CO2-rich Phase Research Articles

Ethyl levulinate regulates traditional sulfolane biphasic absorbent for energy-efficient CO2 capture

Traditional CO2 biphasic absorbents currently suffer from problems such as high initial phase separation loading, poor product distribution selectivity, and weak dynamic phase separation ability, which limit their potential for industrial applications. This study developed a biphasic absorbent regulated by dual physical solvents by introducing partial ethyl levulinate (EL) into a sulfolane biphasic system. The optimal composition of this system was 30 wt% 1-amino-2-propanol (MIPA), 20 wt% sulfolane and 30 wt% EL. Under dual physical solvent conditions, strong electrostatic attraction between MIPA and CO2 promoted generation of MIPA zwitterions and carbamate. Analysis of the interactions between different product components through electrostatic potentials and with an independent gradient model based on Hirshfeld's partitioning revealed only extremely weak van der Waals force-driven interactions between the reaction products and EL. These interactions substantially reduced the initial phase separation loading and offered precise control over phase transition behavior. Compared with MIPA/sulfolane system, the MIPA/sulfolane/EL system achieved a 48.9 % lower initial phase separation loading, an 11.6 % lower proportion of saturated rich phase volume, a 10.1 % higher CO2-rich phase loading, and a 6.7 % lower viscosity. The excellent dynamic phase separation performance was verified using a customized device and the energy consumption for CO2 regeneration decreased to 2.2 GJ/t CO2.

A phase separation prediction model for CO2 capture by biphasic amine absorbents

The biphasic amine absorbent upon absorbing CO2, separates into CO2 poor and CO2 rich phases, making it a third-generation chemical absorbent with energy-saving potential. However, the current method of constructing biphasic amine absorbents involves screening phase separation agents through a large number of experiments, which involves significant amount of trial and error. In this study, a phase separation prediction model was built for CO2 capture by biphasic amine absorbents for quick screening of phase separation agents. The phase separation of CO2 absorption by organic amine 2-amino-2-methyl-1-propanol (AMP) using 34 phase separation agents was statistically analyzed based on 14 molecular descriptors of the solvents. The factors influencing the phase separation were thoroughly explored. It is proposed that the relative dielectric constant or molecular polarity index can replace the traditional polarity evaluation index, dipole moment, to better describe the phase separation situation. Additionally, it is found that the ability of phase separation agents to form hydrogen bonds, particularly as a hydrogen bond donor is the determining factor for phase separation to occur. Ultimately, the preferred molecular descriptors are used as predictors, leading to the development of a prediction model for phase separation that achieves high-accuracy predictions solely through theoretical calculation parameters. The model considerably reducing the construction costs of biphasic amine absorbents.

An experimental methodology to validate the use of hydroethanolic mixtures as suspending medium / modifier for the supercritical CO2 extraction of suspensions

We developed a methodology to study the extraction of high-value solutes directly from suspensions of finely disrupted substrates. For that, we modelled the high-pressure phase equilibrium for the ternary (CO2 + ethanol + water) system using experimental literature data. Different compositions of hydroethanolic mixture and CO2 were loaded into an extraction vessel set at 30–35MPa and 40–50 °C during static extraction, and a gaseous mixture with the composition of the CO2-rich gaseous phase in the extraction vessel was continuously fed during dynamic extraction. Losses of the fed hydroethanolic mixture occurred mainly during dynamic extraction (10-30wt%) and were properly distributed to account for actual flows and compositions of experimental streams. Mostly, equilibrium conditions were reached following about 1h of the 2-h dynamic extraction, and good reproducibility was achieved. In conclusion, equilibrium is reached in which two phases coexist in equilibrium within the extraction vessel: a water-rich liquid phase and a CO2-rich gaseous phase.

