Aqueous Alkanolamine Solutions Research Articles

The Effects of Mass Transfer on the Determination of Gas–Liquid Reaction Kinetics in a Stirred Cell Reactor: In the Case of CO2 Absorption by Aqueous Alkanolamine Solution

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 o...

New Insights and Assessment of Primary Alkanolamine/Sulfolane Biphasic Solutions for Post-combustion CO2 Capture: Absorption, Desorption, Phase Separation, and Technological Process

The sulfolane was, surprisingly, found to be a universal phase splitting solvent in a serial of aqueous primary alkanolamine solution for CO2 removal, the reaction product of carbamate and hydrophilicity of amine can be the key factor for CO2 triggering phase change, also the phase change can have significant effect on CO2 absorption performance. To comprehensively understand the effect of phase change on absorption, stripping and phase separation performance of primary alkanolamine solution for CO2 capture, MEA sulfolane-based solution was chosen as typical biphasic system for investigation. First, the experimental results revealed that phase change can dramatically decrease the absorption rate and lead to less CO2 capacity in an absorption process. Second, the enriched MEA in separated solution can substantially decrease the energy consumption for CO2 stripping, but exorbitant concentration of MEA can significantly reduce the CO2 removal efficiency in a quasi-cycle of absorption and desorption. Third, t...

Heat-Stable Salts and Methods for Their Removal from Alkanolamine Carbon Dioxide Absorbents (Review)

Absorption using aqueous solutions of alkanolamines is the most widely used procedure for removal of carbon dioxide from natural gas, flue gases from power-generating facilities, and other mixtures. Its main drawback is degradation/deactivation of alkanolamine under the process conditions (high temperatures, presence of oxygen and other impurities) with the formation of heat-stable salts consisting of alkanolammonium cation and anions of organic and inorganic acids. The main operation problems caused by heat-stable salts are considered in the review. Three main methods for removal of heat-stable salts from alkanolamine adsorbents are described in detail: distillation, ion exchange, and electrodialysis. The main characteristics of these methods and their advantages and drawbacks are described, and a comparative analysis is made. The history and state-of-the art of studies within the framework of each method are presented.

Solvation and Dynamics of CO2 in Aqueous Alkanolamine Solutions

Carbon dioxide sequestration from flue gases by chemical absorption is the most versatile process. The molecular engineering of novel high-performance biogas upgrading alkanolamine compounds requires detailed information about their properties in mixed solution. The liquid structure properties of four representative alkanolamine molecules (monoethanolamine (MEA) as a reference and standard, 3-aminopropanol (MPA), 2-methylaminoethanol (MMEA), and 4-diethylamino-2-butanol (DEAB)) in the presence of CO2 were investigated over a wide range of solvent alkanolamine/water mixture compositions and temperature. In aqueous solution, for the alkanolamine molecules MEA, MPA, and MMEA, hydrogen bonding with solvent water molecules is dominating over CO2 interactions. Analysis of the liquid structure reveals that carbon dioxide shows no preference of approaching the alkanolamine but is rather displaced by water molecules as the water content increases. CO2 dissolved in aqueous DEAB, however, accumulates within clusters...

Modeling of CO2 solubility in aqueous alkanolamine solutions with an extended UMR-PRU model

The phase and chemical equilibria in aqueous alkanolamine solutions containing CO2 is examined in this work. The alkanolamines considered are monoethanolamine (MEA), methyldiethanolamine (MDEA), as well as blends of these two amines. For the vapor-liquid equilibrium calculations, the UMR-PRU model has been extended by incorporating the extended UNIQUAC activity coefficient model to account for the long range electrostatic interactions. The parameters of the UMR-PRU model are either taken from the literature, when available, or determined in this work through fitting vapor-liquid equilibrium experimental data. Very satisfactory results are obtained in all cases examined, which are similar or better than those obtained by other models proposed in the literature, indicating that the UMR-PRU model is able to accurately describe the phase and chemical equilibria in aqueous solutions of alkanolamines and carbon dioxide.

