Contents lists available at SciVerse ScienceDirect
Thermochimica Acta
jo ur n al homepage: www.elsev ier .com/ locate / tca
eview
easurement and correlation of phase diagram data for polyoxyethylene (10)auryl ether and potassium hydroxide/potassium carbonate/potassiumhosphate aqueous two-phase systems at 298.15 K
ang Lua,b,∗, Juan Hanb, Chengzhuo Shengb, Ping Yua, Zhenjiang Tana, Yongsheng Yanb
School of Computer Science, Jilin Normal University, 1301 Haifeng Street, Siping 136000, ChinaSchool of Chemistry and Chemical Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China
r t i c l e i n f o
rticle history:eceived 17 February 2012eceived in revised form 30 May 2012ccepted 1 June 2012vailable online 9 June 2012
eywords:
a b s t r a c t
The phase diagrams for the systems containing polyoxyethylene (10) lauryl ether (POELE10) and threesalts (KOH, K2CO3 and K3PO4) have been determined experimentally. Three experiential equations wereused to correlate the binodal data. The liquid–liquid equilibrium data of these systems were obtained byexperimental method and calculated method using lever rule. The tie-line data were correlated by usingOthmer-Tobias and Bancroft and simple Setschenow-type equations. Furthermore, the effect of salt onthe binodal curve for the studied systems has been discussed by means of salting-out coefficient, effective
excluded volume (EEV) and Gibbs free energy of hydration of the ions (�Ghyd). It was found that the saltscomposed of anion with a higher valence are better salting-out agents than those with a lower valence.The order of salting-out abilities of salts is K3PO4 > K2CO4 > KOH for the investigated systems. Finally,the phase-separation ability of POELE10 is more powerful compared with that of other polymers andtwo-phase can easily form at the lower concentration, which indicates that lower cost is a remarkable
efficient extraction and purification of metal ions [1–3], antibi-otics [4–8] and biomolecules [9–12]. Because the vast majority ofboth phases consist of water, aqueous two-phase system (ATPS)offers a moderate biocompatible environment over the conven-tional liquid–liquid extraction using organic solvents. The ATPS
has several advantages over the conventional extraction meth-ods, such as the lower cost, nontoxicity, and the possibility oflarge-scale application. ATPSs are formed by compounding twohydrophilic polymers [13] or by mixing a hydrophilic polymer
Table 1Values of parameters of Eq. (1) for aqueous solution of POELE10 + KOH/K2CO3/K3PO4
at 298.15 K.
System n0 a1 a2
Y. Lu et al. / Thermoch
nd a salt [14] in aqueous solution above the certain criticaloncentration. In recent years, a number of new types of ATPSsave been reported, such as ionic liquid–salt [15] systems andydrophilic micromolecule organic-salt [16] systems. However,
ew studies on surfactant–salt ATPSs have been reported. Onlyasumeh et al. [17,18] have studied aqueous two-phase systems
f surfactant polyoxyethylene cetyl ether and salts. It has beenhown that surfactant–salt ATPSs have some advantages over otherTPSs in terms of lower interface tension, saving in material, andase of waste disposal. Surfactant–salt ATPS can use efficientlyor partitioning biological material that usually have lipophilicroperty due to the fact that surfactants have simultaneously
ipophilic and hydrophilic property. Kellermayer et al. [19] havesed surfactant–salt ATPS containing polyoxyethylene cetyl etheror separating lipids and proteins. Wang et al. [20] have usedriton-X100 as a nonionic surfactant for partitioning membraneroteins.
As nonionic surfactant, polyoxyethylene (10) lauryl etherPOELE10, C32H66O11) contains a hydrophobic alkyl tail and aydrophilic polyoxyethylene domain, thus POELE10 can be anppropriate candidate for forming surfactant–salt ATPS, which has
great application potential for the separation and purificationf biological material. Few studies on ATPS composed of POELE10ave been reported yet. In the present work, the phase diagrams forhe systems containing POELE10 and three salts (KOH, K2CO3 and3PO4) have been determined experimentally. The binodal curvesere correlated with three experiential equations, and meanwhilethmer-Tobias and Bancroft and simply Setschenow-type equa-
ions were used to correlate the tie-line data. In addition, the effectf salts on the binodal curve for the investigated systems has beeniscussed. Finally, the phase-separation ability of POELE10 is moreowerful than that of other polymers, which demonstrates thatOELE10 would be a properly candidate to form ATPS.
