(312e) Liquid-Liquid Extraction: Last but Not Least

When we ask chemical engineering students to list equilibrium stage-wise processes, distillation is the first such process on the list, followed by stripping, then, maybe, absorption. They generally don’t list liquid-liquid extraction. What is the reason for this over-sight? First, it comes late in a Unit Operations semester; thus, if the course falls behind the course calendar, it gets dropped. Second, liquid-liquid extraction involves the use of phase diagrams to calculate the number of equilibrium stages for a process; hence, considerable effort must be expended teaching their use and the arcane mathematics required for the calculation. Third, there are no simple liquid-liquid extraction experiments from which students can gain hands-on experience. Taken in toto, most graduating B.S. Chemical Engineers have little knowledge of liquid-liquid extraction.

This presentation investigates liquid-liquid extraction heuristically; i.e., using dimensional analysis. It also discusses a simple, inexpensive laboratory experiment that highlights the pertinent concepts of a dimensional analysis of liquid-liquid extraction.