Aqueous Absorption Research Articles

Dihydroxyl-Cooperative 1,2,4-Triazole-Based Ionic Liquid for Robust Reversible CO2 Absorption.

The development of aqueous absorbents for CO2 capture is significantly important to reduce global industrial gas emissions through high regeneration efficiency and low energy consumption. Herein, we newly designed and prepared a dihydroxylated ionic liquid (IL) bis(2-hydroxyethyl)dimethylammonium 1,2,4-triazole ([N1,1,2OH,2OH][TZ]) for highly efficient CO2 absorption through anion-cation cooperative interactions. A superior capacity of 1.33 mol of CO2 per mol of IL and excellent reversibility have been achieved by the introduction of dihydroxy sites on the ammonium-based Tz IL. 1H and 13C nuclear magnetic resonance, Fourier transform infrared, and quantum chemical calculations demonstrate bihydroxyl-cooperative absorption of CO2 via hydrogen bond interaction between the cation and anion of the IL. The theory calculation shows that IL displays a superlow reactive absorption enthalpy, favorable to the reversible CO2 absorption, which can maintain an initial absorption capacity of 98.5% with the cycle numbers of 100, implying the facile regeneration and superlow energy consumption. Thus, the functionalized ILs toward group cooperative gas absorption and excellent reversibility may open a door to designing new materials for enhancing CO2 absorption and utilization.

A mass transfer study of CO2 absorption in aqueous solutions of isomeric forms of sodium alaninate for direct air capture application

Direct air capture (DAC) of CO2 is a critical emerging technology required to achieve ambitious net-zero emissions. Aqueous amino acid absorbents are ideal candidates for DAC and this work describes the investigation of the CO2 absorption performance of sodium salts of β- and α-alaninate under relevant conditions for DAC by utilising synthetic CO2 gas streams at concentrations levels found in the atmosphere (200–600 ppm). The effects of solution concentration, temperature, gas flowrate, liquid flowrate, and dissolved CO2 concentration (i.e., CO2 loading) on CO2 mass transfer coefficients were investigated. The overall mass transfer coefficient was found to be independent of the gas and liquid flowrates, with larger values determined for β-alaninate solutions (0.75–1.16 mmol m−2 s−1 kPa−1) than that of α-alaninate (0.65–0.87 mmol m−2 s−1 kPa−1), under similar experimental conditions. The results showed that the overall mass transfer coefficient increases with increasing temperature, conversely decreasing steadily with increasing CO2 loading. The maximum CO2 loading capacity of the 5.0 M solutions was ∼10 % higher for β-alanine (0.651 mol CO2/mol alaninate) than α-alanine (0.607 mol CO2/mol alaninate) at 25.0 °C. Precipitation was found to play an important role in the CO2 absorption processes here. Interestingly, beyond CO2 loadings >0.12 mol CO2/mol α-alaninate, the 5.0 M solution of α-alaninate begins to develop precipitate(s) while precipitation in the β-alaninate solution is only initiated at much higher CO2 loadings >0.52 mol CO2/mol β-alaninate. This study provides valuable insights into the suitability of β-alanine and α-alanine for CO2 capture directly from the ambient air.

Simulation of carbon dioxide direct air capture plant using potassium hydroxide aqueous Solution: Energy optimization and CO2 purity enhancement

While various methods of direct air capture (DAC) technology have been implemented, its widespread effectiveness hinges on achieving optimal design and process improvements, largely owing to the high energy costs involved. Literatures reports a substantial heat demand for high-temperature aqueous solutions DAC (HT DAC), ranging from 1420 to 2250 kWh per ton of CO2, accompanied by electricity consumption rates varying from 366 to 2790 kWh per ton of CO2. The present study adopts the HT DAC method with an aqueous KOH absorbent as its focus, aiming to mitigate energy consumption. Given that a substantial portion of energy consumption in comparable processes can be attributed to the calciner and slaker units, our research centers its attention on the Air Separation Unit (ASU) and the steam cycle unit, investigating their impact on the system's production capacity, the enhancement of CO2 purity, and the augmentation of equipment thermal recovery. Process optimization, results a remarkable increase in heat recovery (21.1 %) and significant reductions in utilities consumption. The outcomes indicate that this facility has the capacity to annually capture around 1.1 million tons of CO2 with a purity of 99 mol% for utilization across various industries. The process design necessitates 5.24 gigajoules (GJ) of heat and 343 kW-hours (kWh) of electricity per ton of captured CO2. Notably, in addition to fulfilling the internal electricity requirements, the facility can export 8 MWh of electricity per ton of captured CO2 to the grid.

