Oxygenated Compounds + Hydrocarbon Mixtures in Fuels and Biofuels

Article pubs.acs.org/jced

Oxygenated Compounds + Hydrocarbon Mixtures in Fuels and Biofuels: Excess Enthalpies of Ternary Mixtures Containing 1‑Butoxybutane + Propan-1-ol +1-Hex-1-ene, or Heptane, or 2,2,4-Trimethylpentane at (298.15 and 313.15) K Fatima E.M. Alaoui,†,‡ Fernando Aguilar,† María Jesús González-Fernández,† Ahmed El Amarti,§ and Eduardo A. Montero*,† †

Departamento de Ingeniería Electromecánica, Escuela Politécnica Superior, Universidad de Burgos, E-09006 Burgos, Spain Ecole Nationale des Sciences Appliquées d’El Jadida, Université Chouaib Doukkali-El Jadida, B.P. 1166, 24002 El Jadida Plateau, Morocco § Department of Chemistry, Faculté de Sciences, Université Abdelmalek Essaâdi-Tetouan, B.P. 2121, 93030 Tetouan, Morocco ‡

ABSTRACT: New experimental excess molar enthalpy data (376 points) of the ternary systems 1-butoxybutane + propan-1-ol +1-hex-1-ene, or heptane, or 2,2,4-trimethylpentane and the corresponding binary systems at (298.15 and 313.15) K at atmospheric pressure are reported. A quasi-isothermal flow calorimeter has been used to make the measurements. All of the binary and ternary systems show endothermic character at both temperatures. The experimental data for the binary systems have been fitted using the rational equations.

1. INTRODUCTION Oxygenates produced from renewable sources, including higher alcohols (those containing more than two carbon atoms), have been proposed as blend components in gasoline to reduce the petroleum consumption and greenhouse gas emissions. The addition of fuel oxygenates to gasoline, including those of biological origin, raises combustion temperatures and improves engine efficiencies.1 The results are lower levels of carbon monoxide and unburned hydrocarbons in automobile exhaust.2 The higher alcohols, such as propanols, butanols, and pentanols may have acceptable properties as gasoline blend components. Relative to ethanol, blends of gasoline with higher alcohols or cellulose-derived oxygenates may have higher energy density, lower vapor pressure, and lower affinity for water. Note that many of these properties do not blend linearly into gasoline. This work continues a study of our group on excess molar enthalpies of oxygenates + hydrocarbon mixtures;3−9 where the selected alcohol was 1-butanol. This work concerns 1butoxybutane (also known as dibutyl ether, DBE), propan-1ol (also known as 1-propanol), and the DBE + 1-propanol + hydrocarbon mixtures. Though 1-propanol is rarely discussed as a biofuel, it can be produced by microbial fermentation of biomass (cellulose), and then it should be considered as a potential second generation biofuel additive.10 The issues with microbial production of biopropanol are analogous to the issues with microbial production of biobutanol, so if biobutanol © 2014 American Chemical Society

becomes a more practical biofuel to produce, then biopropanol will also become more feasible. The present paper broadens the study study on mixtures of ether + alcohol + hydrocarbon. The selected compounds are DBE, 1-propanol, unsaturated hydrocarbons (hex-1-ene, also known as 1-hexene), and the saturated hydrocarbons (heptane and 2,2,4trimethylpentane), which are usual compounds in gasoline. New experimental excess molar enthalpy data (376 points) of the ternary systems DBE + 1-propanol + 1-hexene, or heptane, or Table 1. Purity and Related Data of Chemicals molar mass

stated puritya

compound

molecular formula

g·mol−1

mol %

CAS no.

dibutyl ether 1-propanol 1-hexene heptane 2,2,4-trimethylpentane

C8H18O C3H7OH C6H12 C7H16 C8H18

130.2 60.1 84.2 100.2 114.2

99.3 99.9b 99.3 99.8 99.9

142-96-1 71-23-8 592-41-6 142-82-5 540-84-1

a Determined by gas chromatography (GC). bThe water content was checked to be less than 0.01 %.

Received: May 30, 2014 Accepted: August 7, 2014 Published: August 18, 2014 2856

dx.doi.org/10.1021/je5004912 | J. Chem. Eng. Data 2014, 59, 2856−2864

Journal of Chemical & Engineering Data

Article

Table 2. Experimental Excess Molar Enthalpies of Binary Systems DBE + 1-Propanol, 1- Hexene + 1-Propanol, Heptane + 1-Propanol, and 2,2,4-Trimethylpentane + 1-Propanol at (298.15 and 313.15) K at Atmospheric Pressurea HE x