Tertiary amine based-biphasic solvent using ionic liquids as an activator to advance the energy-efficient CO2 capture

The newly developed tertiary amine-based biphasic solvents have low reaction heat, and good desorption performance, but no CO2 reactivity under low CO2 pressure. A novel tertiary amine-based biphasic solvent (DMEA/[DETAH]Lys/n-BuOH/H2O, abbreviated as D-DL-B-H) using ionic liquids (ILs) as the activator was proposed. With the assistance of [DETAH]Lys, the CO2-rich phase exhibited enhanced CO2 loading (from 3.69 to 4.09 mol/L) and CO2 distribution (from 88.5 % to 96.8 %). In addition, at 5 kPa, D-DL-B-H achieved an absorption capacity up to 1.58 mol/L, which was 79 times that of the DMEA/n-BuOH/H2O, suggesting the D-DL-B-H had good CO2 capture property at low CO2 pressure. At 393.15 K, the desorption efficiency of D-DL-B-H was as high as 80.9 %. In addition, the Qreg of D-DL-B-H was reduced to 1.78 GJ/t CO2, accounting for 44.61 % of the 30 wt% MEA. At 323.15 K, the viscosity of the CO2-rich phase was only 4.63 mPa·s, and the corrosion rate was 46.88 % of 30 wt% MEA. The reaction mechanism obtained from 13C NMR and DFT analysis indicated that [DETAH]Lys was more inclined to react with CO2 than DMEA. The main reason for the occurrence of phase splitting was the formation of hydrogen bonds between the CO2 product and the water.

Binary phase behavior of select organosulfur compounds in supercritical carbon dioxide: A Monte Carlo molecular simulation study.

Pressure-composition binary phase diagrams were determined for methanethiol, dimethyl sulfide, thiophene, benzothiophene, or dibenzothiophene with carbon dioxide at temperatures from 363 to 453K and pressures from 2 to 20 MPa. Utilizing Gibbs ensemble Monte Carlo molecular simulation, phase coexistence compositions were determined, along with the impact of 4% water cosolvent on select results. Solution structure as a function of pressure and temperature is characterized via radial distribution functions. Comparison to available experimental composition data gives overall mean absolute percentage deviations of 2.2% for thiophene, 37% for methanethiol, and 99% for benzothiophene. Solubilities in a CO2-rich phase are calculated to be sufficient to allow extraction and detection of the compounds studied here via supercritical fluid chromatography and mass spectrometry as a possible analysis approach for future Mars rover missions.

Intramolecular hybrid diamine DMAPA/n-PeOH/H2O biphasic absorbent for CO2 absorption through combining zwitterion and base-catalyzed hydration mechanism

Biphasic solvents can decrease the regeneration energy of CO2 capture. As an intramolecular hybrid diamine, 3-Dimethylaminopropylamine (DMAPA) had a primary amino group and a tertiary amino group, which could absorb CO2 by combining zwitterion and base-catalyzed hydration mechanism. The derived DMAPA/n-PeOH/H2O biphasic absorbent possessed high CO2 absorption capacity (1.46 mol/mol) and large CO2-rich phase loading (6.27 mol/L), which were superior to existing mixed amine systems. At 393.15 K, this system had a large desorption amount of 4.91 mol/L and a fast desorption rate (6.68 E-3 mol/L·s), which were 2.84 and 3.73 times of 30 wt% MEA. The associated total regeneration energy was reduced to 1.36 GJ/t CO2, only 34.1 % of MEA absorbent. The reaction mechanism and origin of phase separation were revealed by NMR analysis and quantum chemistry calculations. In addition, low viscosity and corrosiveness were revealed and conducive for industrial application.

A novel method to accelerate the three-phase flash calculation of the hydrocarbon-CO2 system

To achieve high computational efficiency and simulation accuracy in the equation-of-state-based compositional simulation, the fast multiphase flash calculation approach is required for the hydrocarbon-CO2 system, allowing for the simultaneous existence of vapour, CO2-lean, and CO2-rich phases. However, the conventional step-by-step method for multiphase flash calculation is associated with a high cost in identifying the three-phase equilibrium, thereby significantly impeding the computation efficiency of compositional simulation when the three-phase equilibrium appears in most grids.To address this challenge, a novel approach to multiphase flash calculation is proposed. In this study, all trial phases exhibiting negative tangent plane distance are employed to identify the three-phase equilibrium, eliminating the need for additional phase stability analysis and two-phase split calculations. Furthermore, this new method incurs minimal computational cost and requires only minor modifications to the existing stepwise procedure. Phase diagram calculations conducted on four cases demonstrate that the newly proposed method dramatically accelerates the identification of the three-phase equilibrium.

