Aqueous Amine Solvents Research Articles

Molecular simulation and experimental understanding of piperazine-promoted 2-cyclopentylaminoethanol for energy-efficient carbon capture

With the serious climate change and carbon emissions issues facing the world, it is becoming increasingly important to find effective methods to reduce the post-combustion CO2 concentrations. Piperazine −enhanced aqueous amine solvents are still being developed due to the technology is more applicable to large −scale industry. However, the sustainability of the CO2 capture process is still hindered by high energy consumption and amine losses. To tackle this issue, a novel secondary amine, 2-cyclopentylaminoethanol, was synthesized from a primary amine, monoethanolamine. It has a more stable structure than monoethanolamine and was further activated by piperazine. Its effectiveness was compared with piperazine-enhanced N-methyldiethanolamine, N-methyldiethanolamine/triethylenediamine, and 2-amino-2-methyl-1-propanol. The experimental results showed that 2-cyclopentylaminoethanol/piperazine presents the fastest CO2 mass transfer rate, the largest CO2 cyclic capacity and a lower latent heat. The regeneration energy consumption of the absorbent is approximately 2.44 GJ/ton CO2, which is approximately 37.45% lower than that of 30 wt% monoethanolamine solvent. The results are in accordance with the findings of a laboratory-scale pilot plant study, which demonstrated an average reduction of 35.3% in energy consumption. Molecular simulations have revealed that 2-cyclopentylaminoethanol exhibits the lowest energy barrier for reacting with CO2, rendering it more conducive to CO2 reaction. The intermolecular interactions indicate that the hydrogen bonding in the solution after monoethanolamine reacts with CO₂ becomes more pronounced, coupled with a higher energy barrier. Consequently, a greater amount of energy is required during desorption. It can be inferred that 2-cyclopentylaminoethanol/piperazine is a promising energy-efficient and stable absorbent for post-combustion CO2 capture.

Rational design of aqueous tertiary amine solvent for integrated CO2 capture and hydrogenation

Several tertiary amine solutions with different structures were tested in the integrated CO2 capture and hydrogenation process in the presence of heterogeneous Pd/NAC catalysts. The tertiary amines of 3-dimethylamino-1,2-propanediol (3DMA-1,2-PD) and 3-diethylamino-1,2-propanedio (3DEA-1,2-PD) with high CO2 absorption capacity and high formate yield were selected as suitable candidates as CO2 capture and hydrogenation solvents. Under mild reaction conditions, a high formate yield of 68% was achieved when using 1 M 3DMA-1,2-PD solution with CO2 loading of 0.5 mol amine/mol CO2. In addition, the physico-chemical properties of the Pd/NAC catalysts were examined and the reaction mechanism of CO2 absorption and hydrogenation in the presence of Pd/NAC was proposed.

Comparative analysis of artificial neural network (ANN) models: CO2 loading in MDEA and blended MDEA/PZ solvents

CO2 loading plays a vital role in gauging a solvent's capability to absorb CO2 from combustion gases and natural gas flow. Yet, the customary approaches for measuring CO2 loading hinge on laborious and costly laboratory experiments. Therefore, researchers employed artificial neural network (ANN) approaches to estimate CO2 loading using various datasets, although case-specific methods and approaches restricted their attempts. This study employed two datasets with 303 (CO2 absorption via MDEA) and 361 (CO2 absorption via MDEA/PZ) acceptable experimental data to create ANN models to estimate CO2 loading in aqueous amine solvents. The CO2 loading is evaluated using a wide range of input parameters, including temperature, CO2 partial pressure, Methyldiethanolamine (MDEA) solvent, and Piperazine (PZ) solvent for cases A and B, respectively. Twelve distinct training algorithms, four distinct activation functions, and three hidden layers with neuron variations created the models. ANN models trained with a blend of PZ and MDEA solvents generated more accurate predictions compared to models trained with solely MDEA solvent. The sigmoidal activation functions (Tansig and Logsig) generated more precise predictions than the linear activation functions (Poslin and Purelin). In addition, “Levenberg-Marquardt (lm)” with the highest coefficient of determination (R2) was selected as the best training algorithm among the twelve training functions. The best average coefficients of determination were determined to be 0.964 for the tansig activation function with [25 18 10] number of neurons in case A and 0.967 for the logsig activation function with [30 20 12] number of neurons in case B. The statistical analysis (R2, MSE, RMSE, AAD, AARD, and run time) confirmed that the network provided accurate estimates of CO2 loading for both datasets. The prediction potential of the network is then further indicated by model generalization inside the training data set.

