Equilibrium Solubility Of CO2 Research Articles

Understanding the potential benefits of blended ternary amine systems for CO2 capture processes through 13C NMR speciation study and energy cost analysis

Aqueous blends of the three amines 2-aminoethanol (MEA), N-methyldiethanolamine (MDEA) and 2-amino-2-methyl-1-propanol (AMP) were tested as sorbents for CO2 capture processes. We formulated three different blends with the same overall amine concentration (5M) but with different amine molar ratio, namely blend-1 (2M MEA+2M MDEA+1M AMP), blend-2 (1M MEA+2M MDEA+2M AMP) and blend-3 (2M MEA+1M MDEA+2M AMP). Their CO2 absorption and desorption performances were investigated in batch experiments in terms of CO2 equilibrium solubility, CO2 absorption at 40 °C and CO2 desorption at 100 °C as a function of time, and energy consumption during the regeneration process. The results were compared to those obtained under the same operating conditions with 5M aqueous MEA, the benchmark sorbent for CO2 absorption processes. The effect of the different amino composition on the CO2 capture mechanism was evaluated by identifying and quantifying the species formed during the capture process through an accurate 13C NMR speciation study. The results obtained showed that all formulated sorbents have higher desorption performance and require less energy for regeneration than conventional aqueous MEA, confirming that blending different alkanolamines has the potential to improve CO2 capture. In particular, blend-2 can be regarded as a promising sorbent for implementation in commercial systems, as it performed a desorption rate up to 5 times higher than conventional aqueous MEA, combined with a significantly lower relative heat duty for regeneration (41.5%) and lower operating costs for CO2 capture.

Prediction of CO2 solubility in potential blends of ionic liquids with Alkanolamines using statistical non-rigorous and ANN based modeling: A comprehensive simulation study for post combustion CO2 capture

Equilibrium CO2 solubility data plays a pivotal role in the process design of the post-combustion CO2 capture Unit. In the current study, statistical non-rigorous models are developed to predict the solubility of carbon dioxide (CO2) in different aqueous blends of ionic liquids (ILs) and blends of ILs with alkanolamines, ethanol, etc. These correlations are utilized to estimate the liquid phase CO2 loading as a function of CO2 partial pressure at different temperature conditions. The correlations can predict CO2 solubility in the liquid phase of different (ILs + alkanolamine + water/ethanol) in the temperature and CO2 partial pressure range of (298–353) K and (50–6200) kPa respectively. The CO2 mole fraction in the liquid phase pertaining to 19 different solvent formulations is considered in the range of (0–0.487). It has been found that there is a good agreement between the results of the proposed models and reported experimental data of CO2 solubility. In addition to this, the predictability of artificial neural network (ANN) for CO2 solubility is also tested for 22 systems of ionic liquid blends with amines. The main advantages associated with these proposed models are their underlying simplicity and minimal input data, namely temperature and pressure.

Investigation of equilibrium CO2 solubility in 35 wt% aqueous 1-(2-aminoethyl) piperazine (AEP) and performance study over monoethanolamine for CO2 absorption

The present study investigates the CO2 absorption capacity of 1-2-(aminoethyl)piperazine (AEP) as a potential solvent for post combustion CO2 capture. The CO2 absorption performance has been evaluated in terms of Equilibrium CO2 solubility at varied temperature and pressure range. The CO2 solubility measurement was conducted using high pressure stirred autoclave reactor within the temperature and Pressure range of (308.15–328.15) and (2–200) kPa respectively. The equilibrium CO2 solubility data are further correlated using semi-empirical model and equilibrium based Modified Kent-Eisenberg model which shows a better agreement with the generated experimental data. In addition to this, a comprehensive parametric study was also carried out in Aspen-Plus Platform to evaluate the performance of proposed solvent over conventional solvent monoethanolamine (MEA). Influence of various important operating parameters such as flow rates of solvent and Gas medium, amine concentration, solvent inlet temperature and (L/G) ratio on the % CO2 removal was studied.

