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Monitoring of the blend monoethanolamine/methyldiethanolamine/water for post-combustion CO2 capture
Abstract
The blend MEA/MDEA (5/25%wt.) was studied on the LEMEDES-CO2 lab-scale pilot plant, with representative conditions of post-combustion CO2 capture for power generation during 900 h. CO2 loadings were determined and showed average values of 0.12 and 0.40 respectively for the lean and rich solvents. Stability of the two amines, namely MEA and MDEA, was monitored using ionic chromatography; results did not show any significant degradation of MDEA during the campaign, in contrary to MEA which showed a significant degradation in the range of 0.03 points per day. Analytical methods involving GC–MS and IC were developed in order to identify potential degradation products in the liquid phase of the solvent. Study of the gaseous emissions’ composition was also realized using sampling on different solid sorbents followed by thermal desorption and GC–MS analysis. A total of 22 compounds were listed including amines, organic acids, and pyrazines derivatives. 12 degradation products were found in the solvent itself and 11 in the treated flue gas among which MDEA, the constituent amine of the blend. A quantitative monitoring was carried out for formic and oxalic acids. Results showed concentrations reaching 500 mg/L for oxalic acid and 1400 mg/L for formic acid.
... The growing concern of increasing CO 2 levels in the atmosphere has intensified research into numerous techniques developed to reduce the greenhouse gas emission, and the chemical absorption method (using amine-based solutions) is regarded as the most promising post-combustion capture technology in response to the global growing demands to remove CO 2 from point source [1][2][3]. Despite the technological successes, corrosion is one of the major operational problems encountered in the postcombustion capture process [4][5][6]. ...
... Alkanolamines are not corrosive until they absorb CO 2 , which is a known primary corrodent, and the order of corrosivity of the conventional alkanolamines on carbon steel was reported to be monoethanolamine > diethanolamine > methyldiethanolamine [6]. Therefore, methyldiethanolamine (MDEA, CH 3 N(C 2 H 4 OH) 2 ) is generally favoured in CO 2 capture because of its relatively low corrosion tendency. As a tertiary amine, methyldiethanolamine does not form carbamate (R 3 NCOO À ) with CO 2 and it also has a high resistance to thermal and chemical degradation [32][33][34][35]. ...
The effect of flow and temperature on the corrosion behavior of carbon steel in an aqueous methyldiethanolamine solution containing different heat stable salts, such as sodium sulfate, sodium sulfite and sodium thiosulfate, has been studied. The introduction of flow and increase in temperature generally caused an increase in the corrosion rate of carbon steel but the presence of the heat stable salts affected the corrosion behavior to different extents. Sulfate increased the corrosivity of the aqueous methyldiethanolamine solution, thus showed accelerated corrosion behavior in the presence of flow and with increase in temperature when compared with the solution without heat stable salts. The presence of sulfite reduced the corrosivity of the methyldiethanolamine solution due to its oxygen scavenging ability. Although flow and temperature stimulated an increase in the corrosion rate of carbon steel, the corrosion inhibiting effects of sulfite ions increased with the salt concentration. Also, the presence of sodium thiosulfate caused a reduction in carbon steel corrosion. Its inhibition ability is largely the result of the formation of FeS product layer resulting from its disproportionation reaction. This layer offered a slight resistance to the influence of flow and increase in temperature when compared with the system without heat stable salts. The mechanisms for the influence of different heat stable salts, namely sodium sulfate, sodium sulfite and sodium thiosulfate on the corrosion behavior of carbon steel in a post‐combustion CO2 capture system is presented. While the sulfate system promoted corrosion, the sulfite and thiosulfate systems exhibited corrosion inhibition effects.
... When unavailable in the literature, simulations of a typical amines-based process for CO2 capture were performed using Aspen Plus © software for the blends of interest, in order to determine the best amines ratio [237]. Results are compared to simulation results of MEA based process 2.1 Modelling amine blend-based process for CO2 capture Heat of absorption was calculated using approximation of Gibbs-Helmholtz equation: ...
... Both blends were characterized for their degradation products formed in the liquid phase of the solvents and for their composition of the treated flue gas [225,237]. Although a slow or no significant loss of amine have been seen during time, some degradations products were identified. ...
Le procédé de captage du CO2 en post-combustion par absorption chimique est aujourd'hui la technologie la plus mature en vue d'une réduction des émissions de CO2 issues de procédés industriels. Les deux principales limitations de la technologie sont la pénalité énergétique engendrée par le procédé, et la formation de produits de dégradation potentiellement toxiques pour l'Homme et l'environnement. Dans le cadre de ce projet de thèse, trois solvants innovants ont été présélectionnés pour leurs bonnes propriétés thermodynamiques de captage : les mélanges 1-méthylpipérazine / pipérazine (1MPZ /PZ), diméthylaminoéthanol / pipérazine (DMEA/PZ) et méthyldiéthanolamine/monoéthanolamine (MDEA/MEA). Ces trois solvants ont été étudiés en termes de stabilité chimique dans des conditions représentatives des conditions industrielles du captage de CO2 en post-combustion sur un dispositif expérimental construit par EDF R&D Chatou. Des méthodes analytiques complémentaires impliquant les chromatographies liquide et gazeuse ont été développées dans l'objectif de suivre les teneurs en amines constituantes du solvant au cours du temps, et d'identifier et quantifier les potentiels produits de dégradation formés aussi bien dans la phase liquide du solvant que dans les fumées traitées émises. Au vu des résultats obtenus au cours de ce projet, le solvant MDEA/MEA semble offrir le meilleur compromis en termes de stabilité chimique et de besoins énergétiques requis pour le procédé. Ce solvant présente des taux de dégradation inférieurs aux mélanges 1MPZ/PZ et DMEA/PZ, et permettrait une réduction de l'énergie au rebouilleur de l'ordre de 10 % par rapport à la MEA 30 %, solvant modèle au procédé.
... Amine solvents are the most used chemical for carbon capture. Other amines such as diethanolamine (DEA) and MDEA have been used in industry for many years for gas purification [16]. However, MEA has advantages over other amines because of its unique features, such as high loading capacity for CO 2 at low partial pressures, fast reaction kinetics and high removal efficiencies [17]. ...
The United States emitted 5.27 billion tonnes of carbon dioxide into the atmosphere in 2018, less than one-sixth of the global emissions that year. The immense amount of greenhouse gases in the air have a detrimental effect on the planet. Rising global temperatures, rising sea levels, drought, wildfires, and other natural disasters are all being accelerated because of carbon emissions. Carbon capture is one solution that could reduce emissions tremendously. The topics of energy consumption, transportation phenomena, and thermodynamics of a wide range of carbon capture methods will be discussed. Keywords: Climate Change, Post-combustion, Carbon Dioxide, Carbon Capture, Absorption, Desorption
... To enhance the absorption process, aqueous blends of amines have been extensively studied in the literature. One common approach is blending MEA with MDEA, a mixture that exploits the high absorption rate of MEA and the high equilibrium capacity of MDEA [11]. ...
