Vicente Gomis * , Alicia Font, María Dolores Saquete, Jorge García-Cano
University of Alicante. PO Box 99 E-03080 Alicante (Spain)
Tel. +34 965903400. vgomis@ua.es
Water, 1-butanol, p-xylene, liquid-liquid equilibrium, vapor-liquid-liquid equilibrium, experimental data.
Abstract
The vapor-liquid, liquid-liquid and vapor-liquid-liquid equilibria of the ternary system water – 1butanol – p-xylene have been determined. Water – 1-butanol – p-xylene is a type 2 heterogeneous ternary system with partially miscible water – 1-butanol and water – p-xylene pairs. By contrast, 1butanol – p-xylene is totally miscible under atmospheric conditions. This paper examines the vaporliquid equilibrium in both heterogeneous and homogeneous regions at 101.3kPa of pressure.
Liquid-liquid equilibrium data at 313.15K have also been determined, and for comparison, the obtained experimental data have been calculated by means of several thermodynamic models:
UNIQUAC, UNIFAC and NRTL. Some discrepancies were found between the vapor-liquid-liquid correlations; however, the models reproduced the liquid-liquid equilibrium data well. The obtained data reveal a ternary heterogeneous azeotrope with mole fraction composition: 0.686 water, 0.146
1-butanol and 0.168 p-xylene.
1. Introduction
Ever since the economic crisis of 1973, due to a sharp rise in the price of oil, and especially during the late 80s, concerns regarding the lack of energy supplies and the effects of man’s use thereof on the environment have taken on greater importance. Various factors, including a reliance on oil producing regions, the inexorable drop in world oil reserves, the rise in carbon dioxide (CO
2
) air concentration – resulting in an increased global surface temperature (greenhouse effect) – have pushed developed countries toward the goal of reducing their fossil fuel consumption.
To achieve this goal, and because economic development is energy intensive, the only viable alternative appears to be to substitute part of the fossil fuel consumed by other energy sources. In several sectors, such as electricity production, fossil fuels have been substituted by nuclear energy on the one hand, but also by renewable energies such as solar farms or wind generators on the other.
However, the transport sector is one of the most dependent on fossil fuels and it is important to note that approximately 33 % of total CO
2
emitted to the environment by human activities in 2012 [1] came from this sector.
Thus, initiatives to reduce polluting emissions in the transport sector are of key importance if governments are to fulfill their promises [2] regarding the control of CO
2
emissions.
Over the short term, substitution of oil by a renewable fuel seems the only viable alternative to achieving the emissions rate goal.
One of the most widely used renewable fuels over the last few years has been ethanol, produced from crop fermentation. Employing ethanol as a fuel is associated with several problems: it has corrosive properties, making it difficult to transport through pipelines; it can damage engines; it is easily hydrated by moisture in the air, which means it has to be handled with care in order to avoid hydration; and it has a lower energy content than gasoline. Finally, the cost of producing it
* Corresponding author