. Experimental
.1. Materials
Nonionic surfactant POELE10 was obtained from Aladdineagent Company (Shanghai, China) with the high-grade purend was used without further purification. The average moleculareight, the hydrophilic lipophilic balance (HLB), the critical micelle
oncentration (CMC) and the melting point of the surfactant are26.86 g mol−1, 16.9, 0.09 mg L−1, and 300.15 K, respectively. KOH,2CO3 and K3PO4 were analytical grade reagents (GR, min. 99%y mass fraction), which were purchased from Sinopharm Chemi-al Reagent Co., Ltd. (Shanghai, China). Double distilled deionizedater was used in the experiments.
.2. Apparatus and procedure
The binodal curves were determined by the titration methodcloud point method) [21]. The determinations of the binodalurves were carried out in a 50 ml glass vessel. The glass vessel wasquipped with an outer skin in which water was circulated using
DC-2008 water thermostat (Shanghai Hengping Instrument Fac-ory, China). The temperature of water was kept at the constantemperature (298.15 K) and the temperature fluctuation was con-rolled within 0.05 K. Surfactant POELE10 solution of known massraction was taken from the stock and put into the vessel. Then the
alt solution of known mass fraction was added until the appear-nce of turbidity. The composition of this mixture was noted inerms of the mass using an analytical balance (BS124S, Beijing Sar-orius Instrument Co., China) with an uncertainty of ±1.0 × 10−7 kg.
The water was added in drops until the mixture becomes clear, andthe above-mentioned procedures were repeatedly performed.
In order to determine the tie-lines, appropriate amounts of sur-factant, salt, and water were added into the vessel and were mixedand stirred which lasted for 0.5 h, then the sample was placed in athermostat water bath in which water temperature was set at thedesired temperature with the temperature fluctuation being con-trolled within 0.05 K. After 72 h, the mixture formed two phases,the concentrations of the salts in both phases were determinedby flame photometry (TAS-968, Beijing Purkinje General Instru-ment Co., Ltd., China). The precision in the measurement of themass fraction of the salts was better than 0.0002. The concentra-tion of POELE10 in the top and bottom phases was determined byrefractive index measurements following Cheluget et al. [22]. Therefractive index of the phases were performed at 298.15 K using arefractometer (WZS-I 811639, Shanghai, China) with a precision of±0.0001. The relation between the refractive index of the mixedsolution, nD, and the mass fractions of POELE10, w1, and the massfractions of salt, w2 is given by
nD = n0 + a1w1 + a2w2 (1)
where n0, a1 and a2 are constants. The values of the coefficients n0,a1 and a2 for the applied systems are given in Table 1. It’s worth not-ing that this equation is only valid within the range of w1 ≤ 0.1 andw2 ≤ 0.045, in which Eq. (1) is obtained. Therefore, it was essentialto dilute the solution to the appropriate mass fraction range beforemeasuring the refractive index. The uncertainty of the mass fractionof POELE10 using above measurement was found to be ±0.0002.
