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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.

This work evaluates the possibility of employing a volatile co-solvent injection for recovering CO2 from loaded monoethanolamine at 120 °C under pressures above those achievable through regular desorption processes. This co-solvent would be fed directly into the reboiler, percolating the column and delivering higher operational pressures without significatively affecting the chemical equilibrium between CO2 and the amine. Removal of this co-solvent would be required before the lean amine is recirculated to the absorber. A shortcut methodology for screening possible co-solvent candidates is presented, and MESH calculations of hypothetical stripping processes employing the high-pressure desorption approach are performed to illustrate the expected behavior of these systems. Pressures above 500 kPa are theoretically obtainable through the use of co-solvents which are less volatile than CO2 but that are still gases at 25 °C and 101.325 kPa, such as isobutane and dimethyl ether. These co-solvents will leave the desorber fractioned between the distillate and the bottom product, thus requiring two additional separation process for recovery. Less volatile solvents will concentrate at the bottom stages of the desorber, while more volatile solvents will flow straight through the column all the way up to the distillate without effectively delivering pressures as high as desired. In other words, this methodology results in a delicate optimization problem of finding ideal volatilities and operational conditions. Though no detailed energy analysis is performed in this preliminary assessment, we have identified a promising opportunity for CO2 production at higher pressures and enumerated the issues one should be concerned with when looking further into high-pressure desorption.

Water-lean solvents have been proposed as a possible alternative to aqueous amine systems in postcombustion carbon capture. There is however little data available on how amine degradation is affected by different solvents. This study presents new insights on the effect of solvent on thermal degradation of alkanolamines from laboratory-scale degradation experiments. Replacing the water in aqueous monoethanolamine (MEA) solutions with organic diluents resulted in varying thermal degradation rates. Overall, all tested organic diluents (triethylene glycol, diethylene glycol, mono ethylene glycol, tetrahydrofurfuryl alcohol, N-formyl morpholine/water, and N-methyl-2-pyrrolidone) resulted in higher thermal degradation rates for loaded MEA. None of the proposed parameters, such as acid–base behavior, polarity, or relative permittivities, stood out as single contributing factors for the variation in degradation rates. The typical degradation compounds observed for an aqueous MEA solvent were also observed for MEA in various concentrations and with various organic diluents.

Knowledge on the solubility of gases, especially carbon dioxide (CO2), in monoethylene glycol (MEG) is relevant for a number of industrial applications such as separation processes and gas hydrate prevention. In this study, the solubility of CO2 in MEG was measured experimentally at temperatures of 333.15, 353.15, and 373.15 K. Experimental data were used to validate Monte Carlo (MC) simulations. Continuous fractional component MC simulations in the osmotic ensemble were performed to compute the solubility of CO2 in MEG at the same temperatures and at pressures up to 10 bar. MC simulations were also used to study the solubility of methane (CH4), hydrogen sulfide (H2S), and nitrogen (N2) in MEG at 373.15 K. Solubilities from experiments and simulations are in good agreement at low pressures, but deviations were observed at high pressures. Henry coefficients were also computed using MC simulations and compared to experimental values. The order of solubilities of the gases in MEG at 373.15 K was computed as H2S > CO2 > CH4 > N2. Force field modifications may be required to improve the prediction of solubilities of gases in MEG at high pressures and low temperatures. This is an open access article published under a Creative Commons Non-Commercial No Derivative Works (CC-BY-NC-ND) Attribution License, which permits copying and redistribution of the article, and creation of adaptations, all for non-commercial purposes.

We have evaluated the vapor-liquid equilibrium and heat of absorption of CO2 over water-lean mixtures of the amines diisopropylamine and N,N-diethylethanolamine (DEEA). This extends our previous re...

Water-lean solvents are typically defined as mixtures between an organic diluent and an amine. These solvents are thought to deliver potential benefits in CO2 capture systems, such as enhanced mass...

Vapor–liquid equilibria data of three poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)/water liquid crystals (LCs) with CO2 has been obtained up to 6 bar. The investigated LCs consist of 60% (EO)3(PO)50(EO)3 (Pluronic L81), 70% (EO)8(PO)47(EO)8 (Pluronic L92), and 70% L92-NH2. The maximum CO2 loading of the LCs was 5–13 g CO2/kg sample. Pure L81 and L92 displayed higher absorption of CO2 than the LCs. Rheology measurements revealed that the increasing viscosity of the samples decreases the CO2 loading. Water diffusion in the LCs was qualitatively investigated by nuclear magnetic resonance, confirming that free water and tightly bound water are present in the LCs. 2020 The Author(s). Published with license by Taylor and Francis Group, LLC This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.

