CO₂ Adsorption on Polyethylenimine-Functionalized SBA-15 Mesoporous Silica: Isotherms and Modeling

Abstract

SBA-15 mesoporous silica was functionalized with polyethylenimine and was used as a substrate for CO 2 adsorption. The synthesized material, denoted SBA-15-PEI, was characterized by means of X-ray diffraction, thermogravimetric analysis, and N 2 adsorption/desorption at 77 K, in order to prove that polymer chains efficiently filled the pores of functionalized samples. CO 2 adsorption isotherms on SBA-15-PEI were evaluated at T = (298, 313, 328, and 348) K for pressures up to 100 kPa by means of a volumetric technique. The experimental data showed a significant dependence of the CO 2 adsorption capacity on temperature, with the highest capacity encountered at the highest temperature explored. Despite this unusual behavior, CO 2 adsorption on SBA-15-PEI was satisfactorily modeled by means of the Sips isotherm. The modeling effort allowed to evaluate the isosteric heat of adsorption as a function of the fractional coverage of SBA-15-PEI. The comparison between the results obtained in the present work and those relative to CO 2 adsorption on "benchmark" microporous substrates, such as 13X zeolite and Cu-BTC metal organic framework, allowed us to highlight significant analogies and differences with those other solids, giving interesting hints on the possible applications of SBA-15-PEI.

Desorption Kinetics and Mechanisms of CO2 on Amine-Based Mesoporous Silica Materials

“…The whole activation energy is 73.02 kJ/mol, in accordance with the result obtained by thermogravimetricanalysis (70.56 kJ/mol) as presented in Table 2. The values obtained here are larger than the values obtained by Liu et al [27], but smaller than the values calculated by Sun et al [28]. However, the actual rate-limiting step for CO 2 adsorption could not be obtained by Avrami's model, which needs further investigation.…”

“…Currently, a lot of kinetic models are proposed to describe the experimental data. For example, Langmuir model [24,25], Langmuir-Freundlichmodel [26,27], pseudo-first-order [28], pseudo-second-order [29], and Avrami's model [21,30,31]. Kinefuchi et al [30] found that Avrami's fractional-order kinetic model could describe the desorption process well.…”

Sr-, Zn- and Cd-exchanged zeolitic materials as water vapor adsorbents for thermal energy storage applications

“…This is a model often used to deal with microporous materials, such as zeolites, for which a pore filling process controls adsorption phenomena. Unlike other theoretical isotherms, such as the Sips [34][35][36][37][38] or Toth one [39], the DA isotherm does not rely on entirely empirical expressions to describe the dependence of the maximum adsorption capacity and of the heterogeneity coefficient on temperature. Moreover, the DA model well describes the behavior of adsorbates, such as water vapor, which are characterized by strong molecular lateral interactions.…”

Polyethylenimine-incorporated zeolite 13X with mesoporosity for post-combustion CO2 capture

“…In this work, we synthesized a hierarchical zeolite X with mesoporosity (Meso-13X) and attempted to make use of the mesoporosity to incorporate increased and better dispersed amine species inside its pore structure. Polyethylenimine (PEI) was chosen as the amine source, which was found to greatly enhance CO 2 capture when supported on mesoporous silica [18][19][20][21][22][23]. The effectiveness of PEImodified Meso-13X (Meso-13X-PEI) as a CO 2 adsorbent was tested in terms of its adsorption capacity, selectivity and stability.…”