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Preparation and Characterization of Mixed-Matrix Composite Membranes Based On Metal-organic Frameworks/Acrylate Polyurethane to Separate Carbon Dioxide from Nitrogen

Molavi, Hossein | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51007 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Shojaei, Akbar; Mousavi, Abbas
  7. Abstract:
  8. Composite membranes are one of the promising membranes for overcoming the limitations of conventional membranes in gas separation application by improving the permeability and selectivity. However, it is still very challenging to achieve adhesion interface between the top selective layer and the bottom support layer. The present study demonstrates that this challenge can be overcome appropriately by utilizing a series of adhesive polymer as selective layer to prepare composite membrane. To this end, in the first section a series of acrylate-terminated polyurethanes (APUs) based on poly(ethylene glycol) (PEG) with different molecular weights (Mn) of 600, 1000, 1500, 2000 and 4000 g/mol, toluene diisocyanate (TDI), and 2-hydroxyethyl methacrylate (HEMA) were synthesized. Composite membranes were prepared with UV-curable acrylate-terminated polyurethane/acrylate diluent (APUAs) as selective layer and polyester/polysulfone (PS/PSF) as support layer. FTIR-ATR and DSC analyses indicated that the micro-phase separation of soft and hard segments increased by increasing the molecular weight of PEG. The experimental results revealed that the gas permeability of both gases increase, while the ideal CO2/N2 selectivity decreases with increasing the molecular weight of PEG, which might be due to increase the micro-phase separation between the soft and hard segments. Effect of operating conditions on gas permeability was also studied. It was found that the permeability of both gases increase by increasing the feed pressure and temperature, while the CO2/N2 selectivity increased with increasing the feed pressure and decrease with increasing the operating temperature. In the second section the effects of reactive diluent content and types on the separation of CO2 from N2 APUA membranes have been investigated. In this regard, a series of APUs based on PEG-1000 g/mol, toluene diisocyanate (TDI), and 2-hydroxyethyl methacrylate (HEMA) were synthesized and diluted with several reactive diluents. The obtained results from FTIR and DSC analyses indicated that the micro-phase separation of soft and hard segments decreased by increasing the reactive diluent content. Furthermore, with increasing the acrylate functionality of reactive diluents the degree of phase separation increased, which mainly be attributed to the higher crosslinking density of APUAs. The results of gas permeation revealed that the permeability of two gases decreases, while the CO2/N2 selectivity increases with increasing the reactive diluent content. Additionally, with increasing the polarity of reactive diluents the CO2 permeability as well as the CO2/N2 selectivity increased. In the third section we present a new approach to overcome the poor interfacial interaction between the polymer matrix and filler nanoparticles at the thin selective layer and improper interfacial adhesion between this selective layer to the porous support layer. To this end, a series of Mixed-Matrix Composite Membranes (MMCMs) based on APU-1000/UiO-66, NH2-UiO-66 and vinyl attached UiO-66 nanoparticles as selective layer and PS/PSF as support layer was synthesized by UV irradiation. GMA-UiO-66 was synthesized via ring opening reaction between the amine species in the framework (NH2-UiO-66) and epoxy groups in glycidyl methacrylate (GMA). Microscopic analysis by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) displayed that desirable nanoscale dispersion of UiO-66, suitable distribution across the membrane thickness as well as strong interface were achieved by using NH2-UiO-66 and in particular GMA-UiO-66 without using any ultrasonic technique. Long-term water stability of g-MMCM-3 showed the strong adhesion between selective layer and support layer after swelling in water, even at long time up to 20 days, which could be due to covalent bonds between matrix and vinyl attached UiO-66 nanoparticles. The MMCMs show significantly improved gas separation performance, most importantly, the CO2 permeability of g-MMCM-5 increased by 130% and the ideal CO2/N2 selectivity increased by 77%. These results suggest that post-synthetic modification of MOFs and chemical crosslinking between polymer matrix and modified MOF nanoparticles can be an effective way to eliminate interfacial voids and improve gas separation performance
  9. Keywords:
  10. Gases Separation ; Acrylated Polyurethane ; Mixed-Matrix Membrane ; Composite Membrane Model ; Metal-Organic Framework ; Post-Synthetic Modification

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