U.S. patent application number 11/128501 was filed with the patent office on 2005-09-15 for crystalline form of sucralose, and method for producing it.
Invention is credited to Catani, Steven J., Merkel, Carolyn M., Vernon, Nicholas M..
Application Number | 20050203290 11/128501 |
Document ID | / |
Family ID | 33309854 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050203290 |
Kind Code |
A1 |
Catani, Steven J. ; et
al. |
September 15, 2005 |
Crystalline form of sucralose, and method for producing it
Abstract
A crystalline form of sucralose, and a method of making it. The
method involves continuously crystallizing sucralose from an
aqueous solution by a process providing continuous removal and
recirculation of the vessel contents, and providing a long
residence time for sucralose in the system. The crystals thus
formed are of a relatively low length/diameter ratio, have an
unsymmetrical shape, and exhibit good stability. The larger
crystals in particular are tapered as compared to the rod-like
larger crystals in prior art product.
Inventors: |
Catani, Steven J.; (Athens,
GA) ; Merkel, Carolyn M.; (North Haledon, NJ)
; Vernon, Nicholas M.; (Daphne, AL) |
Correspondence
Address: |
RATNERPRESTIA
P O BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
33309854 |
Appl. No.: |
11/128501 |
Filed: |
May 13, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11128501 |
May 13, 2005 |
|
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10426387 |
Apr 30, 2003 |
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Current U.S.
Class: |
536/123.13 |
Current CPC
Class: |
C07H 5/02 20130101; C07H
1/06 20130101 |
Class at
Publication: |
536/123.13 |
International
Class: |
C07H 003/00 |
Claims
What is claimed:
1-16. (canceled)
17. A composition comprising stable sucralose crystals, each of at
least a portion of the sucralose crystals comprising a plurality of
crystalline sucralose domains.
18. The composition of claim 17 having an angle of repose of less
than 42 degrees.
19. The composition of claim 17 wherein each of the sucralose
crystals has a crystal length, the crystal length being the longest
dimension thereof, and a greatest crystal width measured at right
angles to the crystal length, wherein the ratio of the crystal
length to the greatest crystal width is on average less than 6.
20. The composition of claim 17 wherein each of the sucralose
crystals has a crystal length thereof, the crystal length being the
longest dimension, and a greatest crystal width measured at right
angles to the crystal length, wherein the ratio of the crystal
length to the greatest crystal width is on average less than 4.
21. The composition of claim 17 wherein 90 wt. % of the sample has
a particle size less than from about 30 .mu.m to about 150 .mu.m,
and 10 wt. % has a particle size less than from about 3 .mu.m to
about 40 .mu.m.
22. The composition of claim 17 wherein the sucralose crystals have
a moisture content from about 0.2% to about 10%.
23. A composition comprising stable sucralose crystals, wherein the
sucralose crystals are generally tapered.
24. The composition of claim 23 wherein each of the sucralose
crystals has a crystal length, the crystal length being the longest
dimension thereof, and a greatest crystal width measured at right
angles to the crystal length, wherein the ratio of the crystal
length to the greatest crystal width is on average less than 6.
25. The composition of claim 23 wherein each of the sucralose
crystals has a crystal length, the crystal length being the longest
dimension thereof, and a greatest crystal width measured at right
angles to the crystal length, wherein the ratio of the crystal
length to the greatest crystal width is on average less than 4.
26. The composition of claim 23 wherein 90 wt. % of the sample has
a particle size less than from about 30 .mu.m to about 150 .mu.m,
and 10 wt. % has a particle size less than from about 3 .mu.m to
about 40 .mu.m.
27. The composition of claim 23 having an angle of repose of less
than 42 degrees.
28. The composition of claim 23 wherein the sucralose crystals have
a moisture content from about 0.2% to about 10%.