Thermodynamic modeling of the system of CO2 and potassium taurate solution for simulation of the carbon dioxide capture process

Absorption of carbon dioxide from gaseous sources such as flue gases from power plants is accomplished for environmental reasons with the aim to reduce emissions of greenhouse gases. Generally, aqueous solutions of alkanolamines are employed with Monoethanolamine (MEA) considered the benchmark solvent. However, it has drawbacks, primarily its volatility and toxicity, and the need for a lot of energy for regeneration. Recently, new solvents such as amino acid aqueous solutions have started to be considered as alternatives to traditional amines.This paper is focused on the development of a model for the simulation of the absorption and regeneration system using potassium taurate for the capture of carbon dioxide. Detailed modelling of this system is currently limited by the lack of thermodynamic parameters for use in simulations. ASPEN Plus® has been chosen as the framework for developing the model. Species not present by default in the database have been added and appropriate parameters have been determined for obtaining a reliable description of the Vapor–Liquid–Solid Equilibrium by means of the Electrolyte-NRTL method.

Improvement of the PR-CPA equation of state for modelling of acid gases solubilities in aqueous alkanolamine solutions

Chemical absorption with alkanolamines processes are commonly applied for natural gas purification. The knowledge of CO2, H2S, hydrocarbons and mercaptans solubilities in aqueous alkanolamine solutions is important in acid gas removal process simulation and design. In previous works, alkanes, aromatics and mercaptans solubilities in different aqueous alkanolamine solutions have been successfully represented by using the PR-CPA EoS. In this work, the PR-CPA EoS with a pseudo-chemical reaction approach is developed and applied to describe the solubility of acid gases in aqueous alkanolamines solutions. The results are in good agreement with a wide range of experimental data. Other relevant properties such as water content, electrolytes speciation and enthalpy of absorption are accurately predictd by PR-CPA EoS.

Carbon dioxide chemical absorption by solvents based on diamine and amines blend

Present work includes research about the influence of the type of amino group using one or two amine molecules on carbon dioxide chemical absorption using aqueous solutions of alkanolamines and diamines. A comparison of chemical absorption processes using aqueous solutions of two individual diamines (3‐(dimethylamino)propan‐1‐amine and 1,3‐diaminopropane) and a mixture of amines (3‐amino‐1‐propanol and 3‐(dimethylamino)propan‐1‐ol) is reported including absorption rate curves, carbon dioxide loading, reaction mechanism or solvent regeneration to obtain useful information about the quality of each solvent for carbon dioxide separation. In general, amines blend of 3‐amino‐1‐propanol and 3‐dimethylamino‐1‐propanol, have shown a better behavior than their individual amines. Diamines and mainly 3‐dimethylamino propylamine that presents primary and tertiary amine groups in its structure, have led similar results. After these studies, 3‐dimethylamino propylamine, can be considered an appropriated amine to industrial carbon dioxide absorption process. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2702–2710, 2018

Molecular Dynamics Study of the Solution Structure, Clustering, and Diffusion of Four Aqueous Alkanolamines.

CO2 sequestration from anthropogenic resources is a challenge to the design of environmental processes at a large scale. Reversible chemical absorption by amine-based solvents is one of the most efficient methods of CO2 removal. Molecular simulation techniques are very useful tools to investigate CO2 binding by aqueous alkanolamine molecules for further technological application. In the present work, we have performed detailed atomistic molecular dynamics simulations of aqueous solutions of three prototype amines: monoethanolamine (MEA) as a standard, 3-aminopropanol (MPA), 2-methylaminoethanol (MMEA), and 4-diethylamino-2-butanol (DEAB) as potential novel CO2 absorptive solvents. Solvent densities, radial distribution functions, cluster size distributions, hydrogen-bonding statistics, and diffusion coefficients for a full range of mixture compositions have been obtained. The solvent densities and diffusion coefficients from simulations are in good agreement with those in the experiment. In aqueous solution, MEA, MPA, and MMEA molecules prefer to be fully solvated by water molecules, whereas DEAB molecules tend to self-aggregate. In a range from 30/70-50/50 (w/w) alkanolamine/water mixtures, they form a bicontinuous phase (both alkanolamine and water are organized in two mutually percolating clusters). Among the studied aqueous alkanolamine solutions, the diffusion coefficients decrease in the following order MEA > MPA = MMEA > DEAB. With an increase of water content, the diffusion coefficients increase for all studied alkanolamines. The presented results are a first step for process-scale simulation and provide important qualitative and quantitative information for the design and engineering of efficient new CO2 removal processes.