3. Results and discussion
3.1. Binodal data and correlation
The binodal data for the aqueous two phase systems containingPOELE10 and three salts (KOH, K2CO3 and K3PO4) at 298.15 K weregiven in Table 2. The phase diagram for three aqueous systems wasshown in Fig. 1. The binodal curves were fitted in accordance withthe following three equations:
w1 = exp(a + bw0.52 + cw2 + dw2
2) (2)
w1 = a + bw2 + cw22 + dw3
2 (3)
w1 = a exp(bw0.52 − cw3
2) (4)
where w1 is the mass fraction of POELE10, w2 is the mass fractionof salts, and a, b, c, and d are fitting parameters. Wang et al. [23]used Eq. (2) to correlate the bimodal data of the alcohol-citrateaqueous two-phase systems at 298.15 K. Eq. (3) was a third-orderpolynomial equation, which was used for the correlation of binodaldata of PEG-salts ATPSs [24]. The binodal curves of many ATPSs[25–30] were correlated with Eq. (4). The fitting parameters a, b,c and d determined through regression analysis of experimentalbinodal data along with the square of correlation coefficients (R2)and the corresponding standard deviations (sd) of Eqs. (2)–(4) for
the investigative systems are given in Tables 3–5, respectively. Ithas been concluded that Eq. (2) for POELE10 + K2CO3 + H2O andPOELE10 + K3PO4 + H2O ATPSs and Eq. (3) for POELE10 + KOH + H2OATPS are satisfactorily used to correlate the binodal curves in
Y. Lu et al. / Thermochimica Acta 543 (2012) 1– 8 3
Table 2Binodal data for the POELE10(1) + KOH/K2CO3/K3PO4(2) + H2O(3) ATPSs at 298.15 K and pressure p = 0.1 MPa.a
ccordance with the obtained correlation coefficients and standardeviations.
.2. Liquid–liquid equilibrium data and correlation
The liquid–liquid equilibrium (LLE) experimental data of threequeous systems containing POELE10 and three salts (KOH, K2CO3nd K3PO4) were given in Table 6. Recently, the equilibrium com-ositions of ionic liquid–salt ATPSs has been calculated successfullysing lever rule [31–33]. In this paper, the LLE data were also calcu-
ated by MATLAB on the basis of lever rule. To show the reliabilityf the lever rule, the comparison between the experimental andorrelated tie-lines is also shown in Figs. 2–4. It was found thathe experimental data and calculated data obtained good agree-
ent. The empirical correlation equations for the tie-lines given bythmer-Tobias and Bancroft [34] (Eqs. (5) and (6)) were used toorrelate the LLE data.
1 − wt1
wt1
)= k1
(1 − wb
2
wb2
)n
(5)
wb3
wb2
)= k2
(wt
3
wt1
)r
(6)
ig. 1. The binodal curves of the POELE10(1) + KOH/K2CO3/K3PO4(2) + H2O(3) ATPSst 298.15 K. �, KOH; �, K2CO3; �, K3PO4; solid line, reproduced by Eqs. (2) and (3).
3 is the mass fraction of POELE10 and water in thetop phase; wb
2 and wb3 is the mass fraction of salt and water in the
bottom phase, respectively; and k1, n, k2 and r are the fit param-eters. Othmer-Tobias and Bancroft equations have been widelyused to correlate the tie-lines data [23,29,30,35]. The values of theparameters in Eqs. (5) and (6), along with the square of correlationcoefficient values (R2) and standard deviations (sd) are presentedin Table 7 for the studied systems. The tie-line compositions of theinvestigated systems were also correlated with another equation(Eq. (7)).
wt2 = (r + k2
3)wt1 − ln(wt
2/wb3)
k23
(7)
where wt1 and wt
2 are the mass fraction of POELE10 and salts in thetop phase, wb
3 is the mass fraction of water in the bottom phase,k3 and r are the fitting parameters. This equation has been usedfor correlating the tie-line data of the polyvinylpyrrolidone [36]and polyoxyethylene cetyl ether [17] systems. The values of theparameters k3 and r and the square of correlation coefficient values
(R2) and standard deviations (sd) are given in Table 8.
a Standard uncertainties u are u(w) = 0.0001, u(T) = 0.05 K, and u(p) = 10 kPa.
Table 7Values of parameters of Eqs. (5) and (6) for the POELE10(1) + KOH/K2CO3/K3PO4(2) + H2O(3) ATPSs at 298.15 K (System 1, POELE10 + KOH + H2O; System 2,POELE10 + K2CO3 + H2O; System 3, POELE10 + K3PO4 + H2O).
