Measurements and Correlations of Liquid–Liquid Equilibria for Water

Sep 7, 2012 - Oxybis(butane) (DBE) has a high octane number similar to ... The temperature uncertainty was ± 0.05 K. The quaternary ... settled for 3...
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Measurements and Correlations of Liquid−Liquid Equilibria for Water + Ethanol + 1,1′-Oxybis(butane) + Methylbenzene or Heptane Mixtures at 298.15 K Yanyan Tang, Yao Chen,* and Jun Zeng Department of Chemistry, Jinan University, Guangzhou, 510632, China ABSTRACT: Tie-line data were experimentally determined at 298.15 K and ambient pressure for two ternary systems of water + 1,1′-oxybis(butane) (DBE) + methylbenzene or heptane and two quaternary systems of water + ethanol + DBE + methylbenzene or heptane. The modified and extended universal quasichemical (UNIQUAC) activity coefficient models were used to correlate the experimental tie-line data. The experimental and the correlated results obtained using the modified UNIQUAC model were comparably presented in the phase diagrams for the ternary and quaternary systems measured in this work. Distribution coefficients of components were calculated to evaluate their solubility in aqueous and organic phases.

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INTRODUCTION Over the last years, ethers have been pointed out as healthier and friendlier antiknock additives for gasoline fuel, replacing typical leaded compounds which had been traditionally used.1,2 2-Methoxy-2-methylpropane (MTBE) is presently used more often in reformulated gasoline owing to its high octane number.3−6 Unfortunately MTBE was disabled in the United States as a gasoline additive due to its relatively high solubility in water and nonbiodegradable property. Therefore, the search for MTBE substitute materials which have octane-enhancing and pollution-reducing properties is extremely urgent. 1,1′Oxybis(butane) (DBE) has a high octane number similar to alcohols and dialkyl carbonates but is less soluble in water. The addition of DBE to gasoline fuel can improve engine efficiencies and reduce carbon monoxide. DBE may be a promising gasoline additive. In the formulation and storage of commercial gasoline, the most valuable data are the liquid−liquid equilibria (LLE) data. Therefore, additional studies on the phase behavior of systems that contain DBE and hydrocarbons are necessary. Experience shows that the commercial gasoline distribution system always contains water, because of air humidity or infiltration into storage tanks. Therefore, water was included in this study. To better understand and model the new formulated gasoline, we have started many years ago a research program on the LLE of ternary and quaternary mixtures containing oxygenated additives (ethers and alcohols) and hydrocarbons. In this work, we reported the LLE data for the ternary systems of water + DBE + methylbenzene or heptane and the quaternary systems of water + ethanol + DBE + methylbenzene or heptane at 298.15 K and ambient pressure. The experimental LLE data were correlated by means of the extended and modified universal quasichemical (UNIQUAC) activity coefficient models.7,8 © 2012 American Chemical Society

The binary parameters of miscible binary systems were obtained from vapor−liquid equilibria (VLE) data,9−14 whereas those of immiscible systems were obtained from mutual solubility data. 15−17 To accurately present the quaternary LLE, the ternary parameters, obtained from the ternary systems of water + ethanol + DBE,1 water + ethanol + methylbenzene,18 water + ethanol + heptane,19 and water + DBE + methylbenzene or heptane measured in this work are necessary.

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EXPERIMENTAL SECTION Materials. DBE was supplied by Tianjin Damao Chemical Reagent Factory with a mass fraction purity greater than 0.990. Heptane and ethanol were obtained from Tianjin Fuyu Chemical Reagent Factory with a mass fraction purity greater than 0.985 and 0.997. Methylbenzene was supplied by Table 1. Purities and Suppliers of the Chemicals chemical DBE (AR)

a

mass fraction purity 0.990

methylbenzene (AR) heptane (AR)

0.996

ethanol (AR)

0.997

a

0.997

supplier Tianjin Damao Chemical Reagent Factory, China Guangzhou Chemical Reagent Factory, China Tianjin Fuyu Chemical Reagent Factory, China Tianjin Fuyu Chemical Reagent Factory, China

AR stands for analytical reagent.

