Deep Eutectic Solvents for Water Vapor Absorption: A New Strategy

doi:10.21203/rs.3.rs-4126991/v1

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Deep Eutectic Solvents for Water Vapor Absorption: A New Strategy

https://doi.org/10.21203/rs.3.rs-4126991/v1

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Gas dehydration plays a critical role in gas refining processes due to the potential problems caused by the presence of water vapor. The inclusion of water vapor can lead to issues such as hydrate formation, pressure drop, and pipeline corrosion. In this research, a deep eutectic solvent (DES) absorbent was employed to absorb water vapor and subsequently, its absorption results were compared with the absorption performance of tri-ethylene glycol (TEG) and lithium chloride as the most common absorbent used in water vapor separation processes. To do so, the influence of several effective parameters, including the inlet air flow rate, different ratios of choline chloride to urea (ChCl:Urea), the weight percentage of liquid water in the absorbent, and the viscosity of DES were investigated. The results revealed that DES is an efficient absorbent for water vapor separation and can separate water vapor from the gas phase far more than TEG and the aqueous solution of lithium chloride. The results also indicated that increasing the inlet air flow rate decreases the absorption recovery due to the reduction of the residence time. Furthermore, it was found that the ratio of 1:2 (ChCl: Urea) results in the highest absorption efficiency.

Absorption

DES

Dehydration

Separation

TEG

Water vapor separation

Natural gas contains varying impurities such as water vapor, carbon dioxide (CO₂), nitrogen, and hydrogen sulfide, which must be removed to reach a standard level before entering the pipelines. Natural gas refining or purification includes processes, such as the separation of heavy hydrocarbons and various liquids, acid gases (hydrogen sulfide and CO₂), and water vapor [1–5]. Separation of water vapor from natural gas is a crucial process to prevent hydrate formation, pressure drop, and corrosion in the pipelines [6–10]. Dehydration process is also an important process in the home industry to maintain the living environment at the desired temperature and humidity [1, 2, 11].

There are various methods including (i) liquid drying methods employing glycol-based nanofluid, (ii) solid desiccant adsorption with molecular sieves, alumina or silica gel, and (iii) refrigeration/cooling with methanol/propanol for water vapor absorption [12–17]. However, there remain some serious challenges to these technologies [18, 19]. For instance, solid adsorbents such as molecular sieves, silica gel, and salts have too high installation and regeneration costs and high pressure drop during the adsorption process [20]. Liquid absorbents can also lead to different unwanted phenomena such as corrosion, foaming, absorbent loss, and decomposition problems, as well as higher operating costs. Finally, the application of nanofluids has always had the problems of nanoparticles’ sedimentation, aggregation and instability which play a key part in reducing the performance of nanofluids in absorption processes [21]. In this work, we employed a DES absorbent that has a very low vapor pressure, and less loss. The DES absorbent has a high absorption capacity and a green technology [13, 22–25].

DESs are new solvents that are similar to some ionic liquids (ILs) in terms of observed properties. In some references, they are categorized as a kind of ILs that are more environmentally friendly. There are some benefits for DESs in comparison to traditional ILs. For example, they are easy to prepare in high purity and cost-effective compared to traditional ILs [26–29]. In addition, they are generally nontoxic and their stability for degradation is high. Further, the same as ILs, they are flexible liquids that could be prepared for a certain type of chemistry [30–35].

A DES generally contains multiple economical and safe components capable of self-association through hydrogen bonding that results in the formation of a eutectic mixture with a melting point lower than that of each individual component [36–41]. DESs are commonly in liquid form at temperature values less than 100 ^oC [35]. Due to these properties, researchers have performed some studies on the use of DESs to absorb CO₂. To date, many studies have been conducted on self-dissolving salts as CO₂ absorbents [42–48]. And, various selected types of DESs were compared for designing CO₂ capturing process.

Interestingly, it is reported that DESs can offer a great performance in ambient operating conditions [48, 49]. This can be considered an important factor in reducing the costs of absorption plants. Our experiments were performed under these operating conditions accordingly.

To the best of our knowledge, this is the first study of applying a DES (ChCl:Urea) for the capture of moisture from the gas stream. The absorption experiment was conducted in a bubble column and the DES absorption performance was compared with TEG and aqueous lithium chloride (as common industrial water vapor absorbents). Finally, the impacts of some effective parameters such as inlet air flow, different ratios of ChCl:Urea, and DES viscosity were studied and discussed.