HE −1

J·mol

x

HE −1

x

J·mol

HE −1

x

J·mol−1

935 951 951 934 895

0.8002 0.8501 0.8992 0.9492

831 731 584 353

634 664 683 690 682

0.7999 0.8505 0.9004 0.9508

659 616 548 427

639 655 661 657 639

0.8001 0.8493 0.8993 0.9503

606 559 492 382

630 648 656 655 640

0.7994 0.8499 0.8998 0.9506

611 566 502 392

1052 1066 1063 1041 993

0.8002 0.8501 0.8992 0.9492

914 797 628 371

860 894 914 919 907

0.7998 0.8505 0.9004 0.9508

875 815 721 547

851 872 881 876 855

0.8000 0.8492 0.8993 0.9503

815 755 668 514

851 875 883 881 862

0.7993 0.8499 0.8998 0.9506

826 769 684 518

J·mol

T = 298.15 K 0.0501 0.0998 0.1500 0.2000 0.2495

130 252 369 477 573

0.2999 0.3500 0.3998 0.4499 0.4997

0.0501 0.1003 0.1501 0.2002 0.2501

61 126 192 256 319

0.3004 0.3501 0.4007 0.4501 0.5001

0.0503 0.1002 0.1501 0.2001 0.2499

96 182 259 329 391

0.3004 0.3505 0.4005 0.4501 0.4997

0.0500 0.1001 0.1505 0.2003 0.2501

87 167 241 308 369

0.2999 0.3499 0.4006 0.4503 0.4997

0.0502 0.0998 0.1501 0.2001 0.2495

150 291 424 547 656

0.3000 0.3500 0.3999 0.4500 0.4997

0.0501 0.1002 0.1501 0.2001 0.2499

92 186 279 370 457

0.3003 0.3499 0.4006 0.4499 0.4998

0.0503 0.1001 0.1500 0.2000 0.2498

122 236 339 433 517

0.3004 0.3503 0.4003 0.4498 0.4996

0.0500 0.1000 0.1504 0.2002 0.2500

118 227 328 419 504

0.2997 0.3498 0.4004 0.4502 0.4995

xDBE + (1 − x)1-Propanol 662 0.5498 739 0.5998 806 0.6494 860 0.6995 903 0.7499 x1-Hexene + (1 − x)1-Propanol 382 0.5504 442 0.5998 498 0.6505 552 0.6998 595 0.7500 xHeptane + (1 − x)1-Propanol 448 0.5505 499 0.5996 544 0.6506 583 0.7005 614 0.7504 x2,2,4-Trimethypentane + (1 − x)1-Propanol 427 0.5504 479 0.5998 526 0.6500 567 0.7008 602 0.7502 T = 313.15 K xDBE + (1 − x)1-Propanol 756 0.5498 843 0.5999 915 0.6495 975 0.6996 1020 0.7499 x1-Hexene + (1 − x)1-Propanol 542 0.5502 621 0.5996 695 0.6503 758 0.6996 814 0.7500 xHeptane + (1 − x)1-Propanol 595 0.5503 665 0.5995 726 0.6505 777 0.7004 819 0.7503 x2,2,4-Trimethypentane + (1 − x)1-Propanol 581 0.5503 653 0.5997 718 0.6498 772 0.7007 817 0.7501

a

Standard uncertainties of temperature T and mole fractions x are as follows: u(T) = 0.05 K; u(x) = 0.0008. The expanded uncertainty with 0.95 level of confidence for the excess enthalpies HE is 10 J·mol−1.

2. EXPERIMENTAL METHOD All of the chemicals used here were purchased from Fluka Chemie AG, and all were of the highest purity available, chromatography quality reagents (of the series puriss p.a.) with a stated mole purity > 99.3 %. The purity of all reagents was

2,2,4-trimethylpentane and the corresponding binary systems at (298.15 and 313.15) K at atmospheric pressure are reported in this work. Excess molar enthalpies have been measured with a quasiisothermal flow calorimeter. The experimental data have been fitted using the Redlich−Kister rational polynomials.11 2857



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Table 3. Summary of Parameters for the Representation of HE by Equation 1, for Binary Systems DBE + 1-Propanol and Hydrocarbon + 1-Propanol at (298.15 and 313.15) K parameters

DBE (1) + 1-propanol (2)

1-hexene (1) + 1-propanol (2)

heptane (1) + 1-propanol (2)

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

A0 A1 A2 A3 A4 A5 AAD (|ΔHE|/HE)/% rms ΔHE/(J·mol −1) max |ΔHE|/(J·mol −1) max (100|ΔHE|/HE)/%

0 3618 1399 959.3 1330 961.2 0.48 2.9 4.0 2.5

−0.9680 2383 −623.3 −715.4 −104.8

−0.9736 2459 −1259 −170.1 −369.2 121.0 0.13 0.7 1.2 0.9

−0.9672 2409 −1086 −310.4 −291.5 163.2 0.15 0.7 1.0 0.8

A0 A1 A2 A3 A4 A5 AAD (|ΔHE|/HE)/% rms ΔHE/(J·mol −1) max |ΔHE|/(J·mol −1) max (100|ΔHE|/HE)/%

0 4083 1488 1086 1254 730.0 0.22 1.7 2.8 1.3

−0.9476 3258 −1052 −744.9

−0.9654 3276 −1674 −192.6 −259.8

0.09 0.5 1.0 0.6

0.17 1.0 2.1 0.9

−0.9317 3269 −1444 −376.0 −157.9 340.1 0.13 0.8 1.5 0.8

T = 298.15 K

0.26 1.0 1.7 1.8 T = 313.15 K

Figure 2. Experimental excess molar enthalpies of hydrocarbon + alcohol. At T = 298.15 K: open squares, 1-hexene (1) + 1-propanol (2); open triangles, heptane (1) + 1-propanol (2); open circles, 2,2,4trimethylpentane (1) + 1-propanol (2). At T = 313.15 K: filled squares, 1-hexene (1) + 1-propanol (2); filled triangles, heptane (1) + 1-propanol (2); filled circles, 2,2,4-trimethylpentane (1) + 1-propanol (2). Lines, calculated values with eq 1, using parameters of Table 2 for hydrocarbon + 1-propanol.

