The term "entrainer" is commonly used in azeotropic distillation.

Azeotropic distillation:
Azeotropic distillation is a process used in chemical engineering to separate azeotropic mixtures. Azeotropic mixtures are liquid mixtures that have a constant boiling point and composition. They cannot be easily separated by normal distillation techniques because the vapor and liquid phases have the same composition. In azeotropic distillation, an entrainer is used to break the azeotropic behavior and separate the components.

Explanation:
- An entrainer is a third component that is added to the azeotropic mixture in order to modify its composition and break the azeotropic behavior.
- The entrainer forms a new azeotrope with one of the components in the mixture, which can then be separated from the other components.
- The addition of the entrainer changes the boiling point and composition of the mixture, allowing for separation by normal distillation techniques.
- The entrainer can be added in either the liquid or vapor phase, depending on the specific system and desired separation.
- The selection of the entrainer is critical and depends on factors such as the desired separation, compatibility with the components, and the economics of the process.
- The entrainer should have a high selectivity for the desired component to ensure efficient separation.
- After the separation, the entrainer can be recovered and reused in the process, reducing the overall cost and environmental impact.

Conclusion:
In summary, the term "entrainer" is used in azeotropic distillation, where it is added to azeotropic mixtures to modify their composition and break the azeotropic behavior. The entrainer forms a new azeotrope, allowing for separation of the components. The selection of the entrainer is crucial for efficient separation and can have economic and environmental implications.