Received: June 15, 2012 Accepted: August 28, 2012 Published: September 7, 2012 2784

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Figure 1. Tetrahedron phase diagram of (water + ethanol + DBE + methylbenzene) and (water + ethanol + DBE + heptane). M1, M2, M3, and M4 denote quaternary section planes.

Table 2. Experimental LLE Data for the Ternary System of Water (1) + Methylbenzene (2) + DBE (3) for Mole Fractions x at the Temperature T = 298.15 K and Pressure p = 0.1 MPaa organic phase x1I

x2I b

0.000 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b

0.164 0.251 0.345 0.396 0.463 0.502 0.584 0.667 0.722

aqueous phase x3I 0.836 0.749 0.655 0.604 0.537 0.498 0.416 0.333 0.278

x1II 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

x2II

x3II b

0.000 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b

Figure 2. Experimental and calculated LLE for the ternary systems of water + methylbenzene + DBE and water + heptane + DBE at 298.15 K. ●- - -●, experimental tie-lines; , correlated by the modified UNIQUAC model with binary and ternary parameters.

0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b

Procedure and Results. Ternary and quaternary LLE measurements were carried out at the temperature 298.15 K. The temperature uncertainty was ± 0.05 K. The quaternary mixtures were prepared by adding water and ethanol into the binary (DBE + methylbenzene) or (DBE + heptane) mixtures, whose compositions are M1, M2, M3, and M4 to cover the two-phase regions. The values of M1, M2, M3, and M4 are 0.20, 0.40, 0.60, and 0.80, respectively, indicating the ratio between the mole fraction of DBE and methylbenzene or DBE and heptane in the binary (DBE + methylbenzene) or (DBE + heptane) mixtures. In the thermostatted water bath, a glass equilibrium cell of volume from (40 to 120) mL is placed at an expected temperature, where the mixtures were loaded in and were stirred vigorously by using a magnetic stirrer for 3 h and settled for 3 h. It was sufficient for separation into aqueous and organic phases. After reaching phase equilibrium, samples of two liquid phases were withdrawn and analyzed by a gas chromatograph (GC-14C) with a thermal conductivity detector. The detector temperature was set at 513.15 K and injection port temperature at 493.15 K, respectively. The hydrogen flow rates were set at 60 mL·min−1 for both the separation and the reference columns. Each component of the mixtures was separated clearly using a stainless steel column with 2 m in length packed with Porapak QS. The peak areas of the components, detected with a chromatopac (N2000), were calibrated and converted to mole fraction. At least three analyses were made for each sample to obtain a mean value. The estimated uncertainty of the mole fraction was about 0.005. Figure 1 draws a tetrahedron diagram of LLE for the quaternary systems of water + ethanol + DBE + methylbenzene and water + ethanol + DBE + heptane. The quaternary systems exhibit type 2 quaternary LLE behavior, which is composed of

a

Standard uncertainties u are u(T) = 0.05 K, u(x) = 0.005, and u(p) = 10 kPa. bLower than the GC detection limit or smaller than the uncertainty estimated.

Table 3. Experimental LLE Data for the Ternary System of Water (1) + Heptane (2) + DBE (3) for Mole Fractions x at the Temperature T = 298.15 K and Pressure p = 0.1 MPaa organic phase x1I

x2I b

0.000 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b

0.120 0.217 0.284 0.352 0.410 0.460 0.528 0.588 0.650

aqueous phase x3I 0.880 0.783 0.716 0.648 0.590 0.540 0.472 0.412 0.350

x1II 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

x2II

x3II b

0.000 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b

0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b 0.000b

a

Standard uncertainties u are u(T) = 0.05 K, u(x) = 0.005, and u(p) = 10 kPa. bLower than the GC detection limit or smaller than the uncertainty estimated.