The chemical stability of aqueous amines is an essential property to study before new amines are introduced in pilot plants, to reduce risks related to the operation, cost and environment. There are no standard methods for studying degradation and no standardized way of knowing which components to search for. This work will give an overview of the current status of amine degradation research with recommendations for further work within this field. Degradation of aqueous amines in the CO2 absorption process will always occur, though some amines are more stable than others. Degradation leads to compounds with various functional groups, some of which require monitoring from an environmental or health perspective. Future experimental activity should focus on closing the knowledge gaps. Improved knowledge could help to better predict and monitor degradation, help design better mitigation technologies, and minimize solvent degradation by fine-tuning the plant operation.

This work reports equilibrium data for two amines, 2-piperidineethanol (2-PPE) and 1-(2-hydroxyethyl)pyrrolidine (1-(2HE)PRLD), and their aqueous solutions. The pressure, temperature, and composition data are used to calculate experimental activities. Data cover temperatures from 363 to 426 K for the pure amines and from 323 to 373 K for the aqueous solutions. A UNIQUAC model was used to represent the binary vapor–liquid equilibria (VLE), whereas the Antoine equation was used for pure components. In an aqueous solution, the vapor pressure of 1-(2-hydroxyethyl)pyrrolidine (1-(2HE)PRLD) over the measured composition and temperature ranges is higher than that of 2-piperidineethanol (2-PPE). The developed UNIQUAC models represent the data well. For 2-piperidineethanol (2-PPE), the model gave 1.9% deviations for total pressure, 12.4% for vapor-phase composition, 12.7% for the calculated activity coefficients, and 16.2% for the excess heat capacity. In the case of 1-(2-hydroxyethyl)pyrrolidine (1-(2HE)PRLD), the model was slightly more accurate, representing the data with 1.7% deviation for total pressure, 5.9% for vapor-phase composition, and 5.2% for the calculated activity coefficient.

Nonaqueous and aqueous mixtures of methyldiethanolamine and monoethylene glycol form promising absorbents for the combined hydrogen sulfide removal and hydrate control, necessary in natural gas pro...

This work studies the potential of using the tertiary amines 3-dimethylamino-1-propanol (3DMA1P), 3-diethylamino-1-propanol (3DEA1P) and 1-(2-hydroxyethyl)pyrrolidine (1-(2HE)PRLD) as an alternative to 2-(diethylamino)ethanol (DEEA) in the blend with 3-(methylamino)propylamine (MAPA). Vapour pressure of the three tertiary amines and vapour-liquid equilibrium (VLE) of the binary mixtures 3DMA1P/H2O, 3DEA1P/H2O and 1-(2HE)PRLD/H2O at T = (353, 363 and 373) K were measured in a modified Swietoslawski ebulliometer. The vapour pressure of the pure amines was fitted to the Antoine equation, and the P-T-x-y data were fitted to NRTL equations. VLE of the CO2 loaded blended amines were measured in the temperature range of T = 313 to 393 K, and speciation data of equilibrated samples at different CO2 loadings were obtained by NMR spectroscopy. The study showed that the tertiary amines 3DMA1P, 3DEA1P and 1-(2HE)PRLD in the binary amine/H2O system were less volatile than DEEA in aqueous solution. The CO2 loaded blended amines showed comparable VLE behaviour, as well as speciation, and obtained a cyclic capacity higher than that of 30 wt% MEA but similar to most of the blended amines studied in the literature. The overall results indicated that the tertiary amines studied in this work can be used as an alternative to DEEA.

Recent years have witnessed a growing academic interest in development of new CO2 capture solvents to reduce the capture costs. This study focused on nine picolylamines (three commercial and six synthesized) and one imidazole-amine, most of which have not previously been reported as amine absorbents. The solvent performance was evaluated by measuring the absorption capacity, desorption tendency and pKa. Several of the amines demonstrated CO2 cyclic capacity significantly higher than that of 30 wt% MEA due to very lean CO2 loadings, driven by low amine pKa. The lean loadings can potentially mitigate solvent degradation. At the same time, absorption rates comparable to 30 wt% MEA were obtained for 3 M picolylamines. The results demonstrate the promising nature of picolylamines and derivatives for CO2 capture.

