Studies on Hydrogen-Pinch Analysis and Application of COSMO-SAC to Electrolytes

Abstract

This thesis describes the results of two process system engineering studies: (1) hydrogen pinch analysis; and (2) application of COSMO-SAC (conductor-like screening model – segment activity coefficient) to electrolytes. Part (1) presents an automated spreadsheet method that can quickly help minimize fresh hydrogen consumption and maximize hydrogen recovery and reuse in petroleum refineries and petrochemical complexes. Part (1) has appeared as a featured article on engineering practice in the Chemical Engineering Magazine, volume 115, pp. 56-61, June 2008. We present an automated spreadsheet on our research group website (www.design.che.vt.edu) and describe procedures for using the spreadsheet in this thesis. Part (2) discusses the application of the conductor-like screening model – segment activity coefficient (COSMO-SAC), a liquid-phase activity-coefficient model, to electrolytes. We offer detailed procedure for obtaining sigma profiles for electrolytes. A sigma profile is a molecular-specific probability distribution of the surface-charge density, which enables the application of solvation-thermodynamic models to predict vapor-liquid and solid-liquid equilibria, and other properties. We propose to add an additional term to the exchange energy to account for ion-ion attractive and repulsive forces. We also look at the resulting exchange energy behavior. Although accurate numerical results are not achieved, we are able to produce results that match literature data by adding an adjustment factor.