The analysis of solubility,absorption kinetics of CO2 absorption into aqueous 1‐diethylamino‐2‐propanol solution

In this present work, the CO₂ absorption performance of aqueous 1‐diethylamino‐2‐propanol (1DEA2P) solution was studied with respect to CO₂ equilibrium solubility, absorption kinetics, and absorption heat. The equilibrium solubility of CO₂ in 2M 1DEA2P solution was measured over the temperature range from 298 to 333 K and CO₂ partial pressure range from 8 to101 kPa. The absorption kinetics data were developed and analyzed using the base‐catalyzed hydration mechanism and artificial neural network models (radial basis function neural network [RBFNN] and back‐propagation neural network [BPNN] models) with an acceptable absolute average deviation of 10% for base‐catalyzed hydration mechanism, 2.6% for RBFNN model and 1.77% for BPNN model, respectively. The CO₂ absorption heat of 1DEA2P was estimated to be ?43.6 kJ/mol. In addition, the ions (1DEA2P, 1DEA2PH⁺, , CO₃^2?) speciation plots of the 1DEA2P‐CO₂‐H₂O system were developed to further understand the reaction process of 1DEA2P with CO₂. Based on a comparison with conventional amines (e.g., MEA, DEA, MDEA) and alternative amines (i.e., 1DMA2P and 4‐(diethylamino)?2‐butanol [DEAB]), 1DEA2P exhibited good performance with respect to CO₂ equilibrium solubility, reaction kinetics, and CO₂ absorption heat. Meanwhile, the overall evaluation of 1DEA2P for application in CCS in terms of absorption and desorption is presented, giving helpful information for the screening of these novel amines. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2694–2704, 2017     

Comprehensive analysis of thermodynamic models for CO2 absorption into a blended N,N-diethylethanolamine-1,6-hexamethyl diamine (DEEA-HMDA) amine

In this work, CO₂ equilibrium solubility of 1M N,N-diethylethanolamine (DEEA):2M 1,6-hexamethyl diamine (HMDA), 1.5M DEEA:1.5M HMDA and 2M DEEA:1M HMDA was studied with a temperature range of 298–333 K and CO₂ partial pressure range of 8–100 kPa. Seven thermodynamic models including Empirical model, Kent and Eisenberg (KE) model, Hu–Chakma model, Austgen model, Helei Liu model, Liu et al. model, and Li–Shen model were developed by correlating reaction equilibrium constants with observed equilibrium solubility of CO₂ in mixed amine solvents. The evaluation of those models was conducted in terms of the average absolute relative deviation (AARD). The results indicated that Liu et al. model considering T, [Amine], P_total and [CO₂(aq)] can better represent this complex system with an AARD of 8.06%. Meanwhile, comprehensive comparison and analysis were also performed to identify the contribution of parameters to develop models, which could provide a guideline for the development of accurate thermodynamic models for representation of thermodynamic behaviors.     

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     

Solubility of CO2 in Aqueous Piperazine and its Modeling using the Kent‐Eisenberg Approach

A systematic investigation of the equilibrium solubility of CO₂ in aqueous piperazine solutions was conducted in a double‐jacketed stirred cell reactor. The solubilities of CO₂ in the solution were measured at 20, 30, 40, and 50 °C with CO₂ partial pressures ranging from 0.4–95 kPa. Generally the aqueous piperazine solution exhibits the same characteristics as conventional alkanolamines. Increasing the CO₂ partial pressure increases the gas loading, however increasing the temperature or concentration decreases the CO₂ loading. The values of the CO₂ loading obtained confirm that the piperazine forms stable carbamates. The equilibrium solubility data were analyzed using a Kent‐Eisenberg approach. Representation of the model is generally in good agreement with that of the experimental data, especially at high temperature.     

Improved Kent-Eisenberg model for predicting CO2 solubilities in aqueous diethanolamine (DEA) solutions

The Kent and Eisenberg model for the determination of CO₂ solubility in aqueous diethanolamine (DEA) solutions has been improved by recorrelating the equilibrium constant relating the main DEA-CO₂ reaction using 626 experimental data points. The new correlation for the equilibrium constant is expressed as functions of temperature, DEA concentration and free CO₂ concentration. The improved model predicts experimental data much better than the original model specially under high temperature and low CO₂ partial pressure conditions.     

