Equilibrium solubility of CO<Subscript>2</Subscript> in aqueous binary mixture of 2-(diethylamine)ethanol and 1, 6-hexamethyldiamine

CO₂ solubility data are important for the efficient design and operation of the acid gas CO₂ capture process using aqueous amine mixture. 2-(Diethylamino)ethanol (DEEA) solvent can be manufactured from renewable sources like agricultural products/residue, and 1,6-hexamethyldiamine (HMDA) solvents have higher absorption capacity as well as reaction rate with CO₂ than conventional amine-based solvents. The equilibrium solubility of CO₂ into aqueous binary mixture of DEEA and HMDA was investigated in the temperature range of 303.13-333.13 K and inlet CO₂ partial pressure in the range of 10.133-20.265 kPa. Total concentration of aqueous amine mixtures in the range of 1.0-3.0 kmol/m³ and mole fraction of HMDA in total amine mixture in the range of 0.05-0.20 were taken in this work. CO₂ absorption experiment was performed using semi-batch operated laboratory scale bubble column to measure equilibrium solubility of CO₂ in amine mixture, and CO₂ absorbed amount in saturated carbonated amine mixture was analyzed by precipitation-titration method using BaCl₂. Maximum equilibrium CO₂ solubility in aqueous amine mixture was observed at 0.2 of HMDA mole fraction in total amine mixture with 1.0 kmol/m³ total amine concentration. New solubility data of CO₂ in DEEA+HMDA aqueous mixtures in the current study was compared with solubility data available in previous studies conducted by various researchers. The study shows that the new absorbent as a mixture of DEEA+HMDA is feasible for CO₂ removal from coal-fired power plant stack gas streams.     

Analysis of equilibrium CO2 solubility and thermodynamic models for aqueous 1-(2-hydoxyethyl)-piperidine solution

1-(2-Hydoxyethyl)-piperidine (1-(2HE)-PP) is a new tertiary amine with desirable properties and can be potentially used to formulate superior absorbents for CO₂ capture. The equilibrium CO₂ solubility of 1-(2HE)-PP solution is measured over temperatures from 298 to 333 K, CO₂ partial pressures from 8.1 to 101.3 kPa and initial amine concentrations from 1 to 5 M. Two thermodynamic models, namely semiempirical model and activity coefficient model are developed for the system. The activity coefficient model shows better estimation solubility with an absolute average relative deviation (AARD) of 7.6%. In the comparison between the two models, a comprehensive analysis is presented. Some suggestions are provided for the similar model development. In addition, the speciation plot of CO₂ loaded 1-(2HE)-PP solution is predicted based on the activity coefficient model. The predictive pH values agree well with experimental data with AARD of 1.0%. Finally, the potential of 1-(2-HE)PP to be an alternative amine in CO₂ capture is evaluated.     

Kinetics and new mechanism study of CO2 absorption into water and tertiary amine solutions by stopped-Flow technique

The objective of the present work was to find the accurate kinetic models and mechanism for CO₂ absorption into tertiary amine solution, aiming at understanding the contribution of the CO₂ reaction with H₂O, OH⁻, and tertiary amines on the overall reaction rate. First, the kinetics of CO₂ absorption into water instead of a buffer solution were studied using the stopped-flow technique at 293–313 K, with initial CO₂ molar concentration of 1.1–37.3 mM. The experimental first-order reaction rate constant () was determined to be about 1000 times larger than the value for CO₂ absorption into buffer solution reported in the reference. The was then correlated by a proposed semiempirical model and a simplified theoretical model, giving the activation energy for CO₂ reacting with H₂O as fitted by the simplified theoretical model in good agreement with the value of previous research. Also, the pH values and hydroxyl ion concentrations of aqueous Diethylaminoethanol (DEEA) solutions were determined at 293–313 K, with DEEA molar concentration of 0.1–0.4 M and CO₂ loading of 0–0.626 mol/mol. In addition, the observed first-order reaction rate constant ( k_{0_DEEA} ) of binary DEEA-H₂O solution with DEEA molar concentration of 0.1–0.4 M reacting with CO₂ was determined at 293–313 K. It should be pointed out that the kinetic experiments of CO₂ absorption into DEEA solution was done with the molar ratio of DEEA to CO₂ fixed at 20. The values of k_{0_DEEA} were then fitted and predicted by four models (i.e., termolecular model, base-catalyzed model, the improved model, and Khalifah model). The results show the improved model and Khalifah model can predict k_{0_DEEA} well with an average absolute relative difference (AARD) <5%. The predicted results indicate that the contribution of OH⁻ to k_{0_DEEA} cannot be ignored for the absorption of CO₂ into tertiary amine solutions, and could be responsible for 50–70% of the total absorption reaction rate. Furthermore, the k₀ value of CO₂ absorption into aqueous triethanolamine and CO₂-loaded DEEA solution were further investigated and comprehensively discussed, suggesting that both pK _a and the CO₂ solubility affect k₀ , with pK _a having a much more significant effect. © 2018 American Institute of Chemical Engineers AIChE J, 65: 652–661, 2019     