Improvement in CO2 Capture of Polyamine with Micro-Interfacial System.

Polyamines have emerged as a promising class of CO2 absorbents due to their remarkable sequestration capacity. However, their potential industrial application as aqueous absorbents is significantly hindered by a low regeneration efficiency and high energy consumption. To address these issues, this study investigates the use of triethylenetetramine (TETA) and ethylene glycol (EG) to develop a nonaqueous absorbent. The incorporation of EG enhances absorption performance and reduces the regeneration energy needed for TETA, whereas the high viscosity of the absorbent impedes absorption rate, amine efficiency, and regeneration efficiency. In order to enhance CO2 capture, micron-sized reaction units (SiO2@TETA-EG) were developed by encapsulating TETA solution with nanosilica. The SiO2@TETA-EG composite exhibits a large specific surface area (99 m2/g), with a porous shell structure and improved fluidity, which effectively counteracts the negative effects caused by high viscosity. Notably, SiO2@TETA-EG indicates a noticeably higher apparent rate constant of 4.29 min-1 at 323.2 K compared to the TETA-EG solution. Furthermore, SiO2@TETA-EG displays a 28.4% boost in regeneration efficiency while maintaining favorable stability in pore size and shape after regeneration.

Robust nitrogen-doped microporous hollow carbon spheres for energy-efficient CO2 capture from flue gas

Nitrogen (N)-doped microporous hollow carbon spheres were prepared by facilely nanocasting spherical SiO2 with N-containing melamine phenolic resin through a simple in-situ polymerization process. Through regulating the dosage of melamine, N content in microporous hollow carbons could be easily tuned to an unprecedented level of 49.2 wt%. Additionally, in order to address the common problem of relatively poor structural porosity of N-doped carbons, especially after incorporating vast N into carbon frameworks in reported literature, a comprehensive strategy including optimizing carbonization temperature and performing further activation by CO2 and KOH were explored, and their effects on material textural properties and CO2 capacity were systematically studied. Although this strategy did not completely avoid the N loss during activation of carbon materials, it sharply promoted the textural properties of carbon materials at the expenses of partial N and efficiently produced a series of highly microporous carbon materials, still with abundant N species (11.5 ∼ 29.9 wt%) and large structural porosity (330 ∼ 1263 m2/g). More importantly, these N-doped microporous hollow carbons, when used for CO2 capture, showed superior CO2 capacities of 3.00 mmol/g (25 °C and 1 bar) and 1.05 mmol/g (40 °C and 0.1 bar), exceptionally robust cyclic stability, and low regeneration energy of 2.75 GJ/ton CO2, which is much lower than aqueous amine-based absorbents and comparable to amine-supported adsorbents. Thus, these outstanding adsorption performances make the N-doped microporous hollow carbon spheres prepared in this study more promising for energy-effective CO2 capture from dilute gas streams.

Catalytic absorption pathway with kinetically favorable dissolution of nitric oxide in aqueous absorbents

AbstractNitrogen capture is a crucial strategy for coping with the environmental crisis arising from continually industrial NO emissions, while it suffers from the generally inefficient aquatic absorbent. This work developed a novel absorbent with favorable gas affinity via using sterically hindered imidazole to regulate the gas–liquid interface of typical K2S2O8 solution, initially achieving an efficiently catalytic absorption of poorly soluble NO. The best catalytic absorption efficiencies increased from 17.83% to 91.90% as compared to traditional one. Moreover, an established absorption kinetic model indicated that both capacity and rate of NO dissolution were increased. The imidazole molecules spontaneously migrated to gas–liquid interface of solution and imparted an additional dissolution impetus to NO. This catalytic absorption method overcoming the conventional NO dissolution limitation in water not only improves commercial NO capture, but also provides a new design of aquatic absorbent for heterogeneous reactions requiring transporting poorly soluble gases in aqueous solvents.

