Solubility Measurements in the Mixed Solvent Electrolyte System

2218

Ind. Eng. Chem. Res. 2009, 48, 2218–2228

Solubility Measurements in the Mixed Solvent Electrolyte System Na2CO3-NaHCO3-Monoethylene Glycol-Water Philip L. Fosbøl,* Kaj Thomsen, and Erling H. Stenby IVC-SEP, Department of Chemical Engineering, Technical UniVersity of Denmark, DK-2800 Kongens Lyngby, Denmark

212 new data points for solubility and density have been measured in the mixed solvent electrolytic CO2-NaHCO3-Na2CO3-monoethylene glycol (MEG)-water system. Measurements were conducted at 2-60 °C at atmospheric pressure. An overview of methods available for determining the carbon dioxide and sodium content is given and the reverse Schreinemakers method was chosen. The method gives the amounts of all the species in the liquid. The solutions have a tendency to form metastable mixtures from which sodium carbonate salt hydrates may precipitate. Thirty metastable data points are reported. Introduction The aim of this study is to investigate CO2 corrosion through experimental work. The experimental work is focused on the CO2-NaOH-MEG-H2O system which is observed in natural gas pipelines also known as wet gas pipelines. The chemical system is a subsystem of CO2-Na2O-MEG-H2O and similarly Na2CO3-NaHCO3-MEG-H2O is also a subsystem of CO2Na2O-MEG-H2O. Therefore solubility measurements are conducted for the Na2CO3-NaHCO3-MEG-H2O system in order to describe the CO2-NaOH-MEG-H2O system. The experimental data may be used at a later point to correlate activity coefficients. Only a few experimental studies of the Na2CO3NaHCO3-MEG-H2O system have been published. This includes Oosterhof et al.1 who published solubility of Na2CO3 in MEG-H2O at temperatures above 40 °C. Ga¨rtner et al.2 continued their work and measured solubility in ternary NaHCO3 and quaternary Na2CO3-NaHCO3 aqueous systems at MEG concentrations of w(MEG) > 50% and 15 to 90 °C, though primarily above 50 °C. The work by Ga¨rtner et al.2 was mainly focused on solubility in the quaternary system; only few of these data concerned solubility in the ternary NaHCO3-MEG-H2O system. The latter system was also investigated by Dugstad,3 who published few experimental data. Unfortunately, a density-dependent concentration unit was used and the density was not given. Atakhodzhaev and Dzhuraev4 illustrated the solubility in figures, but no tabulated data were presented. Sandengen5 recently published two solubility measurements of NaHCO3 in MEG-H2O at 4 °C with high solvent concentration of w(MEG) ) 60% and w(MEG) ) 90%. In this work, we extend the experimental temperature and concentration range and analyze solubility in the ternary systems of NaHCO3-MEG-H2O and Na2CO3-MEG-H2O between 2 and 60 °C in the whole MEG concentration range. Furthermore, the solubility in the quaternary Na2CO3-NaHCO3-MEG-H2O system is determined at approximately w(MEG,salt-free) ≈ 3% and w(MEG,salt-free) ≈ 15% between 10 and 50 °C. Additional quaternary systems up to w(MEG) ) 77% MEG have been investigated. Densities of the solutions were determined while sampling. Analyzing for Sodium and Carbonate. Solubility in the CO2-Na2O-H2O system has been studied by many investiga* To whom correspondence should be addressed. Tel.: +45 4525 2800. Fax: +45 4588 2258. E-mail: [email protected].

tors. Table 1 gives a summary of the experimental methods used previously by different investigators. The methods were used for solubility determination in aqueous systems and may similarly be used for the solubility determination in the mixed solvent Na2CO3-NaHCO3-MEG-H2O system. The techniques fall into two categories: one for determining carbon species, and another for determining sodium content.

Figure 1. Sketch of a SLE equilibrium cell.

Figure 2. Selection of experimental solubility of NaHCO3 in MEG-H2O, measured in this work; see Tables 3-6.

10.1021/ie8011648 CCC: $40.75  2009 American Chemical Society Published on Web 01/20/2009

Ind. Eng. Chem. Res., Vol. 48, No. 4, 2009 2219 Table 1. Overview of Analytical Methods Used in the Literature for Analyzing CO2-Na2O-H2O Systems method

determines

used by reference total alkali: 6-12 2HCO3 and CO3 : 2, 13-15 only HCO3 : 16-20 only CO23 : 21-23 7-11, 20, 24, 25 11, 20, 26, 27 20, 26 11, 15, 20, 28-30 NaCl: 24, 31, 32 Na2CO3: 10, 12 1 33, 34

1

acid titration

total alkalinity (sodium) or total carbon or bicarbonate or carbonate

2 3 4 5 6

acid + absorbed CO2 Winkler’s method gravimetrical precipitation by BaCl2 triple acetate method drying

total carbon content carbonate and bicarbonate or carbonate and hydroxide total carbon (as BaCO3) total sodium total sodium (as NaCl or Na2CO3)

7 8

ICP-AES reverse Schreinemakers method

total sodium total sodium and compositions of salts and solvents

Table 2. Purity of the Chemicals Used chemical

CAS

MEG NaHCO3

107-21-1 144-55-8

anhydrous Na2CO3 HCl water

487-19-8 7647-01-00 7732-18-5

purity

supplier

puriss p.a. ACS >99.5% puriss p.a. ACS >99.7% puriss >99.5% puriss p.a. ACS >99.8% dried at 300 °C puriss (aqueous 36-38%) demineralized, < 0.2 µS

Riedel-deHae¨n Fluka ACROS Riedel-deHae¨n J. T. Baker Technical University of Denmark

Table 3. Experimental Initial and Equilibrium Compositions, Reverse Schreinemakers Results, and Solid Phase in the NaHCO3-MEG-H2O System at 1 bar and 2-10 °C initialc a

b

t (°C)

w˜MEG (%)

mH2O (g)

mMEG (g)

2.45 2.55 2.35 10.20 10.55 10.35 10.40 10.05 10.20 10.15 10.20 10.35 10.20 10.10 10.25 10.20 10.45 10.30

15.60 42.22 63.21 0.00 0.00 3.08 3.15 14.96 15.32 28.05 28.12 42.22 53.05 53.13 63.21 77.89 78.10 100.00

26.1109 17.2869 9.9027 10.0318 10.0009 9.7773 9.6940 8.4850 8.5744 7.2142 7.2232 20.3200 4.7262 4.6877 14.0064 2.2212 2.1872 0.0000

4.8273 12.6312 17.0171 0.0000 0.0000 0.3109 0.3156 1.4924 1.5507 2.8118 2.8261 14.8473 5.3404 5.3131 24.0690 7.8272 7.7994 9.9890

equilibriumd

reverse Schreinemakerse

mNaHCO3 mNa2CO3 STNa (g) (g) (mol/kg)

dev (%)

SCO3 (mol/kg)

dev (%)

Fsat.liq (g/cm3)

dev (%)

4.6238 3.3322 2.4722 1.0104 1.9083 1.0030 1.9070 1.6265 0.9111 1.3677 0.7926 3.5293 0.6002 1.1178 2.5329 0.5056 1.1120 1.3650

0.38 1.24 0.31 1.33 0.49 1.02 1.12 0.07 0.88 0.55 5.33 0.97 0.32 0.20 1.09 1.58

0.115 0.085 0.095 0.054 0.104 0.071 0.118 0.112 0.074 0.118 0.063 0.100 0.037 0.079 0.088 0.024 0.053 0.083

11.57 24.69 16.08 12.62 11.22 11.16 6.02 3.42 11.41 2.57 6.63 37.49 2.40 8.98 15.75

1.057 1.049 1.044 1.048 1.045 1.047 1.055 1.066 1.069 1.091 1.072 1.117 -

0.09 0.24 0.27 2.24 0.21 1.17 0.05 -

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

0.733 0.475 0.375 0.962 1.009 0.910 0.963 0.792 0.747 0.634 0.607 0.477 0.441 0.447 0.382 0.308 0.340 0.647

2-

wNaHCO3 σNaHCO3 (%) (%) 6.16 3.992 3.15 8.08 8.47 7.64 8.09 6.65 6.278 5.33 5.10 4.01 3.702 3.75 3.21 2.589 2.86 5.44

0.024 0.039 0.025 0.11 0.037 0.082 0.075 0.0046 0.047 0.028 0.21 0.036 0.010 0.0052 0.031 0.086

mH2O (g)

wMEG (%)

P1f P2f

26.1109 17.2869 9.9027 10.0318 10.0009 9.7773 9.6940 8.4850 8.5744 7.2142 7.2232 20.3200 4.7262 4.6877 14.0064 2.2212 2.1872 0.0000

14.642 40.534 61.223 0.000 0.000 2.846 2.898 13.963 14.354 26.551 26.688 40.526 51.087 51.133 61.183 75.879 75.868 94.564

B B B B B B B B B B B B B B B B B B

a Equilibrium temperature in °C. b w˜MEG, salt-free weight percent of MEG in the initial composition, mMEG/(mMEG + mH2O). c The weight of the initial composition in grams, mi, of component i. d The equilibrium composition determined by titration. STNa is calculated by method III of Fosbøl33,34 as mol sodium/kg solution and SCO32- by method I of Fosbøl33,34 in mol CO32-/kg solution. Fsat.liq is the density of the saturated liquid at equilibrium temperature in g/cm3. The deviation of STNa, SCO32-, and Fsat.liq (dev) is calculated as the standard deviation, σ, divided by the mean of the samples times 100. e The result of the reverse Schreinemakers method was calculated by equations of Fosbøl.33,34 wi is the weight percent of component i calculated as 100 g i/gram saturated solution and mH2O is the grams of water in the saturated liquid phase at equilibrium. σi is the standard deviation of the weight fraction i. f P1 and P2 are the precipitated solid phases: B, NaHCO3; C, Na2CO3; M, Na2CO3 · H2O; H, Na2CO3 · 7H2O; D, Na2CO3 · 10H2O; T, trona; and W, wegscheiderite.

