Mutual Solubilities of Cyclohexane and Water in Aqueous

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Mutual Solubilities of Cyclohexane and Water in Aqueous Methyldiethanolamine /Cyclohexane Liquid−Liquid Equilibria Rana Danon, Maaike C. Kroon, and Fawzi Banat* Department of Chemical Engineering, Khalifa University of Science and Technology, SAN Campus, Abu Dhabi, UAE S Supporting Information *

ABSTRACT: The aim of this work is to study the solubility of cyclohexane in aqueous methyldiethanolamine (MDEA) solutions. Thermostated jacketed double glass equilibrium cells were used to measure the mutual solubility between two liquid phases of aqueous MDEA and cyclohexane at 298−318 K under atmospheric pressure. The cyclohexane solubility in the aqueous liquid samples was analyzed using GC−MS coupled with purge and trap technique, while that of water in the cyclohexane-rich phase was measured via the Karl-Fischer titration method. It was observed that the solubility of cyclohexane in the aqueous phase increases with increasing temperature. Furthermore, an increase in amine composition, increases the solubility of cyclohexane. The mutual water solubility in the cyclohexane-rich phase increases rapidly with increasing temperature while it was rather nonsensitive toward the amine composition. A simple correlation for the salting-in ratio has been used that allows for a direct comparison between the solubilities of cyclohexane in aqueous solutions of MDEA to those in pure water at various temperatures.

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INTRODUCTION The contact between hydrocarbons and aqueous alkanolamine has been studied and is still considered one of the common features in the physical separation processes in most refineries and petrochemical plants, mainly in the areas of where crude oil and natural gas streams should be treated for acid gas removal1,2 and in extraction towers. In the past, gaining knowledge about hydrocarbon/aqueous alkanolamine mutual solubilities and volatilities was motivated by the need to track their phase distribution throughout the entire process and consequently being able to assess and estimate the amount of hydrocarbon losses, which are eventually considered as valuable energy loss. Nowadays this knowledge has become important not only for the previous reasons but also for the awareness of their effect on foaming tendency during operations.3 Foaming can be enhanced and induced by various contaminants including liquid hydrocarbons4,5 which possess the capability and ability to increase the solution viscosity and density and also reduce the solution surface tension,6−8 when it reaches certain levels of dissolved content. Generally, when hydrocarbons exceed their solubility limit a liquid hydrocarbon phase will begin to form © XXXX American Chemical Society

and lead to enhanced foaming occurrence and eventually more hydrocarbon loss. Foaming is one of the major operational problems that normally leads to serious consequences including absorption capacity loss due to the reduction of mass transfer area because of the carryover of the layer solution to the downstream plant.9 Hence, when foaming takes place, the foamed alkanolamines may carry large amounts of hydrocarbons contributing to hydrocarbon losses, which are far in excess with what would be expected from solubility alone.10 The mutual solubilities between water and most aliphatics up to C20 and the BTEX compounds (benzene, toluene, ethylbenzene, and xylene) have been studied thoroughly in the literature11−19 and the solubility of n-alkanes up to C7 and the BTEX compounds in methyldiethanolamine (MDEA) and other alkanolamine solutions was also investigated by several researches.11,13,20−25 However, so far, only limited information Special Issue: In Honor of Cor Peters Received: October 4, 2017 Accepted: March 6, 2018

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DOI: 10.1021/acs.jced.7b00873 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

