(521b) Self-Supported Branched Poly(ethyleneimine) Scaffolds for CO2 Capture

Structured contactors in the form of monoliths for CO₂ capture not only combat the high energy consumption and corrosion rate observed in traditionally used aqueous amines, but also offer a low pressure drop in comparison to powder adsorbents during operation.¹ Developments so far in monoliths include attachment of functionalized nanoporous materials such as metal organic frameworks (MOFs), zeolites, carbons or inorganic/organic composites containing polymeric amines.² While amine materials have an advantage in terms of better sorption capacities in the presence of humidity, the need for a support that itself does not contribute directly to CO₂ capture remains non-ideal.^3,4 This work therefore focuses on utilizing widely used poly (ethyleneimine) (PEI) to synthesize wholly organic monoliths without any additional support, potentially reducing the sensible heat load in the thermal regeneration cycle. High molecular weight branched poly(ethyleneimine) was crosslinked with poly(ethylene glycol diglycidyl ether) in aqueous media at different cryogenic temperatures using an ice templating method.⁵ The reaction temperature was varied to change the ice crystal structure in the templating process and thereby the nature of the pores in the scaffold. The relative ratio of PEI and crosslinker was varied and it was found that scaffolds formed at -196 °C containing 0.1 equivalent of crosslinker relative to the amines in PEI showed an optimal CO₂ adsorption capacity of 5.5 mmol/g after 12 h at 25 °C in a 10% CO₂ feed stream with 65% RH. Functionalization of PEI before crosslinking and its effect on the morphology of the scaffold as well as the CO₂ adsorption capacity has also been studied. It was found that a hydrophobic capping group resulted in dense polymer domains and using water miscible additives provides additional scope for positively affecting the morphology and thereby improving the CO₂ adsorption capacity using more dilute CO₂ feeds.

References:

(1) Rezaei, F.; Webley, P. Optimum Structured Adsorbents for Gas Separation Processes. Chem. Eng. Sci. 2009, 64 (24), 5182–5191.

(2) Murdock, C. R.; Didas, S. A.; Jones, C. W. Direct Capture of CO₂ from Ambient Air. Chem. Rev. 2016, 116, 11840-11876.

(3) Darunte, L. A.; Terada, Y.; Murdock, C. R.; Walton, K. S.; Sholl, D. S.; Jones, C. W. Monolith-Supported Amine-Functionalized Mg₂(Dobpdc) Adsorbents for CO₂ Capture. ACS Appl. Mater. Interfaces 2017, 9 (20), 17042–17050.

(4) Shi, Y.; Liu, Q.; He, Y. CO₂ Capture using Solid Sorbents. Handbook of Climate Change Mitigation and Adaptation 2016, 1-56.

(5) Yoo, C. J.; Narayanan, P.; Jones, C. W. Self-Supported Branched Poly(Ethyleneimine) Materials for CO₂ Adsorption from Simulated Flue Gas. J. Mater. Chem. A 2019, 7 (33), 19513–19521.