CO2 In Ionic Liquids Research Articles

Wettability regulation of the electric double-layer structural evolution of complex fluids: Insights into thermodynamic and electrical properties

Understanding the structural evolution at the electrode is essential for accurate prediction of complex fluid applications, where the carbon nanotube is chosen as the carrier of CO2-ionic liquids (ILs) in electroreduction. Then, the electrical double layer with tunable wettability is investigated by molecular dynamics simulations. The competition and cooperation between van der Waals and Coulomb interactions are evaluated by examining the structural and electric characteristics. When an external potential (φ) is initiated, the co-ions are repelled from the electrode and the counter-ions compete with CO2 in the electric double layer (EDL), with different thermodynamics produced by varying the proportion of CO2/ionic liquid. As the solid–liquid interaction parameter (β) increases, more counter-ions aggregate, producing double density peaks for Tf2N− and sharply increasing the density of CO2. With increases in β and φ, the local charge density and local field potential increase, and the EDL thickness decreases. However, the location of the CO2 density layer shifts ahead to the counter-ions, weakening their shielding effect and capacitance. Using a combination of structural analysis, the first and second peaks of Tf2N− of EDL are composed of sulfonyl and trifluoromethyl, respectively. As a response, the steric hindrance of CO2 decreases, and more molecules migrate to the surface in a parallel orientation. The structural evolution is quantitatively evaluated in terms of the entropy, results show that the orientation transition is prominent in structural evolution. The coupling relation between thermodynamic and electrical properties plays a pivotal role in determining the structural evolution of complex mixtures, and these findings could benefit the advancement of ILs-based CO2 electroreduction and other complex fluid applications.

Prediction of solubility of CO2, H2S, and their mixture in ionic liquids using the Cubic Two State equation of state

In this work, the capability of the Cubic Two State (CTS) equation of state (EoS) has been evaluated using the solubility of carbon dioxide (CO2), hydrogen sulfide (H2S), and their mixture in ionic liquids (ILs). The imidazolium-based ILs with [BF4], [PF6], and [Tf2N] anions have been studied. The self-association between IL molecules, CO2, and H2S molecules has been considered to optimize the pure model parameters. In addition to self-association between similar molecules, the cross-association between CO2-IL and H2S-IL in the binary mixtures has been considered. The results show that the CTS EoS can predict (kij=0.0) the solubility of H2S and CO2 in ILs ranging from 1 to 1000 bar satisfactory. The average ARD value for binary CO2-IL and H2S-IL systems has been obtained 20.3 % and 9.02, respectively. The CTS model has been used to predict the phase behavior of ternary systems containing CO2H2S-[C4mim][PF6], CO2H2S-[C8mim][PF6], and CO2H2S-[C8mim][Tf2N] at various temperatures. Finally, the CTS results have been compared to soft-SAFT and PC-SAFT EoSs. The results show that simple association contribution and the cubic term of the CTS EoS can model the molecular interactions between gases and ILs satisfactory. The CTS model can be considered as a robust and efficient thermodynamic model for the prediction of separation of CO2 and H2S using ILs.

Quantitative structure‐property relationship techniques for predicting carbon dioxide solubility in ionic liquids using machine learning methods

AbstractIonic liquids (ILs) are considered unique and attractive types of solvents with great potential to capture carbon dioxide (CO2) and reduce its emissions into the atmosphere. On the other hand, carrying out experimental measurements of CO2 solubility for each new IL is time‐consuming and expensive. Whereas, the possible combinations of cations and anions are numerous. Therefore, the preparation and design of such processes requires simple and accurate models to predict the solubility of CO2 as a greenhouse gas. In the present study, two different models, namely: artificial neural network (ANN) and support vector machine optimized with dragonfly algorithm (DA‐SVM) were used in order to establish a quantitative structure–property relationship (QSPR) between the molecular structures of cations and anions and the CO2 solubility. More than 10 116 CO2 solubility data measured in various ionic liquids (ILs) at different temperatures and pressures were collected. 13 significant PaDEL descriptors (E2M, MATS8S, TDB6I, TDB1S, ATSC4V, MATS8M, ATSC7V, Gats2S, Gats5S, Gats5C, ATSC6V, DE, and Lobmax), temperature and pressure were considered as the model input data. For the test set data (2023 data point), the estimated mean absolute error (MAE) and R2 for the ANN model are of 0.0195 and 0.9828 and 0.0219 and 0.9745 for the DA‐SVM model. The results obtained showed that both models can reliably predict the solubility of CO2 in ILs with a slight superiority of the ANN model. Examination of sensitivity and outlier diagnosis examinations confirmed that the QSPR model optimized using the ANN algorithm is better suited to correlate and predict this property.