Removal of heat stable salts from degraded amine solvent by “BMED+ED” two-stage electrodialysis unit

Due to the degradation reaction and the presence of acidic impurities (HCl, SO2, etc.) in the flue gas, heat stable salts (HSS) are widely present in the aqueous amine solvent for post-combustion CO2 capture. Accumulation of HSS in the solvent can lead to decreased absorption capacity and even corrosion of equipment in post-combustion capture (PCC) pilot plants. This study presents a novel “BMED+ED” two-stage electrodialysis unit for the efficient removal of HSS, including glycolate, formate, Cl−, and SO42−, from degraded amine solvent with an initial loading of approximately 0.38 mol/mol taken from the solvent loop of a PCC pilot plant after over 1000 hours of operation at real conditions. Experimental results showed that 94.93% of HSSs were removed with an initial HSS concentration of approximately 1920 ppm. The amine loss rate in the two-stage electrodialysis unit was much lower than that in a conventional ED unit, as protonated amine is further converted to organic amines by bipolar membrane electrodialysis. The energy consumption of the two-stage electrodialysis unit was 0.1643 kWh/L amine solvent, and the total cost for amine reclaiming was 1.8145 $/kg amine. This method effectively addressed the challenges of high amine loss rate in the traditional ED treatment process and hazardous wastewater disposal.

Energy-efficient carbon dioxide capture using piperazine (PZ) activated EMEA+DEEA water lean solvent: Performance and mechanism

Water vapor contained in industrial waste gas will be accumulated in non-aqueous amine solvents when used for CO2 capture and subsequently affect capture efficiency. While Piperazine (PZ) could be considered as an activator of the solution. Hence the effect of different contents of water and PZ added into the non-aqueous amine solvents on the CO2 capture performance has been investigated. 13C NMR has been used to identify the compounds present in aqueous CO2-rich amine solvents to characterize the mechanism of reactions. The energy consumption using 2-(ethylamino)ethanol (EMEA) water-lean amine solvent and aqueous monoethanolamine (MEA) solution was tested and compared on lab-scale, and further a comprehensive evaluation in a bench-scale pilot plant has been performed; It was found that the regeneration efficiency of the solution was reduced by approximately 10% when the water content was 10 wt%. The addition of PZ can recover the regeneration efficiency of the solvent to 94.2%. And its energy consumption was reduced by about 45% compared to the aqueous MEA solution in a 72-hour continuous absorption-desorption experiment. The results demonstrated that the aqueous PZ solution could improve the regeneration efficiency by involving in the proton transfer process. This work has proven that the blend of water-lean amine solvent and PZ is a novel, energy-efficient absorbent for CO2 capture.

Comparative Study for the Absorption of Carbon Dioxide in Aqueous Amine Solvents for Enhanced Loading

Aims: The current study aimed to investigate the CO2 absorption capacity of the aqueous alkanolamine, including primary, secondary, tertiary, and sterically hindered amines and polyamines, i.e., monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA) and 2- amino-2-methyl-1-propanol (AMP), tetraethylenepentamine (TEPA), triethylenetetramine (TETA), 3- (Methylamino)propylamine (MAPA), and diethylenetriamine (DETA) at 40, 60, and 80°C at 1.1 bar. Methods: An increase in reaction temperature caused a decrement in CO2 loading across the board for all solvents. The trend of CO2 loading was TEA < MEA < DEA < AMP < MAPA < DETA < TETA < TEPA at 40 ºC, TEA < DEA < MEA < AMP < MAPA < DETA < TETA < TEPA, at 60ºC and TEA < DEA < AMP < MEA < MAPA < DETA < TETA < TEPA at 80ºC. Results: The results indicated that TEPA has great potential to be utilized as an energy-efficient and non-corrosive solvent for CO2 capture since it has outperformed all other aqueous amine solvents in this present study. Furthermore, the CO2 loading of sterically hindered amine (AMP) at the same temperature was found to be higher than primary, secondary, and tertiary amines. Heat of absorption (Δ Η abs) was also determined to gauge the energy requirement to regenerate absorbents for cyclic loading from an economic viewpoint. Conclusion: DETA has the highest Δ Η abs = 84.48 kJ/mol. On the contrary, the long-chain tertiary amine TEA resulted in the least Δ Η abs = 40.21 kJ/mol, among all other solvents. Whereas the sterically hindered amine (AMP) was observed to possess mid-range Δ Η abs, i.e., 58.76 kJ/mol. Among all selected solvents, polyamines showed higher Δ Η abs than other conventional amines pertaining to the precedence of TEA<AMP<DEA< MEA<TETA<TEPA<MAPA<DETA.

