醋酸為工業界中常用的藥品，可是醋酸與水會形成類似共沸之混合物，故使用傳統蒸餾無法得到高純度的醋酸。目前醋酸脫水程序都是以共沸蒸餾為主，其分離製程中所加入的共沸劑(entrainer)都是以醋酸酯為主，而本研究構想一個新製程，使用對二甲苯來替代醋酸酯，若此製程可行，則希望可大幅降低醋酸生產之成本。
水-醋酸-對二甲苯三成份是否有三成份共沸一直是個爭議的問題，本研究利用共沸蒸餾裝置去測定，其結果水-醋酸-對二甲苯沒有三成份共沸點存在。
本研究討論水-醋酸-對二甲苯在101.32 kPa 下的相行為包括汽液及汽液液相平衡，實驗設備使用改良自Othmer汽液平衡裝置，在汽相之計算使用Hayden和O’Connell所提的理論，考慮醋酸分子結合效應。
將本實驗所得來之數據使用UNIQUAC和NRTL兩種液相模式進行迴歸，回歸結果，汽液與汽液液平衡都是以UNIQUAC較佳。並觀察實驗數據，發現在醋酸含量較高的部份為汽液平衡，醋酸較少時為汽液液平衡。

Acetic acid and water is a mixture with close-boiling temperature. Therefore, a conventional distillation can not produce high purity acetic acid. In chemical industry, the azeotropic distillation is applied to the dehydration of acetic acid with an entrainer. The final aim of this study is to develop a new process that replaces the old entrainer with p-xylene.
In this work use packed distillation column to find the ternary azeotropic of water-acetic acid-p-xylene. The ternary azeotropic doesn''t exist in this work result.
In this work, the vapor liquid equilibrium and vapor liquid liquid equilibrium data of water-acetic acid-p-xylene were conducted in a modified Othmer type equilibrium still at 101.32 kPa. The measured VLE and VLLE data were correlated by the activity coefficient models of UNIQUAC and NRTL with the consideration of the association by Hayden and O’Connell in the vapor phase. Our calculated results show that the correlation by the UNIQUAC model was in good agreement with the experimental data for VLE and VLLE.

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林慶峰，無參數模式預測非均相混合物的共沸點，國立中央大學化學工程學研究所博士論文，民國九十六。
蔡皇仙，醋酸-水-乙酸異丙酯三成份系統相行為之研究，國立中央大學化學工程研究所碩士論文，民國八十八年。