D Pharmacy First Year

1. Heat Processes
Mr. G.A.Shete

2.  Heat is a form of Energy which is used in processes like Fusion, Ignition, Boiling,
Desiccation, Exsiccation, Evaporation, Distillation, Sublimation, Freeze Drying etc.
 Heat transfers from one place to another place by any one of the following
methods:
 Conduction: Heat transfer takes place by Transmission of momentum of individual
molecules. Heat transfer in solids & Liquids takes place by this method.
 Convection: Heat transfer takes place by the actual motion of particles i.e. during
the process of mixing. Heat transfer in Liquids takes place by this method.
 Radiation: energy transfer take place through space, i.e. without using any
medium.
 Desiccation: The process of complete removal of mechanically admixed water
from substances.

3.  Sublimation: it is the process in which a solid gets converted into vapours without
formation of a liquid & on cooling , the vapours get converted into solid.
 The product obtained after sublimation is called Sublimate.
 Types of Sublimate:
 Cake Sublimate
 Powder Sublimate
 Crystalline Sublimate
 Evaporation
 Evaporation is the free escape of vapour from the surface of a liquid bellow its boiling
point.

4.  Factors Affecting Evaporation
 1)Temperature:
The rate of evaporation is directly proportional to temp of liquid.
 2)Temperature and time of evaporation:
It has been observed that exposure to relatively a high temp for short period of time
may be less harmful to the active principles of a drug than a lower temp with exposure
for a longer period.
 3)Temp and moisture content:
Some drug constituent decomposes more readily in the presence of moisture if heated at
high temp. This is due to the hydrolysis of the active constituent To avoid decomposition to
the active principle of such material the evaporation is done at low temp and then final
drying is done at high temp. When only little moisture remains in it.

5.  4)Types of product required:
On evaporation of the liquid the conc. Liquid, semisolid and solid are formed. The selection
of the method and the equipment required for the evaporation depends upon the type of the
product required
 5)Effect of concentration:
During evaporation the upper layer of the liquid under evaporation has a tendency to form a
film and formation of precipitate in the product which results in lowering down of the rate of
evaporation. Therefore, efficient steering is required in order to prevent degradation of the
product at the bottom due to excessive heat and it will also prevent deposition of solid
 6)Surface area:
The rate of evaporation is directly proportional to the surface area of the evaporator, in
which the liquid is evaporated.
 7)Vapour pressure of the liquid to be evaporated:
The rate of evaporation is directly proportional to the vapour pressure of the evaporating
liquid.

6.  Short tube Evaporator:
 Construction:
It consists of number of tubes which are from 1 to 2 meters in length and from 40-80
mm in diameter. About 1000 tubes are fitted in a vessel up to 2.5 meter or more in
diameter. This part is called as “calandria”. The tubes are filled with liquid and
surrounded by steam.
The level of liquid is maintained slightly above the top of the tube so that the space
which is left in the evaporator can be used for the purpose of separation of from
boiling liquid.
 Disadvantages:
It is quite complicated and expensive in construction.
Difficult to clean.
Maintenance is costly.

7. Fig: Short tube evaporator

8.  Natural circulation evaporators:
 The movement of liquid takes place as a result of convection current set up by heating
process. Ex. evaporating pan, evaporating still, and short tube evaporator.
 Evaporating pan:
It consist of a hemispherical pan made from copper or stainless steel and surrounded by
a steam jacket. Hemispherical shape provide large surface area for evaporation. It
consist of product outlet for fixed evaporating pan. In other type evaporator is mounted
in such a way that they can be tilted.
Fig: Evaporating pan

9.  Advantages:
It is simple and cheap to construction.
Easy to clean and maintain.
Economical.
 Disadvantages:
Poor coefficient of heat transfer.
Heating surface is limited.
Not suitable for concentration of thermolabile material.
Evaporating pan is open so vapour cause discomfort to the worker.

10.  Evaporating still:
It consist of a hemispherical pan made from copper or stainless steel. It is surrounded
by a steam jacket. Still is covered from top and connected to condenser.
Hemispherical shape provide large surface area for evaporation. It consist of product
outlet at bottom.
Fig: Evaporating Still

11.  Advantage:
It is simple to construct.
Easy to clean and maintain.
The vapors are condensed in it. It increases the speed of evaporation and the costly
solvent can be recovered. E.g. ethyl alcohol.
As vapors are condensed there is no chance of discomfort to the operator.
A vacuum pump can be fitted to the condenser for operation under reduced pressure.
 Disadvantage:
The heating surface is limited.
Not suitable for thermolabile material.
Due to natural circulation, the coefficient of the heat transfer is poor.

12. Sr No Evaporation Distillation
1 Free escape of vapors from the surface
of liquid below its boiling point.
Evaporation takes place even at room
temperature.
Process of converting liquid into vapors by
heating and reconverting again into liquid
by condensing the vapors.
2 Liquid is heated below its boiling point Liquid its heated at its boiling point
3 Vapors are formed at the surface of the
liquid
Vapours are formed throughout liquid
4 Vapors formed are not usually collected Vapours formed are condensed and
collected
5 Recovery of solvent is possible in few
methods
Recovery of solvent is always done
6 used for the preparation of Conc.
Liquid, Soft and dry extract.
Used for separation of volatile oil