Equilibrium CO2 solubility of novel tris(2-aminoethyl) amine as a promoter to N-methyldiethanolamine and 2-amino-2-methyl-1-propanol

• An innovative semi-automated stirred-cell apparatus developed for CO 2 absorption. • CO 2 solubility was examined in novel blends of aq. (TAEA + MDEA/AMP) • VLE data was correlated using Modified Kent-Eisenberg and ANN models. • Reaction scheme was analyzed using 13 C NMR and FTIR-ATR. • Speciation and pH of CO 2 absorbed solution were estimated. This study involves the experimental measurements and theoretical analysis of equilibrium CO 2 solubility in a novel activator (tris(2-aminoethyl) amine, TAEA) and its blend with commercial solvents like ( N -methyldiethanol amine, MDEA) and (2-amino-2-methyl-1-propanol, AMP). All the measurements have been conducted at a fixed total amine concentration of 3 M (M) by varying the promoter concentration to (0.1–0.7) in an interval of 0.2 M, and temperatures range from (293.15–323.15) K at different CO 2 partial pressures in the range of 2–500 kPa. The experimental data are modeled using a modified Kent-Eisenberg (KE) equilibrium model and feed forward neural network model. The equilibrium constants linked to TAEA deprotonation and carbamate formation reactions are regressed as a function of CO 2 partial pressure, amine concentration, and temperature to fit the equilibrium CO 2 solubility data using a modified KE model. To know the reaction scheme and recognize the various essential reaction products in the CO 2 -loaded solvents 13 C NMR and FTIR-ATR analysis have been performed.

Experimental investigations and developing multilayer neural network models for prediction of CO2 solubility in aqueous MDEA/PZ and MEA/MDEA/PZ blends

AbstractIn this research, a new set of experimental data for CO2 solubility in aqueous blended amine solvents were investigated experimentally over the CO2 partial pressure range from 8 to 100 kPa at 40 °C and were compared with the benchmark aqueous 30 wt.% MEA solution. This work developed two multilayer neural network models named models A and B, for predicting the CO2 solubility in various aqueous blended amine solvents including 36 wt.% MDEA + 17 wt.% PZ, 24 wt.% MDEA + 26 wt.% PZ, and 6 wt.% MEA + 25 wt.% MDEA + 17 wt.% PZ. Models A and B were developed by using Levenberg–Marquardt back propagation algorithm with 427 and 301 of reliable experimental data sets gathered from the published data, respectively. The results indicate that the high accuracy prediction of the CO2 solubility in Methyldiethanolamine/Piperazine (MDEA/PZ) blends could be obtained by the network developed by Tan‐sigmoid transfer function with two hidden layers consist of eight and four neurons, while the network developed by Tan‐sigmoid transfer function with three hidden layers consist of 20, 10, and five neurons provided the highest accuracy for predicting the CO2 solubility in MEA/MDEA/PZ blends comparing to other model structures. The comparison results show that the neural network modeling provided more closer predictions to the experimental results than the simulator and other thermodynamic models when predicting the CO2 equilibrium solubility in blended amine solvents. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

Prediction of CO2 solubility in aqueous solutions of N, N-Diethyl ethanolamine (DEEA): A modified Kent-Eisenberg model approach

A tremendous increase in the carbon dioxide emissions over the last few decades has caused serious environmental concern. The research fraternity is working towards the discovery of novel solvents for carbon dioxide with greater removal efficiency. N, N-Diethyl ethanolamine (DEEA), a tertiary amine which can be prepared from renewable resources, is a potential absorbent for carbon dioxide removal. Determination of the equilibrium characteristics of the system plays a key role in the designing of industrial plants. In this work, the equilibrium solubility of CO2 in aqueous solutions of DEEA at different temperatures and CO2 partial pressures has been modeled using the modified Kent-Eisenberg model. The model predicted values were found to be in good agreement with the reported experimental data.

Measurement of vapour-liquid equilibrium and e-NRTL model development of CO2 absorption in aqueous dipropylenetriamine.

