Liquid-Liquid Extraction
Al-Balqa Applied University
Faculty of Engineering Technology
Dr. Enshirah Da'na
Introduction Mechanism
Liquid-Liquid extraction is a mass transfer operation in which a liquid solution (feed) 1. Mixing/contacting: 2. Phase separation:
is contacted with an immiscible or nearly immiscible liquid (solvent) that prefers or - turbulent contact between liquid phases. - reverse of above mixing step.
selectively dissolves one or more of the components in the feed. - small droplet dispersion in a continuous phase. - drops come together and coalesce.
- Identify which of the liquid phases is dispersed. - relies on density differences.
- mass-transfer between phases.
- limited by solute loading in solvent .
3. Collection of phases leaving the unit:
- Split the raffinate from the extract.
Basic Principles
Principle: Separation based on solubility differences.
Phases: Typically involves an extract phase and a raffinate phase.
Distribution Coefficient: Ratio of concentrations in the two phases.
𝐶𝐸𝑥𝑡𝑟𝑎𝑐𝑡 Kd: Distribution Coefficient
𝐾𝑑 = C : Concentration of solute in extract phase.
𝐶𝑅𝑎𝑓𝑓𝑖𝑛𝑎𝑡𝑒 Extract
CRaffinate: Concentration of solute in raffinate phase.
Applications
Equipment Pharmaceuticals
Equipment is classified into: • Extracting active ingredients from medicines and medicinal herbs.
Mixers: Used to ensure thorough mixing of phases. • Separating different organic compounds in pharmaceutical
manufacturing processes.
Example: Mixing vessel with variable-speed turbine agitator. (Figure (a))
Separators: Devices like separating funnels or centrifuges to separate the phases
post extraction. Chemical Industry
Example: Tray columns. (Figure (b)) • Purifying and extracting chemicals from mixtures.
• Separating valuable materials from chemical process waste.
Food Industry
• Extraction of flavors and fragrances.
• Purifying oils and fats from mixtures.
Advantages & Disadvantages
Figure (a) Figure (b)
Advantages Disadvantages
Choice of Solvent
Selecting the solvent carefully is crucial for the efficiency and effectiveness
Ease of Use and Emulsification
of the liquid-liquid extraction process: Implementation issues.
The effectiveness of solvent B in separating a solution of A and C is
Selectivity β measured by the ratio of C to A in the B-rich phase compared to the A-rich
phase at equilibrium.
It is defined as the ratio of solute concentration in the extract (y) to that in Common Usage Low Selectivity
Distribution
the raffinate (x). A higher y/x ratio is preferable as it reduces the amount of
Coefficient Kd
solvent needed.
Solvent recovery from the extract phase for reuse is typically achieved by
Recoverability of distillation. It's important to prevent the formation of an azeotrope, which
solvent has higher relative volatility and lower latent heat of vaporization, thus
Material Environmental
minimizing energy consumption during vaporization. Availability and Safety Risks
A significant density difference is crucial for both stagewise and continuous
Choice of Solvent Density contact operations, facilitating easier phase separation. However, at the
plait point, the density difference becomes zero.
Conclusion
High interfacial tension promotes coalescence of droplets or emulsions but Liquid-liquid extraction is a widely used technique in various industries,
makes dispersion of one liquid into the other difficult. This is beneficial for offering efficient separation with high selectivity.
Interfacial tension
extraction operations where coalescence is crucial. At the plait point,
interfacial tension is zero.
References
Chemical The solvent should be thermally stable, chemically inert to other 1) N. Anantharaman, K. M. Meera Sheriffa Begum. (2013). Mass Transfer Theory and Practice.
Reactivity components, and compatible with the construction material.
2) McCabe, Warren L., Smith, Julian C., Harriott, Peter. (1993). Unit Operations In Chemical
Engineering fifth edition.
Low viscosity, vapor pressure, and freezing point ease handling and storage.
Other Properties
Solvents should also be non-toxic, non-flammable, and cost-effective. 3) Fayda Salameh, Lina Abdel Rahman. (2022). Organic Laboratory Manual.
4) Liquid-Liquid vs Supported-Liquid vs Solid-Phase Extraction (aurorabiomed.com)
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