Modeling of CO2 equilibrium solubility in a novel 1‐Diethylamino‐2‐Propanol Solvent

In this work, the equilibrium solubility of CO₂ in a 1‐diethylamino‐2‐propanol (1DEA2P) solution was determined as a function of 1DEA2P concentration (over the range of 1–2 M), temperature (in the range of 298–333 K), and CO₂ partial pressure (in the range of 8–101 kPa). These experimental results were used to fit the present correlation for K₂ (Kent‐Eisenberg model, Austgen model, and Li‐Shen model). It was found that all of the models could represent the CO₂ equilibrium solubility in 1DEA2P solution with ADDs for Kent‐Eisenberg model, Austgen model, and Li‐Shen model of 6.3, 7.3, and 12.2%, respectively. A new K₂ correlation model, the Liu‐Helei model, was also developed to predict the CO₂ equilibrium solubility in 1DEA2P solution with an excellent ADD of 3.4%. In addition, the heat of absorption of CO₂ in 1DEA2P solution estimated by using the Gibbs‐Helmholtz equation was found to be ?45.7 ± 3.7 kJ/mol. Information and guidelines about effectively using data for screened solvents is also provided based on the three absorption parameters: CO₂ equilibrium solubility, second order reaction constant (k₂), and CO₂ absorption heat. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4465–4475, 2017     

A Study on CO2 Absorption Kinetics by Aqueous Solutions of N,N‐Diethylethanolamine and N‐Ethylethanolamine

N‐Ethylethanolamine (EEA) and N,N‐diethylethanolamine (DEEA) represent promising candidate alkanolamines for CO₂ removal from gaseous streams, as they can be prepared from renewable resources. In this work, the reaction rate constant for the reaction between CO₂ and EEA was determined from the absorption rate measurements of CO₂ in a blend comprising DEEA, EEA and H₂O. A stirred‐cell reactor with a plane, horizontal gas‐liquid interface was used for the absorption studies. While the DEEA concentration in the formulated solution was varied in the range of 1.5–2.5 kmol/m³, the initial EEA concentration was 0.1 kmol/m³. A zwitterion mechanism for EEA and a base‐catalyzed hydration mechanism for DEEA were used to describe the reaction kinetics. At 303 K, the second‐order reaction rate constant for the CO₂ reaction with EEA was found to be 8041 m³/(kmol s). The liquid‐side mass transfer coefficient was also estimated, and its value (0.004 cm/s) is in line with those typical of stirred‐cell reactors.     

Untersuchung der CO2‐Absorptionskinetik in wässrigen Lösungen von N,N‐Diethylethanolanmin und N‐Ethylethanolamin

N‐Ethylethanolamine (EEA) and N,N‐diethylethanolamine (DEEA) represent promising alkanolamines for CO₂ removal from gaseous streams, as they can be prepared from renewable resources. In this work, the reaction rate constant for the reaction between CO₂ and EEA and the liquid‐side mass transfer coefficient were determined from the absorption rate measurements in a blend comprising DEEA, EEA and H₂O. A stirred‐cell reactor was applied for the absorption studies, whereas a zwitterion mechanism for EEA and a base‐catalyzed hydration mechanism for DEEA were used to describe the reaction kinetics.     

A novel equation of state (EOS) for prediction of solute solubility in supercritical carbon dioxide: Experimental determination and correlation

Solubility data of organophosphorous metal extractants in supercritical fluids (SCF) are crucial for designing metal extraction processes. We have developed a new equation of state (EOS) based on virial equation including an untypical parameter as BP/RT, reduced temperature and pressure for prediction of solute solubility in supercritical carbon dioxide (SC CO₂). Solubility experimental data (solubility of tributylphosphate in SC CO₂) were correlated with the two cubic equations of state (EOS) models, namely the Peng–Robinson EOS (PR‐EOS) and the Soave–Redlich–Kwong EOS (SRK‐EOS), together with two adjustable parameter van der Waals mixing and combining rules and our proposed EOS. The AARD of our EOS is significantly lower than that obtained from the other EOS models. The proposed EOS presented more accurate correlation for solubility data in SC CO₂. It can be employed to speed up the process of SCF applications in industry.     

