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Fluid Phase Equilibria 315 (2012) 1–8

Contents lists available at SciVerse ScienceDirect

Fluid Phase Equilibria

journa l homepage: www.e lsev ier .com/ locate / f lu id

ther + alcohol + hydrocarbon mixtures in fuels and bio-fuels: Excess enthalpiesf binary mixtures containing dibutyl ether (DBE) or 1-butanol and 1-hexene orethylcyclohexane or toluene or cyclohexane or 2,2,4-trimethylpentane at

98.15 K and 313.15 K

ernando Aguilara, Fatima E.M. Alaouia, José J. Segoviab, Miguel A. Villamanánb, Eduardo A. Monteroa,∗

Departamento de Ingeniería Electromecánica, Escuela Politécnica Superior, Universidad de Burgos, E-09006 Burgos, SpainGrupo de Termodinámica y Calibración TERMOCAL, E.T.S. de Ingenieros Industriales, Universidad de Valladolid, E-47071 Valladolid, Spain

r t i c l e i n f o

rticle history:eceived 29 July 2011eceived in revised form 8 November 2011ccepted 9 November 2011

a b s t r a c t

New experimental excess molar enthalpy data (304 points) of the binary systems dibutyl ether (DBE) or1-butanol and 1-hexene, or methylcyclohexane or toluene at 298.15 K and 313.15 K, and DBE or 1-butanoland cyclohexane or 2,2,4-trimethylpentane (TMP) at 313.15 K at atmospheric pressure are reported. Aquasi-isothermal flow calorimeter has been used to make the measurements. All the binary systems

vailable online 18 November 2011

eywords:xcess enthalpyio-fuels-Butanol

show endothermic character except the system DBE + 1-hexene at both temperatures. The experimentaldata for the binary systems have been fitted using the Redlich–Kister rational equation. The values ofthe standard deviation indicate good agreement between the experimental results and those calculatedfrom the equations.

© 2011 Elsevier B.V. All rights reserved.

ibutyl ether

. Introduction

The increasing worldwide use of bio-fuels constitutes one ofhe measures considered to reduce greenhouse gas emissions. Bio-uels also have an important part to play in promoting the securityf energy supply, and promoting technological development andnnovation. Biobutanol has been recently proposed as new bio-uel that can be blended into standard grade gasoline containingthanol [1,2], and has been included in recent international regula-ions on the promotion of the use of energy from renewable sourcesor transport [3]. 1-Butanol is otherwise a basic component in theynthesis of the ether DBE, which is used as blending agent in refor-ulated gasoline, and therefore is always contained as an impurity.

he alcohol and the ether act as non-polluting, high octane numberlending agents.

This work continues a study of our group on excess molarnthalpies of DBE + hydrocarbon and 1-butanol + hydrocarbon mix-ures [4–7]. Table 1 shows the list of previous published papers.

he hydrocarbons selected are representative of the broad spec-rum of hydrocarbon components in gasoline: alkanes (heptane),ycloalkanes (cyclohexane), aromatics (benzene) and branched

∗ Corresponding author. Tel.: +34 947 258 916; fax: +34 947 259 088.E-mail address: emontero@ubu.es (E.A. Montero).

378-3812/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.fluid.2011.11.005

alkanes (2,2,4-trimethylpentane). To broad the study, alkenes,branched cycloalkanes and branched aromatics have been addedto the list. The 1-hexene has been chosen as the representa-tive for alkenes while methylcyclohexane and toluene are therepresentatives of the branched cycloalkanes and aromatics. Thecorresponding binary systems have been studied at the tempera-tures of 298.15 K and 313.15 K.

New experimental excess molar enthalpy data (304 points) ofthe binary systems DBE or 1-butanol and 1-hexene, or methylcyclo-hexane or toluene at 298.15 K and 313.15 K, and DBE or 1-butanoland cyclohexane or 2,2,4-trimethylpentane at 313.15 K at atmo-spheric pressure are reported in this work. Excess molar enthalpieshave been measured with a quasi-isothermal flow calorimeter. Theexperimental data have been fitted using the Redlich–Kister ratio-nal polynomials [8]. Values of the standard deviation indicate goodagreement between the experimental results and those calculatedfrom the equations.