Figure 1. Experimental excess molar enthalpies of DBE + alcohol. At T = 298.15 K: open squares, DBE (1) + 1-propanol (2); open triangles, DBE (1) + 1-butanol (2). At T = 313.15 K: filled squares, DBE (1) + 1-propanol (2); filled triangles, DBE (1) + 1-butanol (2). lines, calculated values with eq 1, using parameters of Table 2 for DBE + 1-propanol and parameters taken from ref 5 for DBE + 1-butanol.

checked by gas chromatography, and their values are presented in Table 1. Excess molar enthalpies (HE) have been measured with a quasi-isothermal flow calorimeter previously described.3 The calorimeter consists of two precision positive displacement pumps (Agilent, model 1100) that deliver the liquids through stainless-steel tubing at programmable constant flow rates into the mixing coil sitting in the flow cell, which is included in the measurement unit. The temperature of pure liquids is measured by a calibrated standard PRT-100 inserted in the pump body, using as an indicator a resistance bridge (ASL model F250) resolving 1 mK in the reading of temperature and estimating an overall uncertainty of ± 10 mK. Flow rates were calibrated by

means of a weighing method. The flow cell is immersed in a water bath (Hart Scientific, model 6020E) thermostated at the temperature at which the mixing process is taking place. The calorimeter is thermostated at T = (298.15 ± 0.01) K or at T = (313.15 ± 0.01) K. Isothermal calorimetry is based on measuring the energy required to maintain the mixing vessel at a constant temperature. The variation of temperature is detected by a control sensor, a NTC thermistor. The resistance is measured by a four-wire resistance bridge with a microohm meter from Hewlett-Packard, model HP-34420A. The uncertainty in the measure of temperature is estimated to be less than 0.05 K. The 2858



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HE is calculated from differences in the heating power control, once the calibration procedure has been performed. Knowing the volumetric flow rates delivered, the molar masses and the densities of the pure compounds and the mole fractions of the mixtures obtained in the mixing coil can be calculated. The calculated maximum uncertainty of mole fraction is ± 0.0008 at equimolar composition. Densities of pure liquids at the measured temperature of delivery are corrected by interpolating density data obtained from Riddick et al.12 Estimated densities at T = 298.15 K, were (0.7642, 0.7996, 0.6685, 0.6795, and 0.6878) g·cm−3 for DBE, 1-propanol, 1-hexene, heptane and 2,2,4-trimethylpentane, respectively. These results agree within < 0.1 % with values found in the literature.13−20 Mixtures of different compositions are studied, and in this way the dependence of HE on mole fraction can be determined. The expanded uncertainty for the excess enthalpies HE is 10 J·mol−1.

Table 4. Comparison of Literature Data and Our Correlation for Excess Enthalpy of DBE + 1-Propanol and Hydrocarbon + 1-Propanol Mixtures at (298.15 and 313.15) K at Atmospheric Pressurea ref

year

NP

T/K

AAD/%

DBE + 1-Propanol 1982 28 298.15 9.5 Villamañań et al.22 Jiménez et al.23 1997 13 298.15 1.1 Segade at al.24 1999 13 298.15 1.1 Mozo et al.25 2010 21 298.15 3.7 1-Hexene + 1-Propanol Letcher et al.26 1993 16 298.15 11.2 Heptane + 1-Propanol Oswald et al.27 1986 13 298.15 2.7 López et al.28 1993 18 298.15 1.7 2,2,4-Trimethylpentane + 1-Propanol Wang et al.29 1992 19 298.15 4.4 Bich et al.30 1999 21 298.15 3.9 Bich et al.30 1999 22 313.15 1.5

3. RESULTS AND DISCUSSION The experimental excess molar enthalpies obtained in this work for the binary mixtures DBE + 1-propanol, 1-hexene + 1-propanol, heptane + 1-propanol, and 2,2,4-trimethylpentane + 1-propanol at (298.15 and 313.15) K at atmospheric pressure are listed in Table 2. For binary systems, there exist several empirical equations and models proposed to fit the HE measurements. One of them, the Redlich−Kister equation, is given by eq 1, in which the Ai coefficients are determined by the unweighted least-squares method.

ref uncertainty 1 1 1 1

% % % %

3 J·mol−1 2% 1% 0.5 % 1.5 % 1.5 %

a

NP corresponds to the number of data points in the composition range.

