Modeling the performances of a CO2 adsorbent based on polyethylenimine-functionalized macro-/mesoporous silica monoliths

An adsorbent based on polyethylene oxide-templated silica monoliths with hierarchical uniform porosity was functionalized with polyethylenimine and was used as a substrate for CO2 adsorption. Such material, denoted PEI-MonoSil, was characterized by means of thermogravimetric analysis and N2 adsorption/desorption at 77 K, in order to prove that polymer chains efficiently filled the pores of functionalized samples. CO2 adsorption isotherms on PEI-MonoSil were evaluated at T = 298, 313, 333, and 348 K for pressures up to 100 kPa by means of a volumetric technique. CO2 adsorption data revealed a meaningful dependence of the CO2 adsorption capacity on temperature, with the highest capacity registered at 348 K. CO2 adsorption on PEI-MonoSil was convincingly modeled by means of the Toth isotherm. The comparison between the results obtained in the present work and those relative to CO2 adsorption on other nanoporous substrates allowed to highlight a notable affinity of PEI-MonoSil towards CO2 and a high level of heterogeneity in the adsorbent/adsorbate interaction. Eventually, the modeling effort also allowed to evaluate the isosteric heat of CO2 adsorption as a function of the fractional coverage of PEI-MonoSil, showing values that are comparable with experimentally estimated values of the enthalpy of reaction between CO2 and monoethanolamine solutions