Vapour-liquid equilibrium (VLE) of CO2 in aqueous dipropylenetriamine (DPTA) is investigated experimentally using a stirred equilibrium cell setup. Equilibrium solubility of CO2 is measured in the temperature and pressure range of (313-333) K and (1-100) kPa respectively. Composition of aqueous DPTA solvent used for the absorption study is in the range of (5-15) mass%. Experimental data shows higher CO2 loading capacity of this solvent compared to conventional solvents like monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), and N-methyldiethanolamine (MDEA) as well as recently developed polyamine solvents like aminoethylethanolamine (AEEA), piperazine (PZ), and hexamethylenediamine (HMDA). Experimental VLE data is then correlated using the electrolyte non-random two-liquid (e-NRTL) theory which is an activity coefficient-based model for the electrolyte system. Data regression system (DRS) in Aspen Plus® (V8.8) is employed to fit the e-NRTL model equation with the experimental data by regressing the model parameters. Model-predicted data is found to be in good agreement with the experimental VLE data with an average absolute deviation of 22.3%. Performance of aqueous DPTA solvent is also analysed by predicting solvent capacity, equilibrium liquid-phase speciation, and heat of CO2 absorption using the newly developed e-NRTL model for the investigated system.

Thermodynamic modeling and new experimental CO2 solubility into aqueous EAE and AEEA blend, heat of absorption, cyclic absorption capacity and desorption study for post-combustion CO2 capture

In the present study, carbon dioxide (CO2) solubility into aqueous blend of 2-(ethylamino) ethanol (EAE) and aminoehtylethanolamine (AEEA) was measured. The performance of CO2 capture by this amine blend was investigated in terms of CO2 solubility, heat of absorption, cyclic CO2 solubility, and initial rate of change of CO2 solubility. CO2 absorption study was carried out using bubble column reactor in the temperature range of 298.15 to 323.15 K, 8.11 to 20.27 kPa CO2 partial pressure, 0.10 to 0.30 wt fraction of AEEA in EAE and AEEA blend, and 10 to 30 wt% total concentration of blend solution. Desorption experiments were performed at 393.15 K. Maximum CO2 solubility was 1.033 mol CO2/mol amine at 298.15 K, 20.27 kPa, 0.30 wt fraction of AEEA in the blend, and 10 wt% of EAE and AEEA solution. A semi-empirical Kent-Eisenberg thermodynamic model and an empirical model were developed to calculate equilibrium CO2 solubility in the studied range of operating conditions with 2.56% and 0.45% average absolute deviation, respectively. At 313.15 K, 15.20 kPa CO2 partial pressure and total concentration of 30 wt% of EAE and AEEA blend, the equilibrium CO2 solubility was resulted as 0.748 mol CO2/mol amine and cyclic solubility of 0.503 mol CO2/mol amine was achieved. Heat of CO2 absorption was measured based on Gibbs Helmholtz equation and found as −72.25 kJ/mol for 30 wt% aqueous EAE and AEEA blend. Results of absorption capacity of EAE and AEEA solution and monoethylethanolamine (MEA) were compared at same operating conditions. This blend had higher CO2 solubility, lesser heat of absorption, more cyclic capacity and faster rate of change of initial CO2 solubility than MEA.

Thermodynamic analysis of carbamate formation and carbon dioxide absorption in N-methylaminoethanol solution

Protonation and carbamate formation are critical reactions for CO2 capture using amine-based absorbents which impact both CO2 absorption and amine regeneration. In this regard, thermodynamic analysis towards CO2 absorption in N-methylaminoethanol solution is carried out with specific attention to the corresponding protonation and carbamate formation reactions. The CO2 absorption mechanism is investigated with the acquisition of reaction equilibrium constant and heat of reaction. CO2 absorption performance of N-methylaminoethanol solution was evaluated in terms of CO2 loading and solution pH. A thermodynamic model was then developed to mathematically describe the investigated system and make prediction on equilibrium CO2 solubility, species profiles, and absorption/regeneration heat. Results show that the average relative deviation of equilibrium CO2 solubility calculated from the is 4.2%. The predictive species profile and CO2 absorption heat of N-methylaminoethanol solution indicates less energy cost to desorb CO2. This is in line with the relative unstable N-methylaminoethanol carbamate formation and consequential conversion to (bi)carbonate. The position of N-methylaminoethanol as a potential absorbent in amine based carbon capture is shown in terms of chemical reaction constants, equilibrium CO2 solubility, second order rate constant (k2), and pKa.