On the basis of binodal theory [37], the tie-line data can be corre-ated by the relatively simple two-parameter equation, which wasimply Setschenow-type equation (Eq. (8)).
n
(wt
2
wb2
)= ̌ + k4(wb
1 − wt1) (8)
here superscripts “t” and “b” represent the top phase and bottomhase, respectively; subscripts “1” and “2” stand for the POELE10nd salts. The salting-out coefficient k4, and the activity coeffi-ient ̌ are the fitting parameters. The parameters k4 and ˇ, alongith the square of correlation coefficient values (R2) and standardeviations (sd) for the studied systems are given in Table 9. Theomparison of the standard deviations reported in Tables 7–9, indi-ated that Eq. (8) represents the experimental tie-line data with aetter accuracy.
.3. Effect of the type of salt on binodal curves
The binodal curves of the ATPSs composed of POELE10 and dif-erent salts were shown in Fig. 1, in which the region below theurves represents the single-phase region and the region above theurves is the two-phase region. The trend of the binodal curvesemonstrates that two-phase area will expand with increasing
he charge of the anion. In other word, at the same concentrationf POELE10 the concentration of salt at which the ATPS formedecreases with the increase in the charge of the anion. It was foundhat in the investigated systems the effectiveness of the anion on
e lines and j = 1 and j = 2, sd1 and sd2 represent the mass percent standard deviations
forming ATPSs with POELE10 was PO43− > CO3
2− > OH−. A similartrend has been observed in the PEG-(NaOH, Na2SO4, and Na3PO4)ATPSs by Ananthapadmanabhan et al. [38]. The order of the salting-out strength of three anion was PO4
3− > SO42− > OH− in the above
PEG systems. The possible reason is that the ability of hydratingwater of the higher valence anion is stronger than that of the lowervalence anion, which means the residual water that can be hydratedby polymer will decrease. Therefore, anions with a higher valenceis more easily exclude polymer from salt-water phase, which sug-gests that anions with a higher valence are better salting-out agentsthan those with a lower valence. Consequently, the forming two-phase ability of the salt containing anions with a higher valence issuperior to that of the salt containing anions with a lower valenceon the premise that they have the same cation.
The salting-out strength of salts is also measured by the salting-out coefficient k4 of Eq. (8). On the basis of the salting-out coefficientk4 indicated in Table 9, the values of salting-out coefficients risewith increasing the charge of the anion, which is in line with ourphase diagram and experimental data, namely at the same concen-tration of POELE10, the ATPS forms at lower concentration of saltwith higher charge of the anion.
3.4. Effective excluded volume and phase-separation abilities of
salts
The binodal model developed by Guan et al. [37] for aque-ous polymer–polymer systems is based on the statistical geometry
6 Y. Lu et al. / Thermochimica Acta 543 (2012) 1– 8
Table 9Values of parameters of Eq. (8) for the POELE10(1) + KOH/K2CO3/K3PO4(2) + H2O(3) ATPSs at 298.15 K.
same concentration of salt, the concentration of POELE10 which
sd = (i=1
(w1 − w1 )/n) , where w1 is the experimental mass fraction
f POELE10 in Table 1, wcal1 is the corresponding data calculated using Eq. (9). n
epresents the number of binodal data.
ethods from which the effective excluded volume (EEV) is deter-ined. We extended the application of this model to our studied
ystems. The binodal equation for the aqueous surfactant–salt sys-ems is written as
n(
V∗213
w2
M2
)+ V∗
213w1
M1= 0 (9)
here w1 and w2 are the mass fraction of POELE10 and salts, V∗213
s the scaled EEV of salt, M1 and M2 are molecular mass of POELE10nd salts, respectively. For the investigated systems, the EEV valueslong with the square of correlation coefficients (R2) and stan-ard deviations (sd) are given in Table 10. It is shown that, therdering of the scaled EEV of salts at the constant temperature is3PO4 > K2CO3 > KOH, which indicates that salt containing anionith higher valence is easier to exclude POELE10 from the bottomhase to the top phase. The concentration of POELE10 and salts inhe binodals curves of the studied systems which are plotted inig. 5 is shown in molality in order to closely compare the rela-
ionship between phase-separation abilities of salts and the EEValues.
