Aqueous Alkanolamine Solutions Research Articles

Highly efficient CO2 capture using 2-methylimidazole aqueous solution on laboratory and pilot-scale

To date, the primary industrial carbon capture approach is still absorption using aqueous solutions of alkanolamines. Here, to pursue a substitute for the amine-based approach to improve the CO2 capture efficiency and decrease the energy cost further, we report a new carbon capture approach using a 2-methylimidazole (mIm) aqueous solution. The properties and sorption behaviors of this approach have been experimentally investigated. The results show that the mIm solution has higher CO2 absorption capacity under relatively higher equilibrium pressure (>130 kPa) and lower desorption heat than the methyldiethanolamine solution. 91.6% sorption capacity of mIm solution can be recovered at 353.15 K and 80 kPa. The selectivity for CO2/N2 and CO2/CH4 can reach an exceptional 7609 and 4324, respectively. Furthermore, the pilot-scale tests were also performed, and the results demonstrate that more than 98% of CO2 in the feed gas could be removed and cyclic absorption capacity can reach 1 mol·L–1. This work indicates that mIm is an excellent alternative to alkanolamines for carbon capture in the industry.

Catalytic desorption of CO2‐loaded solutions of diethylethanolamine using bentonite catalyst

AbstractThe absorption of CO2 gas into aqueous alkanolamine solutions is the most advanced CO2 separation technology and a key challenge in this technique is the energy‐intensive process of solvent regeneration. The tertiary amine N,N′‐diethylethanolamine (or DEEA) is a candidate CO2‐capturing solvent with potential. To improve the energy efficiency of regeneration of DEEA, several catalysts were used for desorbing CO2 from loaded solutions of DEEA (2.5 M) at T = 363 K. Desorption trials were conducted in batch mode. The initial CO2 loading varied in the 0.3–0.35 mol CO2/mol DEEA range. The performance was analyzed by calculating the rate of CO2 desorption, cyclic capacity, and reduction in sensible energy. The amount of thermal energy needed for amine regeneration was significantly lowered by using nine transition metal oxide catalysts and the hierarchy was as follows: Al2O3 < MoO3 < V2O5 < TiO2 < MnO2 < ZnO < Cr2O3 < SiO2 < ZrO2. Among the metal oxides, Al2O3 increased desorption efficiency compared to blank runs by 89%. A clay‐based powder bentonite was also used as catalyst and its efficacy was compared with the metal oxides. This cheap and easily available bentonite catalyst was tuned through simple ion‐exchange with four acids (HCl, H3PO4, HNO3, and H2SO4). Upon treatment with H2SO4, bentonite remarkably increased desorption efficiency by 100%. Furthermore, bentonite catalyst treated with sulphuric acid (denoted here as Bt/H2SO4) was characterized by Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectrometery (FTIR), X‐ray diffraction (XRD), and ammonia temperature‐programmed desorption (NH3‐TPD). In this way, a comprehensive study on catalytic desorption of DEEA was performed.

The comparative modeling of solubility of carbon dioxide in amine solutions using SAFT-HR and PC-SAFT equation of state

In this paper, we applied PC-SAFT and SAFT-HR equations of state so as to reproduce the solubility of carbon dioxide in aqueous diethanolamine solution. By using these equations, we have been able to model the solubility of carbon dioxide in aqueous amine solution in more than 350 experimental data points with wide range of amine molar concentration (0.01–0.12), temperature (300 K –478 K), carbon dioxide partial pressure (0.0001 KPa –5473 KPa), and carbon dioxide loading (0.04 –1.1). Ternary systems including water, carbon dioxide and diethanolamine have also been modeled by PC-SAFT and SAFT-HR equations of state based on bubble pressure algorithm. Binary interaction parameters are set to zero to show the genuine capability of equations of state in reproducing such experimental data. Provided modeling results have been obtained from MATLAB R2019b software for PC-SAFT equation of state are less deviated with experimental data. Overall average relative deviation of SAFT-HR and PC-SAFT are 45.452% and 4.374% respectively which show that PC-SAFT is a robust equation of state in predicting the solubility data of carbon dioxide in aqueous alkanolamine solutions.