Equilibrium CO2 solubility in the aqueous mixture of MAE and AEEA: Experimental study and development of modified thermodynamic model

In the present study, equilibrium solubility of CO2 was studied in the aqueous blend of 2-(methylamino)ethanol (MAE) and aminoethylethanolamine (AEEA). Total concentration of blend solution, weight fraction of AEEA in aqueous (MAE+AEEA) blend, temperature, and partial pressure of CO2 was varied from 10 to 30 wt %, 0.10 to 0.30, 298.15 to 323.15 K, and 8.11 to 20.67 kPa, respectively. Maximum loading 0.944 mol CO2/mol amine was occurred at 298.15 K, 20.27 kPa of CO2 partial pressure, 10 wt % total concentration with 0.30 wt fraction AEEA. The Kent-Eisenberg thermodynamic model was modified by incorporating newly introduced correction factor (Fk) to predict CO2 solubility in the aqueous blend of MAE+AEEA. Experimental data and model predicted data was in good agreement with each other. In addition, heat of CO2 absorption was also calculated for this amine blend and reported as -73.43 kJ/mol.

Water-lean blend mixtures of amino acid salts and 2-methoxyethanol for CO2 capture: Density, viscosity and solubility of CO2

Water-lean amino acid salt (AAS) solutions have attracted special attentions for energy-efficient CO2 absorbents. In this work, 2-methoxyethanol was proposed as a novel anti-solvent due to its excellent properties such as low volatility, low specific heat capacity and low viscosity. Density and viscosity were measured at atmospheric pressure for water-lean blends of potassium sarcosinate (SarK) or potassium L-prolinate (ProK)/water/2-methoxyethanol over the temperature range from (293 to 353) K and the AAS molality up to 4.914 mol·kg−1. Partially CO2 loaded solutions were also investigated. Equilibrium solubility of CO2 in AAS/water/2-methoxyethanol solutions was measured in a stirred equilibrium cell at temperatures of (313, 333 and 373) K and CO2 partial pressures up to 190 kPa. These property data were correlated using empirical correlations as a function of AAS molality, CO2 molality and/or temperature. The predicted values of density and viscosity matched well with the measured data, with AADs within 0.31% for density and 3.76% for viscosity. The solubility data of CO2 were fairly fitted with a proposed Soft model.

Analysis of equilibrium CO 2 solubility in aqueous APDA and its potential blends with AMP / MDEA for postcombustion CO 2 capture

The utility of polyamine-based solvent-activators for the possible application in postcombustion CO2 capture technology has drawn considerable attention recently owing to its higher loading capacity as well as superior kinetics. The current work involves a comprehensive experimental cum theoretical investigation on the equilibrium solubility of CO2 pertaining to aqueous N-(3-aminopropyl)-1,3-propanediamine and its blends with N-methyldiethanolamine and 2-amino-2-methyl-1-propanol. The analysis was conducted within the operating temperature and CO2 partial pressure range of 303.2-323.2 K and 2-200 kPa, respectively. Two different mathematical models based on nonrigorous approaches such as equilibrium based modified Kent-Eisenberg (KE) model and a multilayer feedforward neural network model have been developed to correlate the CO2 solubility data over a wide range of experimental conditions. Both the model predictions are well-validated with the experimental results. The reaction scheme as well as the prevalence of important reaction products was further confirmed with qualitative 13C NMR as well as ATR-FTIR analysis. Apart from these some of the important thermally induced transport properties viz, density, viscosity, and surface tension of the aqueous single and blended systems were measured and correlated with various consistent empirical models such as Redlich-Kister and Grunberg-Nissan model while surface tension data are modeled using temperature-based multiple linear regression technique.