New experimental and modeling based on the N-Wilson-NRF equation for surface tension of aqueous alkanolamine binary mixtures

In this work, surface tension of aqueous solutions of various alkanolamines; monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), N-methyldiethanolamine (MDEA) and Sulfolane at the temperature range of 298.15–348.15 K and mole fraction ranges of 0–1 are determined. In the studied temperature range, the experimental surface tension values of the binary mixtures increase as the water concentration increases and decrease as the temperature increases. In following, the surface tension results for the binary solutions were correlated simultaneously as a function of temperature and concentration. For this purpose based on a thermodynamic definition of surface tension and the expression of Gibbs free energy, a new surface tension equation is proposed. This new equation is developed by using the nonelectrolyte Wilson nonrandom factor (N-Wilson-NRF) model to represent the excess Gibbs free energy of the system. The model parameters obtained by correlating binary surface tension at two different approaches. In one approach the parameters are assumed as non-temperature dependent and in another approach, a linear temperature dependency is considered. The comparison between the results of the presented model with experimental data and four other models show that the new equation is simple and more accurate in the correlation of these studied systems.

Thermodynamic Modeling and Experimental Study of CO2 Dissolution in New Absorbents for Post-Combustion CO2 Capture Processes

Demixing solvents have been suggested as an alternative to aqueous solutions of alkanolamines for the decarbonation of industrial effluents. These solvents undergo a liquid–liquid phase separation when heated. A phase-separation step could be integrated in the carbon dioxide (CO2) capture process to reduce energetic cost of the solvent regeneration step. As part of a general project on the dissolution of CO2 in aqueous solutions of piperidines, 3-methylpiperidine and 4-methylpiperidine have been investigated. The enthalpies of solution of CO2 in aqueous solutions of those methylpiperidines have been measured using a flow calorimetric technique. This technique makes it possible to simultaneously determine the enthalpies of solution and CO2 solubility limits. The experimental data were used to develop a thermodynamic model representative of phase equilibrium and enthalpy of solution. The carbamate formation constants of the 3-methylpiperidine and 4-methylpiperidine are adjusted in the model. The thermodynam...

The Study of Carbon Dioxide Removal in Membrane Module by Single and Mixture of Alkanolamine Aqueous Solutions

This work presents an investigation on the performance of CO2absorption into aqueous alkanolamine solution using a hollow fiber membrane gas–liquid contactor. Aqueous solution of ethanolamine (MEA), diethanolamine (DEA), 2–amino–2–methyl–1–propanol (AMP) and piperazine anhydrous (PZ) were chosen as the absorption liquids. A microporous hollow fiber membrane made of polyvinylidene fluoride (PVDF) was used as the medium for gasliquid absorption process. In this study, the operating temperature is fixed at 30°C, while the flowrate of CO2 and alkanolamine were in the range of 1000–5000 ml/min and 50–280 ml/min respectively. The feed gas was introduced directly to the shell of the module at 1–1.5 bar and the liquid flowed through the fiber lumen side. The CO2 transfer through the membrane was found to be reaction controlled and dependent on the type of amine used. The use of piperazine as an accelerator in the mixture of the absorption liquids gives a good impact on increasing the performance for the rate of CO2 transfer.

Solubility of Carbon Dioxide in Aqueous Solutions of Three Secondary Amines: 2-(Butylamino)ethanol, 2-(Isopropylamino)ethanol, and 2-(Ethylamino)ethanol Secondary Alkanolamine Solutions

Secondary amines have been proposed as potential solvents for CO2 capture. In this study, the CO2 solubility of three secondary alkanolamine aqueous solutions, 2-(butylamino)ethanol (BAE), 2-(isopropylamino)ethanol (IPAE), and 2-(ethylamino)ethanol (EAE), were measured with a pressure range of 0.02 to 395 kPa at 40, 80, and 120 °C. A static method based on an equilibrium cell unit was used for measurements in high CO2 equilibrium partial pressure regions at over 1 kPa, while the flow method based on a modified gas sparging reactor unit proposed by Kim et al.(2017) was employed for measurements in low pressure regions under 1 kPa. Two amine concentrations, 15 and 30 wt %, were considered for each amine, and their CO2 solubility was represented by the Kent-Eisenberg model. The cyclic CO2 absorption capacity and heat of the reaction for the three secondary alkanolamines were compared with those of monoethanolamine (MEA).

