U.S. patent application number 13/730823 was filed with the patent office on 2016-01-28 for method for the production of polyester granulates from highly viscous polyester melts and also device for the production of the polyester granulates.
This patent application is currently assigned to BKG Bruckmann & Kreyenborg Granuliertechnik GmbH. The applicant listed for this patent is BKG BRUCKMANN & KREYENBORG GRANULIERTECHNIK GMBH, UHDE INVENTA-FISCHER GMBH. Invention is credited to Theodor Anton Bruckmann, Kurt Hanimann, Eike Schulz Van Endert.
Application Number | 20160023377 13/730823 |
Document ID | / |
Family ID | 40243622 |
Filed Date | 2016-01-28 |
United States Patent
Application |
20160023377 |
Kind Code |
A9 |
Hanimann; Kurt ; et
al. |
January 28, 2016 |
Method for the Production of Polyester Granulates From Highly
Viscous Polyester Melts and Also Device for the Production of the
Polyester Granulates
Abstract
The invention relates to a method and device for the direct
production of polyester granulate from a highly viscous polyester
melt with a polymerisation degree of 132 to 165, as well as the
granulates formed thereform. In the method, the highly viscous
polyester melt is subjected to a pre-drying and drying/degassing
after a hot cutting method. Hot cutting is implemented at water
temperatures of 70.degree. C. to 95.degree. C. and with a liquid to
solid ratio of 8 to 12:1.
Inventors: |
Hanimann; Kurt;
(Rodels/Pratval, CH) ; Van Endert; Eike Schulz;
(Berlin, DE) ; Bruckmann; Theodor Anton;
(Breven-Gimbte, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UHDE INVENTA-FISCHER GMBH
BKG BRUCKMANN & KREYENBORG GRANULIERTECHNIK GMBH |
Berlin
Munster |
|
DE
DE |
|
|
Assignee: |
BKG Bruckmann & Kreyenborg
Granuliertechnik GmbH
Munster
DE
Uhde Inventa-Fischer GmbH
Berlin
DE
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130127079 A1 |
May 23, 2013 |
|
|
Family ID: |
40243622 |
Appl. No.: |
13/730823 |
Filed: |
December 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13205464 |
Aug 8, 2011 |
8556610 |
|
|
13730823 |
|
|
|
|
12195962 |
Aug 21, 2008 |
7993557 |
|
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13205464 |
|
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60957806 |
Aug 24, 2007 |
|
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Current U.S.
Class: |
264/5 |
Current CPC
Class: |
B29B 9/12 20130101; B01J
8/12 20130101; B29B 13/065 20130101; B29B 9/16 20130101; B29B
2009/168 20130101; B01J 19/0066 20130101; C08G 63/90 20130101; B01J
2208/00221 20130101; B01J 2219/00779 20130101; B29B 9/065 20130101;
B01J 2219/185 20130101; B01J 19/20 20130101; B01J 2219/1946
20130101; B29B 2009/165 20130101; B29K 2067/00 20130101; B01J
2208/00176 20130101 |
International
Class: |
B29B 9/12 20060101
B29B009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2007 |
DE |
102007040135.5 |
Claims
1. Method for the direct production of polyester granulate from a
highly viscous polyester melt (hiV) with a polymerisation degree
(PG) of 132 to 165, in which the hiV melt is subjected to a
pre-drying and drying/degassing after a hot cutting method,
characterised in that the cutting phase in the hot cutting method
is effected at water temperatures of 70 to 95.degree. C. and a
liquid to solid ratio of 8 to 12:1 is maintained.
2. Method according to claim 1, characterised in that a dwell time
in the water of the hot cutting until entry into the pre-drying of
<1 second is maintained.
3. Method according to claim 1, characterised in that the liquor is
maintained in its entirety until entry into the pre-drying.
4. Method according to claim 1, characterised in that, during the
pre-drying in the upper fifth of the pre-dryer, 99% of the
circulating water is separated within <10 seconds.