The effect of liquid viscosity on the performance of a non-porous membrane contactor is important to study for a proper solvent selection and process design. In this work, the overall mass transfer coefficient for MEA- and NaOH-based solutions was studied using a string of discs contactor in the temperature range 28–64 °C and a thin composite membrane contactor at 40 °C. Also, viscosity, density and N2O solubility of the aqueous solutions were measured in the temperature range 30–70 °C. The solvent viscosity of MEA and NaOH solutions was artificially adjusted from 0.5 to 54.7 mPa s by addition of sugar and/or glycerol. The overall mass transfer coefficient was found to decrease with increasing amount of viscosifier and the decrease seemed to be independent of the solvent system. In the membrane contactor, the decrease in the overall mass transfer coefficient was attributed to the decreasing CO2 solubility and CO2 diffusion coefficient, but as these properties alone were not able to describe the experimental values, the reason was attributed also to the establishment of an additional resistance at the membrane/liquid interface.

Shifting from aqueous to water lean solvents has been evaluated as a mean for increasing the mass transfer rates in regular chemical solvents with amines. An array of amines (monoethanolamine, 2-methylpiperazine and N-methyl diethanolamine) and diluents (sulfolane, ethylene glycol, 1-methylimidazole, dimethyl sulfoxide, N-methyl-2-pyrrolidinone) has been analyzed. Addition of organic diluents seem to generally induce both a shift in chemical equilibrium and an increase in mass transfer rates for a fixed CO2 partial pressure, though not necessarily for a fixed CO2 loading. However, these relative advantages in terms of mass transfer rates decrease the more loaded the water lean solvent is. The equilibrium shift caused by organic diluents has been evaluated in terms of de-stabilization of the species in the solvent, which for monoethanolamine-based solvents can be easily related to a decrease in dielectric permittivity. However, this analysis indicates that such treatment is insufficient for other types of water-lean solvents, suggesting that different kinds of intermolecular interactions should also be considered in future studies.

The CO2 absorption performance of aqueous solvent blends containing four imidazoles (2-MeIm, 2-Et-4-MeIm, 2,4,5-MeIm and 1,2,4,5-MeIm) and four promoters (MEA, DEA, PZ, and MAPA) were investigated ...

Thermal stability and corrosion of seven tertiary amines (20 wt.%) solutions in water and water-glycol [ethylene glycol (MEG)/tri-ethylene glycol (TEG)] loaded with CO2 in stainless steel reactors has been studied for combined acid gas removal along with hydrate control. The pKa of the tested amines varied from 7.85 to 9.75. Titration and inductivity coupled plasma mass spectrometry (ICP-MS) are used to quantify the remaining alkalinity and metal concentrations in amine solutions respectively. The presence of MEG and TEG profoundly influenced the amine stability. Triethanolamine had the highest thermal stability. Furthermore, the results also show that an increase in pKa generally decreases corrosion. 3-(Diethylamino)-1,2-propanediol (DEA-1,2-PD) has the lowest corrosion in water and water-TEG solutions while 2-(Diethylamino)ethanol (DEEA) has the least corrosion in water-MEG solutions.

A computational screening strategy applied to 8 million synthetically diverse ionic liquids, demonstrates its value for sustainable solvent design. In contrast to previous studies which have largely focused on single characteristics, important properties such as viscosity, density, thermal stability and toxicity, were estimated using machine learning. Experimental characterization of 15 compounds selected from the library reinforced the utility of the approach. Over 2600 ionic liquids, a majority of which have never been reported before, were investigated for applications in CO2 and H2S gas separation, and cellulose dissolution, using density functional theory calculations. Among these, around 250 low cytotoxicity and low viscosity ionic liquids merit further investigation.