2. Experimental

All the chemicals used here were purchased from Fluka Chemie

AG and were of the highest purity available, chromatographyquality reagents (of the series puriss p.a.) with a stated purity>99.5 mol%. The purity of all reagents was checked by gas chro-matography, and its values are presented in Table 2.

2 F. Aguilar et al. / Fluid Phase Eq

Table 1Previously reported data by our group on binary mixtures DBE + hydrocarbon and1-butanol + hydrocarbon at atmospheric pressure.

System Our group

Ref. T (K)

DBE + cyclohexane [4] 298.15DBE + benzene [5] 298.15, 313.15DBE + heptane [6] 298.15, 313.15DBE + 2,2,4-trimethylpentane [7] 298.151-Butanol + cyclohexane [4] 298.151-Butanol + benzene [5] 298.15, 313.15

qTa

TP

TEt

r

1-Butanol + heptane [6] 298.15, 313.151-Butanol + 2,2,4-trimethylpentane [7] 298.15

Excess molar enthalpies have been measured with auasi-isothermal flow calorimeter previously described [4].he calorimeter is thermostatted at T = (298.15 ± 0.01) K ort T = (313.15 ± 0.01) K. The uncertainty in the measure of

able 2urity and related data of chemicals.

Compound Formula Molar mass (g

DBE C8H18O 130.2281-Butanol C4H10O 74.1201-Hexene C6H12 84.161Cyclohexane C6H12 84.161Methylcyclohexane C7H14 98.186Toluene C7H8 92.1402,2,4-Trimethylpentane C8H18 84.161

a The water content of 1-butanol was checked to be less than 0.01%.

able 3xperimental excess molar enthalpies of binary systems DBE + 1-hexene, DBE + methylcoluene + 1-butanol at T = 298.15 K.a

x HE (J mol−1) x HE (J mol−1)

x DBE + (1 − x) 1-hexene0.0503 −3.1 0.2998 −18.90.1001 −5.8 0.3502 −20.40.1501 −10.8 0.3994 −21.70.2000 −13.8 0.4502 −22.30.2500 −16.8 0.4995 −22.7x DBE + (1 − x) methylcyclohexane0.0497 23.0 0.3002 86.40.1003 43.3 0.3499 91.20.1501 57.2 0.3993 94.10.1997 69.2 0.4500 95.50.2501 78.9 0.4993 94.6x DBE + (1 − x) toluene0.0497 23.9 0.2999 79.60.1003 42.1 0.3499 82.00.1502 56.0 0.3995 82.50.1999 67.0 0.4497 81.00.2499 74.2 0.5002 78.3x 1-Hexene + (1 − x) 1-butanol0.0500 43.48 0.3005 347.020.1002 98.03 0.3500 404.520.1506 155.69 0.4001 462.170.2003 220.65 0.4499 515.120.2500 282.90 0.5003 560.98x Methylcyclohexane + (1 − x) 1-butanol0.0498 63.0 0.3000 356.50.1000 126.1 0.3502 407.60.1505 187.8 0.4002 454.50.2005 246.0 0.4501 496.40.2506 303.2 0.5007 532.5x Toluene + (1 − x) 1-butanol0.0504 102.7 0.2999 618.90.0998 208.2 0.3495 709.10.1501 315.0 0.3998 791.90.2011 422.6 0.4509 864.90.2510 523.6 0.5009 923.2

a The estimated uncertainty of the measured temperature is 0.05 K. The maximum absolelative uncertainty of the determined HE (J mol−1) is ± 0.01 HE.

uilibria 315 (2012) 1–8

temperature is estimated to be less than 0.05 K. The HE iscalculated from differences in the heating power control, once thecalibration procedure has been performed.