(including agricultural, fermentation and subsequent purification processes) makes it difficult to compete with petrol as a fuel.
An alternative to bioethanol in recent years has been biobutanol. This is because butanol has more desirable properties as a fuel than ethanol (its energy content is 86% of gasoline’s, versus only 67% in the case of the latter) and, in addition, it is not associated with the same problems (as highlighted in the previous paragraph).
To use biobutanol as a fuel, it must be separated from the other substances present during its production, especially water. Several processes, which are more or less energy consuming, can be used for the purpose of purifying biobutanol. If it is intended to be used as a gasoline component, a possible technique to accomplish this is azeotropic distillation, using gasoline components as entrainers – to obtain a blend of butanol and gasoline that is very low in water content.
To follow previous studies [3, 4] on the viability of using hydrocarbons as entrainers in the dehydratation of butanol, it would be useful to obtain experimental data on the vapor-liquid, liquidliquid and vapor-liquid-liquid equilibria for another hydrocarbon, such as p-xylene. The purpose of this would be to determine the ternary system water – 1-butanol – p-xylene, if p-xylene were the hydrocarbon to be used as entrainer in a separation step.
Water – 1-butanol – p-xylene is a type 2 heterogeneous ternary system with partially miscible water
– 1-butanol and water – p-xylene pairs. However, the pair 1-butanol – p-xylene is totally miscible under atmospheric conditions. The present paper is concerned with the determination of the vaporliquid equilibria in both heterogeneous and homogeneous regions at 101.3kPa, and the liquid-liquid equilibrium data at 313.15K.
2. Experimental
2.1. Chemicals
Ultrapure water, prepared using a MiliQPlus system, was employed in experiments The rest of the chemicals were used as supplied.. 1-Butanol was provided by Merck at a chemical purity higher than 99.5%. p-Xylene was provided by Merck at a chemical purity higher than 99%. The internal standard 2-propanol was provided by Merck at a purity of more than 99.8 %. The moisture content of all compounds was measured by the Karl Fisher titration technique and was found to be 640 ppm,
290 ppm and 530 ppm for 1-butanol, p-xylene and 2-propanol respectively.
2.2. Experimental procedure
2.2.1. Liquid-liquid equilibrium determination
The experimental procedure that was followed to obtain the liquid-liquid equilibrium data can be found in a previous paper [3]. However, for the sake of convenience, the most important aspects of it are reproduced here:
Mixtures of water, 1-butanol and p-xylene of known mass were put inside glass tubes and sealed with septum caps. These tubes were then introduced in a thermostatic bath to maintain their temperature constant at 313.15K. After shaking them, their contents were allowed to settle until two phases separated out. Samples from both phases were extracted from the tubes and placed in vials along with 2-propanol, which served as internal standard.
These vials were analyzed in a gas chromatograph equipped with a thermal conductivity detector
(TCD).
The chromatograph was a Shimadzu GC14B equipped with a 2m x 3mm Porapack Q 80/100 packed column, running the Shimadzu CLASSVP Chromatography Data System. The temperature of the column was 493.15K, while it was 513.15K in the injector and the TCD. The helium flow rate was 50 ml/min.
The organic-phase water content was verified by a Karl Fisher titration. The aqueous-phase organics content was also determined by gas chromatography, but this time using a Flame Ionization
Detector (FID). The chromatograph in question was a Thermo Trace gas chromatograph by Thermo

Fischer equipped with a DB624 column. The helium flow was set to 50 mL/min at a split-less ratio of 1:50. The temperatures of analysis were 523.15K in the injector and 573.15K in the detector, while the column temperature was ramped from 313.15K up to 473.15K in increments of 40 K /min and held constant for one minute after ramping.
2.2.2. Vapor-liquid-liquid determination.
This procedure is explained in detail in a previous publication [3]. In a modified Fisher instrument for vapor-liquid equilibrium determinations, coupled to an ultrasound homogenizer that permits thorough mixing between heterogeneous phases, ternary mixtures were introduced and heated up to the boiling point while the pressure was measured and held fixed at 101.3kPa. The vapor was returned to the boiling chamber after condensing, while a fraction thereof was pumped off by means of a six-port valve to a chromatograph for analysis. The liquid phases were separated from the vapor and returned to the boiling chamber by a different conduit than the vapor. Liquid phase samples could be collected from the liquid returning to the boiling chamber by means of a solenoid valve.
After equilibrium had been reached, samples were taken from both the vapor and the liquid. The vapor was analyzed by gas chromatography in a TCD detector. The liquid sample was put in a hermetic tube, sealed with a septum cap. This sample was subjected to the same procedure as used during the liquid-liquid equilibrium determination; however, this time the thermostatic bath was maintained at the boiling temperature of each sample. The organic and aqueous phases were placed in separate vials together with the 2-propanol internal standard, and analyzed in the same manner as in the liquid-liquid determination. The conditions of the chromatographic analysis were also the same as in the case of the liquid-liquid equilibrium determination.
In the homogeneous region, there is one liquid and one vapor phase. The liquid phase sample, once it was taken out from the system, was put inside a vial with a known amount of 2-propanol as internal standard and was analyzed by gas chromatography with the TCD in the same conditions as the heterogeneous phases.
3. Results
3.1 Liquid-Liquid Equilibrium Results
The results obtained from the liquid-liquid equilibrium experiments at 313.15K are presented in
Table 1, and plotted as a ternary phase diagram in Figure 1. For comparison, Figure 1 also includes the liquid-liquid equilibrium data obtained by Letcher et al. [5] at 298.15K. As can be seen, the size of the heterogeneous region of this system does not vary with rising temperature in the range of temperatures studied.
The obtained data has been correlated by means of two thermodynamic models: UNIQUAC and
NRTL. The software CHEMCAD was used to perform the correlations [6]. In the case of the NRTL model, the alpha parameter was fixed at 0.2. The binary interaction parameters calculated by the two models are recorded in Table 2. This table also shows the composition deviation of each of the models. For the purpose of assessing the accuracy of the models in relation to the system in question, the experimental data and those calculated by the models have been plotted in Figure 2.
Figure 2 also shows the equilibrium data predicted by the group contribution model original
UNIFAC.
Inspection of Figure 2 shows that NRTL and UNIQUAC accurately reproduce the experimental data.
However, the UNIFAC model predicts a heterogeneous region for this system that is not consistent with either experiment or the other two models, since it is too large.
3.2 Vapor-Liquid-Liquid Equilibrium Results
Table 3 shows the vapor-liquid equilibrium data from the homogeneous region. The vapor-liquidliquid equilibrium data obtained for the heterogeneous region are recorded in Table 4. The compositions are expressed in mole fractions and the boiling temperature (in Kelvins) of each

