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Kinetics of Carbon Dioxide With Tertiary Amines in Aqueous Solution

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Abstract

The reaction of CO2 with TEA, DMMEA, and DEMEA has been studied at 293, 303, 318 and 333 K. All the kinetic experiments were carried out in a stirred cell reactor operated with a flat, smooth and horizontal gas-liquid interface. A numerical method, which describes mass transfer accompanied by reversible chemical reactions, has been applied to infer rate constants from the experimental data. It is argued that the contribution of the CO2 reaction with OH− to the observed reaction rate may have been overstimated in most literature on tertiary amine kinetics as serious depletion of OH− toward the gas-liquid interface usually occurs. For all the amines studied, the reaction order in amine was found to be about one for each temperature investigated. This is in good agreement with the base catalysis mechanism proposed by Donaldson and Nguyen (1980). All kinetic data could be summarized reasonably well in one Brønsted relationship.

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... A different mechanism applies to the reaction of CO 2 with ternary amines. According to Littel et al. [16], the reaction of CO 2 with tertiary amines can be described satisfactorily using the base-catalysis reaction mechanism proposed by Donaldson and Nguyen [17]: ...
... Following Bosch et al. [6] who studied blends of alkanol amines, we add reaction (5) catalyzed by ternary amines and reaction (16) to account for the decomposition of the ternary ammonium ion: ...
... In order to complete the rate calculations, we collected literature data corresponding to the equilibrium rate constants of reactions (9)-(14) from Bedelbayiev et al. [24] and Greer [2]. In order to deal with reactions (5) and (16) for ternary alkanol amines, we followed many investigators including Haimour et al. [25], Critchfield [26], Littel et al. [16], and Rangwala et al. [27] who fit the rate constant of the reaction as a function of temperature using ...
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The absorption of carbon dioxide is an important process in many practical applications such as reduction of greenhouse gases, separation and purification processes in the chemical and petroleum industries, and capture of radioactive isotopes in the nuclear fuel cycle The goal of this research is to develop a dynamic model to simulate CO 2 absorption by using different alkanolamines as absorption solvents. The model is based upon transient mass and energy balances for the chemical species commonly present in CO 2 gas-liquid absorption. A computer code has been written to implement the proposed model. Simulation results are discussed. The reported model simulates well the response to dynamic changes in input conditions. The proposed model can be used to optimize and control the separation of carbon-14 in the form of CO 2 in the nuclear industry.
... The reaction between CO 2 and DEEA in aqueous solutions was investigated at a single temperature by Kim and Savage (1987) at 323 K and by Benitez-Garcia et al. (1991) at 298 K. Kinetics at various temperatures was measured by Littel et al. (1990), Li et al. (2007), Vaidya and Kenig (2008) and Xu et al. (2013). The reaction rate constants for the CO 2 -DEEA reaction which are reported in the above works are very scarce. ...
... The reaction rate constants for the CO 2 -DEEA reaction which are reported in the above works are very scarce. At 303 K, Littel et al. (1990) measured 59 m 3 kmol −1 s −1 , the result of Xu et al. (2013) is 113 m 3 kmol −1 s −1 while Vaidya and Kenig (2008) reported the highest value of 173 m 3 kmol −1 s −1 . The value of Li et al. (2007) determined by the homogenous stopped-flow technique is 118 m 3 kmol −1 s −1 at the same temperature. ...
... The contribution of the CO 2 reaction with OH − is also ignored due to very small concentration of OH − ions. Therefore, these reactions do not influence the overall rate of reaction and are neglected in several studies (Monteiro et al., 2015a;Sutar et al., 2013;Vaidya and Kenig, 2008;Littel et al., 1990). N-Methyl-1,3-propane-diamine is a very fast amine which reacts twice as fast as piperazine and 15 times faster than monoethanolamine. ...
Article
http://www.sciencedirect.com/science/article/pii/S1750583616306740 The absorption of CO2 into aqueous solution of N,NN,N-diethylethanolamine (DEEA) and its blend with NN-methyl-1,3-propane-diamine (MAPA) is studied in a batch-operated stirred-cell reactor under fast pseudo-first order regime. Since the literature data on the kinetics of CO2 reaction in aqueous DEEA are inconsistent, new kinetic data are obtained over the temperature range of 303–333 K. At 318 K, the reaction rate constant of 168 m3/(kmol s) is determined. Taking the recent findings into considerations, the reasons for the scatter in the reported kinetics are critically discussed. The analysis of literature data reveals the high sensitivity of the reaction rate constant to the value of CO2 solubility and the chosen method of data treatment. The need for a standardized procedure to determine the kinetics of gas-liquid reactions is emphasized. Furthermore, it is found that a fast reacting MAPA acts as an effective absorption activator in aqueous DEEA solutions. A small amount of MAPA in the DEEA solutions results in a considerable enhancement of the CO2 absorption rate as compared to DEEA alone.
... Tertiary amines react with CO 2 in different ways compared to primary and secondary amines, as Donaldson and Nguyen (1980) suggested tertiary amines act as a base-catalyzed for the hydration of CO 2 , which implies that they cannot directly react with CO 2 (Henni et al., 2003). Later works (e.g., Crooks et al. (Crooks and Donnellan, 1989), and Little et al. (Littel et al., 1990)) were in good agreement with the suggested mechanism. This hypothesis is because tertiary alkanolamines do not have a hydrogen atom attached to the nitrogen atom and therefore aid CO 2 hydrolysis reactions to form bicarbonates. ...
... As suggested by Littel et al. (1990), in the temperature range between 293 and 333 K, the second-order rate constant as a function of temperature for the CO 2 reaction with TEA in aqueous solutions is: ...
... Of the Fig. 13. Analytical comparison of various chemical absorbents based on the selection criteria (Barzagli et al., 2010;Bernhardsen and Knuutila, 2017;Borhani et al., 2013;Galindo et al., 2012;Gouedard et al., 2012;Gunasekaran et al., 2013;Kim and Svendsen, 2011;Littel et al., 1990;Ramezani et al., 2021;Samanta and SB-J of C, 2006;Spasojevic et al., 2012;Veawab et al., 1999;Vega et al., 2014). ...
Article
This review paper evaluates the critical selection criteria for slow and medium kinetic chemical solvents used in the CO2 absorption process during natural gas purification. The chemical absorbents’ reaction mechanism, capacities, chemical structure, and operating parameters on the CO2 absorption performance was discussed. Other solvent properties such as vapor pressure, corrosively, viscosity, forming tendency, regeneration energy, thermal stability, and toxicity was investigated to portray their overall potentials industrial applications. Generally, the absorbents absorption rate is the superior determinant factor for their industrial applications. Thus, desirable solvent performance breakthrough will depend on CO2 absorption rate enhancement research via chemical/mechanical methods.
... The k 1 presented in Table 1 is expressed according to the reaction mechanism described by Eq. (6). [10] 0.059 Stirred cell reactor [11] 0.115 Stopped flow [12] CO 2 absorption in aqueous amine solution is accompanied by several chemical reactions which are responsible for the CO 2 capacity and the mass transfer rate. ...
... This method differs from the commonly used ones since the mass transfer from gas to liquid was not considered in it. The values of k ov were determined automatically by fitting the Littel et al. [11] Li et al. [12] lnk 1 1000/T [1/K] exponential function to the measured conductance of the solution over the whole time span of the reaction taking place entirely in the liquid phase. Such a simplified interpretation may be one of the reasons for the observed inconsistency. ...
... Such a simplified interpretation may be one of the reasons for the observed inconsistency. However, the second order rate constants determined in this study show good agreement with the data of Littel et al. [11], who performed the measurements by using the similar experimental technique as in this work. Furthermore, the present results are also very similar to our previous data determined in the analogous measurement system [10]. ...
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The CO2 absorption process using aqueous amine solutions has been the most promising technique used for the removal of CO2 from gas streams in energy sector. In recent years, many researchers tested solutions which are composed of several compounds: a slow reacting tertiary amine-and a fast amine acting as an activator. In this paper, the CO2 absorption rate in an aqueous solution of N,N-diethylethanoloamine (DEEA) and activated solutions DEEA is investigated experimentally. The activators considered are sterically hindered amines: 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-methyl-1,3-propanediol (AMPD) and N-methyl-1,3-propanediamine (MAPA) from the group of polyamines. The experiments were conducted over the temperature range of 303-333 K and the total amine concentration of 2 M. From the CO2 absorption experiments into mixed aqueous solutions of DEEA and MAPA, it was found that the addition of small amounts of MAPA into aqueous DEEA solutions has a significant effect on the enhancement of the CO2 absorption rate. The application of hindered amines: AMP or AMP as activators resulted in a marginally improvement of the absorption rate of CO2.
... The reaction rate of CO 2 with H 2 O is extremely slow, therefore the term of k H 2 O H 2 O ½ can be ignored. 25 Little et al. 26 found that the concentration of OH 2 ions in amine solution is very low due to the very fast reaction rate of CO 2 with OH 2 leading to the hydroxyl ions being quickly consumed, and the effect of hydroxide ions on the overall reaction rate can be neglected as well. Therefore the overall reaction rate expression can be simplified as: ...
... As mentioned above, the concentration of OH 2 ion in amine solution is very low, so the contribution of hydroxide ions can be neglected. 26 In addition, considering the weak basicity of H 2 O relative to R 3 N and MEA, the contribution of H 2 O can be disregarded as well. 25 Therefore, Eq. 16 is further simplified as: ...