Chemical Stability and Characterization of Degradation Products of Blends of 1-(2-Hydroxyethyl)pyrrolidine and 3-Amino-1-propanol.

Aqueous amine solvents are used to capture CO2 from various flue gas sources. In this work, the chemical stability of a blend of 3-amino-1-propanol (3A1P) and 1-(2-hydroxyethyl)pyrrolidine [1-(2HE)PRLD] was studied. The chemical stability tests were conducted both in batch and cycled systems using various oxygen and NOx concentrations, additives (iron), and temperatures. In the thermal degradation experiments with CO2 present, the blend was more stable than the primary amines [(3A1P or monoethanolamine (MEA)] but less stable than the tertiary amine 1-(2HE)PRLD alone. Similar stability was observed between MEA, 3A1P, and the blend in the batch experiments at medium oxygen concentration (21% O2) and no iron present. 1-(2HE)PRLD was more stable. However, the presence of high oxygen concentration (96% O2) and iron reduced the stability of 1-(2HE)PRLD significantly. Furthermore, in the case of the blend, the chemical stability increased with increasing promoter concentration in batch experiments. During the cyclic experiment, the amine loss for the blend was similar to what was previously observed for MEA (30 wt %) under the same conditions. A thorough mapping of degradation compounds in the solvent and condensate samples resulted in the identification and quantification of 30 degradation compounds. The major components in batch and cycled experiments varied somewhat, as expected. In the cyclic experiments, the major components were ammonia, 3-(methylamino)-1-propanol (methyl-AP), N,N'-bis(3-hydroxypropyl)-urea (AP-urea), pyrrolidine, formic acid (formate), and N-(3-hydroxypropyl)-glycine (HPGly). Finally, in this paper, formation pathways for the eight degradation compounds (1,3-oxazinan-2-one, AP-urea, 3-[(3-aminopropyl)amino]-1-propanol, tetrahydro-1-(3-hydroxypropyl)-2(1H)-pyrimidinone, methyl-AP, N-(3-hydroxypropyl)-formamide, N-(3-hydroxypropyl)-β-alanine, and HPGly) are suggested.

Probing strong steric hindrance effects in aqueous alkanolamines for CO2 capture from first principles

Carbon dioxide (CO2) absorption into aqueous amine solvents is known to be governed by two competing reactions leading to carbamate or bicarbonate formation. Sterically hindered alkanolamines with different degrees of methylation are experimentally known to cause different favorability in forming carbamate or bicarbonate. However, the fundamental mechanisms responsible for the preferential formation of carbamate or bicarbonate still remain unclear. Herein, we present CO2 absorption behavior with several different sterically hindered amines, especially the effects of methylation and temperature. Our ab initio metadynamics simulations clearly demonstrate that free-energy barriers for the carbamate and bicarbonate formation reactions strongly depend on the degree of steric hindrance of hydrophobic methyl groups. This in turn directly impacts on the kinetic favorability of the two competing reaction pathways. Our analysis shows that various degrees of steric effects cause considerably different temperature-dependent degrees of solvation of the nitrogen atom of hindered amines, which may directly affect CO2 accessibility to form carbamate. Moreover, the enhanced solvation as a result of increased steric effects particularly at low absorption temperatures lead to kinetically facile protonation of the nitrogen atom of amines, initiating and promoting bicarbonate formation. Our work sheds light on the effects of various degrees of steric hindrance, with different temperature-dependent solvation degrees governing reaction mechanisms and rates during CO2 capture.

