Ternary LiquidâLiquid Equilibrium Data for the Water + Acetonitrile +

Article pubs.acs.org/jced

Ternary Liquid−Liquid Equilibrium Data for the Water + Acetonitrile + {Butan-1-ol or 2‑Methylpropan-1-ol} Systems at (303.2, 323.2, 343.2) K and 1 atm Caleb Narasigadu,* Muven Naidoo, and Deresh Ramjugernath Thermodynamics Research Unit, School of Engineering, University of KwaZulu-Natal, King George V Avenue, Durban, 4041, South Africa S Supporting Information *

ABSTRACT: Ternary liquid−liquid equilibrium (LLE) data were measured and correlated for the water + acetonitrile + (butan-1-ol or 2-methylpropan-1-ol) systems at (303.2, 323.2, and 343.2) K and 1 atm. A double-walled glass cell with the direct analytical method was used to measure the liquid−liquid equilibrium data. The phase equilibrium samples were analyzed and quantified using gas chromatography. The nonrandom two-liquid activity coefficient model was used to fit the experimental tie-lines using nonlinear least-squares regression of the data. Relative selectivity values for solvent separation efficiency were calculated from the tie-line data. The plait point for each temperature was estimated with the graphical Coolidge method.

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INTRODUCTION Liquid−liquid extraction is an important separation process in chemical processing since it can offer substantial energy savings when compared to distillation. Accurate phase equilibrium data (especially ternary liquid−liquid equilibrium, LLE) is required to design and evaluate such a separation process. Acetonitrile can be used as an effective extractive solvent because of its selective miscibility. However, because of its toxicity, acetonitrile must be removed from aqueous waste in chemical industries.1 The use of conventional distillation to separate acetonitrile from water is not realistic owing to the formation of a minimum boiling azeotrope.2 This study forms part of a larger investigation within our research unit to explore potential extractive solvents for the separation of acetonitrile and water.3 In this study the use of butan-1-ol or 2methylpropan-1-ol as a potential extractive solvent for the separation of acetonitrile and water is investigated. Ternary LLE data for the water + acetonitrile + (butan-1-ol or 2methylpropan-1-ol) systems at (303.2, 323.2 and 343.2) K and 1 atm were measured. To our knowledge there is no published ternary LLE data for water + acetonitrile + (butan-1-ol or 2methylpropan-1-ol).

The refractive index measurements, with an overall uncertainty of 0.0001, were obtained with an Atago refractometer, model RX 7000α.4 The temperature of the refractometer was controlled to within an uncertainty of 0.01 K. The chemical characterization is summarized in Table 1. All reagents used in the study did not show significant impurities and were therefore used without further purification. Table 1. Chemical Purity Analysis

acetonitrile butan-1-ol 2-methylpropan-1-ol water

0.998 0.991 0.991 1.000

mass fraction puritya > 0.999 > 0.99 > 0.99

measured nDb,c

lit. nDb

1.34386 1.39928 1.39563 1.33299

1.343617 1.399318 1.395518 1.332818

a

As stated by supplier. bnD is the refractive index at T = 293.15 K; u(T) = 0.01 K. cu(nD) = 0.0001 (k = 2).

Equipment. The direct analytical method using a doublewalled glass cell with a magnetic stirrer for agitation was employed to obtain the LLE measurements. The double-walled glass cell is a modification of the one used by Raal and Brouckaert.5 The modifications include the use of a magnetic stirrer, an adjustable thermo-well for improved temperature measurements, and a sampling port for the more dense phase

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EXPERIMENTAL SECTION Chemicals. Acetonitrile was purchased from Sigma-Aldrich. Butan-1-ol and 2-methylpropan-1-ol were purchased from Merck, while water was obtained using a Elga PURELAB Option Q purification system from our laboratory. All reagents used in this study were subjected to a purity check using gas chromatographic analysis and refractive index measurement. © XXXX American Chemical Society

chemical

GC peak area fraction

Received: August 1, 2014 Accepted: October 10, 2014

A

dx.doi.org/10.1021/je5007218 | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Figure 1. Schematic of the double-walled glass cell. (A) O-ring; (B) upper sampling port cap; (C) septum; (D) outer wall of cell cap; (E) cell cap; (F) upper sampling port; (G) inner cell cavity; (H) bottom sampling port; (I) cell wall cavity for heating fluid; (J) adjustable thermo-well for temperature probe; (K) cell heating fluid inlet; (L) cell cap heating fluid inlet; (M) magnetic stirrer.