Guangzhou Chemical Reagent Factory with a nominal minimum mass fraction of 0.995, respectively. Gas chromatography analysis gave mass fractions of 0.990 for DBE, 0.996 for methylbenzene, 0.997 for heptane, 0.997 for ethanol, and 0.999 for water. Redistilled water was used. The purities and suppliers of the chemicals used in this work are listed in Table 1. 2785

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Table 4. Experimental LLE Data for the Quaternary System of Water (1) + Ethanol (2) + Methylbenzene (3) + DBE (4) for Mole Fractions x at the Temperature T = 298.15 K and Pressure p = 0.1 MPaa organic phase x1I

x2I

aqueous phase x3I

x1II

x2II

organic phase x3II

{x1 Water + x2 Ethanol + x3 Methylbenzene + (1 − x1 − x2 − x3) DBE}b x′4 = 0.20c d 0.000 0.006 0.799 0.975 0.025 0.000d d 0.000 0.012 0.798 0.953 0.047 0.000d 0.000d 0.021 0.783 0.929 0.071 0.000d 0.000d 0.034 0.772 0.902 0.098 0.000d d 0.000 0.048 0.765 0.882 0.118 0.000d d 0.000 0.060 0.752 0.861 0.139 0.000d 0.011 0.078 0.719 0.841 0.159 0.000d 0.014 0.091 0.714 0.817 0.183 0.000d 0.013 0.099 0.699 0.805 0.195 0.000d 0.019 0.114 0.688 0.783 0.217 0.000d 0.019 0.119 0.687 0.770 0.230 0.000d 0.021 0.133 0.671 0.753 0.247 0.000d c x′4 = 0.40 0.000d 0.010 0.658 0.965 0.035 0.000d 0.000d 0.023 0.655 0.934 0.066 0.000d d 0.000 0.041 0.644 0.901 0.099 0.000d 0.011 0.057 0.603 0.872 0.128 0.000d 0.012 0.079 0.612 0.850 0.150 0.000d 0.020 0.117 0.539 0.820 0.180 0.000d 0.021 0.118 0.555 0.795 0.205 0.000d 0.031 0.152 0.528 0.767 0.233 0.000d 0.031 0.157 0.523 0.748 0.252 0.000d 0.033 0.171 0.497 0.733 0.267 0.000d 0.043 0.193 0.483 0.712 0.288 0.000d 0.053 0.206 0.460 0.699 0.298 0.000d

x1I

x2I

0.000d 0.000d 0.006 0.013 0.016 0.018 0.022 0.029 0.028 0.034 0.043 0.053

0.009 0.019 0.038 0.060 0.084 0.101 0.121 0.141 0.151 0.170 0.193 0.203

0.000d 0.000d 0.007 0.009 0.014 0.020 0.023 0.029 0.034 0.044 0.042 0.046

0.009 0.023 0.040 0.063 0.085 0.105 0.120 0.139 0.163 0.187 0.192 0.205

aqueous phase x3I

x1II

x′4 = 0.60c 0.559 0.964 0.554 0.932 0.543 0.902 0.530 0.873 0.510 0.855 0.493 0.825 0.480 0.798 0.471 0.773 0.462 0.760 0.442 0.735 0.425 0.707 0.413 0.689 x′4 = 0.80c 0.514 0.964 0.508 0.932 0.496 0.901 0.490 0.873 0.477 0.850 0.460 0.824 0.450 0.800 0.431 0.778 0.418 0.758 0.395 0.726 0.392 0.705 0.378 0.688

x2II

x3II

0.036 0.068 0.098 0.127 0.145 0.175 0.202 0.227 0.240 0.265 0.288 0.303

0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d

0.036 0.068 0.099 0.127 0.150 0.176 0.200 0.221 0.240 0.267 0.287 0.301

0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.005 0.006

a

Standard uncertainties u are u(T) = 0.05 K, u(x) = 0.005, and u(p) = 10 kPa. bObtained by mixing pure water and ethanol with the binary mixtures of {x′4 DBE + (1 − x′4) methylbenzene}. cMole fraction ratio of DBE and methylbenzene in the binary mixtures. dLower than the GC detection limit or smaller than the uncertainty estimated.