The measurements are always converted to solubility of solid Na2CO3, NaHCO3, or NaOH, and rarely tabulated as ionic species. The solubility of salt in the ternary Na2CO3-MEG-H2O and NaHCO3-MEG-H2O systems may be determined using one or more of the methods mentioned in Table 1. A second or third analysis only serves to check the result of the first. If the precipitating salt is a hydrate, it changes the water-MEG ratio from the initial value. This ratio needs to be determined separately using for example the reverse Schreinemakers method.33,34 The determination of solubility of salts in quaternary Na2CO3-NaHCO3-MEG-H2O solutions requires the use of at least two different methods from Table 1, one for determining sodium content and another for determining carbon content. From these results, the composition of the solution can be determined. Again, if a salt hydrate precipitates from the initial

quaternary solution, the water-MEG ratio is changed from its initial value. The first method mentioned in Table 1 is titration. It is a well-known method for analyzing carbonate mixtures which is also applied in this study. The solution is titrated using a strong acid. The titration may reveal different results depending on the interpretation of the titration curves. Table 1 shows that authors determined total alkali (OH- + HCO3- + 2CO32- H+), HCO3- and CO32-, HCO3- only, or CO32- only. Clearly, interpretation of the equivalence points is not a trivial task as discussed by Fosbøl.33,34 He also shows that titration can be used for determining the composition of the liquid phase, including solvent composition. In the second approach shown in Table 1, total carbon content is determined by adding an excess of strong acid to a sample to convert carbonates and bicarbonates to CO2. It is stripped off with nitrogen. The vapor must be dried, and the total carbon

2220 Ind. Eng. Chem. Res., Vol. 48, No. 4, 2009

Figure 3. Selection of experimental solubility of Na2CO3 in MEG-H2O, measured in this work; see Tables 7 and 8.

is determined by weight of post absorption of CO2 or by the weight loss of the solution. This method requires relatively big sample sizes and very accurate weights. It has been used by many authors over the years despite the difficulties.7-11,20,24,25 This method was also attempted in this study, but consistent results were not obtained. Winkler’s method35 shown in Table 1 may be applied in two different ways: for analyzing either mixtures of carbonate and hydroxide or mixtures of carbonate and bicarbonate. In both cases the total sodium is determined by a preliminary titration. Hydroxide in a carbonate/hydroxide solution is determined by precipitating carbonate as BaCO3 and titration of hydroxide to the equivalence point.26 The bicarbonate in a carbonate/ bicarbonate solution is determined by adding a known excess of NaOH, precipitating the existing and formed carbonate as BaCO3 and back-titrating the excess hydroxide. The amount of bicarbonate is calculated from the difference of the added and back-titrated NaOH.11,20,27 In a fourth method, aqueous BaCl2 is added to precipitate carbonates as BaCO3. The total carbon is determined gravimetrically or by titration of the precipitated BaCO3.20,26 The gravimetrical determination may require big samples and careful filtration. Barium requires special handling in the laboratory. The total amount of sodium may be determined by one of the three following methods or by titration. Titration was used in this work. One method is the triple acetate method, in which sodium is precipitated as the triple uranyl acetate salt and weighed gravimetrically as (UO2)3ZnNa(CH3COO)9 · 6H2O. Small amounts of sodium can be determined, due to the large molecular mass of triple uranyl acetate. A description is given by Barber and Kolthoff29 and Salit,28 but the method has limitations30 and the uranium makes the solutions hazardous. Another method in which total sodium is determined is drying of the liquid phase. By adding excess amounts of HCl, CO2 vaporizes and sodium is determined as precipitated NaCl by drying.24,31,32 If carbonate is the only anion, it may be determined by drying and weighing as Na2CO3.10,12 Drying is problematic in solutions containing bicarbonate which decomposes at temperatures above 60 °C by 2NaHCO3 f Na2CO3 + CO2(g) + H2O(g)

(1)

This method is also problematic when used for Na2CO3-NaHCO3-MEG-H2O solutions because of the low vapor pressure of MEG. The third method of determining total sodium is ICP-AES (inductively coupled plasma-atomic emission spectrometry). This method was used by Oosterhof et al.1 The benefit of using potentiometric titration is the low cost per experiment, high precision, the high number of automated measurements that can be performed simultaneously, the simplicity of the method, and the use of nonhazardous chemicals. This cannot be obtained if, for example, the Winkler and Warder36 manual indicator titration is used. Interpreting the Titration Results. Very few authors have reported the complete compositions of the solvents of the saturated solutions. The solvent composition may change significantly if solvent molecules precipitate together with the salts. Na2CO3 can precipitate with various amounts of hydrate water, as, for example, Na2CO3 · 10H2O. The amount of solid phase precipitated must therefore be known in order to determine the new solvent composition. This is a general problem in mixed solvent electrolyte systems. Oosterhof et al.1 solved this problem by applying a total organic carbon method (TOC) for their polyethylene glycol mixtures. Unfortunately, they did not apply this method for their MEG mixtures. Instead, they assumed the amount of precipitated solvent to be negligible. The solvent compositions they reported are therefore not accurate. In this work, the reverse Schreinemakers method is applied to solve this problem as described by Fosbøl.33,34 This method reveals the exact amounts of salts and solvents in a solution. Experimental Methods and Apparatus Used Chemicals. The purities of the chemicals used are listed in Table 2. The solid chemicals were analyzed by powder X-ray diffraction and titration and showed no impurities. The demineralized water used was produced on site and had a conductivity of less than 0.2 µS. Experimental Setup. The experimental setup consisted of two units: an equilibrium unit and an analysis unit. The equilibrium unit consisted of seven cells connected in parallel to a Julabo F25 heating/cooling circulation bath which controlled temperature within (0.01 K. Each cell consisted of a glass lid and a heat jacket surrounding an equilibrium chamber; see Figure 1. The equilibrium chamber was a closed 50 mL polyethylene container with screw cap and a magnetic stirrer. A deadweight was placed on top of the containers to keep them submerged. Water was used for transferring heat from the heat jacket to the equilibrium chamber. The saturated solutions were analyzed by potentiometric titration using an autoburette, ABU93 triburette, from Radiometer. The pH electrodes were an Orion 617500 and a Metrohm 6.0228.000 connected to a ThermoOrion 635 unit and a Metrohm 694 pH meter, respectively. The ABU unit allows up to three simultaneous titrations but only two were used. Software to control the ABU unit with respect to the measured pH was developed. The developed software allowed high-precision titrations to be performed and the accuracy of the equivalence points is on average precise to approximately 0.01 mL of 0.1 M HCl. Experimental Procedure. The solutions were mixed from the pure chemicals listed in Table 2 as given by Tables 3-11 and a magnet was added to the equilibrium chamber. Containers were kept closed until sampling. The size of the vapor phase was kept low and assumed to consist mainly of air. No CO2

Ind. Eng. Chem. Res., Vol. 48, No. 4, 2009 2221 Table 4. Experimental Initial and Equilibrium Compositions, Reverse Schreinemakers Results, and Solid Phase in the NaHCO3-MEG-H2O System at 1 bar and 20 °C initialc a

b

t (°C)

w˜MEG (%)

mH2O (g)

mMEG (g)

20.15 20.00 20.10 20.00 20.10 20.00 20.10 20.00 20.10 20.00 19.60 20.10 20.00 20.10 19.60 20.10 20.10 20.00 20.10 20.10 20.10 20.10 20.00

0.00 0.00 2.70 2.93 3.21 15.09 15.12 15.43 27.89 28.42 42.22 52.82 52.99 60.02 63.21 67.44 75.01 78.07 82.48 90.02 97.42 100.00 100.00

10.0660 9.9966 9.6800 9.7341 9.6970 8.5923 8.5210 8.4692 7.2172 7.1993 20.3200 4.7172 4.7049 4.0003 14.0064 3.2574 2.4977 2.2024 1.7574 0.9995 0.2592 0.0000 0.0000

0.0000 0.0000 0.2684 0.2942 0.3215 1.5275 1.5173 1.5448 2.7908 2.8586 14.8473 5.2816 5.3028 6.0058 24.0690 6.7474 7.4957 7.8396 8.2719 9.0123 9.7689 10.0005 9.9970

equilibriumd



dev (%)

SCO3 (mol/kg)

dev (%)

Fsat.liq (g/cm3)

dev (%)

wNaHCO3 (%)

σNaHCO3 (%)

mH2O (g)

wMEG (%)

P1f P2f

1.8708 1.9238 1.8776 1.1232 1.8969 2.0342 1.5716 1.1100 1.3003 1.3270 3.5293 1.1088 1.0919 0.9790 2.5329 1.0456 0.9924 1.1731 0.9970 1.0003 0.9833 1.2820 1.3853

0.86 0.08 2.15 0.12 0.04 0.21 0.17 0.31 1.38 0.23 0.02 1.24 0.27 0.43 4.81 0.94 1.34 1.43 0.30 0.28 0.16 0.10 0.08

0.163 0.217 0.153 0.190 0.206 0.170 0.129 0.169 0.089 0.126 0.141 0.045 0.077 0.057 0.093 0.060 0.055 0.057 0.047 0.046 0.051 0.045 0.086

