Abstract
Composite electrospun fibrous membranes are widely studied for the application of membrane distillation. It is an effective approach to enhance the membrane distillation performance in terms of anti-wetting surface and permeate flux by fabricating composite fibrous membranes (CFMs) with a thin skin layer on a thick supporting layer. In this work, various membranes prepared with different pore sizes and porosities by polyacrylonitrile and polyvinylpyrrolidone were prepared. The membrane characteristics and membrane distillation performance were tested. The mass transfer across the membranes was analyzed experimentally and theoretically in detail. It is shown that the skin layer significantly increases liquid entry pressure of the CFM by 5 times. All the membranes have a similar permeate flux. The permeate flux of membranes is stable at 19.2 ± 1.2 kg/m2/h, and the salt rejection ratios remain above 99.98% at 78 ± 1 °C for 11 h. The pore size and porosity of membranes have an insignificant effect on the temperature distribution of membrane. The porosity and pore size of the skin layer have an insignificant effect on the mass transfer process of the CFM. The mass transfer process of the CFM is governed by the supporting layer.
Highlights
Membrane distillation (MD) is a phase-change membrane-separation process driven by the transmembrane-saturated vapor-pressure difference induced by temperature difference [1,2]
air-gap membrane distillation (AGMD), the skin layer and supporting layer parameters have an insignificant effect on the temperature distribution in the membrane
The composite fibrous membranes (CFMs) can be fabricated by electrospinning a thin skin layer (7–9 μm) of PAN and PVP with various morphologies on a thick supporting layer (~50 μm) of PAN
Summary
Membrane distillation (MD) is a phase-change membrane-separation process driven by the transmembrane-saturated vapor-pressure difference induced by temperature difference [1,2]. To prevent membrane wetting and ensure the diffusion space of vapor molecules, commonly used membranes have micron or submicron pore size (0.1–1 μm) [5,6]. The hydrophobic membrane plays two main roles in MD: preventing the contact between the feed and permeate through the membrane pore; and providing efficient transfer space for vapor molecules [7]. Membrane is the core component of MD The membrane parameters, such as pore size, porosity, and hydrophobicity, are constantly optimized with the development of MD [8,9,10]. The commonly used intrinsic hydrophobic membrane materials include polyvinylidene fluoride (PVDF) [11], polytetrafluoroethylene (PTFE) [12,13], polypropylene (PP) [14], and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) [15,16]. In the follow-up study, hydrophilic materials such as polyacrylonitrile (PAN) [17] and nylon [18] with hydrophobic surface modification can be used in MD
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