Prediction of equilibrium solubility of CO2 in aqueous alkanolamines using differential evolution algorithm

The design of sour‐gas treating processes with alkanolamine solvents requires knowledge of the vapour–liquid equilibrium (VLE) of the aqueous acid gas–alkanolamine systems. Representation of the experimental data with a thermodynamically rigorous model is required, so that one can systematically correlate and predict the VLEs of these systems. The modified Clegg–Pitzer equations have been used to correlate and predict the VLE of CO₂ in the aqueous N‐methyldiethanolamine (MDEA) and 2‐amino‐2‐methyl‐1‐propanol (AMP) systems. Differential evolution (DE), an evolutionary computational technique, has been used for parameter estimation of the developed VLE model in an effort to predict the VLE of CO₂ in aqueous MDEA and AMP solutions with a comparable accuracy to that by using the non‐traditional simulated annealing (SA) and deterministic technique like Levenberg–Marquardt (LM), if not better. In this work, the DE/rand‐best/1/bin strategy has been used for finding near global minimum solutions to the multivariable optimization problem as a part of the numerical solution of the developed model.     

Rapid Prediction of CO2 Solubility in Aqueous Solutions of DEA and MDEA

In the present work, a simple‐to‐use correlation is developed to predict the solubility of CO₂ in aqueous solutions of DEA and MDEA as a function of the reduced partial pressure and temperature. Using the interaction parameters generated, the model is applied to correlate the CO₂ loading in different amine solutions. The results from the proposed correlation have been compared with the reported experimental data and it was found that there is a good agreement between the observed data and the model predictions over a wide range of operating conditions in aqueous solutions of both diethanolamine (DEA) and methyldiethanolamine (MDEA).     

The development of kinetics model for CO2 absorption into tertiary amines containing carbonic anhydrase

CO₂ absorption into aqueous solutions of two tertiary alkanolamines, namely, MDEA and DMEA with and without carbonic anhydrase (CA) was investigated with the use of the stopped‐flow technique at temperatures in the range of 293–313 K, CA concentration varying from 0 to 100 g/m³ in aqueous MDEA solution with the amine concentration ranging from 0.1 to 0.5 kmol/m³, and CA concentration varying from 0 to 40 g/m³ in aqueous DMEA solution with the amine concentration ranging from 0.05 to 0.25 kmol/m³. The results show that the pseudofirst‐order reaction rate (k_{0, amine}; s^?1) is significantly enhanced in the presence of CA as compared with that without CA. The enhanced values of the kinetic constant in the presence of CA has been calculated and a new kinetics model for reaction of CO₂ absorption into aqueous tertiary alkanolamine solutions catalyzed by CA has been established and used to make comparisons of experimental and calculated pseudo first‐order reaction rate constant (k_{0, with CA}) in CO₂‐MDEA‐H₂O and CO₂‐DMEA‐H₂O solutions. The AADs were 15.21 and 15.17%, respectively. The effect of pKa on the CA activities has also been studied by comparison of CA activities in different tertiary amine solutions, namely, TEA, MDEA, DMEA, and DEEA. The pKa trend for amines were: DEEA > DMEA > MDEA > TEA. In contrast, the catalyst enhancement in amines was in the order: TEA> MDEA> DMEA> DEEA. Therefore, it can be seen that the catalyst enhancement in the amines decreased with their increasing pKa values. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Absorption of carbon dioxide in piperazine activated concentrated aqueous 2-amino-2-methyl-1-propanol solvent

In this work new experimental data on the rate of absorption of CO₂ into piperazine (PZ) activated concentrated aqueous solutions of 2-amino-2-methyl-1-propanol (AMP) over the temperature range 303–323 K are presented. The absorption experiments have been carried out in a wetted wall contactor over CO₂ partial pressure range of 5–15 kPa. PZ is used as a rate activator with a concentration ranging from 2 to 8 wt% keeping the total amine concentration in the solution at 40 wt%. The physical properties such as density and viscosity of concentrated aqueous AMP+PZ, as well as physical solubility of CO₂ in concentrated aqueous AMP+PZ, are also measured. New experimental data on vapor liquid equilibrium (VLE) of CO₂ in these concentrated aqueous solutions of AMP+PZ in the temperature range of 303–323 K have also been presented. The VLE measurements are carried out in an equilibrium cell in CO₂ pressure range of 0.1–140 kPa. A thermodynamic model based on electrolyte non-random two-liquid (eNRTL) theory is used to represent the VLE of CO₂ in aqueous AMP+PZ. Liquid phase speciations are estimated considering the nonideality of concentrated solutions of the amines and the calculated activity coefficients by eNRTL model. The CO₂ absorption in the aqueous amine solutions is described by a combined mass transfer-reaction kinetics model developed according to Higbie's penetration theory. The model predictions have been found to be in good agreement with the experimental results of the rates of absorptions of CO₂ into aqueous AMP+PZ.     