The absorption of water vapor by DES was investigated in a bubble column under ambient operating conditions. Besides, the solution of choline chloride: urea as DES, TEG and the aqueous solution of lithium chloride were applied as absorbents. The materials, equipment, and methods applied to perform the experiments will be described below.

2.1. Materials

The materials used for water vapor absorption in this work are choline Chloride (≥ 99.00, Sigma-Aldrich), urea (≥ 99.00, Samchun), TEG (≥ 99.00, Jam Petrochemical) and Lithium Chloride (≥ 99.00, Kimia Mavad).

2.1.1. Definition of DES and synthesis

DESs belong to a new class of ILs made by mixing a hydrogen bond donor and a hydrogen bond acceptor (called HBD and HBO) to produce a substance with a very low melting point. ILs and DESs have many interesting features in common, including low vapor pressure. They are liquid in a wide range of temperatures. Unlike ionic liquids, DESs are easily produced with higher purities and are economically more feasible. Some of them are also less sensitive to moisture than ILs and they are biodegradable. DESs are considered as eco-friendly solvents for many chemical and industrial applications. Although the absorption of CO₂ with these solvents has been extensively studied, other applications of these solvents such as dehumidification have remained an uncovered subject over the recent years.

To prepare DES, two or three components, with certain molecular ratios, were first selected and placed in a glass container attached to a vacuum pump in the constant temperature bath of 80–90 ^oC and then stirred by a magnet to get a colorless liquid (Fig. 1).

The following equations was used to obtain the ChCl and urea volumes (ml) in DES solution.

$${m}_{DES}=\rho *V$$

$${M}_{{W}_{DES}}=\frac{1}{3}*\left[\left(1*{M}_{{W}_{ChCl}}\right)+\left(2*{M}_{{W}_{Urea}}\right)\right]$$

$${mol}_{DES}= {m}_{DES}*{\left({M}_{{W}_{DES}}\right)}^{-1}$$

$${mol}_{ChCl}=\frac{1}{3}*{mol}_{DES}$$

$${mol}_{Urea}=\frac{2}{3}*{mol}_{DES}$$

$${m}_{ChCl}={mol}_{ChCl}*{M}_{{W}_{ChCl}}$$

$${m}_{Urea}={mol}_{Urea}*{M}_{{W}_{Urea}}$$

The melting point of initial materials in pure form is much higher than the DES, while the DES is liquid after being made at room temperature. For example, the melting point of pure choline chloride is 302 ^oC, and for pure urea, it is 133 ^oC to 135 ^oC. However, they remain liquid at room temperature after mixing and becoming DES. Figure 2 is a melting point diagram, showing the difference between the initial and final melting temperatures for a binary solution of a salt and an HBD, in the formation of a DES.

an HBD [50].

2.2. Description of absorption experiment

First, the exhaust air from the compressor is contacted with distilled water using the first bubble column (34 cm height and 6.4 cm diameter) to be saturated with water vapor. This moisture is identified as the initial moisture of the inlet gas and it is recorded using a humidity meter (TH300, KIMO Instrument Co., France). The output of this tower enters a gas flowmeter, which determines the air flow rate and then moves to the second bubble column (moisture absorption column, 25 cm height and 4.2 cm diameter), containing 20 ml of the desired DES. After passing the gas stream through the DES or other absorbents, some of its moisture is absorbed by the liquid phase. The output of this tower moves to another gas flowmeter, and its water vapor concentration is measured by using a humidity meter. The experimental setup is illustrated in Fig. 3.

To evaluate the impact of the input air flow rate, choline chloride and urea with different ratios were prepared. Then, their performances in water vapor absorption were compared with TEG and the aqueous solution of lithium chloride. DES solutions were made with two ratios of 1: 2 and 1: 2.5 of ChCl:Urea.

The following equation was used to survey the recovery factor of water vapor removal:

$$\text{R}\text{F}={(\text{Q}}_{\text{i}\text{n}} {\text{C}}_{\text{i}\text{n}}-{\text{Q}}_{\text{o}\text{u}\text{t}} {\text{C}}_{\text{o}\text{u}\text{t}}).{{(\text{Q}}_{\text{i}\text{n}} {\text{C}}_{\text{i}\text{n}})}^{-1}$$

RF = Recovery factor of water vapor removal (dimensionless)

${Q}_{out},{Q}_{in}$ = Output and input gas flow rates (m³.s⁻¹).

