Designing Liquid-Liquid Extraction Columns by Pilot Plant Testing.

Almost every liquid-liquid extraction (LLE) project involves a pilot test to provide the basis for commercial plant design. Unlike distillation, which can often be design by simulations and known capacity/efficiency parameters for column internals, LLE usually has many unknown factors such as equilibrium, efficiency, and capacity data. Small trace impurities can have a significant impact on all of the above. The development procedure for LLE generally requires three basic steps; (1) solvent selection and generation of liquid-liquid equilibrium data, (2) column selection and pilot plant testing to generate the optimal performance data, and (3) accurate scale-up technique to design the production scale equipment. As the diameter of an LLE column increases the tendency for back mixing increases resulting in lower efficiency. Thus, a key for scale-up from the pilot plant test work to the production column is to understand how the efficiency changes with diameter and to correlate this into the design of the production column. Over years of experience with many different LLE systems, proven scale up correlations have been developed for a number of different types of extraction columns and used for the design of production columns which have met or exceeded expectations. This presentation will conclude by presenting case studies for two extraction processes including data generated in the pilot plant and then calculations for sizing the production columns.