A comparative study of CO₂ capture by amine grafted vs amine impregnated zeolite 4A

Zeolite 4A was functionalized via grafting and impregnation techniques using 0.3 wt% of isopropylamine (IPA) and (3-aminopropyl) trimethoxysilane (APTMS) respectively. Physicochemical properties of zeolite 4A containing binder were changed after amine loading, as both specific surface area and pore volume was decreased by 1.52 % 18.18 % and 28.06 % 90.90 % for Z4A-IPA (IPA impregnated zeolite 4A) and Z4A-APTMS (APTMS grafted zeolite 4A) respectively. The adsorbed CO₂ amount of Z4A, Z4A-IPA, and Z4A-APTMS were 1.58 mmol g^-1 (6.95 wt%), 2.31 mmol g^-1 (10.16 wt%) and 1.05 mmol g^-1 (4.62 wt%) respectively at 1 bar and 25 °C. Noticeably, among all the studied adsorbents, Z4A-IPA displayed the highest adsorption capacity of 1.39 mmol g^-1 (6.11 wt%) at 0.15 bar, which is akin to the CO₂ partial pressure of post-combustion flue gas. The multilayer tethering of the bulkier APTMS on the zeolite external surface resulted in the partial blockage of the pores and hence the facile access of CO₂ inside the pores of zeolite was hindered. However, Z4A-APTMS was found to be more thermal stable than Z4A-IPA. Furthermore, we observed that physisorption was playing a vital role in CO₂ adsorption for pristine zeolite 4A (Z4A), whereas, after amine incorporation, the presence of amine induced the heterogeneous interaction between CO₂ and sorbents.