A novel ionic liquid (1-aminoethyl-3-methylimidazolium lysinate, [C2NH2MIm][Lys]) functionalized with three amino groups had been developed for carbon dioxide (CO2) capture in this work. The CO2 absorption loading of [C2NH2MIm][Lys] solution was found to be 1.59 mol CO2/mol IL with a concentration of 0.5 mol/L at 313.15 K, which was much higher than that of the most existing dual functionalized ILs. Besides, [C2NH2MIm][Lys] also owned a good regenerability even after 6 regeneration cycles. According to the results of 13C nuclear magnetic resonance (13C NMR), CO2 absorption into [C2NH2MIm][Lys] solution could be divided into two stages, which began with the formation of carbamate, and followed by the hydration of CO2 to form carbonate/bicarbonate. Meanwhile, the desorption of the saturated [C2NH2MIm][Lys] was proven to be a reverse process of the adsorption. Based on the mechanism results, the kinetics of CO2 capture into [C2NH2MIm][Lys] solution was investigated by using a double stirred-cell absorber at temperatures ranging from 303 to 333 K. Under the pseudo-first-order regime, the overall reaction rate constants (kov) and the forward second-order rate constants (k2) under different concentrations and temperature were obtained, which were both increased considerably as temperature increased. Moreover, the values of enhancement factor (E) were linear with CRNH2 and temperature. The Arrhenius equation of CO2 absorption was also estimated, and the activation energy was calculated to be 25.5 kJ·mol–1.

Amino-acid-functionalized ionic liquids (AAILs) show significant potential for energy-efficient post-combustion CO2 capture. In this work, the interaction energy calculation was performed with the Gaussian 09 package, and the activation barriers and energy change calculation were performed with the Material Studio 7.0 package. The experimental and quantum chemical calculation results showed that both the CO2 absorption capacity and the viscosity of AAILs were negatively correlated to their interaction energy. The results of 13C nuclear magnetic resonance analysis and activation barriers indicated that, under the same conditions, the effect of the AAIL cation on the regeneration ability was more significant than that of the anion. In our previous work, CO2 absorption into AAIL solution was proven to be divided into two periods. In the first period, carbamate was produced after the CO2 absorption reaction, and in the second period, the production was carbonate. Research on thermodynamic properties in this work made the mechanism for CO2 capture into AAILs more clear. The activation barrier, energy change, and enthalpy change during the two periods revealed that the AAIL–CO2 absorption reaction should be a neutralizing and exothermic reaction in the first period and a hydrolysis and endothermic reaction in the second period.

•The highly dispersive MgAC-nZVI was synthesized for Cr(VI) removal.•The MgAC-nZVI owned a considerable ability to reduce Cr(VI) at a wide pH range.•The removal of Cr(VI) followed the pseudo-second-order adsorption kinetics.•The mechanism of Cr(VI) removal by MgAC-nZVI was discussed.Nanoscale zero-valent iron (nZVI) coated by Mg-aminoclay (MgAC) was prepared by the liquid-phase reduction method for high-efficiency removal of Cr(VI). The particles (MgAC-nZVI) were characterized by X-ray diffraction (XRD), fourier transform infrared (FTIR), transmission electron microscope (TEM), zeta potential analysis and X-ray photoelectron spectroscopy (XPS). It was found that the positively charged MgAC was capable of inhibiting the aggregation of nZVI particles and improving their dispersion stability in aqueous solution. Batch experiments showed that an iron dose of 0.125 g·L−1 in the form of MgAC-nZVI, at an initial Cr(VI) concentration of 20 mg·L−1 could maintain a good performance on Cr(VI) removal at a wide pH range. It was proved that the presence of co-existing ions (Cu2+, Ni2+ and SO42−) except PO43− in the solution had positive influence on the removal of Cr(VI). Due to the large accessible surface area and the protonated amino groups (-NH3+) on the particle surface, MgAC-nZVI could remove Cr(VI) through fast adsorption and efficient reduction. The removal of Cr(VI) by using MgAC-nZVI was proved to be in accordance with the pseudo-second-order adsorption kinetics. Based on the identification of the reduction products, Cr(VI) was reduced by Fe0 to form Cr(III). Eventually, the Cr(VI) was removed in a way of Cr(III)-Fe(III) co-precipitates adsorbed on the surface of MgAC-nZVI particles. Moreover, the MgAC-nZVI particles have a better performance of reusability than the uncoated nZVI.Download high-res image (129KB)Download full-size image