... The calculated values of second-order reaction rate constants of DEEA (k 2,DEEA ) from Eq. 20 are in relatively good agreement with experimental values with an ARD (average relative deviation) of 5.39%, which demonstrates that this correlation model can be successfully applied. Furthermore, the second-order reaction rate constants of DEEA (k 2,DEEA ) of the aqueous DEEA solution are compared to the values from Kim et al., 15 Littel et al., 26 Benitez-Garcia et al., 33 Li et al., 14 Vaidya et al., 16 and Kierzkowska-Pawlak, 34 and a graphical representation is presented in Figure 4. Although some distinction can be observed, upon consideration of the difference in the measurements, it can be concluded that the experimental results agree well with those found in the literature. ...
Article
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 293K to 313K. 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. This article is protected by copyright. All rights reserved.
... DEAB and MDEA in this study) complies with base-catalyzed mechanism. Instead of direct reaction with CO 2 , tertiary amine acts as a base catalyst for hydration of CO 2 as described in reactions (9)-(10) [25]. Moreover, compared to traditional primary or secondary amines, AMP is a sterically hindered primary alkanolamine with formation of bicarbonate due to the instability of the hindered amine carbamate, which is similar to reaction of CO 2 with tertiary amine as described in reaction (11) [26]. ...
... where D M and D Kn represent the molecular and Knudsen diffusion coefficients (m 2 /s), respectively. The molecular self-diffusion coefficient of CO 2 can be determined based on the kinetic gas theory [31]: (25) where R denotes the ideal gas constant, M represents the molecular weight of the gas; μ represents the dynamic viscosity of the gas; P represents the gas pressure (kPa). Ω u and Ω D demote the viscosity collision integral and diffusion collision integral, respectively. ...
Article
4-diethylamino-2-butanol (DEAB), as a novel tertiary amine, shows a promising potential for CO2 capture. In this study, the mass transfer performance of CO2 absorption into aqueous DEAB solution in a non-wetted and partially-wetted mode of hollow fiber membrane contactor (HFMC) was theoretically investigated in comparison with that of monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA) and 2-amino-2-methyl-1-propanol (AMP). A 2D mathematical model based on finite element method (FEM) was established to solve the steady-state continuity equations for the shell, tube and membrane sides simultaneously. The influences of the operating parameters on the CO2 absorption flux in HFMC including liquid and gas velocity and CO2 partial pressure were comprehensively investigated. The numerical results show that the CO2 absorption flux can increase with the increasing liquid velocity and CO2 partial pressure, and slightly increases with the increasing gas velocity. Moreover, the CO2 absorption performance of aqueous DEAB solution was further compared with different amine solutions, which reveals that the CO2 absorption flux of DEAB is higher than those of DEA, MDEA and AMP, and is also comparable to MEA. The analysis on the mass transfer resistance indicates that the proportion of the membrane mass transfer resistance increased rapidly from 13.7% to 75.3% as membrane wetting ratio increased from 0% to 20%. Instead of the liquid phase, the mass transfer in wetted membrane phase becomes the rate-controlling step ultimately. The increase in the membrane wetting leads to the significant decrease in CO2 absorption performance with 49.4% and 80.5% decrease in CO2 absorption flux and the overall mass transfer coefficient at membrane wetting ratio of 5% and 50%, respectively. Based on the analysis on enhancement factor, it demonstrates that the chemical reaction between CO2 and DEAB for the non-wetted mode generally occurs in the intermediate fast-instantaneous regime and gradually transfers to the instantaneous regime with membrane wetting.
... In addition, accurately understanding the effect of OH − in tertiary amine solution on the observed reaction rate constant (k obs ) for CO 2 capture also requires further investigation, although the OH − depletion in the gas-liquid interface occurs very quickly. 12 According to some research, there are alternative perspectives about the effect of [OH − ] on the second-order reaction rate constant of tertiary amine with CO 2 (k 2_am ). Versteeg and van Swaaij 13 measured the k 2_am of TEA, dimethylaminoethanol, Ndimenthylethanolamine, and TREA, 13 and Li et al. 14 investigated the k 2_am of 3-diethylamino-1, 2-propanediol (3DEA-1,2-PD). ...
... According to Eq. 13, when k eq 2am is much less than k OH − . the [OH − ] will be depleted immediately to zero, 12 and then the effect of the [OH − ] on k obs can be omitted. Under the circumstances and based on the termolecular reaction mechanism, 6 the loose molecular pairs (R 3 N Á H 2 O), would attack the CO 2 molecule directly. ...
Article
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. Firstly, the kinetics of CO2 absorption into water instead of a buffer solution was 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 (k0_CO2) was determined to be about 1000 times larger than the value for CO2 absorption into buffer solution reported in the reference. The k0_CO2 was then correlated by a proposed semi‐empirical 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 (k0_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 k0_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 k0_DEEA well with an AARD less than 5%. The predicted results indicate that the contribution of OH⁻ to k0_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 TEA and CO2‐loaded DEEA solution were further investigated and comprehensively discussed, suggesting that both pKa and the CO2 solubility affect k0, with pKa having a much more significant effect. This article is protected by copyright. All rights reserved.
... Because of its slow reaction rate in comparison with reactions (2) and (3) due to its slow reaction rate in terms of mass transfer in comparison with those reactions, the contribution of reaction 4 can be neglected. (Hagewiesche et al., 1995;Henni et al., 2008;Kadiwala et al., 2012;Littel et al., 1999) , Therefore, the expression of r CO 2 can be expressed as the following equation: ...
... In the work of Chen and Rochelle (2013), the authors reported the Brønsted plots of morpholine (MOR), 2methylperazine (2MPZ) and perazine (PZ) at a temperature of 298 K. Da Silva and Svendsen (2007) also showed the Brønsted relationships of some other amine solvents. In this work, the Brønsted plots for nine tertiary amines (Triethanolamine (TEA), MDEA, Dimethylmonoethanolamine (DMMEA), Diethylmonoethanolamine (DEMEA), 1-dimethyl-amino-2-propanol (1DMA2P), Triethylamine (TREA), 4-(diethylamino)-2-butanol (DEAB), 1-(2-hydroxyethyl)piperidine (1-(2-HE)PP), and 1-(2-HE) PRLD were developed at the temperature range of 298-313 K (Benitez-Garcia et al., 1990;Kadiwala et al., 2012;Littel et al., 1999;Littel et al., 1990;Pérez-Salado Kamps and Maurer, 1996;Sema et al., 2012a;Shi et al., 2012;Versteeg et al., 1996;Versteeg and van Swaaij, 1988). All the results are shown in Fig. 8. From Fig. 8, it was found that the pKa value of 1-(2-HE) PRLD was higher than that of the other six amines (TEA, MDEA, DMMEA, DEMEA, 1DEMA2P, and 1-(2-HE)PP) but lower than that of DEAB and TREA at the same temperature. ...
... In Fig. 13, the second order reaction rate constant (k 2 ) and pKa of various primary, secondary and tertiary amines are extracted from the references for comparison. Those amines include MEA, AMP, MAE, DEA, MDEA, triethanolamine (TEA), dimethylethanolamine (DMEA), 3-dimethylamino-1-propanol (3DMA1P), 1DMA2P, diethylethanolamine (DEEA), 1DEA2P, DEAB, 1-(2-hydroxyethyl)-piperidine (1-(2HE)-PP), 1-(2-hydroxyethyl)-pyrrolidine 1-(2HE)-PRLD and triethylamine (TREA) [25,30,31,[49][50][51][52][53][54][55][56][57][58][59]. ...
Article
Protonation and carbamate formation are critical reactions for CO2 capture using amine-based absorbents which impact both CO2 absorption and amine regeneration. In this regard, thermodynamic analysis towards CO2 absorption in N-methylaminoethanol solution is carried out with specific attention to the corresponding protonation and carbamate formation reactions. The CO2 absorption mechanism is investigated with the acquisition of reaction equilibrium constant and heat of reaction. CO2 absorption performance of N-methylaminoethanol solution was evaluated in terms of CO2 loading and solution pH. A thermodynamic model was then developed to mathematically describe the investigated system and make prediction on equilibrium CO2 solubility, species profiles, and absorption/regeneration heat. Results show that the average relative deviation of equilibrium CO2 solubility calculated from the is 4.2%. The predictive species profile and CO2 absorption heat of N-methylaminoethanol solution indicates less energy cost to desorb CO2. This is in line with the relative unstable N-methylaminoethanol carbamate formation and consequential conversion to (bi)carbonate. The position of N-methylaminoethanol as a potential absorbent in amine based carbon capture is shown in terms of chemical reaction constants, equilibrium CO2 solubility, second order rate constant (k2), and pKa.
... In each system it is seen that, the maximum CO 2 concentrations expressed as (nm −3 ) is located at approximately 35 Å and 65 Å, which indicate that CO 2 molecules are preferentially accumulated at the CO 2 /amine aqueous solution interface region at two sides of the simulation cell. This behavior has been observed by experimental measurement and by numerical calculation models (Littel et al., 1990). The concentration of CO 2 in aqueous tertiary amine systems as presented in Fig. 12 indicates that the CO 2 maximum concentrations are in the increasing order of: MDEA < DEA-1P < DEA-1,2-PD < 1M-2PPE. ...
Article
Quantum mechanical (QM) methods were utilized to study the effect of substitution on the tertiary amines, for their application as the efficient absorbents, to capture CO2, known globally, as an undesirable greenhouse gas. For this purpose, by using density functional theory, the tertiary amine absorbents 1-M-2PPE, DEA-1,2-PD, DEA-1P and MDEA were examined by calculating the transition state activation energies of their absorption reactions. By considering the results obtained, the mechanism of the reaction kinetics, for CO2 absorption reaction, on these tertiary amines was proposed. The absorption results of QM calculations and the related interpretations were compared with the reported experimental results and those obtained by molecular dynamics (MD) simulations for similarly simplified systems. The pKa values for the tertiary amines were evaluated by QM calculations and their effects on the rate of CO2 absorption, were examined. The results of CO2 absorption on the studied tertiary amines aqueous solutions were compared with those obtained for conventional tertiary amine absorbent MDEA, which is used widely in various industries. It was found that for CO2 absorption, the tertiary amines 1M-2PPE and DEA-1,2-PD have higher reaction rate, along with higher diffusion coefficient and solubility, compared with MDEA. Therefore, it would be advantageous to use 1M-2PPE, DEA-1,2-PD in industrial units for CO2 capture in respect to both absorption performance, and energy consumption considerations.