29. Stable sucralose crystals prepared by a method comprising:
introducing a feed stream of sucralose solution into a system
comprising a crystallization vessel, a heat exchanger, and a pump
configured to recirculate the sucralose solution out of and back
into the crystallizer vessel and through the heat exchanger:
causing sucralose crystals to form continuously in the system:
removing an output stream of sucralose solution including sucralose
crystals from the system: and continuously recirculating a part of
the output stream including sucralose crystals to the
crystallization vessel, and separating sucralose crystals from the
remaining part of the output stream; wherein the rates of
introducing, removing, and recirculating are controlled so that
sucralose passing through the system has, on average, a residence
time in the system of at least four hours: and drying the separated
sucralose crystals at a drying temperature of about 85.degree. F.
or below.
Description
FIELD OF THE INVENTION
[0001] This invention relates to stable crystals of sucralose
having improved handling properties, and a method for making the
crystals.
BACKGROUND OF THE INVENTION
[0002] Sucra lose,
4,1',6'-trichloro-4,1',6'-trideoxygalactosucrose, a sweetener with
a sweetness intensity several hundred times that of sucrose, is
made from sucrose by replacing the hydroxyl groups in the 4, 1',
and 6' positions with chlorine. Synthesis of sucralose is
technically challenging because of the need to selectively replace
specific hydroxyl groups with chlorine atoms, while preserving
other hydroxyl groups including a highly reactive primary hydroxyl
group. Numerous approaches to this synthesis have been developed.
See, e.g. U.S. Pat. Nos. 4,362,869, 4,826,962, 4,980,463, and
5,141,860, which are expressly incorporated herein by
reference.
[0003] Crystallization is widely used to purify and recover
compounds, including, but not limited to, sugar, sucralose, and
related substances. Crystallization is carried out by inducing the
formation of crystals in a solution, followed by separating the
crystals from the remaining solution (the "mother liquor"), i.e.,
recovering the crystals.
[0004] Sucralose typically crystallizes from water as needle-shaped
crystals, as described for example in U.S. Pat. Nos. 4,343,934,
5,136,031, 4,980,463, 4,977,254, 5,530,106, 5,498,709, and
4,950,746. Many of these crystals typically have a
length-to-diameter (L/D) ratio ranging from about 4:1 to about
10:1, and in some cases even higher. Indeed, all previously known
crystallization processes of which the applicants are aware produce
needles of this type. Typically, many such needles are broken,
which produces undesirable dust. Nonetheless, at least a
significant fraction of the needles remain that have high L/D
values. Such crystalline sucralose has poor handling
characteristics, including poor flow, which makes it difficult to
incorporate into formulations with other ingredients.
[0005] Attempts to overcome these difficulties have been reported
in the patent literature. For example, U.S. Pat. No. 5,932,720 to
Sankey discloses a method for increasing the flowability of
crystalline sucralose by treating the crystalline material in a
fluidized bed at ambient temperature with additions of water,
followed by a fluidized drying phase.
[0006] In U.S. Pat. No. 4,918,182 to Jackson et al, there is
disclosed crystalline sucralose said to have a mean particle size
of at most 10 microns (with 5 microns preferred), the maximum
particle size being no more than twice the mean (preferably at most
10 microns). This product is said to exhibit enhanced stability to
heat. A method of enhancing the thermal stability of crystalline
sucralose is also disclosed, comprising jet milling the sucralose
to reduce the particle size, and render the size distribution such
lo that the maximum size is no more than twice the mean.
[0007] Notwithstanding the foregoing, there remains a need for
stable sucralose crystals that have good flowability
characteristics, preferably not requiring post-crystallization
processes to modify the crystal shape.
SUMMARY OF THE INVENTION
[0008] In one aspect, the invention is a method of producing stable
sucralose crystals from a sucralose solution. The method
comprises:
[0009] introducing a feed stream of sucralose solution into a
system;
[0010] causing sucralose crystals to form continuously in the
system;
[0011] removing an output stream of sucralose solution including
sucralose crystals from the system; and
[0012] continuously recirculating a part of the output stream to
the system, and separating sucralose crystals from the remaining
part of the output stream;
[0013] wherein the rates of introducing, removing, and
recirculating are controlled so that sucralose passing through the
system has, on average, a residence time in the system of at least
four hours; and
[0014] drying the separated sucralose crystals at a drying
temperature of about 85.degree. F. or below.