Solubility of CO2 in 15, 30, 45 and 60 mass% MEA from 40 to 120 °C and model representation using the extended UNIQUAC framework

New experimental data for vapor–liquid equilibrium of CO₂ in aqueous monoethanolamine solutions are presented for 15, 30, 45 and 60 mass% MEA and from 40 to 120 °C. CO₂ partial pressures over loaded MEA solutions were measured using a low temperature equilibrium apparatus while total pressures were measured with a high temperature equilibrium apparatus. Experimental data are given as CO₂ partial pressure as function of loading in solution for temperatures from 40 to 80 °C and as total pressures for temperatures from 60 to 120 °C for the different MEA concentrations. The extended UNIQUAC model framework was applied and model parameters were fitted to the new experimental VLE data and physical CO₂ solubility data from the literature. The model gives a good representation of the experimental VLE data for CO₂ partial pressures and total pressures for all MEA concentrations with an average absolute relative deviation (AARD) of 24.3% and 11.7%, respectively, while the physical solubility data were represented with an AARD of 2.7%. Further, the model predicts well literature data on freezing point depression, excess enthalpy and liquid phase speciation determined by NMR.     

Catalytic desorption of CO2-loaded solutions of diethylethanolamine using bentonite catalyst

The absorption of CO₂ gas into aqueous alkanolamine solutions is the most advanced CO₂ separation technology and a key challenge in this technique is the energy-intensive process of solvent regeneration. The tertiary amine N,N′-diethylethanolamine (or DEEA) is a candidate CO₂-capturing solvent with potential. To improve the energy efficiency of regeneration of DEEA, several catalysts were used for desorbing CO₂ from loaded solutions of DEEA (2.5 M) at T = 363 K. Desorption trials were conducted in batch mode. The initial CO₂ loading varied in the 0.3–0.35 mol CO₂/mol DEEA range. The performance was analyzed by calculating the rate of CO₂ desorption, cyclic capacity, and reduction in sensible energy. The amount of thermal energy needed for amine regeneration was significantly lowered by using nine transition metal oxide catalysts and the hierarchy was as follows: Al₂O₃ < MoO₃ < V₂O₅ < TiO₂ < MnO₂ < ZnO < Cr₂O₃ < SiO₂ < ZrO₂. Among the metal oxides, Al₂O₃ increased desorption efficiency compared to blank runs by 89%. A clay-based powder bentonite was also used as catalyst and its efficacy was compared with the metal oxides. This cheap and easily available bentonite catalyst was tuned through simple ion-exchange with four acids (HCl, H₃PO₄, HNO₃, and H₂SO₄). Upon treatment with H₂SO₄, bentonite remarkably increased desorption efficiency by 100%. Furthermore, bentonite catalyst treated with sulphuric acid (denoted here as Bt/H₂SO₄) was characterized by Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectrometery (FTIR), X-ray diffraction (XRD), and ammonia temperature-programmed desorption (NH₃-TPD). In this way, a comprehensive study on catalytic desorption of DEEA was performed.     

Effects of piperazine concentration and operating conditions on the solubility of CO2 in AMP solution at low CO2 partial pressure

In this study, new equilibrium solubility data for carbon dioxide in aqueous solutions of 2-amino-2-methyl-1-propanol and piperazine (PZ) are provided. The two famous Deshmukh–Mather and Kent Eisenberg thermodynamic models are utilized to predict the CO₂ absorption. The experimental data show that the solubility of CO₂ decreases as the temperature increases. Our data suggest that the addition of PZ has different effects on CO₂ absorption under different partial pressure of the CO₂ in the gas stream. For high partial pressure, the addition of PZ promotes the absorption performance. However, at low CO₂ partial pressure, PZ addition results in less saturated CO₂ loading. The Deshmukh–Mather model can provide an accurate prediction of the experimental data at high partial pressure of CO₂ (i.e. AAD = 3.4%) whereas the modified Kent–Eisenberg model can capture the inverse effects of the PZ at low partial pressure and provides a relatively good approximation of experimental data at low partial pressure (i.e. AAD = 10%).     

