COMPLETE SPECIFICATION
AN IMPROVED PROCESS FOR THE DRYING OF MENTHOL CRYSTALS
Nectar Lifesciences Ltd.
An Indian Company having its registered office at
Village Saidpura, Tehsil Derabassi
Distt. Mohali - 140507, Punjab, INDIA
The following specification particularly describes the invention and the
manner in which it is to be performed
1
Abstract
The present application relates to an improved process for the drying of
menthol crystals of Formula I, using compartmentalized fluidized bed dryer of
Fig. 01.
Formula I
1
We Claim:
1. A process for drying of moisture and liquid impurity laden menthol
crystals of Formula I, using a system, comprising:
a) a cooling chamber followed by a heating chamber to generate
dehumidified air;
b) a compartmentalized fluidized bed dryer, comprising:
i) a material inlet at a first end thereof and an outlet of finished
material at a second end thereof;
ii) two compartments fixed with mesh of suitable size which is
further fixed with rotatory motor for the movement of mesh;
iii) both of the compartments having an inlet of dehumidified air
and an outlet separately;
c) a cyclone for collection of light fine menthol particles;
d) a bag filter for collection of very light fine menthol particles.
2. A process for drying of moisture and liquid impurity laden menthol
crystals of Formula I, comprising the steps of:
a) introducing semi-wet crystals into compartmentalized fluidized bed
dryer having suitable differential pressure (~ P), through a hopper
under the control of rotatory air lock valve using motion of vibratory
motor;
b) passing dehumidified air coming from the cooling chamber followed
by heating chamber having a suitable temperature, through first
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compartment of fluidized bed dryer in which menthol crystals are
moving on modified mesh;
c) passing dehumidified air coming from the another cooling chamber
followed by heating chamber having a suitable temperature, through
second compartment of fluidized bed dryer in which menthol crystals
are moving on modified mesh;
d) collecting dried menthol crystals for future use from the second end
of the fluidized bed dryer;
e) collecting lighter and very light fine particles of menthol by the
cyclone and by the bag filter respectively using vacuum created by the
blower induced draft.
3. The process of drying moisture and liquid laden menthol crystals as
claimed in claim 02, the differential pressure (1'1 P) in step a) is
adjusted in the range of 20 - 80 mm of Hg, more preferably in the
range of 20 - 60 mm of Hg and most preferably in the range of 20 - 40
mm of Hg.
4. The process of drying moisture and liquid laden menthol crystals as
claimed in claim 02, said suitable temperature of the dehumidified air
employed in the step iii), is adjusted in the range of 20 - 80° C., more
preferably in the range of 20 - 60° C. and most preferably in the range
of 20 - 40° C..
5. The process of drying moisture and liquid laden menthol crystals as
claimed in claim 02, said mesh used in step iii) include stainless steel
sintered mesh, high silica fiberglass filter mesh, epoxy coated steel
mesh, dutch weave mesh, hollender screen, nylon mesh, metal wire
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mesh (single layered or multi-layered), fish-shaped mesh, hexagonal
wire mesh, welded wire mesh or any combination of two or more
thereof.
6. The process of drying moisture and liquid laden menthol crystals as
claimed in claim 02, said relative humidity (RH) of the dehumidified air
employed in step iii), is adjusted in the range of 20 - 40%, more
preferably in the range of 25 - 35% and most preferably in the range of
30 - 35%.
Dated this tenth (10th
) day of June 2013
for Nectar Lifesciences Ltd.
Executive Director
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AN IMPROVED PROCESS FOR THE DRYING OF MENTHOL CRYSTALS
INTRODUCTION
Aspects of the present application relates to an improved process for
the drying of menthol crystals.
Menthol is an organic compound, mainly obtained from peppermint
and other mint or natural oils. It can be made synthetically or biosynthetically.
