The presentation describes various aspects of the distillation process involved in pharmaceutical industry. It includes definition, applications and types of distillation process. It focuses on simple distillation, fractional distillation, distillation under reduced pressure, steam distillation, molecular distillation vacuum distillation. It also explains boiling point composition curves, Raoult's law, Dalton's law, real solutions and ideal solutions.
2. Distillation
Definition: Separation of components of a liquid mixture by a process
involving vaporization and subsequent condensation at another place.
• Feed – Distilland
• Condensed liquid – Distillate/ condensate
Applications:
o Separation of volatile oils
o Purification of organic solvents
o Manufacture of official preparations
o Refining of petroleum products
o Recovery of solvents
o Quality control methods
o Separation of drugs
o Purification of drugs
3. Theory
• Binary mixtures: When two liquids are miscible with each
other in all proportions. E.g. alcohol and water, water and
acetone
• Ideal solutions: Solution in which there is no change in the
properties of the components other than dilution, when
they are mixed to form a solution. E.g. methanol and water
• Heat is neither evolved or absorbed during mixing
• Characterized by an important physicochemical property –
vapour pressure
• Obeys Raoult’s law.
• Components have similar structure
• Perfect solutions.
• E.g. benzene and toluene
• According to an ideal solution, component with greater VP
will be distilled first.
4. Raoult’s law
• The partial vapour pressure of each volatile
constituent is equal to the vapour pressure of
the pure constituent multiplied by its mole
fraction in the solution at a given
temperature.
5. Dalton’ law
• The total pressure exerted by a mixture of ideal
gases may be considered as sum of the partial
vapour pressure exerted by each gas, if alone
were present and occupied the total volume.
• Ideal gas – Theoretical gas, occupy negligible
volume, no inter-particle interaction, obeys gas
laws
6. Real solutions: Solutions deviating from Raoult’s
law.
• Due to solute-solute. Solvent-splute, solvet-
solvent unequal interactions
• Chloroform and acetone
• Either lower or enhance VP of mixture with
respect to ideal behaviour.
• Positive deviation
• Negative deviation
7. Simple Distillation
Principle:
• Conducted at b.p. of liquid
• Higher relative volatility – better separation
• Vapours transferred – condensed
• Purification/ Separation
Construction:
o Distillation flask with side arm
o Condenser with jacket
o Receiver flask and adapter
14. Binary Mixtures
• Type I – Miscible Liquids
• Type II – Minimum Boiling Point Azeotropic
Mixtures
• Type III – Maximum Boiling Point Azeotropic
Mixtures
15. Type I – Miscible Liquids (Zeotropic Solutions)
• Boiling point of the mixture is always between
those of pure components
• Neither a maximum or a minimum in the
composition curves
• E.g. Benzene + Toluene
Carbon tetrachloride + cyclohexane
Water + methanol
17. Azeotropic mixtures:
o Constant boiling mixtures
o Can not be separated completely by simple
distillation
o Equal volatilities
o Distills unchanged
o E.g. 89.43% mixture of ethanol and water at
atmospheric pressure……Relative Volatility is
1.0
o Can not be separated by simple distillation
18. Type II – Minimum Boiling Point
Azeotropic Solutions
• The azeotropic mixture has a lower boiling point than
that of the component with the least boiling point
• A minimum value in the boiling point-composition
curve
• At minimum boiling point temperature, liquid
composition remains constant, equal to vapour
composition
• Coincidence at the trough
• E.g. Chloroform + acetone, Pyridine + acetic acid,
Water + nitric acid
20. • All mixtures between C and T – Continuous
fractional distillation
• Pure liquid C – Still
• A mixture with constant composition – Distillate
from condenser (Condensate)
• All mixtures between T and D – Continuous
fractional distillation
• Pure liquid D – Still
• A mixture of constant composition (T) -
Condensate
21. Type III – Maximum Boiling Point Azeotropic
Solutions
• Azeotropic mixture has a higher boiling point
than that of the component with higher boiling
point
• A maximum value in the boiling point –
composition curve
• At maximum boiling point temperature, liquid
composition remains constant and equal to
vapour composition.
