Absorption Of Ionic Liquids Research Articles

Dynamic and interfacial properties for dichloromethane absorption in ionic liquids: Experimental and molecular dynamic insights

In this study, a strategy for dichloromethane (DCM) capture using ionic liquids (ILs) was systematically investigated from the perspective of dynamic analysis. The diffusion coefficient, Henry’s law constant (H), saturated absorption capacity, and overall volumetric liquid-side mass-transfer coefficient (KLao) of four types of ILs were obtained. Among all the ILs studied, tetrabutylphosphonium caproate ([P4444][C5COO]) demonstrated superior DCM absorption capabilities, and its corresponding H value (3.13 Pa m3/mol at 25 °C) was markedly lower than those of solvents documented in the literature. Furthermore, its KLao value was determined to be 2.77 × 10−3/s at 25 °C, which was measured in a customized cylindrical absorption bottle with a height of 150 mm and an inner diameter of 16 mm. The absorption bottle, fitted with a gas inlet tube having an inner diameter of 5 mm and positioned 5 mm above its base, utilized a simple bubbling technique to introduce gas into the liquid phase, eliminating the need for gas-dispersion equipment. Nevertheless, ILs with high affinities showed relatively high initial mass-transfer rates for DCM. Based on molecular dynamics (MD) simulations, the vapor–liquid interface properties, including mass and number density profiles, molecular orientation, and surface tension, were investigated. This revealed that in the pure [P4444][C5COO] system, the alkyl chain of the anion was oriented toward the gas phase, while the carboxyl group was oriented toward the bulk. The tilt angle of [C5COO]− with respect to the interface was within the range of 37° < θ′ < 70°. For the [P4444][C5COO]/DCM mixture, at the interface, the anion exhibits an enhanced ordered orientation, while the cation shows a more disordered orientation.

Techno-Economic Evaluation of Green NH3 Production by Integrating Current-Assisted Reaction and Ionic Liquid Absorption

Techno-Economic Evaluation of Green NH₃ Production by Integrating Current-Assisted Reaction and Ionic Liquid Absorption

Selective absorption of ionic liquids in separating R-1243zf or R-161 from refrigerant blends

In order to recover and reuse pure refrigerants from the mixtures used in waste refrigeration facility, it is necessary to find a good way for separation. Due to the extremely low vapor pressure and good selectivity, ionic liquids (ILs) are regarded as promising entrainers for the extractive separation process of azeotropic or near-azeotropic mixtures. Phase behavior of refrigerant with ILs is the basic property in the design of selective absorption-separation process. In this work, the solubility of 3,3,3-trifluoropropene (R-1243zf) and ethyl fluoride (R-161) with trihexyltetradecylphosphonium chloride ([P6,6,6,14][Cl]) were measured based on the isochoric saturation method. The experimental temperature range was from 283.15 K to 343.15 K. Five activity coefficient models, including Margules, van Laar, Scatchard-Hamer, Wilson and non-random two-liquid (NRTL) model, were used to correlate the experimental data, and the results were discussed. In addition, based on the literature data, the separation capacities of different ILs for refrigerant blends composed of R-1243zf or R-161 were investigated.

Size Matters: A Computational Study of Hydrogen Absorption in Ionic Liquids.

We combined both density functional theory and classical molecular dynamics simulations to investigate the molecular mechanisms governing hydrogen solvation in a total of 12 ionic liquids. Overall, the analysis of the structural properties under high temperature and pressure conditions revealed weak interactions between hydrogen and the ionic liquids, with a slight preference of this gas to be placed at the apolar domains. Interestingly, those ionic liquids comprising nitrate anions allow the accommodation of hydrogen molecules also in the polar areas. The study of the hydrogen velocity autocorrelation functions supports this observation. In addition, the structure of all of the tested ionic liquids was almost insensitive to the addition of hydrogen, so the available free volume and cavity formation are presumably the most important factors affecting solubility.