Towards water-insensitive CO2-binding organic liquids for CO2 absorption: Effect of amines as promoter

Abstract CO2-binding organic liquids (CO2-BOLs) or reversible ionic liquids (RILs), are non-aqueous CO2-triggered switchable polarity solvents which can be used for energy efficient CO2 capture. In this study, the novel three-component CO2-BOLs are introduced. They are comprised of 1,8-Diazabicyclo(5.4.0)undec-7-ene (DBU) as an organic superbase and an alkanol in conjunction with an amine as a promoter. Screening experiments were performed to find the best combination of CO2-BOL components based on CO2 loading and absorption rate. The variables were: the type of alcohol (methanol, n-butanol, sec-butanol, tert-butanol and 1-hexanol) and the type of amine (EEA, MEA, AMP, DEA, AEEA, PZ, TETA and DETA) using the DBU superbase. Statistical mixture design approach using Minitab 18 software was implemented for the design of experiments, modeling and optimization of CO2 loading at the fixed temperature of 35 °C and the initial CO2 pressure of 25 bar. It was found that DBU/MeOH/MEA system with the molar ratio of 0.3/0.17/0.53 has the maximum equilibrium absorption (αeq) and CO2 uptake within 30 min (αR) of 0.444 and 0.267 mol CO2/mol solvent, respectively. Amine additives promoted absorption efficiency and inhibited formation of solid precipitates (bicarbonate salt) in the presence of water impurity. Characterization of ionic species and explaining the water-inhibitory effect of MEA were obtained from FTIR, 1H NMR and 13C NMR spectroscopic analysis. Equilibrium CO2 solubility data in DBU/MeOH (1/2) and DBU/MeOH/MEA (0.3/0.6/0.1) CO2-BOLs were also obtained at temperatures of 308.2 and 318.2 K and pressure range of 0–33 bar. The results of present study can be used to effectively utilize CO2-BOLs in the wet conditions with higher absorption efficiency and lower regeneration energy.

Novel thermodynamic model for vapor-liquid equilibrium of CO2 in aqueous solution of 4-(ethyl-methyl-amino)-2-butanol with designed structures

The aim of this project was to develop a thermodynamic model for the vapour-liquid equilibrium of an amine-water-carbon dioxide system and to evaluate the CO2 capture performance of aqueous EMAB solution. The structurally modified tertiary amine 4-(ethyl-methyl-amino)-2-butanol (EMAB) was chosen because of its molecular structure-activity relationship. Measurements were made of its equilibrium CO2 solubility, viscosity, dissociation constant, and second-order reaction rate constant, and the heat of absorption was then calculated. Additionally, the novel semi empirical model (Extended Cf model) and the novel rigorous thermodynamic model (fugacity-activity model) which take into consideration the association of the partial molar property and the equation of state were developed to predict the equilibrium CO2 solubility. The models can provide reasonable prediction results with AARDs of 2.3% and 3.68%, respectively. Furthermore, the thermodynamic and dynamic properties of EMAB were analyzed and evaluated by a comprehensive method and compared with some new tertiary amines and traditional commercial amines. The study concludes that EMAB has good CO2 capture performance and is expected to be one of the most promising alternative amines for post combustion CO2 capture technology.

