Metal-organic framework (MOF)-based structures and mixed-matrix membranes for CO2 separation

  • Stavroula Anastasiou

Student thesis: Master's Thesis

Abstract

Mixed matrix membranes (MMMs) have gathered great attention for CO2 separation applications due to their enhanced permeability and selectivity values. In this study, mixed matrix membranes comprising ZIF-8 and ZIF-8/GO composite as fillers and polysulfone (PSF) as the continuous phase have been prepared via solution blending method, with 5% wt. ZIF-8 loading. Both fillers have been characterized by SEM, XRD, FTIR and BET and once their desirable filler properties were assured, they were incorporated in the PSF matrix. BET surface areas of ZIF-8 and ZIF-8/GO were 1318 and 688.8 m 2/g, respectively. The CO2 capacities of ZIF-8 and ZIF-8/GO were measured at 25 °C, for pressure range 0-4 bar, with the highest uptakes being 109.1 and 52.7 mg/g, respectively, obtained at maximum pressure 4bar. The prepared PSF+ZIF-8 and PSF+(ZIF-8/GO) MMMs were characterized for their morphology, structure and finally for their affinity towards CO 2. SEM, XRD and FTIR results confirmed that the traits of both polymer and fillers remain intact at both MMMs. A homogeneous dispersion of both fillers in PSF polymeric matrix and intimate filler-polymer interaction was exhibited. PSF+ZIF-8 and PSF+(ZIF-8/GO) MMMs were tested for their permeation properties for the gases N2, CO2 and CH4, at room temperature and pressure 250 kPa and compared to neat PSF membrane. Both PSF+ZIF-8 and PSF+(ZIF-8/GO) MMMs demonstrated enhanced CO2 permeabilities, 1.77 and 1.76 Barrer, respectively, compared to pure PSF membrane (0.94 Barrer). However, PSF+ZIF-8 MMM has shown decreased CO2/CH4 selectivity (αCO2/CH4 = 0.9 for 1.77 Barrer), a 77% decrease compared to the pure PSF membrane (αCO2/CH4 = 3.9 for 0.94 Barrer). On the other hand, the performance of PSF+(ZIF-8/GO) MMM was boosted, as is exhibited a 61% increase in the CO2/CH4 selectivity (αCO2/CH4 = 6.3 for 1.76 Barrer), compared to the pure PSF membrane. PSF+(ZIF-8/GO) MMM exhibited also the highest increase in CO 2/N2 selectivity (αCO2/N2 = 4.9 for 1.76 Barrer), compared to PSF+ZIF-8 MMM (αCO2/N2 = 1.4 for 1.77 Barrer) or the neat PSF (αCO2/N2 = 0.8 for 0.94 Barrer). Finally, PSF+(ZIF-8/GO) MMM was tested also at 125 kPa. The increase in pressure from 125 kPa to 250 kPa resulted to 52% increase in CO2 permeability, 63% decrease in CH4 permeability and 320% increase in CO2 /CH4 selectivity, indicating that higher permeation pressure favors CO2 separation.
Date of Award2016
Original languageAmerican English
SupervisorGeorgios Karanikolos (Supervisor)

Keywords

  • Applied sciences
  • CO2
  • Metal-organic frameworks
  • Mixed matrix membranes
  • Chemical engineering
  • 0542:Chemical engineering

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