Energy-efficient non-aqueous biphasic solvent for carbon capture: Absorption mechanism, phase evolution process, and non-corrosiveness

High latent heat and corrosivity related to H2O inhibit the application of aqueous biphasic absorbents for CO2 capture. An energy-efficient non-aqueous biphasic solvent DETA-EG-PMDETA (D-E-P) was developed with EG-assisted CO2 absorption, interesting phase-transition behavior, and non-corrosiveness. EG could increase the absorption capacity through direct alcoholysis of carbamate and the complex reaction among EG, DETA, and CO2. When EG:PMDETA = 3.5:6.5, the CO2 saturated loading was as high as 2.02 mol/mol. Unlike common biphasic solvents, flue gas saturated-absorbent presented a denser CO2-rich phase with larger CO2 loading (6.01 mol/L) and smaller volume (26.7%), and more convenient homogeneous desorption, whereas the pure CO2-saturated absorbent exhibited an EG-diluted CO2-rich phase (4.34 mol/L, 43.5%) and heterogeneous desorption. Benefiting from low vapor pressure, vaporization enthalpy, and heat capacity of EG, and greatly reduced regeneration volume, the Qlatent (0.0208 GJ/t CO2) and Qsen (0.12797 GJ/t CO2) were considerably decreased, resulting in a regeneration energy of 1.87 GJ/t CO2. It's significantly lower than 30 wt% MEA and other aqueous biphasic absorbents. In addition, because the carbamate hydrolysis and CO2 hydration could not take place in non-aqueous absorbent, the content of H+ was considerably limited, leading to a non-corrosive feature, and the corrosion rate was only 3.70 E−3 mm/a.

Life Cycle Assessment of Post-Combustion CO2 Capture and Recovery by Hydrophobic Polypropylene Cross-Flow Hollow Fiber Membrane Contactors with Activated Methyldiethanolamine

The present study evaluated the environmental impacts of post-combustion CO2 capture and recovery via membrane–gas absorption processes. We have used SimaPro v.9 packages with the Ecoinvent v3.5 database employing two different methods, ReCiPe 2016 Endpoint (H) and Midpoint (H), considering a fundamental methodological framework to determine the most environmentally friendly experimental condition. Life cycle impact categories were examined and assessed supposing a functional unit of 1 kgCO2/h recovered. Fourteen environmental impact categories including global warming, ozone depletion, eutrophication, and toxicity potentials have been evaluated within the context of a gate-to-gate approach focusing on only the process stage. Simulation results showed that the maximum liquid flow rate, sweep helium flow rate together with the minimum solvent concentration demonstrated the highest impact on human health, ecosystem, and resources. The usage of pure methyldiethanolamine (MDEA) activated by piperazine as a reactive absorbent provided the lowest environmental impact due to the elimination of the energy needed to heat and evaporate water present in aqueous absorbent solutions and the prevention of the excess water consumption depending on meeting the water needed for reactive absorption of CO2 in tertiary amine MDEA from simulated humidified flue gas stream. The study highlights the importance of LCA in the determination of an environmentally more sustainable condition during the capture and recovery of post-combustion CO2 by gas absorption and stripping using membrane contactors in tertiary amine MDEA.

Experimental and Thermodynamic Investigation on CO2 Absorption in Aqueous MEA Solutions

The vapor-liquid equilibrium (VLE) of CO2 in a reactive solvent is essential for the proper simulation and design of CO2 absorption processes. This work presents a systematic investigation on CO2 absorption in various aqueous monoethanolamine (MEA) solutions. CO2 solubility in MEA was measured at 298, 313, 333, and 353 K with CO2 partial pressure ranging from 34.5 to 78.0 kPa. A modified Kent-Eisenberg model was developed based on the measured solubility data, showing good predictions over the liquid phase speciation for the CO2-H2O-MEA system. We presented a new analysis based on the first-order difference curve of distribution profiles of the species. Based on the main reactions that occurred, the CO2 absorption process was demonstrated to be divided into four regions with increasing CO2 loading from 0 to 1. Accordingly, kinetic study was proposed to be conducted in the first region, whereas measuring of mass transfer in the first three regions. The findings in this work extend the existing knowledge of CO2 absorption process in terms of speciation and can provide important guidance for further study of the process characteristics using aqueous amine absorbents.

