Kinetics of carbon dioxide absorption in aqueous solution of diethylenetriamine (DETA)

A string of discs contactor was used to measure the kinetics CO₂ absorption in unloaded aqueous solution with the diethylenetriamine (DETA) concentrations ranging between 1.0 and 2.9 kmol m⁻³ and at temperatures ranging between 298.1 and 332.3 K. The reaction rates strongly increase as the increasing the concentrations and temperatures. Both the termolecular and the zwitterion models were applied to interpret the experimental data and gave identical results for all practical purposes. The reaction order with respect to the DETA concentration is found to vary slightly with temperature between 1.71 and 1.76 with an average of about 1.73. Both DETA and water contribute as a base in carbamate formation. It was found that fitting of experimental data to the termolecular mechanism gave statistically more robust results than fitting to the zwitterion mechanism.     

Pilot plant study of two new solvents for post combustion carbon dioxide capture by reactive absorption and comparison to monoethanolamine

Application of new solvents will substantially contribute to the reduction of the energy demand for the post combustion capture of CO₂ from power plant flue gases. The present work describes tests of such new solvents in a gas-fired pilot plant, which comprises the complete absorption/desorption process (column diameters 0.125 m, absorber/desorber packing height 4.25/2.55 m, packing type: Sulzer BX 500, flue gas flow 30–100 kg/h, CO₂ partial pressure 35–135 mbar). Two new solvents CESAR1 (0.28 g/g 2-amino-2-methyl-1-propanol+0.17 g/g piperazine+0.55 g/g H₂O) and CESAR2 (0.32 g/g 1, 2-ethanediamine+0.68 g/g H₂O), which were developed in an EU-project, were systematically studied and compared to MEA (0.3 g/g monoethanolamine+0.7 g/g H₂O). The two new solvents and MEA were studied in the same way in the pilot plant and detailed results are reported for all solvents. In the present study the structured packing Sulzer BX 500 is used. The measurements are carried out at a constant CO₂ removal rate of 90% by an adjustment of the regeneration energy in the desorber for systematically varied solvent flow rates. An optimal solvent flow rate leading to a minimum energy requirement is found from these studies. Direct comparisons of such results can be misleading if there are differences in the kinetics of the different solvent systems. The influence of kinetic effects is experimentally studied by varying the flue gas flow rate at a constant ratio of solvent mass flow to flue gas mass flow and constant CO₂ removal rate. Results from these studies indicate similar kinetics for CESAR1, CESAR2 and MEA. The direct comparison of the pilot plant results for these solvents is therefore justified. Both CESAR1 and CESAR2 show improvements compared to MEA. The most promising is CESAR1 with a reduction of about 20% in the regeneration energy and 45% in the solvent flow rate.     

Kinetics of carbon dioxide absorption into aqueous amine amino acid salt: 3-(methylamino)propylamine/sarcosine solution

A string of discs contactor apparatus was used to measure the CO₂ absorption kinetics into an unloaded aqueous amine amino acid salt, 3-(methylamino)propylamine/sarcosine, SARMAPA solution. The solution was prepared by mixing equinormal proportions of sarcosine, SAR and 3-(methylamino)propylamine, MAPA. Experiments were carried out for the concentration range 1.0–5.0 kmol m⁻³ and for temperatures 25–62 °C. The termolecular mechanism was applied to interpret the experimental data after correcting for non-idealities from the ionic strength using an ionic correction factor. A model correlation without the ionic strength correction was found not to give a good fit to the experimental data. The reaction rate constant for aqueous SARMAPA was determined and found to be comparable to values for amines. It increases significantly with temperature and concentration. The reaction rate constant for water is higher in the SARMAPA system than in amine systems indicating that water contributes significantly to the overall absorption rate and more than in amine systems. The reaction order with respect to the amino acid salt, SARMAPA, concentration varies from 1.06 to 1.43 with an average value of 1.21. A simplified approach applied to the complex speciation chemistry of the amine amino acid salt, AAAS, system gave a good representation of the experimentally observed kinetic rate constant.     

