Infrared Study of CO₂ Sorption over “Molecular Basket” Sorbent Consisting of Polyethylenimine-Modified Mesoporous Molecular Sieve

Abstract

An infrared study has been conducted on CO 2 sorption into nanoporous CO 2 "molecular basket" sorbents prepared by loading polyethylenimine (PEI) into mesoporous molecular sieve SBA-15. IR results from DRIFTS showed that a part of loaded PEI is anchored on the surface of SBA-15 through the interaction between amine groups and isolated surface silanol groups. Raising the temperature from 25 to 75 °C increased the molecular flexibility of PEI loaded in the mesopore channels, which may partly contribute to the increase of CO 2 sorption capacity at higher temperatures. CO 2 sorption/desorption behavior studied by in situ transmission FTIR showed that CO 2 is sorbed on amine sites through the formation of alkylammonium carbamates and absorbed into the multiple layers of PEI located in mesopores of SBA-15. A new observation by in situ IR is that two broad IR bands emerged at 2450 and 2160 cm -1 with CO 2 flowing over PEI(50)/SBA-15, which could be attributed to chemically sorbed CO 2 species on PEI molecules inside the mesopores of SBA-15. The intensities of these two bands also increased with increasing CO 2 exposure time and with raising CO 2 sorption temperature. By comparison of the CO 2 sorption rate at 25 and 75 °C in terms of differential IR intensities, it was found that CO 2 sorption over molecular basket sorbent includes two rate regimes which suggest two distinct steps: rapid sorption on exposed outer surface layers of PEI (controlled by sorption affinity or thermodynamics) and the diffusion and sorption inside the bulk of multiple layers of PEI (controlled by diffusion). The sorption of CO 2 is reversible at 75 °C. Comparative IR examination of the CO 2 sorption/ desorption spectra on dry and prewetted PEI/SBA-15 sorbent revealed that presorbed water does not significantly affect the CO 2 -amine interaction patterns.

CO2 Capture Behaviors of Amine-Modified Resorcinol-Based Carbon Aerogels Adsorbents

“…Furthermore, new adsorption peaks at 1460 cm -1 appear in spectra curves of (b), (c) and (d), which can be ascribed to the bending vibrations of CH 2 . This further confirms that the PEI and TEPA have been loaded on CA-K-1 (Wang et al, 2009). …”

A Review of CO2 Capture by Absorption and Adsorption

“…Song and his coworkers reported the effects of polyethylenimine (PEI) loading, gas conditions, temperature, moisture and supports on CO 2 adsorption capacity for the PEI-impregnated mesoporous silica and carbonaceous materials (Xu et al, 2002(Xu et al, , 2005Ma et al, 2009;Wang et al, 2009Wang et al, , 2011a. A higher PEI loading significantly enhanced CO 2 adsorption capacity together with the decreases of surface area, pore size and pore volume of the PEIimpregnated supports.…”

Solid Adsorbents for Low-Temperature CO2 Capture with Low-Energy Penalties Leading to More Effective Integrated Solutions for Power Generation and Industrial Processes

“…Even in the presence of H 2 O, the formation of carbamates is kinetically favored over bicarbonate although the latter is more stable. The co-existence of the two competing reactions as well as the potential mass transfer barriers from the surface to bulk amine groups suggests that the CO 2 adsorption by immobilized amines will depend at least partially on contact time (Vaidya and Kenig, 2007;Serna-Guerrero et al, 2008;Wang et al, 2009). …”