Machine Learning-Based Design of Ionic Liquids at the Atomic Scale for Highly Efficient CO2 Capture

Ionic liquids (ILs) are considered excellent substitutes for aqueous alkanolamine solutions in CO2 capture systems. However, the smart design of ILs, facing the small sparse data set and complex ionic structures, poses a huge challenge. To address this issue, a novel machine learning method based on a syntax-directed variational autoencoder (SDVAE), deep factorization machine (DeepFM), and gradient-based particle swarm optimization (GBPSO) was proposed in this work. The SDVAE converts the molecular structure and chemical space of the ILs, and then DeepFM predicts the solubility of each coordinate in the chemical space representing an IL. Finally, GBPSO identifies the coordinates that represent ILs with ideal properties. Our main optimization objective is a high solubility difference for CO2 between its absorption and desorption conditions in commercial plant capture systems, which represents the CO2 capture ability. The best IL generated has a predicted solubility difference that is 35.3% higher than that of the best one in the data set. A synthetic novel IL [EMIM][TOS] from the generated results was experimentally evaluated; it has a sufficiently high solubility difference to be a capture solvent with low energy consumption. Our model has proved to be a high-efficiency molecular design model that can be used for sparse small data sets.

Design of the process of CO2 removal in NGCC by potassium taurate solvent

One of the most mature technologies for removal of carbon dioxide from gaseous streams is chemical absorption and aqueous solutions of alkanolamines are employed, with Monoethanolamine (MEA) considered the benchmark solvent. However, its volatility and toxicity and the need for a lot of energy for regeneration made research focus on possible solvents that can perform the desired treatment of gaseous streams while reducing production and operating costs and the environmental impact, to be considered as substitutes. The process based on amino acid aqueous solutions, one type of these new solvents, has the advantage of an improved sustainability and, as the one employing aqueous solutions of potassium taurate, can also benefit of the enhancement due to the reaction of precipitation. In this work a rigorous rate-based model, built in the commercial process simulator ASPEN Plus®, properly customized for the representation of the system, is used to carry out a detailed process design for the CO2 removal section of a NGCC plant by an aqueous solutions of potassium taurate, for which no previous papers on the topics have been found in the literature. The scheme is optimized and the performances of the process are evaluated for different targets of CO2 removal.

Vapor Liquid Equilibrium of Aqueous Diethanolamine Solution for Carbon Dioxide Capture Processes

Objectives : Acid gases such as carbon dioxide (CO<sub>2</sub>) and hydrogen sulfide (H<sub>2</sub>S) that cause global warming are mainly generated in chemical processes. As a technology for reducing acid gas, the post-combustion capture process is representative. Aqueous alkanolamine solution, which is mainly used in the carbon dioxide absorption process, is used as the most representative chemical absorbent. Thermodynamic data of vapor-liquid equilibrium are important for the economics of process design and operation. In this study, vapor-liquid equilibrium data of water + DEA are measured so that DEA, a secondary amine, can be used in the carbon dioxide absorption process, so that it can be used for designing a new carbon dioxide absorption process.Methods : Vapor-liquid equilibrium data of a mixture of water + DEA (diethanolamine) were measured under isothermal conditions of 393.15 K using HSGC (Headspace Gas Chromatography).Results and Discussion : The measured vapor-liquid equilibrium data were correlated using NRTL, an activity coefficient model. In addition, as additional thermodynamic data of the absorbent mixture, the density of the DEA aqueous mixture was measured at a temperature of 303.15 K to 333.15 K using a density meter (Anton Paar DMA4500). The measured density data of the mixture was converted into excess volume, and the excess volume data was correlated using the Redilchi-Kister-Muggianu equation. Using the measured water+DEA vapor-liquid equilibrium data, it is expected to reducing the design cost and operating cost of the carbon dioxide absorption processes.

Perstraction of Heat-Stable Salts from Aqueous Alkanolamine Solutions

Amine absorption processes designed to remove acid gases from gas streams generally face a major challenge of solvent degradation. This degradation leads to the formation of heat-stable salts (HSS), corrosive agents that irreversibly bind free alkanolamine. The present study proposes, for the first time, a method for HSS perstraction using a liquid–liquid membrane contactor that allows HSS to transfer through porous membranes from the solvent into a hydrophobic extractant represented by a methyltrioctylammonium solution in 1-octanol. The perstraction provides selective extraction of HSS anions without direct mixing of liquid phases or the formation of stable emulsions of the solvent and the extractant. For this purpose, a number of industrial and laboratory porous membrane samples fabricated from polyvinylidene fluoride, polypropylene, and polysulfone were investigated. Their chemical and morphological stability, surface properties, and transport properties were tested under prolonged (>600 h) contact with a model solvent (an aqueous monoethanolamine solution) and with the components of the selective extractant. The feasibility of HSS perstraction was demonstrated using the formic acid (as an HSS model) extraction from the model solvent. The most promising results were obtained for a system with a polyvinylidene fluoride membrane: up to 50% of formic acid was extracted over 18 h.

