Abstract
Lowering the regeneration temperature for solid CO2-capture materials is one of the critical tasks for economizing CO2-capturing processes. Based on reported pKa values and nucleophilicity, we compared two different polyethylenimines (PEIs): branched PEI (BPEI) and linear PEI (LPEI). LPEI outperformed BPEI in terms of adsorption and desorption properties. Because LPEI is a solid below 73–75 °C, even a high loading amount of LPEI can effectively adsorb CO2 without diffusive barriers. Temperature-programmed desorption (TPD) demonstrated that the desorption peak top dropped to 50.8 °C for LPEI, compared to 78.0 °C for BPEI. We also revisited the classical adsorption model of CO2 on secondary amines by using in situ modulation excitation IR spectroscopy, and proposed a new adsorption configuration, R1(R2)-NCOOH. Even though LPEI is more expensive than BPEI, considering the long-term operation of a CO2-capturing system, the low regeneration temperature makes LPEI attractive for industrial applications.
Highlights
A record-high level of CO2 concentration in the atmosphere poses a global concern about how to suppress or stop anthropogenic CO2 emissions [1]
We focused on desorption properties of Branched PEI (BPEI) and linear PEI (LPEI) in this study
As commonly known [17], in the humid condition, CO2 adsorption capacity increased by a factor of ca. 1.8 for both BPEI and LPEI
Summary
A record-high level of CO2 concentration in the atmosphere (ca. 415 ppm) poses a global concern about how to suppress or stop anthropogenic CO2 emissions [1]. Liquid amine scrubbing has been employed for CO2 capture [5,7] Its downsides, such as loss of volatile amine, corrosion, and high energy consumption in the regeneration step, make industries long for an alternative capturing system [8]. In this regard, solid adsorbents such as mesoporous oxides, zeolites, and metal–organic frameworks (MOFs) have recently gained attention due to their feasibility for desorbing CO2 from a material surface by heating the material. Lowering the regeneration temperature contributes to a considerable decrease in the energy input and the total cost of capturing systems when long-term operation is considered without exchanging adsorbent materials for several years. We report a comparative study of BPEI and LPEI, with a particular focus on CO2 desorption properties
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