the present research work, it is aimed to develop a high stability SLM by employing buckypaper (BP) as supporting membrane and immobilized with an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4] to form a buckypaper supported ionic liquid membrane (BP-SILM). The BP, which is composed of entangled assemblies of multi-walled carbon nanotubes (CNTs), can effectively entrap the infiltrated the ionic liquid membrane due to its smaller pore size and highly tortuous porous structure. In order to further enhance the membrane stability, the [Bmim][BF4] was blended with polyvinyl alcohol (PVA) prior to the immobilization in the BP. The resulted BP-SILM structure, in which the membrane and support phase were merged into a single layer, was found to be different from that of conventional asymmetric membranes. The BP-SILM structure allows the formation of a thinner symmetric membrane without compromising its mechanical properties. The pervaporation performances of the BP-SILM in the binary mixture of ethylene glycol and water showed an excellent capability to dehydrate ethylene glycol aqueous solutions. The presence of BP and [Bmim][BF4] was observed to significantly enhance the separation performance and the intrinsic membrane permeability. The BP-SILM exhibited high pervaporation performance with a permeation flux of 102 g∙m-2∙h-1, separation factor as high as 1014, water permeance of 13106 GPU and membrane selectivity of 13 for water with 10 wt.% feed concentration of water at 30 °C and 5 mmHg downstream pressure. On the other hand, the BP-SILM was also capable to break ternary azeotropic mixtures of ethyl acetate, ethanol and water. A permeation flux of 385 g∙m-2∙h-1, separation factor of 247, water permeance of 4730 GPU and membrane selectivity of 39 for water were obtained at 30 °C and 5 mmHg downstream pressure. The BP-SILM also demonstrated a robust pervaporation performance over an operation of 120 hours. The diffusion coefficients of ethylene glycol and water at different operating parameter were estimated using a semi-empirical mathematical model based on modified Maxwell-Stefan equation. Based on the estimated diffusion coefficient obtained, the separation of BP-SILM in pervaporation dehydration of ethylene glycol/water binary mixture is more on diffusion control.