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Investigation of CO2 and ethylethanolamine reaction kinetics in aqueous solutions using the stopped-flow technique
Abstract
Kinetics of the reaction of CO2 and ethylethanolamine (EMEA) in aqueous solutions has been studied using the stopped-flow technique with conductivity detection. Measurements were performed at 288 K, 293 K, 298 K, and 303 K. Amine concentration ranged from 10 mol m−3 to 37.5 mol m−3. The termolecular mechanism was applied to interpret the kinetic data. In this mechanism, carbamate formation occurs in a single-step reaction without the formation of a zwitterion intermediate. An original method of analyzing the experimental data was proposed allowing the derivation of pseudo second order rate constants from the measured kinetic traces. Based on these values, the third order rate constants
Supplementary resource (1)
... Chemical absorption using amine-based solvents is the most common and proven post combustion method to capture CO 2 from gas streams (Kumar et al., 2014). Therefore, aqueous solutions of alkanolamines, such as monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA) are frequently used as solvents (Kierzkowska-Pawlak et al., 2013;Gardarsdóttir et al., 2015;Alexia Finotello et al., 2008). Amine process consists of continuous circulation of an alkanolamine solution between the absorption and desorption units. ...
... Each experimental set was repeated at least 10 times to obtain consistent pseudo-first-order rate constants (k o ) at each temperature for all concentrations. To satisfy the pseudo-first-order conditions, amine and alcohol concentrations were always much in excess to that of CO 2 (usually the molar ratio was about 20:1) (Kierzkowska-Pawlak et al., 2013). The main advantages of the stopped-flow technique are quick experiment run (˜ 0.05 s), small amount of solvent consumption for each experimental run (∼0.1 mL),easy operation and no effect of mass transfer resistances (Liu et al., 2014). ...
In the scope of this work, new carbon dioxide binding organic liquids (CO2BOLs) were developed and kinetic parameters in terms of pseudo first-order rate constants for homogenous reaction between CO2 and CO2BOLs in 1-hexanol were obtained by using stopped-flow method with conductivity detection. As an amidine DBN (1,5-diazabicyclo[4.3.0]non-5-ene) and as a guanidine TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene) and BTMG (2-tert-butyl-1,1,3,3-tetramethylguanidine) were investigated. Experiments were performed by varying organic base (amidine or guanidine) weight percentage in 1-hexanol medium for a temperature range of 288–308 K. A modified termolecular reaction mechanism was used to analyse the experimental kinetic data. In addition, quantum chemical calculations by using B3LYP, MP2 and CCSD methods were performed to reveal the structural and energetic details of the single step termolecular reaction mechanism. Experimental and theoretical activation energies for these novel carbon dioxide capturing organic liquids were also unveiled.
... Dla bardzo małych stężeń aminy (a takie stosowano w pracy w przypadku EMEA) udział członu pierwszego w równaniu (4) jest bardzo mały [2]. W takim przypadku sumaryczna szybkość reakcji wyraża się wzorem: ...
... gdzie k OV jest stałą szybkości odpowiadającą reakcji pseudo – pierwszego rzędu [2] i bezpośrednio wynika z zależności (4). ...
Jedną z podstawowych metod usuwania CO2 z gazów odlotowych na skalę przemysłową jest absorpcja tego gazu w roztworach amin. Głównie wykorzystywane są aminy pierwszorzędowe (np. monoetanoloamina), rzadziej mniej reaktywne aminy trzeciorzędowe takie jak metylodietanoloamina, które charakteryzują się większą pojemnością absorpcyjną. Dodatek niewielkich ilości innych amin, tzw. aktywatorów do amin trzeciorzędowych pozwala znacznie przyspieszyć proces absorpcji CO2 przy zastosowaniu zalet rozpuszczalnika bazowego. Z tego względu mieszaniny amin mogą być konkurencyjne w stosunku do amin pierwszorzędowych. Badania różnych typów amin pod kątem potencjalnego zastosowania w usuwaniu CO2 ze spalin prowadzone są w ramach wielu europejskich projektów badawczych. Poszukuje się rozpuszczalników zapewniających dużą szybkość absorpcji i desorpcji CO2, wysoką pojemność absorpcyjną i niższe zużycie energii podczas etapu regeneracji niż stosowane do tej pory absorbenty.