Prediction of solute solubility in supercritical carbon dioxide: A novel semi-empirical model

Solubility data of solutes in supercritical fluids (SCF) are crucial for designing extraction processes, such as extraction using SCF or micronization of drug powders. A new empirical equation is proposed to correlate solute solubility in supercritical carbon dioxide (SC CO₂) with temperature, pressure and density of pure SC CO₂. The proposed equation is ln y₂ = J₀ + J₁P² + J₂T² + J₃ ln ρ where y₂ is the mole fraction solubility of the solute in the supercritical phase, J₀ − J₃ are the model constants calculated by least squares method, P (bar) is the applied pressure, T is temperature (K) and ρ is the density of pure SC CO₂. The accuracy of the proposed model and three other empirical equations employing P, T and ρ variables was evaluated using 16 published solubility data sets by calculating the average of absolute relative deviation (AARD). The mean AARD for the proposed model is 7.46 (±4.54) %, which is an acceptable error when compared with the experimental uncertainty. The AARD values for other equations were 11.70 (±23.10), 6.895 (± 3.81) and 6.39 (±6.41). The mean AARD of the new equation is significantly lower than that obtained from Chrastil et al. model and has the same accuracy as compared with Bartle et al. and Mèndez-Santiago–Teja model. The proposed model presents more accurate correlation for solubility data in SC CO₂. It can be employed to speed up the process of SCF applications in industry.     

A new model for correlation and prediction of equilibrium CO2 solubility in N‐methyl‐4‐piperidinol solvent

In this work, the equilibrium CO₂ solubility in the aqueous tertiary amine, N‐methyl‐4‐piperidinol (MPDL) was measured over a range of temperatures, CO₂ partial pressures and amine concentrations. The dissociation constant of the MPDL solution was determined as well. A new thermodynamic model was developed to predict the equilibrium CO₂ solubility in the MPDL‐H₂O‐CO₂ system. This model, equipped with the correction factor (C_f), can give reasonable prediction with an average absolute deviation of 2.0%, and performs better than other models (i.e., KE model, Li‐Shen model, and Hu‐Chakma). The second‐order reaction rate constant (k₂) of MPDL and the heat of CO₂ absorption (–ΔH_abs) into aqueous MPDL solutions were evaluated as well. Based on the comparison with some conventional amines, MPDL revealed a high‐equilibrium CO₂ loading, reasonably fast absorption rate when compared with other tertiary amines, and a low energy requirement for regeneration. It may, therefore, be considered to be an alternative solvent for CO₂ capture. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3395–3403, 2017     

Simulations of vapor–liquid phase equilibrium and interfacial tension in the CO2–H2O–NaCl system

Direct interfacial molecular dynamics simulations are used to obtain the phase behavior and interfacial tension of CO₂–H₂O–NaCl mixtures over a broad temperature and pressure range (50°C ≤ T ≤ 250°C, 0 ≤ P ≤ 600 bar) and NaCl concentrations (1–4 mol/kg H₂O). The predictive ability of several existing water (SPC and TIP4P2005), carbon dioxide (EPM2 and TraPPE), and sodium chloride (SD and DRVH) models is studied and compared, using conventional Lorentz–Berthelot combining rules for the unlike‐pair parameters. Under conditions of moderate NaCl molality (～1 mol/kg H₂O), the predictions of the CO₂ solubility in the water‐rich and CO₂‐rich phase resemble those in the CO₂–H₂O system [Liu et al., J Phys Chem B. 2011;115:6629–6635]. Consistent with our previous work, the TraPPE/TIP4P2005 model combination gives the best overall performance in predicting coexistence composition and pressure in the water‐rich phase. Critical assessments are also made on the ranges of temperature and pressure where particular model combinations work better. The dependence of the interfacial tension on temperature and pressure is better predicted by the TraPPE/TIP4P2005 and EPM2/SPC models, whereas the EPM2/TIP4P2005 model overestimates this property by 10–20%, possibly due to the inadequacy of the combining rules. It is also found that the interfacial tension increases with salt concentration, consistent with experimental observations. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3514–3522, 2013     

Vapour–liquid equilibrium of CO2 in aqueous solutions of N‐methyl‐2‐ethanolamine

The equilibrium solubility of CO₂ into aqueous solution of sterically hindered N‐methyl‐2‐ethanolamine or methyl amino ethanol (MAE) was investigated in the temperature range of 303.1–323.1 K and total CO₂ pressure in the range of 1–350 kPa. The N‐methyl‐2‐ethanolamine aqueous solutions studied were 0.968, 1.574, 2.240 and 3.125 mol kg^?1 of solvent. © 2011 Canadian Society for Chemical Engineering     

Experimental investigation and modeling of the solubility of carvedilol in supercritical carbon dioxide

This study was aimed to measure the solubility of carvedilol in the temperature and pressure ranges of 308⿿338 K and 160 bar to 400 bar, respectively. In this direction, a homemade high pressure visual equilibrium cell was used to measure the solubility of carvedilol using a static method coupled with gravimetric technique. The results revealed that the carvedilol solubility was ranged between 1.12 ÿ 10^⿿5 and 5.01 ÿ 10^⿿3 based on the mole fraction (mole of carvedilol/mole of carvedilol + mole of CO₂) in this study as the temperature and pressure was changed. Finally, the results were correlated using four density-based semi-empirical correlations including Chrastil, Mendez⿿Santiago⿿Teja (MST), Bartle et al., and Kumar and Johnston (K-J) models. Results revealed that although the K-J model leads to the lowest average absolute relative deviation percent (AARD %) of 6.27%, but it could not be considered as the most accurate correlation since all the used four correlations introduces AARD % of about 6⿿10% which may be in the same range as the experimental error.     