Absorption Rate-based model Extended-UNIQUAC A B S T R A C T A rate-based non-equilibrium model is developed for CO 2 absorption with the mixture of piperazine and potassium carbonate solution. The model is based on the mass and heat transfer between the liquid and the gas phases on each packed column segment. The thermodynamic equilibrium assumption (physical equilibrium) is considered only at the gas-liquid interface and chemical equilibrium is assumed in the liquid phase bulk. The calculated mass transfer coefficient from available correlations is corrected by the enhancement factor to account for the chemical reactions in the system. The Extended-UNIQUAC model is used to calculate the non-idealities related to the liquid phase, and the Soave-Redlich-Kwong (SRK) equation of state is used for the gas phase calculations. The thermodynamic analysis is also performed in this study. The enhancement factor is used to represent the effect of chemical reactions of the piperazine promoted potassium carbonate solution, which has not been considered given the rigorous electrolyte thermodynamics in the absorber. The developed model showed good agreement with the experimental data and similar studies in the literature.
... Even though amine aqueous solutions are efficient for CO 2 chemical absorption, it is an expensive and eco-unfriendly technology because of the high energy penalty for solvent recovery. In addition, amine degradation can occur, forming toxic, corrosive and cancerous compounds [3][4][5]. Among the promising porous materials for CO 2 capture, amine-functionalized mesoporous silica, zeolites, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), porous graphene and nitrogen-doped porous carbon (N-carbon) have been broadly studied [6][7][8][9][10][11][12][13]. ...
Carbon dioxide (CO2) and hydrogen (H2) adsorptions were investigated on 3D nitrogen-doped porous graphene (GO-PAA) produced by chemical activation of graphene oxide impregnated with polyallylamine (PAA). GO-PAA characterizations by Raman and X-ray photoelectron spectroscopies, thermogravimetric analysis, N2 adsorption-desorption isotherms, scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed that GO-PAA shows excellent thermal stability, decomposing at temperatures higher than 450 °C, specific surface area of 1155 m² g⁻¹, with pyrrolic, pyridinic and graphitic nitrogen atoms homogeneously dispersed throughout its 3D porous structure. The mesoporous nature of GO-PAA and the nitrogen doping level of 7.5 wt% resulted in remarkable H2 (1.3 wt%) and CO2 (20 mmol g⁻¹) adsorption capacities at room temperature (RT, 25 °C) under high-pressure regime (40 bar). This H2 adsorption capacity at RT is among the highest values reported in the open literature. The role of the nitrogen atoms on the gas adsorption properties was investigated by combining experimental data, such as isosteric heat and Diffuse Reflectance Infrared Fourier Transform spectroscopy, with theoretical calculations using Density-Functional Theory. Inclusion of nitrogen atoms in the graphene structure reduces the energies of the Frontier Molecular Orbitals, facilitating polarization and increasing the interaction energy.
... For example, a typical aqueous alkanolamine process being the best available technology requires a large amount of energy during the desorption stage, mainly because the large enthalpy of the reaction between alkanolamines and CO 2 , enthalpy of vaporization and heat capacity of water (Ma et al., 2018;Shiflett et al., 2010). Traditional absorbents have also disadvantages such as high volatility leading to solvent loss, high rate of corrosion of equipment, and high rate of degradation in the presence of oxygen (Cuccia et al., 2019). ...
Ionic liquids (ILs) mixtures with water, amines, and other solvents have been receiving attention as alternative CO2 absorbents that could offer energy savings compared with traditional aqueous MEA processes and mitigate the high cost or viscosity of pure ionic liquids. In this work, mixtures of two ionic liquids (1-butyl-3-methylimidazolium acetate [bmim][OAc], 1-ethyl-3-methylimidazolium octylsulphate [emim][OcSO4]) and five amines (1,1,3,3-tetramethylguanidine (TMG), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO), triethylamine (TEA), and 2,2′-aminodiethanol (DEA)) were used for CO2 capture. In total, ten model systems were investigated. Generalized patterns of composition-CO2 absorption relationships were identified depending on the underlying mechanism of absorption. Viscosity, degradation and regeneration potential of the selected systems were determined. DBU-[emim][OcSO4] systems showed the temperature of regeneration as low as 60 °C. The viscosity of all systems was greatly reduced by the addition of water. Some CO2-rich solutions displayed non‐Newtonian behavior. Mechanism of CO2 absorption in imidazolium ionic liquids in the presence of DBU was confirmed based on ¹³C NMR.
... The conventionally used primary, secondary, and tertiary amines in industry are monoethanolamine (MEA), diethanolamine (DEA), and N-methyldiethanolamine (MDEA), respectively. 1,2 The concept of blending alkanolamines has received attention as they provide better CO 2 capture efficiency than a single absorbent. 2−5 A number of amine blends have been proposed and investigated. ...
This work contributes to new and complementary experimental viscosity data for blended amine mixtures of aqueous N-methyldiethanolamine + 2-amino-2-methyl-1-propanol (MDEA + AMP) solutions with and without CO2 at different temperatures and mass fractions. For the unloaded MDEA + AMP solutions, measurements were conducted with total amine mass fractions ranging from 0.30 to 0.60. In the case of CO2-loaded aqueous MDEA + AMP solutions, experiments were performed at CO2 loadings ranging from 0.11 to 0.80. Proposed correlations were used to represent viscosity at the unloaded and CO2-loaded solutions within experimental uncertainty.
... Table 1 summarizes the energy performance of three kinds of new amine-based solvents. [29,31] A blend of amines solvents integrates the properties and advantages of various amines, such as a classic combination of primary amines (e.g., MEA) or secondary amines (e.g., DEA) mixed with tertiary amines (e.g., MDEA) [32,33]. The performance of this kind of solvent, which combines the high reaction rate of primary or secondary amines with the high absorption capacity and lower absorption heat of tertiary amines, has been tested at the pilot scale or even higher scales for many years [34,35]. ...
The thermodynamic cycle, as a significant tool derived from equilibrium, could provide a reasonable and rapid energy profile of complicated energy systems. Such a function could strongly promote an in-depth and direct understanding of the energy conversion mechanism of cutting-edge industrial systems, e.g., carbon capture system (CCS) However, such applications of thermodynamics theory have not been widely accepted in the carbon capture sector, which may be one of the reasons why intensive energy consumption still obstructs large-scale commercialization of CCS. In this paper, a kind of thermodynamic cycle was developed as a tool to estimate the lowest regeneration heat (Qre) of a benchmark solvent (MEA) under typical conditions. Moreover, COPCO2, a new assessment indicator, was proposed firstly for energy-efficiency performance analysis of such a kind of CCS system. In addition to regeneration heat and second-law efficiency (η2nd), the developed COPCO2 was also integrated into the existing performance analysis framework, to assess the energy efficiency of an amine-based absorption system. Through variable parameter analysis, the higher CO2 concentration of the flue gas, the higher COPCO2, up to 2.80 in 16 vt% and the Qre was 2.82 GJ/t, when Rdes = 1 and ΔTheat-ex = 10 K. The η2nd was no more than 30% and decreased with the rise of the desorption temperature, which indicates the great potential of improvements of the energy efficiency.
