Carbon Dioxide Capture By Using Pore-Modified Porous Organic Polymers

Abstract

In order to mitigate the recent environmental crises such as global warming, climate change, and ocean acidification, the development of an efficient carbon dioxide (CO2) capture technology from flue gas is very important.1-4 Industrial flue gas is mainly composed of N2 (75%), CO2 (15%), and other gases including water vapor with a temperature between 313 to 333 K.1 Therefore, it is important to develop a material with a high adsorption selectivity for CO2 over N2 at a low CO2 partial pressure, outstanding water stability, as well as a high CO2 uptake capacity at elevated temperatures.1 Porous Organic Polymers (POPs) have gained significant attention as a class of promising CO2 capture material due to their superior physical properties such as high surface areas, extremely low density, and excellent thermal, chemical and water stability.5-9 In particular, the low density of porous organic polymers achieved by covalent bonds of only light elements such as C, N and H results in a high CO2 uptake per g unit mass of adsorbent.8,9 In addition, the polymers display superior stability against water,10 which is crucial for a post combustion CO2 capture material. Therefore, porous organic materials have the potential to be the optimal class of CO2 capture materials provided that their selectivity for CO2 over N2 are also high. In this study, PAF-5, a porous organic polymerl having both low density and excellent water stability, was impregnated with branched polyethylenimine (PEI, MW = ca. 800) to increase the CO2 uptake capacity and adsorption selectivity for CO2 over N2. PAF-5 with a 2D layered hexagonal structure constructed from only phenyl rings displays a high surface area (BET: 1503 m2 g-1) as well as a large pore width (1.66 nm) and pore volume (1.35 cc g-1).11 We expected that numerous amine functional groups of PEI dispersed in the large 1D channels of PAF-5 might act as strong CO2 interaction sites. In particular, PEI(40 wt%)⊂PAF-5 adsorbed 10.0 wt% of CO2 under a stream of 15% (v/v) CO2 in N2 at 313 K within 20 minutes. The adsorbent was completely regenerated within 20 minutes at 343 K under a N2 flow. Even after 10 cycles of adsorption and desorption, PEI(40 wt%)⊂PAF-5 did not show any decrease in the CO2 uptake capacity or decomposition of the adsorbent. In addition, after exposure to water vapor for 7 days at 313 K, the material still adsorbed almost the same amount of CO2 under the aforementioned conditions, which also proves its superior stability against water.