Distillation
Dr.H.S.Ghaziaskar
Mohammad Javad Hosseinishahi Dastjerdi
Vacuum Distillation
Molecular Distillation
Molecular Sublimation
Lyophilization (Freeze Drying)
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Vacuum Distillation
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Vacuum Distillation
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Vacuum Distillation
Perform Vacuum Distillation a if the liquid boils above 150 ̊ C
Boiling Point
Vapor pressure = External pressure
Reduced pressure = Lower boiling point
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Vacuum Distillation
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Vacuum Distillation
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Vacuum Distillation
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Vacuum Distillation
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Vacuum Distillation
If you find a leak
1. Turn off vacuum
2. Introduce air
3. Regrease the joints
4. Try again
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Vacuum Distillation
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Vacuum Distillation
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Vacuum Distillation
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Vacuum Distillation
Example summery:
bp at 760 torr = 320 ̊ C
Pressure = 0.5 torr
Expected bp =120 ̊ C
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Vacuum Distillation
When finished with the vacuum distillation:
1) Remove the heat source
2) Introduce air
3) Stop Stirring
4) Remove the flask
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Molecular Distillation
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Molecular Distillation
What is molecular distillation ?
What is mean free path of molecules ?
When molecular distillation is performed ?
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Molecular Distillation
Difference between molecular distillation an ordinary vacuum distillation
1) The liquid condensed is not allowed to flow back into the sample
2) The pressure reduced that a molecule has a good chance of
reaching the condenser surface without hitting another molecule
3) The ratios at which different component molecules distilled is
proportional to:
partial pressure
molecular weight
4)No equilibrium exists between the vapor and condensed phase.
Ideal distillation conditions are attained when the rate of evaporation is equal to the rate of
condensation .
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Molecular Distillation
Laboratory- scale molecular still
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Molecular Distillation
Diagram of the commercial molecular still
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Molecular Distillation
Commercial stills
The rate of distillation depends on how fast material from
below the surface can get to surface .
Commercial stills provide a large evaporating surface and a
continuous process ( fresh surface).
- Falling Film Stills
-Wiped Film still
-Centrifugal stills
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Molecular Distillation
ASAHI Molecular Distillation
Apparatus are designed for
distillation of heat-sensitive
substances, such as vitamins and
fine chemicals, in very high
vacuum range of 5.0 x 10-3-10-8
mmHg. Moreover, oxidation
of the distillation is eliminated
since it is operated in high vacuum
conditions.
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Molecular Distillation
Applications of Molecular Distillation
-Removal of odors and colors from plasticizers
-vitamin recovery
-Isolation of natural oils
-Purification of drugs
-Distillation of waxes and fatty acids
-Isolation of perfumes
-Deodorizing oils
-Solvent stripping
-Remove color bodies from materials of high molecular weight
-Stripping monomer from polymer
-Concentrating fruit juices
and ….
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Molecular Distillation
Theory
Langmuir ‘s method to determine the maximum amount of
material that can be distill
N
P
 moles/seco nd/cm2
2π R M T
P=pressure in dynes/cm2
M=m.w
T=temperature(K)
6 M
p

1
.
013

10
W
7608.314107  T
W=amount of distillated in grams/sec/cm2 p=vapor pressure (torr)
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Molecular Distillation
Evaporative Coefficient (f)
(f) considers three factors:
1) The fraction of molecules reaching the condenser without
collision
2) The fraction that collides first and how many reach the
condenser
3) Those that have collided and reach the condenser by random
motion
W  0.0583 M f  grams/sec/ cm 2
T
Equation to more closely represent what actually take place
5 p M D
1
.
6

10
W
Td
D=diffusivity of the organic molecules in an air atmosphere
The lower vacuum ,the higher D
d=distance in cm from evaporation surface to the condensing surface
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Molecular Distillation
Referring to langmuir ‘s equation :
P
P
P
1 : 2 : 3
M
M
M
1
2
3
A nomograph used to estimate the rate of molecular distillation
Example: Molecular distillation at 600 K ,M=700,p=0.001,f=0.1
6.3E-6
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Molecular Sublimation
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Molecular Sublimation
What is Sublimation ?
High Purity in sublimation
External Pressure =Vapor pressure  in lower melting point
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Molecular Sublimation
Sublimand
Sublimate
-Theoretically, all compounds can be sublimed , However , for most
compounds , the triple point is at such a low pressure and temperature,
that sublimation is not practical.
-The subliming temperature at reduced pressure is usually several
degrees below the melting point ,so less compound destruction occurs
during a sublimation than during a distillation.
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Entrainer Sublimation
-Sublimation can be speeded up by passing an inert gas ( Carrier
or entrainer)
-The purpose of this gas is to reduce the partial pressure of the
sublimate
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Molecular Sublimation
Entrainer sublimators
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Molecular Sublimation
Differences between a Molecular Distillation and a Sublimation at low pressure
1) The molecular distillation goes from solid to liquid to gas ,which
usually requires more energy than a sublimation.
2) The surface of the subliming compound is continuously renewed
by evaporation ,convection ,or diffusion .thus a sublimation in
many cases is faster and more economical.
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Lyophilization (Freeze Drying)
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Lyophilization (Freeze Drying)
What is Lyophilization(Freeze Drying) ?
-This works well heat sensitive materials .
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Lyophilization (Freeze Drying)
History
-The Incas prepared their food by drying it on mountain tops.
-1890 R.Altman was report microscopic investigation
-1942 (WWII), freeze drying was developed on a large scale for
processing blood plasma.
-1949 , used for food .
A freeze dried material undergoes fewer adverse changes than other
methods.
The product requires simpler storage and transportation system and
if sealed under vacuum or an inert gas , usually retain most of its
biological and physical characteristics indefinitely.
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Lyophilization (Freeze Drying)
Process
-Frozen to a temperature just below its lowest eutectic.
-Vacuum of from 4-6 torr . The heat loss by subliming water
usually will keep material frozen.(reduced the water content about 90%)
in large-scale commercial applications ,heat must be applied to provide
the sublimation energy
-Reduced pressure to a few tenths of torr to remove bound water
Freeze Rate Effects
slow freezing  large ice crystals
fast freezing tiny crystals
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Lyophilization (Freeze Drying)
A Techniques
B
C
A: Freeze drying sample holder
B: Freeze drying connecting valve
C: multi port condenser
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Laboratory- scale
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Commercial scale
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Lyophilization (Freeze Drying)
--dehydrating frozen foods
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Lyophilization (Freeze Drying)
Taxi-Dry
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Lyophilization (Freeze Drying)
--Freeze Dried Floral Art & Keepsakes
--Freeze-drying in the mycological collection
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Refrence
-Clifton E .Melon :Chemical Separations Principles ,Techniques ,and Experiments;
-Georg Wilhelm Oetjen : Freeze Drying
www.Ocw.mit.edu
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