Practical application using Microsoft Excel for calculations
Basics of Liquid-Liquid Extraction
Definition: Mass transfer operation to separate two components based on solubility differences.
Process: Involves using a solvent to extract one component from a mixture.
Outcome: The extraction results in a new mixture of the component of interest with the solvent.
Comparison with Distillation
Distillation: Preferred for first-stage separation with near-pure output.
Liquid-Liquid Extraction: Used when distillation is not feasible due to:
Complex Inorganic Substances: Components form complexes, behaving like single substances, making distillation ineffective.
Low Concentration Components: Distillation becomes economically unfeasible with small concentrations due to tightly spaced operating and equilibrium curves.
High Boiling Components: Requires high temperatures, making distillation difficult or expensive.
Heat-Sensitive Materials: Decompose at high temperatures, necessitating costly high-vacuum distillations.
Close Boiling Points: Ineffective for distillation.
Azeotropes: Can't be separated by distillation.
Process Steps in Liquid-Liquid Extraction
Mixing: Mixing the solvent with the mixture containing the solute.
Ensures efficient mass transfer and extraction.
Separation: Allowing the two phases to separate.
Extract: Solvent with solute.
Raffinate: Feed mixture after solute extraction.
Selection of Solvent
Selective Solvent: Dissolves only the solute, not other components.
High Affinity: High solubility of solute in the solvent.
Cost-Effective: Not too expensive, considering inevitable losses and make-up requirements.
Safe to Use: Preferably non-corrosive, non-explosive, and non-flammable.
Easy to Separate: Solvent should be easily separable from solute to make the process feasible.
Equipment Used in Liquid-Liquid Extraction
Mixer-Settler Extractors:
Batch Process: Involves a mixing tank with agitators and a separation tank.
Combined Mixer-Separator Tanks:
Combines mixing and separation in one tank.
Continuous Process Extractors: STRAKE Towers:
Resemble distillation columns with trays for countercurrent flow of liquids.
Agitated Towers:
Towers with multiple mixers to ensure adequate mixing and mass transfer.
Conclusion
Next Steps: Overview of calculations and phase diagrams in the next video.