It is a waxy, crystalline substance and occurs in nature as (-)-menthol. The
IUPAC nomenclature of menthol is (1 R,2S,5R)-2-isopropyl-5methylcyclohexanol
and represented by the Formula I,
Menthol, marketed under the trade name SALONPAS®, is used in
liqueurs, cigarettes, nasal inhalers, cough drops, perfumery and
confectionery. It has also been used as topical analgesic, local anesthetic,
antiseptic, gastric sedative and carminative.
Menthol crystals obtained from the natural oils, are separated from the
dementholised oil by decantation and centrifugation. The centrifuged crystals
obtained are still laced with oil, required to be dried and to be free from any oil
traces which may be menthone or menthols or any other alike or any mixture
thereof.
Un-dried crystals of menthol are charged into batch type drying trays
mounted on frames. These drying trays are of 20 mesh wire and placed in
2
racks of suitable size. Wire mesh provided for passing of air from bottom of
tray. Material is allowed to dry for 24 hours in forced air circulation having
relative humidity (RH) of 50% - 55%. Racking by hand is carried out
periodically to have effective drying. There is about 2.5 % to 2.75 % loss of
product which takes place while drying and handling of the crystals. The
forced air circulation has no consistency in drying resulting in yield fluctuation.
It also enriches the room with oil vapors. These vapors cause bad effect on
the environment and the health of human being.
US Patent Number 4,052,794 claims the process of providing product
granule in a fluidized bed dryer by a) passing heated air upward in a fluidized
bed dryer; b) spraying feed solution into the dryer forming fluidized bed
therein drying particles aggregate and grow into granules to fall from the
fluidized bed; c) withdrawing aggregated particles, recovering fines blown
upward, passing fines through scrubber and d) finally, withdrawing dust laden
water from the scrubber and adding it to fluidized bed.
US Patent Number 6,231,825 claims a method of preparing sodium
borohydride from sodium borohydrate dehydrate particles. It is also disclosed
that the dihydrate particles are preferably dried in a fluidized bed formed with
a flowing stream of nitrogen.
US Patent Number 4,444,129 claims a method of drying fine coal
particles by passing coal particles to be dried from an inlet to an outlet of a
fluidized bed type dryer and directing the gases from the regenerative
separator through the fluidized bed dryer to dry the coal particles as they are
passed therethrough.
US Publication Number 20100146814 claims a system for drying and
conveying a moisture-laden material using vibratory fluid bed dryer
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comprising a flash dryer in fluid communication with said finished product
outlet having an exhaust for pulling dried material from said finished product
outlet, and a cyclone storage hopper into which dried material is deposited.
US Publication Number 20110283555 claims an indirectly heated
fluidized bed dryer for drying moist, fine-granule bulk materials comprising
housing with a gas-injection bottom, with built-in heat exchanger parts
extending above the gas-injection bottom and with at least one discharge
device.
peT Publication Number W02007096103 claims a method of batch
drying of bulk or pourable goods, in a fluidized bed dryer with a drying vessel
wherein the material flows by the drying gas through the formation of a
fluidized bed. It is also disclosed that during the drying operation, drying gas
to be fed to the gas distribution space through at least two gas inlets arranged
at a distance from one another.
The various processes available in the prior-art are suitable for drying
coal particles, food products, fine grained bulk materials, chemical and
pharmaceutical products.
But, there still remains a need to provide an improved process for the
drying of crystals including but not limited to menthol crystals, which is simple,
cost effective, commercially viable, sustainable, eco-friendly, and free from
impurities.
The present invention discloses an improved process for the drying of
menthol crystals using compartmentalized fluidized bed dryer.
The main object of the present application is to provide an improved
drying process for menthol crystals to minimize loss in yield.
4
Yet another objective of the present application is to provide a cost
effective process for the drying of menthol crystals of Formula I.
Yet another objective of the present application is to provide a process
for the drying of menthol crystals with consistency in yield.
Yet another objective of the present application is to provide a process
for the drying of menthol crystals with increase in rate of drying.
Yet another objective of the present application is to provide a process
for obtaining menthol crystals of required size.