platinum was used as electrode for both coulometry as well as for generator electrode with diaphragm. On the other hand, samples from the aqueous phase were withdrawn using a liquid tight syringe, from which 0.5 mL was first diluted with a definite amount of ethanol of approximately 2.5 mL, and then filled further to the 50 mL volumetric flask mark with water. A gas chromatograph−mass spectrometer (GC−MS) was used for sample analysis. Numerous samples from each cell were withdrawn and analyzed to ensure the repeatability of the results. The relative standard uncertainty in the mole fraction of cyclohexane based on the repeatability and reproducibility measurements was ur(x) = 0.2. All analyses were performed using Brucker-Scion GC−MS equipped with an MS detector preceded by a purge and trap unit; Figure 2 shows the schematic diagram. The quadrupole mass spectrometer is fitted with BR-624 ms fused silica capillary column (20 × 0.18 mm; 1.0 μm film thickness. Table 2 shows the oven thermal programming.27 Helium was used as the carrier gas at a linear velocity of about 44.3 cm/s. The injector and ion source temperatures were 275 and 250 °C. Split injection mode was used and adjusted to achieve better reproducibility. The best split ratio was found to be 20%.27 Mass spectra were recorded at 70 eV over a mass scan range of 45−900 m/z. In addition to a frequent conditioning of the column, a blank injection of deionized water was used continuously between sampling procedures to ensure accurate peak area readings of the samples chromatograms and to avoid the possibility of any accumulated cyclohexane throughout the GC lining and column.

is available for cyclohexane and some selected amines such as perfluorotributylamine.26 Recently Alhseinat et al.3 have reported about the effect of dissolved n-parrafins and carboxylic acids as well as BTEX compounds on foaming in aqueous MDEA solutions. They found that cyclohexane has much higher influence on the foam volume than n-hexane. Therefore, it is important to study the solubility of cyclohexane in aqueous MDEA solutions. To the best of the authors’ knowledge, no previous work has been performed on the cyclohexane/-alkanolaminemutual solubilities and thermodynamic equilibria. In this work, the solubility of cyclohexane in aqueous MDEA solutions as well as water solubility in the cyclohexane-rich phase has been studied.

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EXPERIMENTAL PROCEDURE FOR CYCLOHEXANE SOLUBILITY MEASUREMENT Apparatus and Experimental Procedures. A thermostated double-jacketed glass cell with two orifices ended with rubber caps, placed on a magnetic stirrer kept at a fixed temperature in the range of 298−318 K and under atmospheric pressure, was used to study thermodynamic equilibrium between two liquid layers of pure cyclohexane and aqueous MDEA solution in the range of 25−50 wt % MDEA. Figure 1 shows a schematic diagram of the cell used. The origin and purity of the above-mentioned chemicals are reported in Table 1.

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RESULTS AND DISCUSSION The influence of both temperature and amine concentration on the liquid−liquid equilibrium between the cyclohexane-rich phase and aqueous MDEA phase has been investigated. In this study, both the solubility of cyclohexane in the aqueous MDEA phase as well as that of water in the cyclohexane-rich phase has been collected. The obtained solubility data shows that adding MDEA to the pure water leads to an increase the solubility of cyclohexane in the aqueous phase while it does not affect the solubility of water in the rich cyclohexane phase. Two steps should occur for any solute to dissolve into a solvent. The first one is the dissolution of solute−solute as well as solvent−solvent intermolecular forces, followed by the solvation step which corresponds to solute−solvent attraction. Many intermolecular forces can contribute to solvation including hydrogen bonding. Water molecules, known as associating species, attract each other by strong hydrogen bonding since each molecule has hydrogen donor and hydrogen acceptor sites. When a tertiary amine such as MDEA is added to water, an attractive interaction between the two molecules occurs. The new interaction between water-amine species is also of hydrogen bonding kind; however, it is weaker since the amine molecule has only a hydrogen acceptor site (solvation). In other words, the new hydrogen bonding interrupts the macromolecular structure of water clusters and decreases the order of water and its surface tension. MDEA species are called nonionic chaotropes10,28−30 which break down the hydrogen-bonded network of water, allowing more water structural freedom which encourages the solubility of hydrophobes (cyclohexane species) to increase. This can also be viewed as causing a disturbance in the equilibrium status

Figure 1. Schematic diagram for the equilibrium cell: (1) upper and lower orifices, (2) cyclohexane layer, (3) aqueous MDEA layer, (4) magnetic stirrer, (5) water jacket in, (6) water jacket out.

Table 1. . Chemical’s Origin and Purity chemical name and formula cyclohexane analytical reagent grade MDEA water a

purity from sourcea

CASRN

source

C6H12

110-82-7

Fischer Chemical

≥99.96%

C5H13NO2 H2O

105-59-9

Merck

≥98.0% >18.2 MΩ· cm

No further purification was carried out.