5. Method according to claim 1, characterised in that, during the
pre-drying in the pre-dryer, a crystallisation degree of at least
5% is achieved so that the agglomeration of granulates is
prevented.
6. Method according to claim 1, characterised in that an outlet
moisture of the granulate from the pre-drying of <200 ppm is
achieved.
7. Method according to claim 1, characterised in that the dew point
during pre-drying in the pre-dryer is controlled to 8 to 12.degree.
C. by means of a quantity of purging air from a subsequently
connected collecting container.
8. Method according to claim 7, characterised in that a moisture of
the granulate at the outlet of the collecting container of <200
ppm to >100 ppm is achieved.
9. Method according to claim 7, characterised in that a
crystallisation degree at the outlet of the collecting container of
<25% is reached.
10. Method according to claim 1, characterised in that classifying
with a classifying screen is implemented between pre-drying and
drying/degassing.
11. Method according to claim 10, characterised in that the dwell
time on the classifying screen is at most 30 seconds.
12. Method according to claim 10, characterised in that the
granulate after classification is purged with
temperature-controlled, dry air before drying/degassing in a
collecting container.
13. Method according to claim 12, characterised in that a maximum
dwell time of 8 minutes is maintained in the collecting container,
the temperature-controlled/dried air quantity being used to control
the moisture of the pre-dryer.
14. Method according to claim 1, characterised in that the
granulate is brought from the collecting container to the drying in
a temperature-control/cooling silo by means of hot air conveyance.
Description
[0001] This application claims the benefit of the filing date of
U.S. Provisional Application Ser. No. 60/957,806 filed Aug. 24,
2007. This application is a divisional of application Ser. No.
12/195,962, filed Aug. 21, 2008, which is incorporated by
reference.
[0002] The present invention relates to a method for the continuous
production of polyester granulates from highly viscous polyester
melts which is characterised in that the reduction in the
polycondensation degree starting from the polyester melt to the
polyester granulate is less than 2%. The invention relates in
addition to a polyester granulate which is produced with this
method, and also to a device for the production of the
granulate.
[0003] A series of methods has been developed for the production of
polyester granulates, in particular PET (polyethylene
terephthalate), which methods press the molten polymer out of a
nozzle and the obtained "strands" are then cooled in a water bath
such that these solidify, then are cut by means of a cutting device
to form cylindrical chips, thereafter are cooled further to
50.degree. C. to 60.degree. C. and subsequently are treated to a
surface drying after removing the conveying water quantity in a
centrifugal dryer or in another drying appliance. These chips are
then ready for a subsequent treatment device for increasing the
viscosity, which generally comprises a plurality of steps, e.g.
crystallisers, and one or more reactors and is operated under inert
gas at up to 220.degree. C.
[0004] A further method which has become more and more accepted
even for PET is "die-face" cutting or also hot cutting. It differs
in that the nozzle, from which the polymer is pressed out, is in
direct contact with the cutting- and water chamber, a circulating
water flow constantly conveying away the "pellets" of a round to
oval form which are produced by a simple blade ring passing by the
nozzle holes, the melt heat being withdrawn and supercooling of the
"pellets" taking place. The chips/water mixture is separated and
the surface water is removed in an agitating centrifuge so that
pre-dried granulate is obtained at the end which is conveyable.
[0005] This method was improved with respect to use of the internal
heat of the polymer for crystallisation of the polyester in that
the cooling of the melt is interrupted below the melting point at
temperatures of 100.degree. C. to 190.degree. C. In this range,
crystallisation begins and, by subsequent arrangement of a
horizontal crystallisation channel, crystallisation grades of
>38% are achieved, which suffice to avoid adhesion
(agglomeration) of the chips at higher further processing
temperatures, e.g. in a drying or subsequent condensation unit. On
the other hand, the still hot "pellets" can be further
temperature-controlled at a constant temperature for further drying
and gas evolution of disruptive reaction by-products of the
polyesters in a storage container over a few hours with slight
throughflow with an entraining gas, e.g. air or an inert gas.