mixture is also shown. All the data presented so far have been subjected to the Wisniak thermodynamic consistency test [7] and are thermodynamically consistent. The Antoine parameters for this test are shown in Table 5 [8, 9].
In order to visually inspect the obtained data, several figures have been plotted.
First among these is Figure 3, which shows the liquid mixtures pertaining to the homogeneous region and their corresponding equilibrium vapor phases. It is interesting to note that although the liquid mixtures cover most of the homogeneous region, their respective vapors occur within only a small region of the ternary diagram. Many liquid phases in the homogeneous region have an associated equilibrium vapor phase with a butanol composition ranging between 0.18 and 0.56 mole fractions, and between 0.1 and 0.4 mole fractions in p-xylene. As a consequence, if a homogeneous liquid mixture were to undergo a distillation process the condensed vapor would probably be a two phase mixture.
Additionally, Figure 4 shows a plot of the vapor–organic and –aqueous equilibria listed in Table 4.
The straight lines connect several equilibrium organic and aqueous phase pairs. The dashed lines, in turn, connect these liquid phases with their associated vapor phase. Figure 4 has several notable features. As was seen in the case of the liquid-liquid equilibrium, this type 2 system likewise possesses an aqueous phase whose composition does not vary very much relative to its respective organic phase. As for the vapor region for heterogeneous liquids – in this case the vapor line lies within a narrow composition range. In fact, the maximum concentration of p-xylene that can be read off the vapor line is 0.25, and in the case of 1-butanol ranges between 0 and 0.25. The shape of the equilibrium triangles, as well as the variation in boiling temperature, arouses the suspicion that this system possesses a ternary heterogeneous azeotrope. It has not been possible to find any bibliographic reference regarding the existence of the ternary water – 1-butanol – p-xylene. While it has also not been possible to determine the azeotrope’s composition experimentally, it has been possible to predict it by means of interpolation of the experimental data. This calculated ternary azeotrope has the following composition in mole fraction: 0.686, 0.146 and 0.168 for water, 1butanol and p-xylene respectively. The corresponding liquid phases in equilibrium with the azeotrope have also been calculated by interpolation of the experimental data, with 0.152, 0.385 and
0.463, and 0.989, 0.011 and <0.0001 mole fractions of water, 1-butanol and p-xylene in the organic and aqueous phases respectively.
The present system can be compared with another comprised of similar compounds: water -1butanol – hydrocarbon. Figure 5 makes this comparison by showing the vapor-liquid-liquid equilibrium of the system water -1-butanol – cyclohexane, obtained previously [4]. It is evident that the vapor line in the cyclohexane system is longer than in the system containing p-xylene. The ternary azeotrope also has a much lower 1-butanol concentration in the case of cyclohexane.
As was done for the liquid-liquid equilibrium, several correlations were performed to test the accuracy of thermodynamic models in predicting the vapor-liquid-liquid equilibrium of this system.
The same models were again used here. The data employed to carry out these correlations were the homogeneous and heterogeneous experimental data presented in this paper, the binary water – 1butanol vapor-liquid equilibrium data from DECHEMA [9] and the binary azeotropes of the pairs water – 1-butanol, water – p-xylene and 1-butanol – p-xylene from reference [10]. The parameters and the standard deviations in composition and boiling temperature obtained from the correlations using UNIQUAC and NRTL are presented in Table 6.
To assess the adequacy of these models, the experimental vapor and organic phases and those obtained through interpolation by UNIQUAC and NRTL, and prediction by UNIFAC, are plotted in
Figure 6. Since it is very little changed, the aqueous phase has not been plotted. The vapor line predicted by all these models resembles the experimental one. However, when the organic phases are compared, greater discrepancies become apparent: none of the models accurately reproduce the behavior of the organic phase, nor the azeotropic compositions. Concretely the discrepancies can be considered noteworthy for increasing ratios of 1-butanol and water. The bigger differences between experimental and calculated data appear near the binary water
–
1-butanol pair.