To the empty cell, a definite layer of cyclohexane was loaded, followed by a fresh gravimetrically prepared layer of MDEA aqueous solution (the denser phase). The phases were stirred for about 5 h and then left to settle overnight to ensure equilibrium. Karl Fischer coulometric titrator (851 Titrando-Metrohm) was used to measure the trace amounts of water in cyclohexane rich phase. The measurements were conducted in a 250 mL clear glass vessel having each sample volume of 1.0 mL. The B



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Figure 2. . Schematic diagram of GC−MS system coupled with purge and trap unit: (1) helium (purging gas), (2) sparger, (3) trap, (4) transfer line, (5) helium (carrier gas), (6) interface, (7) source, (8) single quadrapole analyzer, (9) detector, (10) control and acquisition, (11) data processing, (12) output.

literature, in aqueous MDEA was made to confirm the high level reliability of the collected data. Solubility of Cyclohexane in Water and Reliability Check. A comparison between selected literature data for another two C6 hydrocarbons namely hexane and benzene with cyclohexane, all tested in 50 wt % MDEA, was made to validate the high degree of reliability of the current work as shown in Figure 3. Figure 3 shows the ability of cyclohexane to dissolve in the same aqueous solution as it lies midway between hexane and benzene by order of magnitudes more or less 10 times their abilities according to the logarithmic scale. Although these three compounds have the same carbon number in common, their molecular configurations and consequently their polarities play the key role in determining their properties and the strength of the intermolecular forces between each compound and the solvent gives the extent to which the solubility could reach. The benzene molecule is an aromatic, polar and planer compound, while cyclohexane and hexane are both nonpolar molecules. However, cyclohexane is a cyclic compound compared to the acyclic straight chain hexane. In addition, attention should be paid to their molecular sizes when these compounds are compared. The larger is the molecular size, the more difficult for solvent molecules to surround the solute molecules. Hence for all the prementioned reasons, this work is validated. Moreover, It was mentioned in ref 11 that the mutual solubilities are only weakly pressure dependent (at least up to 100 MPa) for all pressures above the three phases pressure P3.

Table 2. . Thermal Programming of the Oven starting ramp 1

ramp rate °C/min

final temp °C

holding time min

0 10

35 290

4 2

between solute−solvent which by consequence forces the system to shift to the direction that allows for a new equilibrium. Thus, it can be easily estimated that adding more amine to the system will continue weakening water shells which consequently allows for more cyclohexane to dissolve into the aqueous phase. On the basis of the previous discussion, one can realize the reason for having no sensitivity for water solubility in the cyclohexane rich phase. Since, MDEA interrupted only the aqueous phase. This result can also be used to support the assumption of having no significant amount of MDEA in the organic phase. In addition, it is also shown that increasing temperature increased the solubility for both cyclohexane and water in the aqueous amine and cyclohexane phases, respectively. These findings comply well with the trend of solubility of these species with temperature in the cyclohexane−water binary system. On the other hand, cyclohexane solubility was tested in pure water (for validation of the applied method), and the result is in excellent agreement and fit well with the available data in literature.11 Moreover, a comparison of solubility between cyclohexane and other C6 hydrocarbons, critically selected from

Figure 3. Solubility for some C6 hydrocarbons expressed in mole fraction ×105 in log scale versus temperature in K. C



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Table 3. Solubility of Cyclohexane in Water According to Reference 11 solubility at T3c

solubility minimum cyclohexane

A

B

C

T, K

xcyclohexane

T3c, K

xcyclohexane

−209.11689

8325.49

29.8231

279.2

1.193 × 10−5

529.4

1.748 × 10−3

Solubility of Cyclohexane in Aqueous MDEA Liquid Phase. Adding methyldiethanolamine (MDEA) to the binary system of cyclohexane−water has increased the solubility of cyclohexane in the aqueous solution more than that would be expected in water alone. This effect is known as the salting-in effect.10,28−30 On the other hand, increasing the temperature for the ternary system, increases the solubility of cyclohexane, this can be clearly seen in Figures 4 and 5 and in Table 5 as well. Solubility of Water in Cyclohexane Phase. A measured solubility data for water solubility in cyclohexane at 295 K of this work has been compared to selected data from ref 11 one more time. As previously described it should show good agreement with a slight lower value due to the pressure differences between the two points. An equation adopted from ref 11 calculates the solubility of water in cyclohexane as a function of temperature has the following form:

