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In this paper, the thermally coupled side-rectifier and side-stripper configurations are studied in the separation of component sets with a curved distillation boundary. A solving procedure is introduced that can be used in the determination of the minimum total energy consumption for the studied complex separation structures. The results show that thermally coupled side-column configurations enable distillation boundary crossing with high product flow purities. In fact, the achievable purities are higher than is possible with conventional column sequences. It is also noted that in some methanol/ethanol/water separations the energy consumption of the thermally coupled side-stripper configuration may partly decrease with increasing methanol distillate purity.

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In this study, the modified bounded homotopies presented by Malinen and Tanskanen (Malinen, I.; Tanskanen, J. Modified bounded homotopies to enable a narrow bounding zone. Chem. Eng. Sci. 2008, 63, 3419) are investigated in order to solve phase stability analysis problems in liquidÀliquid equilibrium cases for phase-splitting calculations. The tangent-plane distance criterion is used to analyze the phase stability. The emphasis is on approaching the first root on the homotopy path. According to the observations, the bounding of the homotopy path with respect to the problem variables aids in the solving of a phase stability analysis problem. The main shortcomings of the modified bounded Newton, affine, and fixed-point homotopies are the starting point isolas, the existence of unfeasible solutions, and the convergence to only certain roots, respectively. The attraction domain of the global minimum was observed to be the largest with the fixed-point homotopy. Sequential usage of the fixed-point homotopy and starting points near pure components results in a robust algorithm for phase stability analysis and gives feasible initial estimates for the solving of phase splitting.