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

CO2 absorption into aqueous solutions of two tertiary alkanolamines, namely, MDEA and DMEA with and without carbonic anhydrase (CA) was investigated with the use of the stopped‐flow technique at temperatures in the range of 293–313 K, CA concentration varying from 0 to 100 g/m3 in aqueous MDEA solution with the amine concentration ranging from 0.1 to 0.5 kmol/m3, and CA concentration varying from 0 to 40 g/m3 in aqueous DMEA solution with the amine concentration ranging from 0.05 to 0.25 kmol/m3. The results show that the pseudofirst‐order reaction rate (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

Viscosity Data of Aqueous MDEA–[Bmim][BF4] Solutions Within Carbon Capture Operating Conditions

Post–combustion capture with chemical absorption shows higher potential for commercial scale application compared with other technologies. To capture CO2 from the industrial and power plant's flue gases, aqueous alkanolamine solutions are widely used. However, several drawbacks from utilizing the aqueous alkanolamines such as MEA still need to be solved. For example, alkanolamine solutions require intensive energy for regeneration and cause severe corrosion to the equipment though they have high reactivity in capturing CO2. Ionic liquids have been of interest in the recent development of chemical absorption according to their unique characteristics including wide liquid range, negligible volatility and thermal stability. However, due to their high price, high viscosity and low absorption capacity compared to alkanolamines, ionic liquids are still non–desirable for industrial applications. One possible solution to improve the performance of ionic liquids is to use mixtures of ionic liquids and alkanolamines. For a better understanding of the absorption using the mixture of aqueous alkanolamines and ionic liquids, the knowledge of thermo–physical properties of the solutions, especially the viscosity and density are of importance. This paper reports the measured viscosity of MDEA–[Bmim][BF4] aqueous mixtures at various temperatures and concentrations. It was found that the viscosity increase with an increase in [Bmim][BF4] concentration, but decrease with an increase in temperature. Moreover, the impact of temperature on the viscosity is more significant at low temperature range.

Screening tests of aqueous alkanolamine solutions based on primary, secondary, and tertiary structure for blended aqueous amine solution selection in post combustion CO2 capture

In this work, hindered primary, secondary and tertiary aqueous alkanolamine solutions with different numbers of hydroxyl groups were investigated for their initial rates of absorption and desorption which show how fast the amine solution will reach equilibrium and will be regenerated, respectively, and also investigated pKa, equilibrium solubility of CO2, heat duty (Qreg) for solvent regeneration, and heat of CO2 absorption (ΔHabs). These experimental data were used as a screening tool to enable the selection of the best amine components for designing an optimal blended aqueous amine solution system. The absorption experiments were performed at 313K and atmospheric pressure using 15% CO2 (in N2 balance) as feed gas whereas desorption experiments were performed at 363K and atmospheric pressure. Alkanolamines with a larger number of hydroxyl groups exhibited lower performance in all the CO2 capture activities because of the negative electron withdrawing effect of the hydroxyl group. Consequently, based on the results of individual primary, secondary, and tertiary aqueous alkanolamine solutions, the ones with only one hydroxyl group (2-amino-2-methyl-1-propanol (AMP), 2-(ethylamino) ethanol (EAE), and 2-(dimethylaminoethanol) (DMAE)) were selected for formulation into aqueous amine blends. Two binary aqueous amine blends of AMP/DMAE and EAE/DMAE and one ternary aqueous amine blend of AMP/EAE/DMAE at various molar ratios were tested. All solvent combinations showed better performance than 5M MEA, especially in the initial desorption rate and energy efficiency. Of these aqueous amine blends, the 2.5M AMP/2.5M DMAE exhibited the best performance with an equilibrium CO2 solubility of 0.56mol CO2/mol amine, initial absorption rate of 0.26×10−2mol CO2/min, initial desorption rate of 2.62×10−2mol CO2/min, and heat duty of 53.81kJ/mol.