That is for P > P3, the solubilities are not drastically different from those at P = P3 but they are of opposite direction; the hydrocarbon solubility increases, while the water solubility decreases with increasing pressure. This can be simply viewed as applying more of a load of orthogonal force above the hydrocarbon phase, which will drive both cyclohexane and water molecules from the cyclohexanerich phase to dissolve in to the aqueous amine phase. On that basis, cyclohexane solubility in pure water at LLE was measured and compared to the available data from the reference.11 The authors had found an adequate fitting to calculate the solubility of cyclohexane in water at the VLLE pressure according to ln xhc = A +

B + C ln T , T

T in K

(1)

The values of A, B, and C for cyclohexane are listed in Table 3. Hence, the solubility of cyclohexane in water at LLE measured in this work is expected to be slightly higher than the cyclohexane solubility in water at VLLE from literature, as both are presented in Table 4 at 295 K. Figure 4 shows the good agreement between the compared data and confirm the used approach.

ln x w = A +

solubility of cyclohexane inwater at VLLE mole fraction(xcyclohexane) at P3 ≈ 0.015 MPa

Experimental solubility in water at LLE mole fraction (xcyclohexane)aat P ≈ 0.1 MPa

295

1.25 × 10−5

1.67 × 10−5

T in K

(2)

The parameters of the equation are listed in Table 6. In addition, the water solubility at VLLE calculated from the previous equation and the measured water solubility in the cyclohexane-phase at LLE in the current work are compared in Table 7. The results show that water is indeed less soluble in the cyclohexane-phase at the LLE compared to that at the VLLE. Moreover, Figure 6 and Table 8, show that the solubility of water in cyclohexane-phase increases rapidly with increasing temperature in both the systems. In addition, the water solubility in the cyclohexane-rich phase is rather nonsensitive toward the amine composition as it is shown in Figure 7. Figure 8 shows the ternary diagrams of the systems MDEA− water−cyclohexane. According to the classification by Sørensen

Table 4. Comparison between This Work and a Reference Data11 for the Solubility of Cyclohexane in Water at 295 K temp (K)

B + CT + D ln T , T

a

This value represents an average over four repeatable samples and was confirmed by another two reproducible cells. ur(x) = 0.2.

Figure 4. . Experimental data for cyclohexane solubility, in mole fraction, at different temperatures and MDEA compositions at LLE along with the work of Tsonopolous11 for binary water−cyclohexane at VLLE. D



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Figure 5. . MDEA salting-in effect on cyclohexane solubility at constant temperature for the water − MDEA−cyclohexane LLE system.

Table 5. . Experimental Mole Fraction Solubilities (x) of Cyclohexane (1) Water (2) and MDEA (3) in the Aqueous MDEA Phase (A) at Temperature T and Pressure P = 0.1 MPaa solvent

T/K

0% MDEA

295 298 308 318 298 308 318 295 298 308 318

40% MDEA

50% MDEA

x1̅ ,A 1.67 × 10−5

10.2 15.8 19.8 20.2 22.5 33.5 46.4

× × × × × × ×

10−5 10−5 10−5 10−5 10−5 10−5 10−5

x2̅ ,A 0.99998

x3̅ ,A 0 0 0 0 0.091524 0.091521 0.091519 0.13131 0.13131 0.13130 0.13129

0.90837 0.90832 0.90828 0.86848 0.86846 0.86837 0.86825

solvent

T/K

x1̅ ,A

x2̅ ,A

x3̅ ,A

25% MDEA

295 298 308 318 298 308 318

3.97 × 10−05 5.22 × 10−05 11.3 × 10−5 16.68 × 10−5 21.1 × 10−5 26.0 × 10−5

0.95201 0.95199 0.95216 0.88980 0.88976 0.88971

0.0479536 0.0479539 0.047951 0.110030 0.110028 0.110026

45% MDEA

Standard uncertainty for temperature is u(T) = 0.1 K. X3 standard uncertainty = ±1.2 × 10−5. Relative standard uncertainties for pressure and cyclohexane solubility are ur(p) = 0.01 and ur(x1,A) = 0.2, respectively. a

