Recent advances in multi-layer composite polymeric membranes for CO2 separation: A review

AbstractThe development of multilayer composite membranes for CO2 separation has gained increasing attention due to the desire for energy efficient technologies. Multilayer composite membranes have many advantages, including the possibility to optimize membrane materials independently by layers according to their different functions and to reduce the overall transport resistance by using ultrathin selective layers, and less limitations on the material mechanical properties and processability. A comprehensive review is required to capture details of the progresses that have already been achieved in developing multilayer composite membranes with improved CO2 separation performance in the past 15–20 years. In this review, various composite membrane preparation methods were compared, advances in composite membranes for CO2/CH4 separation, CO2/N2 and CO2/H2 separation were summarized with detailed data, and challenges facing for the CO2 separation using composite membranes, such as aging, plasticization and long-term stability, were discussed. Finally the perspectives and future research directions for composite membranes were presented

Highly CO2-permeable membranes derived from a midblock-sulfonated multiblock polymer after submersion in water

To mitigate the effect of atmospheric CO2 on global climate change, gas separation materials that simultaneously exhibit high CO2 permeability and selectivity in gas mixtures must be developed. In this study, CO2 transport through midblock-sulfonated block polymer membranes prepared from four different solvents is investigated. The results presented here establish that membrane morphology and accompanying gas transport properties are sensitive to casting solvent and relative humidity. We likewise report an intriguing observation: submersion of these thermoplastic elastomeric membranes in liquid water, followed by drying prior to analysis, promotes not only a substantial change in membrane morphology, but also a significant improvement in both CO2 permeability and CO2/N2 selectivity. Measured CO2 permeability and CO2/N2 selectivity values of 482 Barrer and 57, respectively, surpass the Robeson upper bound, indicating that these nanostructured membranes constitute promising candidates for gas separation technologies aimed at CO2 capturepublishedVersio

Effects of the Morphology of the ZIF on the CO2 Separation Performance of MMMs

In this study, three zeolitic imidazolate frameworks (ZIFs) with different shapes—particles (0D), microneedles (1D), and leaves (2D)—were synthesized by tuning the polymeric additives. These ZIFs have been dispersed into a Pebax 2533 matrix with a loading varying from 0 to 20 wt %. The resultant mixed matrix membranes (MMMs) have been systemically characterized by various techniques. A mixed gas permeation experiment was also employed to evaluate the CO2 separation performance. The results show that there exists an optimal ZIF loading for these three series of membranes, but the values are highly dependent on the morphologies of the added ZIFs. The membranes containing ZIF particles and microneedles display the highest CO2 permeability and CO2/N2 selectivity simultaneously at 10 wt % loading, while a much lower loading, that is, ∼5 wt %, is the optimized value for ZIF leaves. Moreover, the increment in CO2 permeability is related to the ZIFs’ morphology and the order is 0D < 1D < 2D. On the other hand, the effects of the morphology on selectivity seems to be the opposite, with the ZIF of the 0D structure showing the highest selectivity. Moreover, the influences of adding ZIF fillers on the performances of the resultant MMMs under varied operating temperatures and the feed pressures were also investigated. The membrane with a 10 wt % 1D ZIF shows the highest increment in CO2 permeability (727.4 Barrer) with a CO2/N2 selectivity of ∼14 at 60 °C

Synthesis of Crosslinked PEG/IL Blend Membrane via One-Pot Thiol–Ene/Epoxy Chemistry

Poly(ethylene glycol) (PEG)-based membranes have obtained considerable attentions for CO2 separation for their promising CO2 separation performance and excellent thermal/ chemical resistance. In this work, a one-pot thiol–ene/epoxy reaction was used to prepare crosslinked PEG-based and PEG/ionic liquids (ILs) blend membranes. Four ILs of the same cation [Bmim]+ with different anions ([BF4]−, [PF6] −, [NTf2]−, and [TCM]−) were chosen as the additives. The chemical structure, thermal properties, hydrophilicity, and permeation performance of the resultant membranes were investigated to study the ILs’ effects. An increment in CO2 permeability (~34%) was obtained by optimizing monomer ratios and thus crosslinking network structures. Adding ILs into optimized PEG matrix shows distinct influences in CO2 separation performance depending on the anions’ types, due to the different CO2 affinities and compatibilities with PEG matrix. Among these ILs, [Bmim][NTf2] was found the most effective in enhancing CO2 transport by simultaneously increasing the solubility and diffusivity of CO2