As a heat stable salt, sodium sulfide remains thermally-unregenerable during the regeneration process for post-combustion capture. Therefore, it became important to undertake a full assessment of its potential presence in the system. The paper investigates the mechanism and influence of sodium sulfide on the corrosion behavior of Q235 steel in amine-based post-combustion CO2 capture technology with respect to exposure time and temperature. The inhibitive influence of sulfide in the system was first confirmed by electrochemical techniques, while gravimetry was used to evaluate the effect of time and temperature on the inhibitive actions. SEM/EDX and XPS were used to characterize the corrosion product films on the steel surface. The behavior of sulfide was largely dependent on its concentration as its inhibition ability decreased with increasing concentration, and this is credited to the presence of FeS corrosion film layer. Time-dependent corrosion studies of steel conducted at 50 °C for the solution with 0.05 M and 0.1 M sulfide showed that the inhibition efficiency decreased from 89.1% and 75.0% to 82.4% and 68.6%, respectively, after 7 and 14 days immersion. At 80 °C, the inhibition efficiency of 0.05 M sulfide decreased from 89.1% to 48.9% after 7 days immersion and 82.4% to 46.1% after 14 days immersion. Together with FeS layer, FeCO3, Fe2O3 were also confirmed on the steel surface by XPS measurement. The research provides practical information on the influence of sulfide in the absorber and rich-lean heat exchanger sections of a CO2 capture unit.
Degradation of amines is a significant issue allied to amine-based carbon dioxide (CO2) absorption in post-combustion CO2 capture. It becomes essential to have a detailed understanding of degradation products for advanced post-combustion CO2 capture technology. Identification and quantification of degradation products of amines help in practicability and environmental assessment of amine-based technology. Gas, liquid, and ion chromatographic techniques are the benchmark tools for qualitative and quantitative analyses of the amines and their derivatives. Among others, gas chromatography has been more in use for this specific application, especially for the identification of degradation products of amines. This review focuses on the critical elucidation of gas chromatographic analysis and development of methods to determine the amine degradation products, highlighting preparation methods for samples and selecting columns and detectors. The choice of detector, column, sample preparation, and method development are reviewed in this manuscript, keeping in view the industry and research applications. Furthermore, obtained results on the quantitative and qualitative analyses using gas chromatography are summarized with future perspectives.
In this study, the waste eggshell has been utilized to synthesise structure modified CaO using organic acids and employed for CO2 capture in the thermogravimetric analysis (TGA) based systems. Different characterization techniques were used such as XRD, SEM/EDS, XRF, N2 sorption-desorption (BET) and TGA to investigate the suitability for CO2 adsorption. The modified CaO using organic acids showed high surface area, easy upgradation of pore structure makes the CaO a suitable sorbent for CO2 capturing as an economical sorbent. Three of the organic acid modified sorbent achieved the highest conversion and stability over a period of 20 cycles. Citric acid modified sorbent (CaO CA-10%) obtained a CO2 uptake of 0.38 g CO2/g sorbent (CaO conversion of 55%) that was highest among the acid used whereas in term of stability malic acid modified sorbent (CaO MA-10%) has the lowest average decay rate of 4.43 mg CO2/cycle as compared to various acids used in this work. It is concluded that modified surface structure by employment of organic acids lead to the reduction of sintering and led towards better sorbents performance towards CO2 capturing for multiple cycles.
Carbon dioxide capture with absorption is the main method to reduce CO2 emission. In this article CO2 solubility data were measured and thermodynamic models are established for CO2 capture with a new solvent 1-methylpiperazine (1-MPZ) with piperazine (PZ). Then the simulations are carried out with commercial software to calculate energy consumption of absorption processes with different operating parameters including amine concentration, CO2 partial pressure, regeneration pressure, and the results are compared with the MEA and AMP solvent. The energy consumption with the new solvent 1-MPZ+PZ is smaller than those with MEA by 20%.
This paper reviews the operational flexibility and emissions of gas- and coal-fired power plants today and in the future with higher renewables. Six study cases were considered: heavy duty gas turbines in simple and combined cycle, aero-derivative gas turbines, large-scale supercritical coal power plants and small- and mid-scale sub-critical coal power plants. The most critical operational processes and pollutants associated with these plants were identified. Then, data was collected mainly from manufacturers, but also from academic research and grey literature. The data was compared and analyzed. Detailed comparisons of the power plant characteristics as well as the current and future flexibility and emissions are provided. Furthermore, a method to quantify the ability of conventional power plants to back-up renewables and the expected benefits from improved flexibility is proposed and evaluated. Results show that gas-fired power plants are not only more efficient, but also faster and generally less polluting than coal-fired power plants. However, at their respective minimum complaint load, gas plants are less flexible and produced more NOx and CO emissions than coal-fired power plants. Results also show that on average, an improvement of approximately 50% to 100% on power ramp rates, minimum power load, number of major power cycles and emissions for these plants is sought in the future to complement renewables.
In the past, several research programs were undertaken at European Carbon Capture (CC) pilot plants. The results of these individual MEA based campaigns are brought together in order to better understand the solvent degradation at CC pilot plants. The data correlation analysis shows that nickel catalyzes significantly the formation of some degradation products (e.g. HEPO) at low concentrations of 2mg/l. The iron impact was less clear than determined for nickel. All pilot plants show HEGly and HEPO as the main degradation products, followed by HEF. Within the group of carboxylic acids, formate is the major degradation product.
In the field of greenhouse gas emission, a promising approach consists in CO2 storage and capture. However most of the processes are based on amine solutions which are likely to degrade and produce potentially harmful compounds. So there is a need for analytical methods to identify and quantify these products. Monoethanolamine was used as a model compound for the amines used for CO2 capture.
A liquid chromatography tandem mass spectrometry method was developed and validated for the quantification of six products of degradation of monoethanolamine (Glycine, N-(2-hydroxyethyl)glycine, N-glycylglycine, bicine, N,N′-bis-(2-hydroxyethyl) urea (BHE Urea), and diethanolamine) that were systematically detected with a LC-MS Scan method in real samples from CO2 capture and storage processes. The main difficulty of this study and its originality ly in the strategy developed to overcome the complexity of the matrix which is a mix of water and amine (70/30): the combined use of deuterated internal standards and a recent chemiometric approach to validate the method, i.e. the accuracy profile. For five compounds it was possible to validate the method with acceptance limits of 20%. This method was then successfully applied to real samples from pilot plant and lab-scale experiments.
The purpose of this work was to evaluate the absorption-regeneration performances of different types of amine(s) based solvents (primary, secondary and tertiary alkanolamines, sterically hindered amines, non-cyclical tetramine and cyclical absorption activators), previously selected thanks to a methodological study and separate laboratory absorption and regeneration tests. In this work absorption-regeneration experiments were carried out using a newly developed CO2 capture laboratory micro-pilot and applying a high gaseous CO2 content (from 20% to 30%) representative of cement plant flue gases.
One key criterion of CO2 capture solvents is their resistance to ageing - a set of thermal and chemical mechanisms - leading to a degradation of the process optimal operation and possible emissions. From literature, many lab-scale studies on solvent degradation are not sufficiently representative of industrial capture conditions. In order to address this issue, EDF R&D decided to set up a lab for studying degradation of solvents used for CO2 capture, named “LEMEDES-CO2”. In particular, LEMEDES- CO2 lab-scale apparatus has been designed to reproduce the dynamic cycling of the solvent between the absorber and the stripper columns. The technical features of this original lab-scale apparatus are based on the chemical absorption principle with short cycles of absorption and stripping and a fast heating up and cooling down of the solvent. Using MEA solvent as benchmark case, an important number of degradation products has been detected and most of the species are identified, in agreement with literature. Those results showed this bench scale set up capacity to mimic observed degradation behavior witnessed on industrial pilot plant, thus validating the capacity of the lab-scale experiment to simulate the operating conditions seen by the solvent during cycles of absorption and stripping.