Knowing the volumetric flow rates delivered, the molar massesand the densities of the pure compounds, the mole fractions ofthe mixtures obtained in the mixing coil can be calculated. Themaximum absolute uncertainty of mole fraction at equimolarcomposition is ±0.0008. Densities of pure liquids are deter-mined by interpolating density data obtained from Riddick et al.[9] at the measured temperature of delivery. Estimated den-sities at T = 298.15 K, were 0.76417, 0.80575, 0.66848, 0.77389,0.68780, 0.76470 and 0.86219 g cm−3 for the DBE, 1-butanol, 1-hexene, cyclohexane, 2,2,4-trimethylpentane, methylcyclohexaneand toluene, respectively. These results agree within <0.1% with

values found in the literature [10–16]. Mixtures of different com-positions are studied and in this way the dependence of HE on molefraction can be determined. The estimated relative uncertainty ofthe determined HE (J mol−1) is ±0.01 HE.

mol−1) Stated purity (mol%) CAS number

>99.6 42-96-1>99.9a 1-36-3>99.3 92-41-6>99.9 10-82-7>99.7 08-87-2>99.9 08-88-3>99.9 40-84-1

yclohexane, DBE + toluene, 1-hexene + 1-butanol, methylcyclohexane + 1-butanol,

x HE (J mol−1) x HE (J mol−1)

0.5494 −22.3 0.7995 −12.40.5996 −21.4 0.8501 −9.70.6491 −20.1 0.8996 −6.50.7001 −18.3 0.9504 −3.00.7491 −16.0

0.5499 92.1 0.8002 55.00.5999 87.8 0.8501 43.00.6491 82.2 0.9001 29.60.6997 74.2 0.9500 14.90.7493 65.2

0.5498 74.7 0.7990 39.70.5995 69.3 0.8492 30.00.6502 63.1 0.9000 20.00.6994 56.3 0.9498 10.00.7495 48.0

0.5503 596.52 0.8006 615.670.5996 623.73 0.8503 576.100.6505 642.58 0.9002 512.910.7006 647.96 0.9501 405.510.7499 639.78

0.5497 559.9 0.7999 539.50.6004 579.2 0.8504 495.10.6505 587.8 0.8997 435.00.6999 584.7 0.9505 340.60.7498 568.8

0.5495 967.2 0.7992 929.40.6009 998.4 0.8500 848.20.6509 1011.9 0.8993 726.40.6996 1005.9 0.9493 518.20.7512 978.6

ute uncertainty of mole fraction at equimolar composition is ±0.0008. The estimated

F. Aguilar et al. / Fluid Phase Equilibria 315 (2012) 1–8 3

Table 4Experimental excess molar enthalpies of binary systems DBE + 1-hexene, DBE + methylcyclohexane, DBE + toluene, DBE + cyclohexane, DBE + 2,2,4-trimethylpentane, 1-hexene + 1-butanol, methylcyclohexane + 1-butanol, toluene + 1-butanol, cyclohexane + 1-butanol and 2,2,4-trimethylpentane + 1-butanol at T = 313.15 K.a

x HE (J mol−1) x HE (J mol−1) x HE (J mol−1) x HE (J mol−1)