4. Conclusions
The liquid-liquid equilibrium of the water – 1-butanol – p-xylene system has been determined at
313.15K. Contrary to the data and findings of other authors, the present authors have found this equilibrium to be little affected by temperature. In addition, the vapor-liquid equilibria of both the homogeneous and heterogeneous regions have been determined experimentally. The observed behavior of these equilibria implies that the vapor in equilibrium with the liquid phases in this system tends to be located in the heterogeneous region. This fact would make heterogeneous azeotropic distillation a suitable candidate for separating such mixtures. The system exhibits a ternary heterogeneous azeotrope.
On the other hand, several thermodynamic models have been tested against the obtained experimental data and while the liquid-liquid equilibrium at 313.15K was rightly predicted by some of those models (NRTL and UNIQUAC), the vapor-liquid-liquid equilibrium exhibited discrepancies between predictions and experimental data. It would be, in fact, necessary to improve the thermodynamic models if the simulations that use those models as bases to simulate industrial processes want to be more accurate in their predictions and thus more useful in the design step.
Nevertheless the experimental data presented in this paper would fill the gap in the literature regarding this system and might help in the testing of new or modified thermodynamic models.
5. Acknowledgment
The authors thank the DGICYT of Spain for the financial support of project CTQ2009-13770.
References
(1) European Environment Agency (2012). Retrieved March 13, 2013, from http://www.eea.europa.eu/themes/transport/intro
(2) Kyoto Protocol to the United Nations Framework Convention on Climate Change, United
Nations 1998
(3) V. Gomis, A. Font, M.D. Saquete, J. García-Cano. LLE, VLE and VLLE data for the water – nbutanol – n-hexane system at atmospheric pressure. Fluid Phase Equilibria 316 (2012) 135– 140
(4) V. Gomis, A. Font, M.D. Saquete, J. García-Cano. Liquid-liquid, vapor-liquid and vapor-liquidliquid equilibrium data for the water – n-butanol – cyclohexane system at atmospheric pressure: experimental determination and correlation. J. Chem. Eng. Data, 58, (2013) 3320–3326
(5) T.M. Letcher, P.M. Siswana, P. van der Watt, S. Radloff, Phase equilibria for (an alkanol + pxylene + water) at 298.2 K. J. Chem. Thermodyn. 21, (1989), 1053-1060.
(6) CHEMCAD VI, Process Flow sheet Simulator , Chemstations Inc.: Houston, 2002.
(7) J. Wisniak, A new test for the thermodynamic consistency of vapor-liquid equilibrium. Ind. Eng.
Chem. Res. 32, (1993), 1531–1533.
(8) NIST Chemistry Webbook, http://webbook.nist.gov/chemistry/ .
(9) J. Gmehling, U. Onken, Vapor Liquid Equilibria Data Collection DECHEMA Chemistry Data
Series, Vol. I, Part 1a. DECHEMA: Dortmund, 1998.
(10) J. Gmehling, J. Menken, J. Krafczyk, K. Fischer, Azeotropic Data , VCH: Weinheim, 1994.