Effects of different alkyl chain lengths on excess properties of CO2-1-Butyl-1-methyl-pyrrolidinebis(trifluoromethanesulfonyl)imide, CO2-1-hexyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, CO2-1-octyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide systems

The study investigates the solubility of carbon dioxide (CO2) in three ionic liquids [BMP][Tf2N] (1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide), [HMP][Tf2N] (1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide) and [OMP][Tf2N] (1-octyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide). The research is conducted over a temperature range of 303.15 to 363.15 K. The phase equilibria of the binary systems are predicted using the Peng-Robinson (PR) equation of state, the Wilson (WS) mixing rule and the UNIFAC activity coefficient model. The interaction parameter kij is regressed from the vapor-liquid equilibrium (VLE) experimental data. The study also calculates the excess Gibbs free energy (GE), excess enthalpy (HE), and excess entropy (SE) for these systems. The research results indicate that the length of the alkyl chain in the cation has a significant effect on the excess properties of the CO2-ionic liquid systems. As the alkyl chain length increases, the excess Gibbs free energy and excess enthalpy decrease, while the excess entropy increases. The CO2-[OMP][Tf2N] system exhibits stronger interactions between CO2 and the ionic liquid, indicating a higher capacity for CO2 absorption. The study results are helpful for optimization of CO2 capture processes and the broader comprehension of fluid phase equilibria in complex systems.

Extensive data analysis and modelling of carbon dioxide solubility in ionic liquids using chemical structure-based ensemble learning approaches

The significant rise in carbon dioxide (CO2) emission due to industrial growth is a major global challenge. As a result, there is a need to implement various techniques to reduce and regulate this phenomenon. One such technique involves the utilization of ionic liquids (ILs) as solvents in CO2 capturing and separation processes, which is already commonly practiced. In this study four advanced intelligent models, Extreme Gradient Boosting (XGBoost), Gradient Boosting (GBoost), Light Gradient Boosting Machine (LightGBM), and Categorical Boosting (CatBoost) have been proposed to predict the solubility of CO2 in 160 different ILs based on factors such as temperature, pressure, and the chemical structure of the ILs. Findings indicate that the XGBoost model is the most accurate among the four models, with the root mean square error (RMSE) and coefficient of determination (R2) values of 0.014 and 0.9967, respectively. Moreover, the results reveal that increasing pressure, decreasing temperature, and lengthening the alkyl chain all increase the solubility of CO2 in ILs. Furthermore, pressure and the number of –CH2 substructure in ILs have the most significant impact on the CO2 solubility in ILs, respectively. To ensure the XGBoost model's reliability, the model's data has been assessed using the leverage technique. The results show that 92.44 % of the data fell within the valid area, which is a substantial percentage and indicates the model's high reliability. The findings of this study will assist in designing and fine-tuning the chemical structure of ionic liquids specifically for CO2 capture purposes.

