The Gibbs鈥揌elmholtz Equation and the Thermodynamic Consistency of Chemical Absorption Data

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• 作者：Paul M. Mathias ; John P. O鈥機onnell
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2012
• 出版时间：April 4, 2012
• 年：2012
• 卷：51
• 期：13
• 页码：5090-5097
• 全文大小：497K
• 年卷期：v.51,no.13(April 4, 2012)
• ISSN：1520-5045

文摘

The Gibbs鈥揌elmholtz (G-H) equation connects vapor鈥搇iquid equilibrium (VLE) and calorimetric data. If experimental measurements for the heat of solution are not available, they may be estimated through the G-H equation. Further, if both VLE and heat-of-solution data are available, their mutual thermodynamic consistency can be evaluated through the G-H equation, to develop the most accurate and reliable model. This kind of analysis is particularly useful for chemical-absorption systems, such as the capture of CO₂ using aqueous solutions of amines, where regeneration energies are significant. In this work, the G-H equation is derived to unambiguously relate the commonly used form to the rigorous and general form, including for systems where phase equilibrium is accompanied by chemical reactions in any phase. The effect of approximations and the range of applicability of the common G-H equation are first applied to data generated for a simple VLE system by an equation of state, with different reliability found for the vapor and liquid phases. Next, consistency is evaluated for many VLE and calorimetric data for CO₂ absorption in aqueous MEA (monoethanolamine). It is shown that some VLE and/or calorimetric data sets are likely to be in error and that the experimental VLE and CO₂ heat of solution at the highest temperatures are currently uncertain.