Though the mechanism of MEA-CO2 system has been widely studied, there is few literature on the detailed mechanism of CO2 capture into MEA solution with different CO2 loading during absorption/desorption processes. To get a clear picture of the process mechanism, 13C nuclear magnetic resonance (NMR) was used to analyze the reaction intermediates under different CO2 loadings and detailed mechanism on CO2 absorption and desorption in MEA was evaluated in this work. The results demonstrated that the CO2 absorption in MEA started with the formation of carbamate according to the zwitterion mechanism, followed by the hydration of CO2 to form HCO3–/CO32–, and accompanied by the hydrolysis of carbamate. It is interesting to find that the existence of carbamate will be influenced by CO2 loading and that it is rather unstable at high CO2 loading. At low CO2 loading, carbamate is formed fast by the reaction between CO2 and MEA. At high CO2 loading, it is formed by the reaction of CO3–/CO32– with MEA, and the formed carbamate can be easily hydrolyzed by H+. Moreover, CO2 desorption from the CO2-saturated MEA solution was proved to be a reverse process of absorption. Initially, some HCO3– were heated to release CO2 and other HCO3– were reacted with carbamic acid (MEAH+) to form carbamate, and the carbamate was then decomposed to MEA and CO2.

To enhance the bioregeneration of Fe(II)EDTA and to avoid the inhibition of the components in nitrogen oxides (NOx) scrubbing solution, a novel integrated process of metal chelate absorption and two-stage bioreduction was developed. In this process, magnetically stabilized fluidized beds (MSFB) were used as the bioreactors, and the phase diagram for the MSFB operation was determined. Factors including inlet NO, O2 and SO2 concentrations, magnetic field intensity, gas flow rate and liquid circulation rate, were studied experimentally to investigate their effects on NO removal. In addition, a mathematical model for NO removal in this integrated system was developed. The results revealed that the integrated system could be steadily operated with a high NO removal efficiency and elimination capacity, even under the condition of high NO and O2 shock-loading. The established model showed that NO removal efficiency was related to the spray column property and the active Fe(II)EDTA concentration, while the latter depends on the bioregeneration of the disabled absorbent in the MSFB.

•Fe–Cu mixed oxide catalyst was synthesized via citrate–nitrate combustion route.•The catalyst notably improved the removal efficiency of Acid Red B compared to single ozonation.•The catalyst has a good reusability and stability.•The Fe–Cu–O catalytic ozonation of ARB was through direct and indirect oxidation.The catalytic ozonation of Acid Red B (ARB) solution in the presence of Fe–Cu oxide (Fe–Cu–O) catalysts was investigated under different operating conditions. The effects of solution pH (3–11), ozone flow (3.6–30 mg/min) and initial ARB concentration (100–500 mg/L) on color and COD removal were evaluated. The optimum pH and ozone flow were determined to be 6.8 and 30 mg/min, respectively. In the presence of 1 g/L Fe–Cu–O powder, after 60 min, the color and the COD removal efficiency was 90% and 70%, while that of the single ozonation process was 66% and 48%, respectively. The repeated use of the catalyst proved that the Fe–Cu–O catalyst had a good reusability and stability. Finally, the possible mechanism of the catalytic ozonation of ARB was proposed, and the kinetics model of the color and COD degradation were established.