n

E

−1

H /(J·mol ) =

x1x 2 ∑i = 1 Ai (x1 − x 2)i − 1 1 + A 0(x1 − x 2)

(1)

Results of data correlation for the binary systems at (298.15 and 313.15) K are summarized in Table 3. For the purpose of comparing the experimental excess enthalpy values with those obtained by eq 1, we have used the absolute average deviation, AAD, root-mean-square deviation, rms, the maximum absolute deviation, max |ΔHE|, and the maximum relative deviation, max(|ΔHE|/HE), which are defined as follows: AAD =

100 ndat

ndat

∑ i=1

Figure 3. Comparison of literature data and our correlation (eq 1 and parameters of Table 3) for excess enthalpy of DBE + 1-propanol and hydrocarbon + 1-propanol mixtures at atmospheric pressure. At 298.15 K: DBE + 1-propanol (open squares, Villamañań et al.;22 open triangles, Jiménez et al.;23 open circles, Segade et al.;24 black filled squares, Mozo et al.25); 1-hexene + 1-propanol (black filled triangles, Letcher et al.26); heptane + 1-propanol (black filled circles, Oswald et al.;27 plus signs, López et al.28); 2,2,4 trimethylpentane + 1-propanol (asterisks, Wang et al.;29 gray filled squares, Bich et al.30). At 313.15 K: 2,2,4 trimethylpentane + 1-propanol (gray filled triangles, Bich et al.30).

E E − Hcal Hexp E Hexp

(2)

⎡ ∑ndat (H E − H E )2 ⎤1/2 exp cal i ⎥ rms = ⎢ ⎢⎣ ⎥⎦ ndat − n par

(3)

E E max|ΔHE| = max|Hexp − Hcal |

(4)

E E ⎞ ⎛ |Hexp − Hcal | ⎟ max(|ΔHE| /HE) = max⎜⎜100 ⎟ E Hexp ⎝ ⎠

(5)

All of the binary systems DBE + 1-propanol and hydrocarbon + 1-propanol show endothermic behavior in the whole range of composition. The maximum endothermic character of the system DBE + 1-propanol is shown at x = 0.60, with experimental values of HE = (951 and 1066) J·mol−1 at T = (298.15 and 313.15) K, respectively. The binary mixture DBE + 1-propanol contains one strong self-associating component (1-propanol) and a non-self-associating component (DBE) which, however, can form associates with the alkanol through hydrogen bonding. The HE curves are skewed toward low mole fractions of alcohol, reflecting its strong self-association character. In this case, the chemical contribution dominates the excess property. The endothermic behavior of the mixture is explained by the greater positive contribution of the destruction of alkanol−alkanol hydrogen bonds upon mixing with respect to the negative term due to the formation of alkanol−-ether complexes. With the increase of the temperature,

where HEexp, HEcal, ndat, and npar are the values of the experimental and calculated excess molar enthalpies, the number of experimental data, and the number of parameters of the model, respectively. The degree of the polynomial expansion of eq 1 was optimized using the F-test.21 It must be pointed out that the AAD is well under experimental uncertainty for all of the binary systems. A plot of the experimental and correlated data of DBE + 1-propanol with eq 1 is shown in Figure 1, while Figure 2 shows the same for the systems hydrocarbon + 1-propanol. 2859



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Table 5. Experimental Excess Molar Enthalpies HE2+13 at 298.15 K at Atmospheric Pressurea for the Addition of Hydrocarbon (1-Hexene, or Heptane, or 2,2,4- Trimethylpentane) to (DBE (1) + 1-Propanol (3)) To Form x1DBE + x2Hydrocarbon + (1 − x1 − x2)1-Propanol, and Values of HE123 Calculated from Equation 6, Using the Smooth Representation of HE13 by Redlich−Kister Equation 1 with Parameters Given in Table 3 HE2+13 x2

0.9498 0.8996 0.8506 0.8005 0.7006 0.6006 0.9502 0.8998 0.8498 0.7993 0.7000 0.5995 0.9504 0.8996 0.8504 0.8000 0.7004 0.5999 0.9496 0.8999 0.8501 0.8002 0.7001 0.6000

0.9003 0.8007 0.6996 0.6004 0.5005 0.4000 0.8995 0.7999 0.7005 0.6004 0.5001 0.4001 a