Kinetics of absorption of carbon dioxide in aqueous piperazine solutions

In the present work the absorption of carbon dioxide into aqueous piperazine (PZ) solutions has been studied in a stirred cell, at low to moderate temperatures, piperazine concentrations ranging from 0.6 to , and carbon dioxide pressures up to 500 mbar, respectively. The obtained experimental results were interpreted using the DeCoursey equation [DeCoursey, W., 1974. Absorption with chemical reaction: development of a new relation for the Danckwerts model. Chemical Engineering Science 29, 1867-1872] to extract the kinetics of the main reaction, 2PZ+CO₂→PZCOO^-+PZH⁺, which was assumed to be first order in both CO₂ and PZ. The second-order kinetic rate constant was found to be at a temperature of , with an activation temperature of . Also, the absorption rate of CO₂ into partially protonated piperazine solutions was experimentally investigated to identify the kinetics of the reaction . The results were interpreted using the Hogendoorn approach [Hogendoorn, J., Vas Bhat, R., Kuipers, J., Van Swaaij, W., Versteeg, G., 1997. Approximation for the enhancement factor applicable to reversible reactions of finite rate in chemically loaded solutions. Chemical Engineering Science 52, 4547-4559], which uses the explicit DeCoursey equation with an infinite enhancement factor which is corrected for reversibility. Also, this reaction was assumed to be first order in both reactants and the second-order rate constant for this reaction was found to be at 298.15 K.     

Kinetics and modeling of carbon dioxide absorption into aqueous solutions of piperazine

In this work, the kinetics of the reaction between CO₂ and aqueous piperazine (PZ) have been estimated over the temperature range of 298-313 K from the absorption data obtained in a wetted wall contactor. The absorption data are obtained for the PZ concentrations of 0.2- and for CO₂ partial pressures up to 5 kPa. A coupled mass transfer-kinetics-equilibrium mathematical model based on Higbie's penetration theory has been developed with the assumption that all reactions are reversible. The model is used to estimate the rate constants from the experimental data for absorption of CO₂ in aqueous PZ. The estimated rate constants of this study are in good agreement with those reported in the literature.     

Kinetics of absorption of carbon dioxide into aqueous solution of 2-(1-piperazinyl)-ethylamine

The absorption of CO₂ into aqueous solution of 2-(1-piperazinyl)-ethylamine (PZEA) were studied at 303, 313, and 323 K within the amine concentration range of 0.083-1.226 kmol m⁻³ using a wetted wall column absorber. The experimental results were used to interpret the kinetics of the reaction of CO₂ with PZEA within the amine concentration range of 0.150-1.226 kmol m⁻³ for the above mentioned temperature range. Based on the pseudo-first-order condition for the CO₂ absorption, the overall second order reaction rate constants were determined from the kinetic measurements. The reaction order was found to be in between 0.99 and 1.03 with respect to amine for the later mentioned concentration range. The kinetic rate parameters were calculated and presented at each experimental condition. The second-order rate constants k₂, were obtained as 31867.6, 56354.2, and 100946 m³ kmol^-1 s^-1 at 303, 313, and 323 K, respectively, with activation energy of 47.3 kJ mol⁻¹. This new amine in the field of acid gas removal can be used as an activator by mixing with other alkanolamine solvents due to its very high rate of reaction with CO₂.     

Kinetics of the reactive absorption of hydrogen sulfide into aqueous ferric sulfate solutions

The reactive absorption of H₂S into aqueous Fe₂(SO₄)₃ solutions, was studied in a stirred cell reactor operated batchwise with and without a flat interface. The temperature was varied from 25°C to 65°C and the concentrations of aqueous Fe₂(SO₄)₃ solutions ranged from 0.025 to . The corresponding initial pH values ranged from 2 to 0.8, respectively. Additional measurements were conducted at other pH values by addition of NaOH. The H₂S partial pressure was varied between 0 and . The rate of H₂S absorption was measured by recording the pressure drop as a function of time during batch absorption experiments. In this system the absorbed H₂S reacts with ferric iron and is oxidized to elemental sulfur. The kinetic results are in agreement with enhanced absorption due to a fast chemical reaction according to the film theory. The reaction of ferric sulfate and H₂S appears to proceed irreversibly and is first order in both the total concentrations of ferric iron and H₂S. The activation energy for the reaction was calculated to be .     

