Aqueous Alkanolamine Research Articles

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...

Carbon dioxide absorption in aqueous alkanolamine blends for biphasic solvents screening and evaluation

Using biphasic solvents for carbon dioxide (CO2) capture is regarded as a promising technology to drastically reduce the regeneration energy. However, this technology hasn’t been put into commercial application due to lack of the biphasic solvents with high stabilities and low costs. To overcome this challenge, we developed a novel type of biphasic solvent based on alkanolamine-alkanolamine blends, i.e., aqueous blends of 2-(diethylamino)-ethanol (DEEA, 50 wt%) and monoethanolamine (MEA, 25 wt%) or 2-((2-aminoethyl) amino) ethanol (AEEA, 25 wt%). The aqueous DEEA-AEEA solvent demonstrated a cyclic capacity as high as 0.64 mol CO2/mol which is significantly higher than those of 30 wt% MEA and other reported biphasic solvents. In addition, a phase split time as short as a few minutes is obtained. The phase split dynamics were analyzed to investigate the effects of CO2 loading, temperature, gas flow rate and height-to-diameter ratio. Quantitative 13C NMR analysis was then performed to reveal the reaction and phase split mechanism of CO2 absorption in the DEEA-AEEA solvent. It indicated that the reaction of AEEA with CO2 dominated at the beginning of CO2 absorption and the products are formed as carbamates. Then, DEEA began reacting with CO2 to yield bicarbonate and carbonate. The phase split mechanism indicated that the reaction products of carbamates and HCO3−/CO32− migrated to the lower phase while DEEA and unreacted AEEA migrated to the upper phase. Finally, the cyclic tests were repeated and the energy consumption was evaluated. The regeneration energy of the biphasic solvent, without process optimizations, is 2.58 GJ/tCO2, which is 32% lower than that of the traditional 30 wt% MEA solvent.

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.

CO2 Capacity and Heat of Sorption on a Polyethylenimine-Impregnated Silica under Equilibrium and Transient Sorption Conditions

Amine-based solid sorbents represent promising replacements for aqueous alkanolamines for CO2 capture because they reduce significantly the sorbent regeneration energy and avoid instrument corrosio...

Thermodynamic characterisation of aqueous alkanolamine and amine solutions for acid gas processing by transferable molecular models

The development of new alkanolamines/amines is a topic which has attracted a great deal research interest, particularly as absorbents for the removal of acid gases from industrial sources and CO2 capture applications. One of the major challenges when evaluating the techno-economic performance of selected new single amines or blends is the lack of experimental data on the thermophysical properties required for a reliable process design and simulation. In this contribution, a robust theoretical framework for the description of key thermophysical properties of aqueous solutions of single and mixed alkanolamines/amines at relevant gas separation process conditions is proposed. The approach is based on the coupling of the Free-Volume Theory and the Density Gradient Theory with a molecular-based equation of state (soft-SAFT) for the integrated modelling of phase behaviour, enthalpies, densities, viscosities and interfacial tensions. The alkanolamines and amines investigated differ in their family and structure, and included primary (monoethanolamine), secondary (diethanolamine), tertiary (methyldiethanolamine), sterically hindered (2-amino-2-methyl-1-propanol) and cyclic amines (piperazine). The study was performed in a systematic manner, starting from the development of the models for the pure amines, the description of their thermophysical properties, and the properties of the aqueous mixtures. Compared to other models described in literature, the present modelling approach preserves the effects due the chemical structure and key intermolecular interactions of the examined alkanolamines/amines through a set of molecular parameters obtained from pure substance data, whenever available, or transferred from substances of different chemical families. This enabled the development of a consistent modelling framework which can provide reliable thermodynamic property predictions of both single and blended amine solutions over a broad range of temperatures (298–373 K) and compositions (0–50 wt% amine). The proposed approach is well-suited for implementation and extension to other alkanolamines and amines, making it a valuable tool for having reliable process simulations as well as for the screening and discovery of new amine systems, which will be required for the deployment of more economical acid gas removal processes.

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.

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.

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.

Removal of heat stable salts (HSS) from spent alkanolamine wastewater using electrodialysis

The formation of heat stable salts (HSS) is a tough problem for aqueous alkanolamines solution in gas processing industry. In this study, a self-made electrodialysis stack was assembled to remove the HSS from spent amine wastewater. Results indicated that the optimum current density is 15mA/cm2. An increase in pH is beneficial for amine recovery but is harmful to the lifespan of membranes. The ED process cost is estimated to be 14.6$/t with the energy consumption of 39.4kWh/T. Comparison with the conventional neutralization or replacement methods, ED is not only energy-saving but also environmentally friendly for the removal of HSS from the spent amine wastewater.