Analysis of the heat of reaction and regeneration in alkanolamine-CO<Subscript>2</Subscript> system

The estimation of regeneration heat of absorbent is important because it is a key factor that has an effect on the process efficiency. In this study, thermal stability and regeneration heat of aqueous amine solutions such as monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), N-methyldiethanolamine (MDEA), and 1,8-diamino-pmenthane (KIER-C3) were investigated by using TGA-DSC analysis. The thermal characteristics of the fresh and CO₂ rich amine solutions were estimated. The CO₂ rich amine solutions were obtained by VLE experiments at T=40 °C. The regeneration heat of aqueous MEA solution was 76.991–66.707 kJ/mol-CO₂, which is similar to heat of absorption. The reproducibility of the results was obtained. The regeneration heat of aqueous KIER-C3 20 wt% solution (1.68 M) was lower than that of aqueous MEA 30 wt% solution (4.91 M). Therefore, the KIER-C3 can be used as an effective absorbent for acid gas removal.     

Absorption of co2 into aqueous tertiary amine/mea solutions

Absorption rates for CO₂ into aqueous solutions of TEA, MDEA and blends of MEA with MDEA and TEA were measured in a stirred cell by a method similar to that used by Laddha and Danckwerts (1981). Second order rate constants for CO₂-TEA and CO₂-MDEA were obtained from the single amine data for temperatures in the range of 25-60°C. A modified pseudo first order model based on the film theory is used to predict the rate of absorption of CO₂ into mixed amine solutions. This model accounts for the variation of amine concentration in the film and assumes a shuttle mechanism for rate enhancement. Bulk liquid concentrations of the various species present are obtained from a simplified thermodynamic model. The model predicts absorption rates that are in agreement with experimental measurements.     

A study on the reaction between CO2 and alkanolamines in aqueous solutions

Literature data on the rates of reaction between CO₂ and alkanolamines (MEA, DEA, DIPA, TEA and MDEA) in aqueous solution are discussed. These data induced us to carry out absorption experiments of CO₂ into aqueous DEA, DIPA, TEA and MDEA solutions from which the respective rate constants were derived. The experimental technique was similar to that used by Laddha and Danckwerts[30].The results for DEA and DIPA were analysed by means of a zwitterion-mechanism which was derived from the mechanism originally proposed by Danckwerts[16The reaction rate of CO₂ with aqueous TEA and MDEA solutions shows a significant base catalysis effect which is also reported by Donaldson and Nguy     

A study of species formation of aqueous tertiary and hindered amines using quantitative 13C NMR spectroscopy

Tertiary and sterically hindered amines have been chosen as potential candidate absorbents, recommended for their high carbon dioxide (CO₂) loading capacity and easy regeneration. In this study, the CO₂ absorption characteristics of these amines were studied using ¹H nuclear magnetic resonance (NMR) and quantitative ¹³C NMR. The equilibrium experiments were conducted in the vapor–liquid equilibrium (VLE) apparatus, which was used to measure the CO₂ absorption capacities and relative absorption rates of aqueous solutions of methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP). The CO₂ loaded absorbents were used for NMR measurement to determine the distribution of species formed in the absorbents. This process confirmed the reaction mechanisms of the individual absorbents in relation to CO₂ absorption capacities.     

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     

Methyl-diethanolamine degradation — Mechanism and kinetics

Methyl-diethanolamine (MDEA) degradation reactions between aqueous solutions of MDEA and CO₂ have been carried out in a 600 mL stirred autoclave under the following conditions: initial MDEA solution concentration 20-50 mass%, solution temperature 100-200°C, CO₂ partial pressure 1.38-4.24 MPa. It was found that MDEA degrades quite rapidly (although more slowly than diethanolamine under comparable conditions) at elevated temperatures and CO₂ partial pressures. Degradation products are identified by gas chromatography and mass spectrometry (GC/MS). An MDEA degradation reaction mechanism and kinetic model predicting concentration changes is proposed and verified.     