Dynamic Modeling of CO2 Absorption Process Using Hollow-Fiber Membrane Contactor in MEA Solution

In this work, a comprehensive mathematical model was developed in order to evaluate the CO2 capture process in a microporous polypropylene hollow-fiber membrane countercurrent contactor, using monoethanolamine (MEA) as the chemical solvent. In terms of CO2 chemical absorption, the developed model showed excellent agreement with the experimental data published in the literature for a wide range of operating conditions (R2 > 0.96), 1–2.7 L/min gas flow rates and 10–30 L/h liquid flow rates. Based on developed model, the effects of the gas flow rate, aqueous liquid absorbents’ flow rate and also inlet CO2 concentration on the removal efficiency of CO2 were determined. The % removal of CO2 increased while increasing the MEA solution flow rate; 81% of CO2 was removed at the high flow rate. The CO2 removal efficiency decreased while increasing the gas flow rate, and the residence time in the hollow-fiber membrane contactors increased when the gas flow rate was lower, reaching 97% at a gas flow rate of 1 L‧min−1. However, the effect was more pronounced while operating at high gas flow rates. Additionally, the influence of momentous operational parameters such as the number of fibers and module length on the CO2 separation efficiency was evaluated. On this basis, the developed model was also used to evaluate CO2 capture process in hollow-fiber membrane contactors in a flexible operation scenario (with variation in operating conditions) in order to predict the process parameters (liquid and gaseous flows, composition of the streams, mass transfer area, mass transfer coefficient, etc.).

The insensitive cation effect on a single atom Ni catalyst allows selective electrochemical conversion of captured CO2 in universal media

We demonstrate Ni–N/C is an effective electrocatalyst for the direct conversion of captured CO2 in monoethanol amine-based aqueous absorbents showing high CO faradaic efficiency (78%) and its high selectivity is maintained in various amine solvents.

Hydrophobic deep eutectic solvents as green absorbents for hydrophilic VOC elimination

As a common hydrophilic volatile organic compound (VOC), acetone is known to harm human health and the atmospheric environment. Absorption is a typical technique applied to capture hydrophilic VOCs; however, the difficulty of separating and recovering absorbed hydrophilic VOCs (e.g., acetone) from aqueous absorbents has become one of the major challenges in practical applications. Hydrophobic deep eutectic solvents (DESs) have therefore been developed as novel green absorbents for capturing hydrophilic VOCs in the present work. The compiled results show that efficient hydrophilic VOC elimination can be accomplished by the proposed hydrophobic DESs through high absorption capacity and thermodynamically favorable gas-to-liquid mass transfer. Among the explored DESs, the hydrophobic DES containing thymol [Thy] and decanoic acid [DecA] with a molar ratio of 1:1 has achieved the highest absorption capacity of acetone, i.e., 6.57 mg acetone per g DES at 20 °C and 1480 ppm acetone. The oxygen of acetone interacts favorably with the hydrogen atom of [Thy] upon absorption, rendering hydrogen bonding interaction surpassing polarity as the key factor in attaining superior solubility of acetone in DESs. Moreover, the absorbed acetone can be easily removed from Thy-based DESs, realizing an effective hydrophilic VOC elimination process with economic and ecological benefits.

Mass transfer and kinetic characteristics for CO2 absorption in microstructured reactors using an aqueous mixed amine

Microreactors are frequently used for the process intensification of CO2 absorption, but most CO2 absorption studies in microreactors are restricted to a low flow rate ratio of feed gas to absorbent because of insufficient CO2 loading of conventional amines. Herein, we investigated mass transfer and kinetic characteristics of CO2 absorption using an aqueous mixed amine absorbent composed of 25 wt.% N-methyldiethanolamine (MDEA) and 5 wt.% hexamethylenediamine (HMDA) at the gas to liquid flow rate ratio range from 88.9 to 666.7 in four microstructured reactors with metal foams as packing materials in the packed-bed section. The CO2 loading of this amine absorbent reached 0.32 mol of CO2 per mol of MDEA at the gas to liquid flow rate ratio of 400, which is significantly higher than the conventional amines. Regeneration efficiency of this mixed amine absorbent was remarkable in three successive regenerated cycles at the gas to liquid flow rate ratios of 181.8 and 222.2. The second-order rate constants of HMDA were higher than the conventional amines, reflecting its high ability to reduce energy barrier and accelerate the CO2 absorption rate. The overall volumetric mass transfer coefficient and absorption efficiency were raised to 13.5 s−1 and 97% at the gas to liquid flow rate ratios of 153.8 and 88.9, which are obviously higher than those reported for other microreactors. Optimization of overall reaction rate constant and mass transfer coefficient was executed through multi-objective optimization using genetic algorithm and validated through experimentation. Finally, the comparison of the mass transfer characteristics among various microreactors indicated that the strategy of combining this remarkable mixed amine absorbent with microstructured reactors with metal foams packing has strong process intensification potential for CO2 absorption at high gas to liquid flow rate ratios.