Simulation of acid gas removal unit using DIPA+TEA amine solvent

Due to the inexpensive cost of amine solvent, more than 95 % of natural gas (NG) processing plants use an acid gas removal unit that utilizes an aqueous amine solvent to remove sour gas components such as carbon dioxide (CO2) and hydrogen sulfide (H2S). Different technologies are available to capture CO2 from NG. However, chemical absorption is the most reliable and used technology all over the world. However, it is challenging to determine the amine blend’s optimal composition for the effective removal of CO2 and H2S and solvent regeneration. This is mainly due to the difference in reservoir gas compositions, affecting gas removal efficiency and solvent regeneration energies. The present investigation addresses the performance of using a novel solvent blend of diisopropanolamine (DIPA) and Triethanolamine (TEA) to determine the absorption capacity of CO2 & H2S using Aspen HYSYS software. A study on the effects of solubility on CO2 absorption was performed at varying pressure (10-80 bar) and temperature (25°C to 50°C). The percentage of CO2 removal increased from 80% to 98% as the temperature increased from 25°C to 50°C. The results revealed that the concentration of CO2 and H2S in sweet gas decrease with the increase in pressure while the concentration of CO2 and H2S increases with the increase in temperature.

Carbon Capture from CO2-Rich Natural Gas via Gas-Liquid Membrane Contactors with Aqueous-Amine Solvents: A Review

Gas–liquid membrane contactor is a promising process intensification technology for offshore natural gas conditioning in which weight and footprint constraints impose severe limitations. Thanks to its potential for substituting conventional packed/trayed columns for acid-gas absorption and acid-gas solvent regeneration, gas-liquid membrane contactors have been investigated experimentally and theoretically in the past two decades, wherein aqueous-amine solvents and their blends are the most employed solvents for carbon dioxide removal from natural gas in gas-liquid membrane contactors. These efforts are extensively and critically reviewed in the present work. Experimentally, there are a remarkable lack of literature data in the context of gas–liquid membrane contactors regarding the following topics: water mass transfer; outlet stream temperatures; head-loss; and light hydrocarbons (e.g., ethane, propane, and heavier) mass transfer. Theoretically, there is a lack of complete models to predict gas-liquid membrane contactor operation, considering multicomponent mass balances, energy balances, and momentum balances, with an adequate thermodynamic framework for correct reactive vapor–liquid equilibrium calculation and thermodynamic and transport property prediction. Among the few works covering modeling of gas-liquid membrane contactors and implementation in professional process simulators, none of them implemented all the above aspects in a completely successful way.

Research on oxygen solubility in aqueous amine solvents with common additives used for CO2 chemical absorption

Oxidative degradation in amine based post-combustion carbon capture (PCCC) leads to solvent losses and decreased solvent performance. Oxygen (O2) in the flue gas is dissolved into the aqueous solvent and can reactively degrade the amine component. Advanced aqueous amine solvents are designed to contain additional surfactant and anti-foam additives as well as two types of corrosion inhibitors. These additives contribute to improve the solvent performance while reducing foaming and corrosion of expensive equipment. This work examines the impact of these additives on oxygen solubility (or dissolved oxygen - DO) in various aqueous amines used in PCCC including ethanolamine (MEA), 1-amino-2-propanol (A2P), 2-amino-1-propanol (2A1P), 2-(methylamino)-ethanol (NMEA), 2-(ethylamine)-ethanol (2EAE), diethanolamine (DEA), methyl-diethanolamine (MDEA), dimethylethanolamine (DMEA), piperazine (PZ), 1,2-ethyldiamine (EDA), and 1,6 hexadiamine (HDA). The impact of carbon loading on oxygen solubility with and without these additives was also examined. The surfactant and anti-foam additives had minimal impact on DO for all the solvents investigated. The two anti-corrosion additives had opposite effects in the measured DO, 2- mercaptobenzothiazole (MBT) decreased the DO concentration, and sodium metavanadate showed an increase. These results indicate that several of these common additives can be expected to minimally affect DO related oxidative degradation in these advance amine solvents.