Linear relationships for modeling CO2 absorption in aqueous alkanolamine solutions in a thermodynamically consistent way

AbstractA thermodynamically consistent model for the carbon dioxide (CO2) absorption in aqueous alkanolamine system is of great importance in the research and development of a CO2 capture process. To facilitate the development of thermodynamic models, linear Gibbs free energy, enthalpy, and heat capacity relationships using well‐known amines as reference are used to correlate the standard reference state properties of ionic species with those of molecular species in the electrolyte system, which has been approved to provide a reliable and consistent way to estimate required parameters when there is minimal or no appropriate experimental data available. The proposed relationships have been applied to the development of an electrolyte nonrandom two liquid (NRTL) activity coefficient model for CO2 absorption in aqueous 1‐amino‐2‐propanol (A2P) solution, as an example to demonstration the methodology. With limited vapor–liquid equilibrium data and other thermodynamic properties, the parameters in the electrolyte NRTL model are identified with good accuracy.

CO2 absorption mechanism in aqueous ternary solutions of alkanolamines: Experimental and thermodynamic modeling approaches

The absorption mechanism of CO2 in an aqueous solution containing three alkanolamines was analyzed experimentally and theoretically. The vapor–liquid equilibrium of a CO2–monoethanolamine (MEA)–diisopropanolamine (DIPA)–2-amino-2-methyl-propanol (AMP)–H2O system was evaluated experimentally over a wide temperature range (323.15–393.15 K) at several MEA:DIPA:AMP:H2O blending ratios (15:10:5:70, 10:10:10:70, 7.5:7.5:15:70, and 5:15:10:70 wt%). The successive substitution method was used to calculate the concentrations of five molecules (CO2, MEA, DIPA, AMP, and H2O) and nine electrolytes (four cations and five anions) in the liquid phase by solving eight equilibrium equations, four mass balance equations, and one charge balance equation. The Deshmukh–Mather model, which is based on an activity coefficient approach, and the fugacity coefficient model were used to evaluate the nonideality of the liquid and vapor phases, respectively. Thereafter, the effect of the MEA:DIPA:AMP blending ratio was evaluated using the triangular diagrams of the carbamate, bicarbonate and carbonate molar fractions in liquid phase, CO2 loading ratio, CO2 cyclic capacity, and heat of CO2 absorption.

Combined theoretical and experimental studies on CO2 capture by amine-activated glycerol

Although CO2 capture by alkanolamine aqueous solutions is a well-established technology, it demands high energy penalties and water consumption. Therefore, the development of new methods for CO2 removal is still a challenge. Herein, we employed the Density Functional Theory (DFT) to explore the potential of different mixtures composed of glycerol and nitrogen-containing bases to capture CO2. By combining glycerol, CO2 and the bases, it was possible to show that aliphatic amines are able to form intermolecular hydrogen bonds with the primary hydroxyl groups of glycerol, increasing their nucleophilicity and assisting the reaction with CO2 to form glycerol carbonate as the most stable product. To confirm that glycerol carbonate would be experimentally obtained from the given mixture, we selected triethylamine (TEA) to assist glycerol (Gly) in its reaction with CO2. The resulting product was characterized by Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR), 1D and 2D Nuclear Magnetic Resonance spectroscopy (1H and 13C NMR) and Thermogravimetric Analysis (TGA). The ATR-FTIR results showed that TEA is protonated after bubbling CO2 in the glycerol/TEA mixture, suggesting that the reaction with CO2 occurs after deprotonation of glycerol, forming organic carbonates, as also indicated in the NMR spectra. The combined theoretical and experimental results indicate that TEA is able to activate glycerol in its reaction with CO2 to form organic carbonates, being an alternative procedure for CO2 capture.

Accurately Predicting CO2 Reactive Absorption Properties in Aqueous Alkanolamine Solutions by Molecular Simulation Requiring No Solvent Experimental Data

