Silane modification of polyvinylidene fluoride membrane incorporated with TiO2 nanoparticles and nanocellulose for membrane distillation-crystallization
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Date
2019-06
Authors
Tan, Hoi Fang
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Abstract
The number of desalination plants in the world have grown drastically in the last few decades due to the increment of water demand, including water scarcity countries. The brine generated from these desalination plants requires proper management since the disposal of brine via surface discharge and deep well injection affects the quality of our water sources. Membrane distillation-crystallization (MDC) offers water recovery and salt collection from brine using solar energy or waste heat. The hydrophobic and macroporous membrane works as the barrier of two phases in membrane distillation crystallization, allowing only the water vapor to be transported from the hot brine into the cold permeate phase under the partial pressure difference. In this work, polyvinylidene fluoride (PVDF) membranes with/without TiO2 nanoparticles or/and nanocellulose (NC) were post-modified with octadecyltrichlorosilane to enhance the mass transfer by reducing membrane wetting. The effects of silane modification on membrane characteristics and performance in membrane distillation-crystallatization were studied. The wetting of PVDF membranes fabricated via phase inversion was reduced after silane modification. The water contact angle on PVDF/TiO2/NC membrane was improved up to 124 ยบ after modification using 1 ml of silane in 50 ml of ethanol. Hydrophobic octadecyltrichlorosilanol groups were successfully grafted after hydrolysis and condensation reactions as proven by Fourier-transform infrared spectra. As shown in scanning electron microscopic images, the membrane pore size and porosity were significantly increased by incorporating NC due to the accelerated exchange rate in phase inversion. Hence, the modified PVDF/TiO2/NC membrane achieved the highest water permeate flux with salt rejection as high as 97 %. The high permeability of PVDF/TiO2/NC membrane showed its potential in membrane distillation-crystallization to recover water and produce salt crystals. More future studies are required to improve the permeability, supersaturation degree and nucleation rate for crystal formation in MDC.