W pracy przeprowadzono badania kinetyczne absorpcji CO2 w wodnych roztworach etyloetanoloaminy (EMEA) oraz 2-((2-aminoetylo)amino)etanolu (AEEA), które mogą być dobrymi aktywatorami amin trzeciorzędowych. Aminy te z punktu widzenia kinetyki reakcji z CO2 są bardzo słabo przebadane w literaturze. Ważną zaletą amin wybranych do badań jest ich odporność na działanie czynników utleniających i wysokiej temperatury stosowanej w etapie regeneracji rozpuszczalnika. Struktura cząsteczkowa aminy oraz parametry układu reakcyjnego, w szczególności stężenie aminy mają istotny wpływ na mechanizm i kinetykę złożonych reakcji chemicznych zachodzących w układzie. Badania kinetyczne przeprowadzono zarówno w układzie homogenicznym jak i heterogenicznym. W układzie homogenicznym pomiary prowadzono przy wykorzystaniu aparatury do konduktometrycznych badań kinetyki szybkich reakcji chemicznych techniką zatrzymanego przepływu. Badania kinetyczne w warunkach heterogenicznych wykonano w reaktorze zbiornikowym z mieszadłem, z płaską powierzchnią wymiany masy.
... The most accepted reaction mechanisms are schematized in Figure 1. In a dry condition, only primary and secondary amines can react directly with CO 2 (Figure 1a and b) generating a carbamate anion (Yang et al., 2017;Kierzkowska-Pawlak et al., 2013). As for the tertiary amines, they can react with CO 2 but only in presence of water forming a bicarbonate anion (Figure 1e) (Versteeg and van Swaaij, 1988). ...
One of the most promising technologies to capture CO2 molecules directly from ambient air involves a polyethylenimine (PEI) layer deposited on a microporous solid support. The CO2 adsorption is achieved through a chemisorption process in which CO2 molecules react with amine groups of the polymer. This process was widely investigated from an experimental front point of view and accordingly once the reaction occurred, the further diffusion of CO2 molecules within this layer is heavily hindered. The aim of this study is to elucidate this phenomenon from a nanoscale perspective through molecular dynamics simulations. Starting from a branched unreacted PEI chain and a branched reacted PEI chain, three different systems were generated by arranging these two compounds in different configurations. Simulation results highlighted that the CO2 molecules are more prone to interact with the branched reacted PEI chains because of the higher electrostatic attraction. As a consequence, their further diffusion towards the unreacted region, where Coulombic interactions are weaker, is strongly hindered and it remains unexploited.
... Temperature was controlled by Lauda water bath model Alpha RA8 within ± 0.1 K. In all cases, the change of the amine concentration within the run time was very small and can be considered negligible for very low CO2 loading (such as our case) as was demonstrated by Kierzkowska-Pawlak et al [11]. The reaction was monitored by measuring the conductivity, 'Y', change as function of time as described by Knipe et al. [12]. ...
Removal of carbon dioxide (CO2) from natural gas streams is mandatory to avoid pipeline corrosion, increase the heating value of the gas and reduce the gas volume in case of liquefied natural gas (LNG). The use of N-Methyldiethanolamine (MDEA) solution combined with other rate promoters such as Piperazine (PZ) is a common practice in Gas treatment technology. In this work, the use of Aminobutanol (AB) mixed with MDEA for the removal of (CO2) from natural gas streams is presented. The reaction kinetics of (CO2) with mixtures of MDEA and AB was investigated using stopped flow technique. The experiments were performed over a temperature range of 293 to 313 K and solution concentration of 0.5 and 1 moles/l in different MDEA/AB proportions. Obtained kinetics data were interpreted using zwitterion mechanisms for the primary amine AB. The individual rate constants of the participating reactions were regressed and their corresponding activation energies were estimated.