[0015] In another aspect, the invention is a composition comprising
stable sucralose crystals, at least a portion of the sucralose
crystals each comprising a plurality of crystalline sucralose
domains.
[0016] In still another aspect, the invention is a composition
comprising is stable sucralose crystals, generally tapered in
shape.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic illustration of a crystallizer system
suitable for making crystalline sucralose according to the
invention.
[0018] FIG. 2 is a photomicrograph of prior art sucralose
crystals.
[0019] FIG. 3 is a photomicrograph of sucralose crystals according
to the invention.
[0020] FIG. 4 is a photomicrograph of a sieved fraction of prior
art sucralose crystals.
[0021] FIG. 5 is a photomicrograph of a sieved fraction of
sucralose crystals according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The invention is described with reference to the figures.
Such figures are intended to be illustrative rather than limiting
and are included herewith to facilitate the explanation of the
present invention. The figures representing process equipment for
practicing the invention are not to scale, and are not intended for
use as engineering drawings.
[0023] Referring now to FIG. 1, there is shown in schematic form a
crystallization system suitable for preparing stable sucralose
crystals, according to one exemplary embodiment of the invention.
Crystallizer vessel 10 contains an aqueous solution 12 of sucralose
containing suspended sucralose crystals 13. Recirculation pump 14
recycles a portion of the outlet stream from vessel 10 as
recirculation stream 16, which passes through and is heated by heat
exchanger 18 and empties back into crystallizer vessel 10, thus
providing for the presence of circulating sucralose crystals.
Although an external heat exchanger is shown in FIG. 1 (heat
exchanger 18), other means of heating may be used as well, for
example internal heating coils or a heating jacket on vessel 10. A
portion of the outlet stream from vessel 10 is drawn off by
centrifuge pump 20 and sent to a crystal separator, such as
centrifuge 22, which separates moist sucralose crystals 24 from
mother liquor 26. This mother liquor is passed on to a separate
crystallizer unit (not shown), returned to the vessel 10,
discarded, or a combination of these. The moist sucralose crystals
24 are passed through a dryer 40 to provide dried sucralose
crystals 42 as the final product, as discussed further below.
[0024] As shown in the exemplary embodiment of FIG. 1, water vapor
may optionally be drawn from crystallizer vessel 10 by vacuum pump
30 and condensed in condenser 32 to form a liquid water stream 34,
which is discarded. By otherwise controlling the temperature of
solution 12 in vessel 10, such as by controlling the temperature of
recirculation stream 16 using heat exchanger 18 and/or by removing
water, the concentration of sucralose is increased to the point of
saturation, resulting in the formation of more sucralose crystals.
Fresh aqueous sucralose is introduced to the crystallizer vessel as
feed stream 36, which in this embodiment is added to recirculation
stream 16. An optional agitator assembly 38 may be employed to
increase circulation and/or turbulence of sucralose solution 12, to
help keep the circulating sucralose crystals 13 suspended and/or to
fracture at least a portion of those crystals.
[0025] Feed stream 36 may contain from 1% up to the saturation
point of sucralose in aqueous solution, with about 20 wt. % being
typical. Feed stream 36 may be introduced into the crystallizer
system at a temperature of about 100.degree. F. It will be
appreciated by those skilled in the art that higher or lower
sucralose concentrations and higher or lower temperatures may be
used, without departing from the teachings of the invention.
[0026] Rates of flow of feed stream 36, in combination with the
rate of removal of water 34, moist sucralose crystals 24 and mother
liquor 26 from the process, relative to the volume of sucralose
solution 12, are typically controlled to give a residence time of
sucralose in the crystallizer vessel 10 with a lower limit of about
4 hours, preferably about 6 hours, more preferably about 12 hours.