x DBE + (1 − x) 1-hexene0.0503 −4.2 0.3503 −22.6 0.5997 −23.3 0.8501 −11.90.1500 −12.4 0.3995 −23.7 0.6493 −21.8 0.8996 −8.50.2000 −16.0 0.4503 −24.3 0.7002 −19.6 0.9504 −4.50.2500 −18.7 0.4997 −24.5 0.7492 −17.80.2997 −20.8 0.5495 −24.2 0.7996 −15.1x DBE + (1 − x) methylcyclohexane0.0497 20.8 0.3002 80.8 0.5500 86.5 0.8002 51.60.1003 38.0 0.3500 85.1 0.6000 82.5 0.8501 40.40.1501 52.6 0.3994 88.2 0.6492 77.1 0.9001 28.20.1998 64.1 0.4501 89.8 0.6997 70.1 0.9501 14.20.2501 73.4 0.4993 89.1 0.7493 61.3x DBE + (1 − x) toluene0.0503 22.4 0.2997 80.0 0.5485 77.8 0.7990 42.00.0995 40.4 0.3497 83.1 0.6005 72.8 0.8492 31.70.1501 55.9 0.4004 84.6 0.6501 66.5 0.8985 21.80.2006 66.5 0.4495 84.1 0.6994 59.1 0.9498 9.70.2505 74.5 0.4990 81.3 0.7508 50.6x DBE + (1 − x) cyclohexane0.0498 73.8 0.3001 239.8 0.5497 229.9 0.7991 125.10.0997 129.1 0.3502 247.0 0.6002 216.6 0.8500 98.10.1502 171.3 0.3999 249.6 0.6493 198.4 0.9001 65.90.2003 203.2 0.4499 247.4 0.6993 177.7 0.9506 32.70.2498 224.6 0.4992 241.4 0.7502 153.5x DBE + (1 − x) 2,2,4-trimethylpentane0.0497 26.2 0.2995 105.7 0.5495 119.0 0.7996 74.60.0996 49.4 0.3500 113.2 0.5996 114.7 0.8495 59.20.1496 66.8 0.3997 118.4 0.6499 108.2 0.8995 41.20.1998 82.5 0.4495 120.4 0.6993 99.1 0.9497 21.60.2501 95.4 0.4994 121.2 0.7499 88.0x 1-Hexene + (1 − x) 1-butanol0.0500 78.70 0.3004 507.81 0.5501 830.43 0.8005 835.060.1001 166.57 0.3498 588.46 0.5995 861.97 0.8503 781.820.1505 251.91 0.4000 662.53 0.6504 880.18 0.9002 693.250.2002 339.90 0.4498 728.37 0.7005 881.14 0.9501 533.050.2499 426.63 0.5001 784.67 0.7498 867.01x Methylcyclohexane + (1 − x) 1-butanol0.0498 88.6 0.3000 497.2 0.5497 762.3 0.8000 734.60.1000 177.5 0.3502 565.5 0.6004 785.2 0.8504 679.80.1505 263.3 0.4002 627.6 0.6505 795.0 0.8997 602.20.2005 345.6 0.4500 682.1 0.7000 790.3 0.9505 470.20.2507 424.1 0.5006 728.7 0.7498 770.3x Toluene + (1 − x) 1-butanol0.0504 142.5 0.3000 813.9 0.5496 1217.6 0.7992 1146.00.0999 286.6 0.3496 922.6 0.6010 1250.2 0.8500 1039.80.1501 428.8 0.4000 1018.5 0.6511 1261.6 0.8993 878.40.2011 568.0 0.4511 1103.5 0.6998 1248.2 0.9493 597.30.2512 696.2 0.5010 1168.6 0.7513 1211.3x Cyclohexane + (1 − x) 1-butanol0.0505 98.1 0.2999 528.1 0.5500 796.0 0.7995 745.00.1001 192.2 0.3501 598.2 0.5995 816.2 0.8499 681.50.1505 283.9 0.4003 662.5 0.6499 822.2 0.8999 592.50.2000 370.3 0.4504 717.3 0.7000 812.9 0.9496 457.50.2505 452.5 0.5003 762.7 0.7499 786.9x 2,2,4-Trimethylpentane + (1 − x) 1-butanol0.0502 104.9 0.3001 559.9 0.5501 837.2 0.7996 805.80.1001 203.6 0.3504 634.7 0.5999 859.4 0.8502 750.10.1505 301.3 0.4001 700.6 0.6498 866.9 0.9001 667.20.2003 392.8 0.4499 756.7 0.7000 861.8 0.9506 522.60.2505 480.3 0.5008 802.4 0.7500 841.0

absolur

3

fc1a

e

a The estimated uncertainty of the measured temperature is 0.05 K. The maximumelative uncertainty of the determined HE (J mol−1) is ± 0.01 HE.

. Results and discussion

The experimental excess molar enthalpies obtained in this workor the binary mixtures DBE or 1-butanol and 1-hexene, or methyl-yclohexane or toluene at 298.15 K and 313.15 K, and DBE or

-butanol and cyclohexane or 2,2,4-trimethylpentane at 313.15 Kt atmospheric pressure are listed in Tables 3 and 4, respectively.

For binary systems, there are several models and empiricalquations proposed to fit the HE measurements. One of them, the

te uncertainty of mole fraction at equimolar composition is ±0.0008. The estimated

Redlich–Kister rational polynomial, is given by Eq. (1), in whichthe Ai coefficients are determined by the unweighted least-squaresmethod

HE = x · (1 − x) ·∑n

i=1Ai · (2x − 1)i−1

(1)

1 + A0 · (2x − 1)

Results of data correlation for the binary systems of this workand for the binary systems reported in Refs. [4–7] are summarizedin Tables 5 and 6. For the purpose of comparing the experimental

