Fluid Phase Equilibria 254 (2007) 158162

Solubility of sodium chloride in wateo Sumei

bruary2007

Abstract

The solub e ranIn the regio aCl aT)/mol kg1 7.4dard deviat on,T)/mol kg1 T/K)0.14%. The ith thaqueous solu ution 2007 Else

Keywords: So

1. Introdu

Sodium chloride and water constitute a prototypical soluteand solvent pair for solubility studies. The number of investiga-tions measuring the solubility of this system amounts to morethan 100 [1]. Fig. 1 shows the domains where the measurementswere perfoonly fouring 50 MPastudies, whbomb for aTherefore,have not besolubility hnative, therhave beensolute [10,1

We havehigh pressusolids [16[23,24]. Sehigh-pressu

CorresponE-mail ad

ordering

also been improvements to commercially available pumps, pres-sure gauges, and other high-pressure fittings; a flexible tube usedin the present work is one of them. In the present work, weapplied these high-pressure techniques to the measurement of

0378-3812/$doi:10.1016/jrmed at pressures higher than 3 MPa. In this figure,studies, namely #25, employed pressures exceed-

and these were executed about 100 years ago. Suchere a high pressure of over 50 MPa is maintained in along time in order to attain equilibrium was not easy.further direct measurements at such high pressuresen performed, although many measurements of theave continued at atmospheric pressure. As an alter-modynamic estimates of the high-pressure solubilityattempted using the density of the solution and solid1].measured the solubility of several compounds underres; not only inorganics [1215] but also organic19], liquid hydrocarbons [2022], and a fullereneveral improvements of pressure vessels and otherre equipment have been implemented in these stud-

ding author. Tel.: +81 77 566 1111; fax: +81 77 561 2629.dress: sawamura@se.ritsumei.ac.jp (S. Sawamura).

the solubility of sodium chloride in water under high pressures.We also measured the solubility of its hydrate, NaCl2H2O, atlow temperatures and high pressure.

2. Experimental

2.1. Materials

A special grade of sodium chloride (>99.5%) was purchasedfrom Nakarai Tesque Co. and used without further purification.Water was deionized and distilled. The solid hydrate of sodiumchloride, NaCl2H2O, was prepared as follows. An excess quan-tity of sodium chloride and water was mixed in a flask andallowed to stand in a refrigerator at 273 K for 1 day. Then theupper solution portion of the mixture was removed and furthercooled in a freezer at 258 K for one more day. We obtained aplate-like precipitate which used as the solid hydrate. It wasstable up to a temperature of 281 K with hysteresis and wasdissociated into solid NaCl and water at higher temperatures.

see front matter 2007 Elsevier B.V. All rights reserved..fluid.2007.03.003Seiji Sawamura , Nobuaki Egoshi, YoshihirDepartment of Applied Chemistry, Faculty of Science and Engineering, Rits

Received 21 October 2006; received in revised form 26 FeAvailable online 6 March

ility (msat) of sodium chloride in water was measured in the pressurn of high temperature and low pressure, the solubility values of N] = 2.86623 571.361/(T/K) + 77,128/(T/K)2 + 4.0479 104(p/MPa)ion of 0.08%. In the low-temperature and high-pressure regi] = 5.35183 1366.040/(T/K) + 108,664/(T/K)2 + [0.010331 5.8869(experimental values of the high-pressure solubilities were compared wtion of sodium chloride and the activity coefficient of the aqueous solvier B.V. All rights reserved.

lubility; Sodium chloride; High pressure

ction ies inpioneer under high pressureetoguchi, Hiroshi Matsuokan University, Kusatsu, Shiga 525-8577, Japan

2007; accepted 1 March 2007

ge 0.10300 MPa, and temperatures from 263 to 313 K.nhydride obtained were fitted to the equation ln[msat(p,45 107(p/MPa)2 + 6.209 1010(p/MPa)3 with a stan-

the values for NaCl2H2O were fitted to ln[msat(p,1 + 831.7(T/K)2](p/MPa) with a standard deviation ofermodynamic estimates using density data of the solid and.

r to obtain more reliable solubility data. Since thework of Adams et al. [6] and others [4,5] there have

S. Sawamura et al. / Fluid Phase Equilibria 254 (2007) 158162 159

Fig. 1. Diagram of solubility data of sodium chloride in water (p > 3MPa): (1)Moller (1862) [2]; (2) Von Stackelberg (1896) [3]; (3) Cohen and Sinnige (1910)[4]; (4) Sill (1910) [5]; (5) Adams and Hall (1931) [6]; (6) Keevil (1942) [7]; (7)Olander and Liander (1950) [8]; (8) Bischoff et al. (1986) [9]; (9) present work.