Absorption characteristics, model, and molecular mechanism of hydrogen sulfide in morpholine acetate aqueous solution

Absorption characteristics, model, and molecular mechanism of hydrogen sulfide in morpholine acetate aqueous solution

Efficient capture of benzene and its homologues volatile organic compounds with protic [MIM][NTF2] and aprotic [EMIM][NTF2] ionic liquids: Experimental and computational thermodynamics

Using new green solvents to effectively capture volatile organic compounds (VOCs) is considered as an attractive green sustainable chemical development route. In this work, benzene, toluene, ethylbenzene and p-xylene (BTEX) were selected as typical aromatic VOCs. The gas absorption performance of proton [MIM][NTF2] and aprotic [EMIM][NTF2] ionic liquids (ILs) for BTEX were studied by computational thermodynamics combined with gas absorption experiments. Absorption experiments of BTEX and regeneration experiments of ILs were carried out at different temperatures, and ILs had good stability. The interaction type and intensity were determined by Interaction Region Indicator (IRI) analysis of IL-BTEX blend systems. The C-H···π and π-π interaction between imidazole ring and BTEX were the direct reason why ILs can efficiently absorb BTEX. Molecular dynamics simulations were performed to explore the diffusion behavior of gas in ILs. The increase of methyl group increases the interaction strength of the system, and the fractional free volume of IL-BTEX blend systems decreases gradually, which limits the diffusion of BTEX. Non-bond interaction analysis shows that van der Waals interaction was the main driving force of BTEX absorption in ILs.

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.

Vapor-liquid equilibrium of carbon dioxide solubility in a deep eutectic solvent (choline chloride: MDEA) and a mixture of DES with piperazine-experimental study and modeling

In recent decays, many investigators have carried out the CO2 absorption in ionic liquids, but these green solvents are expensive and hard to prepare. In recent years, researchers have introduced deep eutectic (DES) solvents composed of a hydrogen bond donor and a hydrogen bond acceptor. DES melting point is usually lower than the ideal solution of its constituents' components and is in the liquid phase at room temperature. In this work, we have measured CO2 solubility in a deep eutectic solvent composed of choline chloride and methyldiethanolamine (MDEA) in a molar ratio of 1–6. We carried out experiments at 323.15, 333.15, and 343.15 K within the 1–50 bar pressure range. Besides, we added piperazine (Pz) as a physical solvent at 5, 10, and 15 wt% to the DES. Based on the obtained results, we observed enhancing pressure and reducing temperature led to increasing CO2 absorption. Also, increasing piperazine caused to intensify the CO2 absorption in the mixture of the DES + Pz system. Finally, we used a thermodynamic approach for the computation of the vapor–liquid equilibria of the present systems. We applied the Peng-Robinson (PR) equation of state to calculate the gas fugacity coefficient in the vapor phase. The non-random two-liquid (NRTL) activity coefficient model was used to compute the non-ideality of the liquid mixture. The modeling results were in very good agreement with the experimental data.

Research progress of CO2 separation technology by solvent absorption

The combustion of fossil fuels emits a large amount of CO2, which causes the greenhouse effect and leads to global warming and poses a serious threat to life on earth. CO2 capture technology can effectively reduce the concentration of CO2 in the atmosphere, alleviate the greenhouse effect, and improve the environment. CO2 capture technologies include absorption, membrane separation and adsorption separation, among which chemical absorption and separation have the advantages of high efficiency, low cost and easy availability of materials. In this paper, the advantages and disadvantages of three main chemical absorption and separation methods (inorganic reagents, organic amines and ionic liquids) adsorb CO2 are summarized. Among inorganic adsorbents, NH3·H2O can achieve rapid and efficient absorption of CO2, and it is relatively stable and not easy to degrade. Common types of organic amine adsorbents are monoethanolamine, methanolamine, and sterically hindered amine. However, it is difficult for a single organic amine adsorbent to meet the requirements of high absorption rate, high absorption capacity and low reaction heat at the same time. Therefore, mixing organic amine absorbents with different characteristics can improve their performance in absorbing CO2. Ionic liquids have the advantages of good thermal stability, very low saturation vapor pressure, and designable structure, and are a new type of CO2 adsorbent, but ionic liquids have high viscosity themselves. Combining ionic liquids with organic or inorganic porous materials to form loaded ionic liquid materials, which can be used as CO2 adsorbent not only to improve the separation effect, but also to avoid the problem of high viscosity caused by direct absorption of ionic liquids, thus improving CO2 adsorption efficiency.

Predicting CO2 Absorption in Ionic Liquids with Molecular Descriptors and Explainable Graph Neural Networks

Predicting CO₂ Absorption in Ionic Liquids with Molecular Descriptors and Explainable Graph Neural Networks

Understanding Relationships between Free Volume and Oxygen Absorption in Ionic Liquids.