This paper lays out a generic CO2 capture testing methodology that has been applied at multiple sites providing details on the procedure, its key performance indices and their associated specifications, as well as the required pre-test work. Specific application of the methodology for the CO2 Technology Centre Mongstad site, a CO2 capture testing facility located in Norway that performed CO2 capture tests using MEA, is shown as an illustrative example.
The effect of mixing a tertiary amine, N,N-Methyldiethanolamine (MDEA), with a secondary amine, diethanolamine (DEA), on the kinetics of the reaction with carbon dioxide in aqueous media has been studied in a stirred cell reactor with a plane, horizontal gas-liquid interface. Temperature was varied from 293 to 313K over a range of blend composition and total mixture concentration ranging from one to two molars. The proposed model representing the reaction of CO 2 with the blends studied is found to be satisfactory in determining the kinetics of the involved reactions. This model is based on the zwitterion mechanism for the DEA and water hydration catalysis for MDEA. Blending MDEA with DEA results in observed pseudo-first-order reaction rate constant values (k o) that are greater than the sum of the k o values of the respective single amines. This is due to the role played by MDEA in the deprotonation of the zwitterion of the other amine (DEA). Species concentration profile needed to fit the experimental data to the model to extract the kinetic parameters associated with the reactions was calculated using the modified Deshmukh-Mather model.
In the present paper, we investigated CO2 capture with 24 tertiary amine absorbents, including three synthetic amines, with systematic modification of their chemical structures. Aqueous solutions of the amines (mass fraction 30%) were used to evaluate the performance for CO2 capture. Gas scrubbing, vapor–liquid equilibrium (VLE), and reaction calorimetry experiments were conducted in the laboratory to obtain the absorption rate, the amount of CO2 absorbed, cyclic CO2 capacity, and heat of reaction for each absorbent. The results for these absorbents were compared with the conventional tertiary absorbent N-methyldiethanolamine (MDEA). Seven of the investigated absorbents performed well with high absorption rates and cyclic capacities. Among these absorbents, some showed lower heats of reaction than MDEA. These results provide basic guidelines for discovery of potential tertiary amine-based absorbents that may lead to development of new absorbent systems in the CO2 capture area.
The degradation of 2-amino-2-methyl-1-propanol (AMP) has been investigated in the presence of oxygen. AMP was not stable and the overall degradation rate of AMP was close to that of N-methyldiethanolamine (MDEA) under identical conditions. The primary degradation products identified by GC-MS were acetone, 2,4-lutidine and 4,4-dimethyl-2-oxazolidinone. The oxidative degradation rates of AMP strongly depended upon oxygen partial pressure. The effect of temperature on the overall degradation rates was also measured. No significant catalytic effect was observed when 0.1 mM ferrous oxalate (Fe C2O4) and 0.1 mM copper sulphate (CuSO4) were added into the AMP solutions, respectively, and the degradation rates of AMP show a weak dependence on a radical initiator. Carbon dioxide (CO2) was found to speed up the overall degradation rate of AMP.
An important step towards commercial scale post-combustion CO2 capture from coal-fired power stations is understanding solvent degradation. Laboratory scale trials have identified three main solvent degradation pathways for 30% MEA: oxidative degradation, carbamate polymerization and formation of heat stable salts. This paper probes the semi-volatile organic compounds produced from a single batch of 30% MEA which was used to capture CO2 from a black coal-fired power station (Tarong, Queensland, Australia) for approximately 700 hours, followed by 500 hours at the brown coal-fired power station (Loy Yang, Victoria, Australia). Comparisons are made between the compounds identified in this aged solvent system with MEA degradation reactions described in literature.
To understand which part of the CO2 amine-based system is mostly responsible of amine degradation, MEA degradation under real CO2 capture conditions is compared with two laboratory experiments; a thermal degradation experiment representative of the stripper conditions (MEA 30 wt%, CO2 loaded, α=0.5, 135 °C) and an oxidative degradation experiment representative of the absorber conditions (MEA 30 wt%, CO2 loaded, α=0.4, sparged with air+CO2, 55 °C). Liquid Chromatography-Mass Spectrometry (LC-MS) was used for the quantification of the remaining amine and Gas Chromatography-Mass Spectrometry (GC-MS) was used for the identification and quantification of the main degradation compounds. This study suggests that MEA degradation in the pilot plant is more dominated by oxidative degradation than by thermal degradation. It is also found that reactions between MEA and carboxylic acids present in the solution may play a significant role in solvent degradation. This implies that carboxylic acids, usually referred to as “Heat Stable Salts”, are not stable and can react further to give more complex compounds.
The roles of HSS induced acid products of MEA degradation were evaluated. The results show that formic and acetic acids, formed as a result of MEA oxidation, exist in 2 forms in equilibrium; namely, salts and amides. Specifically, these are formate and acetate, and N-(2-hydroxyethyl)formamide and N-(2-hydroxyethyl)acetamide, respectively. Glycolic acid, also formed due to MEA oxidation, is stable and exists mostly bonded with MEA to produce the glycolate HSS. Its amide is unstable, hydrolyzing back to glycolate and MEA. Oxalic acid was found as a reactive intermediate that mostly decomposed to formic acid, which in turn produced a stable N-(2-hydroxyethyl)formamide. Oxalic acid amide (N-(2-hydroxyethyl)oxamide) could also be formed but its formation was considered a minor route compared with the decomposition route. Succinic acid formed a stable imide (N-(2-hydroxyethyl)succinimide) through an intermediate amide (N-(2-hydroxyethyl)succinamide).
The applicability of the equation derived for calculating the dynamic viscosity of ternary non-electrolyte mixtures, to the correlation of viscosity data of the H<sub>2</sub>O- K<sub>2</sub>CO<sub>3</sub>/KHCO<sub>3</sub> system is verified in this work. It was found out that the values of dynamic viscosity obtained experimentally are in good agreement with the viscosity values calculated from this equation. The equation constants - interaction coefficients - were determined from the measurements of dynamic viscosity on mixing the basic solutions of K<sub>2</sub>CO<sub>3</sub> and KHCO<sub>3</sub> of known concentration. The correlation equation makes it possible to calculate viscosity of the K<sub>2</sub>CO<sub>3</sub>/KHCO<sub>3</sub> solutions in the K<sub>2</sub>CO<sub>3</sub> and KHCO<sub>3</sub> concentration range from 0 to about 2.0 kmol m<sup>-3</sup>.