We introduce the addition of stable salts to aqueous MEA as a way of inhibiting oxidative degradation reactions. We performed oxidative degradation studies in aqueous MEA containing sodium chloride (NaCl) and potassium iodide (KI). These “salted amine solvents” have been shortened to SAS. The 2.0 %wt. and 1.0 %wt. KI SAS show remarkable oxidative degradation behavior. Loss of alkalinity after 42 days of oxidative degradation experiments with the 1.0 %wt. KI SAS was of 4%, whereas that of aqueous MEA was of 40% after only 21 days. We evaluated how the addition of stable salts impacts CO2 solubility, viscosity, and thermal degradation and corrosion behavior and verify negligible deviations from aqueous MEA. Thus, addition of stable salts affects oxidative degradation phenomena without deranging CO2 solubility or mass transfer rates. With the promising inhibition behavior of KI on MEA degradation, this work presents the initial steps towards making it a commercially viable degradation inhibitor.

In a previous work focusing on the droplet growth along with the absorber for a post-combustion CO2 capture case based on CESAR1 solvent, a simplified kinetic model was used. A simplified kinetic model based on a pseudo-single amine was utilized but limited our understanding of the results. Improvements were needed as the CESAR 1 solvent is a blend of 2-amino-2-methyl-1-propanol (AMP) and Piperazine (PZ) at a certain mole ratio and the reactive system when CO2 is present becomes complex. In this work, new kinetic models are developed for the individual components AMP and PZ, based on all available experimental information in the literature. Together with an improved eNRTL model for the quaternary AMP/PZ/H2O/CO2 system, the models are implemented in an improved droplet distribution version of the aerosol model.

One of the major issues encountered in the Post Combustion CO2 Capture processes is the degradation of the solvent which can be in great part attributed to the presence of oxygen in the solution. The present report focuses on the demonstration of DORA (Dissolved Oxygen Removal Apparatus), a technology developed by TNO as a counter-measure of oxidative degradation. The DORA was first operated in combination with TNO’s mobile bench-scale CO2 capture pilot (5 Nm3/h flue gas capacity) with artificial flue gas, showing an instant drop of 15% and an overall reduction of approximately 70% in the ammonia emissions from the absorber, which is an indication of reduced degradation. The technology was also demonstrated using the same pilot in an industrial environment in collaboration with the facility PlantOne bringing DORA from TRL5 to TRL6. This campaign proved that DORA contributed to the deacceleration of solvent degradation. The tests were executed with a porous membrane, and it was observed that exposure to degraded solvents led to solvent leakage through this membrane. Therefore, the use of a coated membrane was proposed to optimize the operation and increase oxygen removal. The use of this membrane is demonstrated at TRL3. Along with that, a model was developed to determine mass transfer resistances and the membrane area required to remove different levels of dissolved oxygen.

Eighteen structurally varied amines were subjected to harsh oxidative conditions, and their stability was assessed and seen in the context of biological and thermal stability. Steric effects play a large role in the stabilization of amines under oxidative conditions, and the presence of carbon dioxide plays a vital role in the degradation pathway of ethanolamine (MEA). Tertiary amines are generally very stable, and are known not to form carbamates to any large extent. Many steric effects play a vital role in stabilization, such as chain length, substituents located both close to and farther from the nitrogen atom, and bond strain. A correlation is seen between biodegradability and oxidative degradability, giving similar degradability in both cases. There are, however, promising exceptions to this, such as 3-(dimethylamino)-1-propylamine (DMAPA) and 2-dimethylaminoethanol (DMMEA), which are stable under oxidative conditions, but also biodegradable. Direct correlations between oxidative stability and ecotoxicity or thermal stability are not seen.

The new H2020 project REALISE will demonstrate at pilot scale a CO2 capture technology based on an advanced low-energy solvent, quantify emissions, solvent degradation, and quality of the liquified CO2 when impurities from flue gases from an operating refinery are introduced to the pilot. Several innovative concepts will be demonstrated in the project (some directly at a refinery in Cork, Ireland) allowing realization of the target objectives set in the project resulting in at least 30% reduction in the cost of CO2 capture compared to the reference case based on 30% Monoethanolamine (MEA). Techno-economic analysis will be done for integration of a multi-absorber concept for at least 3 refineries (partners in the project). The results will be implemented in an open-access simulation tool to evaluate the cost of CO2 capture and to decide carbon capture strategy at other refineries. Assessment of transport, utilization and storage options will be performed for the studied cases and societal impact and CCS readiness index estimated for cases in Europe, China and S. Korea