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%).     

Kinetics of CO2 absorption into a novel 1‐diethylamino‐2‐propanol solvent using stopped‐flow technique

A stopped‐flow apparatus was used to measure the kinetics of carbon dioxide (CO₂) absorption into aqueous solution of 1‐diethylamino‐2‐propanol (1DEA2P) in terms of observed pseudo‐first‐order rate constant (k_o) and second‐order reaction rate constant (k₂), in this work. The experiments were conducted over a 1DEA2P concentration range of 120–751 mol/m³, and a temperature range of 298–313 K. As 1DEA2P is a tertiary amine, the base‐catalyzed hydration mechanism was, then, applied to correlate the experimental CO₂ absorption rate constants obtained from stopped‐flow apparatus. In addition, the pK_a of 1DEA2P was experimentally measured over a temperature range of 278–333 K. The Brønsted relationship between reaction rate constant (obtained from stopped‐flow apparatus) and pK_a was, then, studied. The results showed that the correlation based on the Brønsted relationship performed very well for predicting the absorption rate constant with an absolute average deviation of 5.2%, which is in an acceptable range of less than 10%. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3502–3510, 2014     

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     

Determination of kinetics of CO2 absorption in solutions of 2‐amino‐2‐methyl‐1‐propanol using a microfluidic technique

The kinetics for the reactions of carbon dioxide with 2‐amine‐2‐methyl‐1‐propanol (AMP) and carbon dioxide (CO₂) in both aqueous and nonaqueous solutions were measured using a microfluidic method at a temperature range of 298–318 K. The mixtures of AMP‐water and AMP‐ethylene glycol were applied for the working systems. Gas‐liquid bubbly microflows were formed through a microsieve device and used to determine the reaction characteristics by online observation of the volume change of microbubbles at the initial flow stage. In this condition, a mathematical model according to zwitterion mechanism has been developed to predict the reaction kinetics. The predicted kinetics of CO₂ absorption in the AMP aqueous solution verified the reliability of the method by comparing with literatures’ results. Furthermore, the reaction rate parameters for the reaction of CO₂ with AMP in both solutions were determined. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4358–4366, 2015     

Numerical investigation on CO2 absorbed in aqueous N‐methyldiethanolamine + piperazine

A multiphase and multicomponent mass transfer model of CO₂ absorbed in aqueous N‐methyldiethanolamine and piperazine (PZ) was built in the study. In the model, a simple method of mass transfer between phases was proposed. Besides, the hydrodynamics, thermodynamics, and complex reversible chemical reaction were considered simultaneously. The model was validated by comparing with the previous experimental data which showed that simulated results can represent the experimental data with reasonable accuracy. Based on the model, the effects of gas velocity, liquid load and CO₂ loading on the absorption rate, and enhancement factor were analyzed. Model results showed that the enhancement factor increased with a rising gas velocity while decreased with a rising liquid load or CO₂ loading. The change of enhancement factor with CO₂ loading was similar to that of equilibrium concentration of PZ which indicated that PZ was significant to the absorption process. Furthermore, the distributions of specie concentrations were discussed in detail. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2386–2393, 2017     

Gas solubility in long‐chain imidazolium‐based ionic liquids

The gas solubility in 1‐dodecyl‐3‐methylimidazolium [C₁₂MIM] based ionic liquids (ILs) was measured at temperatures (333.2, 353.2, and 373.2) K and pressures up to 60 bar for the first time. The popular UNIFAC‐Lei model was successfully extended to long‐chain imidazolium‐based IL and gas (CO₂, CO, and H₂) systems. The free volume theory was used to explain the gas solubility and selectivity in imidazolium‐based ILs by calculating the fractional free volume and free volume by the COSMO‐RS model. Furthermore, the excess enthalpy of gas‐IL system was concerned to provide new insights into temperature dependency of gas (CO₂, CO, and H₂) solubility in ILs. The experimental data, calculation, and theoretical analysis presented in this work are important in gas separations with ILs or supported ionic liquid membranes. © 2017 American Institute of Chemical Engineers AIChE J, 63: 1792–1798, 2017     

Thermodynamic validation of 1‐alkyl‐3‐methylimidazolium carboxylates as task‐specific ionic liquids for H2S absorption