Yet another objective of the present application is to provide a process
for the drying of menthol crystals to keep production area eco-friendly and
worker-friendly.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is an illustration of a modified compartmentalized fluidized bed dryer
used for drying of menthol crystals of Formula I, in accordance with the
present invention.
SUMMARY
In an aspect, the present application includes an improved process for
the drying of menthol crystals of Formula I,
5
wherein embodiments of the invention comprising one or more of the
following steps, individually or in the sequence recited:
i) Semi-wet menthol crystals are fed into compartmentalized fluidized
bed dryer 27 having suitable differential pressure (~ P), through a
hopper 01 under the control of rotary air lock valve 03 using motion of
vibratory motor A 02.
ii) The outside air is filtered through hepa filter 09 and forced by blower
forced draft 10 into the cooling chamber 11 attached with cooling coil
12 having inlet of chilled water 08 and outlet for chilled water 07. This
air then moves on to heating chamber 15 with heating coil 14 having
inlet of steam 06 and outlet of condensate 05.
iii) This dehumidified or moisture hungry air having suitable temperature
and suitable relative humidity (RH) is then sent to the first
compartment 29 of compartmentalized fluidized bed dryer 27 in which
menthol crystals are moving on modified mesh. This dehumidified or
moisture hungry air withdraws moisture and solvent content from the
crystals, making them dry.
iv) During the movement of menthol crystals from the first compartment
29 of compartmentalized fluidized bed dryer 27, the menthol particles
of very fine size or of powder type having very light weight goes
upward due to the vacuum created by the blower induced draft 43 and
passed on to cyclone 36 followed by bag filter 41.
v) In the same process, when menthol crystals are moving on mesh with
the help of two vibratory motors B & C 28 and reach inside second
compartment 30 of compartmentalized fluidized bed dryer 27, then
6
again these crystals meet with dehumidified or moisture hungry air of
suitable temperature which is coming through hepa filter 20 and forced
by blower forced draft 21 into the cooling chamber 22 followed by
heating chamber 26. At this time, the moisture hungry or dehumidified
air not only withdraws the remaining moisture and solvents from the
crystals but also re-crystallizes the oil laced on the menthol crystals as
L-menthol.
vi) The air coming from the first and second compartments 29 & 30 of
compartmentalized fluidized bed dryer 27 passes on to cyclone 36
where lighter fine particles drop and are collected. The air then passes
on to bag filter 41 for scrubbing. The lightest fine particles collected in
bag filter 41.
vii)The air without any usable particles then goes outside with the help of
blower induced draft 43. The dried menthol crystals come out through
the outlet 32 attached with compartmentalized fluidized bed dryer 27.
DETAILED DESCRIPTION
All temperatures are in degrees Celsius unless specified otherwise. All
measurements made are at about 25°C and about atmospheric pressure, and
all percentages and ratios used herein are by weight of the total composition,
unless otherwise designated.
As used herein, "comprising" means the elements recited, or their
equivalent in structure or function, plus any other element or elements that
are not recited. The terms "having" and "including" are also to be construed in
the same manner. All ranges recited herein include the endpoints, including
those that recite a range "between" two values. Terms such as "about,"
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"generally," "substantially," and the like are to be construed as modifying a
term or value such that it is not an absolute term or value. Such terms will be
defined by the circumstances and the terms that they modify as those terms
are understood by those having skill in the art. This includes the degree of
expected experimental error, technique error, and instrument error for a given
technique used to measure a value.