Britt−Leucke algorithm and Deming Initialisation method were selected.10 The minimization of a nonlinear least-squares objective function was chosen over the maximum likelihood method as suggested by Novák et al.11 The nonrandomness parameter of the nonrandom two-liquid (NRTL) model (αij) was set to the same value for all three binary pairs and fixed at 0.4 as suggested by Walas.12 The root-mean-square deviation (rmsd) was calculated to obtain a good measure of the accuracy of the NRTL model:

thereby avoiding the disturbance of equilibrium during sampling. Figure 1 shows a schematic of the double-walled glass cell. This apparatus was successfully used in previous studies.3,6 Water was used as the heating fluid which was circulated through the cell wall and cap from a constant temperature bath. The method suggested by Alders7 was followed for the experimental procedure. For each measurement undertaken, the contents of the cell were stirred at a low speed for approximately 1 h. Thereafter at least 1 h was allowed for the contents to equilibrate before sampling was done. The system was deemed to be at equilibrium when the composition analysis for three consecutive samples analyzed after 10 min each were within experimental uncertainty. The measurement of temperature in the equilibrium cell was undertaken using a Pt-100 temperature sensor placed in a thermo-well in the cell. The temperature sensor was calibrated against a Wika CTB 9100 temperature calibration unit. The overall uncertainty for the temperature measurement is 0.1 K (k = 2).4 A Shimadzu 2014 gas chromatograph (GC) fitted with a thermal conductivity detector was used to analyze the samples and quantify the equilibrium compositions using the GC Solution software program. A 4 m length 1/8 inch diameter Porapak Q packed column was used in the GC to carry out the analysis with helium as the carrier gas. The GC detector was calibrated using the area ratio method outlined by Raal and Mühlbauer.8 The overall uncertainty for the mole fraction compositions was 0.003 (k = 2).4

⎧ ∑ ∑ ∑ {x (exp) − x (calc)}2 ⎫1/2 abc abc ⎬ rmsd = ⎨ a b c 6 k ⎭ ⎩

β=

■

(1)

(xiγi)I = (xiγi)II

(2)

⎪

⎪

⎪

(3)

where x is the liquid phase mole fraction, k is the number of experimental points, and the subscripts a, b, and c denote the component, phase, and tie-line, respectively. Relative Selectivity and Plait Point. The relative selectivity (β) is an important parameter used to determine the effectiveness of a solvent. For butan-1-ol or 2methylpropan-1-ol to be an effective solvent in the separation of acetonitrile and water, β must significantly exceed a value of 1. For acetonitrile as the solute, water as the carrier, and butan1-ol or 2-methylpropan-1-ol as the solvent, β is defined as (x 2)II /(x 2)I (x1)II /(x1)I

(4)

where the subscripts 1 and 2 represent water and acetonitrile, respectively, and I and II represent the water-rich phase and solvent-rich phase, respectively. The plait point on a ternary LLE diagram represents the point where the two liquid phases become one with an identical composition. The graphical Coolidge method as suggested by Novák et al.11 was used to determine the plait point for each isotherm in this study.13

THEORY Data Correlation. Starting with the mathematical thermodynamic criterion for phase equilibrium, eq 1, the criterion for LLE, eq 2, is obtained: (fi ̂ )I = (fi ̂ )II

⎪

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RESULTS AND DISCUSSION The experimental LLE data for the water + acetonitrile + {butan-1-ol or 2-methylpropan-1-ol} systems at (303.2, 323.2, and 343.2) K and 1 atm are presented graphically in Figures 2 to 7 and tabulated in Tables 2 and 3. The regressed NRTL model parameters are reported in Tables 4 and 5. The plait

where x is the liquid phase mole fraction, γ is the liquid phase activity coefficient, I and II denote the respective equilibrium phases, and i represents a particular species. The tie-line data were correlated with the NRTL9 activity coefficient model using ASPEN Plus version 8.0 software. The B



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Figure 6. Liquid−liquid equilibrium for the water (1) + acetonitrile (2) + 2-methylpropan-1-ol (3) system at 323.2 K and 1 atm: ○, experimental (this study); -•-, NRTL model; ∗, plait point.

Figure 2. Liquid−liquid equilibrium for the water (1) + acetonitrile (2) + butan-1-ol (3) system at 303.2 K and 1 atm: ○, experimental (this study); -•-, NRTL model; ∗, plait point.

Figure 7. Liquid−liquid equilibrium for the water (1) + acetonitrile (2) + 2-methylpropan-1-ol (3) system at 343.2 K and 1 atm: ○, experimental (this study); -•-, NRTL model; ∗, plait point.