CO2 absorption by diethylenetriamine-based phase change absorbents: Phase change mechanism and absorption performance

CO2 phase change absorbents (CPCAs) have garnered significant attention for their potential to reduce energy consumption. However, suitable phase change agent is suffering from the selection among a wide range of organic solvents. In order to explore the phase separation mechanism and minimize screening efforts of CPCAs, the phase separation behaviors of the diethylenetriamine (DETA)-based absorbents constituted with different organic solvents were investigated, and the interaction energies revealed that the ion–dipole interaction is the dominant role in CO2-riched absorbents. The intensification of the self-aggregation of organic solvents by the ion-water interaction, was proposed as the main reason for the differences in the phase separation behavior in different DETA-based absorbents. Based on the relative ET(30) and relative dielectric constant of the organic solvent, a phase separation diagram can be drawn to predict the phase change behaviors of DETA absorbents. Among the DETA-based CPCAs, DETA + DMF + H2O absorbents showed the largest CO2-rich phase loading, and the optimized DETA + DMF + H2O CPCA exhibited 200 % of the CO2 cyclic loading compared to 30 wt% MEA aqueous solution.

CO2 capture performance of a 1-dimethylamino-2-propanol/N-(2-hydroxyethyl) ethylenediamine biphasic solvent

Biphasic solvents are widely used for CO2 capture owing to their low regeneration heats; however, they typically suffer from poor regeneration performance and excessive energy consumption. In this study, a mixture of 1-dimethylamino-2-propanol (1DMA2P) and N-(2-hydroxyethyl) ethylenediamine (AEEA) was proposed for CO2 capture. By optimizing the 1DMA2P and AEEA concentrations, this biphasic solvent achieved superior phase separation and excellent absorption and regeneration performance. The proportion of CO2-rich phase was 66.67 %, with a CO2-rich phase loading of up to 5.07 mol/L. The desorption rate was improved by 106.7 % compared to that of conventional 5 mol/L monoethanolamine, and the regeneration efficiency up to 71.8 % in 60 min. Initially, CO2 reacted with AEEA at a faster rate to form a carbamate product. Subsequently, 1DMA2P acted as a proton acceptor, facilitating the formation of bicarbonates and carbonates. Nuclear magnetic resonance analysis indicated that the reaction products (AEEACOO-, AEEAH+, and HCO3–/CO32–) migrated to one phase, whereas 1DMA2P and any unreacted AEEA migrated to the other phase. Additionally, the disparity in polarity between the reactants and reaction products constituted the primary determinant for the phase transition. Notably, the regeneration heat of the 1DMA2P/AEEA biphasic solvent (1.83 GJ/t CO2) was approximately 54.1 % lower than that of conventional 5 mol/L monoethanolamine. Owing to its superior absorption properties, excellent regeneration performance, and low regeneration heat, the 1DMA2P/AEEA biphasic solvent is a promising candidate for practical CO2 capture systems.

Energy-efficient biphasic solvents for industrial CO2 capture: Absorption mechanism and stability characteristics