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

VLE Determination of Carbon Dioxide Loaded Aqueous Alkanolamine Mixtures Using Modified Kent Eisenberg Model

Abstract A computationally simple thermodynamic framework has been presented to correlate the vapour-liquid equilibria of carbon dioxide absorption in five representative types of alkanolamine mixtures. The proposed model is an extension of modified Kent Eisenberg model for the carbon dioxide loaded aqueous alkanolamine mixtures. The model parameters are regressed on a large experimental data pool of carbon dioxide solubility in aqueous alkanolamine mixtures. The model is applicable to a wide range of temperature (298–393 K), pressure (0.1–6000 kPa) and alkanolamine concentration (0.3–5 M). The correlated results are compared to the experimental values and found to be in good agreement with the average deviations ranging between 6% and 20%. The model results are comparable to other thermodynamic models.

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.

Modeling of CO2 Solubility in Aqueous Potassium Lysinate Solutions at Post-Combustion CO2 Capture Conditions

Aqueous potassium lysinate (LysK) has been proposed as an alternative to aqueous alkanolamines for CO2 capture due to fast kinetics and large absorption capacity. However, thermodynamic modeling for aqueous LysK system has not been available yet. In this work, a modified Kent-Eisenberg model with correlated equilibrium constants was developed to interpret the vapor-liquid equilibrium (VLE) data at postcombustion capture conditions. The predictions from the developed model are in good agreement with the experimental results with AAD within 19 %.

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.

Solid amine sorbents for CO2 capture by chemical adsorption: A review

Abstract Amines are well-known for their reversible reactions with CO 2 , which make them ideal for CO 2 capture from several gas streams, including flue gas. In this respect, selective CO 2 absorption by aqueous alkanolamines is the most mature technology but the process is energy intensive and has also corrosion problems. Both disadvantages can be diminished to a certain extent by chemical adsorption of CO 2 selectively. The most important element of the chemical adsorption of CO 2 involves the design and development of a suitable adsorbent which consist of a porous support onto which an amine is attached or immobilized. Such an adsorbent is often called as solid amine sorbent. This review covers solid amine-based studies which are developed and published in recent years. First, the review examines several different types of porous support materials, namely, three mesoporous silica (MCM-41, SBA-15 and KIT-6) and two polymeric supports (PMMA and PS) for CO 2 adsorption. Emphasis is given to the synthesis, modifications and characterizations -such as BET and PXRD data-of them. Amination of these supports to obtain a solid amine sorbent through impregnation or grafting is reviewed comparatively. Focus is given to the adsorption mechanisms, material characteristics, and synthesis methods which are discussed in detail. Significant amount of original data are also presented which makes this review unique. Finally, relevant CO 2 adsorption (or equilibrium) capacity data, and cyclic adsorption/desorption performance and stability of important classes of solid amine sorbents are critically reviewed. These include severa PEI or TEPA impregnated adsorbents and APTES-grafted systems.

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.

Combined Effect of Temperature and pKa on the Kinetics of Absorption of Carbon Dioxide in Aqueous Alkanolamine and Carbonate Solutions with Carbonic Anhydrase

In present work the absorption of carbon dioxide in aqueous N-methyldiethanolamine, N,N-dimethylethanolamine, and triisopropanolamine solutions with and without the enzyme carbonic anhydrase has been studied in a stirred cell reactor at temperatures varying between 278 and 313 K, at an alkanolamine concentration of 1 kmol m–3 and carbonic anhydrase concentrations ranging from 0 to 2.4 kg m–3, respectively. The experimental data from these experiments have been used to fit the obtained rate constant for the enzymatic CO2 hydration to the Bronsted relation: ln(k) = A(pKa) + B + C/T. In addition to the carbon dioxide absorption in the three tertiary alkanolamines, the absorption of carbon dioxide in next three solvents had been studied: 0.3 kmol m–3 potassium carbonate, 0.3 kmol m–3 sodium carbonate, and 0.2 kmol m–3 2-amino-2-methyl-1-propanol. The kinetics from these solvents are well predicted by the relation fitted to the data of the tertiary amines only.

A hybrid equation of state and Kent-Eisenberg model for accurate prediction of carbon dioxide separation by aqueous alkanolamines

ABSTRACTA hybrid predictive model has been developed for accurate prediction of thermodynamics of carbon dioxide separation by aqueous alkanolamines. The model incorporates equation of state/excess Gibbs energy model into Kent–Eisenberg approach to predict carbon dioxide–alkanolamine–water equilibria. The approach imparts theoretical corrections to Kent–Eisenberg approach and significantly extends their range of application for monoethanolamine, diethanolamine, methyldiethanolamine, and 2-amino-2-methyl-1-propanol solutions. The proposed model suitably predicts thermodynamics of carbon dioxide separation, well beyond the regressed range of parameters. The results are in excellent agreement with experimental data for a wide range of process parameters and found superior to existing thermodynamic approaches.