(610g) Comparative Study of Two Nano-Composite Membranes for Efficient CO2 Removal

Global warming and acid rain are two devastating consequences of CO₂emissions. In recent years the membrane technology has received much attention, as it is more energy-efficient than conventional gas-separation technologies such as absorption [1]. Polymers have been used mostly for fabricating gas-separation membranes for industrial applications [2, 3]. However, the tradeoff between the permeability and selectivity of polymeric membranes is their major drawback [4]. Mixed-matrix membranes (MMMs) is a promising family of hybrid membranes, which can address this permeability and selectivity tradeoff of the membranes. Inorganic membranes have shown excellent seiving ability, however they are still difficult to fabricate. Combining the good processability of polymers and the excellent gas-separation ability of nano-particles results in high performane membranes that can defy the Robeson upper bound [5].

In this paper, we describe two nanocomposite membranes that we have fabricated by embedding modified TiO₂ nanoparticles into Pebax-1657 copolymer. The gas transport properties of nanocomposite membranes containing grafted nanoparticles with 3-aminopropyl-diethoxymethylsilane (AS) are compared to the membranes having carboxymethyl chitosan (CMC)-TiO₂ nanofillers. Results indicate the embedding leads to simultaneous improvements in the CO₂ permeability and CO₂/N₂ selectivity of both membranes, leading to transcending the 2008 Robeson upper bound. Synergetic effects of fixed facilitated transport, localized polyamide and polyethylene oxide domains, and molecular sieving trait of inorganic nanoparticles lead to extraordinary performance of the membranes for CO₂/N₂ separation. Increasing the operating pressure improves both the selectivity and permeability. Results indicate that the nanofiller grafting leads to a higher selectivity, and embedding the modified CMC-TiO₂ nanoparticles increases the membrane permeability. The higher selectivity of AS-TiO₂-Pebax is most likely due to the higher CO₂ adsorption on the AS-TiO₂ nanoparticles. Surface grafting is confirmed using FTIR, and grafting yields are calculated from TGA thermographs. Most likely reactions of the modifiers with TiO₂ nanoparticles and interactions between modified nanoparticles and Pebax backbone are proposed. The compatibility of the nanoparticles and the polymer, thermal stability of the nanocomposite membranes, and dispersion of nanofillers into the polymer are evaluated using different characterization techniques such as FTIR, DSC, TGA, and SEM. Stability tests of the prepared membranes reveal the satisfactory operational durability of the membranes. This study shows the great potential of TiO₂ nanoparticles to apply favorable modifications and incorporate the nanoparticles into polymer matrices for practical CO₂separation.

 

References

[1] Liu, J., Ho X. H., Park, B., Lin, H., High-Performance Polymers for Membrane CO₂/N₂Separation. Chem. - A European J, 2016, 22, 1- 12.

[2] Sanders, D.F., Smith, Z.P., Guo, R., Robeson, L.M., McGrath, J. E., Paul, D.R., Freeman, B.D., Energy-efficient Polymeric Gas Separation Membranes for a Sustainable Future: A Review. Polymer, 2013, 54(18), 4729-4761.

[3] Baker, R.W., Low, B.T., Gas Separation Membrane Materials: A Perspective. Macromolecules, 2014, 47 (20), 6999–7013.

[4] Robeson, L.M., The Upper Bound Revisited. J. Membr. Sci., 2008, Volume 320, 390-400.

[5] Arabi Shamsabadi, A., Seidi, F., Salehi, E., Nozari, M., Rahimpour, A., Soroush, M., Efficient CO₂-removal using novel mixed-matrix membranes with modified TiO₂ nanoparticles, J. Mat. Chem. A, 2017, 5, 4011–4025.