• Coincidence at peak
• E.g. Benzene + ethanol, Water + ethanol
23. • All mixtures between P and A – Continuous
fractional distillation
• Pure liquid A – Distillate
• A mixture of A and B with constant
composition – Still
• All mixtures between B and P – Continuous
fractional distillation
• Pure liquid B – Distillate
• A mixture of A and B - Still
26. Construction (Large Scale)
• Fractionating column
• Steam coil at bottom of column
Working:
• Mixture fed in boiler, steam supplied
• A sequence of events
• Mixture of two miscible liquids -
Liquid A (20%,MVC)
Liquid B (80%, LVC)
• Do not produce constant boiling mixture
• Boiling point composition curves – written several
times – steps in distillation
28. Steps:
• Lowest pair of curves – when boiling point
reached – vapours contain 60% of A
• These vapours condensed – liquid reheated to
b.p. – vapours contain 90% of A
• Vapours contain 98% of A (pure component)
• Condensed in condenser
• Proportion of component B in ascending
vapours decreases progressively
• Distillation ends – MVC (A) in receiver and LVC
(B) in still
29. Fractionating Columns
• A long vertical tube in which vapour passes
upward and gets partially condensed
• Condensate flows down the column – flask
Advantages:
o Large cooling surface
o Obstruction to ascending vapour – easy
condensation
Types:
• Packed column
• Plate column
31. Packed Columns
• Packing in column
• Spirals of wire or glass,
glass rings, cylindrical glass
beads, stainless steel rings
Construction:
• A tower with packing –
various length
• Long – b.p. very close
• Short – b.p. differ
• Used in laboratories, e.g.
Widmer column
Widmer Column
32. Plate Columns
• Types – Bubble cap plate, Turbo
grid plate
Bubble cap plate:
o No. of plates
o A weir leading to down comer
o Caps on each plate
o Ascending vapours pass on plate A
o Rising vapour rich in MVC
o On plate B, partially condensed
o Heat of condensation partially
vaporises liquid
o Vaporisation and condensation
repeated on plate C and so on.
33. Distillation under Reduced Pressure
Principle:
• Liquid distilled at a temperature lower than its b.p. –
vacuum applied by vacuum pump, suction pump
• Liquid boils when VP equals atmospheric Pressure
• Atm. Pressure reduced – b.p. decreases – liquid boils at
low temperature
• E.g. water boils at 100⁰C at atm. Pressure 760mm Hg.
• At 40⁰C, VP of water is 70mm Hg.
• If atm. Pressure reduced to 70mm Hg, water boils at
40⁰C
34. Assembly of apparatus
• A double neck flask, Claisen flask
• Thermometer in one neck
• Second neck – fine capillary tube
• Water bath
• Condenser, receiver
• Vacuum pump through adapter to receiver
• Manometer
37. Steam Distillation
Principle:
• Separation of substances with high b.p. from non-volatile
impurities
• Simple distillation not used – decomposition
• Used for immiscible liquids
• A mixture boils when sum of VP equals atm. Pressure
• Water + turpentine oil
• b.p. of turpentine - 160⁰C, Water - 100⁰C
• Mixture boils at 95.6⁰C
• At this temp., VP of water is 647mm Hg, VP of turpentine
113mm Hg, Total VP = 760mm Hg
• So, distillation below b.p.
40. Molecular/ Evaporative/ Short Path Distillation
Principle:
• A process in which each molecule in the vapour phase
travels mean free path and gets condensed individually
without inter-molecular collisions on application of vacuum
• Mean free path: The average distance through which a
molecule can move without coming into collision with
another
• Substances with very low VP, e.g. viscous liquids, oils,
greases, waxy materials, high molecular weight substances
• Boil at very high temperatures
• High vacuum applied to decrease b.p.
• At very low pressure, distance between evaporating surface
and condenser is approx. equal to the mean free path of
molecules
• Molecule strike to condenser
41. Theory
• Mean free path: The average distance through which a
molecule can move without coming into collision with
another
λ= ɳ
3
𝑝𝜌
Λ – MFP, m
ɳ - Viscosity, Pa.s
P – Vapour Pressure, kPa
𝜌 – Density, kg/m3
• Characteristics of substance influence method of
distillation
o Low viscosity, density – Low MFP
o Substances with high VP – Low MFP
42. • MFP can be increased by – decreasing
viscosity (ɳ) – at high temp. and low pressure
Requirements of the equipment:
o The evaporating surface close to condensing
surface ( Short path distillation)
o High intermolecular distances – minimum
collisions – high vacuum (0.1 – 1.0 pascals)
o Large SA of liquid – vaporisation from surface,
no boiling ( Evaporative distillation)
43. Falling Film Molecular Still/ Wiped Film
Molecular Still
Principle:
• Vaporization from a film of liquid flowing down a
heated surface under vacuum
• Vapour molecule travels a short distance, strikes
condenser
Construction:
o Vessel of diameter 1m with heating jacket
o Wipers – connected to a rotating head through a rotor
o Condensers close wall
o Vacuum pump connected to central pipe
o Outlets for distillate and undistilled liquid
44.
45. Centrifugal Molecular Still
Principle:
• Liquid in vessel, rotating at very high speed
• Film on wall vaporizes on heating
• Strike to adjacent condenser – collected
46. Construction:
• Bucket shaped
vessel, diameter
1-1.5m
• High speed motor
• Radiant heaters
• Condensers
• Vacuum pump at
top
• Feed inlet
• Product and
residue provisions
47. THANK YOU…!!!
(Disclaimer: The images and diagrams in this presentation
have been downloaded from the google source. I am grateful
to all the publishers & the google.)