${{C}_{out},C}_{in}$ = Outlet and inlet concentrations (mol.m⁻³).

The concentration of water vapor in the inlet and outlet gas stream of the absorption tower was measured using a hygrometer which was subsequently used to compute the recovery factor of the removal of moisture. To calculate the concentration of moisture in the gas stream, the relative humidity of the air at the inlet and outlet of the tower was converted to the moisture concentration using the following equation:

$$C=A.{{(M}_{{A}_{water}})}^{-1}$$

C = Concentration of water vapor in the air (mol.m^− 3)

$A=$ Absolute humidity that is computed by employing a psychometric chart or related formulas from relative humidity and air temperature data (g water vapor. m⁻³ air)

${M}_{A}$ = Molecular weight of water (g.mol⁻¹)

Figure 4 shows the relative humidity of inlet and outlet air using the applied DES. A ratio of 1: 2 of ChCl: Urea was used in three air flow rates (100, 300 and 500 ml.min^− 1). As shown, the difference between the humidity of the inlet airflow and the humidity in the outlet air is clearly significant. Furthermore, for all used DES absorbents, the proportions of relative humidity are around 90% lower than the untreated (input) gas stream. Therefore, as a first result, it can be said that DES solvents can absorb water vapor effectively. Figure 4 also shows that the output relative humidity increases in all three flow rates over time. This indicates a decrease in the amounts of absorbed water vapor with time due to the increase of water vapor concentration in the liquid phase.

Figure 5 shows the recovery factor versus time for a choline chloride: urea, (1:2) ratio, demonstrating a very high efficiency of the used DES solvents. This figure also shows that as the input air flow rate increases, the recovery factor decreases. This is because the amount of water vapor, passing through the column is increased. And the residence time of the gas phase decreases with increasing air flow rate.

3.1. Effects of different concentrations of ChCl: Urea on water vapor absorption

As illustrated in Fig. 6, and Fig. 7, the ratios of 1:2 and 1:2.5 of ChCl: Urea were used at the inlet air flow rates of 100, 300 and 500 ml.min^− 1. It is obvious from the figures that both concentrations could significantly absorb the moisture of the air stream. In addition, at the ratio of 1:2, the outlet relative humidity is less and the efficiency is higher compared to the 1:2.5 ratio. To find out the reason, the viscosity of both absorbents was examined and the results are depicted in Fig. 8. As shown, at ambient temperature, the viscosity of ChCl: Urea solution at the ratio of 1: 2 is less than its at the ratio of 1: 2.5, indicating an inverse relationship between the water vapor absorption and the viscosity of eutectic solvents. As a result, higher absorption values could be achieved at lower viscosities owing to hydrodynamic effects and higher turbulency of the liquid media.

3.2. Absorption efficiency of DESs compared to TEG and lithium chloride

To evaluate the performance of DESs, the absorption results were compared with strong and common absorbents of moisture in the petroleum and gas industries, TEG and the aqueous solution of lithium chloride. As shown in Fig. 9 and Fig. 10, the applied DESs have much lower relative humidity and much higher recovery factor than TEG, which is known as a very strong absorbent of water vapor in industry. Aqueous lithium chloride absorbent led to the least absorption performance compared to DESs and TEG. These results reveal that DESs can be introduced as one of the most powerful absorbents of water vapor for industrial and domestic applications.

Figure 11 compares the molecular structure of TEG and the applied DESs. As can be seen, TEG can form O-H bonds while DESs can form O-H and N-H bonds that N-H bond is stronger than the O-H bond so it can be the reason for such influential water vapor absorption by these DESs.

