A novel phase splitter, namely, sulfolane, was proposed to advance the traditional monoethanolamine (MEA) absorption technology for CO2 capture by simultaneously promoting the absorption rate and lowering heat duty. The phase-splitting phenomenon was observed after the CO2 loading level had exceeded 0.73 mol CO2/L, thereby generating a CO2-rich MEA upper layer and a lower layer containing sulfolane. Sulfolane facilitated CO2 absorption because of its strong affinity with acid gases, which resulted in an absorption rate 2.7 times higher than that of the conventional MEA process. The process simulation using Aspen Plus indicated that the regeneration heat with the MEA/sulfolane mixture as a solvent substantially decreased to 2.67 GJ/t-CO2, which was 31% lower than that of the conventional MEA process (3.85 GJ/t-CO2). Moreover, the sensible heat and vaporization heat of MEA/sulfolane were markedly decreased by 62.4% and 47.9%, which could be ascribed to the decreased stripping volume and relatively high CO2 partial pressure caused by liquid–liquid phase separation. The proposed system is proved to be a promising candidate for the advancement of CO2 capture techniques with high CO2 absorption capacity, rapid absorption rate, and low-energy penalty.

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Amine-based CO2 capture technology requires high-energy consumption because the desorption temperature required for carbamate breakdown during absorbent regeneration is higher than 110 °C. In this study, we report a stable solid acid catalyst, namely, SO4 2–/ZrO2-HZSM-5 (SZ@H), which has improved Lewis acid sites (LASs) and Bronsted acid sites (BASs). The improved LASs and BASs enabled the CO2 desorption temperature to be decreased to less than 98 °C. The BASs and LASs of SZ@H preferred to donate or accept protons; thus, the amount and rate of CO2 desorption from spent monoethanolamine were more than 40 and 37% higher, respectively, when using SZ@H than when not using any catalyst. Consequently, the energy consumption was reduced by approximately 31%. A catalyzed proton-transfer mechanism is proposed for SZ@H-catalyzed CO2 regeneration through experimental characterization and theoretical calculations. The results reveal the role of proton transfer during CO2 desorption, which enables the feasibility of catalysts for CO2 capture in industrial applications.

Biphasic solvents containing mixed amines have a phase separation behavior and energy-efficient regeneration for CO2 capture. However, the trade-off between the CO2 absorption capacity and the volume ratio of the CO2-rich phase presents a critical challenge to the reducing potential in regeneration energy consumption. In this study, sulfolane was proposed to regulate the phase separation behavior of a N,N-diethylethanolamine (DEEA)–triethylenetetramine (TETA) biphasic absorbent by simultaneously decreasing the volume ratio and increasing the CO2 loading of the rich phase, without sacrificing the high CO2 capacity. In the DEEA–TETA–sulfolane biphasic absorbent, sulfolane acted as a phase splitter and physical activator. The replacement of a part of H2O by hydrophobic sulfolane contributed to a substantial decrease in the volume ratio of the rich phase from 83 to 39% and an increase in CO2 loading of the rich phase from 3.10 to 4.92 mol/L. The regeneration heat decreased to 1.81 GJ/t CO2, 26.4% less than DEEA–TETA, and 54.6% less than the 5 M monoethanolamine system. Moreover, by promoting the mass transfer coefficient of CO2 in DEEA–TETA–sulfolane to 1.8 times the original DEEA–TETA system, sulfolane was validated as a physical activator. Our study provides a promising strategy for regulating the phase separation behavior of biphasic solvents and enhancing the regeneration energy efficiency for CO2 capture.

High energy duty restricts the application of amine-based absorption in CO2 capture and limits the achievement of carbon neutrality. Although regenerating the amine solvent with solid acid catalysts can increase energy efficiency, inactivation of the catalyst must be addressed. Here, we report a robust metal–organic framework (MOF)-derived hybrid solid acid catalyst (SO4 2–/ZIF-67-C@TiO2) with improved acidity for promoting amine regeneration. The TiO2 coating effectively prevented the active components stripping from the surface of the catalyst, thus prolonging its lifespan. The well-protected Co–N x sites and protonated groups introduced onto the TiO2 surface increased the amount and rate of CO2 desorption by more than 64.5 and 153%, respectively. Consequently, the energy consumption decreased by approximately 36%. The catalyzed N–C bond rupture and proton transfer mechanisms are proposed. This work provides an effective protection strategy for robust acid catalysts, thus advancing the CO2 capture with less energy duty.

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