Referring to the drawing Fig. 01, the process of drying menthol crystals
is given schematically. Semi-wet menthol crystals are fed into
compartmentalized fluidized bed dryer 27 (having differential pressure (~ P)
in the range of 20 - ao mm of Hg created with the help of blower induced
draft 43 and blower forced draft 10 & 21) through a hopper 01 under the
control of rotary air lock feeder 03 using motion of vibratory motor A 02. The
compartmentalized fluidized bed dryer 27 attached with two vibratory motors
B & e 28 to enhance the fluidizing of menthol crystals fed via hopper 01
(vibratory motor e is on another side, not visible in Fig. 01). The outside air is
filtered through hepa filter 09 and forced by blower forced draft 10 into the
cooling chamber 11 attached with cooling coil 12 having inlet of chilled water
08 and outlet for chilled water 07. This air then filter through the filter system
13 and moves on to heating chamber 15 with heating coil 14 having inlet of
steam 06 and outlet of condensate 05. This dehumidified or moisture hungry
air having temperature in the range of 20 - aooe and relative humidity (RH) in
the range of 30 - 35% is then sent to the first compartment 29 of
compartmentalized fluidized bed dryer 27 in which menthol crystals are
moving on modified mesh. This dehumidified or moisture hungry air
withdraws moisture and solvents from the crystal making it dry. During the
movement of menthol crystals from the first compartment 29 of
compartmentalized fluidized bed dryer 27, the menthol particles of very fine
size or of powder type having very light weight goes upward due to the
8
(,
vacuum created by the blower induced draft 43 and passed on to cyclone 36
from the piping system 33 & 35 followed by bag filter 41. The lighter fine
particles of menthol dropped in cyclone 36 and collected in chamber 38 via
rotary air lock valve 37. The lightest fine partiCles passed on to bag filter 41
and collected via valve 42.
In the same process, when menthol crystals are moving on mesh with
the help of two vibratory motors B & C 28 and reach inside second
compartment 30 of compartmentalized fluidized bed dryer 27, then again
these crystals meet with dehumidified or moisture hungry air which is coming
through hepa filter 20 and forced by blower forced draft 21 into the cooling
chamber 22 having inlet of water 19 and outlet of chilled water 18, followed by
heating chamber 26 having inlet of steam 17 and outlet of condensate 16 by
a filter system 24. At this time, the moisture hungry or dehumidified air not
only withdraws the remaining moisture from the crystals but also recrystallizes
the oil laced on the menthol crystals as L-menthol. The air coming
from the second compartments 30 of compartmentalized fluidized bed dryer
27 via piping system 34 & 35 passed on to cyclone 36 where lighter fine
particles drop and are collected in chamber 38 via rotary air lock valve 37.
The air then passed on to bag filter 07 for scrubbing. The lightest fine
particles collected in bag filter 07 and collected via opening 42. The bag filter
41 attached with air jet pulsating system 40 which blow forced air 39 and
helps in detaching the fine particles of menthol held by the bag filter cloth.
The air without any usable particles then goes outside with the help of blower
induced draft 43. The final dried menthol crystals of bold, rice and medium
size come out from through the outlet 32 via valve 31 attached with
compartmentalized fluidized bed dryer 27.
9
In an aspect, the present application includes an improved process for
the drying of menthol crystals of Formula I,
wherein embodiments comprising one or more of the following steps,
individually or in the sequence recited:
i) Semi-wet menthol crystals are fed into compartmentalized fluidized
bed dryer 27 having suitable differential pressure (~ P), through a
hopper 01 under the control of rotary air lock valve 03 using motion of
vibratory motor A 02.
ii) The outside air is filtered through hepa filter 09 and forced by blower
forced draft 10 into the cooling chamber 11 attached with cooling coil
12 having inlet of chilled water 08 and outlet for chilled water 07. This
air then moves on to heating chamber 15 with heating coil 14 having
inlet of steam 06 and outlet of condensate 05.
iii) This dehumidified or moisture hungry air having suitable temperature
and suitable relative humidity (RH) is then sent to the first
compartment 29 of compartmentalized fluidized bed dryer 27 in which
menthol crystals are moving on modified mesh. This dehumidified or
moisture hungry air withdraws moisture and solvent content from the
crystals, making them dry.