The traditional CO2 capture process represented by monoethanolamine has excessive energy consumption, serious oxidative degradation and metal corrosion, which limits its potential for large-scale industrial applications. This study produced a highly effective biphasic 3-amino-1-propanol (MPA)–polyethylene glycol dimethyl ether (NHD)–H2O absorbent with easy modulation of phase separation and low levels of oxidative degradation and metal corrosion. The principal absorbent was MPA, and NHD served as the phase separation solvent. NHD's solvent effect decreased the energy barrier preventing MPA from forming zwitterions (MPA+COO−) and carbamate, thus promoting chemical absorption. The large polarity difference between the reaction products and NHD triggered phase separation, producing a low-polarity CO2-lean phase and a high-polarity CO2-rich phase; 97.41% of the absorbed CO2 accumulated in 43.7% of the CO2-rich phase solution. The sensible heat and latent heat of the MPA–NHD–H2O absorbent were relatively low because of the low saturation vapor pressure, high vaporization enthalpy, and excellent phase separation performance of NHD. The regeneration energy was as low as 2.66 GJ/t CO2, which was 30% less than that for monoethanolamine. Additionally, the oxidative degradation rate for the proposed absorbent was only 10.7% of that for monoethanolamine. This study provides a theoretical reference for application of the MPA–NHD–H2O biphasic absorbent.

Biphasic solvents based on dual-functionalized ionic liquid for enhanced post-combustion CO2 capture and corrosion inhibition during the absorption process

To reduce the energy consumption for solvent regeneration and mitigate the corrosiveness of saturated solvents, dual-functionalized ionic liquid (IL) [DMAPA][TZ] was synthesized as a primary absorbent, and mixed with a phase separation accelerator poly (ethylene glycol) dimethyl ether (NHD) or propylene carbonate (PC) as biphasic solvents, to achieve high efficiency, energy savings, and corrosion inhibition of post-combustion CO2 capture. The results demonstrated a transition from a homogeneous solvent to a biphasic system upon CO2 absorption, with the majority of CO2 being concentrated in the rich phase, which is related to the formation of hydrogen bonds. Molecular dynamics analysis showed that interaction between the IL and PC is significantly stronger than that with NHD, resulting in a reduced absorption capacity of IL-PC relative to IL-NHD, while NHD effectively suppressed the formation of HCO3−/CO32−. At 373 K, both solvents exhibited efficient regeneration of their respective rich phases within 10 min. The calculated absorption enthalpies for IL-NHD and IL-PC are remarkably low at 0.662 and 0.772 GJ·t−1, respectively, and the regeneration energy consumption of IL-NHD was lower to 1.387 GJ·t−1. Notably, the phase separation accelerator exerts a significant influence on the phase-transition behavior and absorption products of biphasic solvents. Furthermore, ILs effectively inhibited corrosion through the adsorption-passivation mechanism; specifically, the corrosion rate of the CO2-rich phase in IL-NHD relative to 20# carbon steel was only 0.1896 mpy, which is only 1/865 of the rate of the saturated 5 M MEA solution.

Experimental study on CO2 capture by MEA/n-butanol/H2O phase change absorbent.

Monoethanolamines (MEAs) are widely used for CO2 capture, but their regeneration energy consumption is very high. CO2 Phase change absorbents (CPCAs) can be converted into CO2-rich and CO2-lean phases after absorbing CO2, and the regeneration energy consumption can be reduced because only the CO2-rich phase is thermally desorbed. In this paper, a novel CPCA with the composition "MEA/n-butanol/H2O (MNBH)" is proposed. Compared with the reported MEA phase change absorbent, the MNBH absorbent has higher CO2 absorption capacity, smaller absorbent viscosity and CO2-rich phase volume. The MNBH absorbent has the highest CO2 absorption capacity of 2.5227 mol CO2 per mol amine at a mass ratio of 3 : 4 : 3. The CO2 desorption efficiency reaches 89.96% at 120 °C, and the CO2 regeneration energy consumption is 2.6 GJ tCO2-1, which is about 35% lower than that of the 30 wt% MEA absorbent. When the mass ratio of MNBH absorbent was 3 : 6 : 1, the CO2 recycling capacity was 4.1918 mol CO2 L-1, which is 76% higher than that of the conventional 30 wt% MEA absorbent. The phase change absorbent developed in this paper can reduce the desorbent volume by about 50% and has good absorption performance for CO2 in flue gas.