Understanding the factors that govern gas absorption in ionic liquids is critical to the development of high-capacity solvents for catalysis, electrochemistry, and gas separations. Here, we report experimental probes of liquid structure that provide insights into how free volume impacts the O2 absorption properties of ionic liquids. Specifically, we establish that isothermal compressibility─measured rapidly and accurately through small-angle X-ray scattering─reports on the size distribution of transient voids within a representative series of ionic liquids and is correlated with O2 absorption capacity. Additionally, O2 absorption capacities are correlated with thermal expansion coefficients, reflecting the beneficial effect of weak intermolecular interactions in ionic liquids on free volume and gas absorption capacity. Molecular dynamics simulations show that the void size distribution─in particular, the probability of forming larger voids within an ionic liquid─has a greater impact on O2 absorption than the total free volume. These results establish relationships between the ionic liquid structure and gas absorption properties that offer design strategies for ionic liquids with high gas solubilities.

Estimation of solubility of acid gases in ionic liquids using different machine learning methods

Ionic liquids (ILs) can capture acid gases that damaged the environment. Due to the properties of low-cost and non-toxic, machine learning can be used to screen ILs for gas absorption. To find the most suitable machine learning method for estimating gas absorption in ILs, 12 different machine learning algorithms are used to train models to estimate CO2 and H2S solubility in different ILs. Temperature (T), pressure (P), molecular weight (Mw), critical temperature (Tc), and critical pressure (Pc) of solutions are used as the input variables; Solubility is used as the output variable in the model training. Mean Square Error (MSE), Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Correlation Coefficient (R2) are used to evaluate the models. Stacking algorithm has the most accurate model in IL- CO2 system, with MSE, RMSE, MAE, and R2 of 0.001, 0.025, 0.018, and 0.969 respectively on average. Voting algorithm performs best in IL-H2S system; the four averaged metrics are 0.002, 0.032, 0.024, and 0.934 accordingly. By combining different algorithms, Voting and Stacking algorithms can balance out each model's weakness and produce a more accurate model. Stacking and Voting algorithms can be considered as a promising candidate for the estimation of acid gases solubility in ionic liquids.

Ionic liquid screening for dichloromethane absorption by multi-scale simulations

• Multi-scale investigation framework on ionic liquids was established. • Dichloromethane absorption in ionic liquids was systematically evaluated. • [C 2 MPip][C 1 COO] was screened as optimal ionic liquid for dichloromethane absorption. Ionic liquids (ILs) have been proposed as potential solvents for absorbing dichloromethane (DCM), while screening a promising IL with high absorption performances from numerous ILs remains challenging. In this work, a framework of multi-scale investigation on DCM absorption using ILs was established. A screening method based on COSMO-RS model that optimized by 79 reported experimental data points was proposed, and the effect of cationic and anionic structures on DCM absorption and the mechanisms were systematically studied combining quantum chemical calculation. Based on the above results, 1-ethyl-1-methylpiperidinium acetate ([C 2 MPip][C 1 COO]) was determined as the optimal IL for DCM absorption with Henry’s Constant of 3.29 kPa. The screened IL was further evaluated through process simulation comparing to the conventional IL and traditional organic solvent. The annual variable operation cost of [C 2 MPip][C 1 COO]-based process for DCM absorption was the lowest among the studied cases, showing broad prospects in applications.

Investigation on Protic Ionic Liquids as Physical Solvents for Absorption of NO at Low Pressures.

Nitric oxide (NO) absorption in ionic liquids (ILs) is an interesting issue, but little attention has been focused on the removal of NO at low partial pressures. Herein, a series of protic ionic liquids (PILs) based on polyamines as the cation and hydroxybenzenes as the anion were prepared for capturing low-concentration NO (0–0.6 bar). Triethylenetetramine phenolate ([TETAH][PhO]) showed an excellent absorption performance, with low viscosity, fast absorption rate, and high absorption capacity. The experimental solubility data were fitted by the Krichevsky–Kasarnovsky (K–K) equation, and the absorption enthalpy (ΔH) of NO in [TETAH][PhO] was thus calculated to be −43.60 kJ/mol. Density functional theory calculations were further performed to better understand the interaction of [TETAH][PhO] with NO on the molecular level, and the results suggest that the weak interaction of NO with the PIL was induced by the presence of H protons. It is believed that this work may provide a new method for the efficient and reversible absorption of low-concentration NO.

