Important Roles of Enthalpic and Entropic Contributions to CO 2 Capture from Simulated Flue Gas and Ambient Air Using Mesoporous Silica Grafted Amines

Type
Article

Authors
Alkhabbaz, Mustafa A.
Bollini, Praveen
Foo, Guo Shiou
Sievers, Carsten
Jones, Christopher W.

KAUST Grant Number
KUSI1-011-21

Online Publication Date
2014-09-12

Print Publication Date
2014-09-24

Date
2014-09-12

Abstract
© 2014 American Chemical Society. The measurement of isosteric heats of adsorption of silica supported amine materials in the low pressure range (0- 0.1 bar) is critical for understanding the interactions between CO2 and amine sites at low coverage and hence to the development of efficient amine adsorbents for CO2 capture from flue gas and ambient air. Heats of adsorption for an array of silica-supported amine materials are experimentally measured at low coverage using a Calvet calorimeter equipped with a customized dosing manifold. In a series of 3-aminopropylfunctionalized silica materials, higher amine densities resulted in higher isosteric heats of adsorption, clearly showing that the density/proximity of amine sites can influence the amine efficiency of adsorbents. In a series of materials with fixed amine loading but different amine types, strongly basic primary and secondary amine materials are shown to have essentially identical heats of adsorption near 90 kJ/mol. However, the adsorption uptakes vary substantially as a function of CO2 partial pressure for different primary and secondary amines, demonstrating that entropic contributions to adsorption may play a key role in adsorption at secondary amine sites, making adsorption at these sites less effi cient at the low coverages that are important to the direct capture of CO2 from ambient air. Thus, while primary amines are confirmed to be the most effective amine types for CO2 capture from ambient air, this is not due to enhanced enthalpic contributions associated with primary amines over secondary amines, but may be due to unfavorable entropic factors associated with organization of the second alkyl chain on the secondary amine during CO2 adsorption. Given this hypothesis, favorable entropic factors may be the main reason primary amine based adsorbents are more effective under air capture conditions.

Citation
Alkhabbaz MA, Bollini P, Foo GS, Sievers C, Jones CW (2014) Important Roles of Enthalpic and Entropic Contributions to CO 2 Capture from Simulated Flue Gas and Ambient Air Using Mesoporous Silica Grafted Amines . Journal of the American Chemical Society 136: 13170–13173. Available: http://dx.doi.org/10.1021/ja507655x.

Acknowledgements
This publication is based on work supported in part by Award KUSI1-011-21, made by King Abdullah University of Science and Technology (KAUST). The work was also supported in part by the Office of Naval Research, via ONR code 33. M.A.A. thanks the Research & Development Center of Saudi Aramco for the Ph.D. scholarship.

Publisher
American Chemical Society (ACS)

Journal
Journal of the American Chemical Society

DOI
10.1021/ja507655x

PubMed ID
25215519

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