... The most common and proven approach to capture CO 2 from gas streams is chemical absorption (Kumar et al. 2014). Therefore, aqueous solutions of alkanolamines, such as monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA) are widely used solvents for the removal of acid gas impurities such as CO 2 and H 2 S (Alexia Finotello et al. 2008;Kierzkowska-Pawlak et al. 2013;Garđarsd ottir et al. 2015). Solvents for such absorption processes absorb CO 2 from gas streams efficiently at low temperatures by an exothermic reaction resulting either carbamate or bicarbonate salts. ...
Carbon dioxide emissions from thermal power plants, hydrogen, and cement factories became one of the most important global concerns. Therefore, development of new sorbent materials and capture technologies to efficiently and economically remove CO2 gained importance. In the scope of this work, novel carbon dioxide binding organic solvents (CO2BOLs) were developed by blending an amidine (or a guanidine) and a 1-hexanol at various concentrations. As an amidine and a guanidine, DBN (1,5-Diazabicyclo[4.3.0]non-5-ene) and TBD (1,5,7-Triazabicyclo[4.4.0]dec-5-ene) respectively were investigated. Experiments were carried out by varying organic base (amidine or guanidine) percentage in 1-hexanol medium and “intrinsic” reaction rates were measured in “stopped flow” equipment for a temperature range of 288–308 K. It was found that the kinetic data could be fitted satisfactorily to a termolecular reaction mechanism and the activation energies for carbon dioxide capturing organic liquids were also obtained.
... The most common and proven approach to capture CO 2 from gas streams is chemical absorption (Kumar, Cho et al., 2014). Therefore, aqueous solutions of alkanolamines, such as monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA) are widely used solvents for the removal of acid gas impurities such as CO 2 and H 2 S (Alexia , Kierzkowska-Pawlak, Siemieniec et al., 2013, Garđarsdóttir, Normann et al., 2015. Solvents for such absorption processes absorb CO 2 from gas streams efficiently at low temperatures by an exothermic reaction resulting either carbamate or bicarbonate salts. ...
Carbon dioxide emission from thermal power plants, hydrogen, ethylene oxide and cement factories became one of the most important global concerns. Therefore, development of new sorbent materials and CO2 capture technologies gained importance. CO2BOLs are the mixture of strong amidine or guanidine bases and n-alcohols. The primary advantages of these systems are high CO2 loading capacities, and a less energy intensive solvent regeneration as compared to aqueous alkanolamine solutions.
In order to evaluate the potential integration of these switchable solvents to industrial carbon dioxide capture applications, the reaction kinetics between CO2BOLs and carbon dioxide were examined. In this work, as an amidine; DBN (1,5-Diazabicyclo[4.3.0]non-5-ene) and as a guanidine; TBD (1,5,7-Triazabicyclo[4.4.0]dec-5-ene) were used in 1-hexanol medium. Intrinsic reaction rates were measured in “stopped flow” equipment for a temperature range of 298 K- 308 K. Experiments were carried out by varying organic base (amidine or guanidine) percentage in a 1-hexanol medium from 5.0 wt% to 20.0 wt%. The observed pseudo-first-order-rate constant (ko) is given by Eq.(1).
r=ko[CO2](1)
It was observed that the kinetic data were fitted well to the termolecular reaction mechanism. To further investigate this dependency, we determine the reaction order according to power law kinetics; i.e. by plotting the natural logarithm of reaction rate constants vs. TBD concentration. The reaction order plot for the TBD/1-hexanol system is shown in Fig. 1. The observed ko values that were obtained experimentally were correlated using the termolecular mechanism to determine the forward reaction rate constant k [m3/ kmol.s]. The reaction rate constants versus TBD concentration were plotted according to Eq. (1). As shown in the Fig. 2, the increase in rate constants with increasing temperature and concentration confirms the direct dependency of the rate constant on these experimental parameters.
