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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]

Promoted aqueous ammonia is a potentialsolvent for CO2separation processes. In this work, weinvestigated the effect of temperature, sarcosinate concentration,and CO2loading on the mass transfer coefficients of CO2absorption in a sarcosinate-promoted aqueous ammonia solutionon a wetted-wall column. We further investigated the kinetics of thereaction between CO2and a blended NH3/sarcosinateabsorbent using stopped-flow spectrophotometric techniques, followingthe pH changes via coupling to pH indicators. Our study revealed thatthe mass transfer coefficient for CO2absorption in a 3M ammonia + 1.5 M sarcosinate blended solution at 288 K is close tothat in 5 M monoethanolamine absorbent at 313 K. We did not observeany synergistic or catalytic effects between NH3and sarcosinatein the blended solution; the mechanism of the reaction of CO2with the NH3/sarcosinate mixture is the simple combinationof the individual reactions of NH3and sarcosinate withCO2. [ABSTRACT FROM AUTHOR]

Aqueous sarcosine salts are fast carbon dioxide (CO2) absorbents suitable for use in postcombustion CO2capturein coal-fired power plants. We have developed a detailed reactionscheme including all the reactions in the sarcosine–CO2–water system. All unknown rate and equilibrium constantswere obtained by global data fitting. We investigated the temperature-dependentrate and equilibrium constants of the reaction between aqueous CO2and sarcosine using stopped-flow spectrophotometry, by followingthe pH changes over the wavelength range 400–700 nm via couplingto pH indicators. The corresponding rate and equilibrium constantsranged from 15.0 to 45.0 °C and were analyzed in terms of Arrhenius,Eyring, and van’t Hoff relationships. The rate constant forthe reaction between CO2and sarcosine to form the carbamateat 25.0 °C is 18.6(6) × 103M–1s–1, which is very high for an acyclic amine;its activation enthalpy is 59(1) kJ mol–1and theentropy is 33(4) J mol–1K–1.In addition, we investigated the slow reaction between bicarbonateand sarcosine using 1H nuclear magnetic resonance spectroscopyand report the corresponding rate and equilibrium constants at 25.0°C. This rate constant is 5.9 × 10–3M–1s–1. [ABSTRACT FROM AUTHOR]

To reduce the huge energy cost of CO 2 capture technology applicable in industry, the CO 2 absorption-desorption performance was conducted in a novel bench-scale pilot plant with hot water as a heat source. The trisolvent MEA(monoethanol amine)-BEA(butylethanol amine)-AMP(2-amino-2-methyl-1-propanol) was prepared at a specific concentration to analyze the CO 2 capture performance and compared with 5 M MEA as the benchmark. Meanwhile, several solid acid catalysts, blended H-ZSM-5/γ-Al 2 O 3 (1/2), or HND-8, were packed in the desorber, and the solid base catalyst, CaCO 3 or CaMg(CO 3 ) 2 , was packed in the absorber with random packing. The CO 2 absorption efficiency (AE), cyclic capacity (CC), and heat duty (HD) were tested onto MEA-BEA-AMP and MEA under various operating conditions. Experimental results indicated that the performance of 4.3 mol/L MEA-BEA-AMP was significantly better than 5 M MEA under both catalytic and noncatalytic operation. The most energy efficient combination of this study was discovered as 0.3 + 2 + 2 mol/L MEA-BEA-AMP, with 50 g (CaCO 3 /CaMg(CO 3 ) 2 ) in the absorber and 150 g H-ZSM-5/γ-Al 2 O 3 (1/2) in the desorber. The heat duty reached as low as 2.4 GJ/tCO 2 at a F G of 7.0 L/min and a F L of 70 mL/min. These results were highly applicable in an industrial amine scrubbing pilot plant for CO 2 capture., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Amine emissions from a post-combustion CO 2 capture process can lead to solvent loss and serious environmental issues. The emission characteristics of amine mixtures and influencing factors are seldom reported. This work comprehensively investigated emissions of AMP (2-amino-2-methyl-1-propanol)/MEA (monoethanolamine) from a 3.6 Nm 3 /h flue gas CO 2 capture platform. The condensation nuclei in flue gas dominated the generation of amine aerosols and resulted in a heavy total amine loss of over 1400 mg/Nm 3 , which is equivalent to 5.88 kg/t CO 2 captured under the high nuclei concentration scenario. Inside the absorber, a higher CO 2 concentration and lower lean solvent CO 2 loading can significantly promote the growth of aerosols due to the intensive reaction of CO 2 absorption. The maximum amine emissions were observed at 8-12 vol % CO 2 . The flue gas temperature and liquid/gas ratio had insignificant effects on aerosol emissions, while amine emissions after the absorber increased 340-500% as the lean solvent temperature increased from 30 to 50 °C. A synergistic control strategy of nuclei pretreatment, operating optimization, and water scrubbing can effectively reduce amine emissions to 4.0 mg/Nm 3 MEA and 8.3 mg/Nm 3 AMP.

A polymeric ionic liquid (PIL), with quaternary ammonium ions attached to the polymer matrix, displays CO 2 affinity controlled by moisture. This finding led to the development of moisture swing absorption (MSA) for direct air capture of CO 2 . This work aims to elucidate the role of water in MSA. For some humidity range, CO 2 absorption is an endothermic process associated with concurrent dehydration of the sorbent. The thermodynamic behavior of water indicates a decreased hydrophilicity of the PIL as the mobile anion transforms from CO 3 2- to HCO 3 - during CO 2 absorption. The decrease in hydrophilicity drives water out of the PIL, carrying heat away. The mechanism is elucidated by molecular modeling based on density functional theory. The finding of spontaneous cooling during absorption and its mechanism in the PIL opens new possibilities for designing an air capture sorbent with a strong CO 2 affinity but low absorption heat.