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Chemical absorbents with low-energy requirements have become the primary focus of the research on CO2 capture from flue gas in power plants. To verify the absorption performance of the NICE absorbent developed by the National Institute of Clean-and-Low-Carbon Energy in China, a performance optimization test was conducted in Zhejiang University's pilot-scale platform, and the effects of the liquid–gas ratio, regeneration pressure, rich liquid fractional flow, and interstage cooling on the absorption performance and regeneration energy consumption were investigated. The results showed that in the CO2 pilot test, the optimized minimum regeneration energy consumption was 2.85 GJ/t CO2, and the corresponding process parameters were as follows: a liquid–gas ratio of 1.82 L/m3, regeneration pressure of 191 kPa, an interstage cooling temperature of 40 °C, and a rich liquid fractional flow ratio of 0.18. This study preliminarily verified the low-energy consumption performance of the NICE absorbent and showed its good potential for industrial applications. Additionally, the NICE absorbent showed promise for capital and operating cost savings because of its low liquid–gas ratio. [ABSTRACT FROM AUTHOR]

• CaO-based adsorbents doped with high aluminum cement were prepared by hydration method. • The adsorbent doped 5 wt.% high aluminum cement had excellent carbon capture capacity in bubbling fluidized bed reactor. • The carbonation reaction time required for modified adsorbents was shortened from 25 min to 6 min from fixed bed to bubbling fluidized bed. • The activation energy of adsorbents doped with 5 wt.% high alumina cement in the rapid reaction and reaction diffusion stage was 40.3 KJ/mol and 120 KJ/mol. CaO-based carbon capture system is a very promising technology to reduce carbon emissions. In this work, modified CaO-based adsorbents doped with high aluminum cement were prepared by hydration method. The effect of operating variables on the performance of modified CaO-based adsorbents in different reactors was studied, including different proportions of high aluminum cement, carbonation temperature and time. The results showed the adsorbent doped with 5 wt.% high aluminum cement had best CO 2 capture capability in all reactors. After 20 carbonation-calcination cycles, the adsorption efficiency of modified CaO-based adsorbent doped with 5 wt.% high alumina cement was around 50.8% at 700 °C in the bubbling fluidized bed reactor, 34.5% at 700 °C in the fixed bed, 23.2% at 750 °C in the TGA reactor, respectively. It was found that the adsorption efficiency of modified adsorbent had obvious advantages in the bubbling fluidized bed. In addition, the effect of carbonation temperature and CO 2 concentration on reaction kinetic for adsorbent was investigated. The results showed that the activation energy of modified CaO-based adsorbent doped with 5 wt.% high alumina cement in the rapid reaction stage and reaction diffusion stage was 40.3 KJ/mol and 120 KJ/mol, respectively. The time required to complete the carbonation reaction was shortened from 25 min to 6 min from fixed bed reactor to small bubbling fluidized bed reactor. This work provides a comprehensive study for the adsorption performance of low-cost CaO-based adsorbents in different reactors. [Display omitted] [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]

Nanoparticles suspended in solutions are considered to have the potential to enhance gas-liquid mass transfer and have been studied for gas separation. In order to reveal the mechanisms of kinetics enhancement, the diffusion and reaction process should be carefully examined. In this paper, CO2 absorption kinetics of amine-based solutions with additive of SiO2 and Al2O3 nanoparticles were investigated by wetted-wall column experiments. Measurements at different conditions, including solid loading, pressure, and solvent flow rate, show a significant enhancement on CO2 absorption kinetics. The experiment and model analysis indicate that the micro convective motion induced by particle Brownian movement plays a primary role in mass transfer enhancement. Three solutions, MEA, MDEA, and PZ which have different kinetics were selected to study the impact of nanoparticles on absorption kinetics of solutions with different reaction rate. It is interesting to find that the increased ratio of absorption kinetics by nanoparticle follows the same order with increased solvent reaction rate with CO2, which is PZ > MEA > MDEA. The wetted-wall kinetic model indicates that a diffusion controlled kinetics for PZ solution could result in much more significant kinetic enhancement with additives of nanoparticles. By operation conditions optimization, the liquid side mass transfer rate of MEA solution can be increased over 15%.© 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]