10
iv) During the movement of menthol crystals from the first compartment
29 of compartmentalized fluidized bed dryer 27, the menthol particles
of very fine size or of powder type having very light weight goes
upward due to the vacuum created by the blower induced draft 43 and
passed on to cyclone 36 followed by bag filter 41.
v) In the same process, when menthol crystals are moving on mesh with
the help of two vibratory motors B & C 28 and reach inside second
compartment 30 of compartmentalized fluidized bed dryer 27, then
again these crystals meet with dehumidified or moisture hungry air of
suitable temperature which is coming through hepa filter 20 and forced
by blower forced draft 21 into the cooling chamber 22 followed by
heating chamber 26. At this time, the moisture hungry or dehumidified
air not only withdraws the remaining moisture and solvents from the
crystals but also re-crystallizes the oil laced on the menthol crystals as
L-menthol.
vi) The air coming from the first and second compartments 29 & 30 of
compartmentalized fluidized bed dryer 27 passes on to cyclone 36
where lighter fine particles drop and are collected. The air then passes
on to bag filter 41 for scrubbing. The lightest fine particles get collected
in bag filter 41.
vii) The air without any usable particles then goes outside with the help of
blower induced draft 43. The dried menthol crystals come out through
the outlet 32 attached with compartmentalized fluidized bed dryer 27.
In an embodiment of the present invention, the said differential pressure
(L'l P) in step i) is adjusted in the range of 20 - 80 mm of Hg, more preferably
11
"
in the range of 20 - 60 mm of Hg and most preferably in the range of 20 - 40
mm of Hg.
Suitable temperature of the said dehumidified air employed in the step iii),
is adjusted in the range of 20 - 80° C., more preferably in the range of 20 60°
C. and most preferably in the range of 20 - 40° C..
Relative humidity (RH) of the said dehumidified air employed in the step
iii), is adjusted in the range of 20 - 40%, more preferably in the range of 25 35%
and most preferably in the range of 30 - 35%.
Modified mesh used in step iii) may include, but is not limited to: stainless
steel sintered mesh, high silica fiberglass filter mesh, epoxy coated steel
mesh, dutch weave mesh, hollender screen, nylon mesh, metal wire mesh
(single layered or multi-layered), fish-shaped mesh, hexagonal wire mesh,
welded wire mesh or any combination of two or more thereof.
In another aspect, the present application includes an improved process
for the preparation of menthol crystals of Formula I,
wherein embodiments comprising one or more of the following steps,
individually or in the sequence recited:
i) Distilling crude mentha oil to get L-menthol, menthane and colored
impurities.
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ii) Charging menthol flakes into the mixing tank and heating the material
by circulating steam through the jacket for maintaining the suitable
temperature. Optionally, adding menthone to the melted mixture to get
the purity of L-menthol in suitable range. The melted solution is mixed
by recirculation through the pump for suitable period of time and
filtered through the sparkler filter.
iii) Loading the melted solution into crystallizer aluminum buckets and
maintaining the suitable temperature during loading of the material.
Check the congealing point of the material.
iv) At congealing point for crystallization, seeding the material with
suitable crystals. Observe the crystallization process and reduce the
temperature of crystallizer till the crystallization completes.
v) Decanting the mass for suitable time period so that the mother liquor
comes out of the crystals completely.
vi) Loading wet crystals into centrifuging machines to centrifuge them for
suitable time period. Semi-dried crystals are collected and mother
liquor stored in ML tank.
vii) Putting semi-dried crystals into the hopper of the fluidized bed dryer
and processing them to get dried crystals of suitable size. The
powdery particles of L-menthol collects in cyclone and bag filter.
viii) Charging dried crystals into sifter machine and doing the
grading through different mesh to obtain crystals of suitable size.
Suitable temperature that may be employed in step ii) is preferably,
maintained in the range of 20° C. to 80° C., more preferably in the range of
30° C to 70° C. and most preferably in the range of 40° C. to 60° C..
13
Suitable temperature of the crystallizer employed in step iii) is
preferably, maintained in the range of 20° C. to 80° C., more preferably in the
range of 30° C. to 70° C. and most preferably in the range of 40° C. to 60° C..