Oxygen Solubility in Aqueous Amine Solvents with Common Additives Used for CO2 Chemical Absorption

Oxygen Solubility in Aqueous Amine Solvents with Common Additives Used for CO2 Chemical Absorption

Kinetic modeling of Polyamine-based Water-Lean solvents for CO2 capture: Reverse temperature dependence of the overall mass transfer coefficient

Amine-based water-lean solvents (WLS) are promising energy-saving alternatives to the aqueous amine solutions for CO2 capture. Herein, we determined the apparent kinetic parameters of WLS containing 3,3′-iminobis(N,N-dimethylpropylamine) (60 wt%), water (10–20 wt%), and a non-amine chemical (balance). For CO2 absorption rate modeling, the termolecular reaction model and reaction rate model of tertiary amines were incorporated into the equilibrium model proposed by previous work, and the absorption rate of CO2 was estimated using a wetted wall column-based apparatus. The average CO2 absorption rates of the studied 10 wt%–H2O WLS at 313 and 333 K were approximately 5.0e-03 and 4.0e-03 mol/m2∙kPa∙s, respectively, which were much higher than that of a conventional aqueous amine solvent for CO2 capture. In addition, we observed that the overall mass transfer coefficient decreased with increasing temperature in low content water of WLS. This is due to the change of physical properties (Henry's law constant and diffusion coefficient) of WLS with decreasing water concentration. In this work, the cause of the reverse temperature dependence of WLS was investigated and verified through experiments and modeling.

Bioconversion of chemically captured carbon dioxide into microalgal lipids, a potential source of biodiesel: An integrated technique

The rise of atmospheric carbon dioxide (CO2) concentration due to extensive anthropogenic activity besides rapid exhaustion of non-renewable energy sources demands evolution of clean and ecofriendly alternative fuel source. Recently, lipid rich microalgal biomass is being considerably researched for generation of biodiesel conversely, the expenses incurred on production of microalgal biomass is a substantial obstacle. Almost 80 % of the production cost is generated from the cultivation medium which majorly consists of carbon, nitrogen and phosphate. CO2 absorption by means of aqueous amine solvents is known to be a mature technology and could be integrated with microalgal cultivation unit for efficient utilization of the captured CO2. In this current investigation, piperazine (PZ) promoted aqueous blend of methyldiethanolamine (MDEA) having mass percentage ratio of (8/22 wt%) was used a CO2 capturing agent and then the captured CO2 was utilized as an inorganic carbon source for growing Chlorella sorokiniana BTA 9031 for biodiesel production. The CO2 absorption rate was governed by series of process variables namely, absorption temperature, initial CO2 concentration, solvent flow rate, gas flow rate and the optimal conditions were 315 K, 15 kPa, 3.6 × 10−4 m3 min−1 and 4 × 10−3 m3 min−1 respectively. The highest biomass strength of Chlorella sorokiniana BTA 9031 was observed to be 1.20 ± 0.028 g L−1. The fatty acid methyl esters (FAME) profile was determined after acid transesterification of the extracted microalgal lipids. It was observed to contain fatty acids suitable for biodiesel production.

A hybrid chemo-biocatalytic system of carbonic anhydrase submerged in CO2-phillic sterically hindered amines for enhanced CO2 capture and conversion into carbonates

The present study highlights a hybrid approach to capture and convert carbon dioxide (CO2) from exhaust gases using bovine carbonic anhydrase (CA) submerged into aqueous amine solvents. Particularly, the sterically hindered amines have unique properties to absorb CO2 and also play a key role in wide range of industrial applications. In this work, the reaction kinetics of CO2 were studied in the aqueous phase of sterically hindered amines (SHAs), 2-amino-2-hyroxymethyl-1,3-propanediol (AHPD) and 2-amino-2-methyl-1-propanol (AMP), mixed with bovine CA as test and without CA as control using the stopped flow technique. The results showed a significant improvement in the rate of reaction between SHAs (either aqueous AHPD or aqueous AMP) and CO2 in the presence of CA. Moreover, the absorption capacity of SHA for CO2 and its initial absorption rate in presence of CA was significantly enhanced. The rate constants of pseudo first-order reaction of CO2 reacting with AHPD and AMP (each 0.5 kmol/m3) with varied concentration of CA were determined at temperature range of 298- 353 K. The aqueous AHPD and AMP systems in the presence of CA and control retained 65% of absorption capacity after 5 repetitive cycles. Also, the amine solvent captured CO2 was converted into calcium carbonate (CaCO3) which is white powder materials. The synthesized CaCO3 was characterized for its morphological and physicochemical properties using scanning electron microscopy (SEM) and Fourier transformer infrared spectroscopy (FTIR) etc. Overall, as the CA present is the amine solvent can efficiently convert the CO2 and that can be removed easily in the form of CaCO3 precipitates.

