(133f) Potential Benefits of Electrified Membrane-Distillation Hybrids over Individual Electrified Processes

Molecular separations (separation of mixtures forming a true solution) are ubiquitous in chemical and petrochemical industries. Such separations are energy-intensive, so improving their efficiency is crucial for the reduction of the overall energy consumption of a chemical plant. Membrane-distillation hybrids are believed to reduce the energy requirement for separation dramatically. Therefore, in this work, we systematically investigate the potential that membrane-distillation hybrids hold in increasing the overall efficiency of separation of a binary non-azeotropic mixture. We begin with the description of a few physical insights that explain when and why is the hybrid more efficient than the individual separation technologies. Based on the insights, we then construct a superstructure that encompasses a wide variety of membrane-distillation hybrids. For this superstructure, we formulate a simplified optimization problem that identifies the most efficient hybrid arrangement. When desired, the solution to the optimization problem is further refined by carrying rigorous simulations in Aspen Plus. Using this framework, we analyze the potential of hybrids for three broad classes of separations: (1) close-boiling liquid separations, for which o-xylene/p-xylene is chosen as a representative mixture, (2) close-boiling gaseous separations, for which propylene/propane is chosen as a representative mixture, and (3) “easy” liquid separations, for which benzene/toluene is chosen as a representative mixture. Our analysis shows that the improvement in efficiency is highly subjective to the feed and product specifications. While the hybrids improved the efficiency substantially in some cases, there were also cases where the improvement in efficiency was very small to justify the increase in the complexity of the process. This implies that the hybrid arrangements are more efficient only in specific cases, and we note that the physical insights described here will help in identifying those cases.