4 F. Aguilar et al. / Fluid Phase Equilibria 315 (2012) 1–8

DBE (1) + Hydrocarbon (2) at 298.15K

-100

-50

0

50

100

150

200

250

300

350

400

1.00.90.80.70.60.50.40.30.20.10.0X 1

HE /

J·m

ol-1

(a)

(b) DBE (1) + Hydrocarbon (2) at 313.15K

-100

-50

0

50

100

150

200

250

300

350

400

10.90.80.70.60.50.40.30.20.10X 1

HE /

J·m

ol-1

Fig. 1. (a) Excess molar enthalpy HE at T = 298.15 K. Experimental results for DBE + 1-hexene, this work, (�); DBE + methylcyclohexane, this work, (�); DBE + toluene, this work,(�); DBE + cyclohexane, data from Ref. [4], (�); DBE + benzene, data from Ref. [5], (♦); DBE + heptane, data from Ref. [6], (O); DBE + 2,2,4-trimethylpentane, data from Ref. [7],(+). ( ) calculated values for DBE + 1-hexene, or + methylcyclohexane, or + toluene, or + cyclohexane, or + 2,2,4-trimethylpentane at T = 298.15 K with Eq. (1) using parametersof Table 4. (b) Excess molar enthalpy HE at T = 313.15 K. Experimental results for DBE + 1-hexene, this work, (�); DBE + methylcyclohexane, this work, (�); DBE + toluene, thiswork, (�); DBE + cyclohexane, data from Ref. [4], (�); DBE + benzene, data from Ref. [5], (♦); DBE + heptane, data from Ref. [6], (O); DBE + 2,2,4-trimethylpentane, data fromR + toluep

eulm

r

m

m

ef. [7], (+). ( ) calculated values for DBE + 1-hexene, or + methylcyclohexane, orarameters of Table 5.

xcess enthalpy values with those obtained by Eq. (1), we havesed the root-mean-square deviation, rms, the maximum abso-

ute deviation, max|�HE|, and the maximum relative deviation,ax(|�HE|/HE), which are defined as follows:

ms =[∑ndat

i (HEexp − HE

calc)2

ndat − npar

]1/2

(2)

ax |�HE| = max |HEexp − HE | (3)

calc

ax

(|�HE|

HE

)= max

(∣∣HEexp − HE

calc

∣∣HE

exp

)(4)

ne, or + cyclohexane, or + 2,2,4-trimethylpentane at T = 313.15 K with Eq. (1) using

where HEexp, HE

calc, ndat and npar are the values of the experimentaland calculated excess molar enthalpy, the number of experimentaldata and the number of parameters of the model, respectively. Thedegree of the polynomial expansion of Eq. (1) was optimized usingthe F-test [17].

The plots of the experimental and correlated data are shown inFigs. 1 and 2. Data obtained from [4–7] at T = 298.15 K and 3131.15 Kare also included.

The excess molar enthalpy of the binary system DBE + 1-hexene

at the temperatures 298.15 K and 313.15 K presents exothermicbehavior (HE < 0) in the whole range of composition. The max-imum values of the excess molar enthalpies are −23 J mol−1

and −25 J mol−1 at the respective temperatures, obtained at the

F. Aguilar et al. / Fluid Phase Equilibria 315 (2012) 1–8 5

Hydrocarbon (1) + 1-Butanol (2) at 298.15K

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1.00.90.80.70.60.50.40.30.20.10.0X 1

HE /

J·m

ol-1

(a)

(b)

Hydrocarbon (1) + 1-Butanol (2) at 313.15K

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1.00.90.80.70.60.50.40.30.20.10.0X 1

HE /

J·m

ol-1

Fig. 2. (a) Excess molar enthalpy HE at T = 298.15 K. Experimental results for 1-hexene + 1-butanol, this work, (�); methylcyclohexane + 1-butanol, this work, (�); toluene + 1-butanol, this work, (�); cyclohexane + 1-butanol, data from Ref. [4], (�); benzene + 1-butanol, data from Ref. [5], (♦); heptane + 1-butanol, data from Ref. [6], (O); 2,2,4-trimethylpentane + 1-butanol, data from Ref. [7], (+). ( ) calculated values for 1-butanol + 1-hexene, or + methylcyclohexane, or + toluene, or + cyclohexane, or + 2,2,4-trimethylpentane at T = 298.15 K with Eq. (1) using parameters of Table 4. (b) Excess molar enthalpy HE at T = 313.15 K. Experimental results for 1-hexene + 1-butanol, thisw is worf ne + 1-+ T = 31

