Antioxidative degradation mechanism of 2‐mercaptobenzimidazole modified TEPA‐MCM‐41 adsorbents for carbon capture from flue gas

Abstract

Solid amine adsorbents can efficiently adsorb CO2, but a significant problem is that amine groups are oxidized. In this research, tetraethylenepentamine‐impregnated MCM‐41 adsorbents (TEPA‐MCM‐41) were functionally modified with sulphur‐containing antioxidant 2‐mercaptobenzimidazole (described as antioxidant MB) and tns‐(2.4‐di‐tert‐butyl)‐phosphite (defined as antioxidant 168), respectively. The antioxidative degradation mechanism of 8% MB–50% TEPA‐MCM‐41 was analyzed by in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectrum and high‐performance liquid chromatography/mass spectrometry (HPLC/mass). The CO2 adsorption capacity of 50% TEPA‐MCM‐41 was 4.30 mmol/g under 15% CO2/85% N2, but decreased to 1.38 mmol/g after oxidation at 100°C for 42 h under 95% N2/5% O2 certain condition. The CO2 capacity of 8% MB–50% TEPA‐MCM‐41 reduced from 3.90 to 2.86 mmol/g. After 30 adsorption cycles under 5% O2/15% CO2/80% N2, the capacity of 8% MB–50% TEPA‐MCM‐41 also only decreased by 16.8%, while 50% TEPA‐MCM‐41 decreased by 63.2%. The reason for the excellent antioxidant stability of 8% MB–50% TEPA‐MCM‐41 is that MB scavenged free radicals from amine oxidation and decomposed the hydroperoxides produced by free radical reactions. The hydroperoxides were decomposed into alcohols (non‐radical products), which were eventually oxidized to sulphonic compounds. The MB modification inhibited the oxidative degradation of solid amine adsorbents guided for the production of antioxidant‐efficient adsorbents.