Four popular thermally desorbable adsorbents used for air sampling (Tenax TA, Tenax GR, Carbopack B, and Carbopack X) are examined for the potential to form artifacts with ozone (O3) at environmental concentrations. The performance of these adsorbents for the ketone and aldehyde species identified as O3-adsorbent artifacts was also characterized, including recovery, linearity, and method detection limits (MDLs). Using gas chromatography/mass spectrometry, 13 different artifacts were identified and confirmed for both Tenax TA and Tenax GR, 9 for Carbopack B, but none for Carbopack X. Several O3 artifacts not reported previously were identified, including: pentanal, 3-hexanone, 2-hexanone, hexanal, 3-heptanone, and heptanal with Tenax TA; pentanal, 3-hexanone, 2-hexanone, hexanal, and 3-heptanone on Tenax GR; and 1-octene and 1-nonene with Carbopack B. Levels of straight-chain aldehyde artifacts rapidly diminished after a few cycles of adsorbent conditioning/O3 exposure, and concentrations could be predicted using a first-order model. Phenyl-substituted carbonyl artifacts (benzaldehyde and acetophenone) persisted on Tenax TA and GR even after 10 O3 exposure-conditioning cycles. O3 breakthrough through the adsorbent bed was most rapid in adsorbents that yielded the highest levels of artifacts. Overall, artifact composition and concentration are shown to depend on O3 concentration and dose, conditioning method, and adsorbent type and age. Calibrations showed good linearity, and most compounds had reasonable recoveries, for example, 90 +/- 15% for Tenax TA, 97 +/- 23% for Tenax GR, 101 +/- 24% for Carbopack B, and 79 +/- 25% (91 +/- 9% for n-aldehydes) for Carbopack X. Benzeneacetaldehyde recovery was notably poorer (22-63% across the four adsorbents). MDLs for several compounds were relatively high, up to 5 ng. By accounting for both artifact formation and method performance, this work helps to identify which carbonyl compounds can be measured using thermally desorbable adsorbents and which may be prone to bias because of the formation of O3-adsorbent artifacts.
Post-combustion CO2 capture process using amine solvents is limited by the high energy penalty and the irreversible degradation of amines. The present work aimed at studying the degradation of the innovative blend 1-methylpiperazine/piperazine (1MPZ/PZ: 30/10%wt.) in a lab-scale pilot plant, LEMEDES-CO2, with conditions representative of post-combustion CO2 capture for power generation. Degradation of the solvent was realized twice during 800 and 955 h. Addition of acidic impurities (H2SO3 and HNO3) in the second campaign was performed in order to study their impact on the solvents degradation. CO2 loadings were determined and showed an average value of 0.28 for the lean solvent and 0.63 for the rich solvent. In order to identify and quantify degradation products, complementary analytical strategies were developed involving LC–MS, ionic chromatography and GC–MS. In order to monitor the gaseous effluents, a sampling on solid sorbents (Tenax® TA) was performed followed by thermodesorption and GC–MS analysis. This study permitted the identification of 23 degradation products in the liquid phase of the solvent, and 16 emitted with the treated flue gas. Among them were found piperazine derivatives, alkylpyrazines and organic acids. Quantification was performed on both liquid and gaseous phases on 10 selected compounds.
A degradation experimental protocol with 30%-wt MEA solvent has been applied successfully on a lab-scale experiment set up to simulate the operating conditions seen by the solvent during cycles of absorption and stripping of the CO2 capture process. Degradation campaign lasted about 750 hours (750 cycles) in the presence of a synthetic flue gas containing 82% of N2, 15% of CO2, 3% of O2. An important number of degradation products (more than 30) was detected and most of the species were identified in agreement with literature.
An advanced 0.7 MWe small pilot coal-fired post-combustion CO2 capture system with heat integration combined with two-stage stripping was tested on a slipstream of flue gas by the University of Kentucky Center for Applied Energy Research (UKy-CAER). Evaluation of solvent degradation products was performed to determine the impact of oxygen exposure due to incorporation of the secondary air stripper into the conventional amine absorber/stripper system. The overall degradation rates and products observed during the testing campaign were comparable to previously published reports using 30% monoethanolamine (MEA) as the baseline/commissioning solvent. The rates of heat stable salt accumulation and amine degradation were similar to those from conventional CO2 capture systems using MEA. Metal accumulation as the result of material corrosion inside the system from an improperly constructed material was observed. The impact of the secondary air stripper appears negligible relative to other published MEA campaigns tested at similar flue gas conditions and system operating hours.
Post combustion CO2 capture using amine-based solvents is currently a very attractive technology for the treatment of flue gases produced in existing power plants. One of the main drawbacks of the process is a degradation of the solvent resulting in the formation of degradation products. Those degradation products, which are potentially detrimental to humans and environment can be emitted in the treated flue gas. The aim of this study was to develop a Thermodesorption–Gas Chromatography–Mass Spectrometry method for the simultaneous quantification in gaseous phase of a wide variety of products. A selection of five MEA degradation products is presented in this work: pyrazine, nitrosodimethylamine, 2-methylpyrazine, dimethylformamide and pyrrole. This method was validated using the accuracy profile concept with acceptance limits of 30%. The method involved active sampling on solid sorbents followed by thermal desorption and GC–MS analysis. The calibration was realized with an Adsorbent Tube Injector System at a temperature of 140 °C during 3 min. This method was applied to samples from an IFPEN CO2 capture pilot plant: the concentration in the absorber gas effluent of each targeted compound was lower than 300 μg/m³ for nitrosodimethylamine and pyrazine, and lower than 30 μg/m³ for pyrrole, dimethylformamide and 2-methylpyrazine.
A pilot plant campaign was performed to study MEA degradation in CO2 capture conditions and anticipate potential degradation products emissions to the atmosphere in industrial case. Aqueous 30% wt MEA was cycled between absorption and regeneration steps during 1700 h in the presence of a synthetic flue gas containing 81% of N2, 14% of CO2, 5% of O2, 97 ppm of NO, 9 ppm of SO2 and 5 ppm of NO2. Specific methods (sampling, sample conditioning and analysis) were developed to improve degradation products identification and to provide a quantification of targeted compounds in liquid phase and above all in absorber and stripper gas effluents. Especially, trace elements were detected in liquid phase thanks to Head Space-Solid Phase MicroExtraction (HS-SPME) and liquid–liquid extraction with ChemElut cartridges and in gas phase thanks to adsorbent tubes of different type: Sep-Pak® for aldehydes and ketones, Orbo 60 for _N_-nitrosodimethylamine, Tenax and active charcoal for non-specific adsorption. 32 degradation products were identified in liquid phase and 38 in gas phase, 17 of which for the first time, especially derivatives of pyridine and oxazolidine, 1H-pyrrole and a new nitrosamine, the _N_-nitroso-2-methyl-oxazolidine.
The reaction mechanism for CO2 absorption in amine solvent was investigated by theoretical analysis. The reactants were CO2 and six amines, and the reactions were designed with or without additional water or amine molecule. These molecules increase the interaction between reactants and withdraw a proton from amino group of amine. From the additional amine model that shows lowest activation energy, zwitterionic and termolecular mechanisms seem to be suitable for CO2 capturing reaction in amine solvents. Moreover, the additional amine model can be applied to understand the enhancement effect of CO2 absorption in blended amine solvents. We report a new attempt that describes reaction mechanism in blended amine solvent by applying additional amine base. The results of CO2 capture ability were analogous to experimental observation. Comparing our results and previous QM/MM and ab initio MD calculations, it was found that the QM treatment including the reactants and surrounding water molecules would be very critical and the QM region should be properly selected large enough in QM/MM.