2.2. Appar

Fig. 2 shsaturated sothe main bis made ofa valve (G)water circuanism is ufluorinatedattached to

Fig. 2. Cylind(B) inner cell;valve with a h

from sample solution. Water and an excess quantity of sodiumchloride was placed in the inner cell with a shaking ball (F) madeof fluorinated plastic. In the case of NaCl2H2O, a mixture of thesolid solute (NaCl2H2O) and a solution prepared as above wasplaced in the inner cell in the previously cooled pressure ves-sel. The sample mixture was separated from the compression oil(kerosine) in the inner cell by a fluorinated plastic piston withtwo fluorinated o-rings. If we used the piston fitted to the pres-sure vessel directly to the cylinder without using the inner cell,expansion of the cylinder, coupled with compression of the pis-ton produces a slight opening between the piston and cylinderof the pressure vessel at pressures higher than 200 MPa, and thecompression oil contaminated the sample solution. Details ofthe inner cell are shown in Fig. 2. For the seal between the pres-sure vessel and plug (I), a commercially available fluorinatedo-ring and a back-up ring, which was made of annealed copperand designed by us with an accuracy of 0.01 mm, were used;these parts were exchanged for every measurement. The valvecone and other metal-to-metal sealing parts were often cut andpolished and some parts were exchanged for new ones. Suchfrequent high-pressure sealing maintenance allows us to easilymaintain the pressure constant at high values for a long timewithout any trouble.

Fig. 3 shows the whole high-pressure system. The pressure(A) was fixed on a seesaw (F) in a water bath (J) of 40 dm3e and the seesaw was moved 23 times a minute in orderthe sample in the pressure vessel. At low temperatures,ter impraulic

outsselatus and procedure

ows the pressure vessel used for the preparation oflutions under high pressures. The outer diameter ofody is 70 mm and the inner bore is 1518 mm. Itcorrosion-resistant 17-4PH stainless steel and hasand an outlet tube (H). A jacket through which hot

lates is attached to the outlet tube and a similar mech-sed to warm the valve. An inner cell (B) made ofplastic was connected to a plug (I). A glass filter wasthe tip of the inner cell to separate the solid solute

vesselvolumto stirthe waThe coa hydr1.6 mmsure verical pressure vessel with a valve and an inner cell: (A) cylinder;(C) piston; (D) sample volume; (E) compression oil; (F) ball; (G)eating device; (H) outlet tube with a heating jacket; (I) plug.

Fig. 3. Mixinpressure vessetube; (F) seesgear; (J) waten the bath was changed to aqueous ethylene glycol.ession oil was pushed into the pressure vessel from

pump (B) through a flexible stainless tube (E) ofer diameter. By using such a flexible tube, the pres-connected to the tube can be shaken on the seesaw.

g equipment for the thermostatted cylindrical pressure vessel: (A)l; (B) hydraulic pump; (C) pressure gauge; (D) valve; (E) flexibleaw; (G) thermoregulator; (H) stirrer; (I) motor with a reductionr bath.

160 S. Sawamura et al. / Fluid Phase Equilibria 254 (2007) 158162

The whole system shown in Fig. 3 was placed in an air-conditioned room at 298 1 K because the pressure in the closedsystem depwas closedsystem whin this closof the soluseveral timcessation oconvenient

After mstopped anto let particsample solslightly loosel (A) wasoil into the(23 cm3) o(79 cm3)after dryingconcentratipressure veand outletsolute.

To measFig. 3) of ta Heise mosmallest diwas used. Ipressure vea standardof 0.01% oInstitute mwere condupressure gagauge of thIndustries.