3.3. Effect of liquid water in solution on water vapor absorption by DESs

In previous sections, DESs were introduced as very strong water vapor absorbents. However, as it was shown in Fig. 8 their high viscosity is a challenge for practical applications on a large scale. Therefore, the viscosity and absorption capacity of the applied DESs were studied by adding specific amounts of liquid water and the results are shown in Figs. 12 to 13. As illustrated, the presence of 10 vol.% of water significantly reduces the viscosity of the absorbents. Also, in the presence of 20 vol.% of water, the viscosity is significantly reduced compared to the solution containing 10% water. For ChCl: Urea 1:2 at 20 ^oC, the viscosities are 1499.6 (mPa.s) and 98.833 (mPa.s) and 18.42 (mPa.s) for pure DES and DES containing 10% and 20% water, respectively. These results show that the presence of water strongly affects the viscosity which can reduce the problem of high viscosity of the DESs. In the next step, the effects of the presence of liquid water in the solution on water-vapor absorption were investigated. As can be seen in Fig. 14, the presence of 10 vol.% of liquid water in the DESs has reduced the absorption efficiency by about 20%, owing to the reduction of the driving force so that the recovery factor has reached about 70%. Considering the impact of water on the reduction of DESs viscosity and a slight reduction in absorption efficiency, it can be deduced that the aqueous solutions of DES can be a logical choice for the cases where completing the dehydration is not required, for example, in air conditioning systems.

Herein, as a new technology, DES with different volume ratios was used for the dehumidification of a wet gas stream. And the results were subsequently compared with TEG and aqueous lithium chloride solution, as two typical absorbents of water vapor. Observations showed that DES had lower output relative humidity and higher recovery factor than both of these absorbents. This indicates that DESs have a higher absorption capacity than the traditional water vapor absorbents. The results also indicated that the high viscosity of DESs can also be addressed markedly by diluting with water without a significant effect on its dehumidification performance. Finally, the maximum recovery factors of around 94 and 77% were achieved for pure and aqueous DES solvents at the best operational conditions. Therefore, DESs can be introduced as excellent candidates for water vapor absorption in various domestic and industrial applications.

Authors Contributions:

Sahar Torkzadeh: Methodology, Data curation, Investigation, Resources, and Writing - original draft.
Abbas Elhambakhsh: Investigation, Data curation, Conceptualization, and Writing - review & editing.
Peyman Keshavarz: Conceptualization, Visualization, Supervision, Project administration, and Funding acquisition.
Sona Raeissi: Conceptualization, Visualization, Supervision.

Funding: This work was financially supported by Shiraz University, Shiraz, Iran (No. 7134851154).

Competing Interests:The authors declare that they have no competing interests.

Availability of data and materials: All data generated or analyzed during this study are included in this published article.