J·mol

−1

HE123 J·mol

−1

HE2+13 x2

−1

J·mol

DBE + 1-Hexene +1-Propanol x1/x3 = 0.2499; HE13/(J·mol−1) = 474 370 393 0.4997 472 467 514 0.4005 398 512 583 0.3006 309 542 636 0.2004 210 555 697 0.1006 106 529 719 x1/x3 = 0.6667; HE13/(J·mol−1) = 808 301 342 0.4992 351 378 459 0.4001 295 410 532 0.3001 228 425 587 0.1995 155 424 666 0.1001 78 397 720 x1/x3 = 1.5005; HE13/(J·mol−1) = 948 225 272 0.5004 249 290 385 0.3999 207 313 455 0.3004 159 320 510 0.1999 108 312 595 0.1005 54 286 665 x1/x3 = 4.0052; HE13/(J·mol−1) = 834 122 164 0.5000 147 174 258 0.4005 120 194 319 0.3004 90 199 366 0.2000 60 191 441 0.1006 30 172 505 DBE + Heptane + 1-Propanol x1/x3 = 0.2502; HE13/(J·mol−1) = 474 425 472 0.3002 389 517 612 0.2004 286 555 697 0.1503 225 554 744 0.0998 157 524 761 0.0499 82 468 752 x1/x3 = 0.6667; HE13/(J·mol−1) = 808 365 446 0.3006 324 435 596 0.2003 238 461 703 0.1501 187 460 783 0.1005 131 436 840 0.0499 68 389 874

HE123

HE2+13

−1

x2

J·mol

−1

J·mol

HE123 −1

J·mol

HE2+13 x2

−1

J·mol

HE123 J·mol−1

HE13/(J·mol−1)

709 682 640 589 532

0.9501 0.8996 0.8496 0.8001 0.6996 0.6001

756 780 793 802 805

0.9503 0.9004 0.8504 0.8002 0.7005 0.6003

723 775 822 866 907

0.9004 0.8002 0.7007 0.6004 0.4999

564 620 674 727 780

0.9006 0.8008 0.7000 0.6004 0.5002 0.4004 0.9004 0.8001 0.7005 0.5998 0.5004 0.4005

720 665 628 584 532

0.9000 0.7996 0.7000 0.6001 0.5000 0.3997

889 884 874 858 835

x1/x3 = 1.5304; = 948 233 280 0.4998 350 298 393 0.3996 313 332 474 0.2997 259 353 543 0.2001 190 373 658 0.0999 103 371 750 x1/x3 = 4.0000; HE13/(J-mol1) = 834 156 197 0.5006 276 217 300 0.4003 247 250 375 0.3006 205 271 438 0.2003 149 291 541 0.1004 82 292 625 DBE + 2,2,4-Trimethylpentane +1-Propanol x1/x3 = 0.2500; HE13/(J·mol−1) = 474 437 484 0.4007 456 522 617 0.3005 375 554 696 0.2001 273 550 739 0.1001 149 515 752 x1/x3 = 0.6667; HE13/(J·mol−1) = 808 373 454 0.2999 313 439 600 0.2005 229 460 702 0.1503 179 454 777 0.0999 124 427 831 0.0503 65 380 864 x1/x3 = 1.5000; HE13/(J·mol−1) = 948 308 402 0.3002 257 362 551 0.2002 188 377 661 0.1498 147 372 751 0.0998 102 350 823 0.0501 53 311 880 x1/x3 = 4.0025; HE13/(J·mol−1) = 834 221 304 0.3004 202 274 441 0.2000 147 292 542 0.1500 115 289 622 0.1005 80 273 690 0.0505 41 244 745

825 882 923 948 957

693 748 788 817 832

740 706 652 576

879 875 866 852 833

920 946 953 955 953

786 815 824 830 833


values of experimental HE = (690 and 919) J·mol−1 (at x = 0.7) at T = (298.15 and 313.15) K, respectively. The binary systems heptane + 1-propanol and 2,2,4-trimethylpentane + 1-propanol present very similar values of HE. The maximum experimental values for heptane + 1-propanol are (661 and 881) J·mol−1 (at x = 0.65), at (298.15 and at 313.15) K, respectively. The maximum HE for the mixture 2,2,4-trimethylpentane + 1-propanol occurs also at x = 0.65, being the experimental values (656 and 883) J·mol−1 at (298.15 and at 313.15) K. For

the alkanol−alkanol hydrogen bonds are weakened and its destruction rate upon mixing increases, therefore the endothermic character of the mixture is more pronounced, as shown in Figure 1. Comparison of these values with those reported for the system DBE + 1-butanol5 at the same temperatures show that the mixing effect decreases as the length of the alcohol chain increases. Concerning the hydrocarbons, the maximum endothermic character is shown by the mixture 1-hexene + 1-propanol with 2860



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Table 6. Experimental Excess Molar Enthalpies HE2+13 at 313.15 K at Atmospheric Pressurea for the Addition of Hydrocarbon (1-Hexene, or Heptane, or 2,2,4-Trimethylpentane) to (DBE (1) + 1-Propanol (3)) To Form x1DBE + x2Hydrocarbon + (1 − x1 − x2)1-Propanol, and Values of HE123 Calculated from Equation 6, Using the Smooth Representation of HE13 by Redlich−Kister Equation 1 with Parameters Given in Table 3 HE2+13 x2

0.9498 0.8997 0.8507 0.8006 0.7007 0.6007 0.9502 0.8998 0.8499 0.8005 0.7000 0.5997 0.9504 0.8996 0.8505 0.8000 0.7004 0.5998 0.9496 0.9000 0.8499 0.7001 0.5999 0.5000

0.9508 0.9004 0.8503 0.8008 0.7010 0.6016 0.9498 0.8994 0.8503 0.7999 0.7005 0.6003 a