Typically, the residence time will be less than about 100 hours,
preferably less than about 50 hours, and more preferably less than
about 24 hours.
[0027] While feed stream 36 is shown in the embodiment of FIG. 1 as
entering the recirculation loop ahead of heat exchanger 18, it may
enter the loop after the heat exchanger, or it may enter
crystallization vessel 10 directly.
[0028] Heat exchanger 18 is typically a tubular heat exchanger, but
other types may be used. It is typically controlled to provide a
temperature increase of about 2.degree. F. in the recirculation
stream 16. Temperature in the crystallizer vessel 10 is typically
controlled to be within a range of about 75.degree. F. to about
110.degree. F., and pressure is typically controlled to be from
about 0.7 psi (pounds/in.sup.2) to 1.2 psi, absolute. It will be
appreciated by those skilled in the crystallization art that a
variety of combinations of temperature increase in the heat
exchanger, vessel temperature, and vessel pressure may be used,
with these parameters specified relative to each other by means
known in the art to achieve vaporization and removal of water
without causing subsurface boiling. Other combinations of
temperature and pressure may therefore be used, provided that the
temperature does not exceed the melting point of the circulating
sucralose crystals 13, and provided that pressure in crystallizer
vessel 10 is low enough to afford sufficient vaporization and
removal of water. Ultimately, all of these variables are
interrelated and controlled to cause the formation of sucralose
crystals in vessel 10.
[0029] The heated recirculation stream 16 is typically introduced
into the head space of the crystallizer vessel 10, where a portion
of the water in the combined feed and recirculation stream 17
vaporizes upon entering vessel 10, thereby cooling the liquid and
increasing the concentration of sucralose.
[0030] Recirculation pump 14 produces a flow rate in recirculation
stream 16 sufficient to provide a turnover of the contents of
crystallizer vessel 10 in about 2 to about 15 minutes, preferably
from about 4 to about 8 minutes. The term "turnover" as used herein
refers to a passage through recirculation pump 14 of a volume of
liquid equal to the total volume of sucralose solution 12 in the
crystallizer vessel 10. Recirculation pump 14 is operated
continuously.
[0031] As used herein, the unmodified terms "continuous" and
"continuously" are to be understood to encompass both fully
continuous and intermittent operation, as distinct from a batch
operation. Without intending to be bound by any particular
explanation or theory, the applicants believe that the continuous
turnover provided as described here is important to the formation
of sucralose crystals according to the invention.
[0032] In the embodiment of the invention depicted in FIG. 1,
isolation of the product begins with the discharge of moist
sucralose crystals 24 from the centrifuge 22, typically at a
moisture level of about 3 wt. %. From the centrifuge the crystals
are fed to a screw hopper that holds the crystals while regulating
their feed to the dryer. One suitable dryer is a Procedyne
Continuous Fluid Bed Dryer, available from Procedyne Corporation of
New Brunswick, N.J. Other dryers suitable for use according to the
invention are described in U.S. patent application Publication No.
2002/0120134 A1, published Aug. 29, 2002, incorporated herein by
reference. Feed to the dryer goes though a rotary valve that acts
as an air lock. Using the Procedyne dryer, air is fed from a
distributor at the bottom through the sucralose crystals, thereby
fluidizing the bed, and exits the dryer through a ceramic filter.
The air is cooled, allowing moisture to condense, recompressed,
heated to the specified temperature, and returned to again enter
the bottom of the dryer. Nitrogen may be used as the drying medium
instead of air. When the fluidized sucralose crystal bed in the
dryer reaches a certain level, it overflows through a discharge
pipe, and then enters another air lock and is subsequently
collected for storage. The moisture content of the dried sucralose
crystals 42 may be from about 0.2% to about 10%, typically about
0.5%.