... Carbonation reaction was conducted in a 1 L vessel that was pressurized to 100 psi by pure CO 2 gas for 4 h to form TMAH 1 and HCO 2 3 . 31,32 The pressure inside the reaction vessel was unchanged over time after closing the intake valve, which meant the reaction was complete. The TMA-CO 2 solution was then depressurized and equilibrated in atmosphere for one day to let the excess CO 2 escape from the solution. ...
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This study evaluates the PRO performance of TMA–CO2 for potential use in osmotic heat engines. Power densities up to 18.6 W m⁻² were achievable at relatively low pressure (10 bar) using 5 M TMA–CO2 draw solutions. Compared to NaCl control tests, the TMA‐CO2 exhibited 20% lower water flux due in large part to its larger molecular size and associated higher solution viscosity and lower diffusion coefficient. Compared to the ammonia‐carbon dioxide draw solution, water flux was comparable but reverse solute flux of TMA–CO2 was nearly one order of magnitude lower. Larger solute size was found to create a performance tradeoff as reduced reverse solute flux improved water flux while higher viscosity and lower diffusion coefficient worsened water flux. This article is protected by copyright. All rights reserved.
... 8 The reaction between CO 2 and DEEA in aqueous solutions has been already studied in our previous works 9, 10 and by others. 11,12 DEEA is characterized by a low reactivity as for CO 2 because of its tertiary amine features. However, the absorption of CO 2 in DEEA solutions can be enhanced by using suitable promoters such as primary, secondary, hindered amines, and polyamines. ...
Article
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The rates of CO2 absorption into aqueous solutions of N-methyl-1,3-propanediamine (MAPA) and its mixture with N,N-diethylethanolamine (DEEA) have been studied in a stirred cell reactor under the fast reaction regime. The experiments were carried out for 0.2 M MAPA and DEEA + MAPA blends with a total amine concentration of 2 M over the temperature range of 303 to 333 K. It was found that relatively low concentrations of MAPA ranging from 0.05 to 0.2 M in DEEA solutions significantly accelerated the rate of CO2 absorption. Kinetic data for the reactions of CO2 with MAPA were not available in the literature within the present experimental range. Based on the experiments in DEEA+MAPA blends, the pseudo-first-order rate constants were calculated and analyzed together in one global analysis. Using the termolecular mechanism, the specific kinetic rate constants for the reactions between CO2 and MAPA were determined and correlated by the Arrhenius equation. Finally, a comparison of the efficiency of the studied MAPA with other fast amines confirmed its potential as an excellent rate promoter for CO2 absorption.
... Post-combustion capture technology is the most plausible way to retrofit existing large CO 2 emitting facilities [3][4][5]. Various aminebased CO 2 absorption processes such as the classic monoethanolamine (MEA)-based process, methyldiethanolamine (MDEA)-based process, and methyldiethanolamine (MDEA)-piperazine (PZ)-based process were adapted to capture CO 2 from flue gas due to their availability and maturity [6][7][8][9][10][11][12]. Many efforts focused on process optimization and energy integration were performed to reduce the energy demand [13]. ...
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Post-combustion CO2 capture (PCC) process faces significant challenge of high regeneration energy consumption. Biphasic absorbent is a promising alternative candidate which could significantly reduce the regeneration energy consumption because only the CO2-concentrated phase should be regenerated. In this work, aqueous solutions of triethylenetetramine (TETA) and N,N-diethylethanolamine (DEEA) are found to be efficient biphasic absorbents of CO2. The effects of the solvent composition, total amine concentration, and temperature on the absorption behavior, as well as the effect of temperature on the desorption behavior of TETA–DEEA–H2O system were investigated. An aqueous solution of 1 mol·L− 1 TETA and 4 mol·L− 1 DEEA spontaneously separates into two liquid phases after a certain amount of CO2 is absorbed and it shows high CO2 absorption/desorption performance. About 99.4% of the absorbed CO2 is found in the lower phase, which corresponds to a CO2 absorption capacity of 3.44 mol·kg− 1. The appropriate absorption and desorption temperatures are found to be 30 °C and 90 °C, respectively. The thermal analysis indicates that the heat of absorption of the 1 mol·L− 1 TETA and 4 mol·L− 1 DEEA solution is − 84.38 kJ·(mol CO2)− 1 which is 6.92 kJ·(mol CO2)− 1 less than that of aqueous MEA. The reaction heat, sensible heat, and the vaporization heat of the TETA–DEEA–H2O system are lower than that of the aqueous MEA, while its CO2 capacity is higher. Thus the TETA–DEEA–H2O system is potentially a better absorbent for the post-combustion CO2 capture process.
... In this work, in order to obtain comparable results, all the experiments were carried out at similar initial partial pressure of CO2. Furthermore, the used partial pressure is similar to those of used in the literature ( [27], [26], [28], [29], [30], [31]). he objective was to inject enough pure CO2 to be able to monitor the decrease of the normal logarithm of PCO2 with the time, but low enough so that short injection time (4 seconds) could be used. Additionally, this also ensures that the loading of the solution will be small, as seen by checking with titration. ...
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Alkanolamine blends are of high interest as solvents to enhance the CO2 capture technology in comparison to the traditional 5M MEA. In the present work, the mass transfer and kinetics coefficients of the unloaded and loaded blend 3M DEEA+ 2M MAPA are measured from 30 to 70°C in a Double Stirred Cell (DSC) under pseudo-first order conditions. Needed physical properties, as density, viscosity and Henry's Law constants of N2O are measured from 25 to 80°C. Results are extracted using the zwitterion mechanism and two-film theory.
... For classical CO 2 absorption experiments in the Lewis Cell, pure CO 2 is injected in the partial pressure range of 100-800 mbar, with stirrer speed of 100 rpm. Theses conditions allow to satisfy fast kinetic regime assumption [11]. For CO absorption, the mass transfer rate is much lower than for CO 2 . ...
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The VALORCO project coordinated by ArcelorMittal and funded by ADEME aims at reducing and valorizing CO2 emissions from steel industry. This paper presents the main results of task 1.1A of the VALORCO project dedicated to CO2 capture on blast furnace gases by means of amine scrubbing technologies. Blast furnace gases are characterized by high CO2 and CO partial pressures and the absence of oxygen. Since few literature data are available on the effect of CO on solvent degradation and CO2 absorption, experimental work was needed. In this context, three IFP Energies nouvelles (IFPEN) processes initially developed for CO2 capture on coal power stations were evaluated for blast furnace applications: HicaptTM process (MEA 30wt.%), Hicapt+TM process (MEA 40wt.%) and DMXTM process (Demixing solvent).
... The reaction between CO 2 and OH À cannot form an extra charged particle, and thus k OH -cannot be detected in stopped-flow apparatus. Littel et al. 33 found that the concentration of OH À ions in amine solution is very low due to the very fast reaction of CO 2 with OH À leading to the hydroxyl ions being quickly consumed, and the effect of hydroxide ions acted as a base on the overall reaction rate can be neglected as well. Thus, Equation 13 can be further simplified as follows: ...
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In order to establish an accurate kinetic model for the aqueous amine blends, monoethanolamine (MEA), 2‐(ethylamino) ethanol (EAE) and 3‐(diethylamino) ‐1‐propanol (3DEA1P) have been chosen as a typical CO2 absorption tri‐solvents. The reaction kinetics of aqueous amine blends with carbon dioxide have been investigated firstly combining experiments and molecular simulations. The stopped‐flow technology has been used to obtain the observed reaction rate constant of the overall reactions over the temperature range of 293 to 313 K and at different amine concentrations. A theoretical kinetic model, based on the first‐principles quantum‐mechanical simulations, has been put forward to interpret the reactions between CO2 and the aqueous tri‐solvent amine blends systems. The proposed model, based on the zwitterion mechanism and the base‐catalyzed mechanism, shows good prediction with an acceptable AAD of 6.32%, and has been found to be satisfactory in determining the kinetics of the involved complicated reactions.
... The main reaction occurring in an aqueous MDEA solution is the base catalysed CO 2 hydration reaction where MDEA functions as the base catalyst [3][4][5]: 2 2 3 CO MDEA H O MDEAH HCO (2) where the concentration of water is set to unity. ...
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Piperazine (PZ) is added to aqueous methyldiethanolamine (MDEA) solutions to achieve a greater CO2 absorption in CO2 capture technology. It is referred to as “activated MDEA solutions” in the industry. However, does PZ really activate rate the CO2 absorption of MDEA, or do PZ and MDEA just have parallel reactions with CO2, the mechanism is not clear. In this work, a semi-batch stirred cell with CO2 continuous operation was used to investigate the “activation” mechanism of PZ in aqueous MDEA solutions. As a comparison, kinetics of CO2 absorbed in MDEA + MEA solution and PZ aqueous solution respectively were performed at the same conditions as MDEA + PZ solution.
... (4)-(6). Eq. (7) shows the reaction between MDEA (a tertiary amine), CO 2 and H 2 O, and it has been documented that MDEA does not react directly with CO 2 but serves as a base that catalyzes CO 2 hydration into bicarbonate (HCO 3 -) (Donaldson and Nguyen, 1980;Hagewiesche et al., 1995;Littel et al., 1990). This is the reason for the slow reaction of aqueous MDEA solution with CO 2 . ...