J·mol

−1

HE123 J·mol

−1

HE2+13 x2

−1

J·mol

DBE + 1-Hexene +1-Propanol x1/x3 = 0.2500; HE13/(J·mol−1) = 545 466 494 0.4998 641 610 665 0.4006 543 680 761 0.3006 426 719 827 0.2004 292 741 904 0.1005 149 710 928 x1/x3 = 0.6667; HE13/(J·mol−1) = 917 369 415 0.5004 484 492 583 0.4001 408 546 683 0.3001 319 570 753 0.2004 219 575 850 0.1001 111 541 908 x1/x3 = 1.5003; HE13/(J·mol−1) = 1065 257 310 0.5003 343 364 471 0.3998 286 407 566 0.3003 221 424 637 0.1999 150 420 739 0.1004 77 389 815 x1/x3 = 4.0036; HE13/(J·mol−1) = 917 125 171 0.5000 198 196 288 0.4003 163 232 369 0.3003 125 246 521 0.1999 84 228 595 0.1006 42 198 656 DBE + Heptane +1-Propanol x1/x3 = 0.2501; HE13/(J·mol−1) = 544 446 473 0.5016 683 576 631 0.4011 605 648 729 0.3011 499 694 802 0.2012 364 735 897 0.1006 198 727 944 x1/x3 = 0.6674; HE13/(J·mol−1) = 915 377 423 0.5000 556 490 582 0.4001 492 544 681 0.3006 405 579 762 0.2002 294 604 879 0.1005 159 594 960

HE123

HE2+13

−1

x2

J·mol

−1

J·mol

HE123 −1

J·mol

HE2+13 x2

−1

J·mol

HE123 J·mol−1

HE13/(J·mol−1)

914 870 807 728 639

0.9501 0.8996 0.8495 0.8001 0.6995 0.6000

942 958 960 952 936

0.9503 0.9004 0.8503 0.8001 0.7004 0.6001

875 925 966 1002 1034

0.9499 0.9003 0.8498 0.8000 0.7004 0.6001

656 713 766 818 867

0.9495 0.9005 0.8504 0.8006 0.6999 0.6002 0.9502 0.9003 0.7999 0.7003 0.5995 0.5001

954 931 879 799 688

0.9497 0.9000 0.8495 0.7995 0.6998 0.5999 0.4998

1014 1041 1046 1026 982

x1/x3 = 1.4997; = 1063 288 341 0.4997 442 392 498 0.3995 389 439 599 0.2996 319 466 679 0.2000 231 485 805 0.0998 124 475 900 x1/x3 = 4.0032; HE13/(J·mol−1) = 916 165 211 0.5004 327 254 346 0.4002 289 302 439 0.3004 237 330 513 0.2002 171 352 626 0.1004 91 348 715 DBE + 2,2,4-Trimethylpentane +1 -Propanol x1/x3 = 0.2500; HE13/(J·mol−1) = 544 462 489 0.5007 680 591 645 0.4003 599 662 743 0.3003 490 703 812 0.1999 354 738 901 0.1001 191 728 946 x1/x3 = 0.6666; HE13/(J·mol−1) = 915 389 435 0.5001 555 505 596 0.4003 489 556 693 0.2998 399 588 770 0.2005 289 611 885 0.0999 156 597 963 x1/x3 = 1.4992; HE13/(J·mol−1) = 1063 293 346 0.4001 389 401 507 0.3000 318 474 687 0.2001 229 491 809 0.0996 123 478 903 0.0500 64 443 974 x1/x3 = 4.0000; HE13/(J·mol−1) = 916 166 212 0.3995 288 257 349 0.3001 237 305 443 0.1998 170 334 517 0.1498 133 355 630 0.1004 92 350 716 0.0504 47 326 785

973 1027 1063 1081 1080

784 838 878 903 915

951 925 870 789 681

1012 1037 1040 1021 979

1026 1062 1080 1080 1073

838 878 903 911 916 917


our binary mixtures hydrocarbon + 1-propanol, the HE curves are skewed toward low mole fractions of alcohol, reflecting again its strong self-association character. The chemical forces of the hydrogen bonds in the alkanol are stronger than the dispersion forces of the hydrocarbon, and an endothermic character of the mixture is expected. Experimental HE data show that, for the given 1-propanol, HE(1-hexene) > HE(heptane, 2,2,4 trimethylpentane). This effect is enhanced by the increase of the temperature and by the weakness of the dispersion forces (Figure 2).

