A Study of CO2 Adsorption of MEA-Modified Zeolite 13X and K2CO3-Impregnated Alumina for Direct Air Capture

Abstract

Rising industrial CO2 emissions have created an urgent need for efficient carbon capture and storage (CCS) technologies. This study compares the CO2 adsorption performance of three sorbents, namely zeolite 13X (Z13), monoethanolamine-modified zeolite (Z13/MEA), and K2CO3-impregnated alumina (K2CO3/Al2O3), under realistic direct air capture (DAC) conditions (∼450 ppm of CO2, RH 60–65%, 26 ± 2 °C). The sorbents were prepared by wet impregnation with actual loadings of 6.98 wt % MEA (CHNS) and 4.01 wt % K2CO3 (XRF), and were characterized by BET, CHNS, XRF, SEM, XRD, FTIR, and TGA. Z13/MEA exhibited the highest uptake (∼40 mgCO2/g), substantially greater than pristine Z13 (12 mg/g) and K2CO3/Al2O3 (5 mg/g). Under the humid DAC pathway (1:1 bicarbonate stoichiometry), these values correspond to 79% amine and 39% carbonate utilization, respectively. The superior performance of Z13/MEA is attributed to chemisorption at the −NH2 sites, confirmed by FTIR bands at 1650 cm–1 (carbamate) and 1380 cm–1 (bicarbonate) and an increase in carbon content from 3.4% to 3.8% after use. Pore blocking by MEA reduced the specific surface area from 502 to 25 m2/g but partially recovered to 262 m2/g after regeneration. XRD results confirmed the zeolite framework remained intact. Z13/MEA retained ≥90% of its initial capacity over 10 cycles under mild TSA regeneration at 80 °C, indicating good cyclic stability and low regeneration-energy demand. These findings provide a comparative basis for designing durable sorbents for CCS technology toward Net-Zero goals.