Influences of uncertainties in thermodynamic models on Pareto-optimized dividing wall columns for ideal mixtures

This article examines the effect of uncertainties in thermodynamic models on the performance of simulated, steady-state Pareto-optimized Dividing Wall Columns. It follows a previous work treating deviations in process variables. Such deviations and uncertainties that may even be unknown during the design process can significantly influence the separation result. However, other than process variables, uncertainties in thermodynamics are usually not systematically considered during design. For the first time, the effects of uncertain thermodynamic properties on Pareto-optimized DWCs with different numbers of stages and for different mixtures are presented and compared qualitatively and quantitatively. Particularly critical properties depending on the number of stages and mixture are identified. On the one hand, this provides information on aspects requiring special attention prior to design, and on the other hand, it also indicates in which section of the DWC a stage supplement might be most beneficial.
Generally, the uncertainties in caloric properties examined were found to be significantly less relevant than those directly linked to the vapor-liquid-equilibrium, causing never more than 0.5 mol% purity losses. Uncertain vapor pressures and activity coefficients on the other hand led to purity losses of up to over 6 mol% for model deviations barely visible in T-x-y diagrams. For combined uncertainties in principle a superposition of the individual effects was found, leading to moderate purity losses of hardly more than 1 mol% for columns with low numbers of stages while at high numbers of stages, 3.5 to over 6 mol% loss of purity resulted, depending on the mixture.