The temusing an onity better theater wasenvironmea three-wir

3. Results

3.1. Equili

The conis plotted athe concenand this valactually all

For thethe two soltime oftenaccurate es

imeessur

l triassurn 28wer

ionssam

e ph

igh-

ues oatmo-Adaf ann theing two equations. For the high-temperature/low-pressure(anhydrous NaCl):t(p, T )/mol kg1]

.86623 571.361(T/K) +77, 128(T/K)2 + 4.0479

104(p/MPa) 7.445107(p/MPa)2 + 6.209 1010(p/MPa)3 (1)for the low-temperature/high-pressure region

2H2O):t(p, T )/ mol kg1]

.35183 1366.040(T/K) +108, 664(T/K)2 + [0.010331

5.8869(T/K)1 + 831.7(T/K)2](p/MPa) (2)standard deviations of the logarithm of the solu-

(ln msat), listed in Table 1 were 0.08% for NaClends on the room temperature. Further, the valve (D)during the shaking to reduce the part of the closed

ich is kept in an ambient condition. As the pressureed system decreased accompanying the dissolutionte, we repeatedly adjusted the pressure in the vesseles until the system attained equilibrium. We used thef the need to adjust the pressure at equilibrium as amethod to signal the achievement of equilibration.

oving the seesaw for several tens of hours, it was thend the pressure vessel was allowed to stand for a whileles of the solid solute in the inner cell sink; then the

ution was taken out drop by drop from the outlet bysening the valve. Throughout this operation, the ves-held at a constant pressure by pushing compressionvessel from the hydraulic pump. The initial portionf the solution was discarded and the subsequent part

was collected. The sample was weighed before andin an electric oven at about 440 K to determine the

on. When the sample solution was taken out of thessel, hot water was circulated around the valve (G)tube (H) in Fig. 2 to avoid any precipitation of the

ure the pressure in the system, a precise gauge (C inhe Bourdon-tube type with an accuracy of 1 MPa,del (45 cm diameter, full scale is 700 MPa and the

vision is 0.5 MPa) produced by Dresser Industries,t was connected to the hydraulic pump (B) and thessel (A) and calibrated by the same company withpressure gauge of free-piston type with an accuracyf full scale based on American National Standardsethods NCSL Z540-1 and ISO-10012. Because wecting long-term measurements of the solubility, theuge (C) was recalibrated by us with a new pressuree same type purchased from and calibrated by Dresser

perature of water bath was regulated within 005 Koff type regulator designed by us with a sensitiv-

han 1 m K. A suitable power level of the regulatingselected or a cooler unit was used depending on the

ntal conditions. The temperature was measured withe platinum-resistance thermometer.

and discussion

bration time

centration of sodium chloride in the pressure vesselgainst the equilibration time in Fig. 4. After 1 day,tration becomes constant at each set of conditionsue was regarded as the solubility. For most cases, weowed more than 1 day for equilibration.measurements close to the transition points betweenid phases of NaCl and NaCl2H2O, the equilibrationbecame much longer (sometimes too long to obtaintimates of the solubility) because of hysteresis. After

Fig. 4. Tin the pr

severa

the prebetweeto or loconditas thenear th

3.2. H

Values atCohentions othose ifollowregion

ln[msa

= 2

and(NaClln[msa

= 5

The

bility,course of the concentration of sodium chloride in the water phasee vessel during mixing.

ls, we selected the solute which should be placed ine vessel as follows. At all pressures and temperatures3.15 and 313.15 K and at 278.15 K at pressures equalthan 100 MPa, we used anhydrous NaCl. For the otherused in the present work, solid NaCl2H2O was usedple solute. In all cases, the approach to equilibriumase-transition point was carefully checked.

pressure solubility

f the solubility obtained are listed in Table 1. Our val-spheric pressure coincide with the rounded values ofd and Lorimer [1] within 0.15% though the propor-hydrous NaCl in the former study are smaller thanlatter by 0.07% on average. We fitted the data to the

S. Sawamura et al. / Fluid Phase Equilibria 254 (2007) 158162 161

Table 1Solubility of sodium chloride in water (mol kg1)p/MPa

5 293.15 298.15 303.15 313.15

0.10a 6.142 6.159 6.179 6.2240.10 6.136 6.152 6.174 6.220

50.0 6.260 6.270 6.295 6.345100.0 6.350 6.367 6.375 6.425150.0 6.457 200.0 6.519 6.550 6.575250.0 6.542 6.586 300.0 6.610

Solutes are N aCl2H2O for all pressures at 263.15273.15 K and 150300 MPa at278.15 K.