Figure 3. Experimental and calculated LLE composition in mole fraction on the planes x′4 = 0.2, 0.4, 0.6, and 0.8 for quaternary mixtures of water (1) + ethanol (2) + methylbenzene (3) + DBE (4) at 298.15 K. ●- - -●, experimental tie-lines; , correlated by the modified UNIQUAC model. 2786

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Table 5. Experimental LLE Data for Quaternary System of Water (1) + Ethanol (2) + Heptane (3) + DBE (4) for Mole Fractions x at the Temperature T = 298.15 K and Pressure p = 0.1 MPaa organic phase x1I

x2I

aqueous phase x3I

x1II

{ x1 Water + x2 Ethanol + x3 Heptane + (1 − x1 x′4 = 0.20c d d 0.000 0.000 0.811 0.968 0.000d 0.006 0.808 0.937 0.000d 0.010 0.802 0.906 0.000d 0.013 0.790 0.866 0.000d 0.018 0.785 0.837 0.000d 0.024 0.781 0.810 0.000d 0.028 0.781 0.787 0.000d 0.027 0.785 0.763 0.000d 0.031 0.781 0.739 0.000d 0.036 0.779 0.721 0.000d 0.041 0.780 0.696 0.000d 0.053 0.772 0.682 x′4 = 0.40c 0.000d 0.003 0.697 0.963 0.000d 0.008 0.694 0.930 0.000d 0.016 0.690 0.898 0.000d 0.019 0.685 0.868 0.000d 0.024 0.695 0.839 0.000d 0.033 0.678 0.816 0.000d 0.039 0.676 0.789 0.000d 0.040 0.680 0.775 0.000d 0.046 0.675 0.746 0.000d 0.048 0.675 0.727 0.000d 0.051 0.684 0.711 0.000d 0.056 0.693 0.692

x2II

organic phase x3II

x1I

x2I

0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.007 0.007 0.007 0.007

0.000d 0.011 0.020 0.027 0.035 0.044 0.047 0.057 0.056 0.060 0.064 0.064

0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.007 0.011 0.012 0.014

0.006 0.013 0.023 0.027 0.041 0.047 0.056 0.061 0.068 0.073 0.075 0.079

− x2 − x3) DBE}b d

0.032 0.063 0.094 0.134 0.163 0.190 0.213 0.237 0.261 0.279 0.303 0.318

0.000 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d

0.037 0.070 0.102 0.132 0.161 0.184 0.211 0.225 0.254 0.273 0.289 0.308

d

0.000 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d

aqueous phase x3I

x1II

x′4 = 0.60c 0.604 0.970 0.601 0.939 0.578 0.899 0.581 0.869 0.577 0.843 0.576 0.816 0.565 0.794 0.569 0.768 0.568 0.765 0.569 0.750 0.569 0.731 0.572 0.716 x′4 = 0.80c 0.491 0.965 0.491 0.934 0.489 0.905 0.484 0.888 0.501 0.865 0.495 0.840 0.479 0.820 0.476 0.798 0.467 0.781 0.470 0.760 0.452 0.734 0.474 0.701

x2II

x3II

0.030 0.061 0.101 0.131 0.157 0.184 0.206 0.232 0.235 0.250 0.269 0.284

0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d

0.035 0.066 0.095 0.112 0.135 0.160 0.180 0.202 0.219 0.240 0.266 0.299

0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d 0.000d

a

Standard uncertainties u are u(T) = 0.05 K, u(x) = 0.005, and u(p) = 10 kPa. bObtained by mixing pure water and ethanol with the binary mixtures of {x′4 DBE + (1 − x′4) heptane}. cMole fraction ratio of DBE and heptane in the binary mixtures. dLower than the GC detection limit or smaller than the uncertainty estimated.

