IUPAC-NIST Solubility Database
NIST Standard Reference Database 106

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 Solubility System: Ethanol with 2,2,4-Trimethylpentane (isooctane) and Water

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Components:
   (1) Water; H2O; [7732-18-5]  NIST Chemistry WebBook for detail
   (2) 2,2,4-Trimethylpentane (isooctane); C8H18; [540-84-1]  NIST Chemistry WebBook for detail
   (3) Ethanol (ethyl alcohol); C2H6O; [64-17-5]  NIST Chemistry WebBook for detail

Evaluator:
   A. Skrzecz, Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland (1996.05)

Critical Evaluation:

      A survey of reported compositions along the saturation curve (sat), and compositions of coexisting phases in equilibrium (eq.) for the system ethanol-2,2,4-trimethylpentane-water is given in Table 37.

Saturation Curve    The system ethanol-2,2,4-trimethylpentane-water forms a miscibility gap of type 1. Experimental points on the saturation curve were reported by Kretschner and Wiebe¹ and Nowakowska et al.² In both references the saturation curves were obtained by the titration method. In Ref. 1 the experimental results at 228, 273, and 298 K were expressed as the water tolerance of the alcohol-hydrocarbon mixture. The binary 2,2,4-trimethylpentane-water system is only partially miscible. The data for this system were compiled and critically evaluated in a previously published SDS volume,⁴ the binary solubility data were not reported together with ternary data in any of the references. The “best” (Ref.4) values of mutual solubility at 293 and 298 K are x"₂=3·10^–7, x'₂=0.9995 and x"₂=3.5·10^–7, x'₂=0.9994, respectively. Compositions of coexisting phases in equilibrium at 273 and 298 K (Refs. 2 and 3) were included and also used for data comparison on saturation curves. All data sets are consistent with one another. The temperature relationship of miscibility gap, (Refs. 1 and 2) is as expected one. At higher temperatures smaller miscibility gaps are found. The water-rich phase with low concentrations of ethanol (x₁<0.20), Ref. 2, was reported to be 2,2,4-trimethylpentane free, presumably due to the analytical methods used. The maximum ethanol concentration is observed on the saturation curve. At 298.2 K it reaches x₁0.71±0.01 when x₂0.10±0.02 mole fraction. All experimental solubility and equilibrium data reported at 298.2 K were used for calculation of the saturation curve (Water-rich and hydrocarbon-rich branches were treated together.) These data were described by the equation: x₁=1.021 78+0.104 50 ln(x₂)–1.018 38x₂.    The parameters were calculated by the least-squares method and the standard error estimate was 0.0243. This equation describes the saturation curve for x₂<0.95 mole fraction. The points on the saturation curve, calculated by the above equation together with the “best” values from Ref. 4 are presented in Table 38 for selected concentration of 2,2,4-trimethylpentane in the mixture and in Figure 19 as calculated binodal curve (solid line).

Phases in equilibrium    Compositions of coexisting phases in equilibrium for the ternary system ethanol-2,2,4-trimethylpentane-water were presented in Refs. 2 and 3 and the reported tie lines cover the whole range of the miscibility gap. They were obtained by various analytical methods: refractive indexes, Ref. 2, or by glc, Ref. 3. The direction of tie lines differ slightly. They may be treated as tentative. Experimental tie lines together with all experimental saturation points at 298.2 K are presented in Figure 19 .

Experimental Data:   (Notes on the Nomenclature)

TABLE 37. Summary of experimental data for the system ethanol-2,2,4-trimethylpentane-water

Author	T/K	DataType	Reference
Kretschmer and Wiebe, 1945	228-298	sat. (12)	1
Nowakowska et al., 1956	273-298	sat. (50), eq. (14)	2
Huber et al., 1972	298	eq. (6)	3

TABLE 38. Calculated compositions along the saturation curve at 298.2 K

T/K	Mole Fraction x1	Mole Fraction x2
298.2	0.0000	.00000035 Ref. 4
298.2	0.2989	0.0010
298.2	0.5303	0.0100
298.2	0.5926	0.0200
298.2	0.6447	0.0400
298.2	0.6667	0.0600
298.2	0.6764	0.0800
298.2	0.6793	0.1000
298.2	0.6780	0.1200
298.2	0.6737	0.1400
298.2	0.6673	0.1600
298.2	0.6593	0.1800
298.2	0.6499	0.2000
298.2	0.6395	0.2200
298.2	0.6282	0.2400
298.2	0.6162	0.2600
298.2	0.6036	0.2800
298.2	0.5904	0.3000
298.2	0.5768	0.3200
298.2	0.5628	0.3400
298.2	0.5484	0.3600
298.2	0.5337	0.3800
298.2	0.5187	0.4000
298.2	0.5034	0.4200
298.2	0.4879	0.4400
298.2	0.4722	0.4600
298.2	0.4563	0.4800
298.2	0.4402	0.5000
298.2	0.4239	0.5200
298.2	0.4075	0.5400
298.2	0.3909	0.5600
298.2	0.3742	0.5800
298.2	0.3574	0.6000
298.2	0.3404	0.6200
298.2	0.3234	0.6400
298.2	0.3062	0.6600
298.2	0.2890	0.6800
298.2	0.2716	0.7000
298.2	0.2542	0.7200
298.2	0.2367	0.7400
298.2	0.2191	0.7600
298.2	0.2015	0.7800
298.2	0.1838	0.8000
298.2	0.1660	0.8200
298.2	0.1481	0.8400
298.2	0.1302	0.8600
298.2	0.1122	0.8800
298.2	0.0942	0.9000
298.2	0.0762	0.9200
298.2	0.0580	0.9400
298.2	0.0535	0.9500
298.2	0.0000	0.9994

View Figure 1 for this Evaluation

Notes:
Table 37  Number of experimental points in parentheses.

References: (Click a link to see its experimental data associated with the reference)

   1  Kretschmer, C.B.; Wiebe, R., Ind. Eng. Chem. 37, 1130 (1945).
   2  Nowakowska, J.; Kretschmer, C.B.; Wiebe, R., J. Chem. Eng. Data Ser. 1, 42 (1956).
   3  Huber, J.F.K.; Meijers, C.A.M.; Hulsman, J.A.R., J. Anal. Chem. 44, 111 (1972).
   4  Shaw, D.G., ed., Solubility Data Series, Vol. 37, Hydrocarbons with Water and Seawater, Part I: Hydrocarbons C8 to C36 (Pergamon, New York, 1989).

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Last updated: February 18, 2015 (Created: August 17, 2007)