Carbon dioxide absorption with aqueous potassium carbonate promoted by piperazine

Many commercial processes for the removal of carbon dioxide from high-pressure gases use aqueous potassium carbonate systems promoted by secondary amines. This paper presents thermodynamic and kinetic data for aqueous potassium carbonate promoted by piperazine. Research has been performed at typical absorber conditions for the removal of CO₂ from flue gas.Piperazine, used as an additive in 20- potassium carbonate, was investigated in a wetted-wall column using a concentration of at 40-80°C. The addition of piperazine to a potassium carbonate system decreases the CO₂ equilibrium partial pressure by approximately 85% at intermediate CO₂ loading. The distribution of piperazine species in the solution was determined by proton NMR. Using the speciation data and relevant equilibrium constants, a model was developed to predict system speciation and equilibrium.The addition of piperazine to potassium carbonate increases the rate of CO₂ absorption by an order of magnitude at 60°C. The rate of CO₂ absorption in the promoted solution compares favorably to that of MEA. The addition of piperazine to potassium carbonate increases the heat of absorption from 3.7 to . The capacity ranges from 0.4 to for PZ/K₂CO₃ solutions, comparing favorably with other amines.     

Kinetics of the absorption of carbon dioxide into mixed aqueous solutions of 2-amino-2-methyl-l-propanol and piperazine

The reaction kinetics of the absorption of CO₂ into aqueous solutions of piperazine (PZ) and into mixed aqueous solutions of 2-amino-2-methyl-l-propanol (AMP) and PZ were investigated by wetted wall column at 30-40 °C. The physical properties such as density, viscosity, solubility, and diffusivity of the aqueous alkanolamine solutions were also measured. The N₂O analogy was applied to estimate the solubilities and diffusivities of CO₂ in aqueous amine systems. Based on the pseudo-first-order for the CO₂ absorption, the overall pseudo first-order reaction rate constants were determined from the kinetic measurements. For CO₂ absorption into aqueous PZ solutions, the obtained second-order reaction rate constants for the reaction of CO₂ with PZ are in a good agreement with the results of Bishnoi and Rochelle (Chem. Eng. Sci. 55 (2000) 5531). For CO₂ absorption into mixed aqueous solutions of AMP and PZ, it was found that the addition of small amounts of PZ to aqueous AMP solutions has significant effect on the enhancement of the CO₂ absorption rate. For the CO₂ absorption reaction rate model, a hybrid reaction rate model, a second-order reaction for the reaction of CO₂ with PZ and a zwitterion mechanism for the reaction of CO₂ with AMP was used to model the kinetic data. The overall absolute percentage deviation for the calculation of the apparent rate constant k_app is 7.7% for the kinetics data measured. The model is satisfactory to represent the CO₂ absorption into mixed aqueous solutions of AMP and PZ.     

Investigation on kinetics of carbon dioxide absorption in aqueous solutions of monoethanolamine + 1, 3-diaminopropane

ABSTRACT

Environmental concerns from global warming and climate change demand carbon dioxide separation from post-combustion gases. Important parameters are involved in choosing the suitable solvent for carbon dioxide separation, including the reaction rate of carbon dioxide and the solvent. In this paper, the kinetics of carbon dioxide (CO₂) absorption in aqueous solutions of Monoethanolamine (MEA) + 1,3-Diaminopropane (DAP), a diamine containing two primary amino group, was developed. The measurements were performed in a stirred cell with a horizontal gas-liquid interface in the temperature range of 313.15–333.15 K and aqueous solutions of 10 wt% MEA + 5 wt% DAP and 12.5 wt% MEA + 2.5 wt% DAP. Experiments were conducted in an isothermal batch reactor with a horizontal gas-liquid interface under pseudo-first-order conditions, enabling the determination of the overall kinetic rate constant from the pressure drop method. Second-order reaction rate constants of CO₂ absorption in amine solutions were estimated using the calculated initial absorption rate. It was found that the rate constants in MEA+ DAP solutions were greater than in MEA solutions which means that DAP increases the reaction rate.     