Mokhatab S, Poe W, Speight J (2006) Natural gas dehydrationHandbook of Natural Gas Transmission and Processing Elsevier, pp. 323–364
Gandhidasan P, Al-Farayedhi AA, Al-Mubarak AA (2001) Dehydration of natural gas using solid desiccants. Energy 26:855–868
Elhambakhsh A, Ghanaatian A, Keshavarz P (2021) Glutamine functionalized iron oxide nanoparticles for high-performance carbon dioxide absorption. J Nat Gas Sci Engineering: 104081 DOI. https://doi.org/10.1016/j.jngse.2021.104081
Mehdipour M, Elhambakhsh A, Keshavarz P, Rahimpour MR, Hasanzadeh Y (2021) CO2 separation by rotating liquid sheet contactor: A novel procedure to improve mass transfer characterization. Chemical Engineering Research and Design
Zandahvifard MJ, Elhambakhsh A, Ghasemi MN, Esmaeilzadeh F, Parsaei R, Keshavarz P, Wang X (2021) Effect of modified Fe3O4 magnetic NPs on the absorption capacity of CO2 in water, wettability alteration of carbonate rock surface, and water–oil interfacial tension for oilfield applications. Ind Eng Chem Res 60:3421–3434
Enteria N, Yoshino H, Mochida A (2013) Review of the advances in open-cycle absorption air-conditioning systems. Renew Sustain Energy Rev 28:265–289
Mei L, Dai Y (2008) A technical review on use of liquid-desiccant dehumidification for air-conditioning application. Renew Sustain Energy Rev 12:662–689
Ertas A, Anderson E, Kiris I (1992) Properties of a new liquid desiccant solution—lithium chloride and calcium chloride mixture. Sol Energy 49:205–212
Ma Z, Liu X, Guan B, Zhang T (2023) Numerical investigation and comparison on energy performance and exergy destruction of cascading deep dehumidification systems with dehumidification amount exceeding 95%. International Journal of Refrigeration
Lecoq L, Derens E, Flick D, Laguerre O (2017) Influence of air dehumidification on water evaporation in a food plant. Int J Refrig 74:435–449
Boualouache A, Akrour S, Amokrane S (2022) Recovery of transient medium-grade heat in temperature swing adsorption natural gas dehydration processes. J Nat Gas Sci Eng 103:104623
Chebbi R, Qasim M, Jabbar NA (2019) Optimization of triethylene glycol dehydration of natural gas. Energy Rep 5:723–732
Ebrahiem EE, Ashour IA, Nassar M (2021) A Comparison of Natural Gas Dehydration Methods. Yanbu J Eng Sci 15:1–16
Shadanfar H, Elhambakhsh A, Keshavarz P (2021) Air dehumidification using various TEG based nano solvents in hollow fiber membrane contactors. Heat Mass Transf 1–9. https://doi.org/10.1007/s00231-021-03057-2
Delhali A, Assen AH, Mohammed A, Adil K, Belmabkhout Y (2023) Enabling simultaneous valorization of tannery effluent and waste plastic via sustainable preparation of Cr-BDC MOFs for water adsorption. Sci Rep 13:14653
Guo X, Wu Y, Xie X (2017) Water vapor sorption properties of cellulose nanocrystals and nanofibers using dynamic vapor sorption apparatus. Sci Rep 7:14207
Liu R, Gong T, Zhang K, Lee C (2017) Graphene oxide papers with high water adsorption capacity for air dehumidification. Sci Rep 7:9761
Carrillo-Berdugo I, Grau-Crespo R, Zorrilla D, Navas J (2021) Interfacial molecular layering enhances specific heat of nanofluids: evidence from molecular dynamics. J Mol Liq 325:115217
Abu-Hamdeh NH, Bantan RA, Golmohammadzadeh A, Toghraie D (2021) The thermal properties of water-copper nanofluid in the presence of surfactant molecules using molecular dynamics simulation. J Mol Liq 325:115149
Yang B, Yin W-Z, Yao J, Zhu Z-L, Sun H-R, Chen K-Q, Wang L-Y (2021) Differential adsorption of a high-performance collector at solid–liquid interface for the selective flotation of hematite from quartz. J Mol Liq 339:116828
Elhambakhsh A, Keshavarz P, Energy, Fuels DOI (2020) https://doi.org/10.1021/acs.energyfuels.0c00234
Chen X, Riffat S, Bai H, Zheng X, Reay D (2020) Recent progress in liquid desiccant dehumidification and air-conditioning: a review. Energy Built Environ 1:106–130
Netusil M, Ditl P (2011) Comparison of three methods for natural gas dehydration. J Nat Gas Chem 20:471–476
Song R, Zou T, Chen J, Hou X, Han X (2019) Study on the Physical Properties of LiCl SolutionIOP Conference Series: Materials Science and Engineering IOP Publishing, pp. 012102
Xiu-Wei L, Xiao-Song Z, Geng W, Rong-Quan C (2008) Research on ratio selection of a mixed liquid desiccant: mixed LiCl–CaCl2 solution. Sol Energy 82:1161–1171
Hu K, Zhang H, Kong M, Qin M, Ouyang M, Jiang Q, Wang G, Zhuang L (2021) Effect of alkyl chain length of imidazolium cations on foam properties of anionic surface active ionic liquids: Experimental and DFT studies. J Mol Liq 340:117197
Wei C, Jiang K, Fang T, Liu X (2021) Insight into the adsorption of Imidazolium-based ionic liquids on graphene by first principles simulation. J Mol Liq 338:116641
