Distillation types discussed here
- Flash Distillation
- Batch Distillation
- Continuous Distillation
- Steam Distillation
- Extractive Distillation
- Azeotropic Distillation
Flash Distillation
Vaporizing a definite fraction of the liquid in such a way that the evolved vapor is in equilibrium with residual liquid.
Batch Distillation
Used when Feed composition changes from batch to batch.
Batches are relatively small where certain components are separated in pure form heating a heavier residue.
Continuous Distillation
Where feed is continuous and products are continuously withdrawn, Uniform Quality, Large scale operations. High Throughput. Most commonly used.
Steam Distillation
1. Possible to distillate an organic compound at much lower temperature.
2. At constant system pressure P1, steam lowers the partial & vapor pressure of organic compounds & its corresponding boiling point.
3. Due to immiscibility of water, it can be separated from product by simple condensation & followed by decantation.
Application : Purification of heat sensitive material as an alternative to vacuum distillation.
Extractive Distillation
1. An agent modifies the relative volatility between key component without forming an azeotrope. The agent is nonvolatile & called solvent.
2. Extractive distillation is simpler process than azeotropic distillation.
3. Solvent boils far above the system component.
4. Because of the low volatility the solvent always leaves the Extractive column with the bottom product.
5.Solvent must be readily separated from the mixture to which it is added. Should have High selectivity or ability to alter the vapor-liquid equilibria of the original mixture & high capacity to dissolve the components in the mixture to be separated.
In extractive distillation, attraction of solvent to one of the components is attributed to
- Hydrogen Bonding
- Polar characteristics of the solvent & members of the mix.
- Formation of weak unstable chemical complex.
- Chemical reaction between solvent & one of the component.
Read in detail
Azeotropic Distillation
1. In rectification of minimum boiling azeotrope the distillate product may be close to the azeotropic conc. But the residue product will be a component A or B depending on concentration.
2. In Maximum boiling Azeotrope mixture the residue will always approach the azeotropic concentration . This mixture can be separated by addition of third component.
3. When the high volatility entrainer is used process is called Azeotropic distillation.
4. Azeotropic composition as well as its boiling point changes with pressure .