Solubilities of H₂S in five 1‐alkyl‐3‐methylimidazolium carboxylates ionic liquids (ILs) have been measured at temperatures from 293.15 to 333.15 K and pressures up to 350 kPa. It is shown that these ILs have significantly larger absorption capacities for H₂S than those common ILs reported in the literature. The solubility is found to increase dramatically with the increasing alkalinity of the anions and slightly with the increasing length of the alkyl chains on the cations. It is further demonstrated that the absorption isotherms are typically nonideal. With the assumption of complex formation between H₂S and ILs, a reaction equilibrium thermodynamic model is developed to correlate the experimental solubilities. The model favors a reaction mechanism of AB₂ type that two IL molecules interact with one H₂S molecule. Thermodynamic parameters such as Henry's law constants, reaction equilibrium constants, and heat of complex formation are also calculated to evaluate the absorption process of H₂S in these ILs. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2227–2235, 2013     

Modelling Vapour − Liquid Equilibrium of CO2 in Aqueous N‐Methyldiethanolamine through the Simulated Annealing Algorithm

The modified Clegg‐Pitzer equation is used to correlate and predict the vapor‐liquid equilibrium of the CO₂‐MDEA‐H₂O system. Simulated annealing (SA), a computational stochastic technique for finding near global minimum solutions to optimization problems, has been used for parameter estimation in the model to predict VLE of CO₂ in aqueous MDEA solution. The solubility of CO₂ in aqueous solutions of 23.8 wt % and 30.0 wt % of N‐methyldiethanolamine (MDEA) has been measured over the temperature range of 303‐323 K and CO₂ partial pressure range of 1 to 100 kPa. The model predicted equilibria have been found to be in good agreement with the experimental results of VLE measurement of this work as well as those in the open literature. In this work, the SA technique has been used as an alternative to the traditional Levenberg‐Marquardt (LM) technique, to predict the VLE data accurately.     

Experimental study and thermodynamic model for respective solubilities of CO2 and ethanol for CO2‐ethanol‐polystyrene ternary system at elevated pressure and temperature

Foamed non‐Fickian diffusion (FNFD) model for a ternary system was proposed for the first time to regress the desorption data obtained by the gravimetric method. Results showed that FNFD model could accurately describe the diffusion behavior of CO₂ and ethanol out of foamed polystyrene (PS) and well predict total solubilities of CO₂ and ethanol in foamed PS. Meanwhile, Sanchez–Lacombe equation of state (S–L EoS) was adopted to calculate the respective solubilities (solubility of CO₂ in PS or solubility of ethanol in PS) and total solubilities of CO₂ and ethanol in PS for CO₂‐ethanol‐PS ternary system. Results showed that the total solubility of CO₂ and ethanol obtained from S–L EoS agreed well with values obtained by FNFD model. Furthermore, the respective and total solubilities of CO₂ and ethanol at 313.15, 338.15, and 343.15 K were calculated by S–L EoS. Results indicated that in the dissolving process, ethanol would be accelerated by CO₂ to dissolve into PS, and ethanol would compete with CO₂ to dissolve into PS, simultaneously. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46281.     

Supercritical antisolvent micronisation of synthetic all‐trans‐β‐carotene with tetrahydrofuran as solvent and carbon dioxide as antisolvent

BACKGROUND: Supercritical antisolvent (SAS) micronisation of synthetic trans ‐β‐carotene was studied using tetrahydrofuran (THF) as solvent and supercritical carbon dioxide (CO₂) as antisolvent, with the objective of increasing its bioavailability and facilitating its dispersion in oil and emulsion formulations as a result of its smaller particle size. The micronised powder was analysed by scanning electron microscopy and high‐performance liquid chromatography. Micronisation experiments were performed in order to evaluate the effects of temperature (308.15–333.15 K), pressure (6.5–13 MPa) and concentration of the liquid solution (6–9 g L^?1). The effect of the supercritical CO₂/THF flow ratio in the range between 4 and 44 (on a mass basis) was also analysed. Determinations of equilibrium concentrations of β‐carotene in the CO₂/THF mixture were also performed. RESULTS: The particle size obtained ranged from 1 to 500 µm, with mean particle diameters around 100 µm. Three types of morphology were found in the precipitated powder: crystalline with superficial pores and leaf‐like appearance; crystalline with regular shapes and blade‐like edges; and crystalline without superficial pores and leaf‐like apearance. The Peng–Robinson equation of state was used to calculate the density of the CO₂/THF binary mixture, and the solubility of β‐carotene in this mixture was correlated with its density. CONCLUSION: The use of the SAS technique to micronise β‐carotene proved to be efficient, and the absence of degradation in the micronised powder allows the industrial application of this technique. Copyright © 2008 Society of Chemical Industry     