[0033] In another exemplary embodiment of the invention, vacuum
pump 30 and condenser 32 may be omitted from the embodiment shown
in FIG. 1, and crystallization of sucralose may be effected by
cooling solution 12 in vessel 10, thereby causing the solubility
limit to be exceeded and causing sucralose crystals to form. This
cooling may be effected in heat exchanger 18, or some equivalent
means of cooling the solution 12. Again, although an external heat
exchanger is shown in FIG. 1, other means of cooling may be used as
well, for example internal cooling coils or a cooling jacket on
vessel 10. By cooling solution 12, the concentration of sucralose
is increased to the point of saturation, resulting in the formation
of sucralose crystals. In this alternative embodiment, fresh
aqueous sucralose is introduced to the crystallizer vessel as feed
stream 36, at a temperature higher than that of sucralose solution
12. Preferably, the feed stream 36 is nearly saturated with
sucralose, so that a good yield of sucralose crystals can be
obtained. As in the first embodiment, an optional agitator assembly
38 may be employed to increase circulation and/or turbulence of
sucralose solution 12.
[0034] In this embodiment, feed stream 36, typically containing
about 50 wt. % sucralose in water, is introduced into the
crystallizer system at a temperature of about 200.degree. F. Heat
exchanger 18, typically a tubular heat exchanger, is controlled to
provide a temperature decrease of about 2.degree. F. in the
recirculation stream 16. Temperature in the crystallizer vessel 10
is controlled to be within a range of about 75.degree. F. to about
110.degree. F. Feed stream 36 may be fed fully continuously into
the system, or the feed may be intermittent.
[0035] Still other embodiments may comprise some combination of the
two embodiments described above.
[0036] It has been found that the shelf life of the dried sucralose
crystals 42 of this invention is higher but has a somewhat higher
sensitivity to drying conditions than do prior art crystals, and a
greater sensitivity to the amount of moisture retained in them.
Shelf life of crystalline sucralose is commonly estimated by
performing an accelerated aging test. In this test the crystals are
maintained in a controlled atmosphere at 50.degree. C. (122.degree.
F.), and sampled periodically. Each sample is dissolved in water
and the pH of a 10% solution is tracked to determine the elapsed
time at which the pH drops by one unit, indicating a slight
sucralose decomposition. Crystals made by traditional methods are
considered stable when such decomposition is not indicated until at
least 3 days in this test. This is considered equivalent to a shelf
life under ambient conditions of about 8 years.
[0037] To obtain stable crystalline sucralose in accordance with
the present invention, i.e. crystalline sucralose meeting the above
shelf life test, it is important to limit the temperature at which
the crystalline product is dried to about 85.degree. F. or less. A
drying temperature in the range of about 50.degree. F. to about
70.degree. F. is preferred, with a temperature of about 60.degree.
F. being typical. In addition, as disclosed in U.S. patent
application Publication No. 2002/0120134 A1, moisture content of
the crystalline product has a substantial effect on stability, with
higher levels tending to improve stability. A moisture level
between about 0.2 wt. % and about 10 wt. % is suitable, with 0.5
wt. % preferred, in order to provide stable crystalline product
according to this invention. When dried at the preferred
temperature and to moisture levels typical of old crystals showing
the noted pH drop under accelerated conditions in 3 days, the new
crystal do not show a drop for at least 3, more typical 4-6, and
often more than 6 days.
[0038] Shelf life or stability of the dried crystals 42 may also be
improved by controlling the pH of the sucralose solution 12 in the
crystallizer. To this end, it is also helpful to buffer the
sucralose solution 12 to a pH of from about 5.5 to about 8.5,
preferably about 6.5 to about 7.8, and more preferably about 7 to
7.8. An exemplary buffer comprises sodium acetate, but others may
be used.
[0039] Attention is now drawn to FIGS. 2-5, which are
photomicrographs of prior art sucralose crystals and crystals made
according to the invention. FIG. 2 shows an unfractionated sample
of typical prior art sucralose crystals, and FIG. 3 shows an
unfractionated sample of typical product made in accordance with
the present invention.
