Enrichment of carbon dioxide using Mg–Al layered double hydroxides

Abstract

Owing to the low atmospheric concentration of CO2 (400 ppm), direct air capture technologies require adsorbents that offer high CO2 adsorption capacities at low CO2 concentrations. In this study, we investigated the potential of CO3·Mg–Al layered double hydroxides (LDHs; Mg/Al molar ratio = 2, 3, and 4) as CO2 adsorbents. The CO2 adsorption and desorption behavior was studied at various molar ratios, adsorption/desorption temperatures, and linear speeds. CO2 adsorption by CO3·Mg–Al LDH followed the Langmuir model, indicating that monolayer adsorption occurs. The maximum CO2 adsorption quantity calculated using the Langmuir equation was 0.794 mmol/g for CO3·Mg–Al LDH with a Mg/Al molar ratio of 3. In dry CO2 adsorption experiments, a maximum CO2 adsorption quantity of 0.319 mmol/g was recorded with a Mg/Al molar ratio of 3 and temperature of 60 °C. In dry CO2 desorption experiments, the CO2 concentration and desorption quantity reached maximum values at 300 °C and a linear speed of 0.250 m/min. Notably, the maximum CO2 concentration was 6232 ppm, showing a 15.6-fold increase in comparison with the initial concentration of 400 ppm. Overall, our results demonstrate that CO3·Mg–Al LDH has high potential as a CO2 adsorbent. The study findings have significant implications for the development of new CO2 adsorbents for the direct air capture and storage of CO2.