The increment of EEV is reflected by the increase in the phase-eparation abilities of salts at the same temperature. It is found
ig. 5. Effect of type of salt on the binodal curves plotted in molality forhe ATPSs at 298.15 K. �, POELE10 + K3PO4 + H2O; �, POELE10 + K2CO3 + H2O; �,OELE10 + KOH + H2O.
e lines and j = 1 and j = 2, sd1 and sd2 represent the mass percent standard deviations
that the phase-separation abilities of the studied salts strengthenedwith the rising of the valence of anion from Table 10 and Fig. 5. Theconcentration of salts at which the ATPS is formed decreases withthe increase in EEV values. The salting-out ability of salt is alsorelated to the Gibbs free energy of hydration of the ions (�Ghyd)[39]. As shown in Fig. 5, it was found that the salts share a uniformcation but contain different anions, the salting-out ability of whichfollows this ordering PO4
3− > CO32− > OH−. Furthermore, it shows
that the more negative Gibbs free energy (�Ghyd) [40] in anions ofthe salt is, the stronger salting-out ability of salt is.
PO43−(−2765 kJ mol−1) > CO3
2−(−1315 kJ mol−1) > OH−
(−430 kJ mol−1)
In summary, the anion of salts with higher valence requireslower concentration to promote formation of ATPS, which resultsin that the binodal curve tends towards to the axis and the biphasicregion expands.
3.5. Comparing phase-separation abilities of POELE10 with otherpolymers
Fig. 6 was plotted to compare the present binodal curve withthe binodal curves referred in the literature at the tempera-ture of 298.15 K, namely, the binodal curves of PEG1000 [41],PEG2000 [41], PEG3400 [41] and PPG400 [42]. Fig. 6 reveals thatthe two-phase area of POELE10 + K3PO4 ATPS is wider than thatof PEG1000/PEG2000/PEG3400/PPG400 + K3PO4 ATPSs, and at the
is required to form ATPS is lower than that of other polymers.For this reason, surfactant POELE10 is a proper candidate forATPSs as well as PEG and PVP, and it can be considered as a
Fig. 6. Comparison of various binodal curves of several systems at 298.15 K. �,POELE10 + K3PO4 + H2O; �, PEG3400 + K3PO4 + H2O38; �, PEG2000 + K3PO4 + H2O38;�, PPG400 + K3PO4 + H2O39; �, PEG1000 + K3PO4 + H2O38.
imica
sa
4
c2dfTAibwsEKoPtpfe
F
FdC2PtT
R
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
Y. Lu et al. / Thermoch
uitable case for separating biological materials, metal ion andntibiotic.
. Conclusion
The binodal data and liquid–liquid equilibrium data of ATPSsomposed of POELE10 + KOH/K2CO3/K3PO4 + H2O were studied at98.15 K. The binodal data for these systems were satisfactorilyescribed by the proposed equations, and the tie-line compositionsor the studied systems were satisfactorily correlated with Othmer-obias and Bancroft and the simple Setschenow-type equations.dditionally, the effect of salt on the binodal curves was stud-
ed, and it was found that anions with the higher valence areetter salting-out agents than anions with the lower valence,hich is corresponded to the value of salting-out coefficient of
alts calculated by Eq. (8) and the value of EEV calculated byq. (9). Therefore, the ordering of salting-out abilities of salts is3PO4 > K2CO4 > KOH in the investigated systems. Finally, the bin-dal curve of POELE10 + K3PO4 ATPS was compared with that of theEG1000/PEG2000/PEG3400/PPG400 + K3PO4 ATPSs. It was foundhat two-phase area of POELE10 ATPS is wider than that of otherolymer ATPSs at the same concentration of salt. Therefore, sur-actant POELE10–salt ATPS is a new option for aqueous two-phasextraction.
unding sources
This work was supported by the National Natural Scienceoundation of China (No. 21076098), the Natural Science Foun-ation of Jiangsu Province (Nos. BK2010349 and BK2011529),hina Postdoctoral Science Foundation funded project (No.0110491352), Ph.D. Innovation Programs Foundation of Jiangsurovince (No. X2211 0584), Jiangsu Postdoctoral Science Founda-ion funded project (No. 1101036C) and the Programs of Senioralent Foundation of Jiangsu University (No. 11JDG029).
eferences
[1] Z.H. Wang, M. Song, Q. Ma, Y.T. Two-ph Gao, W. Wang, Distribution behav-ior and extraction mechanism of gold(III) in polyethylene glycol ammoniumsulphate aqueous biphasic system, Chin. J. Appl. Chem. 19 (2002) 578–580.
