本研究主要探討醋酸與乙酸異丁酯於一大氣壓下之汽液相平衡，採用汽相循環式汽液平衡，進行常壓下之汽液相平衡實驗，溫度與汽液相組成分別由熱偶計量得與GC分析之。 在雙成份系統中，多重共沸是一種很特殊的情形，然而醋酸與乙酸異丁酯於常壓下的汽液平衡即會產生兩個共沸點。在數據處理方面，數據能通過Fredenslund所提出的點對點的熱力學一致性測試，再以UNIQUAC、 NRTL、 van Laar模式與Legendre polynomial進行迴歸，比較迴歸結果可判斷Legendre polynomial對此系統的擬合度較好。 為了去除共沸點，加入醋酸鉀於此系統中直到達到飽合溶液並重新量測汽液平衡之數據。由其結果可知加入此鹽類後可使得共沸點消失。 In this research, the isobaric vapor-liquid equilibrium data for isobutyl acetate and acetic acid were measured at atmospheric pressure. A condensed vapor phase recirculating apparatus is used for our experiment. The equilibrium temperature was measured by thermocouple, the vapor and liquid samples were analyzed by GC to determine the compositions。 Polyazeotropy in binary systems is a uncommon behavior of vapor-liquid equilibrium at a given pressure or temperature. Isobutyl acetate and acetic acid mixture exists two azeotropes at 101.3kPa. Experimental data are thermodynamically consistent according to the point-to-point test of Fredenslund and the data were correlated using NRTL、UNIQUAC、van Laar model and Legendre polynomial. In order to remove the azeotropes , potassium acetate was added to the mixture and run the experiments. It is found that azeotropes disappear by salt effect.