Measurments Of Liquid-Liquid Equilibrium For Multi-Component Systems And Correlations By Using The Models

Dimethyl carbonate (DMC) is a strong contender to help the refining industry meet the Clean Air Act specifications for oxygen in gasoline. DMC has about 3 times the oxygen content as methyl tert-butyl ether(MTBE) and its synthesis is not dependent upon FCU isobutylene yields like MTBE. DMC has a good blending octane, it does not phase separate in a water stream like some alcohols do, and it is both low in toxicity and quickly biodegradable. In this paper, multicomponent liquid-liquid equilibria (LLE) properties of DMC were studied, and the LLE data of ternary and quaternary mixtures which containing DMC or diethyl carbonate (DEC), pure hydrocarbons, alcohol, water was accurately measured, and the corresponding application of the LLE data to assess the performance of DEC in clean gasoline was discussed.Gas chromatograph technique has been applied to determine LLE data for four ternary systems and four quaternary systems composed of DMC or DEC, this method is simple, fast, satisfied repetition, and the accuracy of measurements was estimated within±0.001 in mole fraction. The LLE data for the four ternary mixtures of the water+n-butanol+DMC, water+ n-butanol+DEC, water+n-hexane+DMC and the water+n-hexane+DEC systems, and the four quaternary mixtures of the water+n-butanol+DEC+DMC, water+n-hexane+DEC+ DMC, water+n-butanol+n-hexane+DMC and the water+toluene+isooctane+DMC systems have been investigated at 298.15 K and atmospheric pressure. Analyzing these LLE data, the main conclusions are as following:the addition of DMC alone to a water+hydrocarbon mixtures leads to no measurable increase in different types of hydrocarbons solubility in water, such as paraffin and aromatic which are basis of gasoline. DMC or DEC won't cause potential water pollution of clean gasoline, thus the added performances of DMC are very good. the addition of DEC with DMC to a water+heptane mixtures leads to a decrease in DMC solubility in water and a decrease in water solubility in oil and no measurable increase in hydrocarbons solubility in water. In other word, DMC or DEC could be considered as a suitable alternative gasoline additive in the view of the intersolubility of water and gasoline. They could be considered as a suitable alternative gasoline additive to MTBE, they will have good value in use in the future.The experimental ternary and quaternary LLE data have been satisfactorily correlated by using a Modified UNIQUAC model with additional ternary and quaternary interaction parameters. Further, the calculated results obtained from the Modified UNIQUAC model are compared with those obtained from the Extended UNIQUAC model. The correlated results given by the Modified UNIQUAC model are in good agreement with the experiment result for all the systems investigated here. This model and these multibody interaction parameters obtained in this work can be applied to predict LLE properties of complicated fluid mixtures in separation process.