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Title: Fabrication of novel nanocomposite membranes and 3D printed spacers for forward osmosis process
Authors: Lee, Jian Yuan
Keywords: DRNTU::Engineering::Chemical engineering::Water in chemical industry
Issue Date: 2016
Source: Lee, J. Y. (2016). Fabrication of novel nanocomposite membranes and 3D printed spacers for forward osmosis process. Doctoral thesis, Nanyang Technological University, Singapore.
Abstract: Forward osmosis (FO) is a novel osmotic-driven membrane process with lower energy consumption and many potential applications. However, the water flux of FO membranes was severely affected by concentration polarization (CP) of solutes on both the FO membrane surface and inside the FO membrane substrate. To address the CP issues in FO process, two strategies have been successfully developed. First, silica gel (SG)-based mixed matrix FO membranes have been systematically synthesized and characterized for the first time. The incorporation of SG particles into the polyacrylonitrile (PAN) support layer significantly enhanced water permeability of SG-based mixed matrix FO membranes. Water permeability of these membranes were improved after the embedment of SG particles with the range of 0.25 – 1.0 wt.% SG loading, possibly as a result of the both porous nature of SG particles and the enhanced membrane substrate porosity. However, further increasing in SG loading to 2.0 wt.%, a marginal reduction in both water permeability and salt rejection was observed, most likely due to the agglomeration of SG and hence reduce the mass transfer inside the membrane substrate. The optimal SG-based mixed matrix FO membrane with 1.0 wt.% SG loading had a significantly higher water permeability compared to the neat PAN membrane without embedment of any SG particles. This membrane can achieve the highest FO water fluxes of > 100 L/m2 h by using the 1 M MgCl2 as the draw solution (DS) and DI water as the feed solution (FS). Second, the effect of SG particles with different pore size on SG-based mixed matrix FO membranes was investigated. The objective of this study is to improve the mass transfer in the porous FO substrates and hence improving the internal concentration polarization (ICP) using the mixed matrix strategy. SG-based mixed matrix FO membranes with different pore size were successfully fabricated via non-solvent incudes phase inversion (NIPS) by adding silica gel particles with different pore size into the polyacrylonitrile dope solution. The thin salt rejection layer was synthesized using a layer-by-layer (LbL) self-assembly method on top of the SG-based mixed matrix FO substrate. The current study demonstrates the effect of different pore size of SG particle in mixed matrix FO substrate for improving the ICP in FO application for the first time. Third, the use of environmental-friendly metal-organic frameworks (MOFs) as green template was proven to enhance porosity and interconnectivity of the water treatment membranes. In general, osmotic-driven membranes with high porosity can possibly be fabricated by removing MOFs template, such as low water stability or other nanoparticles, in polymeric matrix. It is important to note that greatly enhanced water permeability was observed, which might be ascribed to the increased mass transfer coefficient of the FO substrate layer, which can be considered as an ultrafiltration (UF) membrane. Fourth, the use of metal-organic frameworks (MOFs) as removable filler was explored to prepare MOF-based porous matrix membranes (PMMs) for improving the mass transfer in the FO substrates and hence controlling the ICP. MOF-based porous matrix substrates (PMSs) with three different types of MOFs were prepared via phase inversion by adding MOF particles into the polyacrylonitrile (PAN) dope solution. The bond dissociation energy (BDE) between metal ions and organic linker of MOF particles played an important role for the selection of fillers of PMMs. For MOF particles with lower BDE (< ~200 kJ/mol), the corresponding MOF-based porous matrix FO membranes had higher membrane bulk porosity. This study shows the effect of different types of MOF particles in MOF-based porous matrix FO substrate for controlling the ICP in FO application for the first time, which provides an additional dimension for ICP control in osmotic-driven membrane processes. Finally, 3D printing is an emerging technology and has attracted massive attention in recent years. This part of thesis focuses on the recent developments on enhancing the spacer design with 3D printing technology. With the recent advancement of 3D printing technology, breakthroughs in fabricating novel FO feed spacers are expected in the near future. Improvement of 3D printing technologies in terms of resolution, materials and speed should assure the production of various 3D printed feed spacers with high efficiency and better performance.
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