Within the transatlantic project LAUNCH, solvent management strategies are validated by test campaigns at four capture plants with an adequate plant size and in an industrial environment (3 pilot facilities with a capture capacity of up to 0.4 tCO2/h and a commercial plant with 12 tCO2/h). At the capture pilot plant at Niederaussem, which separates in 24/7 mode the CO2 from the flue gas of the adjacent 1,000 MW lignite-fired block of the power plant, three degradation control technologies with different effect mechanisms are investigated in testing campaigns with the so-called CESAR1 solvent (>14,000 testing hours with an aqueous solution of 3.0 molar (~26.74 wt.-%) 2-amino-2-methylpropan-1-ol (AMP) and 1.5 molar (~12.92 wt.-%) piperazine (PZ): adsorptive removal of trace elements from the solvent by active carbon, removal of ionic trace elements from the solvent by ion exchange and removal of NO2 from the flue gas by thiosulfate/sulfite dosing. Activation of carbon and particle filters after 5,184 and 6,048 hours testing time resulted in a removal of coloring agents, iron and nickel from the solvent. Additionally, the increase of Cl-, SO42- and NO3- concentrations could be reduced, but no clear effect on the solvent degradation rate was observed. Anionic degradation products and trace components can be effectively removed from the aged solvent by ion exchange with an anionic exchange resin. Laboratory tests with the anionic resin and three cationic resins provide promising results to remove metal ions from the solvent. As iron can be removed from the solvent using the anionic resin, but not nickel, this is a strong indication that iron is dissolved in the solvent in the form of an anionic complex, which highlights the importance of the solvent matrix when investigating the catalytic effect of metal ions on amine degradation. Despite a concentration of 175 mmol/kg thiosulfate and 32 mmol/kg sulfite and a pH value of >8.5 of a scrubbing solution in a pre-treatment scrubber, it was not possible to remove NO2 from the flue gas. Laboratory tests confirmed the effect of the pre-treatment concept. Either the mass transfer is not sufficient in the scrubber or new NO2 is formed after the pre-treatment from NO in the flue gas. This will be

In this study, the thermal stability and corrosivity of various CO2-loaded tertiary amine blends in both aqueous and non-aqueous form in stainless steel cylinders were studied for combined acid gas and water removal. The thermal stability was measured from the remaining amine concentration and the corrosivity was measured from the amount of various metals in blends using titration and inductively coupled plasma mass spectrometry (ICP-MS), respectively. The experimental data were used to calculate the rate constants of amine group loss. The developed model represented the experimental data very well. Solvent change from H2O to triethylene glycol (TEG) in blends decreased the thermal stability and vice versa for corrosivity. The amine stability was increased when contact with stainless steel was reduced. An increase in the amine concentration or CO2 loading at constant temperature decreased the thermal stability and vice versa for corrosivity. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

The thermal and oxidative degradation behavior and the corrosiveness of imidazole (Im), 2-methylimidazole (2MIm), 2-ethyl-4-methylimidazole (2E4MIm), 2,4,5-trimethylimidazole (2,4,5MIm), and 1,2,4,5-tetramethylimidazole (1,2,4,5MIm) were investigated in a CO2 rich environment. The imidazoles demonstrated high thermal stability in all solutions; however, Im and 2MIm were corrosive. Polyalkylated imidazoles were less stable toward oxidation compared to Im. Rat cell (PC-12) toxicology screening of Im and 45 alkylated imidazoles showed reduced toxicity for polyalkylated imidazoles compared to Im. Cell viability correlated negatively with cLogP predictions when cLogP > 3. The high rate of oxidative degradation and formation of potentially carcinogenic degradation products will prevent the use of polyalkylated imidazoles in industrial processes directed toward CO2.

Every year, a plethora of studies focused on developing water-lean solvents for CO2 capture is published in the scientific literature. More often than not, these studies lack a satisfactory contextualization with the previous body of work. The reasons for this are manyfold, but perhaps the main culprit is the multitude of possible diluent and amine constituents for water-lean solvent formulation. This multitude of options can render a comprehensive analysis of water-lean solvents and their common properties quite a challenging task. However, precisely because there is such a diversity of results and observations, the ordering and categorization of distinct phenomena involving water-lean solvents is the more essential. Although there are some novel sophisticated deployements for the concept of organo-amine mixtures (such as the CO2BOLs and the NAS for example), many works on water-lean solvents adopt a traditionalistic approach, one that is conceptually based on the mixing of a physical and a chemical absorbent to generate a so-called hybrid solvent. We have demonstrated in this review that this particular class of solvents have more in common than one could be initially led to believe, and set clear guidelines to contextualize past and future results in terms of CO2 solubility, kinetic rates, mass transfer rates and heat of regeneration analyses. By doing this, we have also identified the main knowledge gaps remaining in the field of water-lean solvents – namely, degradation and corrosion data, as well as pilot plant data. We also believe that our comprehensive categorization and discussion of past literature on water-lean solvents delivers an important trove of references for those willing to carry on working with organo-amine mixtures, traditional or otherwise. With this study, we aim to aid future researchers to have easy access to key concepts for discussing their results.