Figure 4. Experimental and calculated LLE composition in mole fraction on the planes x′4 = 0.2, 0.4, 0.6, and 0.8 for quaternary mixtures of water (1) + ethanol (2) + heptane (3) + DBE (4) at 298.15 K. ●- - -●, experimental tie-lines; , correlated by the modified UNIQUAC model. 2787

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by the modified or extended UNIQUAC models. The predicted results with only binary parameters were not always good for the ternary systems exhibiting type 2 phase behavior. For complicated systems, for example, ternary and quaternary systems containing water and alcohols, it is necessary to accurately correlate ternary and quaternary LLE using ternary and quaternary parameters in addition to binary ones. Calculations of ternary and quaternary LLE were also carried out using eqs 1 and 2. Ternary parameters τ231, τ312, and τ123 and quaternary parameters, τ2341, τ1342, τ1243, and τ1234, were determined from the experimental ternary and quaternary LLE data using a simplex method21 by minimizing the objective function:

two type 1 ternary LLE and one type 2 ternary LLE. The experimental tie-line compositions for the ternary systems of water + DBE + methylbenzene and water + DBE + heptane at 298.15 K are summarized in Tables 2 and 3. The experimental tie-line compositions for the quaternary systems of water + ethanol + DBE + methylbenzene and water + ethanol + DBE + heptane at 298.15 K are listed in Tables 4 and 5. The detection limit of the GC analyses is mole fraction of 0.005 for water, 0.005 for ethanol, 0.001 for methylbenzene, 0.001 for heptane, and 0.002 for DBE, respectively.

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CALCULATION PROCEDURE Ternary and quaternary experimental LLE data were correlated by using the extended and modified UNIQUAC models7,8 with binary and multicomponent interaction parameters. The optimum set of binary energy parameters aji of the models for the miscible binary mixtures were obtained from the VLE data reduction by using a computer program described by Prausnitz et al.20 The binary energy parameters for partially miscible binary mixtures were obtained from the mutual solubility data by solving eqs 1 and 2. (xiγi)I = (xiγi)II

∑ xiI = 1

exp cal 2 F = 100·{∑ ∑ ∑ (xijk − xijk ) /2ni}0.5 k

∑ xiII = 1

i

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CALCULATED RESULTS AND DISCUSSION The molecular structural volume and area parameters of pure component used in the two models, r and q, for DBE can be taken from the literature,1 and the others are taken from Prausnitz et al.20 The interaction correction factor of pure component q′ for self-associating components was taken from the literature,7,8 while that for nonassociating components was set to q′ = q0.75 in the modified UNIQUAC model, and q′ = q0.20 in the extended UNIQUAC model are all given in Table 6. The optimized binary parameters of the modified and extended UNIQUAC models for the constituent binary mixtures are listed in Table 7, along with the standard deviations between experimental and calculated values: δP for pressure, δT for temperature, δx for liquid phase mole fraction, and δy for vapor phase mole fraction. Good agreement between experimental results and those calculated by both models was obtained. Table 8 presents the ternary parameters, together with the root-mean-square deviation (rmsd) between experimental and calculated results. The correlated results with the binary and ternary parameters listed in Tables 7 and 8 are better than the predicted ones with the binary parameters alone in representing

(2)

i

where i = 1 to 3 for ternary mixtures or i = 1 to 4 for quaternary mixtures, I and II represent the equilibrium phases, x is the liquid phase mole fraction, and γ is the activity coefficient given Table 6. Structural Parameters for Pure Components

a

substance

r

q

q′a

q′b

DBE methylbenzene heptane ethanol water

6.090 3.920 5.170 2.110 0.920

5.180 2.970 4.400 1.970 1.400

q0.75 q0.75 q0.75 1.404 1.283

q0.2 q0.2 q0.2 0.920 0.960

(3)

j

where i = 1 to 3 for ternary mixtures or i = 1 to 4 for quaternary mixtures, j = 1, 2 (phases), and k = 1, 2, ..., n (tie-lines).