2.37 0.14 0.30 1.59 0.79 0.65 2.33 9.53 10.52 26.93 0.63 2.32 2.32 35.50 9.29 8.48 2.70 0.06 5.48 6.21 3.58 11.11

1.065 1.072 1.042 1.048 1.065 1.083 1.064 1.068 1.079 1.080 1.094 1.097 1.101 1.098 1.110 1.117 1.117 1.128 1.146 1.160 1.151

0.09 1.15 0.34 0.28 0.42 0.61 0.39 0.04 0.67 0.41 0.21 0.32 0.59 0.64 0.98 0.53 0.14 0.02 0.04 -

9.14 9.383 8.81 8.71 9.003 7.72 7.28 7.12 5.86 5.89 4.7747 4.02 4.03 3.73 3.65 3.46 3.26 3.22 3.137 3.372 4.804 6.249 6.482

0.079 0.0076 0.19 0.010 0.0037 0.017 0.012 0.022 0.081 0.013 0.00093 0.050 0.011 0.016 0.18 0.032 0.044 0.046 0.0094 0.0094 0.0077 0.0065 0.0051

10.0660 9.9966 9.6850 9.7341 9.6970 8.5923 8.5210 8.4692 7.2172 7.1993 20.3200 4.7172 4.7049 4.0003 14.0064 3.2574 2.4977 2.2024 1.7574 0.9995 0.2592 0.0000 0.0000

0.000 0.000 2.459 2.678 2.920 13.928 14.014 14.328 26.253 26.748 40.203 50.701 50.853 57.782 60.905 65.111 72.563 75.554 79.890 86.981 92.735 93.751 93.518

B B B B B B B B B B B B B B B B B B B B B B B

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

1.088 1.117 1.049 1.036 1.072 0.919 0.867 0.847 0.697 0.701 0.568 0.478 0.480 0.444 0.435 0.411 0.388 0.383 0.373 0.401 0.572 0.744 0.772

2-


Table 5. Experimental Initial and Equilibrium Compositions, Reverse Schreinemakers Results, and Solid Phase in the NaHCO3-MEG-H2O System at 1 bar and 25-35 °C initialc a

b

t (°C)

w˜MEG (%)

mH2O (g)

mMEG (g)

24.40 24.60 29.80 29.90 29.90 30.00 29.90 30.00 30.00 30.00 30.00 34.90 34.70 34.90 32.70 34.90 32.70 34.90 33.00 34.90 34.90

42.22 63.21 0.00 2.87 2.93 15.01 15.43 28.11 52.81 77.33 100.00 0.00 3.36 14.96 15.60 28.01 42.22 52.88 63.21 78.17 100.00

20.3200 14.0064 10.0320 9.6877 9.7167 8.5444 8.4689 7.2252 4.7268 2.2914 0.0000 10.0139 9.7142 8.5202 26.1109 7.1995 17.2869 4.7139 9.9027 2.1880 0.0000

14.8473 24.0690 0.0000 0.2858 0.2936 1.5094 1.5447 2.8258 5.2907 7.8158 10.0247 0.0000 0.3375 1.4989 4.8273 2.8007 12.6312 5.2903 17.0171 7.8359 10.0162

equilibriumd



dev (%)

SCO3 (mol/kg)

dev (%)

Fsat.liq (g/cm3)

dev (%)

wNaHCO3 σNaHCO3 (%) (%)

3.5293 2.5329 1.3015 1.3034 1.5166 1.1944 1.4930 1.0006 0.6992 0.6260 0.9025 1.8971 1.9009 1.6346 4.6238 1.3540 3.3322 1.1031 2.4722 1.1269 1.4230

0.34 1.03 1.84 0.34 0.04 0.25 0.17 0.49 0.98 0.31 0.09 0.08 0.11 0.12 0.37 0.09 0.49 0.18 0.35 0.06 1.12

0.095 0.076 0.105 0.116 0.149 0.139 0.135 0.135 0.065 0.031 0.059 0.262 0.261 0.238 0.314 0.174 0.212 0.089 0.148 0.081 0.140

8.22 2.49 13.05 9.97 2.44 4.99 6.93 6.24 9.79 5.77 2.41 2.48 3.52 18.79 23.11 17.48 7.09 3.46 19.86 43.44

1.084 1.071 1.070 1.074 1.085 1.080 1.082 1.110 1.116 1.161 1.110 1.108 1.100 1.114 1.109 1.123 1.149

0.03 0.04 0.16 2.10 0.57 1.42 0.21 0.11 0.34 0.74 0.31 1.21 0.17 0.77 2.61

4.99 3.66 10.60 9.92 10.043 8.65 8.28 6.69 4.34 3.087 6.806 11.311 10.60 9.24 9.05 7.248 5.53 4.787 4.27 3.532 7.32

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

0.594 0.435 1.262 1.181 1.196 1.030 0.986 0.796 0.517 0.367 0.810 1.346 1.261 1.100 1.077 0.863 0.658 0.570 0.509 0.420 0.871

2-

0.017 0.038 0.20 0.034 0.0042 0.022 0.014 0.033 0.043 0.0096 0.0060 0.0086 0.012 0.011 0.034 0.0063 0.027 0.0085 0.015 0.0020 0.082

mH2O (g)

wMEG (%)

P1f P2f

20.3200 14.0064 10.0320 9.6877 9.7167 8.5444 8.4689 7.2252 4.7268 2.2914 0.0000 10.0139 9.7142 8.5202 26.1109 7.1995 17.2869 4.7139 9.9027 2.1880 0.0000

40.113 60.903 0.000 2.581 2.639 13.715 14.148 26.235 50.523 74.942 93.194 0.000 3.002 13.578 14.191 25.977 39.884 50.349 60.513 75.411 92.680

B B B B B B B B B B B B B B B B B B B B B


evaporation and no surplus pressure was observed. Solutions were stirred at approximately 500 rpm and set to equilibrate over a period of 16-78 h. This was found to be sufficient by

mixing a number of ternary solutions. Solubility was analyzed as function of time up to 192 h. The time required for equilibration was determined to be a few hours.

2222 Ind. Eng. Chem. Res., Vol. 48, No. 4, 2009 Table 6. Experimental Initial and Equilibrium Compositions, Reverse Schreinemakers Results, and Solid Phase in the NaHCO3-MEG-H2O System at 1 bar and 40-60 °C initialc a

b

t (°C)

w˜MEG (%)

mH2O (g)

mMEG (g)

39.90 39.40 39.80 39.95 39.60 40.50 39.90 40.00 39.90 40.60 39.90 39.60 39.80 39.90 39.90 39.90 39.85 49.90 48.65 48.70 49.85 49.00 49.80 49.80 49.75 49.70 56.85 59.65 59.75 59.60 59.60 59.50 59.40

0.00 2.97 3.04 15.13 15.34 15.60 27.85 42.22 53.03 63.21 70.01 75.09 78.10 82.44 89.81 97.51 100.00 0.00 2.89 3.04 14.74 15.34 27.86 53.02 78.05 100.00 3.16 0.00 14.93 27.93 53.05 77.91 100.00

10.0165 9.7180 9.7116 8.4968 8.3722 26.1109 7.2561 17.2869 4.7096 9.9027 3.2669 2.4916 2.1983 1.7665 1.0243 0.2487 0.0000 10.0034 9.7089 9.6849 8.5482 8.4856 7.1944 4.6912 2.1902 0.0000 9.7463 10.0668 8.5408 7.2290 4.7048 2.2126 0.0000

0.0000 0.2975 0.3048 1.5145 1.5168 4.8273 2.8009 12.6312 5.3171 17.0171 7.6250 7.5101 7.8386 8.2936 9.0243 9.7557 10.0544 0.0000 0.2885 0.3040 1.4778 1.5374 2.7780 5.2946 7.7858 10.0219 0.3179 0.0000 1.4984 2.8021 5.3158 7.8048 10.0630

equilibriumd



dev (%)

SCO3 (mol/kg)

dev (%)

Fsat.liq (g/cm3)

dev (%)

wNaHCO3 σNaHCO3 (%) (%)

1.4127 1.3060 1.9159 1.1928 1.9049 4.6238 1.0128 3.3322 0.7055 2.4722 0.5313 0.5415 0.6093 0.5126 0.5135 0.6277 0.9057 1.5841 1.6013 1.9179 1.2886 1.9052 1.2150 0.8969 0.7096 0.8838 0.5975 1.7070 1.4310 1.3035 0.9456 0.7067 0.9045

0.23 0.10 0.04 0.11 1.60 0.23 1.48 3.81 0.19 0.31 0.38 0.22 0.11 0.73 0.22 0.44 0.62 0.14 0.90 0.30 0.10 6.11 0.21 0.18 0.34 0.57 0.26 0.14 0.30 0.09 1.27 0.21 1.51

0.120 0.152 0.238 0.162 0.236 0.083 0.112 0.113 0.070 0.078 0.041 0.032 0.037 0.043 0.032 0.061 0.036 0.207 0.187 0.294 0.197 0.304 0.151 0.072 0.042 0.055 0.216 0.214 0.239 0.181 0.065 0.050 0.075

12.37 8.71 3.03 3.70 4.47 1.77 31.01 2.58 1.34 19.90 16.30 7.39 0.74 7.14 45.41 12.61 1.55 10.34 9.41 5.86 21.19 1.30 1.40 4.37 5.57 3.12 8.23 0.64 5.77 85.38 4.27 3.05

1.093 1.084 1.115 1.122 1.071 1.103 1.090 1.111 1.117 1.125 1.129 1.136 1.149 1.164 1.140 1.139 1.126 1.129 1.114 1.113 1.131 1.166 1.105 1.152 1.121 1.122 1.125 1.132 1.155