Article
This research is a bench-scale pilot plant investigation of novel amine solvent blend containing MDEA and 1,5-diamino-2-methylpentane (DA2MP) for CO2 capture from water-gas shift process plant (H2 production). The CO2 concentration used in this study (50 vol.% CO2 with N2 balance) is similar to that of the water-gas shift product gas. The CO2 capture performance of the MDEA-DA2MP blend was compared to the standard 3 kmol/m3 MDEA-0.5 kmol/m3 PZ blend (34.4 wt.% MDEA-5 wt.% PZ). The low concentration of PZ in this study is because of the chemical toxicity of PZ and possible precipitation at medium to high concentration. The MDEA concentration in the MDEA-DA2MP blend was kept constant at 3 kmol/m3 while the DA2MP was varied from 0.5 kmol/m3 (6.75 wt.%) to 1.5 kmol/m3 (20.3 wt.%). The pilot plant analysis was performed at a gas flow rate, amine solution flow rate, and reboiler temperature of 14 SLPM, 50 mL/min, and 120 °C respectively. Pilot plant results revealed that the higher MDEA-DA2MP blend concentration possesses higher CO2 capture efficiency (up to 24%), higher CO2 absorption rate (up to 23.5%) and higher absorber mass transfer coefficient (up to 23.9%) compared to the MDEA-PZ blend. It was also discovered that the high MDEA-DA2MP concentration has lower regeneration energy (up to 25.4%), lower initial amine solution utilized (up to 20.5%), lower desorber mass transfer coefficient (up to 32.5%) compared to the MDEA-PZ blend. However, the optimal amine concentration is the 3 kmol/m3 MDEA-1 kmol/m3 DA2MP blend. Overall results show that the MDEA-DA2MP blend can offer a cost-effective and energy efficient CO2 capture compared to MDEA-PZ.
... Accordingly, 1-(2-HE)PP is compared with other tertiary amines, that is, triethanolamine (TEA), methyldiethanolamine (MDEA), dimethylethanolamine, 1-dimethylamino-2-propanol, 3-diemthylamino-1-propanol, 1-(2-hydoxyethyl)-pyrrolidine, diethylethanolamine via equilibrium CO 2 solubility and the second order rate constant (k 2 ). The comparison result is displayed in Figure 8. 28,[32][33][34][35] Among the comparison of tertiary amines, 1-(2-HE)PP shows superior performance on CO 2 absorption in both equilibrium CO 2 solubility and the second order rate constant. This is due to the beneficial molecular structure of 1-(2-HE)PP which results in better properties in CO 2 capture. ...
Article
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 298‐333 K, CO2 partial pressures from 8.1‐101.3 kPa and initial amine concentrations from 1‐5 M. Two thermodynamic models, namely semi‐empirical model and activity coefficient model are developed for the system. The activity coefficient model shows better estimation solubility with an AARD (absolute average relative deviation) 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. This article is protected by copyright. All rights reserved.
... Moreover, in alkaline solutions, CO 2 forms with water the carbonates and bicarbonates necessary for the precipitation reaction. For the absorption promoters used in these studies, the rate of CO 2 transport from the gas phase to the liquid phase increases in the TEA, Et 3 N and NH 3 series [42,43]. In previous studies, a mixture of vaterite and calcite was prepared in the presence of ammonia and monoethanolamine, when the time for passing CO 2 through a 0.2 mol/L CaCl 2 solution was relatively long and set at 60 min. ...
Article
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The aim of this work is to compare the effect of selected process parameters, gas flow rate, CO2 absorption promoter concentration and its pKa, on the precipitation of CaCO3 by the gas-liquid method using a model post-distillation liquid from the Solvay process. To ensure effective capture of CO2, the absorption promoters used were ammonia, triethanolamine and triethylamine. The Box-Behnken Design was applied to plan the experiments. The analysis of the influence of selected parameters on the course of the process and the characteristics of the obtained products was performed using the response surface methodology. In the studied range of variables, the type of absorption promoter characterized by its pKa has the most significant impact on the reaction time, polymorphic composition of the obtained CaCO3, particle size and their specific surface area. All precipitated CaCO3 samples were highly agglomerated mixture of vaterite and calcite.
... Reaction kinetics of common alkanolamines like aqueous MDEA with CO 2 are well-known and the theory of gas-liquid absorption via chemical reaction in the mentioned process is clearly described [26][27][28][29][30]. Donaldson and Nguyen [31] firstly proposed its reaction mechanism and reported that is a base catalyzed hydrolysis reaction. ...
Article
Solubility of CO2 in the hybrid solvents composed of aqueous N-methyldiethanolamine (MDEA) blended with 1-methyl-3-octyl-imidazolium tetrafluoroborate ([Omim][BF4]) ionic liquid (IL) was measured at temperatures from (298.15−343.15 K) and pressures of (0.2–4 MPa). The experimental trials were performed in a static high pressure equilibrium cell to determine the CO2 absorption capacity of novel absorbent solutions based on the isochoric saturation technique. The experimental data showed that, by rising the concentration of IL in the absorbent solutions’, the mole fraction of dissolved CO2 gas enhances gradually. Absorption capacity of these aqueous solutions was assessed and compared with pure ILs and alkanolamine solvents, which indicates the solutions studied in this research as better hybrid solvents in terms of CO2 loading. Furthermore, a semi empirical model is used to correlate the solubility data of this work, which presents a good agreement with an absolute average deviation (AAD %) of below 1%.
... 33 Conversely, one would not expect to see the same reaction pathway in hindered amines 34,35 nor in tertiary amines. 36,37 In both these cases, the CO 2 absorption into aqueous solutions follows mostly the bicarbonate formation mechanism. It is a matter of speculation how absorption into nonaqueous solutions of these amines would look like, as the absence of water implies the impossibility of bicarbonate formation. ...
Article
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We have evaluated the vapor-liquid equilibrium and heat of absorption of CO2 over water-lean mixtures of the amines diisopropylamine and N,N-diethylethanolamine (DEEA). This extends our previous research on water-lean solvents containing ethanolamine. The organic diluents N-methyl-2-pyrrolidone (NMP) and ethylene glycol (MEG) have been employed for solvent formulation. Since both diisopropylamine (a hindered amine) and N,N-diethylethanolamine (a tertiary amine) react with CO2 to form mainly bicarbonate in aqueous solutions, their behavior in nonaqueous mixtures is quite different from that of monoethanolamine. While MEG seems to maintain the reactivity of both diisopropylamine and DEEA even in nonaqueous mixtures, nonaqueous solvents with NMP act essentially as physical absorbents. This is an important indication that MEG is able to take part in the reaction mechanism between these amines and CO2, perhaps through alkylcarbonate formation, a fact that can be traced back to its relatively low autoprotolysis constant (pKS). This study represents a departure from our previous treatment on loss of CO2 solubility in water-lean solvents with monoethanolamine based on solvation phenomena alone, as it has become clear that the shift in equilibria in solvents with hindered and tertiary amines must account for Le Chatelier’s principle.
... Little et al. (1990) studied the reaction kinetics between carbon dioxide and TEA and DEMEA (diethyl monoethanolamine) amines. They reported linear relationships between the quadratic velocity constant and temperature (Littel et al., 1990). Wang et al. (2004) used membrane contactors to adsorb CO 2 into amine solutions. ...
Article
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Greenhouse effects are a natural phenomenon that plays a high role in shaping the climate system. In this research, MEA solution was used for CO2 capture in presence of activated carbon particles from waste walnut shells as a biosorbent. The process parameters including temperature, pressure, MEA concentration, and activated carbon were used in the central composite design (CCD) model. The absorption experiments were carried out in a laboratory setup at operational conditions including temperature in range of 20-60°C, pressure in range of 3.5-9.5 bar, MEA concentration in range of 2.5-8.5 wt%, and active carbon amount in range of 0.3-0.9 g/L. The process responses including CO2 loading, the amounts of CO2 absorption, and absorption percentage were obtained in the range of 0.444-0.720 molCO2/molMEA, 0.294-0.687 mol/L, and 19.32-52.25%, respectively. The optimal value of CO2 loading was obtained at temperature of 30 °C, pressure of 5.19 bar, activated carbon of 0.75 g, and MEA concentration of 7.00 wt%. The optimum values of responses were obtained 0.531, 0.609 mol/L and 50.04% for maximum loading, absorption amount, and absorption percentage, respectively. From the results, carbon dioxide loading in MEA solution increases in presence of activated carbon particles.
Article
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 (k0, 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 (k0, 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
Article
Forward osmosis (FO) is an innovative membrane-based process that requires limited external energy input to recover water as it relies on the spontaneous osmotic pressure gradient between a process water stream and a more concentrated solution; the latter is termed a “draw solution”. A suitable draw solution should have properties that allow its solute to be separated into recoverable products that can, in turn, be used to regenerate the initial draw solution with minimum energy requirements. These properties are crucial for the economics of the FO process because the basic energy requirement in FO arises from the separation and regeneration of the draw solution. Recently, it was proposed that such a draw solution can be an aqueous carbonated trimethylamine solution (TMAH:HCO3). In this project, the properties, i.e., composition, pH, and vapor–liquid equilibria (VLE), of the binary TMA–H2O and the ternary TMA–CO2–H2O systems were studied to generate thermodynamic data required to enable accurate speciation calculations by means of OLI-MSE software. Necessary analytical methods to measure accurately total dissolved TMA and total dissolved CO2 (within 4% error) in aqueous TMAH:HCO3 solutions were developed. Both VLE data at 50 and 60 °C and pH–composition data at 4 and 25 °C for the ternary TMA–CO2–H2O system were used to regress the missing binary interaction parameters and improve the model performance. Our resulting databank estimates total pressure (PTotal), partial pressure of TMA (PTMA), partial pressure of CO2 (PCO2), and pH, with 8, 15, 10, and 1% average absolute relative deviations (AARD), respectively.