eat0o

tT9ob

a

ork, (�); methylcyclohexane + 1-butanol, this work, (�); toluene + 1-butanol, throm Ref. [5], (♦); heptane + 1-butanol, data from Ref. [6], (O); 2,2,4-trimethylpentamethylcyclohexane, or + toluene, or + cyclohexane, or + 2,2,4-trimethylpentane at

quimolar composition. Comparison with data for the same systemnd temperature reported by Wang et al. [18] at 298.15 K, showshat our data agree to within 7.7% in the range of composition.3 ≤ x ≤ 0.7. No data were found in the literature for comparisonf this binary system at the temperature of 313.15 K.

With respect the system DBE + methylcyclohexane, the mix-ure shows endothermic behavior (HE > 0) at any mole fraction.he maximum value of the excess molar enthalpy at 298.15 K is6 J mol−1, while at 313.15 K is 90 J mol−1, both at the mole fraction

f 0.45. No data were found in the literature for comparison of thisinary system at both temperatures.

The same endothermic effect presents the system DBE + toluenet 298.15 and 313.15 K. The maximum values of HE are 83 J mol−1

k, (�); cyclohexane + 1-butanol, data from Ref. [4], (�); benzene + 1-butanol, databutanol, data from Ref. [7], (+). ( ) calculated values for 1-butanol + 1-hexene, or3.15 K with Eq. (1) using parameters of Table 5.

and 85 J mol−1 (at x = 0.4) at 298.15 K and 313.15 K, respec-tively.

The excess molar enthalpy of the system DBE + cyclohexaneat T = 313.15 K shows endothermic behavior (HE > 0) in the wholerange of composition. The maximum value of the excess molarenthalpy is 250 J mol−1, obtained at a mole fraction of DBE about0.40. No data were found in the literature for comparison of thisbinary system at the same temperature.

Concerning the excess molar enthalpy of the system DBE + TMP

at T = 313.15 K, the system presents endothermic behavior (HE > 0)in the whole range of composition. The maximum value of theexcess molar enthalpy is 121 J mol−1, obtained at a mole fractionof DBE about 0.50.

6F.A

guilaret

al./FluidPhase

Equilibria315

(2012)1–8

Table 5Summary of parameters for the representation of HE by Eq. (1), for binary systems DBE + hydrocarbon and hydrocarbon + 1-butanol at T = 298.15 K.

Parameters DBE (1) + 1-hexene(2)

DBE (1) + methylcyclohexane(2)

DBE (1) + toluene(2)

DBE (1) + cyclohexane(2)

DBE (1) + benzene(2)

DBE (1) + heptane(2)

DBE (1) + 2,2,4-trimethylpentane(2)

A0 0 0 0 0 0 0 0A1 −90.15 378.5 314.3 1037.1 1295.6 493.6 492.8A2 5.62 −63.8 −133.8 −362.2 −567.1 −37.1 −58A3 4.82 20.2 48.82 166.2 247 12.7 18.2A4 −5.54 −38.2 −28.94 −139.2 −125.5 −51.4 −35.7A5 38.7 20.6 314.3 −29rms �HE (J mol−1) 0.3 0.3 0.4 0.5 0.3 0.4 0.5max|�HE| (J mol−1) 0.7 0.8 0.5 1.2 0.3 0.7 1.0max(|�HE|/HE) 12.8% 2.8% 2.0% 3.6% 0.3% 2.3% 5.0%

Parameters 1-Hexene(1) + 1-butanol (2)

Methylcyclohexane(1) + 1-butanol (2)

Toluene(1) + 1-butanol (2)

Cyclohexane(1) + 1-butanol (2)

Benzene(1) + 1-butanol (2)

Heptane(1) + 1-butanol (2)

2,2,4-Trimethylpentane(1) + 1-butanol (2)

A0 −0.980 −0.977 −0.937 −0.972 −0.932 −0.974 −0.979A1 2233.7 2130.2 3684.1 2354.9 4105.2 2301.3 2309.3A2 −499.8 −854.7 −1309.0 −1102.2 −1543.8 −1089.8 −1018.1A3 −957.6 −611.4 −988.0 −600.7 −1082.4 −478.8 −555.9A4

A5

rms �HE (J mol−1) 2.5 2.2 2.3 2.4 2.3 1.8 1.8max|�HE| (J mol−1) 4.9 3.8 4.0 4.6 3.7 3.4 3.3max(|�HE|/HE) 4.2% 4.0% 2.8% 6.8% 2.0% 1.6% 4.8%

Table 6Summary of parameters for the representation of HE by Eq. (1), for binary systems DBE + hydrocarbon and hydrocarbon + 1-butanol at T = 313.15 K.