Figure 1 . Liquid–liquid equilibrium data (mole fraction) for the water – 1-butanol – p-xylene system at 313.15K and those obtained by other authors at 298.15K.
Experimental data at 313.15 K; Liquid-liquid tie lines; Letcher et al. [5] at 298.15K

Figure 2. Comparison of the LLE data (mole fraction) of the water – 1-butanol – p-xylene ternary system at 313.15K.
Experimental data. Calculated data: ­­­­ predicted using the UNIFAC model; ed with the NRTL model (Table 2); calculated with the UNIQUAC model (Table 2).
calculat-

Figure 3. VLE (mole fraction) diagram for the water – 1-butanol – p-xylene ternary system at
101.3kPa:
vapor-liquid tie lines.
liquid phase; + vapor phase; non-isothermal binodal curve;

Figure 4 . VLLE (mole fraction) diagram for the water – 1-butanol – p-xylene ternary system at
101.3kPa:
liquid phase; + vapor phase; non-isothermal binodal curve; liquid tie lines; liquid-liquid tie lines
vapor line; vapor-

Figure 5 . VLLE (mole fraction) diagram for the water – 1-butanol – cyclohexane or p-xylene ternary systems at 101.3kPa [4].
p-xylene ternary heterogeneous azeotrope; + cyclohexane ternary heterogeneous azeotrope;
non-isothermal binodal curve and vapor curve for p-xylene; curve and vapor curve for cyclohexane.
non-isothermal binodal

Figure 6 . Comparison of the VLLE data of the water – 1-butanol – p-xylene ternary system at
101.3kPa.
Experimental data. Calculated data:
­­­­
predicted using the UNIFAC model; ed with the NRTL model (Table 6); calculated with UNIQUAC (Table 6).
calculat-

TABLES.
Table 1.
Liquid-liquid equilibrium data for the water (1) – 1-butanol (2) – p-xylene (3) ternary system in mole fraction x at the temperature T = 313.15K
1 .
ORGANIC PHASE x
1 x
2 x
3
AQUEOUS PHASE
x
1 x
2 x
3
1 0.003 --- 0.997 1.000 0.000 <0.0001
2 0.021 0.097 0.882 0.992 0.008
<0.0001
3 0.099 0.327 0.574 0.990 0.010
<0.0001
4 0.144 0.402 0.455 0.988 0.011 <0.0001
5 0.190 0.459 0.351 0.988 0.012 <0.0001
6 0.226 0.491 0.283 0.985 0.014
<0.0001
7 0.304 0.534 0.161 0.987 0.013
<0.0001
8
0.348 0.543 0.110 0.985 0.015
<0.0001
9 0.427 0.529 0.045 0.984 0.016 <0.0001
10 0.472 0.508 0.021 0.982 0.018 <0.0001
11 0.516 0.484 --- 0.981 0.019
---
1 Standard uncertainties u are u (T) = 0.1K, u r
( x ) = 𝑢(𝑥) 𝑥
= 0.02.

Table 2. Parameters and mean deviations from the LLE correlation.
A ij (K): binary interaction parameters from the NRTL model. U ij
-U ii
(K): binary interaction parameters from UNIQUAC. Mean deviations of water (1) and 1-butanol (2) in organic phase (1) and aqueous phase (2).
i j
Water
Water
1-Butanol p-Xylene
1-Butanol p-Xylene
Mean Deviation
A ij
A ji
 U ij
-U jj
U ji
-U ii
1520.24
1764.93
208.06
-312.59 0.2
1222.67 0.2
212.429 32.346
83.043 1131.773
-668.56 0.2 -143.313 67.702
D_X
11
D_X
21
D_X
12
D_ X
22
NRTL 0.0044 0.0044 0.0061 0.0050
UNIQUAC
0.0047 0.0047 0.0025 0.0032