Kinetics of carbon dioxide absorption and desorption in aqueous alkanolamine solutions using a novel hemispherical contactor—II: Experimental results and parameter estimation

In Part 1 of this paper, detailed design of the hemispherical apparatus and a rigorous mathematical model applied to CO₂ absorption and desorption in and from aqueous alkanolamine solutions was presented with some preliminary results. This part of the paper provides detailed results on CO₂-amine kinetics under absorption and desorption conditions and present new estimates of the kinetic parameter for aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), methyl-diethanolamine (MDEA) and 2-amino-2-methyl-1-propanol (AMP). The absorption experiments were conducted at near atmospheric pressure with pure humidified CO₂ at 293-323 K using initially unloaded solutions. The desorption experiments were performed at 333-383 K for CO₂ loadings between 0.02 to 0.7 mol of CO₂ per mole of amine using humidified nitrogen gas as a stripping medium at total system pressure ranging from 110 to 205 kPa.The new rigorous mathematical model discussed in Part 1 was used in conjunction with a non-linear regression technique to estimate the kinetic parameters. In all cases, the new model predicts the experimental results well. Also, the new results clearly demonstrate that the theory of absorption with reversible chemical reaction could be used to predict desorption rates. The zwitterion mechanism adequately describes the reactions between CO₂ and carbamate forming amines such as MEA, DEA and AMP. The reactions between CO₂ and aqueous MDEA solutions are best described by a base-catalyzed hydration reaction mechanism. The kinetic data obtained show that desorption experiments could be used to determine both forward and backward rate constants accurately. The absorption experiments, on the other hand, could only be used to determine forward rate constants. It was found that at all operating conditions used in this study, the kinetic parameters for MEA, DEA and AMP obtained using absorption data could not be extrapolated to predict desorption rates. However, for MDEA, these data could be used successfully to obtain reasonably good predictions of desorption rates.     

Influence of polyethylene oxide on absorption of carbon dioxide into aqueous <Emphasis Type="Italic">N</Emphasis>-methyldiethanolamine solution

Carbon dioxide was absorbed into aqueous polyethylene oxide (PEO) solution containing N-methyldiethanolamine (MDEA) in a flat-stirred vessel to investigate the effect of non-Newtonian rheological behavior of PEO on the chemical absorption rate of CO₂, where the reaction between CO₂ and MDEA was assumed to be a first-order reaction with respect to the concentration of CO₂ and MDEA, respectively. A unified correlation equation containing the Deborah number, which reflects the viscoelastic properties of a non-Newtonian liquid, was used to obtain the volumetric liquid-side mass transfer coefficient of carbon dioxide in aqueous PEO solution. The elastic properties of PEO accelerated the absorption rate of CO₂ compared with that of a Newtonian liquid based on the same values of viscosity.     

A study on the reaction between CO2 and alkanolamines in aqueous solutions

Literature data on the rates of reaction between CO₂ and alkanolamines (MEA, DEA, DIPA, TEA and MDEA) in aqueous solution are discussed. These data induced us to carry out absorption experiments of CO₂ into aqueous DEA, DIPA, TEA and MDEA solutions from which the respective rate constantsThe results for DEA and DIPA were analysed by means of a zwitterion-mechanism which was derived from the mechanism originally proposed by Danckwerts [1The reaction rate of CO₂ with aqueous TEA and MDEA solutions shows a significant base catalysis effect which is also reported by Donaldson and Nguy     

Absorption of carbon dioxide in aqueous MDEA solution coupling dust suppression under atomization

ABSTRACT

Large amounts of CO₂ and dust particles coming from power plant flue need to be captured and removed before flue is discharged into the air. In present work, absorption of carbon dioxide in aqueous N-methylidiethanolamine (MDEA) solution coupling dust suppression has been studied in an atomization absorption column, with MDEA concentrations ranging from 0.1 to 0.5mol/L, and with atomization frequencies ranging from 50 to 80 HZ. The obtained experimental results show that absorption rate of CO₂ in aqueous MDEA solution can be enhanced when the absorption process couples a dust suppression one under the condition of atomization. The reason for it is attributed to the adsorption of droplets on the solid particles which restrains the amount of entrainment and makes more droplets contact with gas so as to increase effective mass transfer area, thus resulting in the increase of CO₂ absorption rate. The range of obtained enhancement factor is from 1.1 to 1.7. Mass transfer enhancement factor increases with the increase of MDEA concentration and atomization frequency at a certain range. Effective mass transfer areas and entrainment ratios suppressed have been calculated based on theoretic research. The results calculated agree with our experimental phenomena, and support the enhancement mass transfer mechanism proposed.     