The CO2 post-combustion capture with aqueous solutions of amines is the most mature technology to reduce greenhouse gases emissions. However chemical absorption is suffering from the degradation of amines mainly due to the presence of O2 in flue gases. Formed products, which could be rejected to atmosphere, may be detrimental to environment and human health. The aim of this thesis was to identify as many degradation products as possible thanks to the development of different sampling and analytical methods especially for gas phase analysis. Thus more than sixty products issued from monoethanolamaine (MEA) degradation were observed in pilot plant samples. Thirty of them are novel, they often belong to the same family as pyrazines or oxazolines, or they could be characterized by the increase of carbon chain lengths (C2 between two heteroatoms to C5).Mechanisms such as alkylation/dealkylation, aldehydes/ketones formation, amidification, aldolisation, Eschweiler Clarke, pyridines formation were proposed to explain the formation of novel products and were, most of the time, validated by mixing the reactants proposed in the mechanism. Finally, it has been shown that the transposition of these reactions to three other amines (N-methylaminoethanolamine, 1-aminopropan-2-ol, 3-aminopropan-1-ol) enabled us to predict their degradation products.
In this paper, we present atmospheric pressure liquid densities for binary mixtures of n-methyldiethanolamine + water over the entire composition range at temperatures between 263.15 and 363.15 K. We measure the liquid densities using a vibrating tube densimeter and use them to produce a correlation for excess molar volumes based upon a Redlich-Kister equation. The excess volumes exhibit negative deviations from ideality at all the investigated temperatures and become less negative with increasing temperature.
Solvent is a critical part of the post-combustion CO2 capture process by chemical absorption. Processes using good solvents will have low regeneration duty, high absorption rate, high cyclic capacity, and good resistance to degradation. This study focuses on the screening of cyclic amines (single or blended) of piperazine (PZ) derivatives based on the detailed VLE experiments for CO2 solubility, and analysis through simplified process modelling. With the proposed methodology, a new solvent can be efficiently compared with others in terms of operational cyclic capacity and regeneration duty. The study results showed that the most promising solvent candidate in terms of projected reboiler duty with a value of 2.5MJ/kg is the mixture of 1-MPZ and PZ. Considering the impact of cyclic capacity on the overall cost of the process and the unavoidable uncertainties of the screening procedure, three other solvents can be seen as promising: 1-MPZ, TEDA+PZ and DMPZ+PZ.
The integration of a post-combustion CO2 capture unit in a coal-fired steam power plant leads to a reduction in net power output, where the largest contributors to the power loss are the heat requirement for the regeneration of the chemical solvent in the desorber of the CO2 capture unit (approx. 2/3) and the auxiliary power demand of the CO2 compressor (approx. 1/4). In this review, the layout of the overall process is explained and the interaction of the three sub-processes power plant, CO2 capture process and CO2 compressor is discussed. The optimization of process parameters of the CO2 capture unit – such as solution flow rate and reboiler temperature – is intricate due to the complex interaction of the sub-processes. It is shown that although the heat requirement for solvent regeneration has the largest impact on the power output of the overall process, the optimal process parameters that lead to the lowest possible heat requirement of the capture unit do not necessarily coincide with the optimal process parameters that make for the most energy efficient operation of the overall process. Therefore, when optimizing process parameters of CO2 absorption processes in power plants, one should focus on the minimization of the overall power loss instead of solely reducing the heat requirement for solvent regeneration. The described coherences are illustrated by the results of process simulations based on detailed models of a post-combustion CO2 capture unit using 7 m (30 wt.-%) monoethanolamine (MEA), of a supercritical, hard-coal-fired steam power plant and of a six-stage, intercooled CO2 compressor. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd
Post-combustion CO2 capture based on CO2 absorption by aqueous amine solutions is the most mature gas separation technology. A main problem is amine degradation due to heat, CO2, O2, NOx and SOx. This review proposes to make a critical survey of literature concerning degradation, to list degradation products and to discuss mechanisms proposed by authors. Benchmark molecule is monoethanolamine (MEA) but diethanolamine (DEA), N-methyldiethanolamine (MDEA), piperazine (PZ) and 2-amino-2-methylpropan-1-ol (AMP) are also studied. Uses of other amines and amine blends are also considered. In the case of MEA, ammonia, N-(2-hydroxyethyl)-piperazin-3-one (HEPO) and N-(2-hydroxyethyl)-2-(2-hydroxyethylamino) acetamide (HEHEAA) are the main identified degradation products in pilot plants. Among lab studies, the most cited degradation products are ammonia, carboxylic acids, N-(2-hydroxyethyl)-formamide (HEF), N-(2-hydroxyethyl)-acetamide (HEA) and N-(2-hydroxyethyl)-imidazole (HEI) for oxidative degradation, and oxazolidin-2-one (OZD), N-(2-hydroxyethyl)-ethylenediamine (HEEDA) and N-(2-hydroxyethyl)-imidazolidin-2-one (HEIA) for thermal degradation. Numerous degradation products have been identified but some are still unknown. A lot of degradation mechanisms have been proposed but some are missing or need proofs. SOx and NOx effects are still few examined and much work remains to be done concerning volatile degradation products potentially emitted to atmosphere: their identification and their formation mechanisms need further investigations.
2-Ethanolamine (MEA) degradation has been studied under varying conditions of relevance to postcombustion CO2 capture. Degradation experiments performed in the laboratory were chosen to be representative of the conditions in a CO2 capture plant facility. The thermal degradation of MEA was investigated in closed-batch experiments at 135 °C at different loadings. MEA degradation was also studied in oxidative conditions without additives or by adding FeSO4/fly ash. These experiments were compared with three MEA campaigns performed in pilot plants at Tiller (Norway), Esbjerg (Denmark), and Longannet (U.K.). The same analytical procedures were used to identify and quantify the main degradation compounds. Mechanisms are also proposed to account for the observed degradation products. For the Tiller campaign 99.7% of nitrogen containing compounds in the liquid at the end of the campaign was accounted for by the solvent and quantified degradation products.
Aqueous solutions of alkanolamines such as monoethanolamine (MEA), diethanolamine (DEA), N-methyldiethanolamine (MDEA), di-2-propanolamine (DIPA), and bis[2-(hydroxyamino)ethyl] ether (DGA) are good solvents for the removal of acid gases such as CO[sub 2] and H[sub 2]S from the gas streams of many processes in the natural gas, petroleum, ammonia synthesis, and some chemical industries. The viscosity of aqueous solutions of methyldiethanolamine (MDEA) and of diethanolamine (DEA) have been measured at five temperatures in the range 25--80 C throughout the whole concentration range. The viscosity has been correlated as a function of composition for use in industrial calculations.
Very little information is available concerning the effect of acid gas loading on the physical properties of amine-treating solutions flowing through the absorption and regeneration columns used in gas processing. The densities and viscosities of partially carbonated monoethanolamine (MEA), diethanolamine (DEA), and N-methyldiethanolamine (MDEA) solutions were measured at 298 K. With increasing carbon dioxide loadings, significant increases in both density and viscosity were observed. These results were combined with literature data to produce correlations for alkanolamine solution density and viscosity as a function of amine concentration, carbon dioxide loading, and temperature. The resulting single-amine correlations were used to predict the densities and viscosities of DEA + MDEA and MEA + MDEA blends. Predictions are compared with data measured for these blends.