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A comprehensive two-dimensional mathematical model based on surface renewal theory has been developed to analyze the CO2 absorption into piperazine (PZ)-activated aqueous N-methyldiethanolamine (MDEA) solvent by taking into account the structured packed bed column hydraulics, mass transfer resistances, and chemical reactions. The modeling results have been validated with the experimental data reported in the literature, and they have been found to be in good agreement with the experimental results. The effects of amine concentration, liquid temperature, initial CO2 partial pressure, liquid flow rate, and CO2 loading on the mass transfer performance have been evaluated in terms of overall mass transfer coefficient (KGav). The overall mass transfer coefficient and absorption flux of CO2 into aqueous MDEA+PZ blended solution have been calculated over the CO2 partial pressure range of 4–16 kPa, temperature range of 298–333 K, and solvent concentration of 1–3 M. To evaluate the performance of different solvents on separation process, some common industrial chemical absorbents including monoethanolamine (MEA), diethanolamine (DEA), triethylamine (TEA), MDEA and PZ were compared with a MDEA+PZ blended solution. The results indicate that CO2 absorption reaction with PZ is faster than that with MDEA, but also adding small amounts of PZ as a promoter to MDEA solvents improves significantly the absorption rate. The results show that CO2 absorption reaction with the MDEA+PZ blended solution is faster than that with TEA and MDEA, also comparable with DEA, but slower than those with MEA and PZ. The modeling results illustrate that the KGav enhances with increasing the solvent concentration, liquid temperature, and liquid flow rate, but reduces with increasing the CO2 loading and initial CO2 partial pressure. In addition, the reaction kinetics in terms of enhancement factor was found to decrease as the CO2 loading enhances and increase as the operating temperature rises.
Article
In this work, a comprehensive model has been developed for CO2 absorption into 4-diethylamino-2-butanol (DEAB) as a reactive amino alcohol solution. The mathematical model is developed based on penetration theory by simultaneous considering of mass transfer phenomenon and chemical reactions. The penetration theory provides appropriate absorption rate and enhancement factor for the chemical absorption. A numerical analysis was performed to solve the applied partial differential equations for the liquid and gas phases simultaneously. The model results were validated using the available experimental data in literature. In this study, the absorption of carbon dioxide by monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), methyldiethanolamine (MDEA) and DEAB solutions was compared theoretically in a packed column absorber. The impact of parameters such as DEAB concentration, temperature, liquid flow rate, CO2 loading and CO2 partial pressure on the performance of a split-flow absorber have been examined. The modeling results indicated that the overall mass transfer coefficient (KGav) for CO2 absorption into DEAB solution was lower than MEA and DEA solutions, however much higher than MDEA and TEA solutions in all range of CO2 loading and partial pressure. Increasing the operating temperature, DEAB concentration and liquid flow rate enhanced the overall mass transfer coefficient.
Article
Global warming and associated climate change has resulted in serious efforts towards reducing greenhouse gas emissions, primarily carbon dioxide through carbon capture. There are various technical options in pre- and post-combustion modes available viz., adsorption, absorption, membrane separation, chemical looping combustion with and without oxygen uncoupling and cryogenic separations. Among all these, absorption technology which could be deployed as a post-combustion option to be integrated with power plant, has been commercialized with amines as solvents long back. But there is a long way to go to improve this process in terms of economic viability due to large regeneration costs involved and to make it more environmental friendly with minimum toxic and corrosion problems due to solvents. In this review, absorption based carbon capture has been reviewed comprehensively and critically in terms of various aspects like solvents and their synthesis protocols, performance analysis of different solvent systems, contactors, kinetics and thermodynamics, modeling and simulation studies etc. Every section has been discussed in terms of the trends and developments observed including the contemporary status besides citing future challenges and prospects to improve the technology
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In this work, pseudo first-order reaction rate constants (k0) for the reaction of CO2 with sterically hindered secondary amines at temperatures of 293-313 K and various amine concentrations were studied using the rapid-mixing stopped-flow technique. It was found that the values of k0 increased as the concentration of amine in aqueous solution increased and as solution temperatures were increased. The second order rate constant (k2) at 293-313 K was also determined based on the proposed reaction mechanisms. The termolecular mechanism was able to fit the experimental data with predicted CO2 absorption rates of MAE and EAE with an absolute average deviation (AAD) of 2.81% and 14.96%, respectively. However, the base-catalyzed hydration mechanism is more precise in terms of the hindered amines (IPAE and TBAE) in predicting the CO2 absorption rates with AAD of 7.97 % and 5.15%. The combined data for the CO2 loading showed that all four amines have good properties for the post-combustion CO2 capture process in comparison with MEA. In comparison with the amine reference MEA (CO2 loading = 0.58 mole CO2/mole of amine), the CO2 loading of the four amines is between 0.66 and 0.93 mole of CO2/mole amine. These results show that IPAE and TBAE are good candidates for CO2 capture as alternatives to MEA because of their good CO2 absorption and high reaction rate with CO2.
Article
The precipitation of calcium carbonate was carried out by passing a gasous mixture of carbon dioxide and air into a calcium chloride solution. The selected compounds enhancing carbon dioxide absorption were used as additives which promote the formation of carbonate ions in the solution. The additives were ammonia, monoethanolamine, triethylamine and triethanolamine. The resulting calcium carbonate particles varied in polymorphic composition and the particle size depending on the used absorption promoter. When absorption occurred quickly in ammonia or monoethanolamine solutions, the obtained calcium carbonate particles were mainly vaterite. Calcium carbonate particles were precipitated as calcite in triethylamine or trietahnolamine solutions, while the rate of carbon dioxide mass transfer from gas to liquid phase was much slower. All precipitated calcium carbonate particles had monomodal particle size distributions. Smaller particles of vaterite were produced in the monoethanolamine solution and of calcite in the triethylamine solution.
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In this work, the blends of [C2OHmim][Gly] synthesized by our laboratory and MDEA in aqueous solution were prepared for CO2 capture, and the maximum absorption performance of the blends was obtained at the mole ratio of 8:2 of MDEA to [C2OHmim][Gly] with a total concentration of 1.0mol L⁻¹. CO2 loading of the blended absorbent was less adversely influenced by temperature and O2 concentration than that of MDEA aqueous, and it had a good performance in regeneration ability. The reaction mechanism of the CO2 absorption into MDEA/[C2OHmim][Gly] was investigated by ¹³CNMR. CO2 firstly reacted with [C2OHmim][Gly] to form carbamate, then carbamate promoted the reaction between CO2 and MDEA, which could be described as a shuttle mechanism. The kinetics of CO2 absorption was investigated in a double stirred-cell absorber at different temperatures and some important kinetic parameters were obtained, such as the reaction rate constant (k2) and the overall rate constant (kov). Experimental results indicated that the addition of [C2OHmim][Gly] enhanced CO2 absorption of MDEA under low CO2 partial pressure, which could improve the application of MDEA in industry.
Article
An amine phase-transfer approach is novel designed for the facile and recycle fixation and non-biological min-eralization of CO2 into alkaline earth carbonate (MCO3, M = Ca, Sr, and Ba) crystals with uniformed poly-morphs at room temperature under atmosphere pressure. The amines’ system based on two phases of water and Zn-tetraphenylporphyrin (ZnTPP) in CH2Cl2 provides a green and sustainable CO2 capture and utilization (CCU) strategy for the mitigation of anthropogenic CO2 emis-sion to atmosphere.
Article
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 (298.15-313.15K). 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 1 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. This article is protected by copyright. All rights reserved.
Article
To get a more accurate mass transfer coefficient model of CO2 into aqueous Monoethanolamine (MEA)/N,N-dimethylethanolamine (DMEA) solution in a packed column, the Henry’s law constant, equilibrium CO2 solubility, volumetric overall mass transfer coefficient (KGav), overall gas-phase mass transfer coefficient (KG) and the effective gas-liquid interfacial area (av) were comprehensively studied. The Henry’s law constant was obtained using a jacketed stirred glass reactor, and the equilibrium CO2 solubility was investigated using a bubbling absorption reactor. Additionally, the mass transfer performance was measured and evaluated experimentally in a packed column with DX-Type structured packing in terms of KGav, KG and av. These experiments were conducted under the MEA/DMEA concentration of 6 kmol/m3 with ratio of 5:1. The dynamic changes of solubility, species concentration, absorption heat of solution were analyzed under different CO2 loadings. The experimental results showed that the relationship of successive absorption without synergistic effect from the perspective of equilibrium state for the MEA/DMEA solution and the blended MEA/DMEA solution can reduce the CO2 absorption heat compared to that of MEA solution. Furthermore, the predicted model of KGav which should be suitable for different solution systems with DX-Type structured packings in a packed column, was also proposed and developed based on the KG model and av model in this work.
Article
The kinetics for the reaction of carbon dioxide with primary 3-(dimethylamino)-1-propylamine (DMAPA) in water and methanol systems were investigated using the stopped-flow technique over a temperature range of (298.15 to 313.15) K. Pseudo-first-order rate constants for the reaction of (CO2+DMAPA) in aqueous and methanol systems at (298.15 to 313.15) K were estimated at concentrations ranging from (40 to 150) mol·m-3 and (100 to 300) mol·m⁃3, respectively. Both the Zwitterion and Termolecular mechanisms successfully correlated the experimentally observed pseudo-first-order rate constants. The estimated second-order rate constants were in the range of (9.70 to 19.30) m3·mol⁃1·s⁃1. Aqueous solutions of DMAPA (primary and tertiary amino groups, 1o/3o) exhibited faster kinetics than primary amines such as monoethanolamine (MEA), 1-amino-2-propanol (1AP), 3-amino-1-propanol (3AP), or a hindred amine such as 2-amino-2-methyl-1-propanol (AMP). DMAPA kinetic rate was lower than diamines such as 2-(2-aminoethyl) amino ethanol (AEEA, 1o/2o) and ethylenediamine (EDA, 1o/1o). The estimated reaction orders varied from (1.15 to 1.37) and (1.04 to 1.22) in aqueous and methanol systems, respectively. The activation energies in aqueous and methanol systems were estimated using an Arrhenius expression. The estimated value of the activation energy in aqueous DMAPA was 39.47 kJ·mol-1 which was lower than that of MEA (46.6 kJ·mol-1). As expected, the reaction of CO2 with DMAPA was faster in water than in methanol.