Table 6. Equation 2 Parameters as per Reference 11 solubility at T3c

eq 2 parameters cyclohexane

A

B

C

D

T3c, K

xcyclohexane

−62.7645

−654.027

0

9.99967

529.4

0.276

methyldiethanolamine (MDEA) in the organic phase due to its very low (undetectable) solubility in cyclohexane. The effect of alkanolamine on the solubility of cyclohexane can be viewed using a salting-in ratio (Si),1011,28 where

Table 7. A Comparison between This Work and a Reference Data11 for the Solubility of Water in Cyclohexane at 295 K temp (K)

solubility of water incyclohexane at VLLE as per11 (xwater) at P3 ≈ 0.015 MPa

experimental solubility in mole fraction (xwater)a at P ≈ 0.1

295

0.00029942

0.00025221

Si =

a

This value represents an average over three repeatable samples and was confirmed by another reproducible cell. ur(x) = 0.13.

xiaq x iw

(3)

A correlation for the salting-in ratio Si has been used in the form10,28−30

ln(Si ) = kiCMDEA

et al.,31 all the ternary systems studied showed a Type 2 ternary behavior: that is the MDEA−water binary shows a complete miscibility. On the other hand, water−cyclohexane binary shows only partial miscibility while MDEA−cyclohexane has shown immiscibility. Moreover, the slopes of the tie lines were all negative and seem to have no change in their trend. Correlation. The LLE data were correlated whereby the assumption was made that there is no significant amount of

(4)

Considering the collected solubility data at the temperature range of 298−318 K, a plot of the salting ratios against the molarity of MDEA aqueous solutions was constructed as in Figure 9. From the slope of each fitted straight line, it can be concluded that the ki coefficient is almost constant or only a weak function of temperature in the range of 298−318 K, see Figure 10. E



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Figure 6. Solubility of water in cyclohexane-rich phase as a function of temperature in cyclohexane−water VLLE system and in water−MDEA− cyclohexane LLE systems.

Table 8. . Experimental Mole Fraction Solubilities (x) of Water (1) and Cyclohexane (2) in the Cyclohexane-Rich Phase (B) at Temperature T and Pressure P = 0.1 MPaa solvent

T/K

0% MDEA 25% MDEA

295 298 308 298 308 318 298 308 318 295 298 308 318

40% MDEA

45% MDEA

50% MDEA

x1̅ ,B 2.52 2.52 3.41 2.58 3.53 4.53 2.70 3.56 4.76 2.32 2.59 3.39 4.67

× × × × × × × × × × × × ×

10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4

x2̅ ,B 0.999748 0.999748 0.999659 0.999742 0.999647 0.999547 0.999730 0.999644 0.999524 0.999768 0.999741 0.999661 0.999535

a Standard uncertainty for temperature is u(T) = 0.1 K. Relative standard uncertainties for pressure and water solubility are ur(p) = 0.002 and ur(x) = 0.13, respectively.

Figure 7. Water solubility in cyclohexane-rich phase as a function of MDEA composition.

interruptive role of the amine to the macromolecular structure of water clusters that leads to shift the chemical potential of the solvent−solute solvation and allow for more hydrophobic (cyclohexane) to dissolve. Moreover, it has been shown that cyclohexane solubility is slightly higher at LLE than that at VLLE. This is due to the effect of the exerted pressure on the liquid phases to shift the chemical potential into another potential level. On the other hand, water is less soluble in the cyclohexane at LLE than at VLLE. The solubility has no clear sensitivity toward the amine concentrations in the ternary systems, this is previously expected since amine molecules only interrupt the aqueous phase and have no detectable solubility with the cyclohexane-rich phase as presumed before. While, increasing the temperature increased the solubility of water in a manner