A low energy-consuming phase change absorbent of MAE/DGM/H2O for CO2 capture

The concept of phase change absorbents has been widely studied as a novel and low-energy consumption option for CO2 capture. This work screened diethylene glycol dimethyl ether (DGM) from 17 physical solvent species as a better phase change accelerator for absorbents of 2-(methylamino)ethanol (MAE)-physical solvent-H2O. Then, the optimized mass ratio of 30:49:21 for MAE-DGM-H2O solution was investigated with phase change behaviors, CO2 absorption–desorption performance, cyclic capacity, and energy consumption. The experimental results showed that the cyclic CO2 capacity reached 1.32 mol/L and the CO2-rich phase made up only 50.4 % of the total volume for the 30 wt%MAE-49 wt%DGM-21 wt%H2O, as well as its regenerative energy consumption was 40 % lower than that of 30 wt% monoethanolamine (MEA) solution. Also, the viscosity and surface tension gap of the CO2-rich phase and CO2-lean phase for the optimized absorbent were studied. It was observed that those gaps increase with the increasing mass ratio of DGM. In addition, the possible phase change mechanism was proposed by using the dipole moment values of components calculated by Gaussian (B3LYP/6-31G) coupled with 13C NMR spectra.

Research of novel polyamine-based biphasic absorbents for CO2 capture using alkanolamine to regulate the viscosity and mechanism analysis

Biphasic solvent has attracted widespread attention in CO2 chemical absorption technology due to its significant potential for reducing capture energy consumption. However, the high viscosity of CO2-rich phase after phase split could lead to issues such as high flow resistance, low heat transfer efficiency, and phase separation instability in application. To address these limitations, a strategy of using alkanolamine as a viscosity regulator for biphasic solvents was proposed. Diethanolamine(DEA), an alkanolamine regulator, was introduced to a system of polyamine/amide absorbent, and then a novel biphasic solvent of diethylenetriamine (DETA)/diethanolamine(DEA)/N, N-Dimethylacetamide(DMAC)/water(H2O) was developed. The viscosity of the CO2-rich phase solvent was reduced to 19.02 mPa⋅s, a significant decrease compared to the solution without DEA regulation. The novel solvent exhibited a high cyclic capacity of 2.08 mol/kg, which was 43.4 % higher than that of the solution without DEA, and a desorption rate twice as high as 30 wt% monoethanolamine(MEA). Quantitative 13C Nuclear Magnetic Resonance (NMR) and Molecular Dynamics (MD) simulations revealed the phase split and viscosity regulation mechanisms. It was proved that DETA species, especially carbamates, tend to self-aggregate with each other due to intermolecular hydrogen bonding with the CO2 loading increases, which leads to phase split and high viscosity of the saturated solution. Through DEA regulation, the protonation of carbamates and the generation of HCO3–/CO32– were promoted, which weakened the self-aggregation of carbamates species, decreasing the viscosity and the regeneration energy of saturated CO2-rich phase solution. The regeneration energy reached 2.19 GJ/ton CO2, which exhibited a 42.4 % reduction compared with that of 30 wt% MEA.

Development of dual-functionalized ionic liquids for biphasic solvents: Enhancing the CO2 absorption through two-stage reaction and promoting the energy-saving regeneration

A dual-functionalized ionic liquid was synthesized by facile neutralizing routes from Diethylenetriamine (DETA) and lysine (Lys), which was designated as [DETA]Lys. It could absorb CO2 through a two-stage reaction, achieving a CO2 capacity of up to 2.16 mol CO2/mol ILs. And N-methyl-2-pyrrolidone (NMP) was validated as a good phase splitting agent for [DETA]Lys-based biphasic solvent by tailoring the polarity and hydrogen bonding effect. Thus, DETA-carbamate, Lys-carbamate, and HCO3−/CO32− were formed during CO2 absorption and gathered in the lower layer, while most of the NMP stayed in the upper layer. Finally, the CO2-rich phase took up 53.84 % of the total volume and 99.03 % of the captured CO2, exhibiting a CO2 loading of 4.78 mol CO2/L. The significantly enhanced CO2 loading (4.78 mol/L), decreased stripping volume (53.84 %), and reduced desorption energy (1.28 GJ/ton CO2) allowed for a great reduction in regeneration energy to 1.89 GJ/ton CO2, which was merely 47.37 % of 5 M MEA (3.80 GJ/ton CO2). The regeneration efficiency of the solvent remained at 91.5 % after the 3rd absorption/desorption cycle. Furthermore, the corrosion speeds of the rich and lean phases were merely 0.18 % and 12.35 % of 5 M MEA. The excellent CO2 capture performance and good energy-saving potential enabled the [DETA]Lys + NMP + H2O system an effective absorbent for carbon capture.

