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Aiming to solve the problem of high ammonia loss during ammonia-based CO2 chemical absorption process, an ammonia wash system was recommended to be added after the absorber column. Hence, we need to deal with a lot of wash water. Recently, we proposed a vacuum membrane distillation (VMD) system to regenerate ammonia from ammonia wash water. The stripping gaseous ammonia can be used for producing a high-concentration ammonia solution for solvent make-up in the CO2 capture system, and the wash water after distillation can be reused. In this work, we investigated 0.3 M ammonia solutions on different operation factors such as feed flow rate, feed temperature, pressure in the permeate side, and CO2 loading. The experimental results show that both temperature and pressure in the permeate side have significant influences on the ammonia stripping process. Increasing feed temperature and reducing pressure in the permeate side will not only improve ammonia removal efficiency, but also enhance total transmembrane flux and overall mass transfer coefficient. The increase of feed flow rate can improve the total transmembrane flux, but will lower the ammonia removal efficiency. The increase of CO2 loading in the feed ammonia solution will decrease the ammonia removal rate. Furthermore, we investigated a continuous circulation experiment and found that the ammonia removal efficiency largely depended on the removal time. The removal efficiency can be up to 95.6% with a 120 min continuous circulation time. We think this VMD system has the potential to recover ammonia and solve the solvent loss problem. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

The low CO2 absorption rate and high ammonia volatile loss rate are two major issues for the ammonia-based CO2 capture technology. In this work, we investigated the effect of total pressure on CO2 absorption and ammonia vaporization in ammonia solutions on a wetted-wall column. We found that the elevated pressure absorption process was an effective way to increase CO2 absorption rate and suppress ammonia vaporization at the same time. We also studied the mass transfer mechanism at elevated pressure and found the overall mass transfer coefficients of CO2 absorption in both ammonia and MEA solutions at elevated pressures were lower than that under atmospheric pressure. The overall mass transfer coefficients of CO2 absorption in 3 M NH3 (298 K) at 1, 1.5, 2, 2.5 bar were 0.723 × 10−6, 0.652 × 10−6, 0.591 × 10−6, 0.555 × 10−6 mol/(s m2 Pa) and the corresponding gas side mass transfer coefficients were 13.8 × 10−6, 4.52 × 10−6, 2.61 × 10−6, 2.03 × 10−6 mol/(s m2 Pa), respectively. We also found the gas side mass transfer coefficient in the wetted-wall column was not only dependent on the hydrodynamic conditions of the column but also influenced by the total pressure. © 2014 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

Highlights • Novel type of biphasic solvent with low costs and high cyclic capacity is proposed. • DEEA-AEEA solvent shows regeneration energy as low as 2.58 GJ/tCO 2. • Phase split time as short as minutes enables fast phase separation. • Driving and resistance forces dominating the phase split dynamics are analyzed. • CO 2 reactions and phase split mechanism are revealed by NMR analysis. Abstract Using biphasic solvents for carbon dioxide (CO 2) capture is regarded as a promising technology to drastically reduce the regeneration energy. However, this technology hasn't been put into commercial application due to lack of the biphasic solvents with high stabilities and low costs. To overcome this challenge, we developed a novel type of biphasic solvent based on alkanolamine-alkanolamine blends, i.e., aqueous blends of 2-(diethylamino)-ethanol (DEEA, 50 wt%) and monoethanolamine (MEA, 25 wt%) or 2-((2-aminoethyl) amino) ethanol (AEEA, 25 wt%). The aqueous DEEA-AEEA solvent demonstrated a cyclic capacity as high as 0.64 mol CO 2 /mol which is significantly higher than those of 30 wt% MEA and other reported biphasic solvents. In addition, a phase split time as short as a few minutes is obtained. The phase split dynamics were analyzed to investigate the effects of CO 2 loading, temperature, gas flow rate and height-to-diameter ratio. Quantitative 13C NMR analysis was then performed to reveal the reaction and phase split mechanism of CO 2 absorption in the DEEA-AEEA solvent. It indicated that the reaction of AEEA with CO 2 dominated at the beginning of CO 2 absorption and the products are formed as carbamates. Then, DEEA began reacting with CO 2 to yield bicarbonate and carbonate. The phase split mechanism indicated that the reaction products of carbamates and HCO 3 −/CO 3 2− migrated to the lower phase while DEEA and unreacted AEEA migrated to the upper phase. Finally, the cyclic tests were repeated and the energy consumption was evaluated. The regeneration energy of the biphasic solvent, without process optimizations, is 2.58 GJ/tCO 2 , which is 32% lower than that of the traditional 30 wt% MEA solvent. [ABSTRACT FROM AUTHOR]

• Novel alkanolamine-based biphasic solvent with low regeneration energy and viscosity is proposed for CO 2 capture. • Tertiary amine 3-(dimethylamino)propan-1-ol(3DMA1P) is firstly introduced to decrease regeneration energy. • Phase separation mechanism is revealed by NMR and LogP analysis. • Molecular dynamics simulation is applied to study liquid structure and monitor the phase separation process. Biphasic solvents for CO 2 capture have received significant attention due to their potential for energy conservation. However, traditional biphasic solvents result in highly viscous CO 2 rich-phases and high amine losses. To overcome these drawbacks, we have developed a novel alkanolamine-based biphasic solvent by blending 2-(methylamino) ethanol (MAE), 3-(dimethylamino)propan-1-ol (3DMA1P), diethylene glycol dimethyl ether (DGM), and water. The aqueous MAE/3DMA1P/DGM solvent showed a cyclic capacity of 0.45 mol CO 2 /mol amine, which is 1.8 times that of monoethanolamine (MEA), and a desorption rate and regeneration efficiency twice those of MEA. The viscosity of the biphasic solvents can be reduced to 13.12 mPa⋅s at 313 K, which is lower than that of reported biphasic solvents. The evaluated regeneration energy was 2.33 GJ/ton CO 2. Cation chromatography measurements revealed the tendency of MAE to accumulate in the CO 2 -rich phase with increasing CO 2 absorption loading. Quantitative 13C NMR analyses were performed to investigate the species distribution in both phases, and DGM was found to be the major component of the CO 2 -lean phase. Different solubilities of the MAE molecules and MAE carbamate in DGM resulted in phase separation. Molecular dynamics (MD) simulations on the CO 2 -unloaded and CO 2 -loaded solutions verified the phase separation mechanism. MAE molecules tended to cluster, and the interactions between MAE and DGM dropped significantly, with increasing DGM concentration. [ABSTRACT FROM AUTHOR]