More specifically, ki can be fitted as a function of temperature,

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ki = 0.0069T − 1.4214

(5)

CONCLUSION New mutual solubility data are presented for cyclohexane and water in both (aqueous and cyclohexane-rich) phases in a ternary MDEA−water−cyclohexane system. Cyclohexane solubility increased with increasing temperature at all tested aqueous MDEA compositions in a manner similar to its trend in the binary system of a pure water−cyclohexane system. Also, an increasing MDEA concentration in the aqueous layer increased the solubility of cyclohexane, this is due to the F



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Figure 8. . Phases tie lines between aqueous MDEA (A) + cyclohexane rich (B) of LLE at four different temperatures.

Figure 9. Natural logarithm of cyclohexane salting-in coefficient as a function of MDAE molarity at different temperatures.

at low temperature and low MDEA concentrations. However, increasing amine concentrations results in very comparable data of both mutual solubilities. A simple empirical correlation method that relates the salting-in ratio to the MDEA molarity

similar to its trend in the binary systems of pure water− cyclohexane systems. Water is more soluble in the cyclohexane-rich phase than cyclohexane in either pure water or the aqueous MDEA phases G



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(3) Alhseinat, E.; Keewan, M.; Banat, F. Impact of dissolved and undissolved organics on foaming of industrial amines. Int. J. Greenhouse Gas Control 2017, 60, 156−161. (4) Alhseinat, E.; et al. Foaming study combined with physical characterizationof aqueous MDEA gas sweetening solutins. J. Nat. Gas Sci. Eng. 2014, 17, 49−57. (5) Pauley, C. R.; Hashemi, R.; Caothien, S. Ways to control amine unit foaming offered. Oil Gas 1989, 87 (50), 67−75. (6) Thitakamol, B.; Veawab, A. Foaming behavior in CO2 absorption process using aqueous solutions of single and blended alkanolamines. Ind. Eng. Chem. Res. 2008, 47, 216−225. (7) Al-Dhafeeri, M. A. Identifying sources key to detailed troubleshooting of amine foaming. Oil Gas 2007, 105 (32), 1. (8) Pauley, C. R. Face the facts about amine foaming. Chem. Eng. Progress 1991, 87 (7), 33−38. (9) Chen, S.; Freeman, S. A.; Rochelle, G. T. Foaming of aqueous piperazine and monoethanolamine for CO2 capture. Int. J. Greenhouse Gas Control 2011, 5 (2), 381−386. (10) Hatcher, N. A.; Jones, C.E.; Weiland, R.H. Hydrocarbon and fixed gas solubility in amine treating solvents: a generalized model. Laurence Reid Gas Conditioning Conference, Norman, Oklahoma, February, 2013. (11) Tsonopoulos, T.; Wilson, G. M. High- Temperature Mutual Solubilities of Hydrocarbons and Wwater. AIChE J. 1983, 29 (6), 990−999. (12) Kudchadker, A. P.; McKetta, J. J. Solubility of cyclohexane in water. AIChE J. 1961, 7 (4), 707. (13) Carroll, J. J.; Mather, A. E. A model for the solubility of light hydrocarbons in water and aqueous solution of alkanolamines. Chem. Eng. Sci. 1997, 52 (4), 545−552. (14) Mokraoui, S.; et al. New solubility data of hydrocarbons in water and modeling concerning vapor- liquid- liquid binary systems. Ind. Eng. Chem. Res. 2007, 46, 9257−9262. (15) Jou, F.-Y.; Mather, A. E.; Otto, F. D.; Carroll, J. J. Phase equilibria in the system n-butane-water-methyldiethanolamine. Fluid Phase Equilib. 1996, 116, 407−413. (16) Marche, C.; Ferronato, C.; Jose, J. Solubilities of n-alkanes (C6 to C8) in water from 30 to 180 °C. J. Chem. Eng. Data 2003, 48 (4), 967. (17) Pereda, S.; et al. Solubility of hydrocarbons in water: Experimental measurements and modeling using a group contribution with association equation of state (GCA-EoS). Fluid Phase Equilib. 2009, 275, 52−59. (18) Tsonopoulos, C. Thermodynamic analysis of the mutual solubilities of hydrocarbons and water. Fluid Phase Equilib. 2001, 186, 185−206. (19) Tsonopoulos, C. Thermodynamic analysis of the mutual solubilities of normal alkanes and water. Fluid Phase Equilib. 1999, 156, 21−33. (20) Carroll, J. J.; Maddocks, J.; Mather, A. E. The solubility of hydrocarbons in amine solutions, in laurance Reid Gas Conditioning Conference. Norman, Oklahoma, March, 1998. (21) Valtz, A.; Coquelet, C.; Richon, D. Solubility data for benzene in aqueous solutions of methyldiethanolamine (MDEA) and diglycolamine (DGA). Thermochim. Acta 2006, 443, 245−250. (22) Valtz, A.; Coquelet, C.; Richon, D. Solubility data for Toluene in various aqueous alkanolamine solutions. J. Chem. Thermodyn. 2007, 39, 426−432. (23) Coquelet, C.; Valtz, A.; Richon, D. Solubility of ethylbenzene and xylene in pure water and aqueous alkanolamine solutions. J. Chem. Thermodyn. 2008, 40, 942−948. (24) Danon, R.; et al. Solubility of heptane in aqueous solutions of methyldiethanolamine (MDEA). Fluid Phase Equilib. 2016, 415, 18− 24. (25) Danon, R.; Alhseinat, E.; Peters, C.; Banat, F. Solubility of hexane in aqueous solutions of methyldiethanolamine. J. Chem. Eng. Data 2015, 60 (11), 3101−3105.