A thorough investigation on a set of organic diluents for water-lean solvent formulation has been carried in this work. The performance of aqueous monoethanolamine (MEA) 30 %w/w has been compared to that of mixtures between MEA 30 %w/w and methanol, acetone, monoethylene glycol (MEG), N-methyl-2-pyrrolidone (NMP), tetrahydrofurfuryl alcohol (THFA), sulfolane, cyclopentanone (CC5), furfuryl alcohol and γ-butyrolactone. A small calorimeter was employed to obtain both vapor–liquid equilibrium (VLE) and heat of absorption data. Shifting from an aqueous solvent to a non-aqueous one was observed to have significant implications on the VLE, as all water-lean solvents assessed have lower CO2 solubility than aqueous MEA. However, the heat of absorption is not much affected. The results of these experiments show the limitations of using most ethers, esters and ketones for water-lean solvent formulation, all stemming from the very low dielectric permittivity of these diluents and the difficulty of the stabilization of the intermediary reaction species between MEA and CO2 within these systems. Nevertheless, the low volatility of solvents containing MEG, NMP or THFA could offer opportunities for processes with overall less reboiler heat duties than that of ordinary aqueous MEA. © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).

This work aims to understand oxygen solubility in pure and aqueous amine solvents for CO2 capture. Commercially available dissolved oxygen sensors were studied to evaluate whether these can be used for measuring oxygen solubility in the carbon capture processes. It also aims to understand the possible discrepancies from realistic concentrations of oxygen when using a dissolved oxygen sensor. Two independent measurement principles were used for this purpose, both electrochemical and optical. Furthermore, a Winkler titration method was used to aid the validation of the sensors as well as understanding salting-out effects. A simple model for predicting oxygen solubility in CO2-loaded ethanolamine solutions was made, which also has potential for predicting oxygen solubility in other loaded amine solutions. The results of the study show that dissolved oxygen sensors may be applied for measurement of oxygen concentrations in amine solutions and that different amines and different concentrations in water only show small variations in oxygen solubility. The sensors may also be used in CO2-loaded amine solutions, but here the increased conductivity of the solution may give a higher measured concentration of oxygen, than it is in reality. In ethanolamine, the consumption of oxygen is faster than the mass transfer of oxygen from gas to liquid phase, giving lower concentrations of oxygen than it should be in absence of a chemical reaction between oxygen and amine. 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/

The melting point (Tm) of an ionic liquid (IL) is of crucial importance in many applications. The Tm can vary considerably depending on the choice of the anion and cation. This study explores the use of various machine learning (ML) methods to predict the melting points (− 96 °C–359 °C range) of structurally diverse 2212 ILs based on a combination of 1369 cations and 141 anions. Among the ML models applied to independent training and test sets, tree-based ensemble methods (Cubist, random forest and gradient boosted regression) were found to demonstrate slightly better performance over support vector machines and k-nearest neighbour approaches. In comparison, quantum chemistry based COSMOtherm predictions were generally found to have significant deviations with respect to the experimental values. However, classification models were more efficient in discriminating between ILs with Tm > 100 °C and those below 100 °C.