For the purpose of comparison, we have found some excess molar enthalpy data in the literature22−30 for the same binary systems at (298.15 and 313.15) K, as presented in Table 4 and Figure 3. We found that differences between experimental HE literature data and calculated HE data with our correlations at the same composition and temperature are less than 4.4 % in all cases, except for data from refs 22 and 26, where discrepancy reaches 9.5 % and 11.2 %, respectively. When considering only data in the central range of composition (x = 0.2 to 0.8), the 2861



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Table 7. Summary of the Data Reduction Results Obtained for the Ternary Systems DBE (1) + Hydrocarbon (2) + 1Propanol (3) at (298.15 and 313.15) K Using Equations 7 and 8 correlation B0 B1 B2 B3 B4 B5 B6 B7 AAD (|ΔHE|/HE)/% rms/(J·mol −1) max |ΔHE|/(J·mol −1) max (100|ΔHE|/HE)/% B0 B1 B2 B3 B4 B5 B6 B7 AAD (|ΔHE|/HE)/% rms/(J·mol −1) max |ΔHE|/(J-mol −1) max (100|ΔHE|/HE)/%

1-hexene (2)

heptane (2)

T = 298.15 K 9740.74 8323.14 −34273.3 −25946.4 −9180.54 −2815.74 1937.08 −9071.58 −92193.2 −100834 113059 104765 40441.5 45720.1 139324 146150 4.7 4.6 27.5 30.3 62.1 71.6 23.9 28.2 T = 313.15 K 9444.95 9630.77 −31452.7 −31649.2 −12862.6 −3636.33 −1016.89 −9233.74 −80674.8 −115430 114467 121144 41532.8 51134.2 133297 166600 3.2 3.9 23.4 30.0 52.8 65.6 16.3 18.8

2,2,4-trimethylpentane (2) 11985.2 −36747.4 −22494.3 13623.9 −54102.3 110091 29074.4 108763 3.1 25.9 76.0 25.0 10447.2 −30644.8 −12822.0 −7874.17 −91743.4 118783 48900.1 149409 3.9 30.6 66.0 18.9

same comparison with refs 22 and 26 leads to differences of 5.0 % and 4.3 % for these references. Except for the reference of Bich et al.30 for the system 2,2,4-trimethylpentane + 1-propanol, no data at 313.15 K were found for comparison. From Figure 3 it can be observed that high deviations are only found at very diluted compositions. The ternary mixtures DBE (1) + hydrocarbon (2) + 1-propanol (3) were formed by adding the hydrocarbon (2) to binary mixtures of fixed composition of DBE (1) + 1-propanol (3). Four different starting binaries were used, with values of the ratio x1/x3 close to 0.2500, 0.6666, 1.5000, and 4.0000, respectively. The experimental excess molar enthalpies obtained in this work for the ternary mixtures DBE + hydrocarbon + 1-propanol at (298.15 and 313.15) K at atmospheric pressure are listed in Table 5 and Table 6, respectively. No data for the same ternary systems at the same temperatures were found in the literature for comparison. The experimental excess molar enthalpies are determined by eq 6, using the smooth representation of HE13 by Redlich−Kister, eq 1: E E H123 = H2E+ 13 + (1 − x 2)H13

Figure 4. Contours for constant values of HE123 for (a) DBE(1) + 1hexene (2) + 1-propanol (3) and (b) DBE(1) + heptane (2) + 1propanol (3) at 298.15 K: plus sign, maximum value of HE.

where the parameters Bi were determined by the unweighted leastsquares method. Results of data correlation for the reported ternary systems are summarized in Table 7. Correlation data for HE12 of the mixtures DBE (1) + hydrocarbon (2) were taken from our previous works.8 Concerning the first measured ternary system, DBE (1) + 1-hexene (2) + 1-propanol (3) at 298.15 K, rms is 27.5 J·mol−1 and the AAD is 4.7 %. This system shows an endothermic behavior in the experimental compositions measured. The maximum experimental value of HE is 948 J·mol−1. When temperature is increased to 313.15 K, the maximum experimental value of HE reaches 1065 J·mol−1, the rootmean-square deviation is 23.4 J·mol−1, and AAD is 3.2 %. The ternary mixtures DBE (1) + heptane (2) + 1-propanol (3) also show an endothermic behavior. The root-mean-square deviation is 30.3 J·mol−1 at 298.15 K, and 30.0 J·mol−1 at 313.15 K, while the AAD are 4.6 % and 3.9 % for the respective temperatures. The maximum experimental values of HE are 957 J·mol−1 at 298.15 K and 1081 J·mol−1 at 313.15 K. With respect to the ternary system, DBE (1) + 2,2,4-trimethylpentane (2) + 1-propanol (3) at (298.15 and 313.15) K, the rootmean-square deviations are (25.9 and 30.6) J·mol−1, respectively, while AAD are 3.1 % and 3.9 %, presenting also an endothermic behavior in the whole range of composition. The maximum

(6)

The following equation was used to fit the ternary H E measurements E E E E E H123 = H12 + H13 + H23 + x1x 2x3ΔH123

(7)

with E ΔH123 = B0 + B1x1 + B2 x 2 + B3x12 + B4 x 2 2 + B5x1x 2

+ B6 x13 + B7 x 2 3

(8) 2862



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Table 8. Summary of the Maximum Values of the Experimental Excess Enthalpy, HE, and Its Respective Mole Fraction, Obtained for the Ternary Systems DBE (1) + Hydrocarbon (2) + 1-Propanol (3), or + 1-Butanol (3) at (298.15 and 313.15) K ternary system