[2] Z.H. Wang, M. Song, Q. Ma, Two-phase aqueous extraction of chromium andits application to speciation analysis of chromium in plasma, Mikrochim. Acta134 (2000) 95–99.
[3] L. Bulgariu, D. Bulgariu, Extraction of metal ions in aqueous polyethylene glycol-inorganic salt two-phase systems in the presence of inorganic extractants:correlation between extraction behaviour and stability constants of extractedspecies, J. Chromatogr. A 1196 (2008) 117–124.
[4] Y. Wang, J. Han, X.H. Xu, S.P. Hu, Y.S. Yan, Partition behavior and partitionmechanism of antibiotics in ethanol/2-propanol-ammonium sulfate aqueoustwo-phase systems, Sep. Purif. Technol. 75 (2010) 352–357.
[5] Q. Le, L. Shong, Y. Shi, Extraction of erythromycin from fermentation broth usingsalt-induced phase separation processes, Sep. Purif. Technol. 24 (2001) 85–91.
[6] Q. Liu, J. Yu, W. Li, Partitioning behavior of penicillin G in aqueous two phasesystem formed by ionic liquids and phosphate, Sep. Sci. Technol. 41 (2006)2849–2858.
[7] X.Q. Xie, Y. Wang, J. Han, Y.S. Yan, Extraction mechanism of sulfamethoxazolein water samples using aqueous two-phase systems of poly (propylene glycol)and salt, Anal. Chim. Acta 687 (2011) 61–66.
[8] Y. Wang, X.H. Xu, J. Han, Y.S. Yan, Separation/enrichment of trace tetracyclineantibiotics in water by [Bmim]BF4-(NH4)2SO4 aqueous two-phase solvent sub-lation, Desalination 266 (2011) 114–118.
[9] H.S. Ng, C.P. Tan, M.N. Mokhtar, S. Ibrahim, A. Ariff, C.W. Ooi, T.C. Ling, Recoveryof Bacillus cereus cyclodextrin glycosyltransferase and recycling of phase com-ponents in an aqueous two-phase system using thermo-separating polymer,Sep. Purif. Technol. 89 (2012) 9–15.
10] H.O. Johanssona, T. Matosb, J.S. Luzc, E. Feitosad, C.C. Oliveirac, A. Pes-soa, L. Bülowb, F. Tjernelda, Plasmid DNA partitioning and separation using
poly(ethyleneglycol)/poly(acrylate)/salt aqueous two-phase systems, J. Chro-matogr. A 1233 (2012) 30–35.
11] P. Vázquez-Villegas, O. Aguilar, M. Rito-Palomares, Study of biomolecules par-tition coefficients on a novel continuous separator using polymer-salt aqueoustwo-phase systems, Sep. Purif. Technol. 78 (2011) 69–75.
[
Acta 543 (2012) 1– 8 7
12] P.L. Show, C.P. Tan, M.S. Anuar, A. Ariff, Y.A. Yusof, S.K. Chen, T.C. Ling, Primaryrecovery of lipase derived from Burkholderia cenocepacia strain ST8 and recy-cling of phase components in an aqueous two-phase system, Biochem. Eng. J.60 (2012) 74–80.
13] Y.J. Li, X.J. Cao, Prediction of phase diagrams for new pH-thermo sensi-tive recycling aqueous two-phase systems, Fluid Phase Equilib. 298 (2010)206–211.
14] M.T. Zafarani-Moattar, V. Hosseinpour-Hashemi, Effect of temperature on theaqueous two-phase system containing poly(ethylene glycol) dimethyl ether2000 and dipotassium oxalate, J. Chem. Eng. Data 57 (2012) 532–540.