Kinetics of absorption of carbon dioxide into aqueous solutions of 2-amino-2-hydroxymethyl-1,3-propanediol

In this work the kinetics of the reaction between CO₂ and a sterically hindered alkanolamine, 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD) were determined at temperatures of 303.15, 313.15 and 323.15 K in a wetted wall column contactor. The AHPD concentration in the aqueous solutions was varied in the range 0.5-2.4 kmol m⁻³. The ratio of the diffusivity and Henry's law constant for CO₂ in solutions was estimated by applying the N₂O analogy and the Higbie penetration theory, using the physical absorption data of CO₂ and N₂O in water and of N₂O in amine solutions. Based on the pseudo-first-order for the absorption of CO₂, the overall pseudo-first-order rate constants were determined from the kinetics measurements. By considering the zwitterion mechanism for the reaction of CO₂ with AHPD, the zwitterion deprotonation and second-order rate constants were calculated. The second-order rate constant, k₂, was found to be 285, 524, and 1067 m³ kmol⁻¹ s⁻¹ at 303.15, 313.15, and 323.15 K, respectively.     

Interfacial area and mass transfer in carbon dioxide absorption in TEA aqueous solutions in a bubble column reactor

The hydrodynamic behaviour and mass transfer of carbon dioxide removal process by aqueous solutions of triethanolamine (TEA) are analysed. The experiments were made in a bubble column reactor (BCR) as gas–liquid contactor. The interfacial area and mass transfer coefficient were calculated by using a photographic method based on the bubble diameter determination. The influence of operation conditions, liquid phase nature and chemical reaction on the mass transfer coefficient and gas–liquid interfacial area has been also analysed.     

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

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

Kinetics of carbon dioxide absorption and desorption in aqueous alkanolamine solutions using a novel hemispherical contactor—I. Experimental apparatus and mathematical modeling

This two-parts paper summarizes the experimental and theoretical results of a comprehensive and first of its kind study on the kinetics of carbon dioxide (CO₂) absorption and desorption in and from aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), methyl-diethanolamine (MDEA) and 2-amino-2-methyl-1-propanol (AMP) and their mixtures (i.e., MEA+AMP, MEA+MDEA, DEA+AMP and DEA+MDEA). Part-1 of this paper presents a detailed design of the novel hemispherical apparatus and a rigorous mathematical model applicable to both absorption and desorption conditions with some preliminary results and Part-2 provides detailed results with estimates of kinetic coefficients for CO₂ absorption and desorption for eight different aqueous amine systems.The new hemispherical contactor consists of a 76 mm diameter solid hemisphere housed in a Pyrex glass cylinder with appropriate gas and liquid feed and withdrawal systems. The liquid feed passes through a 4 mm ID tube, which is located in the center of the hemisphere, and discharges at the top. The liquid descends as a well-defined liquid film over the surface of the hemisphere and is collected by a funnel (79 mm ID) at the base of the hemisphere. The interfacial area and hydrodynamics are well defined and the entrance/exit effects as well as surface rippling are minimized. Using this apparatus, the absorption experiments were conducted at near atmospheric pressure with pure CO₂ saturated with water vapor at 293-323 K with initially unloaded solutions and the desorption experiments were performed at 333-383 K for CO₂ loadings between 0.02 and 0.7 moles of CO₂ per mole of amine using humidified nitrogen gas as a stripping medium at total system pressures up to 205 kPa.The new rigorous mathematical model developed to interpret the rate data is based on the principle of diffusional mass transfer accompanied with liquid-phase chemical reactions over a hemispherical liquid film. Also developed in this work is a methodology that uses the rigorous model in conjunction with a non-linear regression technique to estimate kinetic parameters. Preliminary results presented in this part of the paper show that the new experimental apparatus was successful in accurately measuring and the new model and its numerical implementation were successful in accurately predicting both absorption and desorption rates for all aqueous amine systems considered in this study.     