DBE (1) + hydrocarbon (2) + 1-propanol (3)

hydrocarbon

a

1-hexene (2)

max HE/(J·mol x1 x2 x3

−1

max HE/(J·mol x1 x2 x3

−1

)

)

heptane (2)

948 0.6001 0.0000 0.3999

957 0.5444 0.0999 0.3557

1065 0.6000 0.0000 0.4000

1081 0.4800 0.2000 0.3200

DBE (1) + hydrocarbon (2) + 1-butanol (3)

2,2,4-trimethylpentane (2) T = 298.15 K 955 0.5401 0.0998 0.3601 T = 313.15 K 1080 0.5401 0.0996 0.3603

1-hexene (2)

heptane (2)

2,2,4-trimethylpentane (2)

895a 0.6000 0.0000 0.4000

895b 0.5395 0.1014 0.3591

893c 0.5401 0.0998 0.3601

1046a 0.6000 0.0000 0.4000

1054b 0.5398 0.1005 0.3597

1050a 0.4800 0.2000 0.3200

Data taken from ref 9. bData taken from ref 7. cData taken from ref 6.

experimental values of HE are 955 J·mol−1 at 298.15 K and 1080 J·mol−1 at 313.15 K. As an illustration, contours for constant calculated values of HE123 for DBE (1) + 1-hexene (2) + 1-propanol (3) and DBE (1) + heptane (2) + 1-propanol (3) at 298.15 K obtained with eqs 7 and 8 are presented in Figure 4. In this figure, every vertex corresponds to the pure compounds and the sides of the triangle correspond to the binary systems formed by the compounds placed at the respective vertex. To find the composition of any point in the diagram, parallel lines to the sides of the triangle should be drawn, as illustrated in Figure 4b. When adding the hydrocarbon to the ether + alkanol mixtures, it could be expected that the positive contribution to HE associated with the disruption of interaction between like molecules, in connection with the negative contribution due to the creation of interaction between unlike molecules, should explain the endothermic or exothermic character of the mixture. In the case of DBE (1) + 1-hexene (2) + 1-propanol (3) mixtures, the addition of the 1-hexene decreases the endothermic effect of the ether + alkanol mixture, as the maximum excess enthalpy HE is obtained when x2 = 0, as seen in Figure 4a for the temperature 298.15 K. This effect is probably due to rather strong interactions between the double bond of 1-hexene and the oxygenated complex of DBE + 1-propanol, which largely compensate for the endothermic effects due to DBE + 1-propanol and 1-hexene upon mixing. With respect to the addition of the linear or branched alkanes (heptane or 2,2,4-trimethylpentane), data from Tables 5, 6, and 8 present the expected endothermic behavior due to the creation of interaction between unlike molecules. For example, the maximum calculated value of HE at for the system DBE (1) + heptane (2) + 1-propanol (3) at 298.15 K and 960 J·mol−1 is given at x1 = 0.460, x2 = 0.230, and x3 = 0.310, as shown in Figure 4b. Results show that the endothermic character of the mixture is almost the same for the linear hydrocarbon heptane with respect to a branched hydrocarbon such as 2,2,4-trimethylpentane. For all of the ternary systems, the endothermic effect is enhanced by the increase of the temperature and by the weakness of the dispersion forces. Comparison with data of ternary mixtures DBE (1) + hydrocarbon (2) + 1-butanol (3) at the same temperatures, as presented in Table 8, show that the mixing effect decreases as the length of the alcohol chain decreases.

tane at atmospheric pressure at T = (298.15 and 313.15) K were determined using an isothermal flow calorimeter. All of the binary systems DBE + 1-propanol and hydrocarbon + 1propanol mixtures show endothermic effect and strong asymmetric HE behavior at the measured temperatures, being higher than the endothermic effect for 1-hexene + 1-propanol mixtures at both temperatures. All of the ternary systems show positive HE values at the measured temperatures. The addition of the 1-hexene decreases the endothermic effect of the ether + alkanol mixture. When referred to linear or branched alkanes, the endothermic character of the mixture is almost the same for the linear hydrocarbon heptane with respect to a branched hydrocarbon such as 2,2,4-trimethylpentane. For all of the ternary systems, the endothermic effect is enhanced by the increase of the temperature. Intermolecular and association effects involved in these systems have been discussed. The measured excess molar enthalpies data were well-correlated with a rational equation.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +34 947258916. Fax: +34 947258910. Funding

Support for this work came from the Ministerio de Ciencia e Innovación, Spain, Project ENE2009-14644-C02-02, and from the Ministerio de Asuntos Exteriores y Cooperación, Spain, Agencia Española de Cooperación Internacional para el Desarrollo AECID, Project AP/041072/11. Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS This paper is part of the Doctoral Thesis of F.E.M.A. REFERENCES

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4. CONCLUSION Isothermal excess molar enthalpies for the ternary systems DBE + 1-propanol and 1-hexene, or heptane, or 2,2,4-trimethylpen2863



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Oxygenated Compounds + Hydrocarbon Mixtures in Fuels and Biofuels

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