Table 2. Liquid−Liquid Equilibrium Data for the Water (1) + Acetonitrile (2) + Butan-1-ol (3) System at (303.2, 323.2 and 343.2) K and 1 atma


organic phase


Figure 5. Liquid−liquid equilibrium for the water (1) + acetonitrile (2) + 2-methylpropan-1-ol (3) system at 303.2 K and 1 atm: ○, experimental (this study); -•-, NRTL model; ∗, plait point. a

point estimation using the graphical Coolidge method is reported in Table 6. Figures 2 to 7 and the rmsd values reported in Tables 4 and 5 show that the NRTL model describes the water + acetonitrile + {butan-1-ol or 2-methylpropan-1-ol} system at (303.2, 323.2 and 343.2) K and 1 atm well. Figures 2 to 7 also indicate that all systems exhibit type I ternary LLE behavior which is the most common type.10 However, both ternary systems measured at (303.2, 323.2 and 343.2) K and 1 atm display a rather small region of immiscibility. The relative selectivity values reported

x1

x2

0.511 0.542 0.577 0.616 0.659 0.697 0.791

0.000 0.025 0.049 0.069 0.084 0.091 0.082

0.543 0.568 0.589 0.619 0.662 0.714 0.798

0.000 0.019 0.034 0.049 0.066 0.076 0.072

0.581 0.612 0.634 0.690 0.695 0.786

0.000 0.017 0.030 0.050 0.051 0.060

aqueous phase x3

x1

T = 303.2 K 0.489 0.978 0.433 0.969 0.374 0.957 0.315 0.946 0.257 0.935 0.212 0.921 0.127 0.873 T = 323.2 K 0.457 0.982 0.413 0.975 0.377 0.965 0.332 0.960 0.272 0.947 0.210 0.929 0.130 0.887 T = 343.2 K 0.419 0.984 0.371 0.972 0.336 0.965 0.260 0.948 0.254 0.940 0.154 0.912

x2

x3

β

0.000 0.009 0.019 0.028 0.036 0.044 0.060

0.022 0.022 0.024 0.026 0.029 0.035 0.067

4.97 4.28 3.78 3.31 2.73 1.51

0.000 0.007 0.012 0.019 0.027 0.037 0.051

0.018 0.018 0.023 0.021 0.026 0.034 0.062

4.66 4.64 4.00 3.50 2.67 1.57

0.000 0.006 0.011 0.022 0.027 0.037

0.016 0.022 0.024 0.030 0.033 0.051

4.50 4.15 3.12 2.55 1.88

u(T) = 0.1 K (k = 2); u(x) = 0.003 (k = 2); u(P) = 0.02 atm (k = 2).

in Tables 2 and 3 indicate that the extraction of acetonitrile from water using butan-1-ol or 2-methylpropan-1-ol as an extractive solvent is nonetheless possible. The small region of immiscibility in Figures 2 to 7 implies that a binary feed of acetonitrile and water should contain no less than 85 mol % water if butan-1-ol or 2-methylpropan-1-ol is to be used as an extractive solvent at a maximum temperature of 343.2 K.14 Essentially the 85 mol % of water implies the limit of the binary feed composition required for ternary LLE to form when the C



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Table 5. NRTLa Interaction Parameters and Root Mean Square Deviations (rmsd) for the Water (1) + Acetonitrile (2) + 2-Methylpropan-1-ol (3) System at (303.2, 323.2 and 343.2) K and 1 atm

Table 3. Liquid−Liquid Equilibrium Data for the Water (1) + Acetonitrile (2) + 2-Methylpropan-1-ol (3) System at (303.2, 323.2 and 343.2) K and 1 atma organic phase x1

a

x2

aqueous phase x3

0.450 0.481 0.547 0.587 0.646 0.686

0.000 0.029 0.077 0.097 0.110 0.111

0.488 0.509 0.520 0.553 0.577 0.603 0.645 0.679 0.770

0.000 0.016 0.032 0.049 0.062 0.076 0.088 0.093 0.088

0.542 0.554 0.585 0.616 0.644 0.688 0.733

0.000 0.012 0.034 0.051 0.061 0.070 0.073

x1

T = 303.2 K 0.550 0.976 0.490 0.964 0.376 0.943 0.316 0.929 0.244 0.909 0.203 0.893 T = 323.2 K 0.512 0.976 0.475 0.973 0.448 0.965 0.398 0.962 0.361 0.955 0.321 0.947 0.267 0.932 0.228 0.923 0.142 0.882 T = 343.2 K 0.476 0.981 0.434 0.977 0.381 0.968 0.333 0.957 0.295 0.950 0.242 0.935 0.194 0.924