Sustainable Gas-to-Wire via dry reforming of carbonated natural gas: Ionic-liquid pre-combustion capture and thermodynamic efficiency

Remotely located oil fields with high gas-oil ratio and high carbon dioxide content impose challenges for efficient and sustainable gas processing and monetization. This work investigates gas-to-wire coupled to carbon dioxide enhanced oil recovery as a solution to handle the high flow of carbonated natural gas simultaneously accomplishing three missions: high revenues from electricity exportation; and elimination of concerns from long-distance gas transportation and carbon dioxide destination. A novel Gas-to-Wire concept is proposed matching the low-emission target tied to high carbon dioxide intake with a pre-combustion strategy using dry reforming of carbonated gas followed by ionic-liquid absorption carbon capture coupled to high-pressure stripping to lower carbon dioxide compression costs. The novel process is thermodynamically, environmentally and economically compared to an analogous Gas-to-Wire using conventional aqueous-monoethanolamine absorption capture and low-pressure stripping. Results show that the ionic-liquid Gas-to-Wire has cumulatively the following advantages over the aqueous-monoethanolamine counterpart: (i) higher overall thermodynamic efficiency of 23.5% against 16.3%; (ii) lower heat-penalty due to lower stripping heat-ratio; (iii) 7.8% lower power demand due to lower carbon dioxide compression power; and (iv) 60.4% higher net value due to 41.7% greater electricity exportation demanding only 5.3% higher investment due to smaller carbon dioxide compression train.

The Absorption Performance of Ionic Liquids–PEG200 Complex Absorbent for VOCs

A novel complex absorbent composed of polyethylene glycol 200 (PEG200) and ionic liquids (ILs) was prepared for the absorption of volatile organic compounds (VOCs) such as dichloromethane (DCM) and benzene. We prepared complex absorbents composed of [EMIM][Cl], [BMIM][Cl], [HMIM][Cl], [BMIM][BF4], [BMIM][PF6], [BMIM][NTF2], and PEG200, respectively, and studied the absorption properties of these six complex absorbents for DCM and benzene. The results show that under the optimized situation, the absorptivity of [HMIM][Cl]–PEG200 complex absorbent for DCM is 85.46% in the first 5 min, and 87.15% for benzene. No obvious decay in the absorptivity of [HMIM][Cl]–PEG200 for DCM and benzene was observed in five cycles, indicating an impressive regeneration performance. Furthermore, the mechanism of ionic liquid absorption for VOC is explored by thermodynamic analysis and quantum chemical calculations. The theoretical calculation results show that the [HMIM][Cl]–DCM interaction is stronger than the [HMIM][Cl]–benzene interaction, which is consistent with the results of the absorption experiment. Moreover, the strong hydrogen bonds can be formed between both [HMIM][Cl]–DCM and [HMIM][Cl]–benzene.

Molecular understanding of carbon dioxide interactions with ionic liquids

The effectiveness of CO2 absorption in ionic liquids (ILs) depends on the physical properties of cations/anions of the IL and their influence on ion-ion and ion-CO2 interactions. A molecular understanding of these cation-anion and ion-CO2 interactions is vital to identify promising ILs for CO2 capture. Koopmans' theorem based on quantum mechanics was used to compute several interaction descriptors, such as ionization potential (IP), electron affinity (EA), chemical potential, chemical hardness, softness, and electrophilicity index for cations/anions/ILs. Density Functional Theory (DFT) studies were performed to obtain interaction energies (IE) for ion-ion and ion-CO2 interactions. Several cations (imidazolium-based and pyridinium-based), inorganic (F¯, BF4¯, etc.) and organic anions ([TF2N]¯, [bFAP]¯, etc.) and cation-anion combinations were considered in the present study. The analysis of different interaction descriptors provided a better understanding of the relationships between the EA of cation, the IP of anion, and cation-anion IE values with the experimental CO2 solubility. Several inferences can be made based on the results obtained: a) the cation-anion interaction energy and IP of the anion have a strong correlation with the CO2 solubility, b) the IE trends of ion-CO2 and CO2-IL alone do not correlate well with the experimental CO2 solubility trends, (c) free molecular volume or interstitial spaces resulting from entropic effects of cation-anion interactions due to the nature/structure of cation and anion, play a dominant role for an effective CO2 absorption, (d) for a particular anion, changing the cation does not significantly influence cation-anion IE and ion-CO2 IE values, while for a particular cation, the nature of anion dramatically influences cation-anion IE and ion-CO2 IE values – consistent with the experimental CO2 solubility trends. Of the anions and cations studied, the combination of anions containing fluoroalkyl groups, such as [TF2N]¯ and [bFAP]¯, with the cations, such as [hmim]+ and [hmpy]+ constitute promising solvents for efficient CO2 capture. The findings of this study emphasize the importance of assessing cation-anion and ion-CO2 interactions in conjunction with other interaction descriptors to design efficient solvents for CO2 capture.