Design of a water wash column in the CO2 capture process using a polyamine-based water-lean solvent

Amine-based water-lean solvents (WLSs) have been studied as energy-saving alternatives to existing aqueous amine solvents for the capture of CO2. However, despite the low energy requirements of WLS-based processes, WLSs are susceptible to amine vaporization loss due to the high amine concentration. In addition, the water content of WLSs is apt to increase, which is caused by the low vaporization pressure of water from the solvent due to the low water content of the solvent. When this happens, it is expensive to return the water content of the solvent to its original state. To address these problems, in this study, we investigated the design of a water wash section for a CO2 capture process based on a WLS consisting of 60 mass% of 3,3′-iminobis (N,N-dimethylpropylamine) (IBDMPA), 10 mass% of water, and a non-amine chemical as the final content. The heat and mass balance around the water wash section was analyzed, including the IBDMPA/water transfer from gas phase to liquid (water) phase within the water wash bed. To achieve this, the mass transfer coefficients of the IBDMPA and water were measured in a modified wetted wall column system, and the binary and ternary vapor–liquid equilibria for the WLS were also measured and modeled. The computation using the ASPEN Plus® simulator showed that IBDMPA emissions of less than 1 ppm and water balance in the WLS could be successfully achieved through the appropriate design of the water wash section.

Experimental investigations and developing multilayer neural network models for prediction of CO2 solubility in aqueous MDEA/PZ and MEA/MDEA/PZ blends

AbstractIn this research, a new set of experimental data for CO2 solubility in aqueous blended amine solvents were investigated experimentally over the CO2 partial pressure range from 8 to 100 kPa at 40 °C and were compared with the benchmark aqueous 30 wt.% MEA solution. This work developed two multilayer neural network models named models A and B, for predicting the CO2 solubility in various aqueous blended amine solvents including 36 wt.% MDEA + 17 wt.% PZ, 24 wt.% MDEA + 26 wt.% PZ, and 6 wt.% MEA + 25 wt.% MDEA + 17 wt.% PZ. Models A and B were developed by using Levenberg–Marquardt back propagation algorithm with 427 and 301 of reliable experimental data sets gathered from the published data, respectively. The results indicate that the high accuracy prediction of the CO2 solubility in Methyldiethanolamine/Piperazine (MDEA/PZ) blends could be obtained by the network developed by Tan‐sigmoid transfer function with two hidden layers consist of eight and four neurons, while the network developed by Tan‐sigmoid transfer function with three hidden layers consist of 20, 10, and five neurons provided the highest accuracy for predicting the CO2 solubility in MEA/MDEA/PZ blends comparing to other model structures. The comparison results show that the neural network modeling provided more closer predictions to the experimental results than the simulator and other thermodynamic models when predicting the CO2 equilibrium solubility in blended amine solvents. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

Carbon dioxide capture with aqueous amino acids: Mechanistic study of amino acid regeneration by guanidine crystallization and process intensification

