461952 Modification of Staverman-Guggenheim Combinatorial Entropy Expression

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Yifan Hao1, M. R. Islam2 and Chau-Chyun Chen2, (1)Department of Chemical Engineering, Texas Tech University, Lubbock, TX, (2)Chemical Engineering, Texas Tech University, Lubbock, TX

Staverman-Guggenheim1 (S-G) expression has been widely used to describe the non-ideal entropy of mixing in state of art activity coefficient models, e.g. UNIQUAC2/UNIFAC3, COSMO-SAC4 etc. It accounts for both size and shape differences of molecules, while Flory-Huggins5 (F-H) expression only considers size difference and results in an upper limit for entropy of mixing. However, for molecules with large size and shape differences, S-G may return unrealistic results. In this study, a modification is proposed by introducing an exponent on both volume and surface area parameters of S-G. The modified S-G is employed to predict infinite dilute activity coefficients for mixtures containing linear, branched, and cyclic alkanes. It shows significant improvement than original S-G model by comparing to experimental data. The modification is further explained from statistical mechanics point of view. Finally, the modified S-G expression is applied to activity coefficient models like UNIQUAC and NRTL-SAC6 to show the improvement in correlation and prediction.

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