Guide to evaluate low viscous non-aqueous solvent for post-combustion CO2 capture

This work low viscous new amine based non-aqueous solvent (NAS) was developed for recovery of carbon dioxide (CO2) from post-combustion flue gases. The NAS system was made by mixing alkyl-functionalized single amine/polyamine as absorbent and alcohol/non-alcohol as solvent. The developed NAS does not form any precipitate/solid upon exposure to CO2 and showed low viscosity (cP < 20) homogeneous mixture (single phase) at the whole range of CO2 loading with the advantages of higher absorption and regeneration rates, higher cyclic capacities, and higher CO2 recoveries compared to bench mark MEA-based aqueous absorbents.

Fabrication and characterization of a novel nanoporous nanoaerogel based on gelatin as a biosorbent for removing heavy metal ions

In this research, we proposed a synthesis of nano-silica aerogel (NSA, S1–S3) and nano-silica aerogel gelatin (NSA-G, S4–S6), which were hybrid aerogel by sol–gel method via ambient pressure drying. The aerogels’ backbone was modified by montmorillonite (MMT) in NSA and for NSA-G gelatin (G) and MMT were used to stabilize their building block. Also, free hydroxyl groups on their surface were changed to TMS-O and became more hydrophobic aerogels. The porosity results showed that the density of the optimum aerogels (S2 and S5) ranged from 0.084 to 0.047 g/cm3. It was also found that the hydrophobicity of the NSA-G aerogel decreased with increasing the content of gelatin into the silica aerogels. However, these aerogels were fully characterized by FTIR, FESEM, EDS, XRD, BET, and TGA/DTA analysis and they used as the adsorbent of Cu2+ and Ni2+ ions in aqueous media. The prepared aerogels effectively could remove these heavy metals from the aqueous media and NSA-G absorbent also illustrated a favorable result for adsorption. Also, the recyclability test for four adsorption–desorption of aerogels cycles was examined and they had a good effect even after the fourth cycle.

Continuous Flow Solar Desorption of CO2 from Aqueous Amines

Recovery of captured carbon dioxide (CO2) is considered the most energy-intensive stage of postcombustion CO2 capture strategies by aqueous amines. In response, an optically transparent flow reactor with continuous in operando CO2 collection using light-absorbing, graphite-titania composite microparticles is developed for the energy-efficient solar desorption of CO2 from saturated aqueous amine absorbents. The synthesized graphite-titania composite microparticles are demonstrated to be a more effective packing material for continuous CO2 solar desorption in the packed-bed flow reactor compared to other candidates, including titania and carbon black. The effect of continuous and discrete parameters, including irradiance, residence time, amine concentration, and amine chemical structure on the efficiency of solar-enabled CO2 desorption using the developed continuous flow strategy with the graphite-titania composite microparticle packing is studied in detail. Furthermore, the potential for the implementation of a control strategy by adjusting the aqueous amine stream flow rate to achieve constant CO2 desorption efficiency with dynamic solar irradiance is discussed. Finally, the continuous CO2 desorption stability over an extended period of time (12 h) is examined with an average single-pass efficiency of 64%.

Research on Status and Outlook of Using Different Solvents for CO2 Capture in a Rotating Packed Bed

This study investigates the removal efficiency of carbon dioxide by aqueous absorbents containing monoethanolamine (MEA), piperazine(PZ), diethylenetriamine(DETA) and ionic liquids in a rotating packed bed. The performance of an absorbent was assessed in terms of an overall volumetric mass transfer coefficient and regeneration heat duty. The CO2 removal efficiency in a rotating packed bed was observed to be more suitable than that in a packed column, suggesting a potential of a rotating packed bed can replace a traditional packed column to the usage of reduction of the greenhouse gas CO2 from the exhausted gas. The mixture containing PZ and DETA exhibited a high CO2 removal efficiency among these absorbents. Besides, DETA has a lower regeneration heat duty than MEA, which means the finest mixture for industrial CO2 capture system will be the combination of PZ, DETA, and ionic liquids, instead of traditional alkanolamines, MEA.

