J. Chem. Thermodynamics 56 (2013) 6–11

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J. Chem. Thermodynamics

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Excess enthalpies of ternary mixtures of oxygenated additives + hydrocarbonmixtures in fuels and bio-fuels: Dibutyl ether (DBE) and 1-butanol and 1-hexeneor cyclohexane or 2,2,4 trimethylpentane at 298.15 K and 313.15 K q

Fernando Aguilar a, Fatima E.M. Alaoui a, José J. Segovia b, Eduardo A. Montero a,⇑a Departamento de Ingeniería Electromecánica, Escuela Politécnica Superior, Universidad de Burgos, E-09006 Burgos, Spainb Grupo de Termodinámica y Calibración TERMOCAL, Escuela de Ingenierías Industriales, Universidad de Valladolid, E-47071 Valladolid, Spain

a r t i c l e i n f o a b s t r a c t

Article history:Received 27 March 2012Received in revised form 28 June 2012Accepted 9 July 2012Available online 20 July 2012

Keywords:Excess enthalpyBio-fuels1-ButanolDibutylether

0021-9614/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.jct.2012.07.011

q This paper is part of the Doctoral Thesis of F. Agu⇑ Corresponding author. Tel.: +34 947 258 916; fax

E-mail address: emontero@ubu.es (E.A. Montero).

New experimental excess molar enthalpy data (420 points) of the ternary systems dibutyl ether (DBE)and 1-butanol and 1-hexene at 298.15 K and 313.15 K, and DBE and 1-butanol and cyclohexane or2,2,4-trimethylpentane (TMP) at 313.15 K at atmospheric pressure are reported. A quasi-isothermal flowcalorimeter has been used to make the measurements. All the ternary systems show endothermic char-acter. The experimental data for the ternary systems have been fitted using the Redlich–Kister rationalequation. Considerations with respect the intermolecular interactions amongst ether, alcohol and hydro-carbon compounds are presented.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The use of ethers and alcohols as gasoline-blending agents hasbeen proposed to reduce emissions of new bio-gasoline. Ether +alcohol + alkane mixtures are of interest as model mixtures forbio-fuels in which the alcohol and the ether act as non-polluting,high octane number blending agents. Biobutanol has been recentlyproposed as new bio-fuel that can be blended into standard gradegasoline containing ethanol [1,2]. Interest in butanols as a second-generation bio-fuel has increased because they have many advanta-ges over other potential alternative fuel candidates such as ethanol[3]. At 85% by volume with gasoline, butanols can be demonstratedto work in the internal combustion engine designed for use withgasoline without modification (unlike 85% ethanol, E85). They havea higher energy content for a given volume than ethanol, and almostas much as gasoline. And butanol is an oxygenated hydrocarbon likemethanol, ethanol, etc. with a similar contribution to the antiknockeffect. 1-Butanol is otherwise a basic component in the synthesis ofthe ether DBE, which is used as blending agent in reformulated gas-oline, and therefore is always contained as an impurity. The alcoholand the ether act as non-polluting, high octane number blendingagents.

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ilar.: +34 947 259 088.

This work continues a study of our group on excess molarenthalpies HE of DBE and 1-butanol + hydrocarbon mixtures [4–9]. The hydrocarbons selected are representative of the broad spec-trum of hydrocarbon components in gasoline: alkanes (heptane),cycloalkanes (cyclohexane), aromatics (benzene), alkenes (1-hex-ene), branched alkanes (2,2,4-trimethylpentane), branched cyclo-alkanes (methyl-cyclohexane) and branched aromatics (toluene).All the set of fourteen binary systems formed by DBE + hydrocar-bon or 1-butanol + hydrocarbon have been studied at 298.15 Kand 313.15 K. Moreover, four ternary mixtures DBE + 1-buta-nol + hydrocarbon have been studied at the temperatures of298.15 K and two at 313.15 K.

