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J. Chem. Eng. Data 2000, 45, 48-52
Excess Enthalpies of 2,2,4-Trimethylpentane + Hexane + (Octane or Dodecane) at 298.15 K Ding-Yu Peng,† George C. Benson,* and Benjamin C.-Y. Lu Department of Chemical Engineering, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
Microcalorimetric measurements of excess molar enthalpies, measured at 298.15 K, are reported for the ternary systems 2,2,4-trimethylpentane (1) + hexane (2) + octane (3) and 2,2,4-trimethylpentane (1) + hexane (2) + dodecane (3). Smooth representations of the results are described and used to construct constant-enthalpy contours on Roozeboom diagrams. It is shown that the Flory theory provides a reasonable correlation of the results.
Introduction Methyl tert-butyl ether (MTBE) is widely used as a gasoline additive to enhance the octane rating and to reduce pollution effects. However, there have been some concerns of potential adverse health risks associated with MTBE, and a recent study in California suggested that use of MTBE should be phased out of all gasoline sold in that state. Accordingly, investigation of the thermodynamic properties of hydrocarbon mixtures involving other gasoline additives is of relevance. The present paper reports excess molar enthalpies, measured at 298.15 K, for ternary mixtures comprised of the alkylate 2,2,4-trimethylpentane (TMP), normal hexane (nC6), and either normal octane (nC8) or normal dodecane (nC12). Experimental Section The TMP (HPLC Grade), nC6, and nC8 were obtained from Sigma-Aldrich; the dodecane (Pure Grade) was obtained from the Phillips Chemical Co. In all cases, the purities stated by the manufacturers exceeded 99 mol %. Apart from partial degassing, all of the components were used without further purification. The densities, F/kg‚m-3, measured at 298.15 K in an Anton-Paar digital densimeter, were 687.90, 655.46, 698.69, and 745.34, for TMP, nC6, nC8, and nC12, respectively. These values are in reasonable agreement with values in the literature (TRC, 1988). Excess molar enthalpies, H Em, were measured in an LKB-Produkter AB (Bromma, Sweden) flow microcalorimeter (Model 10700-1), thermostated at 298.15 K, maintained within (0.003 K. Details of the equipment and its operation have been described previously (Tanaka et al., 1975; Kimura et al., 1983). In studying the ternary systems, E was determined for the excess molar enthalpy H m,1+23 several pseudobinary mixtures in which component 1 (TMP) was added to binary mixtures of components 2 (nC6) and 3 (either nC8 or nC12). For this purpose, binaries with fixed mole ratios x2/x3 were prepared by mass. The excess E molar enthalpy H m,123 of the ternary mixture was then obtained from the relation E E E ) H m,1+23 + (1 - x1)H m,23 H m,123
(1)
E where x1 is the mole fraction of TMP and H m,23 is the †
Visiting professor from the Department of Chemical Engineering, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5C9.
Table 1. Experimental Mole Fractions x1 and Excess E for TMP (1) + nC12 (3) at Molar Enthalpies H m,13 298.15 K x1
E H m,13 / J‚mol-1
x1
E H m,13 / J‚mol-1
0.0500 0.1001 0.1500 0.2001 0.2499 0.3003 0.3498 0.3998 0.4499 0.4998
20.51 39.77 57.18 73.84 87.24 98.12 106.11 111.26 115.57 117.51
0.5502 0.5997 0.6502 0.7001 0.7501 0.8001 0.8506 0.9000 0.9500
117.94 114.96 109.12 101.47 91.00 77.80 61.14 43.45 21.65
Table 2. Coefficients hk and Standard Deviations s for E the Representation of H m,ij (i < j) by Eq 2 for the Constituent-Binary Mixtures at 298.15 K component i
j
TMP TMP TMP nC6 nC6
nC12 nC6a nC8b nC8c nC12d
d
h1
h2
h3
h4
h5
470.62 -24.85 39.15 6.66 -89.15 -44.61 16.65 1.97 102.1 7.353 2.770 -0.539 156.22 14.58 -11.12
s/J‚mol-1 0.48 0.12 0.1 0.021 0.10
a Lam et al. (1974). b Lundberg (1964). c Hamam et al. (1984a). Hamam et al. (1984b).
excess molar enthalpy of the particular binary mixture. Over most of the mole fraction range, the errors of the excess molar enthalpies and the mole fractions of the final mixtures are estimated to be
