利用活性係數模型計算含氫鍵混合物的相平衡

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Title:	利用活性係數模型計算含氫鍵混合物的相平衡
Other Titles:	Modeling the Phase Equilibria of Associating Mixtures by Activity Coefficient Model
Authors:	溫燕益 Wen, Thomas
Contributors:	符原浩東海大學化學工程與材料工程學系
Keywords:	相平衡;活性係數;氫鍵 phase equilibria;activity coefficient;hydrogen bonding;UNIQUAC-A
Date:	1998
Issue Date:	2011-06-15T02:40:34Z (UTC)
Abstract:	一般而言，相平衡計算的方法可以分為以下兩類：活性係數模型與狀態方程式。這些工程上常用的模型對於可形成氫鍵的純物質或混合物的相平衡計算效果不佳。為了要改進對於此種混合物的計算結果，於是發展出許多種氫鍵鍵結模型。這些模型對於氫鍵鍵結的描述大致上有兩種：化學理論與物理理論。利用化學理論，Nagata與Kawamura（1979）發展出一個UNIQUAC-association活性係數模型。Brandani（1983）將之推展到含醇類混合物。然而化學理論存在著缺陷，為了取代化學理論的應用，根據物理理論之假設，Fu等人（1995）發展出一個基於物理理論的UNIQUAC-association（UNIQUAC-A）活性係數模型。其模型已證明可適用於簡單的含氫鍵混合物如醇類+烷類之汽液相平衡計算。本研究利用Fu等人的UNIQUAC-A活性係數模型來計算含醇類、含酸類、含水與活性（active）物質如酮類混合物的氣液相平衡。對於含醇類與酸類的汽液相平衡來說，UNIQUAC-A模型的結果都比UNIQUAC模型的結果為佳但不顯著。因為在這些混合物中，氫鍵的生成與斷裂同時發生，此兩者的效應相互抵消，造成氫鍵效應並不明顯，所以改進的效果並不顯著。對於含水混合物來說，UNIQUAC-A模型的結果也比UNIQUAC模型的結果為佳，但欠完整性探討，因為這類混合物數據較少不易取得，故數據的完整性與多寡會影響我們進行預測計算的結果。對於含活性物質的混合物，UNIQUAC-A模型的結果與UNIQUAC模型的結果相差不大但仍有改進空間，這可能是因為這類混合物的氫鍵鍵結產生的效應並不大所致。因為UNIQUAC-A活性係數模型應用在汽液相平衡上的結果良好，所以我們嘗試將這個模型自汽液相平衡的計算範圍延伸到液液相平衡計算的範圍。我們選取水+醇類+惰性物質的混合物與水+酸類+惰性物質的混合物來進行液液相平衡計算的測試。而UNIQUAC-A模型的結果與UNIQUAC模型的結果相差不大，這可能是因為在這些混合物中，氫鍵的生成與斷裂同時發生，此兩者的效應相互抵消，造成總氫鍵結合效應並不明顯，故兩模型計算結果類似。 In general, there are two methods to calculate phase equilibrium: the activity coefficient model and equation of state. For pure associating components or associating mixtures, these engineering models can not calculate phase equilibrium very well. To improve the calculated results of such mixtures, a number of association models have been developed. There are two approaches to describe hydrogen bonding in these models:chemical theory and physical theory. Nagata and Kawamura （1979）used chemical theory of hydrogen bonding to develop a UNIQUAC-association activity coefficient model. Brandini（1983）extend this model to the mixture containing alcohol. However, there are disadvantages in chemical theory. Instead of using chemical theory, based on the assumption of physical theory, Fu et al. （1995）develop a UNIQUAC- association （UNIQUAC-A）activity coefficient model based on physical theory. This model had approved to calculating the vapor-liquid phase equilibrium of simple associating mixtures like alcohol + alkane. We used UNIQUAC-A activity coefficient model derived by Fu et al. to calculate the vapor-liquid equilibrium of the mixtures containing alcohol,acid, water and other active components such as ketone. For the mixtures containing alcohol and acid, the results of the UNIQUAC-A model is better than the results of UNIQUAC model. However because hydrogen bonds are formed and broken at the same time in these mixtures, the effect of the hydrogen bonding and the improvement are not obvious. For the mixtures containing water, the results of UNIQUAC-A model is better than UNIQUAC model. Because the experimental data of this kind of mixtures is not sufficient and difficult to find out, the quality of data affected our calculation. For the mixtures containing active compounds, the results of the UNIQUAC-A model is little better than the results of the UNIQUAC model. The reason may be the effects of hydrogen bonding in mixture are weak. For the vapor-liquid equilibrium calculation, the results of the UNIQUAC-A activity coefficient model is very well, therefore, we tried to extend this model to liquid-liquid equilibrium calculation. We selected water+alcohol+inert and water+acid+inert liquid-liquid mixtures to test. The differences in results between the UNIQUAC-A model and UNIQUAC model are small and both of them have small errors. This may be hydrogen bonds are formed and broken at the same time in mixtures, therefore, total effects of hydrogen bonding are not obvious.
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