Fu Min, Chen Yao, Hu Jinghua
(Department of Chemistry, Jinan University, Guangzhou, 510632,China)

Supported by Foundation of Ministry of Education (No.2002247), Foundation of Guangdong province (No.2003C33101) and Foundation of Jinan University (No.640071).

Abstract The experimental tie line data for five ternary mixtures of water + ethanol +diethyl carbonate, water + methanol +diethyl carbonate, water +diethyl carbonate + n-heptane, water + methyl tert-butyl ether + n-heptane, water + methyl tert-butyl ether + diethyl carbonate have been measured at temperature 298.15 K and ambient pressure. The experimental data were correlated by using a modified UNIQUAC model. Furthermore, the calculated results were compared with those obtained from an extended UNIQUAC model.
Keywords Liquid-liquid equilibria, Fuel additives, Ternary mixtures, Modified UNIQUAC and extended UNIQUAC models.

1. INTRODUCTION            
Presently, several fuel oxygenates are added to gasoline to enhance the octane number and reduce air pollution. Methyl tert-butyl ether (MTBE) is currently the primary oxygenated compound being used in lead-free gasoline. Diethyl carbonate (DEC) is recognized as an environmentally benign chemical because of its negligible ecotoxicity and low bioaccumulation and persistence. Its high oxygen content makes it a promising candidate to be used as an oxygenated fuel additive, which has been reported by many researchers ^[1-3]. Engine texts show that DEC reduces particulate emissions almost 50% when the engine is under load. Without load, particulate emissions are reduced by approximately 30% ^[4].
    To assess the effect of the additives in gasoline reformulation, we need a fundamental knowledge about multi-component phase equilibria of the mixtures containing these compounds. In this work, we report liquid-liquid equilibria (LLE) data for ternary mixtures of water + ethanol + DEC, water + methanol + DEC, water + DEC + n-heptane, water + MTBE + n-heptane, water + MTBE + DEC systems measured at 298.15 K. The experimental results were correlated by means of the extended and modified UNIQUAC models ^{[5, 6]} which include additional ternary parameters arising from multicomponent intermolecular interactions, in addition to the binary parameters. The vapor-liquid equilibria (VLE) data and mutual solubilities of the constituent binary mixtures have been available from the literatures ^[7-14], the mutual solubilities of water + DEC was measured in this work.

2. EXPERIMENTS
2.1 Materials  
DEC was obtained from Alfa Aesar Company, with mass fraction of 0.990. MTBE was supplied by Tedia Company, Inc. with mass fraction of 0.998. Methanol and n-heptane were provided from Guangzhou Chemical Reagent Factory, with mass fraction of 0.995 and 0.997, respectively. Ethanol was supplied from Tianjin Chemical Reagent Factory, with mass fraction of 0.997. Water provided from Jinan University was distilled twice and had a mass fraction purity of 0.999. The g.c. analysis gave mass fractions purities of 0.991 for DEC, 0.997 for MTBE, 0.995 for methanol, 0.996 for n-heptane, and 0.996 for ethanol. All chemicals were used directly in this work.
2.2 Apparatus and Procedures                                        
Ternary LLE measurements were carried out at the temperature (298.15 ± 0.01) K. The experimental apparatus was the same that reported in detail previously ^[15]. The mixtures were stirred by using a magnetic stirrer for 3 hours, and settled for 2 hours. It is sufficient to separate into two phases. The samples withdrawn from upper and lower phases were analyzed by a gas chromatography. The accuracy of the measurements was estimated within ±0.001 in mole fraction. Table 1 shows experimental LLE results for the mixtures of water + ethanol + DEC, water + methanol + DEC, water + DEC + n-heptane, water + MTBE + n-heptane, and water + MTBE + DEC.

I, modified UNIQUAC model.
II, extended UNIQUAC model.

5. CONCLUSIONS
The experimental tie line data were measured for five ternary systems of water + ethanol + DEC, water + methanol + DEC, water + DEC + n-heptane, water + MTBE + n-heptane, water + MTBE + DEC at 298.15 K. The correlated results using the modified UNIQUAC model for the experimental ternary LLE data are much better than those obtained from the extended UNIQUAC model.

REFERENCES
[1] Eyring E M, Meuzelaar H L C, Pugmire R J. Annual Report for Cooperative Research in C1 Chemistry (DF-FC26-99FT40540), 2001: 32–36.
[2] Pacheco M A, Marshall C L. Energy Fuels, 1997, 11: 2–29.
[3] Dillon D M. U.S. Patent 4,891,049, Jan. 2, 1990.
[4] Dunn B C, Guenneau C, Hilton S A, et al. Energy Fuels, 2002,16: 177–181.
[5] Nagata I. Fluid Phase Equilib, 1990, 54: 191–206.
[6] Tamura K, Chen Y, Tada K, et al. J Solution Chem, 2000, 29: 463–488.
[7] Rodríguez A, Canosa J, Domínguez A, et al. J Chem Eng Data, 2003, 48: 86–91.
[8] Francesconi R. J Chem Eng Data, 1997, 42: 697–701.
[9] Wisniak J, Magen E, Shachar M, et al. J Chem Eng Data, 1997, 42: 243–247.
[10] Rodríguez A, Canosa J, Domínguez A, et al. J Chem Eng Data, 2002, 47: 1098–1102.
[11] Arce A, Blanco M, Riveiro R, et al. Can J Chem Eng, 1996, 74: 419–422.
[12] Sφrensen J M, Arlt W. Liquid–Liquid Equilibrium Data Collection, Vol. V, Part 1, DECHEMA, Frankfurt am Main, 1979.
[13] Hall D J, Mash C J, Penberton R C. NPL Report Chem, 1979, 95: 1–32.
[14] Kooner Z S, Phutela, R C, Fenby D V. Aust J Chem, 1980, 33: 9–13.
[15] Chen Y, Dong Y H, Pan Z J. J Chem Thermodyn, 2005, 37: 1138–1143.
[16] Prausnitz J M, Anderson T F, Grens E A, et al. Computer Calculation for Multicomponent Vapor-Liquid and Liquid-Liquid Equilibria . Prentice-Hall: Englewood Cliffs, NJ, 1980:19.
[17] Spencer C F, Danner R P. J Chem Eng Data, 1972, 17: 236–241.
[18] Hayden J G, O’Connell J P. J Ind Eng Chem Process Des Dev, 1975, 14: 209–216.
[19] Nelder J A, Mead R. J Comput, 1965, 7: 308–313.