15] J. Han, Y. Wang, C.L. Yu, Y.Y. Li, W.B. Kang, Y.S. Yan, Liquid–liquid equilib-rium of imidazolium ionic liquids + organic salts aqueous two-phase systemsat 298.15 K and the influence of salts and ionic liquids on the phase separation,J. Chem. Thermodyn. 45 (2012) 59–67.
16] M.T. Zafarani-Moattar, E. Nemati-Kande, A. Soleimani, Study of theliquid–liquid equilibrium of 1-propanol + manganese sulphate and 2-propanol + lithium sulphate aqueous two-phase systems at different tempera-tures: experiment and correlation, Fluid Phase Equilib. 313 (2012) 107–113.
17] F. Masumeh, H. Nosrat, M. Maryam, Liquid–liquid equilibrium data for aqueoussolutions of surfactant Brij58 with (NH4)H2PO4, (NH4)2HPO4, and KH2PO4, J.Chem. Eng. Data 53 (2008) 242–246.
18] F. Masumeh, H. Nosrat, M. Maryam, J. Amin, Effect of temperature on the(liquid + liquid) equilibrium for aqueous solution of nonionic surfactant andsalt: experimental and modeling, J. Chem. Thermodyn. 40 (2008) 1077–1081.
19] M. Kellermayer, A. Ludany, A. Miseta, T. Koszegi, G. Berta, P. Bogner, C.F. Hazle-wood, I.L. Cameron, D.N. Wheatley, Release of potassium, lipids, and proteinsfrom nonionic detergent treated chicken red blood cells, J. Cell Physiol. 159(1994) 197–204.
20] H.G. Xie, Y.J. Wang, M. Sun, Modeling of the partitioning of membrane pro-tein and phase equilibria for TritonX-100-salt aqueous two-phase systemsusing a modified generalized multicomponent osmotic virial equation, ProcessBiochem. 41 (2006) 689–696.
21] P.A. Albertsson, Partitioning of Cell Particles and Macromolecules, Wiley Inter-science, New York, 1986.
22] E.L. Cheluget, S. Marx, M.E. Weber, J.H. Vera, Equilibrium in biphasic aqueoussystems: a model for the excess Gibbs energy and data for the system H2O-NaCl-1-propanol at 25◦ , J. Solut. Chem. 23 (1994) 275–305.
23] Y. Wang, S.P. Hu, J. Han, Y.S. Yan, Measurement and correlation of phase dia-gram data for several hydrophilic alcohol + citrate aqueous two-phase systemsat 298.15 K, J. Chem. Eng. Data 55 (2010) 4574–4579.
24] M. Perumalsamy, T. Murugesan, Phase compositions, molar mass, and tem-perature effect on densities, viscosities, and liquid–liquid equilibrium ofpolyethylene glycol and salt-based aqueous two-phase systems, J. Chem. Eng.Data 54 (2009) 1359–1366.
25] M.T. Zafarani-Moattar, P. Seifi-Aghjekohal, Liquid–liquid equilibria of aque-ous two-phase systems containing polyvinylpyrrolidone and tripotassiumphosphate or dipotassium hydrogen phosphate: Experiment and correlation,CALPHAD 31 (2007) 553–559.
26] M.T. Zafarani-Moattar, S. Tolouei, Liquid–liquid equilibria of aqueous two-phase systems containing polyethylene glycol 4000 and di-potassium tartrate,potassium sodium tartrate, or di-potassium oxalate: experiment and correla-tion, CALPHAD 32 (2008) 655–660.
27] M.T. Zafarani-Moattar, A. Zaferanloo, Measurement and correlation of phaseequilibria in aqueous two-phase systems containing polyvinylpyrrolidone anddi-potassium tartrate or di-potassium oxalate at different temperatures, J.Chem. Thermodyn. 41 (2009) 864–871.