Parameters DBE (1) + 1-hexene(2)

DBE (1) + methylcyclohexane(2)

DBE (1) + toluene(2)

DBE(1) + cyclohexane (2)

DBE (1) + benzene(2)

DBE (1) + heptane(2)

DBE(1) + +2,2,4-trimethylpentane (2)

A0 0 0 0 0 0 0 0A1 −97.91 355.5 326.4 962.6 1215.6 487.8 484.1A2 7.66 −60.0 −120.2 −344.3 −530.4 −45.81 −33.5A3 4.55 17.6 29.8 186.5 211.1 16.80 22.5A4 −10.27 −15.8 −26.4 −152.5 −103.7 −39.66 −29.7A5

rms �HE (J mol−1) 0.1 0.2 0.4 0.7 0.4 0.4 0.3max|�HE| (J mol−1) 0.3 0.3 0.9 1.9 0.7 0.9 0.9max(|�HE|/HE) 5.3% 1.5% 9.3% 1.5% 1.4% 1.7% 1.8%

Parameters 1-Hexene(1) + 1-butanol (2)

Methylcyclohexane(1) + 1-butanol (2)

Toluene(1) + 1-butanol (2)

Cyclohexane(1) + 1-butanol (2)

Benzene(1) + 1-butanol (2)

Heptane(1) + 1-butanol (2)

2,2,4-Trimethylpentane(1) + 1-butanol (2)

A0 −0.965 −0.973 −0.901 −0.972 −0.900 −0.968 −0.970A1 3128.4 2906.6 4667.5 3046.6 4967.4 3172.2 3202.5A2 −966.3 −1246.9 −1800.1 −1425.5 −1914.1 −1531.3 −1486.4A3 −958.6 −677.1 −823.9 −694.1 −1004.9 −511.0 −563.8A4

A5

rms �HE (J mol−1) 3.1 1.5 3.8 1.7 3.9 1.8 1.9max|�HE| (J mol−1) 5.6 2.2 6.2 2.9 7.2 3.0 3.5max(|�HE|/HE) 4.0% 1.1% 4.3% 1.8% 2.9% 2.2% 0.8%

ase Eq

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evat20

bm8Wt1

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ciodaifHt

F. Aguilar et al. / Fluid Ph

The excess molar enthalpy of the binary system 1-hexene + 1-utanol at the temperatures 298.15 K and 313.15 K presentsndothermic behavior (HE > 0) in the whole range of composition.he maximum values of the excess molar enthalpies are 648 J mol−1

nd 881 J mol−1 at the respective temperatures, obtained at theole fraction of 0.7 on 1-hexene. No data were found in the lit-

rature.The binary system methylcyclohexane + 1-butanol shows also

ndothermic behavior in the entire composition range. At= 298.15 K, the maximum value of HE is 588 J mol−1, at the mole

raction of 0.65 of methylcyclohexane. The respective maximumalue at 313.15 K is 795 J mol−1, at the same mole fraction. Data forhe same system at 298.15 K reported by Vesely et al. [19] showshat our data agree to within 0.8% in the range of composition.3 ≤ x ≤ 0.7. No data were found in the literature for comparisonf this binary system at 313.15 K.

With respect the system toluene + 1-butanol, the mixture showsndothermic behavior (HE > 0) at any mole fraction. The maximumalue of the excess molar enthalpy at 298.15 K is 1012 J mol−1, whilet 313.15 K is 1262 J mol−1, both at the mole fraction of 0.65 ofoluene. Comparison with data of Mrazek and Van Ness [20] at98.15 K presents an agreement of 1.7% in the range of composition.3 ≤ x ≤ 0.7. No data were found at 313.15 K for comparison.