Suitable range of the purity of L-menthol is adjusted in step ii) by
adding menthone preferably in the range of 65 % to 95 %, more preferably in
the range of 70 % to 90 % and most preferably in the range of 80 % to 90 %.
Reduction in temperature of the crystallizer in step iv) may preferably
be in the range of 50° C to -50° C., more preferably in the range of 40° C. to
- 40° C. and most preferably in the range of 30°C. to - 10°C..
Suitable time period employed for mixing of melted solution in step ii)
may be preferably in the range of 30 minutes to 180 minutes, more preferably
in the range of 60 minutes to 120 minutes.
Suitable time period employed for decantation from the crystallizer
bucket in step v), may preferably be in the range of 10 hours to 30 hours and
more preferably in the range of 12 hours to 24 hours.
Suitable time period employed for centrifuging menthol crystals in step
vi) may preferably be in the range of 20 minutes to 60 minutes and more
preferably in the range of 25 minutes to 55 minutes.
Suitable crystals employed for seeding in step iv) include, but is not
limited to: peppermint crystals, menthol crystals, thymol crystals and the like,
and any mixture thereof.
Dried menthol crystals of suitable size in step vii) includes, but is not limited
to: bold crystals, rice crystals, fines and the like, and any mixture thereof.
14
EXAMPLE 01: Preparation and drying of menthol crystals of Formula I
Charge melted L-menthol flakes (8051 Kg.) in a mixing tank and heat the
material by circulating steam through the jacket to maintain temperature of
55° C. to 60° C.. Add menthone (839 Kg.) to get L-menthol of purity 87 % ±
1.5 %. Mix the contents for two hours and filter through sparkler filter. Load
menthol solution (8890 Kg.) to the crystallizer aluminum bucket at a
temperature of 40° C. to 55° C.. After 3-4 days of loading in crystallizer, seed
each bucket of crystallizer by putting menthol seed (0.500 Kg.). Check the
congealing point of solution and observe the crystallization growth. Reduce
the temperature of the crystallizer (4JO C. to _5° C.) to enhance the
crystallization process for 30 to 60 days. Decant the material for 16 to 24
hours. Centrifuge the wet crystals of menthol for about 30-60 minutes and
collect the mother liquor in ML tank. Place the semi-wet crystals into drying
trays for 20-30 hours at 20° C. to 30° C.. Observe the drying rate (400
Kg/hour) and sift the dried crystals through the sifter machine and do the
grading through different mesh size. Finally, perform sorting to check any
foreign particles. The final output results in a loss of product from 2.5 % to
2.75 %.
EXAMPLE 02: Preparation & drying of menthol crystals of Formula I
Charge melted L-menthol flakes (8051 Kg.) in a mixing tank and heat the
material by circulating steam through the jacket to maintain temperature of
55° C. to 60° C.. Add menthone (839 Kg.) to get L-menthol of purity 87 % ±
1.5 %. Mix the contents for two hours and filter through sparkler filter. Load
menthol solution (8890 Kg.) to the crystallizer aluminum bucket at a
temperature of 40° C. to 55° C.. After 3-4 days of loading in crystallizer, seed
each bucket of crystallizer by putting menthol seed (0.500 Kg.). Check the
15
congealing point of solution and observe the crystallization growth. Reduce
the temperature of the crystallizer (470 C. to _50 C.) to enhance the
crystallization process for 30 to 60 days. Decant the material for 16 to 24
hours. Centrifuge the wet crystals of menthol for about 30-60 minutes and
collect the mother liquor in ML tank. Place the semi-wet crystals into hopper
of the continous compartmentalized fluidized bed dryer and process the
crystals through it. Observe the drying rate (600 Kg/hour ~ 650 Kg/hour) and
sift the dried crystals through the sifter machine and do grading through
different mesh size. Finally, sort the material to check any foreign particles.
The final output results in a loss of product from 1.44 % to 1.65 %.