Determination of mass transfer resistance during absorption of carbon dioxide by mixed absorbents in PVDF and PP membrane contactor

In this study, the absorption of carbon dioxide by the absorbent which was composed of 2-amino-2-methyl-l-propanol (AMP) + piperazine (PZ) or methyldiethanolamine (MDEA) + piperazine (PZ) in polyvinylidinefluoride (PVDF) and polypropylene (PP) membrane contactors werewas examined. Three resistances were considered in each hollow fiber, i.e., liquid-film diffusion, membrane diffusion, and gas-film diffusion. The mass transfer resistance of membrane k_m was influenced by the wetting ratio using an absorbent with higher reaction rate. The wetting ratio was affected by contact angle between the membrane and absorbent and the viscosity of absorbent. The calculated absorption rates considering wetting ratio of membrane and using the modified correlation equation of gas-phase mass transfer coefficient were reasonably agreeable to those of measured ones (standard deviation, 4%). The fractional resistance of each transport step during the experiments was then determined. The rate-controlling step was dominated by the resistance of gas-film diffusion with mixed absorbents. The absorption rates of CO₂ increase with the increasing of gas flow rates in the most experimental cases. The resistance of liquid-film diffusion was only important using an absorbent with lower reaction rate. The rate-controlling step was the membrane diffusion only at higher gas flow rate with the absorbent composed of AMP and PZ in PVDF hollow fiber membrane contactor.     

Form coke reaction processes in carbon dioxide

Uncertainty in metallurgical coke supplies has prompted development of form coke from low quality coals and fines. Reaction rates have been measured and mechanisms identified that control carbonaceous briquette reaction rate in CO₂. Three briquette formulations were prepared, characterized and coked in an inert atmosphere at high temperature. A given weight of each formulation was then reacted in a packed bed with CO₂ at 1373 K for 0.5–2 h. Partially reacted briquettes contained a solid core with some internal reaction surrounded by a loosely adhering layer of carbon-containing ash. The reaction rate of briquettes with CO₂ was affected by diffusion of CO₂ through the bulk gas and the ash-carbon layer to the core surface, as well as CO₂–carbon reaction. Key variables governing briquette reaction rate included CO₂ mole fraction and briquette void fraction.     

Kinetics of absorption of hydrogen sulfide into aqueous Fe(III) solutions

In our recent studies, absorption of H₂S into the aqueous Fe₂(SO₄)₃ and FeCl₃ solutions with various values of ionic strength and pH was investigated in an agitated vessel with a flat interface. The experimental results for both systems revealed that the species which reacts with H₂S is FeOH²⁺. The absorption rates were explained by the theory of gas absorption with an irreversible (l,l)-th order reaction between H₂S and FeOH₂₊. The reaction rate constants were independent of the ionic strength of the solution and correlated as a function of temperature. In this paper, kinetics and mechanism of these absorption reactions are reviewed and the identity for both systems is emphasized.     

Synthesis of PCL/clay masterbatches in supercritical carbon dioxide

Pre-exfoliated nanoclays were prepared through a masterbatch process using supercritical carbon dioxide as solvent and poly(?-caprolactone) as organic matrix. In situ polymerization of ?-caprolactone in the presence of large amount of clay was conducted to obtain these easily dispersible nanoclays, collected as a dry and fine powder after reaction. Dispersion of these pre-exfoliated nanoclays in chlorinated polyethylene was also investigated. All the results confirm the specific advantages of supercritical CO₂ towards conventional solvents for filler modification.     

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

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