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Liquid–Liquid Extraction

  1. Eckart Müller1,
  2. Rosemarie Berger2,
  3. Eckhart Blass3,
  4. Domien Sluyts4,
  5. Andreas Pfennig5

Published Online: 15 JAN 2008

DOI: 10.1002/14356007.b03_06.pub2

Ullmann's Encyclopedia of Industrial Chemistry

Ullmann's Encyclopedia of Industrial Chemistry

How to Cite

Müller, E., Berger, R., Blass, E., Sluyts, D. and Pfennig, A. 2008. Liquid–Liquid Extraction. Ullmann's Encyclopedia of Industrial Chemistry. .

Author Information

  1. 1

    Frankfurt a. Main, Germany

  2. 2

    Ludwigshafen, Germany

  3. 3

    Technische Universität München, München, Germany

  4. 4

    Bayer AG, Antwerpen, Belgium

  5. 5

    RWTH Aachen University, Aachen, Germany

Publication History

  1. Published Online: 15 JAN 2008


The article contains sections titled:

1.Fundamentals and Fields of Application
2.Thermodynamic Fundamentals
2.1.Graphic Representation of Phase Equilibria
2.1.1.Triangular Diagrams
2.1.2.Other Graphic Representations
2.2.Measuring Methods of Phase Equilibria
2.3.Correlation of Phase Equilibria
2.4.Selection of Solvent
2.5.Determination of Mass-Transfer Performance
2.5.1.Specific Methods for Determining the Theoretical Number of Stages
2.5.2.Determining Equipment Behavior Based on Drop-Population Balances
2.5.3.Evaluation of Stage-Number Calculation for Process Design
3.1.1.Columns without Energy Input
3.1.2.Pulsed Columns
3.1.3.Columns with Rotating Internals
3.1.4.Mixer – Settlers
3.1.5.Centrifugal Extractors
3.2.Fluid-Dynamic Fundamentals
3.2.1.Problems and Process Strategy
3.2.2.Operating Characteristics of Pulsed Columns and Columns with Rotating Internals
3.2.3.Fluid Dynamic Calculation Methods
3.3.Apparatus Design
3.3.1.Internals and Operating Conditions
3.3.2.Column Diameter
3.3.3.Column Height
3.4.Criteria for Equipment Selection
4.Phase-Separation Equipment
4.1.Gravity Settlers without Inserts
4.2.Settlers with Coalescing Aids
5.Liquid – Liquid Extraction Processes
5.2.Combined Processes of Extraction and Distillation
5.3.Reactive Extraction
5.3.2.Extraction Mechanism of Different Types of Solvent
5.3.4.Setting up an Extraction System
5.3.5.Diluents and Modifiers

Liquid–liquid or solvent extraction is the separation method of choice where distillation fails, e.g., for azeotropic mixtures or temperature-sensitive components. Separation is achieved by adding a liquid solvent phase to the original liquid carrying the component(s) to be extracted. One of the phases must be dispersed into droplets in the other, continuous phase to achieve a sufficiently large mass-transfer interface. Extraction is performed in mixer–settler equipment or extraction columns, which are frequently equipped with rotating internals or pulsators for energy input to positively influence droplet size. Here the different principles for equipment design are presented: coupling thermodynamic equilibrium and balances for determination of required number of theoretical stages, fluid-dynamic design, and selection of equipment and operating conditions. Additionally, a modern method for linking these aspects more efficiently is shown. A method to characterize coalescence behavior for settler design is explained. Finally, reactive extraction is presented, which is applied, e.g., for metal separation or purification. The separation efficiency in reactive extraction is enhanced by a chemical reaction.