Optimal Design of a Liquid-Liquid Extraction System

Liquid-liquid extraction processes often require one or more downstream distillation columns. This article describes the process design of such systems.

In most chemical separation applications involving liquid-liquid extraction (LLE), the process will require one or more distillation columns downstream of the extraction column. Thus, optimizing the process requires the engineer to focus on the overall integration of the extraction and distillation columns. Typically, the solvent used for the extraction step must be distilled from the extracted solute and then recycled back to the extraction column. 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 recover and recycle the solvent from the aqueous phase (raffinate).

As discussed in previous articles (1–2), design of the extraction column almost always requires pilot plant testing to provide data for accurate scale-up and design of the commercial column. Often, the distillation columns can be designed by first simulating the process and then designing the distillation column internals using known design criteria, hydraulic rating software, and process engineering experience. However, in some cases, phenomena such as foaming and unknown interactions between various components in the system require pilot plant testing of downstream distillation steps to provide a firm basis for the commercial process design.

This article presents three case studies involving the design of complete LLE systems with downstream distillation. 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 third application, a distillation column was designed via pilot plant testing in addition to simulation...