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Title: Using light, vibrations and fillers to improve membrane performance.
Other Titles: Gebruik van licht, vibraties en vullers ter verbetering van de membraanperformantie
Authors: Li, Yanbo
Issue Date: 23-May-2014
Abstract: Membrane research generally involves work at three different levels, including membrane development, module construction and process design. Improving membrane performance enables membrane technology to be used in a broader range of applications. Two main strategies can be adopted to improve membrane performance: using additional technologies or increasing the intrinsic property of membrane itself. Although the former strategy requires extra investments in module construction and even in process design, they are in general more broadly applicable. The latter strategy focuses on optimizing the fabrication method or developing new membrane materials. Such approach is more specific but requires less additional investments. In this thesis, different strategies, including the use of plasmonic heating, vibrations, and incorporation of fillers in the membranes, were investigated to improve the membrane performances. Plasmonic heating is a side effect of optical properties of noble metal nanoparticles (NPs). When the light is absorbed by the NPs, a non-equilibrium electron distribution is generated which then decays through electron-electron scattering. The hot electron gas equilibrates with lattice phonons which transfer this energy into the surrounding medium, resulting in a local temperature increase. If the NPs are incorporated in a polymeric membrane, the membrane can be locally heated up under the light irradiation, resulting in a flux increase during filtration. Earlier work already proved this concept by incorporation of gold nanoparticles (GNPs) in hydrophilic polymers, coupled with a laser device. This proven concept was extended in this PhD to a much more hydrophobic polymer, polydimethylsiloxane (PDMS), which creates an important challenge to keep the surface charged GNPs dispersed well in the apolar polymeric matrix. The successful results confirmed that the concept is indeed applicable to all types of polymer. The applied laser device is energy consuming and its construction in a membrane module is complicated. Considering the energy efficiency and scaling-up difficulties, energy efficient LED lights were introduced in this PhD to replace the laser device, while the GNPs were changed to silver NPs (AgNPs) which are much cheaper and additionally have a higher plasmonic heating effect. The results show that LED light and AgNPs can be very good alternatives to laser devices and GNPs. The concept has already been proven in a pressure driven membrane process. In this PhD, this technique was extended to another type of membrane process—pervaporation (PV), which is a process driven by a partial vapor pressure difference. Involving an evaporation step during permeation, PV requires heat of vaporization which normally is supplied by the feed. It was anticipated that extra vaporization energy can be obtained due to the localized heating effect of these plasmonic NPs. As a proof of principle, AgNPs were incorporated in PDMS based PV membranes. The performance under LED light irradiation was investigated by a lab-scale sweep gas PV module. The results confirm that applying the plasmonic heating can indeed significantly improve the PV performance. Dynamic filtration has been used in many membrane processes, such as microfiltration (MF), ultrafiltration (UF) and even in nanofiltration (NF) and reverse osmosis (RO). The principle is to create a high shear rate at the membrane surface to limit concentration polarization and foulant deposition. A submerged magnetically induced membrane vibration system was used in this thesis to filtrate a lignocellulose hydrolysate. The hydrolysate, originating from a high-loading substrate, is extremely viscous and with a very high solid content, which is extremely challenging for membrane systems. By applying the vibration at high vibration amplitude, an increased membrane flux was achieved. It is expected that this filtration system can be used in the lignocellulose hydrolysis process as a technique to recover the enzymes and increase the lignocellulose conversion.Incorporating the porous materials in membranes has been proven already to be an efficient way to improve the performance. Zeolites were the most often used fillers for hydrophobic PV membranes. ZIF-71, a metal organic framework (MOF) that even more hydrophobic than silicalite-1, is zeolitic imidazolate framework constructed from zinc2+ and 4,5-dichloroimidazole. It can simply be synthesized at room temperature with a very high yield. The hydrophobic property and the flexible structure with a suitable pore dimension enable it to be used as filler for PV membrane fabrication. After filling the ZIF-71 in PDMS based PV membranes, the recovery of bio-alcohol was improved both in selectivity and flux.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Centre for Surface Chemistry and Catalysis

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