Highenergy consumption is a crucial issue for the regenerationof solvent for postcombustion CO2capture by chemical absorption.Primary modeling results show the potential to reduce the energy consumptionthrough a novel solvent regeneration process by direct steam stripping.This work is an extension of our previous exploration and aims tovalidate the direct steam stripping process by experimental studieson a lab-scale stripping platform. We investigated the direct steamstripping and the conventional stripping mode in terms of energy consumptionand steam condensation. The results showed, for the direct steam strippingmode, the optimum energy consumption at 1 atm was 2.98 MJ/kg CO2, 23.2% lower than that of the conventional stripping mode.Higher solvent feeding temperature and carrier steam superheatingtemperature were beneficial to reduce steam condensation in the column.We found 96–99.5 °C feeding solvent temperature was suitableconsidering both the energy consumption and steam condensation. Besides,we proposed an improved direct steam stripping process using carriergases such as hydrocarbon, which could further reduce the latent heatrequired. [ABSTRACT FROM AUTHOR]

Trace carbon dioxide (CO2) removal from an enclosedspace was studied experimentally and theoretically in a hollow-fibermembrane contactor using monoethanolamine (MEA) solution. Changesin trace CO2removal performance with liquid flow rate,gas flow rate, absorption temperature, and CO2loadingwere investigated individually in an apparatus under well-definedand controlled experimental conditions. We developed a two-dimensional(2-D) mathematical model to predict and further analyze the experimentalresults. The modeling results agreed well with the experimental work.Liquid flow rate positively influences trace CO2removal,but is not recommended for operation at a very high level. Increasingthe gas flow rate improves CO2absorption flux at the costof reducing CO2removal efficiency; the optimal gas flowrate for the trade-off between CO2removal efficiency andabsorption flux is presented. The optimal absorption temperatureschange with liquid CO2loading for trace CO2removal. CO2removal efficiency is a decreasing functionof CO2loading; the recommended CO2loadingof MEA solution is below 0.35 mol CO2/mol MEA. To predictthe influence of membrane wetting on trace CO2removal,we also propose a model that incorporates membrane wetting. The minimumbreakthrough pressure are 0.38 and 0.0581 MPa for fresh membrane andold membrane, respectively. Membrane wetting significantly deterioratestrace CO2membrane absorption performance, with CO2removal efficiency decreasing suddenly once the membraneis wetted. [ABSTRACT FROM AUTHOR]

To understand and optimize CO2absorption in binaryamine systems, we experimentally and theoretically investigated CO2absorption using typical amines and blended amines in a polypropylenehollow-fiber membrane contactor. The amines studied were monoethanolamine(MEA), diethanolamine (DEA), and N-methyldiethanolamine(MDEA), and their aqueous blends of MEA/MDEA, DEA/2-amino-2-methyl-1-propanol(AMP), and MDEA/piperazine (PZ). The predicted results, includingoverall mass transfer coefficients and CO2removal ratio,agreed very well with those determined experimentally. For singleamines, the optimal concentration was around 30 wt % for MEA and 20wt % for DEA. MDEA concentration had little effect on the overallmass transfer coefficient. We optimized the formulation of blendedamines using theoretical analysis. The optimal compositions in MEA/MDEA,DEA/AMP, and MDEA/PZ systems were respectively 30 wt % MEA, with MDEAin proportions from 0.1 to 0.3; 15 wt % DEA, with AMP in proportionsfrom 0.5 to 0.8; and 20 wt % MDEA, with PZ in a proportion of 0.3.To further understand the CO2membrane absorption process,we also analyzed individual mass transfer resistances as a functionof additive concentration in blended amines and the effects of liquidvelocity on the overall mass transfer coefficient. This shows thatCO2absorption is controlled by the liquid side for DEA/AMPblends and by combined liquid–gas phases for MEA/MDEA blends.For MDEA/PZ blends, control of CO2absorption is characterizedby a gradual transition from liquid side controlled to liquid–gascombined controlled as the concentration of PZ increases. [ABSTRACT FROM AUTHOR]