The density and viscosity values of binary mixtures of ethanolamine with water were measured at 303.15, 308.15, 313.15 and 318.15K, using this data excess molar volume VE, viscosity deviation Δη and excess Gibbs free energy of activation ΔGE∗ of viscous flow have been calculated. The results were fitted by Redlich–Kister equation. All mixtures show negative values of VE due to increased interactions between unlike molecules or very large differences in the molar volumes of pure components at relatively low temperature.
Detailed thermodynamic and kinetic models are presented in this paper which were developed for acid gas reactions with mixtures of amines. The models permit the extension of the nonequilibrium-stage approach in the simulation of gas treating plants using solvent blends. The prediction of these models indicate a potentially great improvement in sour gas treating processes. The mixing concept enables one to obtain the individual advantages of each amine for absorption as well as desorption without the disadvantages of either. In the absorber, the MEA in the blend at the top of the column serves to remove residual CO2 from the gas while throughout the rest of the column MDEA does a bulk removal job. The use of blended amines to treat natural, refinery and synthesis gases brings about a considerable improvement in absorption and a great savings in energy requirements.
Li M.H. and Shen K.-P., 1993. Calculation of equilibrium solubility of carbon dioxide in aqueous mixtures of monoethanolamine with methyldiethanolamme. Fluid Phase Equilibria, 85: 129-140.The equilibrium solubility of carbon dioxide in aqueous mixtures of monoethanolamine (MEA) with methyldiethanolamine (MDEA) has been correlated on the basis of the model of Kent and Eisenberg. The chemical equilibrium constants involving alkanolamines are expressed as functions of temperature, amine concentration and carbon dioxide loading. The constants in the model were determined by fitting to the solubility data of carbon dioxide in aqueous MEA/MDEA solutions for temperatures ranging from 40 to 100°C and for partial pressures of carbon dioxide up to 2000 kPa. Satisfactory results were obtained for calculations of the solubility of carbon dioxide in aqueous MEA/MDEA solutions for the systems tested. When performing the solubility calculations for the systems which are not included in the database, the model predicts reasonably well the solubility of carbon dioxide in aqueous MEA/MDEA solutions.
Aqueous monoethanolamine (MEA) at concentrations of 5 and 7 M was degraded with 100 mL/min of 98% O2/2% CO2 (98 mL/min O2), with oxygen mass transfer achieved by vortexing in a low-gas-flow degradation apparatus. Degraded samples were analyzed by ion chromatography (IC) and high-pressure liquid chromatography (HPLC) with evaporative light scattering detection (ELSD) for oxidative degradation products. In a high-gas-flow apparatus, 7.5 L/min of 83% N2/15% O2/2% CO2 (1125 mL/min O2) was sparged through a mechanically agitated 5 M MEA solution. A Fourier transform infrared (FTIR) analyzer collected continuous gas-phase data. Formate (HCOO−), hydroxyethyl formamide (HEF), and hydroxyethyl imidazole (HEI) account for 92% of degraded carbon at low-gas-flow conditions and 18−59% of degraded carbon at high-gas-flow conditions. Oxalate (C2O42−), oxamide (C2H4N2O2), glycolate (HOCH2COO−), acetate (CH3COO−), carbon monoxide (CO), ethylene (C2H4), formaldehyde (CH2O), and acetaldehyde (CH3CHO) are oxidation products in lower concentrations. Ammonia (NH3), HEF, and HEI account for 84% of degraded nitrogen at low-gas-flow conditions and 83−92% at high-gas-flow conditions. Nitrogen oxides (NOx), present in lower concentrations, are stripped from solution at high-gas-flow conditions and retained in the degraded solution at low-gas-flow conditions and oxidized to nitrite/nitrate (NO2−/NO3−). A comparison of product rates to MEA losses shows that 25−50% of products remain unaccounted for in unknown HPLC peaks. Oxygen consumption rates vary from 1 to 2 mM/h, whereas the overall oxygen stoichiometry is 0.75 mol of O2/mol of MEA degraded.
Degradation of 12 different amines with CO2 was evaluated in 100 mL stainless steel batch reactors for 15 days at 140 °C using a 4 mol·kg−1 amine solution and a CO2 pressure of 2 MPa. At the end of the run, most of degradation products were identified by gas chromatography (GC)/mass spectrometry (MS); amounts of starting amine and its degradation products were determined with a quantitative GC method. This work compares the degradation of ethanolamines (including MEA) having one or two hydroxyl groups with the degradation of ethylenediamines. They were chosen to establish relationships between amine structure and stability properties: replacement of one alcohol function by one amine function, effect of amine function nature, impact of steric hindrance and cyclic structure. Significant differences were observed. The main degradation products are described, and some mechanisms are proposed to explain their formation.
The kinetics of absorption of CO2 in loaded mixed methyldiethanolamine (MDEA) and monoethanolamine (MEA) solutions was investigated in a laboratory laminar jet apparatus. The experiments were conducted over the temperature range of 298−333 K, MDEA/MEA wt ratio of 27/03, 25/05 and 23/07, total amine concentration of 30 wt %, and CO2 loading from 0.005 to 0.15 (mol of CO2)/(mol of total amine). Physical properties such as density, viscosity, diffusivity, and solubility of the system were calculated from published data and/or models. Reaction mechanisms, namely, zwitterion and termolecular, were used to interpret the kinetic data. It was observed that the zwitterion mechanism in its original form could not predict the individual kinetic rate constants. Equally, the termolecular mechanism with water in the apparent reaction rate term also did not yield any reasonable results. A modified termolecular mechanism, which included the contribution of hydroxide ions, was able to predict the kinetics of a CO2 loaded mixed alkanolamine solution satisfactorily with MDEA not participating with MEA in the kinetics. Individual reaction rate constants were predicted based on the modified termolecular mechanism.
Evaluations of the benefits of using a mixed MEA/MDEA solvent for CO2 capture in terms of the heat requirement for solvent regeneration, lean and rich loadings, CO2 production, and solvent stability were performed by comparing the performance of aqueous 5 kmol/m3 MEA with that of an aqueous 4:1 molar ratio MEA/MDEA blend of 5 kmol/m3 total amine concentration as a function of the operating time. The tests were performed using two pilot CO2 capture plants of the International Test Centre for CO2 Capture (ITC), which provided two different sources and compositions of flue gas. The University of Regina CO2 plant (UR unit) processes flue gas from the combustion of natural gas while the Boundary Dam CO2 plant (BD unit) processes flue gas from a coal-fired electric power station. The results show that a huge heat-duty reduction can be achieved by using a mixed MEA/MDEA solution instead of a single MEA solution in an industrial environment of a CO2 capture plant. However, this benefit is dependent on whether the chemical stability of the solvent can be maintained.
A thermodynamically consistent model was developed for representing vapor-liquid equilibria in the acid gas (H2S, CO2)-alkanolamine-water system. The model accounts for chemical equilibria in a rigorous manner. Activity coefficients are represented, with the Electrolyte-NRTL equation treating both long-range ion-ion interactions and local interactions between all true liquid-phase species. Both water and alkanolamine are treated as solvents. Adjustable parameters of the Electrolyte-NRTL equation, representing short-range binary interactions, were fitted on binary and ternary system VLB data. Calculated H2S and CO2 equilibria are in good agreement with most of the reported experimental data for aqueous solutions of a single acid gas in monoethanolamine (MEA) and diethanolamine (DEA) in the temperature range 25-120 °C. Without fitting additional parameters, representation of experimental equilibria for mixtures of H2S and CO2 in aqueous solutions of MEA or DEA is good.