Study on characteristics of wet compression-absorption refrigeration cycle with CO2-ionic liquid mixture

The novel wet compression-absorption (WCA) refrigeration cycle with CO2-ionic liquid mixture can bring a new solution for the development and promotion of CO2 in the refrigeration field, but the depressurization mechanism of this cycle still needs further research. Based on the vapor-liquid equilibrium data of CO2-[emim][Tf2N] mixture, the p-h diagrams of CO2-[emim][Tf2N] mixture with the specific global CO2 mole fraction were first calculated and constructed. The cycle flow of WCA refrigeration cycle with CO2-[emim][Tf2N] mixture was plotted on the diagram, the cycle characteristics and depressurization mechanisms of this cycle were analyzed. The results show that there is a temperature slip in the CO2-ionic liquid mixture during the absorption/desorption process. Both strengthening the effectiveness of cooling measures and increasing the proportion of ionic liquid in the mixture can further reduce the operating pressure at the high-pressure side, but the latter may cause a reduction in the cycle refrigeration performance and energy efficiency. For the WCA refrigeration cycle with CO2-ionic liquid mixture, it is crucial to equip an internal heat exchanger, which can significantly improve the corresponding refrigeration capacity and energy efficiency. This study can provide important references for the design and optimization of WCA refrigeration system using a CO2-ionic liquid mixture.

Solubility and diffusivity of CO2 and C2H4 in the ionic liquids 1-alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide by tube-in-tube reactor method

In this paper, the solubility and diffusivity of CO2/C2H4 in ionic liquids 1-Ethyl-2,3-dimethylimidazolium Bis(trifluoromethanesulfonyl)imide([Emmim][Tf2N]), 1-Propyl-2,3-dimethylimidazolium Bis(trifluoromethanesulfonyl)imide([Pmmim][Tf2N]), 1-Butyl-2,3-dimethylimidazolium Bis(trifluoromethanesulfonyl)imide([Bmmim][Tf2N]) and 1-Hexyl-2,3-dimethylimidazolium Bis(trifluoromethanesulfonyl)imide([Hmmim][Tf2N])) are measured at the temperature range of 303–333 K with a tube-in-tube reactor. The new device can greatly decrease the measurement time to several minutes in the tube-in-tube reactor. The solubility data is determined by the steady-state method with less than 10% deviation compared with previous reports. The diffusivity data is measured by an unsteady-state method within 3 min. The diffusion coefficient of CO2 in ionic liquids can be predicted with Morgan’s diffusivity correlation equation. For the diffusivity of C2H4 in ionic liquids, an empirical formula is developed and the predicted values using this correlation agree well with measured values with less than 17% deviation. The measured solubility and diffusivity data of CO2/C2H4 in ionic liquids and corresponding correlations can help to develop a more efficient process involving CO2/C2H4/ionic liquids system.

Loosely bonded dual-functionalized ionic liquid-based phase change solvent for energy-saving CO2 capture

A phase change solvent based on a novel loosely bonded dual-functionalized ionic liquids (ILs) containing diethylenetriamine (DETA) and 1-methylimidazole (1-MI), namely [DETA][1-MI], was developed. The strong anion–cation interactions in an ILs inhibited the CO2–ILs interaction and decrease the absorption capacity of the ILs. The weak interaction of [DETA][1-MI] retained most of the absorption capacity of DETA and 1-MI (up to 2.06 mol CO2/mol ILs). When simulated flue gas was fed into the [DETA][1-MI] + dimethylformamide (DMF) + H2O phase change solvent, the CO2-rich phase had a CO2 concentration of up to 6.51 mol CO2/L and a volume ratio of 42.2%. Moreover, a regeneration efficiency of > 90% was maintained even after three regeneration cycles at 393 K. The corresponding regeneration heat (1.40 GJ/ton CO2) was only 36.8% of 30 wt% monoethanolamine (MEA, 3.80 GJ/ton CO2). To the best of our knowledge, it’s well below the reported regeneration energy of amine-based absorbents. In addition, the corrosion rates of the rich and lean phases were only 0.58% and 0.51% of those of the saturated MEA solution, indicating that the corrosivity of [DETA][1-MI] + DMF + H2O was negligible. Moreover, [1-MI]− was observed to promote the formation of m-DETACOO− and HCO3−/CO32−, further enhancing the CO2 absorption capacity. Therefore, the proposed [DETA][1-MI] + DMF + H2O was verified to be a promising absorbent with favorable absorption properties, a low corrosion rate, high cyclic stability, and superior energy efficiency for CO2 capture.