Abstract: A novel membrane vacuum regeneration (MVR) technology was developed to achieve lower regeneration energy demand for CO2 absorption process. Sixteen different amine-based absorbents including primary, secondary, tertiary amines, polyamines, diamines, and sterically hindered amines were analyzed by combined absorption–desorption screening experiments for selecting the most effective absorbents for CO2 membrane vacuum regeneration (MVR) technology. The CO2 absorption experiments were conducted in a hollow fiber membrane contactor (HFMC) at 25°C and 12.5kPa CO2 partial pressure. The CO2 rich solvent was regenerated at 75°C and 20kPa regeneration pressure by using the MVR technology. The chain length, number of functional groups, side chain, and number of hydroxyl groups of amines were investigated to get a better understanding on the effects of the structure in the MVR process. The results show that the tertiary amines have greater regeneration performances than the primary amines, but the CO2 absorption rates of the tertiary amines are worse than the primary amines. For the polyamines, the absorption performance of polyamines can be improved by increasing the number of amine groups while the MVR performance of the polyamines can be reduced. Steric hindered amines exhibited greater MVR performances. In addition, amines with steric hindrance effect caused by the substitution of hydroxyl group or methyl group to amine group in structure has also shown good performance in the MVR process for CO2 desorption. The overall performance of amine-based absorbents was also investigated by an absorption–desorption characters analysis. It shows triethylenetetramine (TETA) and N-methyldiethanolamine (MDEA) have great average CO2 absorption rates and relatively high cyclic capacities per mole absorbent, and ethylenediamine (EDA) is considered to be the promising absorbent as cyclic capacity in mol CO2/kg absorbent. Diethanolamine (DEA) and 2-Amino-2-methyl-1-propanol (AMP) are found to have the best overall performances in terms of CO2 absorption rate at lean loading and cyclic capacity in mol CO2/mol absorbent. In terms of overall performance, MDEA is mostly recommended for using in MVR process. Sweeping steam can significantly improve MVR performance in most selected absorbents except AMP and 2-amino-2-hydroxymethyl-1,3- propanediol (THAM) absorbents which present the potential to reduce the regeneration energy demand by operating without sweeping steam. The study also finds that MVR shows better regeneration performance as compared to traditional thermal regeneration process at the same regeneration temperature. [Copyright &y& Elsevier]

Abstract: The novel regeneration process by using membrane vacuum technology was put forward to reduce the regeneration energy consumption in the chemical absorption process for CO2 separation from flue gas. The rich MEA solution was flowed in the lumen of the hydrophobic PP hollow fiber membrane contactors, and the shell side was maintained at a reduced pressure by a vacuum pump. In addition, the additional low temperature steam whose temperature is the same to rich MEA solution was also provided to act as the sweep gas to improve the regeneration performance and to prevent the water loss of the lean solution. Results showed that this membrane vacuum regeneration process can regenerate rich MEA solution to reach a relatively better regeneration performance and can effectively utilize the low temperature energy or waste heat in the power plants. [Copyright &y& Elsevier]

• Aerosol emissions and vapor emissions of 2 million tons per year CO2 capture plant were evaluated respectively. • A fitting formula for aerosol emission is proposed. • Three control methods were compared on the premise of water balance. • Drain-off water of the water wash is good for the emission control in dry bed. Solvent emissions is a serious problem in the industrialization of the amine scrubbing process. To design pollutant control equipment for a 2 million tons/year CO 2 capture plant, a bench and a pilot facility were tested to investigate the aerosol emissions. And three Aspen models were built to study vapor emission and design emissions control measurement. The emissions assessment showed the treated flue gas after the absorber was about to discharge 1078 mg/Nm3 aerosol-type solvent and 1055 mg/Nm3 vapor-type solvent. The experimental results of particle size distribution indicated that improving the growth of the submicron droplets before the water wash and demister was the key to control aerosol emissions. Three control methods were compared by simulation, the best control measure was the combination of dry bed and water wash section, and the drain-out water is feed to the top of the dry bed. Considering the economy and control efficiency, the packing height of the water wash section is 2.5 m, and the scrubbing flow rate is 5000 Nm3/h. The extra cooling for the dry bed is not necessary and uneconomic. Under this countermeasure, the vapor emissions solvent is as low as 1.27 mg/Nm3 without additional freshwater for the water wash section. [ABSTRACT FROM AUTHOR]