Article
Despite the importance of natural gas (NG) as an energy source, there is a lot of pressurized landfill gas not exploited so far because it contains high CO 2 concentration. Therefore, this study aimed to develop a 2-D mathematical model to simulate CO 2 removal from NG stream contains high CO 2 concentration up to 70% at high-pressure up to 60 bar using three different dimensions of polyvinylidene fluoride (PVDF) hollow fiber membrane contactors. Aqueous solutions of activated methyldiethanolamine (MDEA) with piperazine (PZ) were adopted. The performance of considered absorbent at high-pressure was evaluated at the non-wetting mode condition of membrane contactor. Moreover, the effect of pressure, contact area, gas flow rate, MDEA concentration into the amine mixture, PZ concentration, temperature and membrane properties were theoretically investigated. The findings stated that activated MDEA had different performance in terms of membrane wetting compared with other amines, which used at high pressure in previous studies. In addition, the simulation results showed that CO 2 removal efficiency was significantly enhanced, when the operating pressure, contact area, PZ concentration and temperature were increased. However, increasing gas flow rate leads to reduce CO 2 removal efficiency. Furthermore, the CO 2 absorption was significantly improved by adding a small amount of PZ to MDEA. The predicted model results showed a good agreement with experimental data obtained from the literature.
Article
The stopped-flow technique was applied for the investigation of kinetics of CO2 absorption into loaded MDEA solution over the range of MDEA concentration of 0.4 to 1.0 kmol/m³, CO2 loading of 0.14 to 0.17 mol CO2/mol amine and the temperature of 293 to 308 K. The kinetics of unloaded MDEA was also investigated for the comparison and a huge difference of results which should be equal theoretically was indicated between loaded and unloaded systems. Then, the effect of CO2 loading on the kinetics was studied. As the loading increases, there is a turning point around loading of 0.10, below which the overall reaction constant decreases strongly. It was found that contribution of hydroxyl is a crucial to overall reaction rate constant and cannot be ignored and the influence of reverse reaction of MDEA and CO2 can be ignored. The kinetics of loaded system obtained in this work was modified and interpreted well by the base-catalyzed mechanism with AARD of 6.29% and compares favorably with literature using gas-liquid apparatus. The kinetics of unloaded system in this work is approximately twice as that of literature and loaded system. This work provided literature review and interpretation of MDEA-CO2-H2O and is hopeful to shed light on kinetic study of CO2 absorption in tertiary amine using stopped-flow apparatus.
Article
The equilibrium solubility and kinetics of N1, N2-dimethylethane-1,2-diamine (DMEDA), a new and potential diamine absorbent for CO2 capture, have been investigated in this work. The equilibrium solubility of 2M DMEDA solution was measured at 298.15-333.15 K and with CO2 partial pressures of 5-100 kPa. The heat (-56.47 kJ/mol) of CO2 absorption was obtained by the Clausius-Clapeyron equation. In addition, the NMR analysis further confirmed the formation of dicarbamate and that the reaction rate contribution by dicarbamate can be ignored, and showed the CO2 absorption in the liquid phase can be divided into 3 regions as the CO2 loadings increased. The pseudo-first-order rate constant (k0) of CO2 absorption into aqueous DMEDA solution was then investigated at different amine concentrations (0.025-0.075 mol/L) and temperatures (293.15-313.15 K) with the stopped-flow technology. The results show that the k0 value in the DMEDA solution increases with the increase of temperature and amine concentration. The pseudo first order assumption, zwitterion and termolecular mechanism were respectively applied to DMEDA-CO2-H2O system. The results show that the predicted CO2 absorption rate exhibits good agreement with the experimental data with an absolute average deviation (AAD) of 3.66%, 3.77 % and 4.51 % with respect to the pseudo first order assumption, zwitterion and termolecular models, respectively.
Article
In order to be able to understand and compensate for the mass transfer effects on the reaction kinetics that typically occur in these studies, the influences of diffusion and gas phase resistance on the measurement of kinetics have been investigated. Carbon dioxide (CO2) absorption into monoethanolamine (MEA) and N-methyldiethanolamine (MDEA), have been taken as the fast and slow reaction cases in this work. The inflection point between diffusion control and reaction control regions was found in the fast reaction case, but not in the slow one. Further, there is a low critical value of Pinert, below which its effect can be ignored, in the fast reaction system. Conversely, the critical value of Pinert in the slow reaction system is higher. Additionally, credible intrinsic kinetics of the both systems have been obtained under optimum conditions, and expanding the temperature range to lower than what is available in the literature.
Article
In order to establish an integrative mass transfer coefficient (KGaV) model for CO2 absorption into blended monoethanolamine (MEA)/1-dimethylamino-2-propanol (1DMA2P) solution in packed column, the models of CO2 Henry’s law constants (HeCO₂-MEA/1DMA2P) and the equilibrium CO2 solubility (αeq) were constructed. The experimental produced data can be reasonably analyzed. In this work, the Arrhenius equation was employed to fit the values of HeCO₂-MEA/1DMA2P at different temperature with AARD of 4.06%; the Kent-Eisenberg prediction model and empirical polynomial prediction model were used to predict the data of αeq under different CO2 partial pressures and temperatures with AARDs of 2.64% and 0.83%, respectively; the empirical KGaV model proposed by Li, the empirical KGaV model proposed by Aroonwilas and new KGaV model were used to correlate the average values of KGaV with AARDs of 14.36%, 12.44% and 9.03%, respectively; the model for outlet CO2 concentration (yCO₂,out) in packed column was developed with AARD of 15.97%. Moreover, the heat of CO2 absorption in 6 kmol/m³ MEA/1DMA2P solution was estimated by Gibbs-Helmholtz equation which gave a value of −39.8 kJ/mol. The results show that the blended MEA/1DMA2P solution has advantages that make it a potential absorbent for CO2 capture.
Article
Amine-based post-combustion CO2 capture technology has a great potential to control the CO2 emissions but is expensive because a huge amount of thermal energy is required for solvent regeneration due to the poor CO2 desorption kinetics. Tertiay amines can be efficiently regenerated but the poor CO2 absorption kinetics is a major limitation to its large-scale deployment. Here, we synthesized tripodal nitrate salt and its metal catalysts and investigated catalytic activity in a highly concentrated tertiary amine medium, N-methyldiethanolamine (MDEA), for CO2 capture process. To analyze the catalytic performance, the rate constant for CO2 hydration, CO2 absorption rate, and CO2 desorption rate were experimentally studied. The gathered results suggest that catalyst 2 can improve the CO2 absorption and CO2 desorption efficiencies by 35% and 21%, respectively. Based on the obtained results, the possible reaction mechanism is also presented. These findings can provide a new route for an energy-efficient CO2 capture using tertiary amines.
Article
Abstract: In this paper, a steady-state model based on mass transfer for selective absorption of hydrogen sulfide gas in MethylDiEthanolAmine (MDEA) solution, in the packed absorption tower is presented. This model is able to predict the concentration and temperature profiles in gas and liquid phases for the (MDEA-H2S-CO2H2O) system. In order to predict the profile of CO2 concentration, the second-order kinetic constants of reaction between gas and MDEA solution was used. Also, among the existing kinetic data, the best one was selected. In addition, the effective parameters in obtaining these profiles and the maximum point of selectivity factor were examined in this model. In order to evaluate accuracy of proposed model, the results were compared with from a pilot plant test as well as using operating data from absorption packed tower of the gas sweetening unit of phases 4 and 5 of South Pars Gas Complex. The obtained results reveal an acceptable compatibility between experimental data and prediction of the presented model. http://www.sid.ir/En/Journal/JournalListPaper.aspx?ID=155072
Article
Carbonic anhydrase (CA) is the most effective CO2 hydratase catalyst, but the poor storage stability and repeatability of CA limit its development. Therefore, CA was immobilized on the epoxy magnetic composite microspheres to enhance the CO2 absorption into N-methyldiethanolamine (MDEA) aqueous solution in this work. In the presence of immobilized CA, the CO2 absorption rate of MDEA solution (10 wt%) (0.63 mmol·min⁻¹) was greatly improved by almost 40%, and their reaction equilibrium time was shortened from 150 min to 90 min compared with that into MDEA solution. The results indicated that the absorption of CO2 into MDEA solution had been significantly enhanced by using CA. After the 7th reuse recycle, the activity of the immobilized CA was still closed to its initial value at 313.15 K. Moreover, enzyme catalytic kinetics of immobilized CA was investigated using the p-nitrophenyl acetate (p-NPA) as substrate. The values of Michaelis–Menten constant (Km) and the maximum velocity (Vmax) of the immobilized CA were calculated to be 27.61 mmol/L and 20.14 × 10−3 mmol·min⁻¹·mL⁻¹, respectively. Besides, the kinetics of CO2 reaction into MDEA with or without CA were also compared. The results showed that CO2 absorption into CA/MDEA aqueous solution obeyed the pseudo first order regime and the second order kinetics rate constant (k2) was calculated to be 929 m³·kmol⁻¹·s⁻¹, which was twice higher than that of MDEA aqueous solution without immobilized CA (k2=414 m³·kmol⁻¹·s⁻¹) at 313.15 K.