[0040] FIG. 4 shows material from a typical prior art sample of
sucralose crystals that passed through an 80-mesh sieve but was
retained on a 140-mesh sieve. FIG. 5 shows material from a typical
sample of sucralose crystals according to the invention that passed
through an 80-mesh sieve but was retained on a 140-mesh sieve. Thus
FIGS. 4 and 5 allow a clearer view of the larger size fraction of
crystals present in the prior art and inventive sucralose products,
respectively.
[0041] As seen in FIG. 3, sucralose crystals of this invention
generally have a somewhat elongated, unsymmetrical appearance.
Crystals representing a full (unfractionated) sample typically have
a particle size distribution such that 90 wt. % of the sample has a
particle size less than from about 30 .mu.m to about 150 .mu.m,
more typically from about 40 .mu.m to about 100 .mu.m, while 10 wt.
% has a particle size less than from about 3 .mu.m to about 40
.mu.m, more typically from about 4 .mu.m to about 9 .mu.m.
Sucralose crystals made according to the invention also generally
have, on average for a given sample, a length to diameter (L/D)
ratio of less than about 6, and preferably less than about 4. As
used herein, the crystal length is taken as the length of the
longest dimension of the crystal, and the width is the greatest
width measurable at right angles to the longest dimension.
[0042] As can be seen in comparing FIGS. 4 and 5, the larger
particle size fraction of sucralose crystals made according to the
present invention comprises crystals having a shape that differs
from the long, thin, substantially symmetrical needles that
normally comprise the larger particle size fraction of prior art
sucralose. Rather, crystals in the larger size fraction of the
present invention are characterized in general by the absence of
parallel surfaces on substantially all crystals, and tend instead
to be characterized by tapered or rounded tapered segments, for
example. Many of the crystals comprise a single tapered segment,
and most of the crystals are irregularly shaped with no clear
symmetry.
[0043] Without intending to be bound by any particular theory or
explanation, the applicants believe that the sucralose crystals of
this invention owe their unusual and beneficial shape and
properties to the continuous recirculation of the crystals through
the crystallizer system, and to the control of input and output
rates to give a relatively long residence time of sucralose in the
system. Under these conditions, it is believed that the sucralose
crystals are subjected to sufficient mechanical disturbance that at
least a portion of the crystals, especially long thin ones such as
might be initially formed, are fractured. The fracturing may occur
in the recirculation pump 14, in the heat exchanger 18, in bends in
the piping of the system, by crystal-crystal contact, and/or by
other means.
[0044] Such fracturing of crystals may at least partially account
for the relatively low L/D ratio of crystals formed according to
the invention. In addition, it is believed that, under these
conditions, new sites for crystal growth are generated on existing
crystals, and that subsequent deposition of sucralose from solution
onto these sites results in the formation of the unsymmetrical and
irregularly shaped crystals of this invention. Perhaps in addition
to this crystal growth on new sites, or instead of it, it may be
that, given the relatively long residence time of sucralose in the
system, agglomeration of smaller crystals forms the irregular
shapes that are typically seen in sucralose crystals according to
the invention. It is further believed that, due to such crystal
growth and/or agglomeration, many of the crystals of this invention
comprise a plurality of crystalline sucralose domains.
[0045] Sucralose crystals according to the invention have excellent
handling properties and flowability. One measure of these
characteristics is the angle of repose, defined as the steepest
angle (relative to the horizontal) that can be maintained on a pile
of the crystals. A low angle of repose indicates a powder that
flows well, a desirable characteristic for handling, as well as for
ease of mixing with other ingredients in formulations containing
sucralose. Sucralose crystals according to the invention generally
have an angle of repose less than about 42 degrees. Sucralose
crystals made according to prior art crystallization methods
typically exhibit somewhat higher angles of repose.
[0046] Another advantageous property of the sucralose crystals of
this invention is that, since no mechanical diminution process is
performed on the isolated crystals (as is the case with some prior
art processes), the product is relatively free of dust.