CO2 capture using aqueous 1-(2-Hydroxyethyl) piperidine and its blends with piperazine: Solubility and enthalpy

In this article, equilibrium CO2 solubility in aqueous 1-(2-Hydroxyethyl) piperidine (HEP) solutions pertaining concentrations (1, 2, 3) mol/L in the temperature range (303.15–323.15) K, and CO2 partial pressure range 0.1–100 kPa are presented. HEP; being a tertiary alkanolamine, its rate of CO2 absorption is comparatively slower than primary or secondary alkanolamine. Piperazine (PZ), a rate promoter was added to HEP in 1:4 mol ratio to form blends having enhance rate of CO2 absorption. Equilibrium CO2 solubility in four different aqueous blends; (0.8 mol/L HEP + 0.2 mol/L PZ), (1.6 mol/L HEP + 0.4 mol/L PZ), (2.4 mol/L HEP + 0.6 mol/L PZ), (3.2 mol/L HEP + 0.8 mol/L PZ) were measured over the temperature range of (303.15–323.15) K and CO2 partial pressure spanning over 0–70 kPa. Equilibrium constant for deprotonation reaction of HEP was estimated by measuring pKa of aqueous HEP solution at 298.15, 303.15, 313.15, 323.15 and 333.15 K. Experimentally obtained CO2 solubility data for single and blended amine solutions were correlated efficiently using activity coefficient model with AAD % of 3.76 and 3.22, respectively. Speciation of both single and blended amine solutions in their equilibrated liquid phase were predicted. Interaction parameters obtained through thermodynamic modelling of equilibrium solubility data for single and blended amine solutions were used to predict the enthalpy of CO2 absorption.

Equilibrium Solubility Measurement and Modeling of CO2 Absorption in Aqueous Blend of 2-(Diethyl amino) Ethanol and Ethylenediamine

The equilibrium CO2 solubility in an aqueous blend of 2-(diethyl amino) ethanol (DEEA) and ethylenediamine (EDA) was performed at atmospheric pressure with the use of a laboratory scale bubbling absorber. The total concentration of amine blend solution in the range of 1.13–4.90 mol·kg–1 and the EDA mole fraction in the total amine blend in the range of 0.05–0.20 were taken. The experiments for the measurement of CO2 solubility were performed at a temperature range of 303.15–333.15 K and CO2 partial pressure range of 10.13–20.27 kPa. The analysis of CO2 in the liquid phase was accomplished by a direct titration method using HCl solution. The solubility data of CO2 in DEEA+EDA solution of the present study were compared with data available in the literature. The experimental results were applied to develop an empirical mathematical model with an average absolute deviation of 7.03% to predict the CO2 equilibrium solubility in DEEA+EDA solution within the specified range of operating conditions. In addition, ...

Performance and stability of a bio-inspired soybean-based solvent for CO2 capture from flue gas

A novel bio-inspired soybean-based solvent (SBB solvent) was formulated for the capture of CO2 with the partial pressure less than 15 kPa in the flue gas. The performance of the SBB solvent was thoroughly characterized in terms of equilibrium solubility of CO2, the heat of CO2 absorption, vapor pressure of the SBB solvent, and the CO2 absorption flux under different operating conditions including CO2 partial pressure in the flue gas, initial CO2 loading in the SBB solvent, SBB solvent concentration, and temperature. The results showed that the equilibrium solubility of CO2 in the SBB solvent was much lower than that in the conventional amine-based solvent at the regeneration condition. The heat of CO2 absorption is only at half of the monoethanolamine (MEA). The near-zero vapor pressure made the SBB solvent as a promising and environmentally friendly solvent for CO2 capture. The optimized concentration of the SBB solvent was 1.0 M for the effective absorption of CO2 from the flue gas. The CO2 absorption performance can be further improved by integrating the use of high concentration SBB solvent with reduced CO2-gas mass transfer resistance. Both thermal stability and oxidative stability of the SBB solvent were evaluated through a 120 h CO2 absorption-desorption experiment. The SBB solvent showed high thermal stability at the regeneration temperature up to 200 °C, and also excellent oxidative stability with the O2 concentration up to 17% in the flue gas.