Fig.1. Reaction order plot fot TBD/1-hexanol system at various temperatures.
Fig.2. Pseudo-first order rate constant as a function of TBD concentration at various temperatures.
Furthermore, to determine the activation energies, experiments were conducted at four different concentrations and three different temperatures. The Arrhenius diagrams were plotted for both solvent systems and activation energies were calculated by evaluating the Arrhenius Equation.
The kinetics of catalyst-aided desorption of CO 2 from CO 2 -loaded MEA (5 mol/dm ³ ) and blended MEA-MDEA (7 mol/dm ³ ) solutions at CO 2 loadings from 0.3 to 0.5 mol CO 2 /mol amine were studied over a Lewis acid catalyst (γ-Al 2 O 3 ) and a Brønsted acid catalyst (H-ZSM-5) in an absorber–desorber CO 2 capture bench-scale plant (columns of 0.051 m ID and height of 1.067 m) at temperatures of 348–368 K. The results showed that the conversion increases relative to no catalyst for MEA were 55 and 74% while for MEA-MDEA, they were 65 and 85.2% with γ-Al 2 O 3 and H-ZSM-5, respectively. A comprehensive mechanistic LHHW rate model was developed for the catalytic CO 2 desorption process.
Carbon capture and management plays an important role in the development of new technologies to mitigate anthropogenic global warming. In this work, for the first time, the kinetics of CO2 with aminobutanol (AB) using stopped flow method are presented. The temperature changed from 293 to 313 K for a total amine concentration up to 0.3 mole/l. The kinetics data were analyzed using both zwitterion and termolecular reaction mechanisms with a preference to the zwitterion mechanism. AB was found to react with CO2 (aq) with k2 (M−1 s−1)= 2.93×109exp(-4029.9/T(K)) with an estimated activation energy of 33.51 kJ/mole. Compared to other popular amines, CO2 reaction with aminobutanol has faster kinetics than that of CO2 with diethanolamine (DEA) and 2-amino-2-methyl-1-propanol (AMP) but slower than that with monoethanolamine (MEA). The Brønsted relationship between the rate constant (k2) and pKa values was found to predict well the rate constant with an average absolute deviation (AAD) of 6.1%.
The reaction rates of CO2 with an innovative CO2-capturing organic solvent (CO2COS), consisting of blends of 2-tert-butyl-1,1,3,3-tetramethylguanidine (BTMG) and 1-propanol, were obtained as function of BTMG concentration and temperature. A stopped-flow apparatus with conductivity detection was used. The reaction was modeled by means of a modified termolecular reaction mechanism which resulted in a second-order rate constant, and activation energies were calculated for a defined temperature range. Quantum chemical calculations at the B3LYP/6-31G(d) level also produced the activation energy of this reaction system which strongly supports the experimental findings.
This chapter starts with the discussion of gas treating chemistry with a small primer in organic chemistry. Basically the absorption of CO<SUB>2</SUB> and H<SUB>2</SUB>S in alkaline solutions (based on amines) is mostly about acid-base chemistry. This approach is emphasised in the discussions, first by discussing the acid character of these compounds, and then by discussing their reactions with amines. The chapter examines the basic principles of chemistry and the acid character of CO<SUB>2</SUB> and H<SUB>2</SUB>S, and looks at what is said in the literature with respect to the specific chemistry. It focuses on the chemistry of the alkanolamine solutions. The concept of the reaction between CO<SUB>2</SUB> and tertiary amines is usually attributed to Donaldson and Nguyen.