Table 3 . Homogeneous vapor-liquid equilibrium data (mole fraction) for the water (1) – 1-butanol
(2) – p-xylene (3) ternary system, expressed as liquid phase mole fraction x and vapour phase mole fraction y at temperature T and pressure p = 101.3kPa
2 .
LIQUID PHASE VAPOR PHASE T /K x
1 x
2 x
3
y
1 y
2 y
3
0.312 0.676 0.012 0.737 0.245 0.019 368.02
0.264 0.724 0.012 0.704 0.279 0.017 369.39
0.253 0.735 0.012 0.708 0.276 0.016 369.92
0.231 0.761 0.009 0.684 0.303 0.014 371.26
0.184 0.809 0.007 0.667 0.322 0.012 373.42
0.152 0.843 0.006 0.612 0.379 0.009 375.18
0.126 0.869 0.005 0.560 0.433 0.007 377.07
0.100 0.895 0.005 0.544 0.450 0.006 379.28
0.109 0.887 0.004 0.476 0.518 0.005 379.73
0.109 0.874 0.018 0.524 0.453 0.024 378.00
0.134 0.834 0.032 0.597 0.366 0.037 375.83
0.178 0.777 0.045 0.652 0.301 0.048 372.21
0.204 0.738 0.058 0.659 0.285 0.056 370.44
0.253 0.675 0.072 0.693 0.237 0.070 368.14
0.286 0.629 0.085 0.707 0.213 0.080 366.56
0.316 0.587 0.097 0.703 0.204 0.093 365.23
0.418 0.541 0.041 0.726 0.217 0.057 365.05
0.443 0.527 0.030 0.733 0.220 0.047 365.13
0.420 0.552 0.028 0.734 0.223 0.043 365.46
0.396 0.578 0.027 0.735 0.229 0.036 365.86
0.381 0.593 0.025 0.736 0.227 0.037 366.09
0.357 0.620 0.024 0.737 0.229 0.034 366.40
0.242 0.604 0.154 0.695 0.192 0.113 365.75
0.274 0.557 0.169 0.687 0.188 0.125 364.71
0.230 0.627 0.143 0.685 0.214 0.101 367.16
0.195 0.681 0.124 0.649 0.256 0.094 369.18
0.172 0.724 0.104 0.627 0.287 0.086 371.49
0.138 0.777 0.085 0.604 0.321 0.075 373.95
0.106 0.826 0.067 0.520 0.413 0.067 376.87
0.092 0.857 0.051 0.435 0.511 0.055 378.99
0.083 0.893 0.024 0.399 0.570 0.030 380.55
2 Standard uncertainties u are u (T) = 0.06K, u (p) = 0.1kPa, u r
( y ) = 𝑢(𝑦) 𝑦
0.02 .
= 0.02 and u r
( x ) = 𝑢(𝑥) 𝑥
=

0.048 0.944 0.008 0.267 0.720 0.012 384.65
0.048 0.921 0.032 0.283 0.677 0.040 384.04
0.047 0.891 0.062 0.295 0.636 0.069 383.20
0.057 0.848 0.095 0.299 0.605 0.096 382.13
0.053 0.806 0.141 0.318 0.555 0.127 381.41
0.043 0.783 0.174 0.301 0.553 0.146 381.95
0.039 0.752 0.210 0.276 0.557 0.168 382.20
0.037 0.715 0.248 0.261 0.555 0.184 382.91
0.033 0.674 0.292 0.255 0.544 0.202 382.49
0.043 0.623 0.334 0.359 0.445 0.196 379.96
0.054 0.573 0.373 0.436 0.373 0.191 378.12
0.056 0.526 0.418 0.468 0.339 0.193 376.45
0.059 0.487 0.454 0.496 0.312 0.192 375.26
0.055 0.446 0.499 0.548 0.272 0.180 374.66
0.060 0.406 0.535 0.574 0.248 0.178 373.80
0.063 0.362 0.576 0.585 0.235 0.180 372.87
0.058 0.331 0.611 0.618 0.205 0.176 371.08
0.140 0.520 0.340 0.655 0.202 0.143 368.21
0.133 0.549 0.318 0.641 0.217 0.142 369.19
0.107 0.601 0.291 0.597 0.260 0.143 371.55
0.097 0.666 0.237 0.545 0.314 0.141 373.58
0.082 0.716 0.201 0.465 0.395 0.139 376.41
0.081 0.750 0.168 0.448 0.423 0.129 377.94