0.98 0.24 1.47 1.00 0.51 0.25 0.27 0.19 0.13 0.23 2.39 0.60 1.98 0.38 0.93 0.29 0.68 0.46 0.92 8.01 2.78 0.24 0.25

11.88 11.28 11.579 9.63 9.57 9.30 7.47 5.69 4.866 4.33 3.83 3.472 3.447 3.54 3.578 5.15 7.19 13.47 12.42 13.27 11.06 11.12 8.70 5.544 3.85 6.99 14.29 15.19 12.81 9.959 6.25 4.283 7.34

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

1.414 1.343 1.378 1.147 1.139 1.107 0.890 0.677 0.579 0.516 0.456 0.413 0.410 0.422 0.426 0.613 0.856 1.603 1.479 1.580 1.317 1.323 1.036 0.660 0.458 0.832 1.701 1.808 1.524 1.186 0.744 0.510 0.874

2-

0.028 0.011 0.0051 0.011 0.15 0.021 0.11 0.22 0.0093 0.014 0.014 0.0076 0.0037 0.026 0.0077 0.023 0.045 0.019 0.11 0.039 0.011 0.68 0.019 0.0097 0.013 0.040 0.037 0.021 0.038 0.0094 0.080 0.0090 0.11

mH2O (g)

wMEG (%)

P1f P2f

10.0165 9.7180 9.7116 8.4968 8.3722 26.1109 7.2561 17.2869 4.7096 9.9027 3.2669 2.4916 2.1983 1.7665 1.0243 0.2487 0.0000 10.0034 9.7089 9.6849 8.5482 8.4856 7.1944 4.6912 2.1902 0.0000 9.7463 10.0668 8.5408 7.2290 4.7048 2.2126 0.0000

0.000 2.635 2.691 13.670 13.871 14.152 25.769 39.818 50.449 60.476 67.323 72.481 75.406 79.521 86.593 92.493 92.806 0.000 2.527 2.639 13.110 13.633 25.433 50.082 75.041 93.015 2.707 0.000 13.014 25.152 49.731 74.575 92.655

B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B


The pressure was (1.01 ( 0.05) bar during the experiments, and the temperature was measured in the heat transferring liquid just before sampling at an accuracy of (0.05 K. The liquid was filtered before sampling by one of four methods. Preferably a cone-shaped filter was put into the equilibrium chamber and the liquid was allowed to flow inside the filter. If this method did not produce a sample large enough for analysis, the content of the equilibrium chamber was filtered through a conically shaped filter on top of small beaker. If these two procedures failed to produce enough liquid for analysis, saturated liquid was absorbed with a known amount of paper towel. Finally, liquids of high glycol concentrations were vacuum filtered because they only wet the surface of the filters poorly. Samples were obtained by micropipet when possible at a volume of 100-1000 µL and weighed. Samples were between 0.1 and 1.3 g. They were taken in triple from each equilibrium chamber within a few minutes from being removed from the equilibrium chambers. The saturated liquid was allowed to stand no more than 5 min before being weighed. Therefore, water evaporation and temperature change was kept to a minimum in order to reduce the error on the density and solubility measurement. Approximate densities of the samples were determined as weight per volume sample at system temperature. Samples were stored up to 3 days after sampling in closed weighing containers similar to the equilibrium chambers and

titrated by 0.1 M HCl. The temperature was not held constant during storage. Therefore, CO2 could in principle evaporate in the closed container and salt could precipitate. This does not pose a problem since solutions were only analyzed for sodium content. If CO2 evaporated it created an equivalent amount of sodium hydroxide and if salt precipitated it dissolved in excess water added before analyzing. Approximately 15 g of water was added to the samples prior to the automatic titration which took 30 min on average. Samples were stirred at 400 rpm while titrating. The titration setup was configured to obtain a stable pH over a period of 10 s before the next addition of HCl. Titrations required between 1.5 and 25 mL of HCl. The diluted HCl was produced from concentrated HCl and the concentration was standardized against a known amount of high-purity Na2CO3. The solid phases were analyzed when in doubt by powder X-ray diffraction to determine the identity of solid phase. This was done by decanting the liquid and analyzing the solid within 30 min after separation. These analyses took approximately 20 min per sample, and the decomposition of hydrates in the apparatus was regarded as negligible. Experimental Results The solubility of Na2CO3 and NaHCO3 has been determined in the mixed solvent MEG-H2O at atmospheric pressure

Ind. Eng. Chem. Res., Vol. 48, No. 4, 2009 2223 Table 7. Experimental Initial and Equilibrium Compositions, Reverse Schreinemakers Results, and Solid Phase in the Na2CO3-MEG-H2O System at 1 bar and 10-20 °C initialc a

b

t (°C)

w˜MEG (%)

mH2O (g)

mMEG (g)

10.20 10.15 10.40 10.20 10.20 10.20 10.20 10.20 15.20 15.20 15.20 15.10 15.20 15.20 15.20 15.20 20.10 20.10 20.10 20.10 20.10 20.10 20.10

0.00 3.04 3.94 14.93 27.93 54.34 77.95 100.00 0.00 3.10 9.10 14.97 36.50 44.87 78.11 100.00 0.00 3.07 8.98 15.26 21.02 28.13 39.99

10.0134 9.6966 9.7279 8.5053 7.2202 4.7315 2.2120 0.0000 9.9952 9.7155 9.1058 8.4855 6.3496 5.5182 2.1900 0.0000 10.0175 9.7043 9.1021 8.5166 7.9181 7.2056 6.0083

0.0000 0.3043 0.3990 1.4925 2.7978 5.6305 7.8197 10.0181 0.0000 0.3112 0.9111 1.4940 3.6500 4.4917 7.8164 10.0145 0.0000 0.3075 0.8975 1.5333 2.1070 2.8202 4.0036

equilibriumd



dev (%)

SCO3 (mol/kg)

dev (%)

Fsat.liq (g/cm3)

dev (%)

wNa2CO3 (%)

σNa2CO3 (%)

mH2O (g)

wMEG (%)

P1f P2f

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

0.95 0.00 2.08 3.63 0.33 0.22 0.17 0.31 0.69 0.14 0.44 1.52 0.36 0.15 0.10 0.26 0.08 0.09 0.17 0.14 0.10 0.16

1.109 0.942 1.030 0.876 0.796 1.104 0.557 0.427 1.399 1.311 1.213 1.109 1.131 1.398 0.549 0.410 1.735 1.663 1.541 1.441 1.397 1.417 1.558

0.88 4.41 2.86 3.64 0.61 1.61 0.60 0.47 0.41 0.47 1.17 1.53 0.88 0.15 0.85 0.32 0.08 0.06 0.12 0.07 1.06 0.11

1.123 1.105 1.142 1.144 1.191 1.142 1.118 1.153 1.143 1.128 1.131 1.164 1.210 1.145 1.159 1.176 1.170 1.163 1.163 1.170 1.189 1.166

0.32 0.84 1.14 2.10 0.36 1.16 2.22 0.09 0.46 0.59 0.31 0.62 1.47 0.55 0.90 0.57 0.43 0.59 0.76 0.36 0.26 0.22

11.85 12.17933 11.04 9.39 8.708 11.78 5.99 5.160 14.87 13.99 12.92 11.88 12.14 14.95 5.924 4.603 18.53 17.79 16.47 15.47 14.99 15.24 16.66

0.11 0.000020 0.23 0.34 0.038 0.013 0.0085 0.046 0.097 0.019 0.052 0.18 0.054 0.0090 0.0045 0.049 0.014 0.014 0.027 0.022 0.014 0.026

7.4558 3.2361 6.4640 5.9132 4.7621 4.6642 2.0165 0.0000 7.3395 6.8177 7.7536 6.7621 4.8530 5.3831 2.1505 0.0000 9.2920 8.7673 7.7236 6.8753 6.0142 6.1353 5.9115

0.000 7.549 5.172 18.262 33.786 48.251 74.733 94.840 0.000 3.754 9.156 15.947 37.716 38.688 73.778 95.397 0.000 2.786 8.695 15.414 22.056 26.691 33.650

D D D D D M M C D D D D D M M C D D D D D H M

2.5072 4.2919 2.7720 2.2930 2.1673 1.7704 1.7773 1.7743 2.8448 2.8648 2.0813 2.1267 2.0555 2.5300 0.8600 0.8703 2.5408 2.5149 2.5114 2.5043 2.5518 2.5101 2.5520

2.236 2.298 2.083 1.772 1.643 2.223 1.131 0.974 2.807 2.641 2.438 2.241 2.291 2.820 1.118 0.869 3.497 3.357 3.109 2.919 2.828 2.876 3.144

2-


Table 8. Experimental Initial and Equilibrium Compositions, Reverse Schreinemakers Results, and Solid Phase in the Na2CO3-MEG-H2O System at 1 bar and 30-60 °C initialc

equilibriumd


t (°C)

w˜MEG (%)

mH2O (g)

mMEG (g)

mNaHCO3 (g)

mNa2CO3 (g)

STNa (mol/kg)

dev (%)

SCO3 (mol/kg)

dev (%)

Fsat.liq (g/cm3)

dev (%)

wNa2CO3 (%)

σNa2CO3 (%)

mH2O (g)

wMEG (%)

P1f

29.90 39.80 39.80 39.50 40.00 39.50 40.00 40.00 39.90 39.90 49.60 48.85 49.80 49.60 49.70 49.70 49.70 49.70 59.55 58.20 59.75 59.65 59.55 59.55 59.45

15.43 0.00 3.04 3.06 15.11 15.34 27.94 52.90 78.45 100.00 0.00 2.74 15.04 15.34 27.76 52.72 77.30 100.00 0.00 2.97 15.16 27.92 53.13 77.53 100.00