Reaction Kinetics of Carbon Dioxide in Aqueous Diethanolamine Solutions Using the Stopped-Flow Technique
The pseudo-first-order rate constants (kOV) for the reactions between CO 2 and diethanolamine have been studied using the stopped-flow technique in an aqueous solution at 293, 298, 303 and 313 K. The amine concentrations ranged from 167 to 500 mol·m ⁻³ . The overall reaction rate constant was found to increase with amine concentration and temperature. Both the zwitterion and termolecular mechanisms were applied to correlate the experimentally obtained rate constants. The values of SSE quality index showed a good agreement between the experimental data and the corresponding fit by the use of both mechanisms.
The rate law for reaction of amines with carbon dioxide is rate = kamine(R2NH)(CO2) + kamine′(R2NH)· (OH)(CO2), where the first and second terms are for uncatalyzed and hydroxide-catalyzed pathways. The latter reaction, which involves proton abstraction in the rate-determining step, is not observed with all amines. Values for kamine at 10° follow the Brønsted relationship log kamine (M-1 sec-1) = mpK + Y, with values of m and Y equal to 0.43 and -1.50 for reactions of primary and secondary amines, and 0.48 and -0.20 for the reactions of hydrazine and hydroxylamine derivatives. Second-order rate constants for hydrogen ion catalyzed decarboxylation of carbamates formed from amines of pK -1.05 to approximately 5 may be fitted to a Brønsted relationship log kH + (M-1 sec-1) = 0.77pK + 3.6 at 10°. Rates for carbamates formed from more basic amines are virtually independent of basicity and are approximately 108 M-1 sec-1. The rate-limiting step in carbamate formation and breakdown with weakly basic amines involves carbon-nitrogen bond formation and cleavage. It is suggested that proton transfer may be rate limiting in the synthesis and breakdown of carbamates formed from basic amines.
The mechanism and kinetics of the reaction between aqueous solutions of CO2 and the alkanolamines 1-amino-2-propanol, 3-amino-1-propanol,2-methyl aminoethanol and 2-ethyl aminoethanol were investigated using a stopped flow technique. It was found that the reaction orders according to power law kinetics were between 1.1 and 2.0, depending on the alkanolamine and the concentration ranges investigated This fractional order was therefore considered to be further evidence that carbamate formation takes place according to a zwitterion mechanism rather than a one-step reaction. The kinetic rate parameters for these alkanolamines were evaluated from experimental data at 303 K according to this mechanism.
The CO2 reaction with alkanolamines has received considerable attention by both academia and industry. Commonly, the formation of the carbamate during the CO2 reaction with primary, secondary, and sterically hindered amines is described by a two-step zwitterion mechanism. Alternatively, a single-step termolecular reaction mechanism can also be used to govern carbamate formation. The experimental kinetic data for several amine-based solvents are consistent with this mechanism, and it can satisfactorily explain fractional-order and higher-order kinetics. However, up to now, the termolecular reaction mechanism has not been properly discussed. Here, this mechanism is described in detail, a simple procedure to estimate the kinetic parameters is outlined, and the termolecular reaction kinetics for various systems comprising individual and mixed amines is reviewed.
Rate constants, ΔH‡ and ΔS‡ have been measured by the conductimetric stopped-flow technique for the reaction of carbon dioxide in aqueous solution with the primary amines 2-methoxyethylamine, 2-aminoethanol, 3-aminopropan-1-ol, 2-aminopropan-2-ol, DL-aminopropan-2-ol and the secondary amines 1,1′-iminodipropan-2-ol, 2-amino-2-(hydroxymethyl) propane-1,3-diol, 2,2′-iminodiethanol, 2,2,6,6-tetramethylpiperidin-4-ol, and morpholine. The observed first-order rate constants fit the equation kobs=kAM[R2NH]2+kW[R2NH][H2O]. The much-quoted Danckwerts mechanism is shown to be unlikely.
Ab initio calculations and a continuum model have been used to study the mechanism for formation of carbamate from CO2 and alkanolamines. The molecules studied are ethanolamine and diethanolamine. A brief review is also made of published experimental observations relevant to the reaction mechanism. The ab inito results suggest that a single-step, third-order reaction is the most likely. It would seem unlikely that a zwitterion intermediate with a significant lifetime is present in the system. A single-step mechanism also seems to be in good agreement with the experimental data.