(1)

and

i

Modified UNIQUAC model. bExtended UNIQUAC model.

Table 7. Calculated Values of the Modified and Extended UNIQUAC Binary Parameters with the Fit Goodness Results T/K

a12/K

DBE + methylbenzene

333.15

DBE + heptane

363.15

DBE + ethanol

333.15

ethanol + methylbenzene

333.15

ethanol + heptane

298.15

ethanol + water

298.15

water + DBE

298.15

water + methylbenzene

298.15

water + heptane

298.15

−46.57 −26.17b 412.52 502.31 780.43 778.06 48.97 84.08 107.23 155.99 212.17 157.12 330.68 434.81 752.99 1053.90 1022.10 1839.60

system (1 + 2)

a

a

a21/K

δ(P)/kPa

δ(T)/K

103δ(x)

103δ(y)

reference

43.90 25.88 −231.27 −266.35 −41.02 −69.59 862.96 858.39 1327.88 1325.83 −46.98 37.08 1833.60 1466.20 1713.30 1540.70 1884.20 2135.50

0.85 0.79 17.36 17.38 1.60 1.59 0.05 0.05 0.10 0.10 0.10 0.10

0.01 0.01 0.58 0.58 0.05 0.05 0.00 0.00 0.00 0.00 0.00 0.00

0.00 0.00 0.01 0.01 0.00 0.00 0.20 0.20 0.60 0.50 1.50 0.90

0.01 0.01 0.04 0.04 0.00 0.00 2.20 2.30 7.00 7.50 6.00 4.80

10 11 9 13 14 12 15 16 17

Modified UNIQUAC model. bExtended UNIQUAC model. 2788

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Figure 5. Distribution coefficients of ethanol and methylbenzene in the quaternary system of water + ethanol + methylbenzene + DBE, Di, as a function of mole fraction of DBE in the organic phase, x. ▲, ethanol; ●, methylbenzene.

Table 8. Calculated Results for Ternary LLE at 298.15 K na

τ231

water + DBE + methylbenzene

9

water + DBE + heptane

9

water + ethanol + DBE

9

water + ethanol + methylbenzene

9

−0.0001 −0.0001c 0.0002 0.0001 −0.3205 −0.4256 −0.3546 −0.0910 −0.2730 −0.6339

system (1 + 2 + 3)

water + ethanol + heptane

b

13

τ132

τ123

rmsdd,e (%)

rmsdd, f (%)

reference

−0.0001 −0.0001 0.0001 0.0003 0.4641 −0.1335 0.6667 −0.0010 −0.9130 −0.8177

0.0001 0.0001 −1.0155 −0.1093 0.3514 0.0784 −0.2721 0.0010 0.2883 0.3379

0.34 0.45 0.34 0.46 3.75 10.08 1.80 1.74 4.78 13.61

0.33 0.44 0.28 0.45 1.39 1.90 0.58 0.91 0.55 0.79

this work this work 1 18 19

a

Number of tie-lines. bModified UNIQUAC model. cExtended UNIQUAC model. dRoot-mean-square deviation. ePredicted results using binary parameters alone. fCorrelated results using binary and ternary parameters.