New experimental excess molar enthalpy data (420 points) ofthe ternary systems DBE and 1-butanol and 1-hexene at 298.15 Kand 313.15 K, and DBE and 1-butanol and cyclohexane or 2,2,4-trimethylpentane at 313.15 K at atmospheric pressure are reportedin this work. Excess molar enthalpies have been measured with aquasi-isothermal flow calorimeter. The experimental data havebeen fitted using the Redlich–Kister rational polynomials [10].

2. Experimental section

All the chemicals used here were purchased from Fluka ChemieAG and were of the highest purity available, chromatography qual-ity reagents (of the series puriss p.a.) with a stated purity>99.5 mol%. The purity of all reagents was checked by gas chroma-tography, and its values are presented in table 1.

TABLE 1Purity and related data of chemicals.

Compound Formula Molarmass/g�mol�1

Statedpurity/ mol%

CAS number

DBE C8H18O 130.228 >99.6% 142-96-11-Butanol C4H10O 74.120 >99.9%a 71-36-31-Hexene C6H12 84.161 >99.3% 592-41-6Cyclohexane C6H12 84.161 >99.9% 110-82-72,2,4-Trimethylpentane C8H18 84.161 >99.9% 540-84-1

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

TABLE 2Experimental excess molar enthalpies HE

2+13 at 298.15 K for the addition of 1-hexeneto (DBE (1) + 1-butanol (3)) to form x1 DBE + x2 hydrocarbon + (1 � x1 � x2) 1-butanol,and values of HE

123 calculated from equation (2), using the smooth representation ofHE

13 by Redlich–Kister equation with parameters given in reference [8].a

x2 HE2+13/

J�mol�1HE

123/J�mol�1

x2 HE2+13/

J�mol�1HE

123/J�mol�1

DBE + 1-hexene + 1-butanolx1/x3 = 0.2500 HE

13/J�mol�1 = 447.30.8996 439.2 484.1 0.3997 373.4 642.00.7999 507.9 597.4 0.3000 286.0 599.10.6999 520.2 654.4 0.1997 189.0 547.00.5998 496.3 675.4 0.1000 86.3 488.90.4996 445.6 669.5

x1/x3 = 0.6635 HE13/J�mol�1 = 758.2

0.9000 360.1 435.9 0.3996 279.4 734.60.8004 402.1 553.5 0.3003 216.5 746.90.7002 400.0 627.3 0.2005 146.3 752.50.5995 375.1 678.7 0.1000 68.7 751.00.5004 333.6 712.4

x1/x3 = 1.5001 HE13/J�mol�1 = 894.5

0.8002 299.1 477.8 0.4004 189.8 726.10.7000 288.5 556.8 0.3003 145.1 771.00.5998 264.2 622.2 0.2004 97.4 812.70.5006 231.0 677.8 0.1007 42.0 846.5

x1/x3 = 3.9978 HE13/J�mol�1 = 771.6

0.6999 178.6 410.1 0.4003 109.8 572.60.6003 160.0 468.5 0.3006 82.9 622.60.5003 136.6 522.1 0.2001 54.5 671.7

0.1002 24.7 719.0

a The estimated uncertainty of the measured temperature is 0.05 K. The maximumabsolute uncertainty of mole fraction at equimolar composition is ±0.0008. Theestimated relative uncertainty of the determined HE/J�mol�1 is ±0.01�HE.

F. Aguilar et al. / J. Chem. Thermodynamics 56 (2013) 6–11 7

Excess molar enthalpies have been measured with a quasi-iso-thermal flow calorimeter previously described [4]. The flow cell ofthe calorimeter is immersed in a water bath, (Hart Scientific, model6020E) and is thermostatted at T = (298.15 ± 0.01) K or atT = (313.15 ± 0.01) K. The bath temperature is measured by its cal-ibrated standard PRT-100, resolving 10 mK in the reading of tem-perature and estimating an overall uncertainty of ±30 mK.Isothermal calorimetry is based on measuring the energy requiredto maintain the mixing vessel at a constant temperature. Toachieve this condition, a Peltier cooler removes at constant rate en-ergy from the flow cell and a control-heater compensates this en-ergy and additionally the energy liberated (exothermic) orabsorbed (endothermic) by the mixing process and maintains thetemperature of the flow cell constant. The variation of temperatureis detected by a control sensor, a NTC thermistor. The resistance ismeasured by a 4-wire resistance bridge with a micro-ohm meterfrom Hewlett-Packard, model HP-34420A. The Peltier cooler, thecontrol-heater and the calibration heater are connected, eachone, to its respectively DC power supply. The control of these de-vices is made by a computer through a GPIB connection and spe-cific software that has been developed. The change of heatingpower of the control-heater before, during and after measurementsis a direct measure for the excess enthalpy HE. The calibration ofthe measurement system is made by simulating an exothermicmixing process by a calibration resistor. The uncertainty in themeasure of temperature is estimated to be less than 0.05 K. TheHE is calculated from differences in the heating power control, oncethe calibration procedure has been performed.

