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Aqueous amine solutions have been widely used for the absorption of carbon dioxide (CO 2 ) from the gas mixtures. An understanding of the physical and chemical properties of aqueous amine solutions is important for the successful design and operation of CO 2 absorption processes. Particularly, the absorption capacity, absorption rate, and heat of absorption of CO 2 are major factors that affect the CO 2 absorption and stripping performance. A comparison study of the aqueous piperazine (PZ), 2-methylpiperazine (2-MPZ), homopiperazine (HomoPZ), and hexamethylenediamine (HMDA) solutions was conducted in this study. Absorption capacities and heats of absorption of these diamine solutions were measured using a semibatch-type reactor and a differential reaction calorimeter (DRC). The species distributions of the absorbents were investigated using a nuclear magnetic resonance spectroscopy (NMR), and the CO 2 absorption mechanism was also discussed. Aqueous PZ and PZ derivative solutions (2-MPZ and HomoPZ) displayed excellent characteristics as CO 2 absorbents. Aqueous 10 wt % PZ and PZ derivative solutions had higher absorption capacities and lower heats of absorption than that of aqueous 10 wt % monoethanolamine (MEA) at 313 K (−ΔH abs of the CO 2 -saturated PZ, 2-MPZ, HomoPZ, and MEA solutions: 62, 58, 68, and 80 kJ/mol CO 2 ).

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The amine‐based post‐combustion carbon capture process is one of the most efficient methods for treating large‐scale CO2, but it produces hazardous products due to chemical transition and degradation of the absorbents. In this study, carbon‐based materials were used as adsorbents for the removal of NH3, and their adsorption capacities, adsorption rates, and stabilities were examined by comparing commercial activated carbon (AC) with hierarchically porous carbon (HPC). HPC‐Step4 possessed a higher number of total acid sites, resulting in higher NH3 adsorption compared to AC. Despite the similar porosity, HPC‐Step4 exhibited a higher adsorption rate constant and the improved kinetics was attributed to its increased portion of mesopores, enhancing the diffusion rate of the adsorbate. Furthermore, HPC‐Step4 exhibited better reaction stability than AC.

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