•A new Klebsiella sp. strain (DL-1) was isolated for Fe(II)EDTA-NO reduction.•DL-1 was efficient in denitrifying, and the reduction rate was 4.29 mmol gDCW−1 h−1.•The interaction of DL-1 and FD-3 in the NOx removal system was investigated.•DL-1 inhibited Fe(III)EDTA reduction, while FD-3 promoted Fe(II)EDTA-NO reduction.•Fe(II)EDTA-NO and Fe(III)EDTA could be effectively reduced by the mixed strains.A highly effective strain, referred to as DL-1 and identified as Klebsiella sp., was applied to Fe(II)EDTA-NO reduction. The average reduction rate was approximately 4.29 mmol g DCW−1 h−1, which was higher than those reported in the literature. The relationship between cell growth and Fe(II)EDTA-NO reduction was characterized, and a model was developed based on a logistic equation. To ensure that the simultaneous reduction of Fe(II)EDTA-NO and Fe(III)EDTA was feasible in the integrated NOx removal process of chemical absorption and biological reduction, DL-1 was mixed with a Fe(III)EDTA-reducing bacterium FD-3 to regenerate the scrubbing liquor. There was carbon and nitrogen source competition between these two strains in the mixed system. DL-1 was incapable of reducing Fe(III)EDTA, but FD-3 was capable of reducing Fe(II)EDTA-NO. Therefore, DL-1 would inhibit Fe(III)EDTA reduction, and FD-3 would enhance Fe(II)EDTA-NO reduction. The performance of the mixed strains was also investigated. The system could maintain stable and high reduction efficiencies, after 7 h, the reduction efficiency of Fe(II)EDTA-NO and Fe(III)EDTA were 84.9% and 77.1%, respectively.

•DBU/AMP/ethanol was chosen as the novel absorbent for CO2 capture.•DBU/AMP/ethanol with 50 wt% ethanol was the optimum composition with 2.98 mol kg−1 of absorption loading.•Replacing part of DBU with AMP reduced the viscosity and improved the regeneration efficiency significantly.•DBU/AMP/ethanol and CO2 reaction was reversible, and the main products were carbonates, carbamates, DBUH+ and AMPH+.Switchable ionic liquids (SILs) are novel green non-aqueous absorbents for energy-efficient post-combustion CO2 capture. However, their regeneration efficiency and viscosity still need to be improved. SILs can be activated by some alkylol amines to improve their regeneration efficiency and reduce viscosity. In this work, mixtures of the SIL 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)/ethanol and 2-amino-2-methyl-1-propanol (AMP) were used for CO2 capture. The constitution of the absorbent was optimized. Absorption and regeneration were investigated, and the detailed reaction mechanisms for CO2 capture were analyzed using 13C NMR and FTIR. The results demonstrated that CO2 could be absorbed to form carbonates in two ways. On the one hand, CO2 reacted with DBU and ethanol to directly form carbonates. On the other hand, CO2 initially reacted with AMP to form carbamates, and then, the carbamates reacted with ethanol to form carbonates. The CO2 loading of the optimized absorbent was 2.98 mol kg−1. The saturated absorbent began to desorb at 80 °C, and the regeneration efficiency reached 99.3% when the temperature rose to 120 °C. After five cycles, the regeneration efficiency remained over 90%. Compared to DBU/ethanol, the regeneration efficiency of the DBU/AMP/ethanol mixtures was significantly better, while the viscosity was greatly reduced, which is beneficial for the industrial application.

•A blend of PMDETA and DETA features phase separation upon a change in CO2 loading.•CO2 capacity of PMDETA/DETA (5 M, 4:1) was 0.613 mol CO2/mol of total amine.•The lower phase owned 99.7% of the total capacity with 57% of the total volume.•The reaction products of carbamate and HCO3−/CO32− were enriched in the lower phase.For its high potential in reducing energy penalty of power plant, the biphasic solvent for CO2 capture has recently attracted increasing attention. In this work, a novel blend of N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) and diethylenetriamine (DETA) was used to obtain a liquid-liquid phase separation solvent. The CO2 absorption loading of the PMDETA-DETA solvent (5 M, 4:1) was 0.613 mol CO2/mol of total amine, in which 99.7% of the capacity was contributed by the lower phase with 57% of the total volume. In addition, the PMDETA-DETA solvent maintained a high CO2 absorption capacity and good phase separation at 30–60 °C. Based on the absorption results and the 13C NMR analysis, the reaction mechanism of CO2 absorption into PMDETA-DETA solvent was clarified. In the blend system, DETA played as a reactant to attack CO2 and PMDETA played as a proton acceptor to deprotonate the zwitterion. Therefore, the presence of PMDETA in the solution helped DETA to react with CO2 rather than participate in the deprotonation process of zwitterion, which ensured a high CO2 absorption capacity. The phase change mechanism indicated that, as more CO2 was absorbed into the system, the more products of carbamate and HCO3−/CO32− migrated to the lower phase while more PMDETA migrated to the upper phase, which led to the phase separation.Download high-res image (163KB)Download full-size image