x2

β

x3

i 0.024 0.026 0.029 0.033 0.041 0.049

5.81 4.74 4.04 3.10 2.49

0.000 0.005 0.011 0.016 0.022 0.028 0.036 0.042 0.058

0.024 0.022 0.024 0.022 0.023 0.025 0.032 0.035 0.060

6.12 5.40 5.33 4.66 4.26 3.53 3.01 1.74

0.000 0.004 0.011 0.018 0.023 0.031 0.037

0.019 0.019 0.021 0.025 0.027 0.034 0.039

5.29 5.11 4.40 3.91 3.07 2.49

a

a

1 1 2

2 3 3

1 1 2

2 3 3

1 1 2

2 3 3

gij − gjj

gji − gii

J mol−1

J mol−1

T = 303.2 Kb 3578 −3227 37222 −4790 10276 −17077 T = 323.2 Kb 3298 −3440 38056 −4978 9612 −1649 T = 343.2 Kb 1482 −3653 38645 −5434 9013 −17702

gji − gii J mol−1

rmsd

1 1 2

2 3 3

−3227 2300 1247

0.005

1 1 2

2 3 3

−3440 2042 2067

0.006

1 1 2

2 3 3

−3653 1648 3327

0.004

T = 303.2 K 4334 −2352 −1191 T = 323.2 Kb 4207 −1350 −2296 T = 343.2 Kb 4097 −463.0 −3075

αij = 0.4. bu(T) = 0.1 K (k = 2)

Table 6. Plait Point Compositions Using the Graphical Coolidge Method for the Water (1) + Acetonitrile (2) + {Butan-1-ol (3) or 2-Methylpropan-1-ol (3)} Systems at (303.2, 323.2 and 343.2) K and 1 atm T/Ka

x1

x2

x3

Water (1) + Acetonitrile (2) + Butan-1-ol (3) 303.2 0.837 0.070 0.093 323.2 0.848 0.061 0.091 343.2 0.860 0.050 0.090 Water (1) + Acetonitrile (2) + 2-Methylpropan-1-ol (3) 303.2 0.809 0.091 0.100 323.2 0.833 0.073 0.094 343.2 0.853 0.065 0.082

Table 4. NRTLa Interaction Parameters and Root Mean Square Deviations (rmsd) for the Water (1) + Acetonitrile (2) + Butan-1-ol (3) System at (303.2, 323.2 and 343.2) K and 1 atm j

gij − gjj J mol−1 b

0.000 0.010 0.028 0.038 0.050 0.058

u(T) = 0.1 K (k = 2); u(x) = 0.003 (k = 2); u(P) = 0.02 atm (k = 2).

i

j

a

u(T) = 0.1 K (k = 2).

smaller than for other solvents with acetonitrile + water reported in the open literature except for methyl ethyl ketone.15,16

rmsd

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CONCLUSIONS Ternary LLE data for the water + acetonitrile + {butan-1-ol or 2-methylpropan-1-ol} systems at (303.2, 323.2, and 343.2) K and 1 atm were measured using the analytical method in a double-walled glass cell. It was found that all systems exhibited type I ternary LLE behavior with a small region of immiscibility. The measured experimental data were modeled with the NRTL model which described each ternary system well at all temperatures investigated. The plait point for each temperature was estimated using the graphical Coolidge method. Relative selectivity values indicated that the separation of acetonitrile from water is possible using butan-1-ol or 2-methylpropan-1-ol as an extractive solvent. Other solvents for the separation of acetonitrile from water reported in the open literature show a significantly larger region of immiscibility and higher relative selectivity.15,16

0.007

0.007

0.006

αij = 0.4. u(T) = 0.1 K (k = 2). b

solvent is added. If the water content of the binary feed is less than 85 mol %, then consequently no LLE will occur irrespective of the amount of solvent added. The relative selectivity values of butan-1-ol and methylpropan-1-ol as a potential solvent are significantly lower than for chlorobenzene, xylene (mixed), n-butyl acetate, toluene, isoamyl acetate, and isobutyl methyl ketone reported in the open literature.15,16 The region of immiscibility for water + acetonitrile + solvent (butan1-ol or methylpropan-1-ol) in this study is also significantly

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ASSOCIATED CONTENT

S Supporting Information *

NIST Literature Report. This material is available free of charge via the Internet at http://pubs.acs.org. D



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Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +27 31 260 3734. Fax: +27 31 260 1118. Funding

This work is based upon research supported by the NRF Thuthuka Programme. Notes

The authors declare no competing financial interest.

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REFERENCES

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