a Rounded

Fig. 5. Logarwork; () Coand Hall [6] a

and 0.14%( ( lboundary lfrom theseat 0.10 MProunded vaLorimer [1the figure p

The logato that at atwith literatnot depend[4] and by50 MPa. Atour data forTable 1 areeye view ofthe whole s

hermodynamic analysis

pressure coefficient of the logarithm of the solubility ofchloride in water, p [( ln msat/p)T], can be thermo-

ically derived as Eq. (3) [13]:T/K

263.15 268.15 273.15 278.15 283.1

5.640 5.860 6.095 6.106 6.1155.639 5.859 6.095 6.102 6.112 5.845 6.087 6.221 6.2275.627 5.841 6.059 6.308 6.3255.612 5.804 6.043 6.258 6.3995.605 5.795 5.997 6.4635.599 5.780 5.965 6.192 6.5315.597 5.752 5.960 6.555

aCl for all pressures at 283.15313.15 and 0.10100 MPa at 278.15 K and N

values [1].

3.3. T

Thesodiumdynamithm of relative solubility of sodium chloride in water: (), presenthen and Sinnige [4] at 297.2 K; () Sill [5] at 298.15 K; () Adamst 303.08 K; () Von Stackelberg [3] at 291.7 K.

for NaCl2H2O, respectively, where (ln msat) =n msat)2/(N 1)

)and N is the number of data. The

ine of the two NaCl and NaCl2H2O phases obtainedtwo equations goes through temperatures of 273.2 Ka and 288.6 K at 300 MPa. These are close to thelues of 273.2 K at 0.10 MPa by Cohen-Adad and

] and 288.4 K at 300 MPa which was estimated fromrovided by Adams and Gibson [25].rithm of the solubility of anhydrous NaCl normalized

mospheric pressure is plotted in Fig. 5 and comparedure data. The solid line corresponds to Eq. (1). It doeson temperature. The values by Cohen and SinnigeAdams and Hall [6] fit our line at pressures up tohigher pressures, the latter values seem to lie belowreasons that are not clear. The solubility data listed instereographically plotted in Fig. 6, allowing a birds-the solubility of NaCl and NaCl2H2O in water overet of conditions.

p = [

2

where A isnumber ofhydrated cr

f 1 +(

where is the voluresponds toV sat, of theNaCl2H2Oof the solid

V = V satV

RTf

] [A

A nmsat

](3)

the amount of 1 kg water (55.51 mol) and n is themolecules of hydration water for each molecule ofystal (n = 2 for NaCl2H2O). ln

m

)T

(4)

is the mean activity coefficient of the ions, and Vme change accompanying dissolution, which cor-

the difference between the partial molar volume,solute (including that of 2 mol of water per mole of) at saturated concentration and molar volume, VC,solute, as shown in Eq. (5): VC (5)Fig. 6. Solubility of sodium chloride in water.

162 S. Sawamura et al. / Fluid Phase Equilibria 254 (2007) 158162

As V sat is estimated as 23.67 0.2 cm3 mol1 from the den-sity of aqueous sodium chloride at 0.10 MPa and 298.2 K [26],the VC of NaCl is 27.00 0.02 cm3 mol1 from X-ray data[27,28], and ( ln /m)T,p = 0.759 [29], p can be estimated as(3.82 0.25) 104 MPa1 using Eqs. (3)(5). Using a similarmethod, p for NaCl2H2O at 0.10 MPa and 273.2 K is estimatedto be (0.94 0.47) 104 MPa1 using V sat = 58.6 0.2(=(23.30 0.2) + 2 (17.65 0.02)) cm3 mol1 [26] including2 mol of hydration water, VC = 58.00 0.05 cm3 mol1 [25],and ( ln culated vaand NaCl(2) are (4.0and (0.7respectivelthermodynhigh-pressuthe errors i

4. Conclu

The solsolute andsured as aaccuracy. Tview of thesurements

List of symA amf co

ofm co

msat so

m0 son nu

m

p prR gaT teV vo

(cVC mV sat pa

(c

Greek lette mp pr

(

(ln msat) standard deviation of the logarithm of solubilitydefined as

[ (msat)2/(N 1)], where N is thenumber of data points

Acknowledgements

This work was partially supported by The Salt ScienceResearch Foundation, the 120th Anniversary of RitsumeikanAcademy and the 19th Anniversary of Ritsumeikan Universitys

or throjec

nce

Choen1, whundedMolle. von

96) 3CohenSill, J. Ad. Ke

Oland. Bisc(1986. Ad

GehleSawam93) 2awamh Preawam

(1999Matsuawam

em. 2SawamSuzukssureMatsuSawamSawamSawam9.