Free volume in physical absorption of carbon dioxide in ionic liquids: Molecular dynamics supported modeling

Understanding the mechanisms underlying the carbon dioxide (CO2) absorption in ionic liquids (ILs) is the key to their efficient utilization in industrial flue gas treatment. One of the parameters considered substantially important in the process is the Free Volume. In this study, the Fractional Free Volume (FFV) of 73 ILs was calculated using Molecular Dynamics (MD). A quantitative Structure-Property Relationship (QSPR) study was then employed to predict the FFV, but the validation parameters were unsatisfactory. In the second part, the importance of Free Volume in the absorption of CO2 in ILs was assessed by creating two models to predict Henry’s Law Constant of CO2 in ILs. It was found that the addition of the FFV parameter considerably improved the statistical parameters and predictability of the QSPR model. Furthermore, FFV was found to be heavily dependent on the cation type and its inclusion allowed for the determination of more subtle molecular interactions.

The Cation Effect on the Free Volume and the Solubility of H2S and CO2 in Ionic Liquids Based on Bis(2-Ethylhexyl) Sulfosuccinate Anion

Herein, we report for the first time a study dedicated to acidic gases' solubility in ionic liquids with sterically hindered bulky anion, namely bis(2-ethylhexyl) sulfosuccinate ([doc]), experimentally evaluated at low pressures. The effect of cation change (imidazolium, pyridinium, and pyrrolidinium) on the thermophysical properties and sorption capacities was also discussed. The densities and the activation energies of the tested ILs exhibited minor differences. Furthermore, the COSMO-RS model was used to predict the free volumes of ILs aiming to investigate its influence on gas solubilities. The conducted calculations have revealed an antibate correlation between the fractional free volume (FFV) and Henry's law constant. In particular, the lowest FFV in 1-methylimidazolium [doc] corresponded to the minimal sorption and vice versa. In addition, it was shown that the presence of protic cation results in a significant reduction in CO2 and H2S solubilities. In general, the solubility measurement results of the synthesized ILs have shown their superiority compared to fluorinated ILs based on the physical absorption mechanism.

Solubility‐Boosted Molecular Sieving‐Based Separation for Purification of Acetylene in Core–Shell IL@MOF Composites

AbstractConsidering the small amount of CO2 as a contaminant in industrial gas mixtures, developing CO2‐selective adsorbents exhibit advantages in directly obtaining pure C2H2 in one‐step to reduce the energy consumption. However, it is still a great challenge due to the essential molecular feature of C2H2, including the triple bond and high polarizability. Herein, a simple but effective CO2‐facilitated transport strategy is presented to realize the overwhelming adsorption of CO2 over C2H2 by constructing core–shell composite structures using ionic liquid (IL) and metal‐organic framework (MOF). With the aid of excellent solubility of CO2 in IL and almost total exclusion of C2H2, the obtained materials boost molecular sieving‐based separation of CO2/C2H2. Density functional theory calculations combining molecular dynamic simulations revealed the solution‐diffusion mechanism for CO2, which is rarely reported in solid adsorbents. Ideal adsorbed solution theory selectivity for CO2/C2H2 with 1/1 and 1/3 volume ratios can reach over 104 and 4000 at 100 kPa with a high CO2 uptake of 40.3 cm3 g−1, superior to those of the reported materials so far. More importantly, this solution‐based separation strategy can avoid the difficulty for precise control of the regulation of adsorbent structure, which may be beneficial to practical production.

Vapor-liquid equilibrium experiment and prediction of excess property of new working pair CO2-[BMP][Tf2N] in absorption refrigeration system: Expérience d'équilibre vapeur-liquide et prédiction de la propriété excédentaire de la nouvelle paire de travail CO2-[BMP][Tf2N] dans un système de réfrigération à absorption