We present a general atomistic simulation framework for efficient reactive equilibrium calculations in dilute solutions, and its application to CO2 reactive absorption in aqueous alkanolamine solutions. No experimental data of any kind are required for the solvents, and no empirical adjustments are required for its implementation. This hybrid methodology calculates reaction equilibrium constants by combining high-level quantum chemical calculations of ideal-gas standard reaction Gibbs energies (ΔG0) with conventional solvation free energy calculations obtained from classical force field methodology. For these quantities we use explicit solvent molecular dynamics simulations with the General AMBER Force Field (GAFF). The resulting equilibrium constants are then coupled with a macroscopic Henry Law based ideal solution model to calculate the solution speciation and the CO2 partial pressure, PCO2. We show results for seven primary amines: monoethanolamine (MEA), 2-amino-2-methylpropanol (AMP), 1-amino-2-propanol (1-AP), 2-amino-2-methyl-1,3-propanediol (AMPD), 2-aminopropane-1,3-diol (SAPD), 2-(2-aminoethoxy)ethanol or diglycolamine (2-AEE or DGA, respectively), and 2-amino-1-propanol (2-AP). Experimental speciation and PCO2 data for some of these are available, with which we validate our methodology. We predict new results for others in cases when such data are unavailable, and provide explanations for the experimental inability to detect carbamate solution species in relevant cases. Our results for the pK value of the carbamate reversion reaction are within the chemical accuracy limit of 218.546/T units (corresponding to 1 kcal·mol–1 in the corresponding free energy change) in comparison with experimental results when such data exist, which at 298.15 K corresponds to 0.73 pK units. The precision of our pK predictions is comparable to that which can be obtained from conventional experimental methodologies for these quantities. Our results suggest that the presented molecular simulation methodology may provide a robust and cost-efficient tool for solvent screening in the design of post-combustion CO2 capture processes.

Investigation of Sulfolane Degradation in Aqueous Alkanolamine Solutions Under the Stripping Operational Condition

The measure of stability of sulfolane (SFL) in aqueous alkanolamine solution was investigated. For this purpose, degradation of SFL was experimentally studied under the stripping operational condition (T = 130 °C). The experiments were divided into two general categories: (1) aqueous solution of SFL with and without presence of oxygen to receive a sense of thermal and oxidative SFL degradation; (2) aqueous solution of MDEA/PZ/SFL loaded by hydrogen sulfide and carbon dioxide (both gas-loadings were set to be 0.25 to roughly make a real condition). The results of the experiments showed that SFL resists thermal degradation, but in the presence of oxygen and temperatures of 130 °C which is in accordance with the desorption operational conditions, it would be prone to degradation to anions such as sulfite, sulfate and thiosulfate.

Catalysis of CO2 Absorption in an Aqueous Alkanolamine Solution by Boron Compounds: A Combined Computational and Experimental Study

Theoretical and experimental investigations have been performed to obtain carbonic anhydrase (CA) mimic catalysts that are effective for CO2 absorbents containing highly concentrated amines. One of...

Comparison of aqueous and non-aqueous alkanolamines solutions for carbon dioxide desorption in a microreactor

An experimental study of CO2 desorption from aqueous and non-aqueous saturated alkanolamine solutions carried out in a tubular microreactor, consisting of a stainless steel microtube with an internal diameter of 800 μm and a total length of 35 cm. We tested a total of six solvent mixtures of water or methanol with monoethanolamine, diethanolamine, or activated methyl diethanolamine in a broad range of operational conditions, including temperature (50–100 °C), rich solvent flow rate (0.5–4.5 ml/min), and amine concentration in the solvent (10 and 50% w/w). CO2 desorption was thoroughly characterized with respect to the mass transfer rate and energy consumption, and both were expected to improve with the use of a microreactor due to short diffusion distances and a larger surface-to-area ratio. An increase in the operating temperature or concentration of the amine resulted in a higher percentage of desorption and enhanced mass transfer rates, as shown by the local mass transfer coefficient based on the liquid phase values herein disclosed. Increasing the rich solvent flow rate also increased the local mass transfer coefficient values (80%–95%); however, the overall percentage of CO2 desorption reduced (25%–35%) due to shorter residence times in the microreactor. Similarly, the energetic desorption efficiency improved for all the solutions with increasing temperature (65–75% reduction) and concentration of amine in the solvent (20–35% reduction), yet again decreasing with an increasing flow rate of rich solvent (5–15%). Compared to the literature values for the packed columns and microreactors, our data showed the overall energy consumption up to an 88% reduction in specific CO2 desorption, demonstrating great potential for the intensification of solvent-mediated, energetically demanding CO2 desorption. In addition, the results showed that the energy consumption for CO2 desorption was reduced by 73% by choosing a non-aqueous in preference to an aqueous alkanolamine solvent.

Study on CO2 capture by AAILs-MDEA aqueous solution in packed tower

This study mainly uses N-methyldiethanolamine (MDEA) as the main body of absorption, and uses three kinds of AAILs(AAILs), 1-butyl-3-methylimidazolium lysinate ([Bmim][Lys]), tetramethylammonium glycinate ([N1111][Gly]) and 1-butyl-3-methylimidazolium glycinate ([Bmim][Gly]) as accelerator, respectively. That forms a new blended aqueous solution for CO2 removal. The new AAILs-MDEA aqueous solution absorbent has stronger ability to absorb CO2, faster absorption rate and lower equipment corrosion. When the gas flow rate is 500ml/min and the liquid flow rate is 150ml/min, the best removal efficiency is achieved. At 313.2K, the removal efficiency of MDEA-[N1111] [Gly] absorbent can reach 100%; the effect of the three new alkanolamine aqueous solutions on CO2 absorption is: MDEA-[N1111][Gly]>MDEA-[Bmim] [Gly]>MDEA-[Bmim][Lys].

