Publication: Development of superhydrophobic pvdf-tio2/sio2 nanoparticles membrane for membrane distillation of phenolic rich solution
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Date
2023-05-01
Authors
Norhaziyana Binti Hamzah
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Abstract
The processing of plant-based ingredients requires a lot of water and results in a great amount of wastewater with a high phenolic content. The recovery of pure water and valuable ingredients can be simultaneously achieved using membrane distillation (MD) which requires the minimum chemical usage and involves the minor thermal changes. Water vapor is transported across the porous membrane under the vapor pressure gradient due to small temperature difference between the feed and the permeate. However, membrane wetting and fouling caused a great drop in permeate flux even using the hydrophobic polyvinylidene fluoride (PVDF) membrane. This work aims to further enhance the hydrophobicity of PVDF membranes using phase inversion with dual-bath method for MD of phenolic rich solution. The ethanol content in coagulation bath was first varied to enhance membrane properties. The water contact angle, surface roughness and mean pore size of PVDF membranes were improved by the increasing ethanol content. Subsequently, the effects of titanium dioxide (TiO2) nanoparticles in dope solution and silane modification on surface hydrophobicity were studied. Two different methods were adopted in the silane modification process. Pre-treatment method involved the modification of TiO2 nanoparticles using hydrophobic silane before blending into dope solution. Meanwhile, post-treatment method involved the modification of PVDF membrane incorporated with TiO2 nanoparticles after phase inversion. The effects of different silanes and concentration on membrane characteristics and performance in MD were investigated. Among the three types of hydrophobic silane, (tridecafluro-1,1,2,2-tetrahydrooctyl) triethoxysilane in ethanol at the ratio of 1 :50 resulted in the greatest improvement of permeation in MD. All the membranes achieved phenolic rejection of 99% after blending TiO2 nanoparticles and silane modification. The modified PVDF/TiO2 membranes showed less flux decline compared to the neat PVDF membrane due to the improved hydrophobicity. The post-treated PVDF/TiO2 membrane achieved the highest permeates flux due to the formation of great porosity in phase inversion without the disturbance of silane modification. The membrane thickness was further reduced by fabricating membrane on woven support using dual-bath coagulation with post-treatment. The composition of dope solution such as PVDF loading, LiCl content, and nanoparticle selection were adjusted to develop antifouling properties. Besides TiO2 nanoparticles, Silicon Dioxide (SiO2) nanoparticles and a mixture of TiO2-SiO2 nanoparticles were blended into dope solution. The blending of TiO2 and SiO2 nanoparticles simultaneously in dope solution further improve the surface roughness on membrane. The produced membrane successfully attained to the state of superhydrophobic with water contact angle higher than 160 º with the help of active fluorination site from nanoparticles during the silane modification process.The addition of TiO2-SiO2 mixture into PVDF matrix further raised the permeation flux with relative flux (J/J0) higher than 0.8 after 8 h of operation even with the presence of surfactant in phenolic rich solution. The thermal calculation showed that the post-treated PVDF/TiO2-SiO2 membrane achieved temperature polarization coefficient near to the optimal value of 0.7 with a good thermal efficiency above 84 %.