Article
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.
Article
A numerically solved reaction rate/kinetic model for CO2 removal from a CO2/N2 gas mixture into novel reactive 1-dimethylamino-2-propanol (1DMA2P) solution in a gas–liquid membrane contactor was constructed. The model is assembled by considering the main transport phenomena and all possible reactions. The validated model was applied to investigate the transport phenomena in the different sides of membrane. The impact of main operation parameters on the performance of HFMC were evaluated. The influence of co- and counter-current operational modes on the absorption process was analyzed. The sensitivity analysis under moderate conditions indicated that the mass transfer resistance of gas phase is dominant with respect to liquid phase. Enhancing the liquid temperature, solvent circulation velocity, 1DMA2P concentration and also decreasing gas stream velocity increase the CO2 absorption. The CO2 removal using conventional and alternative amines were analyzed and compared. It is observed that due to high capacity of 1DMA2P for CO2 capture and its low regeneration heat, it could be considered as one of the efficient solvent for CO2 removal.
Article
Draw solute separation from a draw solution is the main source of energy consumption in Forward Osmosis. The draw solute separation efficiency from a TMA-CO2-H2O draw solution and the decomposition kinetics of the latter were investigated in this study from 30 to 50 °C and 0.75 to 0.35 bar. The former proved stoichiometric and efficient with ~100% draw solute removal after 60 min at 50 °C, 0.35 bar. The rate determining step proved to be the physicochemical phenomenon of the desorption of the less volatile gas, TMA. It was found to be first order with respect to TMA(aq) concentration. The combined effects of temperature and pressure on the k values proved that only the temperature has a significant effect. Finally, an Eyring-Arrhenius model was designed to estimate k values for the TMA desorption rate in the temperature and pressure range studied in this work.
Article
Formulation of efficient absorbing solutions for carbon dioxide capture is essential to reduce the operation costs of industrial gas treatment plants. Recently, mixed amine systems, typically composed of a tertiary and a primary or secondary amine, have been a growing interest in academic and industrial research. In particular the so‐called activated methyldiethanolamine (aMDEA), which contains small amounts of piperazine (PZ), has become one of the most promising new candidates. This work intends to perform a comparison between the performance of single amines on the one hand and their blends on the other hand with the aim of elucidating how PZ and MDEA can interact in the latter situation. In the first part, aqueous solutions made up of a pure reagent (either MDEA or PZ) were studied. Rates of CO2 transfer from a gas phase to unloaded and loaded solutions, up to nearly saturation points, were experimentally investigated for a wide range of operating conditions using a membrane contactor. Observed CO2 transfer rates were reproduced with a simple, yet effective, model that captured the main physical and chemical aspects. This article is protected by copyright. All rights reserved
Article
In this work, the equilibrium CO2 solubilities of five tertiary amines, namely Triethanolamine (TEA), N-methylethanolamine (MDEA), 2-(Dimethylamino)ethanol (DMEA), 3-dimethyl-amino-1-propanol (3DMA1P), and Diethylethanolamine (DEEA) were measured over the temperature range of 298.15–313.15 K, and at CO2 partial pressures up to 60.8 kPa. The activity-structure relationship was studied on the molecular level to account for the differences in equilibrium CO2 solubility. The M-KE model was applied to correlate the vapor-liquid-equilibrium data of the five tertiary amine-H2O-CO2 systems. Results show that the model is able to correlate experimental data very well and gives reasonable prediction results with average absolute deviation (AAD) of 2.5% for TEA, 3.3% for MDEA, 1.3% for DMEA, 1.0% for 3DMA1P and 0.8% for DEEA. In addition, the CO2 absorption heat was calculated using the Clausius-Clapeyron equation. The potential for the five amines to be considered as alternative solvents for CO2 capture was evaluated in terms of equilibrium CO2 solubility, second order reaction rate constant and CO2 absorption heat.
Article
Full-text available
In this investigation, experimental measurements of the rate of absorption of N2O and CO2 into aqueous solutions of MDEA were taken, using a single sphere absorber. Diffusion coefficients and kinetic rate constants were calculated from the absorption rate data by allowing for resistance to mass transfer in the gas and liquid phases. The N2O data were used to infer the diffusivity of CO2 in MDEA solutions. As discussed by R.A. Tomcej et al. these fundamental parameters are required by nonequilibrium stage models used to predict the performance of industrial contactors that use MDEA as the chemical solvent for the selective removal of H2S from gaseous streams containing H2S and CO2. The results of the analysis of the N2O absorption studies, along with data from other sources, are presented. The pseudo first-order reaction-rate constants were divided by the free amine concentration to calculate the second-order rate constant, k2, which is independent of concentration. The activation energy was calculated to be 42.7 kJ/mol (10.2 kcal/mol).
Article
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
Article
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
Article
Two models of absorber have been developed which describe the absorption of H2S and CO2 from natural gases by aqueous di-isopropanolamine (DIPA) or methyl-di-ethanolamine (MDEA) solutions. In these models mass transfer, reaction and equilibrium processes as they prevail in conventional tray absorbers and in cascades of trickle bed reactors are incorporated. Owing to the better mass transfer characteristics of the latter type of absorber, i.e. the larger ratio between the gas phase and liquid phase mass transfer coefficients, kg/kℓ, higher selectivities for the absorption of H2S from sour natural gases are realized.
Article
The measurements of the rate of absorption of CO2 into aqueous solutions of KOH, NaOH and LiOH containing neutral electrolytes (carbonates, chlorides, bromides, nitrates and sulphates) have been performed using the laminar-jet technique. The dependence of the reaction rate constant on the temperature and ionic strength has been presented for the reaction of CO2 with hydroxyl ions in aqueous electrolyte solutions.
Article
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.
Article
The reaction between carbon dioxide and amines is of great technical importance and has been the subject of many investigations. The authors have shown that the reaction for secondary amines in anhydrous ethanol and in aqueous solution is exclusively second-order in amine and that the zwitterion intermediate postulated by Danckwerts is probably of negligible significance in the mechanism. The reaction with tertiary amines has also been studied, but the data are less controversial. In order to complete their studies of the reactions of carbon dioxide with amines, using their conductimetric stopped-flow apparatus, they have studied this reaction for MDEA (methyldiethanolamine, IUPAC name N-methyl-2,2â²-iminodiethanol) and TEA (triethanolamine, IUPAC name 2,2â²,2{double prime}-nitrilotris(ethanol)).
Article
The pKa., values were determined potentiometrically for the conjugate acids of 2-(2-aminoethoxy)ethanol (DGA), 2-(methylamino)ethanol (MMEA), 2-(fert-butylamino)ethanol (TBAE), 2-amino-2-methyl-1-propanol (AMP), N-methyldiethanolamine (MDEA), 2-(dimethylamino)ethanol (DMMEA), 2-(diethylamino)ethanol (DEMEA), and 2 (diisopropylamino)ethanol (DIPMEA) at 293, 303, 318, and 333 K.
Article
Solubility and diffusivity of N//2O and CO//2 in water were determined as a function of temperature from the results published in the open literature, and new data were measured in the present work. The solubility of N//2O in several aqueous alkanolamine (DEA, DIPA, DMMEA, and DIPA) solutions at various temperatures was measured and correlated over a wide range of conditions. For both the diffusivity of N//2O and the alkanolamine in aqueous alkanolamine solutions a modified Stokes-Einstein relation was derived. With the aid also of the 'N//2O analogy' the diffusivity of CO//2 in these solutions can be estimated.
Article
Reaction kinetics of CO/sub 2/ with triethanolamine (TEA) and methyldiethanolamine (MDEA) in aqueous solution have been studied by using a stopped-flow technique with pH detection. Rate constants are obtained from the comparison of experimental and theoretical curves giving the optical density as a function of time. At concentrations of CO/sub 2/ well below the saturation limit, the results are consistent with the hydration reactions of the CO/sub 2/ molecules either with neutral water molecules or with hydroxide ions, depending upon the pH, itself governed by the ionization equilibrium of the dissolved amine. Moreover, a specific (catalytic) reaction, first order with respect to both carbon dioxide and amine (rate constant, 2.85 M/sup -1/ s/sup -1/ at 25/sup 0/C), has been shown to contribute significantly to the reaction rate in the case of the first amine (TEA) only.
Article
Reaction kinetics of CO2 with mono-, di-, and triethanolamine and triethylamine have been studied using a tracer 14CO2 membrane transport technique. At low concentrations of mono- and diethanolamine the results are consistent with carbamate formation. At higher concentrations the chemistry appears to be more complex. Transport results are discussed in terms of various potential phenomena. Although triamines do not form carbamates with CO2, both triethanolamine and triethylamine increased the membrane transport flux of CO2. The only reasonable reaction mechanism for triethanolamine consistent with our data is base catalysis of CO2 hydration. Triethylamine, on the other hand, appears to act only as a weak base to produce free OH- which reacts with CO2.
Article
Experiments were carried out over a wide range of contact time for the absorption of carbon dioxide into aqueous amine solutions. It was suggested from the experimental results with a laminar liquid-jet, a wetted wall column and a quiescent liquid absorber that the present absorption processes should be analyzed by a gas absorption with the consecutive reaction of the form of A + 2B →kI R and A + R →kII Products. The values of rate constants for the second-order first reaction step (k1) for the diethanolamine and triethanolamine were estimated as 1340 and 16.8 1/mol-sec, respectively. The value of rate constant for the second reaction step was found to be constant irrespective of the liquid reactant. On a fait des expériences, sur une grande échelle de temps de contact, en rapport avec l'absorption de l'anhydride carbonique dans des solutions aqueuses d'amines. On a suggéré, à la suite des résultats expérimentaux obtenus avec un jet laminaire de liquide, une colonne parois mouillées et un absorbeur de liquide au repos, que les procédés actuels d'absortion soient étudiés au moyen de l'absorption d'un gaz avec une reaction consécutive de la forme de A + 2B →kI R et A + R →kII produits. Les valeurs des constantes de vitesse pour la première étape de réaction de second ordre, dans le cas de la diéthanolamine et de la triéthanolamine, ont été évalués respectivement à 1340 et 16.8 1/mol-s. La valeur de la constante de vitesse pour la seconde étape de réaction s'est avérée constante, quel qu'ait été le réactif liquide.