CO2 capture from powerplant-generated flue gas via a phase-changing process involving absorption with aqueous amino acids (e.g., glycine or sarcosine) and bicarbonate crystallization with bis-iminoguanidines (e.g., glyoxal-bis-iminoguanidine or GBIG) is investigated in this paper. This process is of high interest due to its potential to decrease the energy penalty for CO2 capture by significantly reducing the solvent regeneration energy typically associated with aqueous amine solvents. A critical step in the proposed CO2 capture mechanism is the regeneration of the amino acid by removal of protons and bicarbonate ions from solution through crystallization of GBIGH22+ bicarbonate salt. Here, we investigated the thermodynamics and kinetics of glycine regeneration by crystallization of GBIGH22+(HCO3–)2(H2O)2. A theoretical model was developed and compared to experimental data to simulate and predict the glycine regeneration and determine its reaction mechanism. This combined experimental and theoretical study led to the conclusion that, while the GBIGH22+ bicarbonate crystallization step provides most of the thermodynamic driving force for the glycine regeneration, the rate-limiting step is the protonation of GBIG prior to crystallization. The CO2 loading and amino acid regeneration steps were combined into a single, intensified process using a bubble column reactor. The CO2 loading capacity of GBIG was experimentally determined to be roughly 1.36 mol CO2 per mol GBIG. These results provide the fundamental basis for developing an effective carbon capture technology with phase-changing amino acid/guanidine absorbents.

Development of a rate-based model for CO2 capture using a non-aqueous hydrophobic solvent

Advanced water-lean solvents offer several advantages over aqueous amine solvents for post-combustion CO2 capture, particularly lower parasitic energy penalty, lower regeneration temperatures and lower corrosion. RTI and SINTEF have been working on developing eCO2SolTM, a non-aqueous solvent (NAS) that has shown stripper heat duties of 2.1 - 2.3 GJ/t-CO2 at pilot-scale testing at a 6-kW large bench-scale gas absorption system (BsGAS, RTI International, USA) and at the 60-kW Pilot testing unit (Tiller Plant, SINTEF, Norway). This technology will be demonstrated at the 12 MW scale at Technology Centre, Mongstad (TCM), Norway in early 2022. Development of novel solvent formulations is a time-consuming step, and models are needed to evaluate different process configurations and process conditions, to explore different energy integration strategies to minimize net heat duty and to size equipment and evaluate overall process economics. The non-aqueous solvent formulation includes novel components that have not been studied extensively in the literature. Most of the properties that are needed to develop rate-based kinetic-, thermodynamic and hydrodynamic models are not available and must be generated. This work provides details on the development of a detailed process model including the experimental measurement of properties required for the simulation model. The process model has been tested against quality pilot data gathered from the two pilot plants mentioned. The average absolute deviation (AAD%) between model prediction and experimental data for the specific reboiler duty (SRD) is within 6% for the 6-kW BsGAS at RTI and 7% for 60-kW pilot testing at SINTEF. Mass and heat transfer of the developed rate-based model was validated by predicting the temperature, CO2 loadings (molCO2/molamine) and CO2 concentration profiles of the testing units and compared favourably to experimental data.

Quantitative Kinetic Model of CO2 Absorption in Aqueous Tertiary Amine Solvents.

Aqueous tertiary amine solutions are increasingly used in industrial CO2 capture operations because they are more energy-efficient than primary or secondary amines and demonstrate higher CO2 absorption capacity. Yet, tertiary amine solutions have a significant drawback in that they tend to have lower CO2 absorption rates. To identify tertiary amines that absorb CO2 faster, it would be efficacious to have a quantitative and predictive model of the rate-controlling processes. Despite numerous attempts to date, this goal has been elusive. The present computational approach achieves this goal by focusing on the reaction of CO2 with OH- forming HCO3-. The performance of the resulting model is demonstrated for a consistent experimental data set of the absorption rates of CO2 for 24 different aqueous tertiary amine solvents. The key to the new model's success is the manner in which the free energy barrier for the reaction of CO2 with OH- is evaluated from the differences among the solvation free energies of CO2, OH-, and HCO3-, while the pKa of the amines controls the concentration of OH-. These solvation energies are obtained from molecular dynamics simulations. The experimental value of the free energy of reaction of CO2 with pure water is combined with information about measured rates of absorption of CO2 in an aqueous amine solvent in order to calibrate the absorption rate model. This model achieves a relative accuracy better than 0.1 kJ mol-1 for the free energies of activation for CO2 absorption in aqueous amine solutions and 0.07 g L-1 min-1 for the absorption rate of CO2. Such high accuracies are necessary to predict the correct experimental ranking of CO2 absorption rates, thus providing a quantitative approach of practical interest.