8.4562 9.9823 9.6958 9.7113 8.4945 8.4566 7.2336 4.7177 2.2158 0.0000 9.9849 9.6756 8.5359 8.4741 7.2678 4.7511 2.2837 0.0000 10.0055 9.6703 8.5310 7.1741 4.6970 2.2641 0.0000

1.5425 0.0000 0.3043 0.3068 1.5115 1.5322 2.8046 5.2990 8.0670 10.0301 0.0000 0.2729 1.5107 1.5353 2.7930 5.2973 7.7780 10.0678 0.0000 0.2955 1.5248 2.7784 5.3252 7.8099 9.7490

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

4.5921 5.7611 4.6687 5.7592 4.9300 4.6623 4.2938 1.7583 1.1124 1.1395 5.5709 5.8053 4.1711 4.6669 3.3213 1.5709 0.7996 0.8105 5.8730 5.7978 4.2020 3.2790 1.5942 0.7861 0.8038

4.917 6.537 5.813 6.087 5.018 4.826 3.886 1.950 0.935 1.128 6.273 5.935 4.822 4.701 3.687 1.819 0.972 0.705 6.054 5.817 4.675 3.527 1.756 0.802 0.454

0.20 0.40 0.10 0.18 0.15 0.32 0.26 0.19 2.65 1.92 0.59 0.14 0.44 1.72 0.73 0.79 1.78 2.68 1.61 0.49 0.48 0.70 0.51 0.38 4.60

2.446 3.283 2.902 3.031 2.514 2.391 1.931 0.966 0.453 0.549 3.127 2.963 2.409 2.289 1.832 0.862 0.479 0.317 3.038 2.907 2.320 1.747 0.853 0.389 0.215

0.73 0.61 0.59 0.16 0.47 0.54 0.46 0.44 2.36 2.66 1.23 0.46 0.97 3.38 1.13 2.98 2.32 3.99 2.97 1.35 1.05 0.36 3.63 0.19 4.76

1.283 1.330 1.367 1.307 1.232 1.246 1.225 1.160 1.112 1.143 1.303 1.258 1.321 1.306 1.238 1.178 1.147 1.151 1.367 1.351 1.340 1.267 1.149 1.166 1.122

1.15 1.34 1.93 1.83 0.92 2.28 0.81 1.70 1.48 3.67 2.96 0.87 1.47 1.57 2.30 14.19 0.46 1.66 3.87 1.98 0.81 0.40 2.22

26.06 34.64 30.81 32.26 26.59 25.57 20.60 10.34 4.96 5.98 33.24 31.45 25.55 24.92 19.54 9.64 5.15 3.74 32.08 30.83 24.77 18.69 9.30 4.25 2.41

0.052 0.14 0.030 0.057 0.039 0.082 0.053 0.020 0.13 0.12 0.20 0.045 0.11 0.43 0.14 0.076 0.092 0.10 0.52 0.15 0.12 0.13 0.048 0.016 0.11

8.2630 9.8945 9.6560 9.5285 8.2582 8.2346 6.9331 4.6131 2.1170 0.0000 9.8738 9.4468 8.4055 8.2318 7.1121 4.6647 2.2403 0.0000 9.7938 9.4209 8.3707 6.9988 4.5991 2.2060 0.0000

11.632 0.000 2.114 2.113 11.357 11.675 22.870 47.934 75.287 94.021 0.000 1.925 11.342 11.803 22.689 48.049 73.640 96.264 0.000 2.104 11.592 23.106 48.666 74.662 97.594

M M M M M M M M M C M M M M M M M C M M M M M M C

a

b

2-

P2f



Figure 4. Selection of experimental solubility of Na2CO3 and NaHCO3 in w(MEG,salt-free) ≈ 3% at 10-40 °C measured in this work; see Tables 9-11. The dashed line indicates a small branch of trona precipitation at 20 °C.

Figure 6. Selection of experimental isotherms of density of saturated NaHCO3-MEG-H2O solutions measured in this work; see Tables 3-6.

Figure 7. Selection of experimental isotherms of density of saturated Na2CO3-MEG-H2O solutions measured in this work; see Tables 7 and 8. Figure 5. Selection of experimental solubility of Na2CO3 and NaHCO3 in w(MEG,salt-free) ≈ 15% at 10-40 °C measured in this work; see Tables 9-11. The dashed line indicates a branch of trona precipitation at 20 °C.

between 2 and 60 °C. Tables 3 through 11 give the experimental initial compositions, titration results, densities, the compositions of the saturated solutions, and the identity of the solid phases determined by the reverse Schreinemakers method.34 The initial composition is listed as amounts of pure compounds in grams. The composition of the saturated solution is obtained from the equivalence point of the titration curves as total mol sodium/ kg solution and mol carbonate/kg solution, denoted STNa and SCO32-. SCO32- is determined from the first equivalence point and STNa from the second. Most measurements were repeated three times and the standard deviation is given. Some solutions could only be measured once and the deviation is therefore not given. An approximate value for the solubility of Na2CO3 and NaHCO3 can be determined directly from STNa and SCO32-. This technique is not used here due to the issues raised by Fosbøl.33,34 Basically the solubility becomes inaccurate if SCO32- is used in the calculation. Therefore, the solubility is calculated using the reverse Schreinemakers method which is independent of SCO32-. Results are shown in Tables 3-11 in weight percent Na2CO3, NaHCO3, and MEG in the equilibrium solutions.

The solubility calculated from STNa and SCO32- and the original wet residue method is used in order to make a first guess of the identity of the solid phase. This is done by drawing a line through the initial composition and the approximate composition of the saturated solution. The extension of this line will usually point at one distinct solid phase known to form in the system. The composition of this solid phase is used in the reverse Schreinemakers method in order to calculate the accurate composition of the saturated solution. Results obtained by this method are listed in Tables 3-11. The standard deviation is very low and shows the high reproducibility obtained by this method. The reverse Schreinemakers method cannot yet be used for interpreting titration results of solutions with two solid phases in equilibrium with liquid. The titration results for such solutions were therefore not converted to weight percent. The identities of selected solid phases were determined by X-ray diffraction to verify the results of the reverse Schreinemakers method. Figure 2 shows some isotherms of NaHCO3 solubility in MEG-H2O of data from Tables 3-6. All curves have a minimum at approximately w(MEG,salt-free) ≈ 85%. The phenomenon is unexpected and was validated several times in

Ind. Eng. Chem. Res., Vol. 48, No. 4, 2009 2225 Table 9. Experimental Initial and Equilibrium Composition, Reverse Schreinemakers Results, and Solid Phase in the NaHCO3-Na2CO3-MEG-H2O System at 1 bar and 10-15 °C initialc a

b

t w˜MEG (°C) (%) 10.15 10.50 10.30 10.30 10.25 10.10 10.30 10.20 10.15 10.30 10.15 10.20 10.15 15.10 15.20 15.20 15.20

3.04 3.04 3.04 3.04 3.04 3.04 3.04 15.34 15.34 15.34 15.34 15.34 15.34 3.19 3.05 15.46 14.98

mH2O (g) 9.7296 9.7031 9.6998 9.7057 9.6945 9.7080 9.6841 8.4994 8.4642 8.4954 8.4546 8.4820 8.4844 9.7140 9.7010 8.5047 8.4929

equilibriumd


mMEG mNaHCO3 mNa2CO3 STNa dev SCO3 dev Fsat.liq dev wNa2CO3 σNa2CO3 wNaHCO3 σNaHCO3 (g) (g) (g) (mol/kg) (%) (mol/kg) (%) (g/cm3) (%) (%) (%) (%) (%) 2-

0.3054 0.3046 0.3044 0.3046 0.3043 0.3047 0.3040 1.5399 1.5335 1.5392 1.5318 1.5368 1.5372 0.3205 0.3048 1.5553 1.4963

1.0819 1.7053 1.0567 1.2318 0.1307 0.0614 1.4853 1.0136 1.1697 1.0409 1.2177 0.0619 1.4805 0.3268 0.1588 0.1837 0.0961

0.1704 0.4846 0.7047 1.1119 2.3848 2.3601 3.3331 0.2222 0.4706 0.5814 0.9746 2.3604 3.3366 2.1216 2.0646 2.0719 2.0797

1.152 1.579 1.889 2.375 2.299 2.042 2.491 1.038 1.374 1.517 2.064 1.741 1.949 2.879 2.756 2.402 2.341

2.61 0.40 0.43 1.01 0.98 0.24 1.73 0.16 0.51 0.11 0.38 1.84 0.29 0.21 0.03 0.37 0.18

0.303 0.523 0.716 0.946 0.996 0.960 0.928 0.305 0.469 0.558 0.854 0.794 0.747 1.267 1.288 1.088 1.106

1.87 8.04 6.42 2.76 1.68 0.54 1.71 0.22 2.40 0.83 0.21 0.95 0.46 0.46 0.91

1.083 1.068 1.104 1.147 1.093 1.057 1.084 1.064 1.118 1.156 1.145 1.154 1.134

0.05 0.49 1.20 3.19 2.77 2.14 2.19 2.87 0.97 0.15 0.51 0.76

1.549 4.322 6.181 9.51 11.24 10.36 2.0468 4.282 5.2330 8.555 8.73 13.30 13.657 11.54 11.78

0.0043 0.0027 0.0050 0.024 0.12 0.027 0.00032 0.0029 0.00081 0.0068 0.17 0.034 0.0044 0.049 0.023

7.22 6.41 6.07 4.88 1.499 0.7295 5.48 4.76 4.45 3.78 0.780 3.101 1.5063 1.881 1.0007