Solubility of CO2 in ionic liquids (ILs) is of great importance in absorption refrigeration system as new working pairs. Vapor-liquid equilibrium (VLE) of CO2 in [BMP][Tf2N] (1-butyl-1-methyl-pyrrolidine bis(trifluoromethylsulfonyl)imide) is carried out experimentally using the experiment system at temperature range 303.15 K-363.15 K. The experimental results show that the solubility of CO2 in [BMP][Tf2N] can reach up to 0.1235–0.5324 (molar fraction) within temperature range 283.15∼363.15 K and pressure range of 0.2∼5 MPa. The solubility of CO2 in [BMP][Tf2N] increases with increase of temperature and pressure. The VLE data of CO2-[BMP][Tf2N] binary system is correlated with two models (SRK equation of state +WS mixing rule +UNIFAC activity coefficient model and PR equation of state +WS mixing rule +UNIFAC activity coefficient model). The excess Gibbs free energy (GE), excess enthalpy (HE) and excess entropy (SE) of the system are obtained and the interaction parameters kij is regressed based on the VLE of CO2-[BMP][Tf2N] binary system. The variation trend of GE, HE and SE are obtained with temperature, pressure and molar fraction of CO2. The calculation results show that the accuracy of SRK equation of state is slightly higher than that of PR equation of state in CO2-[BMP][Tf2N] binary system. The accuracy of SRK equation of state and PR equation of state decreases with increase of temperature and pressure.

Predicting the Thermodynamics of Ionic Liquids: What to Expect from PC-SAFT and COSMO-RS?

Two popular thermodynamic modeling frameworks, namely, the PC-SAFT equation of state and the COSMO-RS model, are benchmarked for their performance in predicting the thermodynamic properties of pure ionic liquids (ILs) and the solubility of CO2 in ILs. The ultimate goal is to provide an illustration of what to expect from these frameworks when applied to ILs in a purely predictive way with established parametrization approaches, since the literature generally lacks their mutual comparisons. Two different modeling approaches with respect to the description of the molecular structure of ILs are tested within both models: a cation-anion pair as (i) a single electroneutral supermolecule and (ii) a pair of separately modeled counterions (ion-based approach). In general, we illustrate that special attention should be paid when estimating unknown thermodynamic data of ILs even with these two progressive thermodynamic frameworks. For both PC-SAFT and COSMO-RS, the supermolecule approach generally yields better results for the vapor pressure and the vaporization enthalpy of pure ILs, while the ion-based approach is found to be more suitable for the solubility of CO2. In spite of some shortcomings, COSMO-RS with the supermolecule approach shows the best overall predictive capabilities for the studied properties. The ion-based strategy within both models has significant limitations in the case of the vaporization properties of ILs. In COSMO-RS, these limitations can, to a certain extent, be surpassed by additional quantum mechanical calculations of the ion pairing in the gas phase, while the ion-based PC-SAFT approach still needs a sophisticated improvement to be developed. As an initiating point, we explore one possible and simple route considering a high degree of cross associations between the counterions in the gas phase.

Molecular screening of ionic liquids for CO2 absorption and molecular dynamic simulation

Abstract Though ionic liquids (ILs) are considered potential materials for CO2 capture because of their unique properties, it is time-consuming and costly to choose task-specific and suitable IL using the traditional “try-and-error” method. From the point of molecular design view, 25 cations and 20 anions are combined and screened using COSMOtherm to predict CO2 solubility at 298 K and 100 kPa. The prediction result showed that ILs with bFAP(tris(nonafluorobutyl)trifluorophosphate) anion could dissolve more CO2 than any others. To further understand the absorption performance of CO2 in ILs, molecular dynamic simulations are carried out to explore the interactions between CO2 and the four selected ILs, namely, [EMPyr][bFAP](1-ethyl-2-methylpyrazolium tris(nonafluorobutyl)trifluorophosphate), [B(Hex)3P][bFAP](butyl-trihexyl-phosphonium tris(nonafluorobutyl) trif-luorobutyl trifluorophosphate), [(Me)5isobuGua][bFAP](n,n,n,n,n-pentamethyl-n-isopropylguanidinium tris(nona-fluorobutyl)-trifluorophosphate), and [BEIM][bFAP] (1-butyl-3-ethyl-imidazolium tris(nonafluorobutyl)trifluo-rophosphate), at the atomic and molecular levels.

