(72c) Optimal Design of a Liquid-Liquid Extraction System

In most separation applications involving liquid-liquid extraction (LLE), the process will require one or more distillation columns downstream of the extraction column. Thus, optimization of the process requires a focus on the overall integration of extraction and distillation columns in order to provide the most economical solution. Typically the solvent used for the extraction step must be distilled from the extracted solute and then recycled back to the extraction column. Also, if the solvent has some solubility in the feed, as is often the case for systems that include an aqueous feed and an organic solvent, then a distillation column will be required to recovery and recycle the solvent from the aqueous phase (raffinate). As discussed in previous papers (1) (2), design of the extraction column almost always requires pilot plant testing in order to provide data for accurate scale-up and design of the commercial column. Many times the distillation columns can be designed by simulations following by selecting the best internals (packing or trays) for the column and then utilizing known design criteria for sizing these internals. However, in some instances, such as potential foaming, and unknown interactions between multiple compounds, pilot plant testing of distillation steps may also be require in order to provide a firm basis for the commercial column design. This paper will present three case studies involving the design of complete extraction/distillation systems. In each case, the extraction column was sized via pilot plant testing. In two of the applications, the distillation columns were designed via simulations only, and in the other application a distillation column was designed via pilot plant testing plus simulation. All three system have been successfully operating in the commercial installations.