0.26 0.057 0.076 0.24 0.0072 0.00073 0.015 0.064 0.015 0.076 0.0047 0.0045 0.00028 0.0036 0.00089

mH2O (g) 9.7296 9.7031 9.6998 9.7057 7.3067 7.1789 8.4994 8.4642 8.4954 8.4546 5.6488 8.4903 8.6391 6.8987 6.8802

wMEG (%) P1f P2f 2.776 2.716 2.670 2.605 3.489 3.620 14.185 13.952 13.854 13.447 19.352 3.041 2.891 15.928 15.581

B B B B D D B B B B B D B D D D D

D

D


Table 10. Experimental Initial and Equilibrium Composition, Reverse Schreinemakers Results, and Solid Phase in the NaHCO3-Na2CO3-MEG-H2O System at 1 bar and 20-30 °C initialc a

b

t w˜MEG (°C) (%) 20.10 20.00 20.00 20.00 20.00 20.10 20.10 20.00 20.00 20.10 20.10 20.00 20.00 20.00 20.00 20.00 20.10 20.10 20.00 20.10 29.80 30.00 30.00 29.90 29.80 30.00 30.00 29.90 30.00

2.93 2.93 2.93 2.93 2.93 3.01 2.99 2.93 2.93 2.93 15.43 15.43 15.43 15.43 15.43 15.43 15.21 14.95 15.43 15.43 2.93 2.93 2.93 2.93 15.43 15.43 15.43 15.43 15.43

mH2O (g) 9.7292 9.6991 9.7237 9.7171 9.7268 9.7138 9.6938 9.7010 9.7060 9.7172 8.4512 8.4543 8.4606 8.4529 8.4598 8.4677 8.5024 8.5242 8.4715 8.4610 9.7021 9.7264 9.7254 9.7080 8.4709 8.4575 8.4640 8.4631 8.4584

equilibriumd


mMEG mNaHCO3 mNa2CO3 STNa dev SCO32- dev Fsat.liq dev wNa2CO3 σNa2CO3 wNaHCO3 σNaHCO3 mH2O (g) (g) (g) (mol/kg) (%) (mol/kg) (%) (g/cm3) (%) (%) (%) (%) (%) (g) 0.2940 0.2931 0.2939 0.2937 0.2940 0.3013 0.2986 0.2932 0.2933 0.2937 1.5415 1.5421 1.5432 1.5418 1.5431 1.5445 1.5257 1.4983 1.5452 1.5433 0.2932 0.2939 0.2939 0.2934 1.5451 1.5427 1.5439 1.5437 1.5429

1.1381 1.1647 1.2183 1.2884 1.3226 0.3269 0.1626 1.4289 1.4271 1.3712 1.1279 1.1652 1.2227 1.2485 1.4300 1.4939 0.1515 0.3177 1.2890 1.3521 1.1946 1.5389 1.6170 1.3653 1.1963 1.4907 1.6168 1.3154 0.4061

0.1453 0.5314 0.9686 1.5513 1.9235 2.5787 2.5346 2.8880 2.8647 2.3268 0.1213 0.4610 0.9750 1.2541 2.8600 3.3353 2.1462 2.1697 1.5319 2.1621 0.7175 3.8482 4.5138 2.2428 0.7237 3.3510 4.5217 1.6136 5.5990

1.186 1.661 2.207 2.912 3.358 3.627 3.488 3.470 3.451 3.483 0.987 1.413 2.086 2.443 2.741 3.067 3.098 3.158 2.550 2.510 2.033 3.956 4.408 3.467 1.850 3.148 4.168 2.514 4.900

0.12 0.32 0.11 0.25 0.18 0.14 0.14 0.19 0.23 0.18 0.22 0.18 0.23 0.23 0.02 0.04 0.10 0.11 0.10 0.17 0.13 0.28 0.35 0.12 0.26 0.04 0.29 2.26 0.26

0.263 0.521 0.822 1.219 1.467 1.641 1.660 1.537 1.532 1.532 0.232 0.464 0.833 1.026 1.242 1.443 1.467 1.477 1.083 1.065 0.657 1.832 2.115 1.490 0.648 1.478 2.056 1.029 2.441

1.45 0.09 0.93 0.13 0.49 0.30 0.21 0.35 0.54 6.52 0.98 0.75 0.65 0.27 0.46 0.68 0.55 0.35 0.24 0.41 0.60 0.32 0.44 0.30 0.48 1.97 0.91

1.066 1.088 1.120 1.166 1.180 1.186 1.169 1.197 1.193 1.195 1.072 1.096 1.128 1.156 1.169 1.172 1.166 1.173 1.152 1.149 1.107 1.203 1.245 1.192 1.110 1.203 1.215 1.176 1.268

0.35 0.40 0.43 0.53 0.81 0.19 0.16 0.56 0.40 0.29 0.31 0.15 0.09 0.80 0.50 0.65 0.53 0.31 0.10 0.66 0.90 1.50 0.34 1.59 0.34 0.37 3.78 1.39 1.44

1.3164 4.723 8.349 12.87 15.52 17.38 17.56 1.1212 4.177 8.525 10.763 12.807 15.079 15.57 6.214 19.19 22.22 6.372 15.400 21.59 -

0.00018 0.0025 0.0020 0.010 0.011 0.029 0.026 0.00023 0.0010 0.0041 0.0063 0.0019 0.0034 0.017 0.0016 0.033 0.043 0.0030 0.0035 0.034 -

7.88 6.47 5.30 4.05 3.60 2.911 1.463 6.51 5.24 4.01 3.46 2.727 1.860 1.344 7.23 2.81 1.80 5.44 2.037 0.79 -

0.013 0.049 0.023 0.078 0.069 0.0043 0.0020 0.019 0.023 0.046 0.057 0.0019 0.0038 0.0011 0.024 0.041 0.062 0.045 0.0039 0.049 -

9.7292 9.6991 9.7237 9.7171 9.7268 8.6482 8.7037 8.4512 8.4543 8.4606 8.4529 7.9783 7.9178 7.8365 9.7021 9.2133 9.1278 8.4709 7.9183 7.8114 -

wMEG (%) P1f P2f 2.664 2.605 2.533 2.437 2.373 2.683 2.686 14.249 13.973 13.493 13.232 13.689 13.558 13.540 2.539 2.412 2.370 13.604 13.463 12.810 -

B B B B B D D B T B B B B B T T D D B B B T T B B T T B T

T B T

T T T

T

T M


this study. It was also confirmed by powder X-ray diffraction, that the solid phase is pure NaHCO3 and it is not a complex or

solid solution formed by MEG and NaHCO3. Ga¨rtner et al.2 suggested that the solubility increase may be explained by the

2226 Ind. Eng. Chem. Res., Vol. 48, No. 4, 2009 Table 11. Experimental Initial and Equilibrium Compositions, Reverse Schreinemakers Results, and Solid Phase in the NaHCO3-Na2CO3-MEG-H2O System at 1 bar and 40-50 °C initialc ta w˜MEGb (°C) (%) 39.90 39.60 39.80 39.80 39.70 39.80 39.90 39.20 39.80 39.60 39.90 39.90 39.90 39.80 39.90 49.70 49.75 49.70 48.80 49.60 49.75 49.70 49.40

mH2O (g)

equilibriumd


mMEG mNaHCO3 mNa2CO3 STNa dev SCO32- dev Fsat.liq dev wNa2CO3 σNa2CO3 wNaHCO3 σNaHCO3 mH2O (g) (g) (g) (mol/kg) (%) (mol/kg) (%) (g/cm3) (%) (%) (%) (%) (%) (g)

0.00 10.0081 0.0000 0.2910 3.04 9.7036 0.3046 1.2050 3.04 9.6833 0.3039 1.5510 3.04 9.7284 0.3053 1.6437 3.04 9.6826 0.3039 1.3556 3.04 9.7064 0.3047 0.4710 3.86 9.7241 0.3905 0.2979 15.34 8.4632 1.5333 1.1500 15.34 8.4733 1.5352 1.2068 15.34 8.4627 1.5332 1.4300 15.03 8.5264 1.5086 0.2587 14.95 8.5100 1.4961 0.2762 28.13 7.2394 2.8331 0.3182 54.19 4.7356 5.6010 0.2300 77.61 2.2556 7.8178 0.2096 3.04 9.7088 0.3047 1.2223 3.04 9.7056 0.3046 1.4822 3.04 9.6974 0.3044 1.5275 15.34 8.4761 1.5357 1.0151 15.34 8.4610 1.5330 1.1913 15.34 8.4607 1.5329 1.4304 15.34 8.4660 1.5338 1.5161 15.34 8.4716 1.5349 1.5757

4.4064 0.8367 3.8741 4.7442 2.3409 5.0355 3.5821 0.3445 0.8436 2.8565 2.8435 2.8792 1.7991 0.7296 0.3681 0.9949 3.3377 3.6444 0.3467 0.7143 2.8570 3.6380 4.1760

5.566 2.253 4.074 4.600 3.527 5.802 4.889 1.515 2.178 2.943 4.081 4.075 2.696 1.211 0.675 2.625 4.002 4.163 1.607 2.093 3.804 4.540 4.519

0.93 0.55 0.26 0.05 0.14 0.10 0.66 0.16 0.21 0.25 0.06 0.18 0.95 1.68 0.79 0.11 0.06 0.14 0.44 0.65 0.26 0.18 0.08

2.771 0.750 1.873 2.221 1.459 2.881 2.404 0.418 0.783 1.293 1.984 1.972 1.278 0.515 0.255 0.907 1.766 1.876 0.407 0.659 1.800 2.207 2.099