• We proposed a novel desorption process based on ion exchange for CO 2 sorbents. • The sorbents were demonstrated with high working capacity and improved desorption kinetics. • Key factors of kinetics improvement were discussed among optimization of the OH–/HCO 3 – ratio at inlet, concentration, and external diffusion. • The solution after desorption (ion exchange) could be regenerated through an electrochemical DAC system to utilize renewable energy efficiently. To satisfy the Paris Agreement's 1.5 °C goals, direct air capture (DAC) has become an increasingly crucial technology. However, the ultralow partial pressure of CO 2 in ambient air contributes to a low desorption rate and high regeneration energy consumption. In this study, we proposed a fast regeneration method for CO 2 sorbents based on an ion exchange process. Utilizing an alkaline solution rich in hydroxide (OH–) ions, the quaternary ammonium (QA)-based ion exchange resin can be changed from carbonate (CO 3 2–) to OH– form, which directly captures CO 2 from ambient air. The results showed that the working capacity of the sorbents in the OH– form was 1.85 mmol⋅g−1, which was double that of the CO 3 2– form (0.88 mmol⋅g−1). The kinetics showed that the ratio of OH–/HCO 3 – at inlet, concentration, and external diffusion influence the desorption rate of CO 3 2– because of the ion exchange reaction. With a high ratio of OH–/HCO 3 – at inlet, 1 M alkaline solution, and 3 mL⋅s−1 cyclic flow rate, the desorption time of the sorbents was approximately 20 min. Finally, because the energy consumption of the entire process comprises mainly electric energy required to regenerate the alkaline solution after ion exchange, it is expected to establish an electrochemical DAC system to utilize renewable energy efficiently. [ABSTRACT FROM AUTHOR]

• China has implemented a huge CO 2 capture project, the 150,000 tons/year CO 2 capture and purification project of Shaanxi Guohua Jinjie Power Plant, which is the largest flue gas capture project in China. • The energy consumption level of regeneration reaches the leading level of flue gas CO 2 capture demonstration project. New energy-saving process of "interstage cooling + MVR heat pump + desorption heat energy recovery" is applied, and comprehensive regeneration energy consumption is less than 2.4GJ/tCO 2. • The final research results show that the project has technical feasibility and economic feasibility. The results show that the regeneration energy consumption per unit product is 2.32GJ/tCO 2 , and the loss of absorbent is less than or equal to 1.0 kg/tCO 2. There was little research and demonstration experience in large flue gas carbon projects in China. 150 kt/a flue gas CO 2 capture project in the Guohua Jinjie power plant, which is the largest-scale flue gas carbon capture project in China, effectively solved this technical bottleneck. The performance of the used compound amine absorbent, phase change absorbent, and the ionic liquid was described, and the compatibility of performance was considered in the project; new energy-saving processes integrated mechanical vapor recompression heat pump, interstage cooling, and split flow desorption. The plane layout of the project was put forward, and the utility consumption of the capture system was analyzed. The paper explained the health, safety, and environmental protection instructions, presented test category tables, and developed energy consumption and economic analyses. The results showed that the renewable energy consumption per unit product was 2.32 GJ/t CO 2 , the loss of absorbent was less than or equal to 1.0 kg/t CO 2 , and the total investment (excluding tax) of the project was 13.8398 million yuan. When the CO 2 sales price (excluding tax) was 203.43 Yuan/t, the yield was 0 %, and when the CO 2 sales price (excluding tax) was 260.949 Yuan/t, the yield was 8 %. The feasibility study research conclusions indicated that the project was technically and economically feasible. [ABSTRACT FROM AUTHOR]

Amine blends have been extensively studied as advanced solvents modification for CO 2 absorption. Due to the lack of knowledge on mechanism of amines interaction, reaction in blends was traditionally regarded as parallel reactions between CO 2 and different amines. In this work, the kinetics of CO 2 reaction with blends of two promising diamines, piperazine (PZ), N-(2-aminoethyl) ethanolamine (AEEA), were studied in a wetted wall column. The reaction rate constants of single amine were derived from kinetic data based on the zwitterion and termolecular mechanism for PZ and AEEA, respectively. It is interesting to find that the overall reaction rate of the blend is 12.0–28.1% lower than the calculated value through parallel reaction mechanism, which indicates the strong interaction between PZ and AEEA. A ‘zwitterion bridge’ reaction pathway was proposed as the microscopic mechanism of the interaction in the blend. Based on the kinetic models and experimental data, the interaction that PZ can promote the reaction in amines blend by transferring CO 2 to AEEA through the PZ-CO 2 intermediate was revealed. Besides, the interaction was proved to be a fast reaction with the reaction rate of same magnitude compared with the zwitterion hydrolysis reaction. The mechanisms of interaction between the two amines are further investigated through density functional theory (DFT). Results of simulation, in terms of activation energy and molecular geometry deformation, indicate that the PZ prefers a direct reaction with CO 2 rather than the reaction with the AEEA-CO 2 intermediate. [ABSTRACT FROM AUTHOR]