Article
The kinetics of the reaction of carbon dioxide with mono- and diethanolamine in such nonaqueous solvents as methanol, ethanol, and 2-propanol and in water were studied using a stirred tank absorber with a plane gas-liquid interface at 303 K. The reaction was found to be of first order with respect to carbon dioxide for every solvent. The order of reaction with respect to ethanolamine was found to be unity only for an aqueous solution of monoethanolamine and for the other solutions, ranged from 1.4 to 2, depending on the solvent species. The reaction order was increased in the order of water, methanol, ethanol, and 2-propanol. The variation of the reaction order with the solvent species could be explained in terms of a reaction scheme via a zwitterion. Almost linear dependence of the logarithm of the reaction rate constant on the solubility parameter of the solvent was derived.
Article
Steady- and unsteady-state theories for interfacial mass transfer are used to model gas absorption with second-order, reversible reaction and the absorption of CO2 into aqueous MDEA (methyldiethanolamine). The latter case represents a system of industrial interest, having both finite rate and equilibrium reactions. Steady-state theories studied are film theory, simplified eddy diffusivity theory, and an approximation to surface renewal theory. Higbie's penetration and Danckwert's surface renewal theories are the unsteady-state theories reviewed. The Nernst-Planck equations for diffusion and reaction in ionic systems are solved numerically using orthogonal collocation on finite elements. Comparisons are made between the absorption enhancement factor obtained for all theories. The applicability of approximate methods of solution for absorption with chemical reaction is also discussed.
Article
Differential rates of CO2 adsorption into 0.90, 0.47 and 0.24 M aqueous solutions of 2-(diethylamino)ethanol (DEAE) were measured at 323 K over a wide range of carbonation ratios. A rigorous thermodynamic model was used to define species activities which were coupled with Danckwerts' gas-liquid reaction model to deduce the kinetics. The reaction of CO2 with this highly basic tertiary amine occurs by two pathways: (1) a minor path via the CO2 reaction with hydroxide ion and (2) a predominant reaction pathway that can be characterized by its first order dependency on the free amine concentration. The second reaction was proposed to involve an internal salt-like intermediate,.
Article
A recent paper by Blauwhoff et al. (1984) has incited us to reexamine some of our previous results concerning the kinetics of reaction of CO2 with methyldiethanolamine (MDEA). The results can be very satisfactorily interpreted if an amine-catalyzed reaction with a rate constant 3.2 ( ± 1.0) M −1 s −1 is introduced in the theoretical simulations. This value agrees fairly well with the value obtained by the authors mentioned above (4.8 M −1 s −1. The influence of the pKA value of the amine on the theoretical simulation is also examined. The mechanism proposed by Blauwhoff et al. for the diethanolamine (DEA) reaction with CO2 is discussed and the values of their kinetic constants are compared with our value.
Article
The kinetics of the reactions of carbon dioxide with monoethanolamine, diethanolamine and triethanolamine in aqueous solutions were studied at various
Article
The kinetics of the reaction of carbon dioxide in MDEA solutions were studied both experimentally and theoretically. It is concluded that MDEA acts as a homogeneous catalyst for CO2 hydrolysis, and as a result the rate of absorption in aqueous MDEA solutions is significantly larger than one would calculate by simply taking into account the alkalinity of the reaction. A possible zwitterion mechanism is proposed for this reaction. The minor effect of ionic strength were also studied with the presence of other ions.
Article
An absorption model has been developed which can be used to calculate rapidly absorption rates for the phenomenon mass transfer accompanied by multiple complex parallel reversible chemical reactions. This model can be applied for the calculation of the mass transfer rates, enhancement factors and concentration profiles for a wide range of processes and conditions, for both film and penetration model. With the aid of this mass transfer model it is demonstrated that the absorption rates in systems with multiple reversible reactions can be substantially greater than the summation of the absorption rates derived for the single systems. This latter fact provides a scienctific basis for the application of aqueous mixed amine solutions for industrial sour gas treating. Also it is shown that for kinetic studies by means of abosorption experiments for reversible reactions the presence of small amounts of fast reacting contaminants can have an overruling effect on the outcome of the determination of the reaction kinetics. It is shown that the concepts of shuttle mechanism and homogeneous catalysis refer to asymptotic situations,for practical situations intermediate behaviour was observed which was previously not accessible for analysis. Experimentally determined absorption rates of CO2 in aqueous solutions of various mixtures of alkanolamines (MMEA-MDEA, MEA-MDEA, DIPA-MDEA and MEA-DEA-MDEA) can be prdicted extremely well for the several mass transfer regimes which were studied experimentally. The experiments were carried out in a stirred vessel with a flat surface over a wide range of process conditions.
Article
The reaction between CO2 and primary and secondary alkanolamines (DEA and DIPA) has been studied both in aqueous and non-aqueous solutions (ethanol and n-butanol) at various temperatures. Reaction kinetics have been established by chemically enhanced mass transfer of CO2 into the various solutions. The experiments were performed in a stirred vessel operated with a horizontal interface which appeared to the eye to be completely smooth. The reaction can be described with the zwitterion-mechanism originally proposed by Caplow (1968) and reintroduced by Danckwerts (1979). Literature data on the reaction rates can be correlated fairly well with this mechanism. As all amines react with CO2 in a reversible way, and the mass transfer models used for the interpretation of the experimental data neglect this reversibility and take only the forward reaction rate into account, the influence of the reversibility is studied. With the aid of numerical mass transfer models (Versteeg et al., 1987b,c) the experimental method with its underlying assumptions have been verified and the applicability and the limits of this method were determined. Special attention has been paid to the influence of small amounts of impurities (amines) on the measured mass transfer rates. A Brønsted relationship exists between the second-order rate constant, k2, for the formation of the zwitterion and the acid dissociation constant of the alkanolamine.
Article
An improved numerical technique was used in order to develop an absorption model with which it is possible to calculate rapidly absorption rates for the phenomenon of mass transfer accompanied by a complex reversible chemical reaction. This model can be applied for the calculation of the mass transfer rates (and enhancement factors) for a wide range of processes and conditions, for both film model and penetration model, complex kinetic expressions and equilibrium reactions. With the aid of this method it is demonstrated that reversibility has a substantial effect on the absorption rate. Approximate analytical solutions for the calculation of the mass transfer rates presented in literature are checked for their validity. All approximations are of restricted use and can be applied only for a limited number of reactions and it is desirable to check the approximation with the aid of a numerical solution before it is used for mass transfer calculations. The linearization method of Hikita and Asai (Kagaku Kogaku11, 823–830, 1963) cannot be applied generally for reversible reactions and therefore can lead to erroneous results. Experimentally determined absorption rates of H2S and CO2 in various aqueous alkanolamine solutions can be predicted satisfactorily for the several mass transfer regimes studied.
Article
Mass transfer has been studied in gas-liquid stirred vessels with horizontal interfaces which appeared to the eye to be completely smooth. Special attention has been paid to the influence of the coefficient of molecular diffusion. The results are compared with those published before. The simplifying assumptions of identical hydrodynamical conditions at the same stirrer speed in one particular geometry, which have been made in some previous investigations, is shown to be wrong and may lead to incorrect conclusions on the influence of the diffusion coefficient. For the gas phase the mass transfer can be described by the penetration theory (Higbie, R., 1935, Trans. Am. Inst. Chem. Engrs35, 36–60) or surface renewal model (Danckwerts, P. V., 1951, Ind. Engng Chem.43, 1460–1467). With the use of a dimensionless equation, Sh, Re and Sc numbers, all data, even experiments carried out at elevated pressures, could be well correlated. For the liquid phase the results indicate that the mass transfer cannot be described by a simple model. The King model (King, C.J., 1976, Ind. Engng Chem. Fundam.5, 1–8), a combination of molecular and eddy diffusivity, is able to explain qualitatively the observed phenomena and the literature data.
Article
A stirred cell gas-liquid contactor was used to investigate the kinetics of the reaction between carbon dioxide and methyldiethanolamine (MDEA) in aqueous solutions. Experiments were conducted over the temperature range 15–35°C and for MDEA concentrations from 0.85 to 1.70 g mol/l. The kinetic data support a previously proposed mechanism in which MDEA acts as a homogeneous catalyst for CO2 hydrolysis. The second-order rate constant was found to have a value of 2/47 l/g mols at 25°C, in good agreement with existing literature values. The second-order rate constant is correlated well by the Arrhenius expression
Selective H,S Removal by Mixed Solvents
  • J A M Spaninks
  • W H Hesselink
  • M M Suenson
Spaninks, J. A. M., W. H. Hesselink, and M. M. Suenson, " Selective H,S Removal by Mixed Solvents, " AIChE Meeting, New Orleans (Mar. 6-9,1988).
Reactions between Carbon Dioxide and Amine Alcohols
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Jfrgensen, E., and C. Faurholt, " Reactions between Carbon Dioxide and Amine Alcohols, " Acra Chem. Scand., 8, 1141 (1954).
  • Aqueous Alkanolamine
  • Solutions
Aqueous Alkanolamine Solutions, " J. Chem. Eng. Data, 32, 29 (1988~).