New data comprising CO2 partial pressure, total pressure, and the heat of absorption of CO2 for over aqueous solution of 3 mol/dm3 AMP and 1.5 mol/dm3 PZ and total pressure and heat of absorption for different mol ratios of AMP/PZ (3.0/0.0, 0.0/1.5, 0.5/4.0, 1.5/3.0, 2.25/2.25, 3.0/1.5, 4.0/0.5) are presented as functions of CO2 loading and temperature. Measured solubility data and selected data reported in the literature were used in the regression of binary interaction energy parameters in the quaternary system (AMP/PZ/H2O/CO2) using the eNRTL model. The equilibrium constants and binary interaction energy parameters from our previous work on the ternary systems of AMP/H2O/CO2 and PZ/H2O/CO2 were used without refitting. Good agreement with the literature was observed for the total pressure data over aqueous solutions of 3.0 mol/dm3 AMP and 1.5 mol/dm3 PZ, and the CO2 partial pressure and heat of reaction data over aqueous solutions of 3.0 mol/dm3 AMP+1.5 mol/dm3 PZ at different loadings and temperatures. The results reflect that the new data are consistent with reported data from the literature. The modeling results show that the eNRTL model represents the data well with AARD values of 13.1% for total pressure and 20.9% for CO2 partial pressure. The volatility of AMP and PZ as function of loading and temperature and published speciation data for A M P / A M P H + , P Z / P Z H + / P Z H 2 2 + , P Z C O 2 − / P Z H + C O 2 − , P Z ( C O 2 − ) 2 and H C O 3 − / C O 3 2 − were also well predicted. Only the heat of absorption data over an aqueous solution of 3.0M AMP+1.5M PZ from this work can be compared with literature data, and good agreement is observed. The eNRTL model also predicts satisfactorily the experimentally obtained heat of absorption data for all different ratios of AMP/PZ. Individual reaction contributions show that when the AMP/PZ ratio increases, the predicted total heat of absorption goes toward the single solvent AMP system where only protonated AMP is the main contributor. When the AMP/PZ ratio decreases, the predicted total heat of absorption also approaches the single solvent PZ system where the protonated PZ, PZ-monocarbamate and zwitterion reactions play important roles. In systems with high PZ-concentration, the contribution of the zwitterion, protonated PZ and PZ-carbamate cancel each other at high loadings.

Biogas upgrading is an important industrial process for producing biomethane, a sustainable energy source with low carbon footprint. There are three main solvent-based alternatives for biogas upgrading: water scrubbing, physical scrubbing and chemical scrubbing with amines. Though assessments have been published regarding which technologies are more cost-effective and energetically efficient, these often either neglect inspecting the impact of raw biogas concentrations and biomethane delivery pressures on the overall performance of the plant, or they do not consider that the separated CO2 has to be conditioned for transportation for properly fulfilling the requirements of BECCS (bioenergy with carbon capture and storage). In fact, many assessments of physical scrubbing processes forfeit CO2 recovery altogether. This work intends to rehabilitate physical scrubbing as an alternative for BECCS by showing that, depending on the conditions of the raw biogas, the requirements for biomethane delivery, and the cost of carbon taxes, biogas upgrading can be feasible by scrubbing either with amines or with organic solvents. We introduce a review on organic physical solvents for CO2 recovery, a simulation framework for the evaluation of energetical operational costs of biogas upgrading, and a simplified economic analysis. High biomethane delivery pressures and high CO2 concentrations in raw biogas benefit the use of physical solvents such as N-formyl-morpholine, N-methyl-2-pyrrolidone and poly(ethylene glycol)dimethyl ether, whereas the opposite conditions are advantageous to aqueous monoethanolamine. Finally, the implementation of carbon taxes of around 10 USD/ton CO2 emitted are sufficient to increase the attractiveness of CO2 recovery as opposed to CO2 wasting.

Water-lean solvents are solvents for CO2 capture which contain at least one amine and one organic diluent. Carbamate-forming amines in nonaqueous water-lean solvents typically absorb CO2 through the formation of carbamate species. Conversely, tertiary amines in nonaqueous amino-organic mixtures cannot form carbamate nor undergo bicarbonate formation. However, protic organic diluents might take part in an alkylcarbonate formation pathway: in this route, the diluent is deprotonated by the amine, and its conjugate base is then able to react directly with CO2 to form an alkylcarbonate. This is an interesting reaction mechanism, as it offers a possibility for formulating solvents that deviate from the two most common reaction pathways for CO2 absorption (i.e., carbamate and bicarbonate formation). The present study introduces a simple way for evaluating alkylcarbonate-forming water-lean solvents based on the properties of its single constituents, namely the basicity of the amine and the autoprotolysis constant of the organic diluent. Our theoretical framework shows that higher CO2 absorption capacities can be obtained for solvents containing amines with high pKa and diluents with low pKs. We assess both the challenges and possibilities for alkylcarbonate-forming solvents and propose a framework for their development and utilization in the industry.