• Eight diamines and two cosolvents are screened for use in water-lean solutions. • DMEDA- and DMPDA-based water-lean solutions are developed for CO 2 capture. • A diamine-based water-lean solution using NMP as a cosolvent shows comparable viscosity with aqueous MEA. • A 140% improvement in cyclic capacity is achieved in ENH-5% H 2 O compared with that of aqueous MEA. • Diamine water-lean solutions have high sensitivity to the CO 2 partial pressure. In an effort to reduce energy penalties, a range of advanced water-lean solutions blended from one of 8 diamines, an organic solvent diluent and water, were screened. The diamines N,N -dimethyl-1,3-propanediamine and N,N -dimethyl-1,2-ethanediamine with one primary and one tertiary amino group remain homogenous during CO 2 uptake with the addition of cosolvents (1-methyl-2-pyrrolidinone or sulfolane) and are further investigated for absorption and desorption performance compared with their corresponding aqueous solutions. Water-lean solutions with different water concentrations are tested to explain the impact of water content on the solution performance. Physical properties such as density and viscosity are also measured for a versatile evaluation. The results show that diamine water-lean solutions obtain low viscosity, preferable cyclic capacities and rapid absorption and desorption rates. ENH-5% H 2 O (mass ratio DMEDA: NMP: H 2 O = 3:6.5:0.5) shows the most competitive advantages with comparable viscosity (1.49 mPa∙S at 313 K) to aqueous MEA-H 2 O and a 140% improvement in cyclic capacity. Four-fold higher desorption rate is gained ESH-5%H 2 O (mass ratio DMEDA: SFL: H 2 O = 3:6.5:0.5) compared with MEA-H 2 O. Considerable reduction in energy penalties is expected to be achieved in diamine water-lean solutions. In addition, the equilibrium solubility of diamine water-lean solutions also shows potential for industrial application due to their sensitivity to CO 2 partial pressure in contrast with aqueous solutions. [ABSTRACT FROM AUTHOR]

• 25% AEEA/50% DEEA forms organic and aqueous phases at P CO2 * greater than 100 Pa. • The organic phase absorbs CO 2 2–7 times faster than aqueous phase. • Instantaneous reaction model was built to explain the fast rate of organic phase. • CO 2 capacity of aqueous phase is 2–10 times greater than organic phase. • Biphasic solvent of AEEA/DEEA is superior to 30% MEA and competitive with 30% PZ. Amine scrubbing is currently the most promising technology for CO 2 capture from gas turbine and coal-fired flue gas. It is hindered by high regeneration energy and high capital cost. Biphasic solvent of 25% aminoethylethanolamine (AEEA)/50% diethylethanolamine (DEEA) could be a potential solution as it may achieve significant reduction in regeneration energy. A fast CO 2 absorption rate is preferred to reduce the capital cost of the absorber. In this work, the CO 2 absorption rate (k g ′) of the biphasic solvent was measured in a wetted wall column at 40 °C and at the loading conditions in the absorber. At CO 2 equilibrium partial pressure (P CO2 *) lower than 100 Pa, 25% AEEA/50% DEEA is homogeneous. The CO 2 absorption rate, k g ′, is as fast as 30% PZ (3 times faster than 30% MEA). When P CO2 * is greater than 100 Pa, 25% AEEA/50% DEEA forms aqueous and organic phases after CO 2 absorption. It was first found that the organic phase of 25% AEEA/50% DEEA absorbs CO 2 2–7 times faster than the aqueous phase because of greater physical CO 2 solubility at the same P CO2 * and physical mass transfer coefficient. The k g ′ of the organic phase is much faster than 30% MEA and 25% AEEA at lean and rich loading and even greater than 30% PZ at lean loading. The instantaneous reaction mechanism fits the kinetics of CO 2 absorption in the organic phase at low P CO2 *. The slow k g ′ of the aqueous phase results from greater viscosity which significantly reduces the physical mass transfer coefficient. The CO 2 capacity of the aqueous phase is 2.9 times, 1.8 times, and 5.3 times greater than that of 30% MEA, 30% PZ, and the organic phase, respectively. [ABSTRACT FROM AUTHOR]