An experimental/computational study of steric hindrance effects on CO2 absorption in (non)aqueous amine solutions

The reaction kinetics and molecular mechanisms of CO₂ absorption using nonaqueous and aqueous monoethanolamine (MEA)/methyldiethanolamine (MDEA)/2-amino-2-methy-1-propanol (AMP) solutions were analyzed by the stopped-flow technique and ab initio molecular dynamics (AIMD) simulations. Pseudo first-order rate constants (k₀) of reactions between CO₂ and amines were measured. A kinetic model was proposed to correlate the k₀ to the amine concentration, and was proved to perform well for predicting the relationship between k₀ and the amine concentration. The experimental results showed that AMP/MDEA only took part in the deprotonation of MEA-zwitterion in nonaqueous MEA + AMP/MEA + MDEA solutions. In aqueous solutions, AMP can also react with CO₂ through base-catalyzed hydration mechanism beside the zwitterion mechanism. Molecular mechanisms of CO₂ absorption were also explored by AIMD simulations coupled with metadynamics sampling. The predicted free-energy barriers of key elementary reactions verified the kinetic model and demonstrated the different molecular mechanisms for the reaction between CO₂ and AMP.     

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     

CO2 Absorption into Aqueous Solutions of a Polyamine (PZEA), a Sterically Hindered Amine (AMP), and their Blends

Among numerous techniques existing for reducing CO₂ emissions, CO₂ capture by absorption in aqueous alkanolamine solutions was specifically studied in this work. For the choice of the adequate amine solution, two major criteria must be taken into account: absorption performances (higher with primary and secondary amines) and energy costs for solvent regeneration (more interesting with tertiary and sterically hindered amines). The different types of amines can also be mixed in order to combine the specific advantages of each type of amines, an activation phenomenon being observed. Aqueous solutions of (piperazinyl‐1)‐2‐ethylamine (PZEA, a polyamine known as absorption activator) and 1‐amino‐2‐propanol (AMP, a sterically hindered amine), pure or mixed with other amines, are experimentally compared with respect to CO₂ removal performances by means of absorption test runs achieved in a special gas‐liquid contactor at 25 °C. The positive impact of addition of PZEA to monoethanolamine (MEA), N‐methyldiethanolamine (MDEA), and AMP solutions was clearly highlighted. The absorption performances have also been satisfactorily simulated with coherent physicochemical data.     

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.     

Enhancement of kinetic rates of CO2 in aqueous solutions of piperazine and methyldiethanolamine with addition of sulfolane

Measurements of kinetics rates of CO₂ in aqueous solutions of methyldiethanolamine (MDEA), piperazine (PZ), and mixtures of (MDEA + PZ), (PZ + sulfolane) and (MDEA + sulfolane) were carried out using the stopped flow technique, and reported in terms of pseudo-first-order rate constants (k₀). When possible, the second-order reaction rate constants (k₂) were regressed from the data. Experiments were performed over new concentration ranges of (10–60), (200–800), (200–800, 10–40), (10–40, 10–200), and (200–800, 10–200) mol/m³ for the above-mentioned five systems, respectively, and at temperatures varying from (298.15–313.15 K). When sulfolane was added to the amine solution, pseudo-first-order rate constants in the mixed solvents were higher than in aqueous MDEA and PZ solutions at all temperatures. The kinetic rates were highest at 298.15 K and decreased at higher temperatures for aqueous (MDEA + sulfolane) solutions but increased with temperature for aqueous (PZ + sulfolane) systems. Reaction orders for both PZ and MDEA were practically one at all sulfolane concentrations and temperatures. The base catalysis mechanism was used to regress very well data for aqueous MDEA and (MDEA + sulfolane + water) and the termolecular mechanism was used for (PZ + sulfolane + water) system. Both the zwitterion and termolecular models were able to fit the experimental data for the aqueous PZ system well. Finally, the termolecular and a hybrid model based on the combination of the Zwitterion and base catalysis mechanisms were able to successfully correlate the experimental data for the mixed aqueous (MDEA + PZ) systems.     

Protic ionic liquid as excellent shuttle of MDEA for fast capture of CO2

A cheap protic ionic liquid (PIL), 3‐(Dimethylamino)‐1‐propylamine acetate (abbreviated as [DMAPAH][Ac]), is investigated in this work as the activator of N‐methyldiethanolamine (MDEA) for fast capture of CO₂. The PIL‐activated MDEA solutions show excellent performance in absorption rate and capacity (≥2.5 mol·kg^?1). A novel absorption mechanism is proposed to account for the phenomenon, where the shuttling role of the PIL is described in detail. Additionally, the enthalpy change ΔH_SOL (?45 to ?52 kJ·mol^?1), the turnover number of the PIL and the regeneration efficiency (>92%) are also measured. All these data show that the PIL‐mediated MDEA solutions may be used as a kind of promising absorbents for fast capture of CO₂. © 2017 American Institute of Chemical Engineers AIChE J, 63: 209–219, 2018