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Organic Solvent Extraction
Maceration (Steady State Extraction)
General Procedure for Maceration Process
Maceration process for organized and unorganized herbs
Organized herbs are those herbs which have
specific cell structure like roots, stems, leaves, flowers etc.
These are solid in nature. e.g. Digitalis, cinchona, clove, fennel,
jalap, ephedra etc. Maceration from organized herbs is called
“Simple Maceration”.
Unorganized herbs are those herbs which have no
cellular or tissue structure and are obtained from plants as their
exudates for like Gums, resins, juices etc. they are solid, semi
solid or liquids in nature e.g.- aloe, agar, colophony, opium,
castor oil, bees wax etc. maceration from unorganized herb is known
as “Maceration with Adjustment”.
Apparatus: - A wide mouth container
which can be well stoppered is used for maceration process. A closed
container is essential to prevent the evaporation of menstruum which
is mostly concentrated alcohol.
Simple Maceration:- In this process the
herb is placed with the whole of the menstruum in the closed vessel
for the seven days. During this period shaking is done occassionaly.
After seven days, the liquid is strained and marc is pressed. The
expressed liquid is mixed with strained liquid. It is done filtered
to make a clear liquid. The final volume is not adjusted.
Maceration with adjustment: - In this
process the unorganized is placed with 4 / 5th of the
menstruum in a closed vessel for a period of two to seven days
during this period shaking is done occasionally. After that liquid
is filtered and final volume is made up by passing the remaining 1 /
5th of the menstruum through the filter. The marc is not
pressed.
Modification of the Maceration Process:
-
For concentrated preparations and for Multiple
Maceration process.
Repeated maceration may be more effective than
single maceration, because an appreciable amount of active
constituents may be left behind in the first pressing of the marc
which may be extracted out in the next maceration. It is established
that maximum extraction is obtained in multiple maceration when the
total quantity of menstruum to be used is divided in such a way that
same quantity of menstruum is present during each maceration.
However allowance must be made for the quantity of menstruum
retained by the marc at the end of the process. Multiple maceration
may be done by double or triple maceration processes.
(i)
Double Maceration: - During this process the maceration of the
herb is carried out twice and the total volume of the menstruum to
be used is divided in two parts in such a way that same quantity of
menstruum is used for each maceration. For first maceration the
weighed amount of the herb is allowed to remain in contact with the
specified amount of menstruum with occasional shaking for a definite
time. After the time is over the liquid is strained and marc passed,
combining the strained and expressed liquid. The 2nd part
of the menstruum is then added to the marc and allowed to stand for
some time. The clear liquid is strained, marc pressed and liquids
obtained and evaporated to get a product of required concentration.
(ii) Triple Maceration: - Triple maceration process is
sometimes used where the marc cannot be pressed. As in double
maceration, in the case of triple maceration, the menstruum is
divided into three parts and maceration is done thrice.
In this process a weighed amount of herb is allowed to remain in
contact with the calculated amount of menstruum for a specified time
with occasional shaking, the clear liquid is strained and reserved.
Similarly second and third maceration is carried out by adding the
calculated quantities of menstruum. The marc is pressed at the end
of the third maceration and expressed liquid is mixed with the
liquids obtained from the 2nd and 3rd
maceration. The liquid obtained in the first maceration is quite
concentrated as compared to the liquids obtained in 2nd
and 3rd maceration hence the latter are combined and
evaporated before mixing it with the first macerate. Before the
final volume, alcohol 90% equal to 1/ 4th of the final
volume of liquid to be prepared is added to prevent the growth of
micro organisms.
Large Scale Maceration Processes
Circulatory Extraction: - The efficiency
of the maceration process can be improved by continuously
circulation of the solvent through the herb. Solvent is entered in
the vessel through the inlet where it is distributed by spray
nozzles over the surface of the herb.
Multiple Stage Extraction: - In a simple
maceration process extraction is incomplete, since mass transfer
will cease when equilibrium is set up. This problem can be resolved
by using a multi stage maceration process. The equipment is attached
to the number of tanks to receive the extracted solution. The
equipment (extractor) and tanks are connected with piping and
valves.
Advantages:-
1. The herb is
extracted many times because of receivers.
2. The last treatment of the herb before it is discharged is with
fresh solvent, giving maximum extraction.
3. The solution is in contact with fresh herb before removal of
solvent by evaporation and thus giving the highest possible
extraction.
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Percolation (Exhaustive Extraction)
The various percolation processes used for the
extraction of herbs are: -
1. Simple
Process for Tinctures
2. Percolation process for concentrated preparations such as:
(a)
Reserve Percolation Process.
(b)
Modified Percolation Process.
