ANS:A - evaporation followed by vacuum distillation.

The correct answer is: evaporation followed by vacuum distillation.

Explanation:

Glycerine is typically recovered from lye (the byproduct of soap production) through a process that involves evaporation to concentrate the glycerine and then vacuum distillation to separate it from other components, ensuring a higher purity of glycerine.

Evaporation followed by vacuum distillation is a two-step process commonly used to recover glycerine from lye or other mixtures in chemical production. Here’s how each step works:

1. Evaporation

• Purpose: The primary aim of evaporation is to concentrate the glycerine solution by removing a significant portion of water and other volatile components.
• Process: In this step, the lye is heated to a temperature that causes water to evaporate, leaving behind a thicker glycerine solution. This is typically done in evaporators that allow for efficient heat transfer and vapor removal.

2. Vacuum Distillation

• Purpose: Following evaporation, vacuum distillation is employed to further purify the glycerine by separating it from any remaining impurities and non-volatile components.
• Process: In this step, the concentrated glycerine solution is placed in a distillation apparatus under reduced pressure (vacuum). The lower pressure allows glycerine and any lighter components to boil at lower temperatures, minimizing thermal degradation.
• Separation: As the mixture is heated under vacuum, glycerine vaporizes and is collected as a distillate, while heavier impurities remain in the distillation vessel.

Advantages of This Process

• Purity: This two-step process ensures high purity of glycerine by effectively removing water and impurities without exposing the glycerine to excessive heat.
• Efficiency: Both evaporation and vacuum distillation are energy-efficient methods for recovering valuable products from liquid mixtures.

Summary

Evaporation followed by vacuum distillation is an effective method for recovering glycerine from lye. The evaporation step concentrates the solution by removing water, while vacuum distillation further purifies the glycerine, ensuring a high-quality final product suitable for various applications.