Modelling phase equilibria in the CO2/CH4-H2O-NaCl system using the association equation of state

A new association model, CPA-MHV1, is developed by combining the Soave-Redlich-Kwong (SRK) equation of state (EoS) with the Cubic-Plus-Association (CPA) EoS based on Michelsen's improved Huron-Vidal mixing rule. The model is utilized to investigate the vapor-liquid equilibrium (VLE) of binary mixtures involving methane (CH4), carbon dioxide (CO2), and water (H2O) binary mixtures, as well as ternary mixtures containing sodium chloride (NaCl). CO2 is modeled as a non-associating, non-self-associating (solvation in water) component and as a self-associating component with two, three, or four association sites; furthermore, CH4 is modeled as a non-associating and pseudo-associating component. In the regression of the adjustable parameters, dependence on temperature is considered and the parameters are fitted as functions of temperature. The results demonstrate that the best performance is achieved when solvation between CO2 and H2O is considered, with the average absolute relative deviation (AARD) of 4.50 % in the H2O-rich phase, 5.48 % in the CO2-rich phase, and 3.28 % in NaCl solution. CH4 with pseudo-association scheme has the highest comprehensive prediction performance, and AARD values in H2O-rich phase, CH4-rich phase and NaCl solution are 5.26 %, 5.90 % and 9.19 %, respectively.

High-pressure melting in metapelites of a 2 Ga old subducted oceanic crust (Usagaran belt, Tanzania): implications from melt inclusions, fluid inclusions and thermodynamic modelling

Investigation of polymineralic melt inclusions preserved in garnet of eclogite-facies metapelites of the Usagaran belt, Tanzania, is of particular importance as these metapelites, intercalated in oceanic metabasites, document the rare case of partial melting at high temperatures in a subducted oceanic crust. With an age of 2 Ga the rocks represent one of the oldest oceanic crusts and confirm a subduction process already at Paleoproterozoic times. Partial melting probably was initiated by dehydration melting under the presence of a CO2-rich fluid phase. The melt is preserved in siliceous polymineralic inclusions, while CO2 locally reacted with the garnet host to form dolomite-quartz-kyanite inclusions. During this reaction, the REE spectrum of garnet is adopted by the dolomite. Furthermore, graphite inclusions in garnet must have precipitated from the CO2 fluid by reduction. The highly ordered graphite structure indicates a formation temperature of at least 700 °C. Rehomogenization experiments of the siliceous polymineralic inclusions yield a homogeneous melt of rhyolitic, peraluminous composition. Thermodynamic modelling enables to deduce a P–T path in accordance with high P–T conditions (minimum 2.0 GPa, 900 °C) where a partial melt formed due to phengite breakdown leading to the preserved peak mineral assemblage garnet, alkali feldspar, kyanite, quartz and rutile. A very fast uplift of the oceanic crustal rocks can be deduced from the occurrence of very finely exsolved metastable ternary feldspar and from the preserved prograde zoning in garnet.