Table 4. Heterogeneous vapor-liquid-liquid equilibrium data for the water (1) – 1-butanol (2) – pxylene (3) ternary system, expressed as liquid phase mole fraction x and vapour phase mole fraction y at temperature T and pressure p = 101.3kPa
3 .
ORGANIC PHASE AQUEOUS PHASE VAPOUR PHASE T /K x
1 x
2 x
3
x
1 x
2 x
3 y
1 y
2 y
3
BIN 0.010 --- 0.990 1.000
1 0.012 0.016 0.973 0.999 0.001
2 0.017 0.033 0.950 0.998
--- <0.0001 0.759 --- 0.241 365.40
0.002
<0.0001 0.721 0.028 0.251 364.82
<0.0001
0.721 0.049 0.230 364.46
3 0.017 0.044 0.939 0.997 0.003
4 0.019 0.066 0.915 0.996 0.004
<0.0001
0.712 0.062 0.226 364.21
<0.0001 0.707 0.078 0.216 363.83
5
6
0.027
0.046
0.121 0.852
0.160 0.794
0.994
0.993
0.006
0.007
<0.0001 0.686 0.113 0.202 363.17
<0.0001
0.687 0.117 0.196 362.93
7
8
0.050
0.088
0.194 0.756
0.280 0.632
0.992
0.991
0.008
0.009
<0.0001
0.689 0.123 0.188 362.75
<0.0001
0.687 0.137 0.176 362.56
9
10
11
0.127
0.177
0.208
0.341 0.532
0.426 0.397
0.444 0.347
0.989
0.988
0.988
0.011
0.011
0.012
12 0.211 0.468 0.320 0.988 0.012
13 0.239 0.485 0.276 0.988 0.012
<0.0001 0.688 0.143 0.169 362.42
<0.0001 0.685 0.153 0.162 362.27
<0.0001
0.681 0.157 0.161 362.33
<0.0001
0.683 0.159 0.158 362.36
<0.0001 0.683 0.164 0.153 362.52
14 0.319 0.502 0.179 0.986 0.014
15 0.342 0.503 0.155 0.986 0.014
16 0.392 0.499 0.109 0.985 0.015
17
0.418 0.497 0.084 0.985 0.015
18 0.476 0.479 0.045 0.984 0.016
19 0.501 0.464 0.036 0.983 0.017
BIN 0.638 0.362 --- 0.979 0.021
<0.0001 0.692 0.172 0.136 362.79
<0.0001 0.688 0.178 0.135 362.86
<0.0001
0.697 0.179 0.124 363.11
<0.0001
0.699 0.187 0.114 363.32
<0.0001 0.714 0.203 0.082 363.93
<0.0001 0.725 0.204 0.071 364.14
---
0.754 0.246 --- 365.85
3 Standard uncertainties u are u (T) = 0.06K, u (p) = 0.1kPa, u r
( y ) = 𝑢(𝑦) 𝑦
0.02 .
= 0.02 and u r
( x ) = 𝑢(𝑥) 𝑥
=

Table 5. Antoine equation parameters a of the pure substances.
Compound
Water b
1-Butanol c p-Xylene c
A
7.1961
6.546
6.111
B
1730.63
C
-39.724
1351.555 -93.34
1450.68 -58.2
Temperature Range /K
274.15 / 373.15
295.65 / 390.85
331.44 / 412.44 a Antoine Equation: log( P ) = A – B/  T + C  , with: P /kPa and T /K b Reference [9] c
Reference [8]

Table 6. Parameters and mean deviations from the VLE correlation. A ij
binary interaction parameters from the NRTL model (K), and U ij
-U jj from the UNIQUAC model (K). Mean deviations of temperature (T/K), and water (1) and 1-butanol (2) compositions in the vapor phase. i j
Water
Water
1-Butanol p-Xylene
1-Butanol p-Xylene
Mean Deviation
A ij
A ji
 U ij
-U jj
U ji
-U ii
1500.14 176.33 0.3634 329.21 50.79
3528.84 1311.51 0.2300 298.72 952.10
98.14 309.83 0.2993 -154.07 357.80
D T D Y
1
D Y
2
NRTL
UNIQUAC
0.89
0.90
0.0238
0.0218
0.0262
0.0246