(109e) Overview of Hybrid PSA-Distillation Processes

Ritter, J. A., University of South Carolina
Ebner, A. D., University of South Carolina
Wu, F., University of South Carolina

Consider the separation of tetrahydrofuran-water mixtures, which exhibit highly non-ideal vapor-liquid equilibrium (VLE) and form a pressure sensitive azeotrope. This mixture is typically separated using two distillation columns, each operating at a different pressure to reverse the relative volatility between the species and move past the azeotrope to separate them. What if a pressure swing adsorption (PSA) process could be retrofitted to each distillation column, creating identical hybrid PSA-distillation systems that now perform the job of the two original distillation columns but at double the throughput? Consider the separation of propane-propylene mixtures, which exhibit nearly ideal VLE but with a very low selectivity. This mixture is separated using cryogenic distillation at high pressures with a very large number of trays and exorbitant condenser costs. What if a PSA process could be retrofitted to the distillation column, creating a hybrid PSA-distillation system that achieves the same performance but with a significant reduction in condenser costs? Consider the separation of ethanol-water mixtures, which also exhibit highly non-ideal VLE and form an azeotrope. One way this mixture is separated is by using a PSA unit retrofitted to a distillation column to go beyond the azeotropic composition, a true hybrid PSA-distillation system. What if this hybrid process could be substantially improved by reducing its energy costs? What if it is possible to gain sufficient understanding of these hybrid systems to come up with some heuristic rules for the design and development of hybrid PSA-distillation systems that perform the same separation as distillation alone but with far less energy and reduced capitol costs?

The objective of this project is to provide some answers to the above questions by 1) developing a set of modeling tools of varying complexity for designing, developing and gaining a fundamental understanding of PSA-distillation hybrid processes for energy efficient separations, and 2) utilizing these modeling tools to come up with user friendly systematic or heuristic rules for the design and development of such PSA-distillation hybrid processes. This objective will be accomplished initially by studying the industrial separations discussed above as key model systems. The goal of this presentation is to provide an understanding of and appreciation for PSA-distillation hybrid processes that is essentially missing from the literature.