Process simulation, optimization and assessment of post-combustion carbon dioxide capture with piperazine-activated blended absorbents

High efficiency, large capacity, and low energy consumption have become an important challenge in performances of post-combustion carbon dioxide (CO2) capture and regeneration. Blended absorbents have shown great potential but their process simulation, modeling, and optimization have not been known definitively. This work developed the blended aqueous absorbents based on piperazine (PZ) activators: PZ-activated methyldiethanolamine (MDEA), potassium carbonate solution (K2CO3), and aqueous ammonia (NH3.H2O) to improve their techno-economic performances. The whole process simulation was conducted using a validated rate-based model under given a CO2 capture efficiency of 85%. In this process, the key factors including the molar concentration of the absorbent, PZ molar ratio, CO2 load of lean liquid, lean-liquid temperature, flue-gas temperature, and rich-liquid temperature, were employed for the design of experiment using response surface methodology. A series of nonlinear regression equations were developed using the flow rate of absorbents, the reboiler heat duty (in the units of gigajoules per ton of CO2), and the cooling-water flow rate as the multi-objective function. Subsequently, the optimal Pareto solution set and compromise solutions were determined using the multi-objective genetic algorithm and finally, their performances were assessed using the fuzzy close-degree algorithm. It was found that the optimal operating parameters can be determined effectively according to the proposed approach. For each PZ-activated blended absorbents, the trade-off effect exists between absorbent flow rate, reboiler heat duty, and cooling water consumption. The absorbents having optimal techno-economic performance were recommended to be PZ-activated MDEA, followed by PZ-activated K2CO3 and PZ-activated NH3.H2O when considering the regeneration energy consumption. The results may provide a positive reference for process design and optimization of the industrial post-combustion CO2 capture system.

Study on CO2 capture by AAILs-MDEA aqueous solution in packed tower

This study mainly uses N-methyldiethanolamine (MDEA) as the main body of absorption, and uses three kinds of AAILs(AAILs), 1-butyl-3-methylimidazolium lysinate ([Bmim][Lys]), tetramethylammonium glycinate ([N1111][Gly]) and 1-butyl-3-methylimidazolium glycinate ([Bmim][Gly]) as accelerator, respectively. That forms a new blended aqueous solution for CO2 removal. The new AAILs-MDEA aqueous solution absorbent has stronger ability to absorb CO2, faster absorption rate and lower equipment corrosion. When the gas flow rate is 500ml/min and the liquid flow rate is 150ml/min, the best removal efficiency is achieved. At 313.2K, the removal efficiency of MDEA-[N1111] [Gly] absorbent can reach 100%; the effect of the three new alkanolamine aqueous solutions on CO2 absorption is: MDEA-[N1111][Gly]>MDEA-[Bmim] [Gly]>MDEA-[Bmim][Lys].

Post-combustion CO2 capture and recovery by pure activated methyldiethanolamine in crossflow membrane contactors having coated hollow fibers

Gas absorption and stripping using membrane contactors is one of a number of carbon capture and storage technologies being investigated for separating CO2 from flue gas. Energy consumption in CO2 absorption-stripping employing amine-containing aqueous absorbent solutions is strongly influenced by demanding stripping conditions involving higher temperatures. The utility of using pure methyldiethanolamine (MDEA) activated by piperazine as a reactive absorbent was studied using a compact hollow fiber device for the absorber as well as the stripper. Water needed for reactive absorption of CO2 in tertiary amine MDEA was obtained from simulated humidified flue gas stream which is saturated with moisture in actual practice. This study investigated also the absorption and stripping performances of aqueous absorbent solutions containing 80% and 90% activated MDEA (aMDEA). Considerable CO2 stripping from CO2-loaded pure aMDEA absorbent was achieved at 92 °C while absorption was carried out at 25–46 °C. Further, the CO2 stripping rate was far higher for pure MDEA compared to the other two aMDEA solutions with water. Results are reported for the performance of the absorption-stripping process as a function of humidified simulated flue gas flow rate and the absorbent flow rate. High values of the overall mass transfer coefficients (MTCs) have also been reported for absorption. The highest volumetric gas phase based overall MTC obtained was 0.504 sec−1. This system has a much lower absorbent circulation load, eliminates the energy needed to heat and evaporate water present in aqueous absorbent solutions and benefits from the absence of excess water during stripping.