(76b) Consider Preflash Separation (and Droplet Removal) for Purification of Wide-Boiling Range Mixtures

Conventional chemical distillation columns are developed to receive a feed at an intermediate tray or between packing sections. Preheating with or without bottoms interchange is often used to optimize distillation energy. Locating the best position of the feed point relative to theoretical stages can be determined by analysis and rules developed using McCabe-Thiele diagrams, for which the operating and the V-L equilibrium curves are determined for the key components. For systems with very high relative volatility between the key components, a relatively deep Preflash step can be combined with a stripping section or with a rectification section to provide a reliable, and simpler, yet optimized separation solution. Processes suited to this approach include: ? Some processes with reactant or solvent removal and recycle ? Purity requirements for top or bottom products that require distillation to low levels, ie. ppm levels; however, usually both top and bottom products do not require high purity. ? Polymer-solvent systems with relatively lower MW polymers and lower viscosities,