Experimental and Theoretical Investigation of CO2 Adsorption on Amine-Modified Pumice as an Affordable Adsorbent

In the present work, experimental and theoretical aspects of CO2 adsorption on the amine-modified pumice, as a new adsorbent, was investigated. CO2 adsorption measurements were performed at three different temperatures (298, 328, and 348 K), and pressures up to 1 atm. To determine the best-fitting isotherm, the experimental equilibrium data were analyzed using eight adsorption isotherm models with two and three parameters. Four two-parameter equations, namely the Langmuir, Freundlich, BET, and Temkin, and four three-parameter equations, namely the Redlich-Peterson, Sips, Toth, and Dubinin- Astakhov were used. To evaluate the adequacy of the fitting of the isotherm models, the average relative error was calculated. Furthermore, Henry's law constant for evaluating the adsorption affinity of CO2 on the adsorbent was estimated by the Virial model. The results showed the modified pumice demonstrated better adsorption at the temperature of 298 K. Its adsorption capacity (0.510 mmol/g) was almost twice as much as that of raw pumice. The Freundlich model, in comparison with the other two-parameter models, and the Sips model, compared to the other three-parameter models, showed the best correspondence with CO2 adsorption’s experimental data, with average relative errors of less than 3% observed at all temperatures. The results suggest that the amount of E (kJ/mol) (the characteristic energy of adsorption D-A isotherm) at 298K and 328K was lower than 8, which indicates the domination of the physical adsorption mechanism in the process of CO2 adsorption on modified pumice.