Catalytic activity of facilely synthesized mesoporous HZSM-5 catalysts for optimizing the CO2 desorption rate from CO2-rich amine solutions

Post-combustion CO2 capture using aqueous alkanolamine solutions has a great potential to reduce anthropogenic CO2 emissions but the large-scale deployment of this technique is hindered due to a highly energy-intensive solvent regeneration mainly because of poor CO2 desorption kinetics. To overcome this limitation, we synthesized a series of mesoporous HZSM-5 catalysts through facile alkaline desilication and surfactant-induced re-assembly of dissolved species originating from the parent HZSM-5 crystals, and evaluated their performance to optimize the CO2 desorption rate from benchmark 30 wt% monoethanolamine (MEA) solution under mild temperature condition (40–82 °C). X-ray diffraction (XRD) patterns showed that the synthesized catalysts retained their crystallinity. Desilication by treatment in the alkaline medium led to a remarkable development of mesoporosity, with an increase in the Brunauer–Emmett–Teller (BET) surface area as well. The experimental results suggested that the synthesized catalysts significantly enhanced the CO2 desorption rate at low temperatures (up to 350–580% at ≤82 °C), improved the total amount of desorbed CO2 up to 60%, and minimized the heat duty by 24–37%. Detailed characterization revealed that the synergistic effect of higher mesoporosity and increased number of Lewis acid sites (LAS) and Brønsted acid sites (BAS) was crucial to improve the CO2 desorption rate. Based on the characterization and experimental results, a plausible reaction mechanism for catalyst aided CO2 desorption was also presented. This investigation highlights the role of catalysts in optimizing the CO2 capture process and presents new understanding for the design of high-performance catalysts for this purpose.

Screening of ionic liquids for gas separation using COSMO-RS and comparison between performances of ionic liquids and aqueous alkanolamine solutions

Ionic liquids (IL) are considered viable alternative solvents for CO2 capture. Because of this and the unlimited number of possible combinations between cations and anions, it is important to develop a systematic approach based on a reliable model for defining the best combinations to promote natural gas sweetening by enabling the most efficient CO2 capture accompanied by minimal hydrocarbons losses. Hence, in this study, the conductor-like screening model for real solvents (COSMO-RS) model was employed to predict the solubility of CO2, CH4, C2H6, and C3H8 in eight selected ILs with varying combinations of cations and anions. All predictions have been compared against experimental data from the literature which was obtained at the same conditions. The model and experimental data show similar trends and moderate agreement for each of the selected ILs. The observed deviations were 8–62%, 8–40%, 1–37%, and 29–35%, for CO2, CH4, C2H6, and C3H8, respectively. Both the experimental data and predictions confirm that [hmim][TCB] IL is more suitable for natural gas sweetening because of its higher CO2 solubility and selectivity than that of other ILs. Finally, the experimentally determined solubilities of these gases in ILs and conventional amine solvents are compared with highlight the greater efficiency of ILs.

Thermodynamic modeling for the carbonate system K-HCO3-CO3 in alkanolamine solutions: An extended application for CO2 scrubbing

The K2CO3 slurry-based, CO2 absorption technology in amines involves in-depth analysis of chemical equilibrium for all three phases. However, the reported studies regarding solubility and thermodynamics modeling of the solid-liquid system: K-CO3-HCO3 in alkanolamine solutions are limited. We first performed vapor-liquid equilibrium calculation to study the absorption profile of CO2 in monoethanolamine (MEA) /diethanolamine (DEA) solutions using OLI Studio Stream Analyzer, results were in good agreement with literature data. We further applied the dissolution method to measure the solubility of K2CO3 and KHCO3 in the aqueous alkanolamine solution from 283 to 353 K, P = 0.1 MPa. A chemical model was developed for the purpose of conducting thermodynamic analysis by the regression of solubility data via the mixed-solvent-electrolyte, activity coefficient model. The relative deviations are within 5% for each solid-liquid system after reparameterization. Tuning the newly-regressed parameters allowed for a better prediction of solubility, they also come vital in evaluating the absorption performance of CO2 in quaternary systems, which are made available to aid in process modeling.

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

In order to be able to understand and compensate for the mass transfer effects on the reaction kinetics that typically occur in these studies, the influences of diffusion and gas phase resistance o...

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

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