In the present work, a series of MOF-74 (Ni) materials with narrow micropore channels and abundant unsaturated metal sites was respectively prepared via hydrothermal (HT), condensation reflux (CE), and microwave-assisted (MW) methods. The physicochemical properties of synthesized materials were characterized by powder X-ray diffraction, N2-sorption, field-emission scanning electron microscopy, Fourier-transform infrared (FTIR), thermogravimetric (TG)/TG-FTIR, X-ray photoelectron spectroscopy, UV–vis–near infrared, NH3/CO2-temperature programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy. Their CO2/N2 adsorption performances were evaluated by isotherm adsorption and dynamic adsorption experiments. We found that the MW is a rapid and facile protocol for the synthesis of MOF-74 (Ni) materials with highly efficient CO2 capture capacity. The well-shaped MW-140 adsorbent with superior CO2 adsorption capacity of 5.22 mmol/g at 25 °C can be obtained within 60 min by the MW process, almost 6 times higher than that of the commercial activated carbon (0.89 mmol/g). Results of dynamic adsorption experiments showed that the MW-140 material possesses the highest CO2 adsorption capacity of 3.37 mmol/g under humid conditions (RH = 90%). Importantly, MW-140 has excellent adsorption stability and recyclability, superior CO2 capture selectivity (CO2/N2 = 31), and appropriate isosteric heat in CO2 adsorption (21–38 kJ/mol), making it a promising and potential material for industrial CO2 capture. Characterization results demonstrated that the high capture capability of MOF-74 (Ni) materials can be attributed to the synergistic effect of abundant narrow micropore channels and rich five-coordinated Ni2+ open metal sites which are beneficial for the trapping of CO2 molecules.

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To reduce the regeneration costs of capturing CO2 with absorbents, a two-dimensional desorption model for two-phase flow has been proposed. The temperature and pressure predicted by the model were found to agree well with the experiment data. A new synergy pinch concept was proposed to determine the interactive synergy impacts on mass and heat transfer. According to the proposed synergy pinch principle, the carbon surplus (SAC) and energy surplus (SAE) were defined to quantify the synergy effects for mass and heat transfer, respectively. The proposed synergy pinch principle is that the lower the values of SAC and SAE, the more effective the CO2 desorption. In addition, the synergy pinch point can be identified at the ideal value of zero SAC and SAE. Based on this analysis, a stripper with fin internals was introduced that could contribute energy savings of about 10–14% by synergizing the fluid flow between mass and heat transfer. Thus, it was verified that the synergy pinch method can be effectively applied in CO2 emissions control.

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