SawamSawam

. Ad.Z. RH. H

Fun, SpriBoeh. Milllution./m)T,p = 0.797 [29]. We can compare these cal-lues with the experimental values of p for NaCl2H2O estimated from the curves of Eqs. (1) and5 0.04) 104 MPa1 at 0.10 MPa and 298.2 K

4 0.05) 104 MPa1 at 0.10 MPa and 273.2 K,y. Our experimental values for p coincide with theamic estimates and confirms the reliability of ourre measurements, although we should be aware that

n the thermodynamic estimation are large.

sions

ubility of sodium chloride in water, a prototypicalsolvent pair for solubility investigations, was mea-function of pressure and temperature with high

he results of the present work finally provide a globalsolubility after a 100-year gap since the first mea-

of high-pressure solubility of this pair were made.

bolsount of 1 kg water (= 55.51 mol)

ncentration coefficient of mean activity coefficientions, Eq. (4)ncentration (mol kg1)lubility (mol kg1)lubility (mol kg1) at 0.10 MPamber of hydration water molecule per hydratedoleculeessure (MPa)s constant (J K1 mol1)mperature (K)lume change accompanying dissolutionm3 mol1)olar volume of solid (cm3 mol1)rtial molar volume at saturated concentrationm3 mol1)

rsean activity coefficient of ions in morality.essure coefficients of the solubility defined asln msat/p)T (MPa1)

Fund ftier P

Refere

[1] R.199ro

[2] K.[3] E.F

(18[4] E.[5] H.[6] L.H[7] N.B[8] A.[9] J.L

50[10] L.H[11] H.[12] S.

(19[13] S. S

Hig[14] S. S

16[15] H.[16] S. S

Ch[17] S.[18] Y.

Pre[19] H.[20] S.[21] S.[22] S.

242[23] S.[24] S.[25] L.H[26] P.S[27] K.-

und7-a

[28] R.[29] F.J

So25)e Promotion of Research, and the Academic Fron-t from MEXT of Japanese Government, 20032007.

s

-Adad, J.W. Lorimer, Solubility Data Series 47, Pergamon Press,ere the solubility evaluated from many reference data is called thevalue..

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37., K. Inouye, C. Euwen, Z. Phys. Chem. 75 (1910) 257.. Am. Chem. Soc. 38 (1916) 2632.ams, R.H. Hall, J. Wash. Acad. Soc. 21 (1931) 183.evil, J. Am. Chem. Soc. 64 (1942) 841.er, H. Liander, Acta Chim. Scand. 4 (1950) 1437.hoff, R.J. Rosenbauer, K.S. Pitzer, Geochim. Cosmochim. Acta.) 1437.

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i, H. Matsuo, Y. Koga, K. Mukae, T. Kawakita, S. Sawamura, HighRes. 21 (2001) 93.o, Y. Suzuki, S. Sawamura, Fluid Phase Equilib. 20 (2002) 227.ura, K. Suzuki, Y. Taniguchi, J. Solution Chem. 16 (1987) 649.ura, K. Kitamura, Y. Taniguchi, J. Phys. Chem. 93 (1989) 4931.ura, K. Nagaoka, T. Machikawa, J. Phys. Chem. B 105 (2001)

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ams, R.E. Gibson, J. Am. Chem. Soc. 52 (1930) 4252.ogers, K.S. Pitzer, J. Phys. Chem. Ref. Data 11 (1982) 15.ellwege, A.M. Hellwege (Eds.), Landolt-Bornstein Zahlenwertektionen aus Naturwissenschaften und Technik, Neue Serie, vol.nger-Verlag, 1973, p. 344.ler, G.C. Kennedy, J. Phys. Chem. Solids 41 (1980) 517.ero, in: R.M. Rytkowicz (Ed.), Activity Coefficients in Electrolytes, vol. 2, CRC Press Inc., Boca Raton, FL, 1979 (chapter 2, Table

Solubility of sodium chloride in water under high pressureIntroductionExperimentalMaterialsApparatus and procedure

Results and discussionEquilibration timeHigh-pressure solubilityThermodynamic analysis

ConclusionsAcknowledgementsReferences