A comparative kinetics study of CO2 absorption into aqueous DEEA/MEA and DMEA/MEA blended solutions

The kinetics of CO₂ absorption into aqueous solutions of N,N‐diethylethanolamine (DEEA), and N,N‐dimethylethanolamine (DMEA), and their blends with monoethanolamine (MEA) have been studied in a stopped‐flow apparatus. The kinetics experiments were carried out at the concentrations of DEEA and DMEA varying from 0.075 to 0.175 kmol/m³, respectively, and that of MEA ranging between 0.0075 and 0.0175 kmol/m³, over the temperature range of 293–313 K. Two kinetics models are proposed to interpret the reaction in the blended amine systems and the results show that the model which incorporates the base‐catalyzed hydration mechanism and termolecular mechanism resulted in a better prediction. Furthermore, the kinetics behaviors of CO₂ absorption into two blended systems are comprehensively discussed according to their molecular structures. It can be concluded that the interaction between tertiary amines and primary amines as well as the alkyl chain length of tertiary amines have a significant influence on the kinetics. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1350–1358, 2018     

Removal of carbon dioxide by absorption in mixed amines: modelling of absorption in aqueous MDEA/MEA and AMP/MEA solutions

This work presents an investigation of CO₂ absorption into aqueous blends of methyldiethanolamine (MDEA) and monoethanolamine (MEA), as well as 2-amino-2-methyl-1-propanol (AMP) and monoethanolamine (MEA). The combined mass transfer–reaction kinetics–equilibrium model to describe CO₂ absorption into the amine blends has been developed according to Higbie's penetration theory following the work of Hagewiesche et al. (Chem. Eng. Sci. 50 (1995) 1071). The model predictions have been found to be in good agreement with the experimental rates of absorption of CO₂ into (MDEA+MEA+H₂O) of this work and into (AMP+MEA+H₂O) reported by Xiao et al. (Chem. Eng. Sci. 55 (2000) 161), measured at higher contact times using wetted wall contactor. The good agreement between the model predicted rates and enhancement factors and the experimental results indicate that the combined mass transfer–reaction kinetics–equilibrium model with the appropriate use of model parameters can effectively represent CO₂ mass transfer for the aqueous amine blends MDEA/MEA and AMP/MEA.     

Solubility and kinetics of soybean oil and fatty acids in supercritical CO2

Supercritical CO₂ extraction of soybean oil was investigated. The fatty acid composition was determined using GC. The solubility and kinetic experiments were performed in the pressure range of 100–300 bar and in the temperature range of 313–323 K. The solubility data were correlated using empirical equation proposed by Gordillo et al. Mass transfer model described by Martinez et al. was used to describe the kinetic curves of soybean oil. The main fatty acids of soybean oil were linoleic, oleic, palmitic, stearic and linolenic acid. The improved Gordillo et al. equation was proposed to correct the effect of temperature on the solubility. The new equation was successfully applied for calculating the solubility of fatty acids and soybean oil in supercritical CO₂.     

Density and N2O solubility of sodium and potassium carbonate solutions in the temperature range 25 to 80 °C

To deduce kinetic parameters for the reactions of carbon dioxide (CO₂) in carbonate solutions the physical solubility of CO₂ into the reacting solution is needed. To measure the physical solubility directly with CO₂ is not possible, so the solubility of nitrous oxide (N₂O) is normally measured instead. The physical solubility of CO₂ can then be calculated based on the solubility of CO₂ and N₂O into water and the solubility of N₂O in the solution of interest invoking the so called N₂O analogy (Clarke, 1964; Laddha et al., 1981). To obtain good accuracy of the solubility measurements the accurate density of the solution is needed. In this study the densities were measured with pycnometers up to 353 K.In this paper the parameters in the model of Weisenberger and Schumpe (1996) were refitted specifically for the two carbonate systems using experimental data up to 353 K and up to 30 wt% (3.7 kmol/m³) aqueous sodium carbonate and up to 50 wt% (5.5 kmol/m³) aqueous potassium carbonate solutions.