Knowing the volumetric flow rates delivered, the molar massesand the densities of the pure compounds, the mole fractions of themixtures obtained in the mixing coil can be calculated. The maxi-mum absolute uncertainty of mole fraction at equimolar composi-tion is ±0.0008. Densities of pure liquids are determined byinterpolating density data obtained from Riddick et al. [11] at themeasured temperature of delivery. Estimated densities at T =298.15 K, were 0.76417, 0.80575, 0.66848, 0.77389 and 0.68780,g�cm�3 for the DBE, 1-butanol, 1-hexene, cyclohexane, and 2,2,4-trimethylpentane respectively. These results agree within <0.1 percent with values found in the literature [12–16]. Mixtures of differ-ent compositions are studied and in this way the dependence of HE

on mole fraction can be determined. The estimated relative uncer-tainty of the determined HE/J�mol�1 is ±0.01�HE.

3. Results and discussion

The experimental excess molar enthalpies obtained in this workfor the ternary mixtures DBE and 1-butanol and 1-hexene at298.15 K and 313.15 K, and DBE and 1-butanol and cyclohexaneor 2,2,4-trimethylpentane at 313.15 K at atmospheric pressureare listed in tables 2 and 3, respectively.

The Redlich–Kister rational polynomial [10], given by equation1, has been used to fit the HE measurements for binary systems, inwhich the Ak coefficients are determined by the unweighted least-squares method.

HE ¼ xi � xj �Pn

k¼1Ak � ðxi � xjÞk�1

1þ A0 � ðxi � xjÞ; ð1Þ

The ternary mixtures DBE (1) + hydrocarbon (2) + 1-butanol (3)were formed by adding the hydrocarbon (2) to binary mixtures offixed composition of DBE (1) + 1-butanol (3). Four different startingbinaries were used, with values of the ratio x1/x3 close to 0.2500,0.6666, 1.5000 and 4.0000, respectively. The experimental excessmolar enthalpies, also listed in tables 2 and 3, are determined byequation (2), using the smooth representation of HE

13 by Red-lich–Kister:

HE123 ¼ HE

2þ13 þ ð1� x2ÞHE13: ð2Þ

The following equation was used to fit the ternary HE

measurements

HE123 ¼ HE

12 þ HE13 þ HE

23 þ x1x2x3DHE123 ð3Þ

with

DHE123 ¼ B0 þ B1x1 þ B2x2 þ B3x2

1 þ B4x22

þ B5x1x2 þ B6x31 þ B7x3

2; ð4Þ

where the parameters Bi were determined by the unweighted least-squares method.

Results of data correlation for the reported ternary systems aresummarized in table 4. For the purpose of comparing the experi-mental excess enthalpy values with those obtained by equations(3) and (4), we have used the root-mean-square deviation, Drms,the maximum absolute deviation, Dmax|DH

E|, and the maximum

relative deviation, Dmax(|DHE

|/HE

), which are defined as follows:

Drms ¼Pndat

i HEexp � HE

calc

� �2

ndat � npar

264

375

1=2

; ð5Þ

TABLE 3Experimental excess molar enthalpies HE

2+13 at 313.15 K for the addition of hydrocarbon (1-hexene, or cyclohexane, or 2,2,4-trimethylpentane) to (DBE (1) + 1-butanol (3)) toform x1 DBE + x2 hydrocarbon + (1 � x1 � x2) 1-butanol, and values of HE