Novel biphasic solvent based on 2MPRZ absorbent for post-combustion CO2 capture with low viscosity, superior phase-splitting behavior and low energy consumption

The CO2 phase change absorbents(CPCAs) formed by introducing phase-splitting agents have attracted increasing attention because of their great energy-saving potential. However, the volatilization problem of the phase-splitting agents and the high viscosity of the solution affect the application of CPCAs. In this work, a novel CPCAs based on 2-Methylpiperazine (2MPRZ)/H2O was established by introducing triethylene glycol monobutyl ether (TGBE) with a high boiling point as a phase-splitting agent, and the 2MPRZ/H2O/TGBE system exhibited low volatility and low viscosity. The CO2 capture performance of the novel CPCAs with different ratios was investigated in this work. The best CO2 absorption rate was achieved by 2.5 M 2MPRZ/H2O/TGBE. The viscosity of this system before and after the CO2 absorption process was merely 7.68 mPa·s and 11.64 mPa·s, respectively, and no volatilization of the phase-splitting agent was observed simultaneously. A convenient and rapid titration method was employed to determine the distribution of the 2MPRZ products in the two phases, which showed that 98 % of the 2MPRZ products were located in the CO2-rich phase. In addition, the CO2-rich phase captured 99 % of the total CO2, indicating that this system has superior phase-splitting behaviors. The regeneration energy consumption of this biphasic absorbent was 2.59 GJ/t CO2, which was 32.6 % lower than that of traditional MEA. Furthermore, the salting-out effect was proved to be the cause of the phase-splitting behavior by 13C NMR analysis.

Influence of ionic liquid on polar organic compounds solubility in dense CO2 phase

Accurate measurement and prediction of the phase behaviour of mixtures involved in a chemical process are crucial for its optimisation. Given the importance of CO2 conversion technologies and considering possible benefits of CO2-ionic liquid biphasic systems, i.e., facilitating a product separation, we investigated the high-pressure behaviour of components of interest in a recently developed process of cyclic carbonate synthesis directly from CO2 and potentially bio-based alcohols. The solubility of 1,2-butanediol and 1,2-butylene carbonate in a dense carbon dioxide phase was determined experimentally at the temperature of 313.2 K and pressures between 6 and 18 MPa. The influence of 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ionic liquid, [hmim][FAP], as a solvent, on the solubility of these compounds in CO2-rich phase, in ternary (CO2 + 1,2-butanediol + [hmim][FAP]), CO2 + butylene carbonate + [hmim][FAP]) and quaternary (CO2 + 1,2-butanediol + butylene carbonate + [hmim][FAP]) mixtures was investigated. The experimental results of the two binary systems were correlated using the density-based Chrastil equation. The knowledge of phase equilibria behaviours reported in this work will be useful for designing chemical conversions of carbon dioxide using [hmim][FAP] ionic liquid as reaction solvents.

Effect of water on CO2 absorption by a novel anhydrous biphasic absorbent: Phase change behavior, absorption performance, reaction heat, and absorption mechanism

The ionic liquids (ILs)-based biphasic absorbents are viewed as promising substitutes for CO2 capture due to their remarkable CO2 absorption performance, excellent stability and low energy requirement for regeneration. Further decreasing the regeneration heat requirement can be achieved by utilizing ILs-based anhydrous biphasic absorbents, whose solid CO2-rich phase contained small volume and low specific heat capacity. Given the high hygroscopicity of ILs and the water present in the flue gas, comprehending the effect of water is crucial for post-combustion carbon capture using ILs-based anhydrous biphasic absorbents. In this work, the effect of water on CO2 absorption by an anhydrous biphasic absorbent, tetramethylammonium glycinate ([N1111][Gly])/ethanol, was studied. The experimental results demonstrated that the CO2 loading and absorption rate were decreased in the presence of water, but the CO2 desorption efficiency was enhanced. Besides, the presence of water slightly reduced the reaction heat of CO2 absorption by [N1111][Gly]/ethanol to 69.48 kJ/mol CO2, which was 20% lower than that of monoethanolamine (MEA) absorbent. Furthermore, the 13C NMR results indicated that the primary CO2-product was bicarbonate in the presence of water rather than carbamate. There were three possible pathways for bicarbonate generation: zwitterion hydrolysis, carbamate hydrolysis, and base-catalyzed CO2 hydration. Water and ethanol competed to react with carbamate. When a large amount of water was present (≥70 wt%), the reaction of ethanol with the carbamate hardly occurred.