Exploring the potential energy surface of nCO2 (n = 1–5) capture by imidazole-and fluorine-based ionic liquids: A DFT study

One of the reasons for global warming is the rising of greenhouse gasses causing the planet's temperature to increase; among these gases, CO2 accounts for 80%. For this reason, it is essential to contemplate environmentally sustainable alternatives for CO2 capture and storage, such as the use of ionic liquids (ILs), which represent an excellent option due to their high affinity for CO2. This theoretical study considered ILs based on imidazole ([bmim]+ and [emim]+) and fluorinated ([TFSI]- and [PF6]-) dimers, thorough exploration of the potential energy surfaces of nCO2[bmim]+[PF6]−, nCO2[emim]+[TFSI]−, nCO2[bmim]+[PF6]− and nCO2[emim]+[TFSI]− molecular clusters, n = 1–5, by using a stochastic SnippetKick searching algorithm. Followed by the optimisation of the molecular cluster geometries using Density Functional Theory (DFT) calculations to describe the effect of physisorption of up to five CO2 in ILs. It was revealed an aggregation of CO2 molecules between the imidazole ring and the anion, mainly surrounding [TFSI]- or [PF6]-, in the form of an orbital in putative global minimum-energy structures, which allows a higher CO2 physisorption. Finally, a detailed analysis of the thermodynamic properties and intermolecular interactions between ILs and CO2 molecules was performed with different approximations of the electron density scalars. Overall, this confirms the use of the ILs studied to capture CO2 efficiently.

Electroreduction of low concentration CO2 at atomically dispersed Ni-N-C catalysts with nanoconfined ionic liquids

Most studies on electrochemical CO2 reduction reaction use pure CO2, which requires extra energy for CO2 capture and enrichment from atmosphere. Herein, nanoconfined ionic liquids are introduced into porous atomically dispersed nickel-nitrogen-carbon (Ni-N-C) catalysts to enrich local CO2 concentration and increase the CO2RR kinetics. A series of high-CO2-solubility ionic liquids (ILs) were impregnated into the pores of the columnar Ni-N-C catalyst to alter the CO2-Ni sites interactions and create a solid/liquid interface with high CO2 concentration. The optimal Ni-N-C/[Bmim][PF6] composite outperforms the Ni-N-C catalyst for pure CO2 electroreduction with a maximum FECO of 99.6% and 2.7-fold larger jCO. The high solubility of CO2 in ILs compared to aqueous electrolyte enables direct electrolysis of CO2 at low concentrations. When fed with 5–10% (v/v) CO2, the Ni-N-C/[Bmim][PF6] composite exhibited up to 1.5-fold higher FECO and a 68% increase of jCO, in comparison to Ni-N-C, and robust stability over 30 h.

Investigation of the intermolecular voids at the dissolution of CO2 in ionic liquids

Empty intermolecular volume in pure liquids and solutions is an important factor determining the mobility of molecules and the ability to dissolve other substances. The investigation of computer models gives insight into the role of intermolecular voids in these processes. In this work, we demonstrate an application of the Voronoi-Delaunay method to describe quantitatively the voids in ionic liquids on the example of the dissolution of carbon dioxide. Molecular dynamics models of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Cnmim][NTf2]) ionic liquids (ILs) with different lengths of the alkyl substituent n (from 2 to 8 carbon atoms in the alkyl chain), as well as their mixtures containing CO2 at different concentrations have been studied. The contributions of the anions and the cations to the empty volume of the pure ILs and the mixtures are studied. It was shown that the increase in the empty volume with the growth of the alkyl substituent length of the cation is mainly determined by the methyl groups of the substituent, while the empty volume related to the anions and the imidazole ring of the cations practically does not change. CO2 molecules add additional empty volume to the mixture, instead of filling available voids preliminarily formed in a pure IL. The apparent molar volume of CO2 molecules in the studied ILs exceeds their intrinsic volume, defined as their Voronoi volume. However, the distribution of the interstitial spheres radii remains practically the same in the pure ILs and in the mixtures. Moreover, the radial distribution of large intermolecular voids (comparable to the size of a CO2 molecule) in pure ILs does not correspond to the real distribution of CO2 molecules in the mixtures.