28] M.T. Zafarani-Moattar, S. Nasiri, (Liquid + liquid) and (liquid + solid) equilib-rium of aqueous two-phase systems containing polyethylene glycol di-methylether 2000 and di-sodium hydrogen phosphate, J. Chem. Thermodyn. 42 (2010)1071–1078.
29] J. Han, R. Pan, X.Q. Xie, Y. Wang, Y.S. Yan, G.W. Yin, W.X. Guan, Liquid–liquidequilibria of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroboratesodium and ammonium citrate aqueous two-phase systems at (298.15,308.15,and 323.15) K, J. Chem. Eng. Data 55 (2010) 3749–3754.
30] J. Han, C.L. Yu, Y. Wang, X.Q. Xie, Y.S. Yan, G.W. Yin, W.X. Guan, Liquid–liquidequilibria of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate andsodium citrate/tartrate/acetate aqueous two-phase systems at 298.15 K: exper-iment and correlation, Fluid Phase Equilib. 295 (2010) 98–103.
31] F.J. Deive, M.A. Rivas, A. Rodríguez, Sodium carbonate as phase promoter inaqueous solutions of imidazolium and pyridinium ionic liquids, J. Chem. Ther-modyn. 43 (2011) 1153–1158.
32] Y. Deng, J. Chen, D. Zhang, Phase diagram data for several salt + salt aqueousbiphasic systems at 298.15 K, J. Chem. Eng. Data 52 (2007) 1332–1335.
33] Y. Deng, T. Long, D. Zhang, J. Chen, S. Gan, Phase diagram of [Amim]Cl + saltaqueous biphasic systems and its application for [Amim]Cl recovery, J. Chem.Eng. Data 54 (2009) 2470–2473.
34] P.G. Gonzalez-Tello, F. Camacho, G. Blazquez, F. Alarcon, Liquid–liquid equi-librium in the system poly ethylene glycol + MgSO4 + H2O at 298.15 K, J. Chem.Eng. Data 41 (1996) 1333–1336.
35] Y. Wang, S.P. Hu, Y.S. Yan, W.S. Guan, Liquid–liquid equilibrium of potas-
sium/sodium carbonate + 2-propanol/ethanol + water aqueous two-phase sys-tems and correlation at 298.15 K, CALPHAD 33 (2009) 726–731.
36] M. Foroutan, Liquid–liquid equilibria of aqueous two phase polyvinylpyrroli-done and K2HPO4/KH2PO4 buffer effects of pH and temperature, J. Chem. Eng.Data 52 (2007) 859–862.
8 imica
[
[
[
[
[
Y. Lu et al. / Thermoch
37] Y. Guan, T.H. Lilley, T.E. Treffry, A new excluded volume theory and its appli-cation to the coexistence curves of aqueous polymer two-phase systems,Macromolecules 26 (1993) 3971–3979.
38] K.P. Ananthapadmanabhan, E.D. Goddard, Aqueous biphase formation in
polyethylene oxide-inorganic salt systems, Langmuir 3 (1987) 25–31.
39] R.D. Rogers, A.H. Bond, C.B. Bauer, J. Zhang, S.T. Griffin, Metal ion separations inpolyethylene glycol-based aqueous biphasic systems: correlation of partition-ing behavior with available thermodynamic hydration data, J. Chromatogr. B680 (1996) 221–229.
[
Acta 543 (2012) 1– 8
40] Y. Marcus, Thermodynamics of solvation of ions Part 5—Gibbs free energy ofhydration at 298.15 K, J. Chem. Soc. Faraday Trans. 87 (1991) 2995–2999.
41] G.H. Jonathan, D.W. Heather, D.R. Robin, Phase diagram data for several PEG-salt aqueous biphasic systems at 25 ◦C, J. Chem. Eng. Data 48 (2003) 1230–
1236.
42] X.Q. Xie, J. Han, Y. Wang, Y.S. Yan, G.W. Yin, W.S. Guan, Measurement, Correla-tion of the phase diagram data for PPG400 + (K3PO4, K2CO3, and K2HPO4) + H2Oaqueous two-phase systems at T = 298.15 K, J. Chem. Eng. Data 55 (2010)4741–4745.