Study of solubility and swelling ratio in polymer‐CO2 systems using the PC‐SAFT equation of state

We use the PC‐SAFT equation of state to model the solubility of CO₂ in various homopolymers. We also model the swelling ratio of the PP (polypropylene)‐CO₂ mixture using PC‐SAFT and then compare the results with Sanchez‐Lacombe (S‐L) and Simha‐Somcynsky (S‐S) equations. The results show that PC‐SAFT can describe the solubility of CO₂ in polymers very well. We compare two sets of parameters in the PC‐SAFT equation, Gross et al.'s and Chen et al.'s. As for the swelling ratio, PC‐SAFT using Chen et al. parameters is better than S‐L equation, which is commonly used by early researchers in studying the solubility of CO₂ in polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44804.     

Hybrid neural network for prediction of CO<Subscript>2</Subscript> solubility in monoethanolamine and diethanolamine solutions

The solubility of CO₂ in single monoethanolamine (MEA) and diethanolamine (DEA) solutions was predicted by a model developed based on the Kent-Eisenberg model in combination with a neural network. The combination forms a hybrid neural network (HNN) model. Activation functions used in this work were purelin, logsig and tansig. After training, testing and validation utilizing different numbers of hidden nodes, it was found that a neural network with a 3-15-1 configuration provided the best model to predict the deviation value of the loading input. The accuracy of data predicted by the HNN model was determined over a wide range of temperatures (0 to 120 °C), equilibrium CO₂ partial pressures (0.01 to 6,895 kPa) and solution concentrations (0.5 to 5.0M). The HNN model could be used to accurately predict CO₂ solubility in alkanolamine solutions since the predicted CO₂ loading values from the model were in good agreement with experimental data.     

Caged CO2 for the Direct Observation of CO2‐Consuming Reactions

CO₂‐consuming reactions, in particular carboxylations, play important roles in technical processes and in nature. Their kinetic behavior and the reaction mechanisms of carboxylating enzymes are difficult to study because CO₂ is inconvenient to handle as a gas, exists in equilibrium with bicarbonate in aqueous solution, and typically yields products that show no significant spectroscopic differences from the reactants in the UV/Vis range. Here we demonstrate the utility of 3‐nitrophenylacetic acid and related compounds (caged CO₂) in conjunction with infrared spectroscopy as widely applicable tools for the investigation of such reactions, permitting convenient measurement of the kinetics of CO₂ consumption. The use of isotopically labeled caged CO₂ provides a tool for the assignment of infrared absorption bands, thus aiding insight into reaction intermediates and mechanisms.     

Comprehensive reaction kinetics model of CO2 absorption into 1-dimethylamino-2-propanol solution

In the present work, the kinetics of the reactive absorption of CO₂ in 1-dimethylamino-2-propanol (1DMA2P) solution were experimentally measured using a laminar jet absorber over a temperature range of 298–313 K, 1DMA2P concentration range of 0.5–2.0 mol/L, and CO₂ loading range of 0–0.06 mol CO₂/mol amine. The measured kinetics data were then used to develop a comprehensive numerical kinetics model using a FEM-based COMSOL software. The reaction rate model of the CO₂ absorption into 1DMA2P solution were then validated by comparing model rates with the experimental rates. An excellent agreement of model data with experimental data was achieved with an absolute average deviation (AAD) of 6.5%. In addition, vapor–liquid equilibrium plots of all ions in the 1DMA2P-H₂O-CO₂ system were also developed. Further, this work has provided an effective criterion for evaluating CO₂ absorption, that can be used for both the conventional amines and alternative amines for the purpose of providing guidelines or information on how to effectively screen solvents.     

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