The next binary system studied is the system cyclohexane + 1-utanol at T = 313.15 K, showing also endothermic behavior. Theaximum value of the excess molar enthalpy of the mixture is

22 J mol−1 obtained at a mole fraction of cyclohexane of 0.65.hen compared to data published by Vesely et al. [21] at the same

emperature, the agreement in the central range of composition is.2%.

The last binary system which has been studied is the systemMP + 1-butanol at T = 313.15 K, showing also endothermic behav-or. The maximum value of the excess molar enthalpy of the mixturet the temperature of 313.15 K is 867 J mol−1 at the mole fractionf TMP of 0.65 approximately. No data were found at the sameemperature for comparison.

Interaction effects occurring in the solutions containing someon-polar and polar compounds influence the excess molarnthalpy data presented in this work. The endothermic characterf the mixtures DBE + hydrocarbon reveals the positive contribu-ion to HE associated with the disruption of interaction betweenike molecules respect the negative contribution due to the cre-tion of interaction between unlike molecules. Our results showhat for the given ether DBE, HE (benzene) > HE (cyclohexane) > HE

heptane, 2,2,4-trimethylpentane > HE (methylcyclohexane) > HE

toluene) > HE (1-hexene). Only the mixture DBE + 1-hexene showsxothermic effect in the entire range of composition at both tem-eratures, due to rather strong interactions between the doubleond of 1-hexene and the oxygen of DBE which largely compen-ate for the endothermic effects due to both DBE and hexane uponixing.The HE curves are skewed towards small mole fractions of ether,

eflecting the more active behavior of ether molecules. Because ofhe increase of kinetic energy of molecules with the temperature,decrease of the dispersion forces is expected and therefore, the

ndothermic effect is lower.Respect the binary mixtures hydrocarbon + 1-butanol, the HE

urves are skewed towards low mole fractions of alcohol, reflect-ng its strong self-association character. The chemical forcesf the hydrogen bonds in the alkanol are stronger than theispersion forces of the hydrocarbon and an endothermic char-cter of the mixture is expected. This effect is enhanced by the

ncrease of the temperature, by the weakness of the dispersionorces. Experimental HE data show that for the given 1-butanol,E (benzene) > HE (toluene) > HE (1-hexene) > HE (heptane, 2,2,4-

rimethylpentane) > HE (cyclohexane) > HE (methylcyclohexane).[

uilibria 315 (2012) 1–8 7

An interesting case is the comparison of the interactionsbetween DBE and benzene or toluene. The difference observedresults from stronger interactions with toluene than with benzene,which compensate more the endothermic effects of disruption ofmolecular interactions between like molecules in toluene and inbenzene, respectively. Similarly, the less positive enthalpy for 1-butanol with toluene than with benzene results from strongerinteractions with toluene than with benzene. As a matter of factthe methyl group of toluene has an inductive effect for strongerinteractions and at the same time reduces considerably the wellknow stacking organization of benzene molecules.

4. Conclusions

Isothermal excess molar enthalpies at T = 298.15 K andT = 313.15 K for the binary systems DBE or 1-butanol and 1-hexene, or methylcyclohexane, or toluene, or cyclohexane or2,2,4-trimethylpentane at atmospheric pressure were determinedby using an isothermal flow calorimeter. All the binary systemsDBE + hydrocarbon show endothermic effect and slight asymmet-ric HE behavior at the measured temperatures. Only the binarymixture DBE + 1-hexene at 298.15 K and at 313.15 K shows exother-mic behavior. All the 1-butanol + hydrocarbon mixtures showendothermic effect and strong asymmetric HE behavior at themeasured temperatures. Intermolecular and association effectsinvolved in these systems have been discussed. The measuredexcess molar enthalpies data were correlated well with a polyno-mial equation.

List of symbolsAi adjustable parameters of the correlation equations and

modelsHE molar excess enthalpyi,j constituent identification: 1, 2 or 3max maximum value of the indicated quantityrms root mean squareT absolute temperaturex mole fraction

Greek letters� signifies difference

Acknowledgements

This paper is part of the Doctoral Thesis of F. Aguilar.Support for this work came from the Ministerio de Ciencia e

Innovación, Spain, Projects ENE2009-14644-C02-01 and ENE2009-14644-C02-02.

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