1.51 0.62 0.47 0.10 0.53 0.45 1.15 1.31 0.88 0.43 0.25 0.04 0.84 1.51 2.11 5.07 0.48 0.17 1.31 1.74 0.24 0.37 9.72

1.250 1.109 1.226 1.233 1.236 1.324 1.289 1.123 1.186 1.204 1.250 1.222 1.165 1.119 1.138 1.164 1.240 1.260 1.137 1.167 1.108 1.228 1.291

2.54 0.62 2.24 0.37 1.97 0.79 2.27 0.65 1.86 0.68 1.05 1.16 1.76 2.61 0.30 1.48 1.25 0.31 0.96 2.20 0.93 6.89 1.75

29.22 7.127 19.60 23.343 25.09 3.0696 7.244 13.45 20.975 21.02 13.50 5.60 2.71 8.223 18.043 19.26 3.057 6.148 18.76 23.205 -

0.12 0.0092 0.032 0.0062 0.084 0.00071 0.0034 0.024 0.0072 0.021 0.081 0.070 0.019 0.0025 0.0073 0.017 0.0021 0.0086 0.010 0.0055 -

0.43 7.63 3.16 1.641 1.30 7.86 6.81 3.40 1.04 0.91 1.25 1.29 1.37 9.01 5.021 4.43 8.66 7.83 2.21 1.35 -

0.25 0.12 0.040 0.0094 0.14 0.021 0.044 0.024 0.010 0.029 0.087 0.061 0.015 0.028 0.0081 0.020 0.062 0.13 0.065 0.059 -

8.8586 9.7036 8.4886 8.2897 8.7618 8.4632 8.4733 7.5050 7.6981 7.6717 6.6564 4.4454 2.0746 9.7088 8.6524 8.5585 8.4761 8.4610 8.4607 8.4660 -

wMEG (%) P1f P2f 0.000 T 2.594 B 2.670 T 2.665 T B T T M 3.141 T 13.663 B 13.183 B 14.106 T 12.779 T 12.740 T 25.451 T 51.909 T 75.803 T 2.519 B 2.617 T 2.620 T 13.542 B 13.194 B 12.121 W 11.572 W W M


presence of a liquid complex. It may rather be explained by the increase in CO2 solubility at high MEG concentrations. Solubility isotherms of Na2CO3 in MEG-H2O are shown in Figure 3 from data in Tables 7 and 8, plotted as function of equilibrium salt-free solvent fraction, which is different than initial salt-free solvent fraction. The isotherms at 10-20 °C show maxima at w(MEG,salt-free) ) 40% to w(MEG,salt-free) ) 50%. The reason is the change of solid phase. The saturated solution of Na2CO3 in pure water is in equilibrium with a solid phase of Na2CO3 · 10H2O. On addition of MEG, water activity drops and at w(MEG,salt-free) ) 40% to w(MEG,salt-free) ) 50%, Na2CO3 · 10H2O changes to Na2CO3 · 7H2O, further it changes to Na2CO3 · H2O above w(MEG,salt-free) ) 50% and finally Na2CO3 above approximately w(MEG,salt-free) ) 80%. At higher temperature above 40 °C only Na2CO3 · H2O and Na2CO3 precipitate. The solubility of Na2CO3 · H2O drops with increasing weight percent MEG and changes to Na2CO3 at approximately w(MEG,salt-free) ≈ 80%. It shows that solubility of Na2CO3 · 10H2O and Na2CO3 · 7H2O increases with temperature whereas Na2CO3 · H2O and Na2CO3 decreases with temperature. Two-salt isothermal solubility curves are shown in Figures 4 and 5 from experimental data in Tables 9-11, more data are found in the two tables than plotted in the figures. The data seem to be scattered since the solvent composition is not exactly w(MEG,salt-free) ) 3% and w(MEG,salt-free) ) 15% in all solutions and the temperature cannot be controlled exactly to the desired set point. The tables give the exact experimental conditions and the accuracy is high. In spite of the scatter in the data, it may be seen that solubility in the mixed solvent is similar to the solubility in pure water by comparing to the figures of Garrett.37 The water activity has most likely dropped and the solubility has in general decreased for all salts by addition

of MEG. This is observed by comparing Figures 4 and 5. Addition of MEG from initial w(MEG,salt-free) ≈ 3% to w(MEG,salt-free) ≈ 15% reduces solubility. Trona (Na2CO3 · NaHCO3 · 2H2O) which usually does not precipitate in pure water at 20 °C precipitates in a small branch indicated by the dashed line in Figures 4 and 5. The branch becomes wider on the addition of more MEG. This is also the case for wegscheiderite (Na2CO3 · 3NaHCO3) at 50 °C which can be read from the data of Ga¨rtner et al.2 The density measurements were difficult to reproduce and the deviations are high. In some cases, the determination of density failed completely due to one or more reasons: the micropipet took in air, or it was not completely emptied, or too small samples were used. In a few cases the density could not be measured, in other cases only one measurement could be made, and the standard deviation could not be determined. The sampling technique was refined over time and the density measurements of saturated Na2CO3, which were measured last, are more accurate than the corresponding data for solutions saturated with NaHCO3. Figure 6 shows the measured density of saturated NaHCO3-MEG-H2O solutions given in Tables 3-6. The isotherms increase from a low density in saturated pure water to high density in saturated pure glycol and the density increases with temperature. The density does not show a minimum compared to the solubility isotherm in Figure 2. There may be a tendency to form a minimum at high temperatures at approximately w(MEG) ≈ 20%, even though this is not completely proved by the measurements. The densities of saturated Na2CO3-MEG-H2O solutions are shown in Figure 7. The curvature is similar to the solubility plot shown in Figure 3. It has the same noticeable maximum in solubility at approximately w(MEG,salt-free) ≈ 40% to w(MEG,salt-free) ≈ 50%. Densities of two-salt mixtures have not been plotted.

Ind. Eng. Chem. Res., Vol. 48, No. 4, 2009 2227 Table 12. Experimental Initial Compositions and Metastable Compositions, Results of the Reverse Schreinemakers Method, and Solid Phase Information for the Na2CO3-Na2CO3-MEG-H2O System at 1 bar and 20-30 °C initialc ta w˜MEGb (°C) (%) 30.00 29.90 30.00 29.90 29.80 29.90 20.00 20.00 20.00 20.10 20.00 20.00 20.00 20.10 20.00 20.00 20.10 20.00 20.00 20.00 20.00 20.10 20.00 20.00 30.00 29.80 29.90 30.00 29.90 30.00

2.93 2.93 15.17 15.43 15.43 27.93 2.93 2.93 2.93 2.93 2.93 2.93 2.93 2.93 2.93 15.43 15.43 15.43 15.43 15.43 15.43 15.43 15.43 15.43 2.93 2.93 2.93 15.43 15.43 15.43

mH2O (g) 9.7162 9.7317 8.5091 8.4678 8.4507 7.2273 9.7135 9.7023 9.7021 9.7144 9.7253 9.7234 9.7055 9.7235 9.7249 8.4662 8.4573 8.4614 8.4606 8.4653 8.4678 8.4698 8.4623 8.4635 9.7058 9.7129 9.7225 8.4640 8.4597 8.4630

metastable solutionf

reverse Schreinemakersd

mMEG mNaHCO3 mNa2CO3 STNa dev SCO32- dev Fsat. liq dev wNa2CO3 σNa2CO3 wNaHCO3 σNaHCO3 (g) (g) (g) (mol/kg) (%) (mol/kg) (%) (g/cm3) (%) (%) (%) (%) (%) 0.2936 0.2941 1.5221 1.5445 1.5414 2.8006 0.2936 0.2932 0.2932 0.2936 0.2939 0.2939 0.2933 0.2939 0.2939 1.5443 1.5427 1.5434 1.5433 1.5441 1.5446 1.5449 1.5435 1.5438 0.2933 0.2935 0.2938 1.5439 1.5431 1.5437

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.9606 0.7427 0.5215 0.3914 0.4096 1.6334 0.4132 0.7449 0.4399 1.6138 1.5409 0.0603 0.5692 0.1216 0.1742 0.2601 0.4161 0.7440 0.0275 0.5414 0.1836 0.5630 0.0280 0.1868

4.9251 4.5903 2.8568 4.7036 4.5941 2.5354 2.7433 2.6877 2.6353 2.5992 2.7680 4.5144 2.9801 4.1752 4.0581 4.5150 3.8445 3.3499 3.5209 3.3729 3.3933 3.4191 3.4759 4.1814 4.6715 4.9622 4.6845 3.0946 4.6156 4.6814

4.429 5.421 3.403 4.935 5.101 2.704 3.563 3.685 3.804 3.871 3.993 4.312 4.148 4.832 4.530 4.334 3.509 4.556 4.319 4.511 4.537 4.517 4.353 4.723 5.997 5.423 4.488 3.811 4.745 3.330

0.01 0.31 0.90 3.14 0.12 0.75 0.15 0.07 0.22 0.24 0.30 0.03 0.14 0.11 0.17 0.24 2.68 0.19 0.50 0.21 0.50 0.75 0.19 0.39 0.13 0.49 0.04 0.08 0.35 0.90

2.207 2.696 1.692 2.484 2.531 1.337 1.594 1.675 1.767 1.804 1.874 2.075 1.982 2.387 2.201 2.138 1.703 2.246 2.117 2.230 2.232 2.228 2.144 2.355 2.981 2.682 2.183 1.856 2.359 1.631

0.11 0.60 1.16 2.86 0.24 1.07 0.36 0.60 0.65 0.10 0.33 0.52 0.01 0.13 0.23 0.21 2.63 0.01 0.47 0.68 0.70 0.23 0.51 0.62 0.34 0.32 0.15 0.85