Characteristics of CO2-ionic liquids/PEG200 as new working pairs for absorption-compression refrigeration system

Absorption-compression refrigeration system using CO2-Ionic Liquids (ILs) as working pairs could avoid the high operating pressure in transcritical CO2 refrigeration cycle. This work proposed using PEG200 as the additive to improve the physical properties of the pure ILs, making the absorption-compression refrigeration system being more efficient and less corroded. The effects of PEG200 on the CO2-ILs absorption and desorption, the viscosity and the corrosion behavior on stainless steel were investigated experimentally. Results show that PEG200 has positive effect on these key parameters at temperature of 293.15 K to 343.15 K and pressures up to 10.0 MPa. The addition of PEG200 to [emim][FAP] could increase the CO2 solubility by 10.17% maximally, reduce the viscosity by 24.43% maximally, and accelerate the desorption rate. The CO2 solubility increases with the pressure increasing, and decreases with the temperature increasing. The viscosity of the mixed solvent decrease with the increase of the temperature and pressure. The addition of PEG200 to [emim][Tf2N] effectively weakens the corrosion on the 316L stainless steel, the corrosivity of ILs/PEG200 is less than that of the pure ILs. This work shows ILs with PEG200 added have better physical properties as the CO2 absorbent, providing a new approach of selection for CO2 absorption.

Thermodynamic analysis of carbon dioxide hydrogenation to formic acid and methanol

Direct hydrogenation of carbon dioxide (CO2) to formic acid is unfavorable thermodynamically, which makes its production limited. In this study, a thermodynamic analysis of CO2 hydrogenation to binary product systems of methanol and formic acid promoted by ionic liquid (IL) (1-ethyl-2,3-dimethylimidazolium nitrite, ([Edmim][NO2]) is presented. The analysis is conducted in Aspen Plus using the Gibbs energy minimization approach combined with a vapor–liquid equilibrium (VLE) for the solvation of CO2 in IL. It is demonstrated that solvating CO2 in ILs is an attractive alternative to overcome the thermodynamic difficulty associated with the product yield, especially formic acid. The [Edmim][NO2] promoted system is very effective for the simultaneous production of formic acid and methanol at 25 °C and 17 bar with a yield of 35% formic acid and 30% methanol at a CO2/H2/IL ratio of 1/2/2. The results show a marked improvement in the yield of formic acid to other previously conducted studies on formic acid production.

Study on viscosity characteristics of CO2-ionic liquid mixture used for compression-absorption refrigeration systems

To provide a suitable absorbent for the carbon dioxide (CO2) compression-absorption refrigeration (CAR) system and promote the development of this system, the viscosities of CO2 + 1-ethyl-3-methylimidazolium tris(perfluoroethyl)trifluorophosphate ([emim][FAP]) and CO2 + 1-hexyl-3-methylimidazolium tris(perfluoroethyl)trifluorophosphate ([hmim][FAP]) mixtures at vapor-liquid equilibrium were measured within the temperatures of 303.15–343.15 K and pressures of 1–10 MPa. The effects of CO2 solubility, pressure, temperature and ionic liquid structure on the mixture viscosity were investigated. The results showed that the mixture viscosity decreased with the increase of pressure and temperature. The longer the cationic alkyl chain of ionic liquid was, the larger the viscosities of ionic liquid and the corresponding mixture after absorbing CO2 were. But the mixture viscosity was less affected by the ionic liquid structure with the increase of temperature and pressure. The dissolution of CO2 could effectively reduce the mixture viscosity, to below 5.5 cP at most. Considering the CO2 absorption performance of ionic liquid and the viscosity of corresponding mixture, [hmim][FAP] is more suitable for the CO2 CAR system. In addition, to accurately predict the mixture viscosity within a certain working conditions for subsequent theoretical research of this system, an improved Grunberg equation was obtained by correlating the measured data and introducing the pressure factor. The overall average relative deviation between the calculated and measured data was 9.33%. The equation can be used to calculate the viscosity of the above CO2-ionic liquid mixtures.