(173j) Effects of Cyanuric Chloride and Its Derivatives on Gas Separation Properties of Polyurethane Membranes

The potential of rubbery polymers to offer high solubility of polar gases such as CO₂ [1] and no physical aging [2] has generated considerable interest in the polymers for use in CO₂capture and separation. Polyurethanes (PUs), a kind of block rubbery copolymers containing hard and soft segments, have shown promise in fabricating selective gas separation membranes [3]. Ethereal groups in PUs backbone impede crystallization of polymers containing ethylene oxide groups, leading to improved permeability. The polymer chemistry and the incorporation of fillers into the polymer allow for synthesizing highly permeable PU membranes with excellent sieving ability [4]. Mixed-matrix membranes (MMMs), a promising family of hybrid membranes, contain dispersed nanoparticles in a polymer matrix [5]. MMMs offer permeability and selectivity higher than those of classical membranes. Combining the good processability of polymers and the excellent gas-separation ability of nanoparticles lead to the fabrication of membranes that can surpass the Robeson upper bound [6]. Compared to pristine polymer membranes, MMMs have better mechanical, chemical, and thermal stability as well as higher performance [7].

This papers presents a study on the effects of cyanuric chloride and its derivatives on gas separation properties of polyurethane membranes. A two-step bulk polymerization method is used to prepare a PU from polytetramethylene glycol and isophorone diisocyanate. Also, 2,4,6-Trihydazino-1,3,5-triazine (THDT) particles are synthesized via a facile and fast one-step reaction from cyanuric chloride. Novel MMMs are then fabricated by embedding cyanuric chloride and its derivatives (melamine and THDT) into the synthesized PU polymer. Dispersion of the nanoparticles in the PU is evaluated via FTIR, XRD, and SEM analyses, and gas transport properties. H-bonding of the PU backbone and the nanoparticles, peak assignment of the bonded carbonyl, crystallinity change, and permeation tests show the tendency of nanoparticles for scattering in the soft or hard segment of the PU membranes. The results show that cyanuric chloride is dispersed most likely in the hard segment, whereas melamine and the THDT nanoparticles are distributed in the soft segments. Compared to pure PU, as the cyanuric chloride nanoparticle content of the MMMs increases, gas permeability, O₂/N₂ selectivity, CO₂/CH₄ selectivity, and CO₂/N₂ selectivity increase. The permeability of CO₂ increases with the THDT concentration. In the case of THDT and melamine, as the filler loading increases, the permeability of the gasesdecreases, whereas O₂/N₂ selectivity, CO₂/CH₄ selectivity, and CO₂/N₂ selectivity increase. The performance of PU-THDT-10 (PU containing 10% THDT) membrane approaches the 2008 upper bound for CO₂/N₂ and CO₂/CH₄ separations. This work shows that incorporating 10 % THDT nanoparticles leads to significant improvement in the CO₂-separation performance of the PU-THDT-10 membrane, due to the extraordinary CO₂-philic characteristics of THDT.

 References

[1] Lin, H., B.D. Freeman, Gas solubility, diffusivity and permeability in poly (ethylene oxide). J. Membr. Sci., 2004, 239 (2004), 105–117.

[2] Arabi Shamsabadi, A., Behbahani, R.M Seidi, F., Soroush, M., Physical Aging of Polyetherimide Membranes. J. Natural Gas Sci. Eng., 2015, 27, 651-660.

[3] Pournaghshband Isfahani, A., Ghalei, B., Bagheri, R., Kinoshita, Y., Kitagawa, H., Sivaniah, E., Sadeghi, M., Polyurethane gas separation membranes with ethereal bonds in the hard segments. J. Membr. Sci., 2016, 513, 58–66.

[4] Lin, H., B.D. Freeman, Ekiner, O.M., Gas permeation properties of poly(urethaneurea)s containing different polyethers. J. Membr. Sci., 2011, 369, 49–58.

[5] Zhang, C., Koros, W.J., Tailoring the Transport Properties of Zeolitic Imidazolate Frameworks by Post-Synthetic Thermal Modification. ACS Appl. Mat. Interf., 2015, 7 (42), 23407-23411.

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

[7] Zarshenas, K., Raisi, A., and Aroujalian, A., Mixed Matrix Membrane of Nano-Zeolite NaX/poly (ether-block-amide) for Gas Separation Applications. J. Membr. Sci., 2016, 510, 270-283.