Distillation and its types, Exams of Pharmaceutical Chemistry

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DISTILLATION

PREPARED BY: ANKITA YAGNIK ASSISTANT PROFESSOR AKSHAR-PREET INSTITUTE OF PHARMACY, JAMNAGAR. 1

DEFINITION

 “Distillation is an unit operation which involves separation of a vaporizable component from a multi-component system and subsequent condensation of vapours.”  “Distillation is a process of separating the component substances from a liquid mixture by selective evaporation and condensation.”  “Distillation is defined as the separation of the components of a liquid mixture by a process involving vaporization and subsequent condensation at another place.” 2

TERMINOLOGY

 Binary Mixture

When two liquids mixed together, they may be miscible

with each other in all proportion, such miscible liquid are

known as binary mixtures of liquid.

Example:

• Ethanol + Water
• Acetone + Water
• Benzene + Carbon tetrachloride 4

TERMINOLOGY

 Ideal Solution (Perfect solution)

Ideal solution is defined as the one in which there is no

change in the properties of components other than

dilution, when they mixed to form a solution.

Property of ideal solution

 Total volume of solution is equal to sum of volumes of

each component

 No heat absorbed and No heat evolved

 No Chemical reaction in-between

 Final volume of solution represents additive property of

individual components

 Follow Raoult’s low 5

TERMINOLOGY

 Volatility The volatility of any substance in solution may be defined as the equilibrium partial pressure of substance in vapour phase divided by the mole fraction of substance in the solution. For example, a substance A in a liquid mixture has partial pressure PA and its concentration in the mixture is XA on mole fraction scale. Partial vapour pressure of A Volatility of component A, = Mole fraction XA of A in solution vA = PA/XA The volatility of a material in the pure state is equal to the vapour pressure of the material. (^) 7

TERMINOLOGY

 Relative Volatility

Consider a liquid mixture containing two component A and

B, In such case, the volatility of one component is

expressed in terms of second as below,

Volatility of component A (VA)

Relative Volatility ( ) =

_____________________________

Volatility of component B (VB) = VA/VB (^) 8

TERMINOLOGY

Azeotropic Mixture(Constant boiling Mixture) Mixture of special composition giving minimum or maximum boiling point than individual component with minimum or maximum boiling point respectively.  Examples  Mixture with Maximum Boiling point: Mixture containing 20.2 ml HCl + 79.8 ml water  Mixture with Minimum Boiling point Mixture containing 95.5 ml Alcohol + 4.5 ml water 10

RAOULT’S LAW

 It express a quantitative relationship between the

concentration and vapour pressure.

 It states that partial vapour pressure of each volatile

constituent is equal to vapour pressure of the pure

constituent multiplied by its mole fraction in the solution at

a given temperature.

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POSITIVE DEVIATION & NEGATIVE DEVIATION

(REAL SOLUTION)

 Positive Deviation: In some liquids systems, the total vapor pressure is greater than the sum of the partial pressures of the individual components Ex: benzene and ethanol. Differ in their polarity, length of hydrocarbon chain and degree of association.  Negative Deviation: In some liquid systems, the total vapor pressure is lower than that of the sum of the partial pressures of the individual components. Ex: Chloroform and acetone Due to hydrogen bonding, salt formation and hydration 14

DISTILLATION ASSEMBLY

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GENERAL EQUIPMENT FOR DISTILLATION:

STILL :

 It is a vaporizing chamber and used to place the material

to be distilled.

 The still is heated by a suitable means for vaporization of

the volatile constituents.

 On laboratory scale round bottom flasks made of glass

are used so that the progress of the distillation can be

noticed.

 A condenser is attached to the still using appropriate

joints. A trap is inserted between distillation flask and

condenser.

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GENERAL EQUIPMENT FOR DISTILLATION:

CONDENSER :

Bulb type Straight Tube type Spiral type Coiled type Cold finger, Spiral type Lucas’s Double Surface 19

GENERAL EQUIPMENT FOR DISTILLATION:

RECEIVER :

 It is used to collect the distillate.

 It may be a simple flask.

 It immersed in ice-bath to minimize loss of volatile

matter.

 Florentine receivers are used for the separation of

oil and water.

Types of Florentine receivers :

 Type-I :- for separation of oil heavier than water.

 Type-II :- for separation of oil lighter than water.

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