Alkanolamine solutions are frequently used as solvent for the removal of acid compounds from industrial gases (Kohl and Riesenfeld, 1979). Depending on the process requirements, e.g., selective removal of H2S, CO2-bulk removal, several options for alkanolamine based treating solvents with varying compositions of the solution have been proposed.In this paper an overview is presented of the mechanisms that have been proposed in literature and the kinetic data for the various reactions are critically evaluated. Conclusions on the applicability and restrictions are discussed along with perspectives. In addition white spots in the present knowledge are indicated.The reaction between CO2 and primary/secondary amines both in aqueous and non-aqueous solutions can be described over a wide range of conditions and amine concentrations with the zwitterion-mechanism as originally proposed by Caplow (1968) and reintroduced by Danckwerts (1979). All published results, both non-aqueous and aqueous solutions, amine-promoted carbonate processes, blends of amines and sterically hindered amines can be satisfactorily explained with this mechanism. The validity of the kinetic relations that are derived is restricted to about 313 K. Above this temperature the results are severely affected by the limitations of the used experimental techniques. Both stopped flow or rapid mixing and absorption techniques show their limitations because the rates of the reactions are too fast and because of the reversibility (for absorption experiments) of the reaction. For the formation of the zwitterion, an acid-base reaction, a Brønsted relation exists between the rate constant for this step of the reaction, k2, and the basic strength, pKa, of the amine.The reaction between CO2 and tertiary amines can be described with the base catalysis of the CO2 hydration as proposed by Donaldson and Nguyen (1981). The formation of monoalkylcarbonate is not responsible for the reactivity measured in aqueous tertiary amine solutions at low pH as can be concluded from the results published for TREA. In non-aqueous solvents no reaction occurs for tertiary amines.The determination of reaction mechanism and reaction rate constants from mass transfer experiments can be substantially affected by effects of reversibility of the absorption reactions. The condition of pseudo first order irreversible reaction cannot always be met, e.g., in those cases where the conversion is relatively high or the equilibrium constant is low as is the case for e.g., AMP. If this condition is not fulfilled the interpretation of the mass transfer experiments neglecting reversibility can lead to erroneous conclusions. For tertiary amines also the presence of even small amounts of fast reacting contaminants, e.g., primary or secondary amines has a pronounced effect
The reaction between CO2 and tertiary alkanolamines (MDEA, DMMEA, TREA) has been studied in aqueous solutions at various temperatures. Also the absorption of CO2 in a solution of MDEA in ethanol has been studied. Reaction kinetics have been established by chemically enhanced mass transfer of CO2 into the various solutions. The experiments were performed in a stirred vessel with a horizontal interface which appeared to the eye to be completely smooth. The reaction of CO2 with tertiary amines can be described satisfactorily with the base-catalysis mechanism proposed by Donaldson and Nguyen (1980). Also attention has been paid to the influence of reversibility and small amounts of impurities (primary and secondary amines) on the measured mass transfer rate. For the reaction rate constant, k2, of the reaction between carbon dioxide and tertiary amines exists a Brønsted relation. There is a linear relation between the logarithm of k2 and pKa at 293 K.
The kinetics of the reaction of CO2 with secondary an alkanolamine linked with alkyl group, methylaminoethanol (MAE), ethytaminoethanol (EAE) and n-butylaminoethanol (BAE), for CO2 recovery from power plant flue gases was investigated using a stirred tank absorber with a plane unbroken gas-liquid interface at 298 K. To evaluate the reaction rate constant from the CO2 absorption rate data under the fast-reaction regime, a combined parameter containing the solubility and diffusivity for N2O in aqueous solutions of sterically hindered amines; MAE, EAE and BAE, was measured using a wetter-wall column apparatus at the same temperature. For further practical evaluation of the reaction rate, apparent rate constants for EAE under the process condition of CO2 removal from power plants were investigated.
