Article Contents
What Is Distillation ?
Before to study it , you have to know about boiling point ,relative volatility ,vapor pressure ,
Raoult’s law .If you know this ,it easy to understand this process. In this article we will study about distillation – definition, detailed process, types.
It is separation process in which components separate due to difference in boiling .
In this process two or more than two components are separated with help of
difference in there relative volatility .
It is process in which we can separate the components using Following property
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| Fig-Selection of distillation type |
- Difference in boiling point
- Difference relative volatility
- Difference in vapor pressure
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| Fig-Distillation |
Definition
It is process of separation as well as purification . Some times it is used for concentration of component in mixture of chemicals . This is engineering technology for separation of one or more than one component from a mixture of chemicals ,on the basis of there boiling point difference.
Process
This process contents , boiling or evaporation , or condensation .In this process we heat the liquid using heating source then liquid will get boil. Initially low boiling compound start to boil and vapor of low boiling compound is get condensed using condenser.In short , mixture is get vaporize by heating medium and and vapor get condensed using cooling medium. Every type of distillation has different process.
Principle
Distillation use Raoult’s law or Dalton’so law of partial pressure or total pressure for separation of chemical components. As per Raoult’s low ” partial pressure of components is equal to vapor pressure multiply by its mole fraction”.
p=Pv . Xa
p = Partial pressure in Kg/CM2
pv = vapor pressure component
Xa = Mole fraction of Component a in mixture
As per Dalton’s law ” Total pressure of ideal mixture is equal to addition of partial pressure of its components”.
Mathematical formula for total pressure is ,
P = (pv)a + (pv)b
Or
P = pa . Xa + pb . Xb
Where ,
Xb. = Mole fraction of component “a”
Xa = Mole fraction of component “b”
P = Total pressure of mixture
pa = vapor pressure of ” a “
pb = vapor pressure of ” b”.
Types of Distillation
we can classify it as bellow
- Simple
- Steam
- Vacuum
- Fractional distillation
- Azeotropic distillation
- Extractive
- Short path method
Simple Distillation
It is used when boiling point difference is large . In this process we can separate the mixture of two components bu using there boiling difference. In simple distillation
we heat the mixture ,then vapor of compound is go to the condenser and get condensed .
we heat the mixture ,then vapor of compound is go to the condenser and get condensed .
Steam Method
In this process we add steam to mixture of chemical . Main aim of this process is to separate the components bellow its de-composition temperature .
Vacuum distillation
This method is sued to save time and energy . In this type we reduce the pressure of distillation system by using vacuum generation system. There are many types of vacuum generation systems available ,like oil pump , vacuum ejector , steam ejector . We can reduce the pressure of simple distillation as well as fractional distillation .If you want distill out compound having more boiling but heating system is not available as per boiling point f that component.Example – If you have heating system with maximum temperature 150 Degree C and you want to distilled out a compound having boiling point 180 DegC. In This Case you reduce the boiling pint of that compound bu reducing temperature of distillation system.
Fractional Distillation
If you want get purify material or get separation of compound having boiling small boiling difference, you can use it. This type is applicable chemical mixture having relative volatility greater than one .This system use column for separation of compound. There are two types of distillation column . packed bed fractional column and ray type column. In this system you can use vacuum to reduce the pressure of system . Every fractional distillation should content ,Reboiler , seperation column , condenser and receiver .
You can use fractional method as continue or batch type.
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| Fig-Fractional Distillation |
Selection of Process
As we study above , there are many types are available . As an engineer we have to select correct method to separate the compounds or to get purity of components.
Some key factor or properties for selection of process are as follows ,
Boiling point difference
Relative volatility
Temperature sensitivity
Apart from above factor , costing is also one of the most important factor for selection of method. If we want to reduce costing of system we can use vacuum application . You can use fractional method under full vacuum , simple under vacuum .
Boiling point difference greater than 50 degree and relative volatility greater than 1 — use simple distillation.
Boiling point difference is greater than 50 degree but relative volatility is 1 , use Azeotropic or extractive method .
Boiling point difference is greater than 50 degree but material is temperature sensitive and relative volatility also greater than 1 — Use sort path method.
Boiling point difference is greater than 50 degree , relative volatility is greater than 1 and material is temperature sensitive also you want to optimum costing — Simple method under vacuum.
If boiling point difference is smaller than 50 degree and relative volatility is greater than 1 — Use fractional distillation.
If boiling point difference is smaller than 50 degree and relative volatility also large than 1 , and material is temperature sensitive then – use fractional method under vacuum.
Applications
Purification of Drinking water
Pharmaceutical industry
Chemical industry
Sugar industry
vine industry
Refinery
dye industry
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