Design of Multiple Extractors for Optimizing Liquid-Liquid Extraction Processes

Separation processes involving liquid-liquid extraction cannot always be solved by a single, counter current extraction column.  In some applications, two columns or a column with mixer/settler in series should be considered and may offer the best solution from a process optimization and/or economic standpoint.  Fractional extraction is an obvious process whereby two columns in series can be considered in lieu of a single column.  However, other processes such as columns with backwash, extractions with reaction, unfavorable density gradient and presence of solids can also involve more than a single column.  In any of these types of processes, pilot plant testing is critical to the optimal design of the system.  This paper covers a number of different applications where a single column was considered vs two extractors in series.  The results from pilot plant testing are presented along with the eventual design for scale up to the commercial processes.