The observed pseudo-first-order rate constants (ko) for the reactions between CO 2 and ethylenediamine (EDA), ethyl ethanolamine (EEA), and diethyl monoethanolamine (DEMEA) have been studied using the stopped-flow technique in an aqueous solution at 298, 303, 308, and 313 K. The amine concentrations ranged from 26.2 mol/m 3 to 67.6 mol/m 3 for EDA, 28.2 mol/m 3 to 81.9 mol/m 3 for EEA, and 196.5 mol/m 3 to 997.4 mol/m 3 for DEMEA. The zwitterion mechanism was used to correlate the experimentally obtained rate constants. Both the zwitterion formation step and the proton removal step had a significant role for the primary and secondary amines (EDA and EEA). The reaction rate of CO 2 in an aqueous EDA solution was observed to be much faster than that in aqueous MEA solution. The rate in aqueous EEA was much faster than in aqueous DEA, under the conditions studied. Finally, the reaction rate constant of CO 2 in an aqueous tertiary amine (DEMEA) solution was observed to be much faster than that in methyl diethanolamine (MDEA). Only the zwitterion formation step had a significant role in the overall reaction. The base catalysis of the CO 2 hydration mechanism could explain the reaction between CO 2 and the tertiary amine. Therefore, the three selected amines are considered to be of interest to the gas sweetening industry.
The observed pseudo-first-order rate constants (k0) for the reactions between CO2 and ethylenediamine (EDA), ethyl ethanolamine (EEA), and diethyl monoethanolamine (DEMEA) have been studied using the stopped-flow technique in an aqueous solution at 298, 303, 308, and 313 K. The amine concentrations ranged from 26.2 mol/m3 to 67.6 mol/m3 for EDA, 28.2 mol/m3 to 81.9 mol/m3 for EEA, and 196.5 mol/m3 to 997.4 mol/m3 for DEMEA. The zwitterion mechanism was used to correlate the experimentally obtained rate constants. Both the zwitterion formation step and the proton removal step had a significant role for the primary and secondary amines (EDA and EEA). The reaction rate of CO2 in an aqueous EDA solution was observed to be much faster than that in aqueous MEA solution. The rate in aqueous EEA was much faster than in aqueous DEA, under the conditions studied. Finally, the reaction rate constant of CO2 in an aqueous tertiary amine (DEMEA) solution was observed to be much faster than that in methyl diethanolamine (MDEA). Only the zwitterion formation step had a significant role in the overall reaction. The base catalysis of the CO2 hydration mechanism could explain the reaction between CO2 and the tertiary amine. Therefore, the three selected amines are considered to be of interest to the gas sweetening industry.
In view of increased requirements on absorption rates and loading capacity for carbon dioxide (CO2) absorption solvents, more research is directed toward alkanolamines having more than one amino group. In the present work, AEEA {2-((2-aminoethyl)amino)ethanol}, a diamine containing primary and secondary amino groups, is used to study the CO2 absorption kinetics. The reaction kinetics between CO2 and aqueous solutions of AEEA were measured over a range of temperatures from 32 to 49 °C with the concentrations of AEEA ranging between 1.19 and 3.46 kmol m-3 using a string of discs contactor. All kinetic experiments were interpreted using the single-step−termolecular mechanism approach as proposed by Crooks and Donnellan (J. Chem. Soc., Perkin Trans. 2 1989, 331) and reviewed by da Silva and Svendsen (Ind. Eng. Chem. Res. 2004, 43, 3413).
