DISTILLATION

Distillation is a process involving the conversion of a liquid into vapour that is subsequently condensed back to liquid form. It is exemplified at its simplest when steam from a kettle becomes deposited as drops of distilled water on a cold surface.

Distillation is used to separate liquids from Non-Volatile Solids, as in the separation of alcoholic liquors from fermented materials, or in the separation of two or more liquids having different boiling points, as in the separation of Gasoline, Kerosene, And Lubricating Oil from crude oil .

Other industrial applications include the processing of such chemical products as formaldehyde and phenol and the desalination of seawater.

The distillation process appears to have been utilized by the earliest experimentalists. Aristotle (384–322 BCE) mentioned that pure water is made by the evaporation of seawater. Pliny the Elder (23–79 CE) described a primitive method of condensation in which the oil obtained by heating rosin is collected on wool placed in the upper part of an apparatus known as a still.

TYPES OF DISTILLATION

Types of distillation include

1.Simple Distillation.

2. Fractional Distillation(different volatile ‘fractions’ are collected as they are produced)
3. Destructive Distillation (usually, a material is heated so that it decomposes into compounds for collection).

SIMPLE DISTILLATION

Simple distillation may be used when the boiling points of two liquids are significantly different from each other or to separate liquids from solids or nonvolatile components. In simple distillation, a mixture is heated to change the most volatile component from a liquid into vapor.

The vapor rises and passes into a condenser. Usually, the condenser is cooled (e.g., by running cold water around it) to promote condensation of the vapor, which is collected.

STEAM DISTILLATION

Steam distillation is used to separate heat-sensitive components. Steam is added to the mixture, causing some of it to vaporize. This vapor is cooled and condensed into two liquid fractions. Sometimes the fractions are collected separately, or they may have different density values, so they separate on their own.

An example is steam distillation of flowers to yield essential oil and a water-based distillate.

FRACTIONAL DISTILLATION

Fractional distillation is used when the boiling points of the components of a mixture are close to each other, as determined using Raoult’s law. A fractionating column is used to separate the components used a series of distillations called rectification.

 In fractional distillation, a mixture is heated so vapor rises and enters the fractionating column. As the vapor cools, it condenses on the packing material of the column.

The heat of rising vapor causes this liquid to vaporize again, moving it along the column and eventually yielding a higher purity sample of the more volatile component of the mixture.

VACUUM DISTILLATION

Vacuum distillation is used to separate components that have high boiling points. Lowering the pressure of the apparatus also lowers boiling points. Otherwise, the process is similar to other forms of distillation. Vacuum distillation is particularly useful when the normal boiling point exceeds the decomposition temperature of a compound.

CRYSTALLIZATION

Crystallization is defined as a process by which a chemical is converted from a liquid solution into a solid crystalline state. The widespread use of crystallization within industry is in part due to the fact that crystallization acts as both a separation and purification step.

How does the crystallization process occur?

The crystallization process consists of two major events:

• Nucleation– Molecules gather together in clusters in a defined manner. Clusters need to be stable under current experimental conditions to reach the “critical cluster size” or they will redissolve.

It is this point in the crystallization process that defines the crystal structure.

• Crystal Growth– Nuclei that have successfully achieved the “critical cluster size” begin to increase in size. Crystal growth is a dynamic process, with atoms precipitating from solution and becoming redissolved. Supersaturation and supercooling are two of the most common driving forces behind crystal formation.

Development of crystallization processes represents a complex and challenging issue, requiring simultaneous control of various product properties, including purity, crystal size and shape, and molecular level solid structure.