Table 9. Calculated Results for Quaternary LLE at 298.15 K system (1 + 2 + 3 + 4)

na

water + ethanol + DBE + methylbenzene

48

water + ethanol + DBE + heptane

48

τ2341 b

0.0047 −0.5932c −0.7598 0.0030

τ1342

τ1243

τ1234

rmsdd,e (%)

rmsdd, f (%)

−1.1924 −0.0162 −0.7781 0.1351

0.0294 0.0057 0.0831 0.0110

−0.1332 −0.1304 0.1999 −28.6530

0.79 1.26 0.52 0.66

0.52 0.60 0.37 0.61

a

Number of tie-lines. bModified UNIQUAC model. cExtended UNIQUAC model. dRoot-mean-square deviation. ePredicted results using binary and ternary parameters. fCorrelated results using binary, ternary, and quaternary parameters.

Table 9 summarizes the correlated results obtained in fitting the two models with binary, ternary, and quaternary parameters to the experimental quaternary LLE data, together with the predicted results by the models with binary and ternary parameters listed in Tables 7 and 8. For the two measured quaternary systems, the average rmsd of correlated results was 0.61 % and 0.45 % for the extended and modified UNIQUAC models, respectively. The correlated results obtained using the both models are better than the predicted ones in representing

the ternary LLE measured in this work. For the measured ternary systems, the average rmsd of correlated results was 0.45 % and 0.31 % for the extended and modified UNIQUAC model, respectively. The correlated results of the experimental LLE data provided by the modified UNIQUAC model are slightly better than ones of the extended UNIQUAC model. Figure 2 shows the experimental and the correlated results of the modified UNIQUAC model for the ternary systems of water + DBE + methylbenzene and water + DBE + heptane measured in this work. 2789

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Figure 6. Distribution coefficients of ethanol and heptane in the quaternary system of water + ethanol + heptane + DBE, Di, as a function of mole fraction of DBE in the organic phase, x. ▲, ethanol; ●, heptane.

and relevant ternary systems of water + DBE + methylbenzene and water + DBE + heptane. The experimental LLE data were correlated by the modified and extended UNIQUAC models. The correlated results show a good agreement with experimental LLE results, as shown in the phase diagrams. These results confirm that both the modified and the extended UNIQUAC models are satisfactorily represented the experimental LLE. The calculated results provided sets of the optimum interaction parameters of the modified and extended UNIQUAC models for the investigated systems.

the quaternary LLE measured in this work. Figures 3 and 4 compare the experimental and correlated results obtained by the modified UNIQUAC model for the quaternary systems of the water + ethanol + DBE + methylbenzene and water + ethanol + DBE + heptane. As seen from Figures 3 and 4 and Table 9, good agreement between experimental and correlated results have been obtained for the quaternary systems using the extended and modified UNIQUAC models. To understand well the effects of adding DBE on the solubility of the mixture compositions in the two phases, the distribution coefficient, Di, calculated from the experimental quaternary LLE data, is defined by Di =

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Corresponding Author

xi aqueous phase xi organic phase

AUTHOR INFORMATION

*Fax: +86-20-85221697. E-mail: [email protected].

(4)

Funding

The authors thank the National Scientific Research Foundation of China (20971056) for financial support.

where i denotes the components. The distribution coefficients of ethanol, methylbenzene, and heptane as a function of the mole fraction of DBE in organic phase are shown in Figures 5 and 6 for the quaternary systems of water + ethanol + DBE + methylbenzene and water + ethanol + DBE + heptane. Reviewing Figures 5 and 6, with the addition of the mole fraction of DBE in organic phase, the distribution coefficients of methylbenzene and heptane are almost unchangeable, while one of ethanol increases obtrusively in the area which the concentration of DBE is larger. This indicates that the solubility of methylbenzene and heptane does not increase evidently in aqueous phase with the addition of DBE, adding DBE effects the distribution of ethanol in two phases. DBE can be more soluble with gasoline fuel.

Notes

The authors declare no competing financial interest.

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REFERENCES

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CONCLUSIONS The experimental LLE data were investigated at 298.15 K and ambient pressure for the quaternary systems of water + ethanol + DBE + methylbenzene and water + ethanol + DBE + heptane 2790

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