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J. Chem. Eng. Data 1999, 44, 1158-1162
Isobaric Vapor-Liquid Equilibrium in the Systems 2,3-Dimethylpentane + Methyl 1,1-Dimethylethyl Ether, + Diisopropyl Ether and + Methyl 1,1-Dimethylpropyl Ether Juan B. Monto´ n,* Javier de la Torre, M. C. Burguet, Rosa Mun ˜ oz, and Sonia Loras Departamento de Ingenierı´a Quı´mica, Facultad de Quı´mica, Universitat de Vale`ncia, 46100 Burjassot, Valencia, Spain
New, consistent vapor-liquid equilibrium data for the binary systems 2,3-dimethylpentane + methyl 1,1-dimethylethyl ether, + diisopropyl ether, and + methyl 1,1-dimethylpropyl ether are reported at 101.3 kPa. The measured systems deviate slightly from ideal behavior, and only the system methyl 1,1-dimethylpropyl ether + 2,3-dimethylpentane presents an azeotrope. The activity coefficients for the solutions were correlated with their compositions by the Wilson, UNIQUAC, and NRTL models. WisniakTamir equations were used to correlate the boiling points of the solutions with their compositions.
Introduction Environmental legislation around the world has forced the use of oxygenates for gasoline blending to phase out the lead additives and to reduce the reactive evaporative and exhaust emissions. Methyl 1,1-dimethylethyl ether (MTBE) is the primary oxygenated compound being used to reformulate gasolines to improve their octane rating and pollution-reducing capability. However, potential and documented contamination of water resources by MTBE has become a major public issue over the past few years and restrictions in its use as an additive are expected. MTBE readily dissolves in water, can move rapidly through soils and aquifers, is resistant to microbial decomposition, and is difficult to remove via water treatment. Finally, it is reported to have an unpleasant taste and odor in water. These factors have caused widespread concern that drinking water supplies and human health may be at risk, a situation which promotes further research with other branched ethers as potential additives. Diisopropyl ether (DIPE) and methyl 1,1-dimethylpropyl ether (TAME) show good characteristics as gasoline additives, including low volatility, low water solubility, high octane value, and large reductions in carbon monoxide and hydrocarbon emissions. Phase equilibrium data of hydrocarbon and oxygenated compound mixtures are important to predict the vaporphase composition that would be in equilibrium with reformulated gasolines, and the systems reported here constitute examples of such mixtures. The present work was undertaken to measure vapor-liquid equilibrium (VLE) data of the 2,3-dimethylpentane + methyl 1,1dimethylethyl ether, + diisopropyl ether, and + methyl 1,1dimethylpropyl ether binary systems at 101.3 kPa, for which no data have been previously reported. Experimental Section Chemicals. 2,3-Dimethylpentane (99+ mass %), MTBE (99.8+ mass %, HPLC grade), DIPE (99 mass %), and TAME (97 mass %) were purchased from Aldrich Ltd. 2,3Dimethylpentane, MTBE, and DIPE were used without * Corresponding author. E-mail:
[email protected].
further purification after chromatography failed to show any significant impurities. TAME was purified to 99.9+ mass % by batch distillation in a Fisher SPALTROHR column HMS-500, controlled by a Fisher System D301-C. The densities and refractive indexes of the pure liquids were measured at 298.15 K using an Anton Paar DMA 55 densimeter and an Abbe refractometer Atago 3T, respectively. Temperature was controlled to (0.01 K with a thermostated bath. The accuracies in density and refractive index measurements are (0.01 kg‚m-3 and (0.0002, respectively. The experimental values of these properties and the boiling points are given in Table 1 together with those given in the literature. Appropriate precautions were taken when handling ethers in order to avoid peroxide formation. Apparatus and Procedure The equilibrium vessel was an all-glass, dynamicrecirculating still equipped with a Cottrell circulation pump. General details of the experimental equipment and procedure appear in Walas (1985). The still (Labodest model), manufactured by Fischer Labor und Verfahrenstechnik (Germany), is capable of handling pressures from 0.25 to 400 kPa and temperatures up to 523 K. The Cottrell pump ensures that both liquid and vapor phases are in intimate contact during boiling and also in contact with the temperature-sensing element. The equilibrium temperature was measured with a digital Fischer thermometer with an accuracy of (0.1 K. For the pressure measurement a digital manometer with an accuracy of (0.01 kPa was used. The temperature probe was calibrated against the ice and steam points of distilled water. The manometer was calibrated using the vapor pressure of ultrapure water. The still was operated under constant pressure until equilibrium was reached. Equilibrium conditions were assumed when constant temperature and pressure were obtained for 60 min or longer. Then, samples of liquid and condensate were taken for analysis. The sample extractions were carried out with special syringes that allowed one to withdraw small volume samples (1.0 µL). Analysis. The compositions of the liquid- and condensedphase samples were determined using a CE Instruments
10.1021/je990110p CCC: $18.00 © 1999 American Chemical Society Published on Web 09/18/1999
Journal of Chemical and Engineering Data, Vol. 44, No. 6, 1999 1159 Table 1. Densities d, Refractive Indexes nD, and Normal Boiling Points Tb of Pure Components d(298.15 K)/ kg‚m-3) component MTBE DIPE TAME 2,3-dimethylpentane
exptl
lit. 735.28a
735.29 718.13 718.36d 765.98 765.77g 690.80 690.89b
nD (298.15 K) exptl
Tb (101.3 kPa)/K
lit.
exptl
lit.
1.3663b
328.2 341.6 359.2 363.0
328.11c 341.42f 359.33c 362.93a
1.3664 1.3658 1.3655e 1.3862 1.3859a 1.3894 1.3895a
a DIPPR (Daubert and Danner, 1989). b TRC tables, a-6040. Martinez-Ageitos (1996). d Nakanishi and Shirai (1970). e Kobe et al. (1956). f Reid et al. (1977). g Linek (1987).
c
Table 2. Experimental Vapor Pressures Determined for DIPE and 2,3-Dimethylpentane 2,3-dimethylpentane
DIPE
T/K
P /kPa
T/K
P /kPa
309.3 313.2 316.3 320.1 322.8 326.2 329.4 332.5 335.3 337.8 339.4 342.4 344.5 347.8 350.1 350.4 352.8 354.7 356.5 358.1 359.9 361.8 363.3 363.1 364.2 365.4 366.7 368.1 369.4 371.3
15.40 18.05 20.45 23.83 26.36 30.08 33.78 37.75 41.66 45.45 47.96 53.13 56.98 63.45 68.33 68.73 74.23 78.73 83.29 87.51 92.36 97.55 101.63 101.48 104.62 108.39 112.50 117.09 121.48 127.95
306.5 310.1 312.7 315.6 318.2 321.1 323.1 325.2 327.4 329.0 330.9 332.6 334.9 336.6 338.3 340.0 341.6 342.7 344.1 345.4 345.3 346.5 347.6 349.3
28.49 32.96 36.45 40.78 45.01 50.16 53.93 58.19 62.92 66.50 71.04 75.29 81.32 85.99 90.90 96.06 101.08 104.61 109.44 114.02 113.61 117.97 121.85 128.35
liquid and vapor composition. The standard deviation in the mole fraction was usually