Experimental and thermodynamic analysis of NH3 absorption in dual-functionalized pyridinium-based ionic liquids

A novel type of dual-functionalized pyridinium-based ionic liquids (ILs) with acidic protons and hydroxyl groups, were designed and synthesized for ammonia (NH3) absorption. The NH3 absorption isotherms in dual-functionalized pyridinium-based ILs at temperatures from 303.15 to 343.15 K and pressures up to 600 kPa were computed using gas-liquid equilibrium method. It revealed that 4-pyridinemethanol bis(trifluoromethane)sulfonamide [4-MeOHPy][NTf2] showed the maximum NH3 solubility of 3.43 mol NH3/mol IL at 313.15 K and atmospheric pressure, surpassing any nonmetallic ILs previously reported. Furthermore, the characteristics of isotherms under low pressures behaved an obvious chemical reaction between ILs and NH3, and all experimental solubilities were regulated by a reaction equilibrium thermodynamic model (RETM). The thermodynamic properties were further obtained to better understand the NH3 absorption process. The results indicated that this model endorses the 1:1 (NH3-IL) mole ratio of chemical reaction mechanism and the reaction enthalpy is main driving force of NH3 absorption in ILs.

Investigation on the thermal performances of [Na(TX-7)]SCN/NH3 absorption systems based on physical properties measurement of the working fluid

The application of ionic liquid in the ammonia absorption system is current research hotspot. The low solubilities of ammonia in common ionic liquids lead to poor thermal performances of absorption systems, which is the main obstacle faced by ionic liquid absorption systems. Hence, we proposed a new idea of using ionic liquids containing metal cations to enhance the thermal performances of the absorption systems. The specific ionic liquid being studied is [Na(TX-7)]SCN. The vapor–liquid equilibrium and heat capacities of [Na(TX-7)]SCN/NH3 were studied by experimental methods. Based on above physical properties, the thermal performances of absorption refrigeration and absorption heat transformer using [Na(TX-7)]SCN/NH3 were simulated and compared with those of other systems. The thermal performances of [Na(TX-7)]SCN/NH3 absorption refrigeration are better than NH3/H2O system and other ionic liquid systems, but is a bit lower than NaSCN/NH3 system. The thermal performances of [Na(TX-7)]SCN/NH3 absorption heat transformer are better than those of the [mmim]DMP/H2O and [mmim]DMP/CH3OH systems, similar to those of the NaSCN/NH3 system, and slightly lower than those of the LiBr/H2O system. Overall, the proposed working fluid obviously improves the thermal performances of ionic liquid system and solves the crystallization problem of NaSCN/NH3 and LiBr/H2O systems.

Prediction of ammonia absorption in ionic liquids based on extreme learning machine modelling and a novel molecular descriptor SEP

The large amounts of ammonia emissions generated from industrial production have caused serious environmental pollution problems, such as soil acidification, eutrophication, the formation of fine particles and changes in the global greenhouse balance, and also greatly endanger human health. At present, effectively reducing ammonia emissions or recovering ammonia is still a huge challenge. Ionic liquids (ILs) as a new class of green solvent have been introduced for ammonia absorption with great potential, but a huge number on combination systems of ILs lead to the difficulty of measuring the ammonia solubility in all ILs by experiments (e.g., danger and cost). Hereby, this study proposed a novel approach for estimating the ammonia solubility in different ILs. A predictive model was developed based on the novel Algorithm - extreme learning machine (ELM) and the molecular descriptors of electrostatic potential surface areas (SEP) as input parameters. Besides, 502 data points of ammonia solubility in 17 ILs were gathered with a wide range of pressure and temperature. For the total set, the determination coefficient (R2) and the average absolute relative deviation (AARD) of the developed model were 0.9937 and 2.95%, respectively. The regression plots revealed good consistency between predictive and experimental data points. Results show the good performance and reliability of the developed model, indicating that the proposed approach can be potentially applied for screening reasonable ILs to absorb ammonia from chemical industry processes.