123 calculated from equation (2), using the smooth representation of HE13 by Redlich–Kister equation with

parameters given in reference [8].a

x2 HE2+13/J�mol�1 HE

123/J�mol�1 x2 HE2+13/J�mol�1 HE

123/J�mol�1

DBE + 1-hexene + 1-butanolx1/x3 = 0.2500, HE

13/J�mol�1 = 526.90.8997 589.1 641.9 0.3996 524.1 840.50.8000 690.2 795.5 0.2999 409.0 777.80.6999 707.6 865.7 0.1998 277.5 699.10.5998 680.5 891.3 0.1499 206.1 654.00.4997 609.5 873.1

x1/x3 = 0.6666, HE13/J�mol�1 = 890.8

0.9000 473.8 562.9 0.3997 393.6 928.30.8004 554.6 732.3 0.3004 306.8 929.90.7003 556.7 823.6 0.2005 210.5 922.70.5997 523.8 880.3 0.1001 106.6 908.20.5005 467.4 912.4

x1/x3 = 1.5000, HE13/J�mol�1 = 1045.6

0.8002 412.6 621.5 0.4003 273.8 900.80.7000 407.5 721.2 0.3003 211.8 943.40.5998 376.0 794.5 0.2004 144.3 980.50.5005 330.2 852.4 0.1006 72.7 1013.1

x1/x3 = 4.005, HE13/J�mol�1 = 891.6

0.6999 240.3 507.9 0.4003 157.4 692.10.6003 220.9 577.4 0.3005 120.2 743.90.5003 191.6 637.1 0.2000 80.2 793.5

0.1001 39.6 841.9

DBE + cyclohexane + 1-butanolx1/x3 = 0.2500, HE

13/J�mol�1 = 526.90.9001 526.0 578.6 0.4003 585.0 900.90.8002 649.9 755.1 0.2997 474.0 843.00.6996 702.7 860.9 0.2002 338.8 760.10.6002 704.9 915.6 0.1001 177.3 651.40.5002 663.2 926.5

x1/x3 = 0.6666, HE13/J�mol�1 = 890.8

0.8999 455.5 544.7 0.4006 495.4 1029.40.7997 561.0 739.4 0.3006 403.5 1026.50.6998 601.0 868.4 0.2004 285.9 998.20.6002 597.5 953.6 0.0997 146.9 948.80.5002 559.9 1005.1

x1/x3 = 1.4988, HE13/J�mol�1 = 1045.6

0.8000 481.4 690.5 0.4001 419.6 1047.00.6997 514.3 828.3 0.2995 340.1 1072.50.5998 510.3 928.7 0.2003 236.1 1072.30.4998 477.8 1000.8 0.1000 123.0 1064.0

x1/x3 = 3.9998, HE13/J�mol�1 = 891.7

0.6997 420.9 688.7 0.3998 346.5 881.70.5996 420.8 777.8 0.3006 279.8 903.50.5001 393.9 839.6 0.2008 195.4 908.1

0.0995 90.5 893.5

DBE + 2,2,4-trimethylpentane + 1-butanolx1/x3 = 0.2501, HE

13/J�mol�1 = 527.00.9003 579.9 632.5 0.3999 591.7 907.90.8005 687.8 792.9 0.3000 482.3 851.20.7005 724.4 882.2 0.2005 346.9 768.20.6007 715.7 926.1 0.0998 184.3 658.70.5002 670.1 933.5

x1/x3 = 0.6666, HE13/J�mol�1 = 890.8

0.9003 491.2 580.1 0.3999 477.8 1012.40.8006 575.3 752.9 0.3000 390.8 1014.30.7003 596.5 863.4 0.2001 282.6 995.10.6000 584.1 940.4 0.0999 151.7 953.40.5000 542.1 987.5

x1/x3 = 1.5002, HE13/J�mol�1 = 1045.6

0.8000 458.0 667.1 0.4005 370.1 996.90.6999 470.5 784.3 0.3003 301.3 1032.90.6000 454.4 872.6 0.2000 213.7 1050.20.5005 421.8 944.1 0.0999 107.3 1048.5