New AMP/polyamine blends for improved CO2 capture: Study of kinetic and equilibrium features

Abstract2‐Amino‐2‐methyl‐1‐propanol (AMP), which is the sterically hindered form of monoethanolamine (MEA), is a credible substitute to conventional CO2‐capturing solvents. Its performance can be improved by blending with a highly reactive polyamine promoter. Two such aqueous blends of AMP/TETA and AMP/TEPA were chosen here (TETA = triethylenetetramine and TEPA = tetraethylenepentamine). The kinetics of CO2 absorption in the proposed blends was investigated at 308, 313, and 318 K using the stirred cell technique. The concentrations of AMP and polyamine were varied between 2 to 3 kmol/m3 and 0.1 to 0.5 kmol/m3, respectively. From the measured values of the fast pseudo‐first order constants, the second‐order rate constants for the reactions of CO2 with TETA (14 695 m3/(kmol s)) and TEPA (19 250 m3/(kmol s)) were determined at T = 313 K. Both TETA and TEPA react faster with CO2 than MEA. Further, the respective activation energy values were found (40 and 37 kJ/mol). Finally, the equilibrium solubility of CO2 for both blends was measured at T = 303 K. The loading capacity was higher than that for the aqueous blends of AMP/MEA, AMP/DEA, and AMP/MDEA (here, DEA and MDEA denote diethanolamine and N‐methyldiethanolamine). The highest value of loading capacity (1.12 mol CO2/mol amine at 2.01 kPa equilibrium partial pressure of CO2) was noted in AMP/TEPA mixtures. The new findings on our proposed blends will strengthen the AMP/polyamine application in CO2 separation.

CO2 equilibrium solubility in and physical properties for monoethanolamine glycinate at low pressures

In practical applications, water vapor always coexists with natural gas. As such, the concentration of the ionic liquids (ILs), as promising absorbents for carbon dioxide (CO2) removal, is a crucial parameter sensitively affecting CO2 solubility. In this work, a novel amino acid anion (Glycinate) based IL was synthesized, characterized, and applied for CO2 uptake. Preliminary physicochemical measurements at temperatures of 303–323K showed that increasing the IL purity has adverse effects on density, viscosity, and surface tension of the [MEA][GLY].The impact of the presence of water in the IL samples was also investigated on the CO2 loadings over the temperature ranges of 303–323K and up to a pressure of 600kPa. Among the four aqueous solutions of the IL, the highest CO2 loading of 1.02 (mol CO2/mol IL) was achieved for aqueous IL of 25wt% at an equilibrium pressure of 1.35bar and a temperature of 303.15K. It is found that with increasing equilibrium pressure to about 6.2bar, the loading rate has reached 1.32 (mol CO2/mol IL), which is almost 2.64 times higher than that of the conventional primary amine (0.5mol CO2/mol IL). It is found that although the proposed IL is a promising absorbent for the capture of CO2, highly concentrated of the [MEA][GLY] is not the feasible concentration for CO2 uptake.

Experimental and modeling studies of bicarbonate forming amines for CO2 capture by NMR spectroscopy and VLE

Three tertiary diamines, N,N,N',N'-tetramethyl-1,2-ethanediamine, N,N,N',N'- tetramethyl-1,3-propanediamine and N,N,N',N'-tetramethyl-1,4-butanediamine, were investigated for application in post-combustion CO2 capture. The acid-base properties of the diamines were studied through measuring pH values of the acidified amine solutions to obtain reaction constants and corresponding enthalpies/entropies of the reactions. Competitive formation of monoprotonated and diprotonated diamines was observed. CO2 absorption using these diamine solutions was carried out through a continuous flow method. NMR spectroscopy was used to detect speciation of the bulk solution. Then a general evaluation of the diamines was made in comparison with the monoamines in terms of equilibrium CO2 solubility and pKa. The results demonstrated the potential of the structurally modified diamines to be promising bicarbonate forming absorbents in CO2 absorption. Finally, the equilibrium CO2 solubility of aqueous N,N,N',N'-tetramethyl-1,2-ethanediamine solution was measured at a wider range of temperatures, CO2 partial pressures and initial amine concentrations to establish a thermodynamic model. The model provided reasonable prediction of equilibrium CO2 solubility and species concentration profiles.