3. Continuous
Hot Percolation process or Soxhlet Extraction.
1. Simple Process for Tinctures:
- Simple percolation process is used for the preparation of
tinctures. There are three stages in the official method for
preparation of tinctures by simple percolation process. These are:
(A)
Imbibition: - The powdered herb is moistened with a sufficient
quantity of menstruum and allowed to stand for 4 hours in a closed
vessel. Pack the moistened herbs into a percolator and add
sufficient quantity of menstruum to saturate the material. When
liquid starts coming out from the outlet of percolator, the outlet
is closed. Then a sufficient quantity of menstruum is added in order
to leave a layer above the herb.
(B)
Maceration: - The moistened herb is left in contact with menstruum
for 24 hours. During this period, the menstruum dissolves the active
constituents of the herb and becomes almost saturated with it.
(C)
Percolation: - It consists of the download displacement of the
saturated solution formed in maceration and extraction of the
remaining active constituents present in the herb by the slow
passage of the menstruum through the column of the herb.
After collecting the 3 / 4th of the
required volume of the finished product or when the herb is
completely exhausted, the marc is pressed. Mix the expressed liquid
with the percolate. Add sufficient quantity of menstruum to produce
the required volume and then filter.
Apparatus: - Conical percolator, cylindrical
percolator and steam jacketed percolator.
Examples: - Tincture of Belladonna, compound
tincture of cardamom and strong tincture of ginger etc.
2. Percolation Process for Concentrated
Preparations: - In general process of percolation,
particularly in the manufacture of concentrated preparations like
liquids extracts, the following problems may arise:
(A)
If
the active substances are thermo-labile, evaporation of large volume
of dilute percolate may result in partial loss of the active
constituents.
(B)
In
the case of alcohol-water mixture, evaporation results in
preferential vaporization of alcohol leaving behind an almost
aqueous concentrate which may not be able to retain the extracted
matter in solution and hence get precipitated.
This percolation process is used for preparing
liquids extracts and solid extracts. The various processes used for
concentrated preparations are:
(a)
Reserve Percolation Process: In this process, a part of the
percolate, generally 3 / 4th the volume of the finished
preparation, is reserved. Then the percolation process is continued
till the herb is completely exhausted. The percolate is subjected to
evaporation or distillation (to recover the costly menstruum) to
convert it into a soft extract. This soft extract is dissolved in
the reserve portion of percolate and then sufficients menstruum is
added to produce the required volume. The portion of the percolate
which is reserved must be the first percolate because it is more
concentrated. The portion of the percolate which is evaporated
contained traces of active constituents of the herb. Hence, the
major portion of the active constituents of the herb are saved from
deterioration.
(b)
Modified Percolation Process: - In percolation process for
preparation of tinctures, the herb percolate (d\p) ratio is about 1:
4 the d/p ratio is reduced to 1 : 3 by modifying the percolation
process and hence there is a lot of saving in heat, time and menstruum.
Percolation is a displacement process. The
strong of active constituents of herb formed during maceration is
displaced by the fresh menstruum when percolation process is
started. It is proved that stationary menstruum (menstruum remaining
in contact with the herb) dissolves more matter that the flowing menstruum. Hence, more menstruum is required to exhaust the
herb
when simple percolation process is used. But if continuous
percolation stage has suitable breaks by short maceration stages,
the d/p ratio can be reduced to 1: 3.
3.
Continuous Hot Percolation Process or Soxhlet Extraction:
- When active constituents of herbs are not freely soluble in the
solvent then it becomes necessary to extract the crude herb by the
action of hot menstruum for a considerable length of time. The fixed
oils from seeds and alkaloids from the herb are extracted continuous
hot percolation process using benzene, chloroform, petroleum ether
etc.
Apparatus: -
(a)
Soxhlet Apparatus for laboratory scale.
(b) Continuous Hot extraction for Large Scale Production.
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Digestion
In digestion process the herb is extracted by
heating at a particular pressure. This will increase the penetration
power of the menstruum, so that there is complete extraction of the
herb. Precautions should be taken so that the increased temperature
may not harm the active constituents of the herb.
The apparatus known as “Digestor” is used for
extraction of the herb by this method. It is a vessel made up of
metal. The whole of the herb along with the menstruum is placed in
the body of digestor. Place the cover over it and belt it with the
help of nuts. The herb is treated with menstruum for a definite
period under specified conditions of temperature and pressure.
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Countercurrent
This is a liquid extraction process and highly
effective process whereby solvent flows in the opposite direction to
plant a material. Unlike maceration and percolation, which are batch
processes, this method is continued.
Screw extractors and carouser extractors are two types of equipments
used for countercurrent extraction. |