Sun S, Lv Y, Wang G, Chen X (2021) Soybean oil-based monoacylglycerol synthesis using bio-compatible amino acid ionic liquid as a catalyst at low temperature. J Mol Liq 340:117231
Han W, Zhou G, Xing M, Yang Y, Zhang X, Miao Y, Wang Y (2021) Experimental investigation on physicochemical characteristics of coal treated with synthetic sodium salicylate–imidazole ionic liquids. J Mol Liq 327:114822
Yadav A, Pandey S (2014) Densities and viscosities of (choline chloride + urea) deep eutectic solvent and its aqueous mixtures in the temperature range 293.15 K to 363.15 K. J Chem Eng Data 59:2221–2229
Bright FV, McNally MEP (1992) Supercritical fluid technology-theoretical and applied approaches to analytical chemistry Washington. DC (United States); American Chemical Society
Baker GA, Baker SN, Pandey S, Bright FV (2005) An analytical view of ionic liquids. Analyst 130:800–808
Scurto AM, Aki SN, Brennecke JF (2002) CO2 as a separation switch for ionic liquid/organic mixtures. J Am Chem Soc 124:10276–10277
Blanchard LA, Hancu D, Beckman EJ, Brennecke JF (1999) Green processing using ionic liquids and CO 2. Nature 399:28–29
Zhang Q, Vigier KDO, Royer S, Jerome F (2012) Deep eutectic solvents: syntheses, properties and applications. Chem Soc Rev 41:7108–7146
Haghbakhsh R, Raeissi S (2018) Densities and volumetric properties of (choline chloride + urea) deep eutectic solvent and methanol mixtures in the temperature range of 293.15–323.15 K. J Chem Thermodyn 124:10–20
Abbott AP, Boothby D, Capper G, Davies DL, Rasheed RK (2004) Deep eutectic solvents formed between choline chloride and carboxylic acids: versatile alternatives to ionic liquids. J Am Chem Soc 126:9142–9147
Abdul-Wahab S, Zurigat Y, Abu-Arabi M (2004) Predictions of moisture removal rate and dehumidification effectiveness for structured liquid desiccant air dehumidifier. Energy 29:19–34
D'Agostino C, Harris RC, Abbott AP, Gladden LF, Mantle MD (2011) Molecular motion and ion diffusion in choline chloride based deep eutectic solvents studied by 1 H pulsed field gradient NMR spectroscopy. Phys Chem Chem Phys 13:21383–21391
Leron RB, Li M-H (2012) High-pressure density measurements for choline chloride: Urea deep eutectic solvent and its aqueous mixtures at T=(298.15 to 323.15) K and up to 50 MPa. J Chem Thermodyn 54:293–301
Sun H, Li Y, Wu X, Li G (2013) Theoretical study on the structures and properties of mixtures of urea and choline chloride. J Mol Model 19:2433–2441
Pahlavanzadeh H, Zaamanian (2005) two dimentional mathematical model for fixed desiccant wheel dehiumidifier. Iran Jornal Sci Technol 30:353–362
Nia FE, Van Paassen D, Saidi MH (2006) Modeling and simulation of desiccant wheel for air conditioning. Energy Build 38:1230–1239
Daou K, Wang R, Xia Z (2006) Desiccant cooling air conditioning: a review. Renew Sustain Energy Rev 10:55–77
Abbott AP, Capper G, Davies DL, Rasheed RK, Tambyrajah V (2003) Novel solvent properties of choline chloride/urea mixtures. Chemical Communications: 70–71
García G, Aparicio S, Ullah R, Atilhan M (2015) Deep eutectic solvents: physicochemical properties and gas separation applications. Energy Fuels 29:2616–2644
Li X, Hou M, Han B, Wang X, Zou L (2008) Solubility of CO2 in a choline chloride + urea eutectic mixture. J Chem Eng Data 53:548–550
Ali E, Hadj-Kali MK, Mulyono S, Alnashef I (2016) Analysis of operating conditions for CO2 capturing process using deep eutectic solvents. Int J Greenhouse Gas Control 47:342–350
Abbott AP, Capper G, Gray S (2006) Design of improved deep eutectic solvents using hole theory. Chemphyschem: Eur J Chem Phys Phys Chem 7:803–806
Haider MB, Jha D, Marriyappan Sivagnanam B, Kumar R (2018) Thermodynamic and kinetic studies of CO2 capture by glycol and amine-based deep eutectic solvents. J Chem Eng Data 63:2671–2680
Longo LS Jr, Craveiro MV (2018) Deep eutectic solvents as unconventional media for multicomponent reactions. J Braz Chem Soc 29:1999–2025

No competing interests reported.

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Deep Eutectic Solvents for Water Vapor Absorption: A New Strategy

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Abstract

Figures

1. Introduction

2. Material and methods

2.1. Materials

2.1.1. Definition of DES and synthesis

2.2. Description of absorption experiment

3. Results and discussion

3.1. Effects of different concentrations of ChCl: Urea on water vapor absorption

3.2. Absorption efficiency of DESs compared to TEG and lithium chloride

3.3. Effect of liquid water in solution on water vapor absorption by DESs

4. Conclusions

Declarations

References

Additional Declarations

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