Figure 10. . Salting-in coefficient ki as a function of temperature.

was adopted over the temperature range of the experiment. The new measurements were analyzed together with critically selected literature data.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00873. Experimental details and additional calculations (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Maaike C. Kroon: 0000-0002-5985-986X Fawzi Banat: 0000-0002-7646-5918 Funding

The authors are grateful to the Petroleum Institute Gas Processing and Materials Science Research Center, Abu Dhabi, for funding the project (GRC006) Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge the contribution of Abu Dhabi Research Innovation Center by the use of its wellequipped laboratory.

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NOMENCLATURE P2 = pressure at which two phases are present at equilibrium P3 = pressure at which all three phases are present at equilibrium xi̅ = average mole fraction of component i Si = salting-in ratio ki = salting-in coefficients CMDEA = concentration of MDEA in molarity

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REFERENCES

(1) Speyer, D.; Bottger, A.; Maurer, G. Solubility of hydrogen sulfide in aqueous solutions of n-methyldiethanolamine and piperazine. Ind. Eng. Chem. Res. 2012, 51, 12549−12556. (2) Younas, O.; Banat, F. Parametric sensitivity analysis on a GASCO’s acid gas removal plant using ProMax simulator. J. Nat. Gas Sci. Eng. 2014, 18, 247−253. H



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(26) Fujishiro, R.; Hildebrand, J. H. The liquid-liquid solubility of cyclohexane and perfluorotributylamine at 25°. J. Phys. Chem. 1962, 66, 573−574. (27) Chemical Tests Residual Solvents; United States Pharmacopeial Convention, 2007. (28) Kalra, A.; et al. Salting-In and Salting-out of Hydrophobic Solutes in Aqueous Salt Solutions. J. Phys. Chem. B 2001, 105 (27), 6380−6386. (29) Huang, X.; et al. Effects of water factors on the effectiveness of EDC Adsorption on Novel Tailored Activated Carbon. Water, Air, Soil Pollut. 2016, DOI: 10.1007/s11270-016-3104-8. (30) Hooper, H. H.; Michel, S.; Prausnitz, J. M. High temperature mutual solubilities for some binary and ternary aqueous mixtures containing aromatic and chlorinated hydrocarbons. J. Chem. Eng. Data 1988, 33, 502−505. (31) Sørensen, J. M.; et al. Liquidliquid equilibrium data: Their retrieval, correlation and prediction Part II: Correlation. Fluid Phase Equilib. 1979, 3 (1), 47−82.

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Mutual Solubilities of Cyclohexane and Water in Aqueous

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