x1/x3 = 4.0002, HE13/J�mol�1 = 891.6

0.7003 342.9 610.1 0.3999 276.9 812.0

8 F. Aguilar et al. / J. Chem. Thermodynamics 56 (2013) 6–11

TABLE 3 (continued)

x2 HE2+13/J�mol�1 HE

123/J�mol�1 x2 HE2+13/J�mol�1 HE

123/J�mol�1

0.6001 337.9 694.5 0.3000 226.8 851.00.5003 314.9 760.5 0.2005 162.7 875.6

0.1005 82.9 884.9

a The estimated uncertainty of the measured temperature is 0.05 K. The maximum absolute uncertainty of mole fraction at equimolar composition is ±0.0008. The estimatedrelative uncertainty of the determined HE/J�mol�1 is ±0.01�HE.

TABLE 4Summary of the data reduction results obtained for the ternary systems DBE (1) + hydrocarbon (2) + 1-butanol (3) at 298.15 and 313.15 K using equations (3) and (4).

Correlation 1-Hexene (2) 1-Hexene (2) Cyclohexane (2) 2,2,4-Trimethyl pentane (2)

T/K 298.15 313.15 313.15 313.15

B0 9982.3 10710.6 12936.8 12817.8B1 �33771.3 �31150.3 �42000.1 �44625.8B2 �19332.0 �27340.1 �26320.3 �29450.7B3 14661.0 3830.3 20111.8 34067.6B4 �40889.1 �35183.0 �42718.1 �25539.4B5 96784.5 110097.0 115691.0 112654.2B6 23432.2 33835.0 25062.5 10026.1B7 85040.6 92826.7 98526.1 78305.2Drms/J�mol �1 18.5 19.4 20.8 19.0Dmax |DH

E|/J�mol �1 50.0 49.5 55.5 53.1

Dmax (|DHE

|/HE

)/% 12.2 9.8 9.1 7.7

FIGURE 1. Contours for constant values of HE123 for DBE(1) + 1-hexene (2) + 1-butanol (3) at 298.15 K.

F. Aguilar et al. / J. Chem. Thermodynamics 56 (2013) 6–11 9

DmaxjDHE j ¼max HEexp � HE

calc

������; ð6Þ

DmaxðjDHE j=HEÞ ¼maxHE

exp � HEcalc

������

HEexp

0@

1A; ð7Þ

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. As anillustration, contour for constant values of HE

123 for DBE (1) + 1-hexene (2) + 1-butanol (3) at 298.15 K obtained with equations(3) and (4) is presented in figure 1.

TABLE 5Summary of the maximum values of the experimental excess enthalpy HE, and itsrespective mole fraction, obtained for the ternary systems DBE (1) + hydrocarbon(2) + 1-butanol (3) at 298.15 and 313.15 K using equations (3) and (4).

Hydrocarbon 1-Hexene(2)

Cyclohexane(2)

2,2,4-Trimethylpentane (2)

T/K = 298.15Max HE/J�mol�1 894.6 928.4a 893.0b

x1 0.6000 0.4795 0.5401x2 0.0000 0.2005 0.0998x3 0.4000 0.3200 0.3601

T/K = 313.15Max HE/J�mol�1 1045.6 1072.5 1050.2x1 0.6000 0.4203 0.4800x2 0.0000 0.2995 0.2000x3 0.4000 0.2802 0.3200

a Data taken from [5].b Data taken from [8].

10 F. Aguilar et al. / J. Chem. Thermodynamics 56 (2013) 6–11

Concerning the first measured ternary system, DBE (1) + 1-hex-ene (2) + 1-butanol (3) at 298.15 K, the root mean square deviation,Drms, is 18.5 J�mol�1, and the maximum value of the absolute devi-ation, Dmax|DH

E|, is 50.0 J�mol�1. This system shows an endothermic

behaviour in the whole range of composition. The maximum valueof HE is 895 J�mol�1. When temperature is increased to 313.15 K,the maximum value of HE reaches 1046 J�mol�1, the root meansquare deviation is 19.4 J�mol�1, and the maximum value of theabsolute deviation is 49.5 J�mol�1. No data of the same ternary sys-tem at the same temperatures were found in the literature forcomparison.