Synthesis of Crosslinked PEG/IL Blend Membrane via One-Pot Thiol–Ene/Epoxy Chemistry

Poly(ethylene glycol) (PEG)-based membranes have obtained considerable attentions for CO2 separation for their promising CO2 separation performance and excellent thermal/ chemical resistance. In this work, a one-pot thiol–ene/epoxy reaction was used to prepare crosslinked PEG-based and PEG/ionic liquids (ILs) blend membranes. Four ILs of the same cation [Bmim]+ with different anions ([BF4]−, [PF6] −, [NTf2]−, and [TCM]−) were chosen as the additives. The chemical structure, thermal properties, hydrophilicity, and permeation performance of the resultant membranes were investigated to study the ILs’ effects. An increment in CO2 permeability (~34%) was obtained by optimizing monomer ratios and thus crosslinking network structures. Adding ILs into optimized PEG matrix shows distinct influences in CO2 separation performance depending on the anions’ types, due to the different CO2 affinities and compatibilities with PEG matrix. Among these ILs, [Bmim][NTf2] was found the most effective in enhancing CO2 transport by simultaneously increasing the solubility and diffusivity of CO2

Mathematical modeling and validation of CO2 mass transfer in a membrane contactor using ionic liquids for pre-combustion CO2 capture

Mass transfer and mathematical modelling of CO2 absorption in a tubular membrane contactor using 1-Butyl-3-methylimidazolium Tricyanomethanide ([Bmim][TCM]) for pre-combustion CO2 capture has been studied in this work. A 1D-model was developed based on resistance in series model and CO2 material balance. The developed model was validated with the experimental data, and good agreement was observed between the simulated and experimental results. A new mass transfer resistance term is added to reflect the non-flat concentration profile in the liquid phase. Simulation results indicate that the liquid phase resistance contributes 67% and 44% to the total mass transfer resistance for non-wetted and wetted modes of membrane respectively. The resistance that occurred due to considering transport in liquid phase contributes 31 and 20% for non-wetted and wetted modes of membrane contactor respectively. CO2 flux along the axial length of membrane contactor was modeled, giving the maxima at the gas outlet. The influences of operational constraints including liquid/gas flow rates, operation pressure/temperature, length of membrane contactor, and CO2 concentration in feed gas were also inspected

Incorporation of an ionic liquid into a midblock-sulfonated multiblock polymer for CO2 capture

In the present work, hybrid block ionomer/ionic liquid (IL) membranes containing up to 40 wt% IL are prepared by incorporating 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) into a midblock-sulfonated pentablock polymer (Nexar) that behaves as a thermoplastic elastomer. Various analytical techniques, including thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, small-angle X-ray scattering (SAXS), and water sorption have been employed to characterize the resultant membrane materials. Single- and mixed-gas permeation tests have been performed at different relative humidity conditions to evaluate membrane gas-separation performance and interrogate the molecular transport of CO2 through these membranes. Addition of IL to Nexar systematically enhances CO2 permeability through membranes in the dry state. Introduction of water vapor into the gas feed further promotes CO2 transport, yielding a maximum permeability of 194 Barrers and a maximum CO2/N2 selectivity of 128 under different test conditions. These results confirm that humidified Nexar/IL hybrid membranes constitute promising candidates for the selective removal, and subsequent capture, of CO2 from mixed gas streams to reduce the environmental contamination largely responsible for global climate change.publishedVersio

Morphologically tunable MOF nanosheets in mixed matrix membranes for CO2 separation

This study first develops a facile method to synthesize zeolitic imidazolate framework cuboid (ZIF-C) nanosheets with tunable thickness from 70 to 170 nm from aqueous polymer solutions. The obtained ZIF-C nanosheets were characterized by various techniques, including X-ray diffractometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), N adsorption and thermogravimetric analysis (TGA), to understand their compositional and structural properties. The synthesized ZIF-Cs nanosheets with different thicknesses were further applied as nanofillers to prepare Pebax-based mixed matrix membranes (MMMs) to study the effect of the morphology on membrane properties and CO/N separation performances under different relative humidity (RH) conditions. Results reveal that the incorporation of these ZIF-Cs simultaneously enhances CO permeability and CO/N selectivity in the mixed matrix membranes. In addition, MMMs with the thickest ZIF-C nanosheet present better performance. A CO permeability of 387.2 Barrer accompanied with a CO/N selectivity of 47.1 has been documented, nearly doubled in CO permeability with slightly increased selectivity compared with membranes containing thinner nanosheets