The kinetics of the reaction between CO2 and aqueous potassium salts of taurine and glycine was measured at 295 K in a stirred-cell reactor with a flat gas–liquid interface. For aqueous potassium taurate solutions, the temperature effect on the reaction kinetics was measured at 285 and 305 K. Unlike aqueous primary alkanolamines, the partial reaction order in amino acid salt changes from one at low salt concentration to approximately 1.5 at salt concentrations as high as 3,000 mol·m−3. At low salt concentrations, the measured apparent rate constant (kapp) for potassium glycinate is comparable to the values in literature. In the absence of reliable information in the literature on the kinetics and mechanism of the reaction, the applicability of the zwitterion and termolecular mechanism (proposed originally for alkanolamines) was explored. For the zwitterion mechanism, the forward second-order reaction rate constant (k2) of the CO2 reaction with amino acid salt seems to be much higher than for alkanolamines of similar basicity, indicating that the Bronsted plot for amino acid salts might differ from that of alkanolamines. The contribution of water to the deprotonation of zwitterion seems to be more significant than reported values for aqueous secondary alkanolamines.
Alkanolamines are the most popular absorbents used to remove CO2 from process gas streams. Therefore, the CO2 reaction with alkanolamines is of considerable importance. The aim of this article is to provide an overview on the kinetics of the reaction of CO2 with aqueous solutions of alkanolamines. The various reaction mechanisms that are used to interpret experimental kinetic data – zwitterion, termolecular and base-catalyzed hydration – are discussed in detail. Recently published data on reaction kinetics of individual amine systems and their mixtures are considered. In addition, the kinetic behavior of several novel amine-based solvents that have been proposed in the literature is analyzed. Generally, the reaction of CO2 with primary, secondary and sterically hindered amines is governed by the zwitterion mechanism, whereas the reaction with tertiary amines is described by the base-catalyzed hydration of CO2.
The kinetics of the reaction between carbon dioxide and high CO2-loaded, concentrated aqueous solutions of monoethanolamine (MEA) were investigated over the temperature range from 293 to , MEA concentration range from 3 to 9M, and CO2 loading from ∼0.1 to 0.49 mol/mol. The experimental kinetic data were obtained in a laminar jet absorber at various contact-times between gas and liquid. The obtained experimental data were interpreted with the aid of a numerically solved absorption-rate/kinetic model. The results showed that only the termolecular mechanism of Crooks and Donnellan could be used to explain all observed kinetic phenomena. These results allowed us to develop a new termolecular-kinetics model for CO2 reaction with MEA solutions, which proved to be better than previously published kinetic models. The model was comprehensive enough to describe for the first time the absorption of CO2 in highly concentrated and high CO2-loaded aqueous MEA solutions for a wide temperature range.
Reaction kinetics of carbamate formation and chemical breakdown with alkaline amine solutions
Ab initio study of the reaction of carbamate formation from CO2 and alkanolamines. Industrial & DOI: 10.1021/ie030619k
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- E F Svendsen
Performance of CO2 absorption in mixed aqueous solution of MDEA
- H. Kierzkowska-Pawlak
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Kinetics of reactive absorption of carbon dioxide in high CO - loaded , concentrated aqueous monoethanolamine solutions
- Aboudheir
Termolecular kinetic model for CO - alkanolamine reactions : An overview Chemical
- Vaidya
Kinetics of reaction between carbon dioxide and sterically hindered amines for carbon dioxide recovery from power plant flue gases
- Mimura
Reaction kinetics of carbon dioxide in aqueous diethanolamine solutions using the stopped - flow technique Ecological Chemistry and
- Siemieniec
Kinetics of the reaction of carbon dioxide with aqueous solutions of - aminoethyl ) amino ) ethanol Industrial
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Kinetics of the reaction CO with aqueous potassium salt of taurine and glycine
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CO - alkanolamine reaction kinetics of recent studies
- Vaidya
Performance of CO absorption in mixed aqueous solution of MDEA In Proceedings of the st International Conference of the Slovak Society of Tatranske Matliare of Chemical
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da Ab initio study of the reaction of carbamate formation from CO and alkanolamines Industrial
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Reaction kinetics of CO in aqueous ethylenediamine , ethyl ethanolamine , and diethyl monoethanolamine solutions in the temperature range of using the stopped - flow technique Industrial
- Li