EXAMPLE
[0047] A system as seen in FIG. 1 comprises a vertical cylindrical
tank as the crystallizer vessel, with a 4-foot diameter, a 12-foot
straight side, a 45-degree cone bottom, and an 8-inch bottom
discharge nozzle.
[0048] Crystallizer recirculation pump 14 comprises a Model MPAF
axial flow centrifugal pump, in which the inlet, outlet, and
impeller are all ten inches in diameter (source: Goulds Pumps of
Seneca Falls, N.Y.). The pump is operated fully continuously (i.e.
not intermittently) at a rate sufficient to provide a turnover of
the vessel contents about every 5 minutes.
[0049] The entry point of the recirculation stream into the
crystallizer vessel is configured to provide a tangential entry of
the liquid, resulting in a turbulent or swirling motion that
assists in keeping circulating sucralose crystals suspended in the
vessel contents. The system is provided with a TEMA class BEM
shell-and-tube single pass heat exchanger 18. Such heat exchangers
are widely available from a number of manufacturers, and are well
known in the industry. The heat exchanger has a 0.5-in to 1.5-in
tube size, and is positioned relative to the crystallizer vessel 10
such that a static liquid head of 2-5 feet is maintained over the
exchanger, thereby preventing premature flashing of water vapor
from the heated recirculation stream before entering the headspace
of the vessel. Typically, boiling of the liquid in the system is
minimized in order to avoid uncontrolled nucleation of sucralose
crystals, as well as the formation of encrustations of sucralose
crystals on the inner surfaces of the crystallizer.
[0050] Centrifuge 22 is a model HZ 1250 Ph (Pharmaceutical)
Horizontal Peeler centrifuge, available from Krauss-Maffei Process
Technology Inc. of Florence, Ky. The unit is equipped with an
assisted discharge unit, and has a 49.2" diameter X 25.125" deep
opening, housing a 1-piece seamless polyester screen with built-in
coarse backing. The dryer is a Procedyne Continuous Fluid Bed
Dryer.
[0051] Vessel 10 is operated about half full. A 20% aqueous
sucralose solution feed stream is introduced intermittently into
the recirculation loop ahead of heat exchanger 18, at a temperature
of about 100.degree. F., and the heat exchanger is set to heat the
recirculation stream by 2.degree. F. The vessel contents are
maintained at a temperature of about 100.degree. F., with
regulation being effected by balancing heat input by the heat
exchanger with evaporative cooling by flash evaporation of water,
the latter being controlled by adjusting the pressure in the
headspace of the vessel to about 1.0 psi absolute.
[0052] Rates of flow of the feed stream, in combination with the
rate of removal of water, moist sucralose crystals and mother
liquor from the process, are controlled to give a residence time of
sucralose in the crystallizer vessel of about 24 hours. Crystals
are collected intermittently by the centrifuge, and are dried using
the above-described Procedyne dryer at a dryer temperature of about
60.degree. F. to give a final product having a moisture content of
about 0.5 wt. %.
[0053] Particle size analysis of the product is performed using a
Coulter LS100Q Particle Size Analyzer, available from Coulter
Corporation of Miami, Florida. The analyzer operates by light
scattering, using Isopar.TM. G isoparaffin fluid, available from
ExxonMobil Chemical of Houston, Tex., as the dispersing medium. The
sucralose product crystals have a particle size distribution such
that 90 wt. % of the sample has a particle size less than 62 .mu.m,
while 10 wt. % has a particle size less than from about 4 .mu.m,
with a mean of 30 .mu.m.
[0054] The stability of this product in the previously described
accelerated aging test is at least 3 days, which corresponds to
about 8 years of shelf life under typical ambient storage
conditions.
[0055] Although the invention is illustrated and described herein
with reference to specific embodiments, the invention is not
intended to be limited to the details shown. Rather, various
modifications may be made in the details within the scope and range
of equivalents of the claims and without departing from the true
spirit and scope of the invention.
* * * * *