(152au) Designing Bottlebrush Poly(1,3-dioxolane) Acetate for CO2 Capture | AIChE

(152au) Designing Bottlebrush Poly(1,3-dioxolane) Acetate for CO2 Capture


Tran, T., University at Buffalo
Lin, H., University of Buffalo, State University of New Yor
Poly(ethylene oxide) (PEO) based polymers are leading membrane materials for CO2/N2 separation with a balanced high CO2 permeability and CO2/N2 selectivity because the ether oxygen groups show affinity towards CO2. Herein, we synthesize polymers based on 1,3-dioxolane with higher ether oxygen content than PEO and thus improved CO2/N2 separation performance. Specifically, macromonomers of poly(1,3-dioxolane) acrylate (DXLAn) with short DXL branches (n = 4 – 12) were synthesized via cationic ring-opening polymerization of 1,3-dioxolane, and polymers (pDXLAn) were synthesized by free radical polymerization. The chemical structure of the macromonomers was confirmed using NMR, and the amorphous nature of the polymers was validated using DSC and WAXD. Pure- and mixed-gas CO2/N2 separation properties were determined as a function of feed pressure, composition, and temperature, and the effect of PDXLA chain-end group on the gas separation performance was also investigated. Increasing the n value decreases glass transition temperature (Tg) and increases CO2 permeability. The PDXLA12 exhibits the best separation performance with CO2 permeability of 250 Barrer and CO2/N2 selectivity of 58 at 35 oC, above the 2008 Robeson’s upper bound. Moreover, the hydroxyl (-OH) chain-end group in PDXLAn can be converted to acetyl- (PDXLAcn) to disrupt the hydrogen bonding, thus increasing polymer chain flexibility. For example, converting PDXLA8 to PDXLAc8 increases CO2 permeability from 165 to 340 Barrer with a slight decrease of CO2/N2 selectivity from 57 to 51. This can be attributed to the increase in polymer chain flexibility, indicated by the decreased Tg from -57 to -62°C. The structure/property relationship in this series of amorphous, highly polar polymers with exciting separation performance will be elucidated. Thin-film composite membranes based on PDXLAc8 were prepared and exhibit pure-gas CO2 permeance of 1600 GPU and CO2/N2 selectivity of 47 at 25°C. We will also discuss the mixed-gas separation properties and the performance when challenged with simulated flue gas and compare them with state-of-the-art membranes for this application.