Alkane solubilities in aqueous alkanolamine solutions with CPA EoS

Absorption with aqueous alkanolamine solution is often used for acid gas removal processes. Thermodynamic model is very important to predict phase behaviour for designing and optimizing acid gas absorption units. To estimate alkanes losses in these processes, the knowledge of alkanes solubility in aqueous alkanolamine solutions is essential. In the present work, Cubic-Plus-Association Equation of State (CPA EoS) was applied to represent alkanes solubility in aqueous alkanolamine. The Average Relative Deviation on alkanes solubility in aqueous alkanolamine solution is less than 15%. Due to our model, the temperature of alkanes minimum solubility in pure water and alkanolamine solutions are correctly predicted. Water content is also well predicted at Vapour Liquid Equilibrium condition.

Modeling of CO2 solubility in aqueous N-methyldiethanolamine solution using electrolyte modified HKM plus association equation of state

In this work, a new type of electrolyte cubic plus association equation of state as emHKM-CPA EoS has been developed and was used to modeling the CO2 solubility in aqueous alkanolamine such as N-methyldiethanolamine (MDEA) and diethanolamine (DEA) solutions. This EoS consists of the several terms as the cubic HKM part for dispersion contribution, electrolyte part and association term. The Mean Spherical Approximation (MSA) term together with Born term are used for electrostatic long-range interaction and charging processes, respectively, and for association the Wertheim equation was applied. Using the present EoS, the solubility of CO2 in aqueous MDEA solutions is modeled so that the 470 experimental solubility data were used at the different solution compositions, temperatures, pressures and acid gas loadings. At first, the pure components parameters were obtained through regression of the pure components vapor pressure and saturated liquid density experimental data. Consequently, the binary interaction parameters were calculated using the binary vapor-liquid equilibrium data. Finally, the ternary H2O-CO2-MDEA and H2O-CO2-DEA systems were modeled using a reactive bubble point pressure calculation method. Moreover, the present EoS is applied for LLE calculation of heptane-MEA system. The results showed that the calculated values were in good agreement with the experimental data. For the H2O-CO2-MDEA and H2O-CO2-DEA systems, the percentage of Absolute Average Deviation (AAD%) were 12.14 and 9.17, respectively, that shows emHKM- CPA is an efficient EoS which can be successfully applied to representation of the solubility of CO2 in aqueous alkanolamine solutions in wide ranges of temperature, pressure, acid gas loading, and amine concentration.

Modeling of gaseous hydrocarbons solubility in aqueous-amine systems by VTPR model

It is crucial to know the solubility of gaseous and liquid hydrocarbons in aqueous alkanolamine solutions in order to quantify accurately the hydrocarbon losses in treating processes. Hence, consistent experimental data and accurate models are essential for the efficient design and optimization of these processes. In this work, a homogeneous approach based on the modified Volume Translation Peng-Robinson (VTPR) cubic equation of state was adopted to represent the solubility of methane, ethane and propane in aqueous mono-ethanol-amine, di-ethanol-amine and methyl-di-ethanol-amine which are the most common solvents used in the effluent treatment processes. The model parameters were estimated on the basis of binary and ternary vapor-liquid and liquid-liquid equilibrium data. The model developed shows a satisfactory representation of the experimental data with average deviations ranging from 1 to 28% for all systems, and gives a solid foundation for predicting hydrocarbon solubility in aqueous alkanolamine solutions.

Experimental Measurement and Thermodynamic Modeling of the Solubility of Carbon Dioxide in Aqueous Alkanolamine Solutions in the High Gas Loading Region

The solubility of carbon dioxide in aqueous alkanolamine solutions was investigated in the high gas loading region based on experimental measurements and thermodynamic modeling. An experimental phase equilibrium study was performed to evaluate the absorption of carbon dioxide in aqueous solutions of five representative alkanolamines, including monoethanolamine, diethanolamine, N-methyldiethanolamine, 2-amino-2-methyl-1-propanol and piperazine. The carbon dioxide loadings of these solutions were determined for a wide range of pressures (62.5 kPa to 4150 kPa), temperatures (303.15 K to 343.15 K) and alkanolamine concentrations (2 M to 4 M). The results were found to be largely consistent with those previously reported in the literature. Furthermore, a hybrid Kent–Eisenberg model was developed for the correlation of the experimental data points. This new model incorporated an equation of state/excess Gibbs energy model for determining the solubility of carbon dioxide in the high-pressure–high gas loading region. This approach also used a single correction parameter, which was a function of the alkanolamine concentration. The results of this model were in excellent agreement with our experimental results. Most notably, this model was consistent with other reported values from the literature.