1.259 1.301 1.198 1.303 1.306 1.173 1.203 1.207 1.203 1.227 1.232 1.255 1.236 1.258 1.253 1.267 1.187 1.277 1.269 1.273 1.278 1.280 1.272 1.268 1.355 1.287 1.265 1.227 1.270 1.215

0.28 1.22 0.29 1.27 0.63 0.45 0.79 0.49 0.24 0.46 0.05 2.23 0.63 0.46 0.47 0.20 1.64 0.41 0.48 0.99 0.37 0.76 0.25 0.41 1.03 0.93 0.51 0.02 1.59 0.06

23.472 28.73 18.04 26.15 27.03 14.33 16.76 17.735 18.7 19.23 20.01 21.901 21.07 25.3 22.04 17.86 23.85 22.61 31.66 19.93 25.01 -

0.0033 0.088 0.16 0.82 0.031 0.11 0.016 0.0078 0.025 0.027 0.034 0.0034 0.017 0.013 0.029 0.28 0.045 0.059 0.042 0.0088 0.088 -

0 0 0 0 0 0 3.36 2.843 2.31 2.04 1.83 1.506 1.45 0.49 1.48 1.17 0.4578 0.45 0.1875 0.42 0.2142 -

mH2O (g)

9.3835 9.6315 8.3944 8.2586 8.2888 7.0772 0.018 9.4781 0.0092 9.5346 0.031 9.6027 0.034 9.6570 0.045 9.6495 0.0049 9.1021 0.023 9.6077 0.023 9.4314 0.041 7.8518 0.35 7.8550 0.00034 8.4261 0.089 8.2410 0.00015 9.7010 0.012 8.2446 0.00031 8.2309 -

wMEG (%) P1e P2e 2.322 2.112 12.581 11.635 11.442 24.289 2.400 2.370 2.340 2.323 2.310 2.395 2.295 2.242 12.571 13.292 11.717 12.136 2.000 12.563 11.805 -

M M M M M M T T T T T T T T M T T M T T T T T T M T M T M D

T

M M M M M M T

T

System temperature given in °C. b w˜MEG, salt-free weight percent of MEG in the initial composition, wMEG/(wMEG + mH2O). c The weight of the initial composition in grams, mi of component i. d The result of the reverse Schreinemakers method was calculated by equations of Fosbøl.33,34 wi is the weight percent of component i, calculated as 100 g of i per gram of saturated solution, and mH2O is the number of grams of water in the saturated liquid phase at equilibrium. σi is the standard deviation of the weight fraction i. e P1 and P2 are the precipitated solid phases: B, NaHCO3; C, Na2CO3; M, Na2CO3 · H2O; H, Na2CO3 · 7H2O; D, Na2CO3 · 10H2O; T, trona; and W, wegscheiderite. f The metastable composition is determined by titration. STNa is calculated by method III of Fosbøl33,34 as mol sodium/kg solution and SCO32- by method I of Fosbøl33,34 in mol CO32-/kg solution. Fsat.liq is the density of the saturated liquid at equilibrium temperature in g/cm3. The deviation of STNa, SCO32-, and Fsat.liq (dev) is calculated as the standard deviation, σ, divided by the mean of the samples times 100. a

Figure 8. Stable and metastable data at 20 °C in the Na2CO3-NaHCO3-MEG-H2O system. Solid circles and triangles: NaHCO3. Dark gray triangles, squares, and circles: trona. Light gray triangles and circles: Na2CO3 · 10H2O. Light gray tilted squares: Na2CO3 · H2O. Dotted line: metastable trend.

Metastable Solutions. A challenge when measuring solubility in the Na2CO3-NaHCO3-MEG-H2O system at lower temperature is the formation of metastable solutions. Several different metastable phases may form depending on the initial concentration and the added seed crystals. Metastable solutions have a tendency to form below 35 °C from initial solutions from which salt hydrates were expected to precipitate. For example,

Na2CO3 solutions may stand for several days at very high supersaturation at 10-25 °C without solids precipitating. By seeding, precipitation occurs instantly. Seeding an aqueous Na2CO3 solution at 10 °C by anhydrous Na2CO3(s) will make Na2CO3 · H2O precipitate, but seeding using Na2CO3 · 10H2O initiates Na2CO3 · 10H2O precipitation. The equilibrium experiments related to Na2CO3 were carried out by supersaturating a solution by a few weight percent Na2CO3, seeding, and determining the composition by the reverse Schreinemakers method. Na2CO3 · 7H2O was not used as a seeding crystal, but the reverse Schreinemakers method revealed that one solution precipitated Na2CO3 · 7H2O. Table 12 shows the metastable data determined in this study. The columns of Table 12 correspond to those of Tables 3-11. Figure 8 shows a selection of metastable data from Table 12 determined in this study. The stable branches of the isotherms consist of a NaHCO3 branch, a trona branch, and a Na2CO3 · 10H2O branch as shown by the figure. The real equilibrium isothermal trona branch at w(MEG,salt-free) ≈ 3% is very short. The metastable isotherms have longer trona branches, and the Na2CO3 · 10H2O branch is replaced by a Na2CO3 · H2O branch as illustrated in the figure. The metastable solutions in equilibrium with trona can easily be reproduced and it is difficult to get the stable phase of Na2CO3 · 10H2O without using seed crystals. Conclusion In this work, solubility and density in ternary and quaternary mixtures of NaHCO3-Na2CO3-MEG-H2O were measured.


This was done in order to extend the temperature and composition range of the previous solubility experiments. The mixtures were analyzed by potentiometric titration, and the reverse Schreinemakers method was applied for the calculation of solubility. The experimental work showed that ternary mixtures of Na2CO3-MEG-H2O and NaHCO3-MEG-H2O both have unusual isothermal solubility profiles. The isotherms go through local minima and maxima with respect to MEG concentrations and the isotherms do not always increase toward higher temperature. The quaternary solubility isotherms are similar to the pure water system, even though solubility is lower. Trona and wegscheiderite precipitate much earlier than expected when MEG is added probably due to lowering of the water activity. The study showed that trona and the hydrates of Na2CO3 easily form metastable phases. Density was measured in this work using a known sample volume and weighing. The method has relatively low accuracy and is only precise to approximately 0.5%. The measurements presented in this work may be used in corrosion modeling of gas pipelines, carbonate scale prediction, CO2 capture, or gas drying simulators in the mixed solvent electrolyte system of CO2-NaHCO3-Na2CO3-MEG-H2O. Acknowledgment This project was financed in part by Maersk Oil and Gas A/S. We acknowledge the valuable funding. Literature Cited (1) Oosterhof, H.; Witkamp, G. J.; van Rosmalen, G. M. Some Antisolvents for Crystallisation of Sodium Carbonate. Fluid Phase Equilib. 1999, 155, 219–227. (2) Ga¨rtner, R. S.; Seckler, M. M.; Witkamp, G.-J. Solid Phases and Their Solubilities in the System Na2CO3 + NaHCO3 + Ethylene Glycol + Water from (50 to 90)°C. J. Chem. Eng. Data 2004, 49, 116–125. (3) Dugstad, A.; Seiersten, M. pH-stabilisation, a Reliable Method for Corrosion Control of Wet Gas Pipelines. SPE Corrosion Conf. 2004, 87560. (4) Atakhodzhaev, A. K.; Dzhuraev, B. Solubility Sodium Bicarbonate in Mixed Alcohol-water Solvents. Dokl. Akad. Nauk USSR 1988, 7, 39– 40. (5) Sandengen, K. Prediction of Mineral Scale Formation in Wet Gas Condensate Pipelines and in MEG (mono ethylene glycol) Regeneration Plants Ph.D. Dissertation, NTNU, Norway, 2006. (6) Oglesby, N. E. A Study of the System Sodium Bicarbonate-Potassium Bicarbonate-Water. J. Am. Chem. Soc. 1929, 51, 2352–2362. (7) Waldeck, W. F.; Lynn, G.; Hill, A. E. Aqueous Solubility of Salts at High Temperatures II. The Ternary System Na2CO3-NaHCO3-H2O from 100-200. J. Am. Chem. Soc. 1934, 56, 43–47. (8) Hill, A. E.; Bacon, L. R. Ternary Systems VI. Sodium Carbonate, Sodium Bicarbonate and Water. J. Am. Chem. Soc. 1927, 49, 2487–2495. (9) Hill, A.; Smith, S. Equilibrium Between the Carbonates and Bicarbonates of Sodium and Potassium in Aqueous Solution at 25 °C. J. Am. Chem. Soc. 1929, 51, 1626–1636. (10) Hill, A. Double Salt Formation Among the Carbonates and Bicarbonates of Sodium and Potassium. J. Am. Chem. Soc. 1930, 52, 3813– 3817. (11) Green, S. J.; Frattali, F. J. The System Na2CO3-Na2SO4-NaOHH2O at 100 °C. J. Am. Chem. Soc. 1946, 68, 1789–1794. (12) Itkina, L. S.; Chaplygina, N. M. The Solubility Isotherm in the 2Li+, 2Na+, CO32-, 2OH- + H2O System at 50 °C. Russ. J. Inorg. Chem. 1963, 8 (6), 768–772. (13) Morozova, V. A.; Rzhechitskii, E. P. Solubility in the Sodium Fluoride-Sodium Bicarbonate-Water, Sodium Fluoride-Sodium SulfateWater, and sodium fluo. Russ. J. Inorg. Chem. 1977, 22, 485–486.

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ReceiVed for reView July 29, 2008 ReVised manuscript receiVed October 27, 2008 Accepted November 24, 2008 IE8011648

Solubility Measurements in the Mixed Solvent Electrolyte System

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