Aqueous solutions of MDEA, MDEA + DEA and MDEA + MEA containing 4.2 kmol/m3 total amine, were contacted with CO2 at a partial pressure of 2.58 MPa and temperatures ranging from 120 to 180°C, in a stainless steel batch reactor. The reaction products include the known degradation compounds of the amines as well as products formed from secondary interactions in the amine blends. The rate of degradation was first order in the amines and, in magnitude, followed the sequence MDEA < MEA < DEA. Furthermore, the rate constant for MDEA was independent of amine substitution level and blend constituents. From a practical standpoint, MDEA + DEA blends would require frequent DEA make-up to maintain treating efficiency.
Des solutions aqueuses de MDEA, MDEA + DEA et MDEA + MEA contenant 4,2 kmol/m3 d'amines au total ont été mises en contact avec du CO2 à une pression partielle de 2,58 Mpa et des temperatures comprises entre 120 et 180°C, dans un réacteur en acier inoxydable discontinu. Les produits de réaction comprennent les composés connus de dégradation des amines ainsi que des produits issus des interactions secondaires dans les mélanges d'amines. La vitesse de dégradation est du premier ordre dans les amines et, en ordre d'importance, suit la séquence MDEA < MEA < DEA. De plus, la constante de vitesse pour le MDEA est indépendante du degré de substitution des amines et des constituants du mélange. Sur le plan pratique, les mélanges de MDEA + DEA demanderaient un apport fréquent en DEA pour maintenir l'efficacité du traitement.
Methyl-diethanolamine (MDEA) degradation reactions between aqueous solutions of MDEA and CO2 have been carried out in a 600 mL stirred autoclave under the following conditions: initial MDEA solution concentration 20-50 mass%, solution temperature 100-200°C, CO2 partial pressure 1.38-4.24 MPa. It was found that MDEA degrades quite rapidly (although more slowly than diethanolamine under comparable conditions) at elevated temperatures and CO2 partial pressures. Degradation products are identified by gas chromatography and mass spectrometry (GC/MS). An MDEA degradation reaction mechanism and kinetic model predicting concentration changes is proposed and verified.
Des réactions de dégradation de méthyldiéthanolamine (MDEA) entre des solutions aqueuses de MDEA et de CO2 ont été réalisées dans un réservoir autoclave agité de 600 ml dans les conditions suivantes: concentration de solution de MDEA initiale de 20 à 50% massique, température de solution entre 100 et 200°C, pression partielle de CO2 entre 1,38 et 4,24 Mpa. On a trouvé que le MDEA se dégradait assez rapidement (quoique plus lentement que la diéthanolamine dans des conditions comparables) à des températures et à des pressions partielles de CO2 élevées. Les produits de dégradation ont été déterminés par chromatographie gazeuse et spectrométrie de masse. On propose et vérifie un modéle de mécanisme de réaction de dégradation de MDEA et de cinétique prédisant les changements de concentration.
One of the highest priorities in carbon sequestration science is the development of techniques for CO 2 separation and capture, because it is expected to account for the majority of the total cost (∼75%). The most common currently used method of CO 2 separation is reversible chemical absorption using monoethanolamine (MEA) solvent. In the current study, solvent degradation from this technique was studied using degraded MEA samples from the IMC Chemicals Facility in Trona, California. A major pathway to solvent degradation that had not been previously observed in laboratory experiments has been identified. This pathway, which is initiated by oxidation of the solvent, is a much more significant source of solvent degradation than the previously identified carbamate dimerization mechanism.
The kinetics of the reactions of carbon dioxide with monoethanolamine, diethanolamine and triethanolamine in aqueous solutions were studied at various
Aqueous amine solutions loaded with CO2 were degraded in stainless steel sealed containers in forced convection ovens. Amine loss and degradation products were measured as a function of time by cation chromatography (IC), HPLC, and IC/mass spectrometry. A full kinetic model was developed for 15-40 wt% MEA (monoethanolamine) with 0.2 – 0.5 mol CO2/mol MEA at 100°C to 150°C. Experiments using amines blended with MEA demonstrate that oxazolidone formation is the rate-limiting step in the carbamate polymerization pathway. With 30 wt% MEA at 0.4 mol CO2/mol MEA and 120°C for 16 weeks there is a 29% loss of MEA with 13% as hydroxyethylimidazolidone (HEIA), 9% as hydroxyethylethylenediamine (HEEDA), 4% as the cyclic urea of the MEA trimer, 1-[2-[(2-hydroxyethyl)amino]ethyl]-2-imidazolidone, 3% as the MEA trimer, 1-(2-hydroxyethyl)diethylenetriamine, and less than 1% as larger polymeric products. In the isothermal experiments, thermal degradation was slightly more than first order with amine concentration and first order with CO2 concentration with an activation energy of 33 kcal/mol. In a modeled isobaric system, the amount of thermal degradation increased with stripper pressure, but decreased with an increase in amine concentration and CO2 concentration due to a reduction in reboiler temperature from the changing partial pressure of CO2. Three-fourths of thermal degradation in the stripper occurred in the reboiler due to the elevated temperature and long residence time which offset the decrease in CO2 concentration compared to the packing. The amount of degradation for other amines tested starting with the least degraded include; cyclic amines with no side chains < long chain alkanolamines < alkanolamines with steric hindrance < tertiary amines < MEA < straight chain di- and triamines. Piperazine and morpholine had no measurable thermal degradation under the conditions of this experiment and were the most resistant to thermal degradation. Diethyelenetriamine and HEEDA had the largest amount of degradation with over 90% loss at 135°C for 8 weeks. Chemical Engineering
Amine scrubbing has been used to separate carbon dioxide (CO2) from natural gas and hydrogen since 1930. It is a robust technology and is ready to be tested and used on a larger scale
for CO2 capture from coal-fired power plants. The minimum work requirement to separate CO2 from coal-fired flue gas and compress CO2 to 150 bar is 0.11 megawatt-hours per metric ton of CO2. Process and solvent improvements should reduce the energy consumption to 0.2 megawatt-hour per ton of CO2. Other advanced technologies will not provide energy-efficient or timely solutions to CO2 emission from conventional coal-fired power plants.
To improve the efficiency of the carbon dioxide cycling process and to reduce the regeneration energy consumption, a sterically hindered amine of 2-amino-2-methyl-1-propranol (AMP) was investigated to determine its regeneration behavior as a CO2 absorbent. The CO2 absorption and amine regeneration characteristics were experimentally examined under various operating conditions. The regeneration efficiency increased from 86.2% to 98.3% during the temperature range of 358 to 403 K. The most suitable regeneration temperature for AMP was 383 K, in this experiment condition, and the regeneration efficiency of absorption/regenerationruns descended from 98.3% to 94.0%. A number of heat-stable salts (HSS) could cause a reduction in CO2 absorption capacity and regeneration efficiency. The results indicated that aqueous AMP was easier to regenerate with less loss of absorption capacity than other amines, such as, monoethanolamine (MEA), diethanolamine (DEA), diethylenetriamine (DETA), and N-methyldiethanolamine (MDEA).