Spectroscopic Investigation into Oxidative Degradation of Silica‐Supported Amine Sorbents for CO2 Capture

Chakravartula S Srikanth,Steven S C Chuang

doi:10.1002/cssc.201100662

Chakravartula S Srikanth, Steven S C Chuang

Open Access

https://doi.org/10.1002/cssc.201100662

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Abstract

Oxidative degradation characteristics of silica-supported amine sorbents with varying amounts of tetraethylenepentamine (TEPA) and polyethylene glycol (PEG; P200 or P600 represents PEG with molecular weights of 200 or 600) have been studied by IR and NMR spectroscopy. Thermal treatment of the sorbents and liquid TEPA at 100 °C for 12 h changed their color from white to yellow. The CO2 capture capacity of the TEPA/SiO2 sorbents (i.e., SiO2-supported TEPA with a TEPA/SiO2 ratio of 25:75) decreased by more than 60 %. IR and NMR spectroscopy studies showed that the yellow color of the degraded sorbents resulted from the formation of imide species. The imide species, consisting of NH associated with two C—O functional groups, were produced from the oxidation of methylene groups in TEPA. Imide species on the degraded sorbent are not capable of binding CO2 due to its weak basicity. The addition of P200 and P600 to the supported amine sorbents improved both their CO2 capture capacities and oxidative degradation resistance. IR spectroscopy results also showed that TEPA was immobilized on the SiO2 surface through hydrogen bonding between amine groups and the silanol groups of SiO2. The OH groups of PEG interact with NH2/NH of TEPA through hydrogen bonding. Hydrogen bonds disperse TEPA on SiO2 and block O2 from accessing TEPA for oxidation. Oxidative degradation resistance and CO2 capture capacity of the supported amine sorbents can be optimized through adjusting the ratio of hydroxyl to amine groups in the TEPA/PEG mixture.

Highlights

CO2 emission from coal-fired power plants constituted more than 40 % of anthropogenic CO2 released into the atmosphere in 2010.[1]
The solid amine sorbents could potentially decrease the cost of CO2 capture by 1) reducing the energy needed for sorbent regeneration, 2) avoiding equipment corrosion, and 3) increasing the rate of CO2 adsorption/absorption and desorption
Solid amine sorbents should possess a minimum CO2 capture capacity of 2.0 mmol per gram of sorbent to provide a performance comparable to that of a large-scale liquid amine process.[2a,3] Solid sorbents studied so far include supported amine sorbents,[2a,3a,4] carbon-based amine sorbents,[5] amines coated on glass fibers,[3b,6] zeolites,[7] SiO2,[7] SBA-15,[3a,8] and MCM-41.[9]. The approaches to immobilize amines include 1) amine grafting,[3a,4c][3b,6] using aminosilanes, and 2) physical adsorption of amines on the support surface.[8a,9a,10] Recently, covalently tethered hyper-branched aminosilane (HAS) materials have been prepared on SBA-15, which has CO2 adsorption sites that can be regenerated.[11]

Summary

Introduction

CO2 emission from coal-fired power plants constituted more than 40 % of anthropogenic CO2 released into the atmosphere in 2010.[1]. S. Srikanth other studies, PEG has been used as an additive to improve the CO2 capture capacity of the amine-based sorbents[9a,16] and for SO2 capture.[17] The oxygen in a flue gas stream, which can be trapped in the porous structure of the supported-amine sorbent, could initiate oxidative degradation during thermal desorption of adsorbed CO2 on the sorbent. The presence of PEG in the sorbents increased the CO2 capture capacity, and slowed down the degradation of SiO2-supported amine sorbents in the oxidative (i.e., flue gas) environment. Ents prepared, the number of moles of amines from TEPA (NH2 and NH), the number of moles of hydroxyl groups from PEG present on each sorbent, and the sorbent color changes observed after the oxidative degradation studies.

Oxidative degradation study

Conclusions

Experimental Section

Oxidative degradation mechanism