MIL-101(Cr) has drawn much attention due to its high stability compared with other metal-organic frameworks. In this study, three trace flue gas contaminants (H2O, NO, SO2) were each added to a 10 vol% CO2/N2 feed flow and found to have a minimal impact on the adsorption capacity of CO2. In dynamic CO2 regeneration experiments, complete regeneration occurred in 10 min at 328 K for temperature swing adsorption-N2-stripping under a 50 cm3/min N2 flow and at 348 K for vacuum-temperature swing adsorption at 20 KPa. Almost 99% of the pre-regeneration adsorption capacity was preserved after 5 cycles of adsorption/desorption under a gas flow of 10 vol% CO2, 100 ppm SO2, 100 ppm NO, and 10% RH, respectively. Strong resistance to flue gas contaminants, mild recovery conditions, and excellent recycling efficiency make MIL-101(Cr) an attractive adsorbent support for CO2 capture.

The adsorption/desorption kinetics of carbon dioxide on tetraethylenepentamine (TEPA) impregnated industrial grade multiwalled carbon nanotubes (IG-MWCNTs) was investigated to obtain insight into the underlying mechanisms on the fixed bed. After evaluating four kinetic models for CO 2 adsorption at various adsorption temperatures, CO 2 partial pressure, and amine loadings, it was found that Avrami's fractional-order kinetic model provided the best fitting for the adsorption behavior of CO 2 . In order to find the optimal regeneration method, three desorption methods were evaluated for the regeneration of solid sorbents. The activation energy E a of CO 2 adsorption/desorption was calculated from Arrhenius equation and used to evaluate the performance of the adsorbent. The E a decreased with increasing CO 2 concentration, indicating that CO 2 adsorption of amine-functionalized IG-MWCNTs is possibly intraparticle controlled. Meanwhile, because of the energy input of a vacuum pump, E a for the vacuum swing regeneration method was less than that for temperature swing regeneration.

The major drawback of aqueous alkanolamine-based CO2 capture processes is the high energy penalty for regeneration. To overcome this weakness, we studied the absorption of CO2 with amines dissolved in nonaqueous solvents. It was observed that triethylenetetramine (TETA) dissolved in ethanol produces a solid precipitate after absorption, which can then be easily separated and regenerated. As a comparison, a TETA/water solution does not form any precipitate after absorbing CO2. The TETA/ethanol solution offers several advantages for CO2 capture in absorption rate, absorption capacity, and absorbent regenerability. Both the rate and capacity of CO2 absorption with the TETA/ethanol solution were significantly higher than with a TETA/water solution, because ethanol not only promotes the solubility of CO2 in the liquid phase but also facilitates the chemical reaction between TETA and CO2. This approach was able to capture 81.8% of the absorbed CO2 in the solid phase as TETA-carbamate. In addition, results show that the decomposition of TETA-carbamate can be completed at 90 °C. Moreover, the cycling absorption/regeneration runs of the TETA/ethanol solution display a relatively stable absorption performance.

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The adsorption behavior of adsorbents for carbon dioxide can be significantly affected by flue gas contaminants. In this work, we examined the performance of tetraethylenepentamine (TEPA) impregnated industrial grade multiwalled carbon nanotubes (IG-MWCNTs) in trace amounts of flue gas contaminants such as H2O, NO, and SO2. It was observed that H2O and NO had a minimal impact on CO2 adsorption capacity, while the effect of SO2 on CO2 adsorption was influenced by adsorption temperature and SO2 concentration. Compared with silica-based adsorbents, i.e., TEPA-impregnated MCM-41, amine-functionalized IG-MWCNTs show significantly better tolerance to H2O and SO2. In addition, we examined the variation of CO2 adsorption with and without SO2 with various experimental methods (N2 adsorption/desorption isotherms, X-ray diffraction, and differential scanning calorimetry analysis) and molecular simulation. Experimental results show that irreversible sulfate/sulphite species deposited into the adsorbent contributes to the decrease on CO2 adsorption, while the results from simulation studies reveal that the enthalpy difference between the isolated TEPA with SO2 and TEPA···SO2 (ΔH(TEPA···SO2)) is larger than that of CO2 (ΔH(TEPA···CO2)), indicating that SO2 has a stronger reaction activity with TEPA than CO2. The increase of the ratio of ΔH(TEPA···SO2)/ΔH(TEPA···CO2) with increasing temperature illustrates that the difference of CO2 adsorption capacity with and without SO2 increases with elevated temperatures.