The ternary mixtures DBE (1) + cyclohexane (2) + 1-butanol (3)at 313.15 K also show an endothermic behavior. The root meansquare deviation, Drms, is 20.8 J�mol�1, and the maximum valueof the absolute deviation, Dmax|DH

E|, is 55.5 J�mol�1. The maximum

value of HE is 1073 J�mol�1.With respect the ternary system, DBE (1) + 2,2,4, trimethylpen-

tane (2) + 1-butanol (3) at 313.15 K, the root mean square devia-tion, Drms, is 19.0 J�mol�1, and the maximum value of theabsolute deviation, Dmax|DH

E|, is 53.1 J�mol�1, presenting also an

endothermic behavior in the whole range of composition. No dataof the ternary systems with cyclohexane and 2,2,4, trimethylpen-tane at the same temperature was found in the literature.

The maximum relative deviation for the four ternary systemsranges from 7.7% to 12.2%.

table 5 shows the summary of the maximum values of theexperimental excess enthalpy HE obtained for the ternary systemsDBE (1) + hydrocarbon (2) + 1-butanol (3) at 298.15 and 313.15 Kusing equations (3) and (4).

For the mixtures presented in this work, containing some polarand non-polar compounds, interaction effects influence the excessmolar enthalpy data. The binary mixture DBE + 1-butanol containone strong self-associating component (1-butanol) and a non-self-associating component (DBE) which, however, can form asso-ciates with the alkanol through hydrogen bonding. The greater po-sitive contribution of the destruction of alkanol–alkanol hydrogenbonds upon mixing with reference to the negative term due to theformation of alkanol–ether complexes, explains the endothermicbehavior of the mixture. When adding the hydrocarbon to theether + alkanol mixtures, it could be expected that the positivecontribution to HE associated with the disruption of interaction be-tween like molecules, in connection with the negative contributiondue to the creation of interaction between unlike molecules,should explain the endothermic or exothermic character of themixture. In the case of DBE (1) + 1-hexene (2) + 1-butanol (3)mixtures, the addition of the 1-hexene decreases the endothermiceffect of the ether + alkanol mixture, as the maximum excess

enthalpy HE is obtained when x2 = 0. This effect is probably dueto rather strong interactions between the double bond of 1-hexeneand the oxygenated complex of DBE + 1-butanol, which largelycompensate for the endothermic effects due to both DBE + 1-buta-nol and 1-hexene upon mixing.

With respect to the addition of the cyclic or branched alkanes(cyclohexane or 2,2,4 trimethylpentane), data from table 5 presentthe expected endothermic behavior due to the creation of interac-tion between unlike molecules. Results show that the endothermiccharacter of the mixture increases slightly for the cyclic hydrocar-bon with respect to a branched hydrocarbon such as TMP. For allthe ternary systems, the endothermic effect is enhanced by the in-crease of the temperature, by the weakness of the dispersionforces.

4. Conclusions

Isothermal excess enthalpies at 298.15 K and 313.15 K for theternary systems dibutylether + 1-butanol + 1-hexene, or + cyclo-hexane, or + 2,2,4, trimethylpentane were determined by usingan isothermal flow calorimeter. All the ternary systems show posi-tive HE values at the measured temperatures. The addition of the 1-hexene decreases the endothermic effect of the ether + alkanolmixture. When referred to alkanes, the endothermic character ofthe mixture increases slightly for the cyclic hydrocarbon cyclohex-ane with respect to a branched hydrocarbon such as TMP. For allthe ternary systems, the endothermic effect is enhanced by the in-crease of the temperature.

Acknowledgements

Support for this work came from the Ministerio de Ciencia eInnovación, Spain, Projects ENE2009-14644-C02-01 and ENE2009-14644-C02-02.

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JCT 12-183