Consequently, an already marketable resin product can be produced.
The use of such devices has proved its worth for further
conventional production of PET.
[0006] From WO 03/042278 A1, a corresponding method is known in
addition for the production of high-molecular polyester. These PET
products have, because of the large chain length, particular
susceptibility to hydrolytic degradation under specific boundary
conditions, such as high temperature with simultaneous presence of
water or water vapour or also a long storage time with the effect
of moisture. It has thereby been shown that when there is intensive
contact of the melt with hot water with the formation of water
vapour, strong hydrolysis must be taken into account which reduces
the polycondensation degree within a few minutes by up to 20%.
[0007] For a new technology which, starting from highly viscous
melt without the use of an energy-wise and intensively complex
subsequent condensation, provides a finished product directly which
is better comparably and qualitatively than the conventionally
produced polyester granulate/pellets, disadvantages are evident
which make industrial use difficult. The following defects in
particular should be observed:
[0008] 1. rapid hydrolysis in a water vapour atmosphere already in
the pre-dryer,
[0009] 2. inadequate control of the crystallisation,
[0010] 3. high water losses by evaporation,
[0011] 4. controllability of the subsequent isothermic drying.
[0012] Starting herefrom, it is the object of the present invention
to indicate an improved method in which a hydrolytic degradation of
the polycondensation degree of directly produced polyester
granulates is avoided as far as possible. The granulate is intended
in addition to have a low content of acetaldehyde (AA content).
[0013] A further object of the present invention is to indicate a
corresponding granulate and a device for implementing such a
method.
[0014] The object is achieved with reference to the method by the
characterising features of patent claim 1, with reference to the
granulate by the features of patent claim 22 and with respect to
the device by the features of patent claim 32. The sub-claims
reveal advantageous developments.
[0015] According to the invention, it is proposed according to
patent claim 1 to optimise the method in that the hot cutting is
implemented at water temperatures of 70.degree. C. to 95.degree. C.
and with a liquid to solid ratio of 8 to 12:1. It has now been
shown that a polyester granulate or pellets can be obtained whilst
maintaining these method conditions, the polycondensation degree of
which is less than 2% below the polycondensation degree of the
highly viscous (hiV) melt. Since now, with the method according to
the invention, polyester granulates or pellets with a high
polycondensation degree, as mentioned previously, can be obtained,
it is possible furthermore to use these directly for a bottle and
film application without intermediate devices for increasing
viscosity, with which cooling of the granulate/pellets,
intermediate storage, reheating and long-term temperature control
at high temperature and also complex inert gas circulations and
renewed cooling are associated.
[0016] The method according to the invention starts from a
polyester melt which is produced with a continuous polycondensation
unit, preferably a PET melt, with a polycondensation degree of up
to 162. Methods of this type for producing highly viscous polyester
are known per se in the state of the art. In this respect, see the
already mentioned WO 03/042278 A1.
[0017] It was now shown surprisingly that, with the method
according to the invention, merely a degradation of the
polycondensation degree to values of less than 2%, preferably to
values of less than 1.5%, relative to the polycondensation degree
of the hiV melt are effected. It should be referred to with the
method according to the invention in particular that normal water
pre-separation, in order to relieve the pre-dryer, of the conveyed
water from the supply pipe of the cutting device to the pre-dryer
did not produce the expected reduction in hydrolysis, i.e. the
forming water vapour had a significantly stronger effect on the hot
surface of the pellets/granulates than a cooling water layer. It is
thereby important in order to achieve the effect that the liquid to
solid ratio, i.e. the ratio of water to pellets/granulate, is
adjusted to a liquid to solid ratio of 8 to 12:1 and that the water
temperature during the hot cutting is in the range of 80.degree. C.
to 90.degree. C. Only small differences in hydrolysis effect
resulted herefrom which are within the scatter range of the
analysis.
[0018] During the method according to the invention, PET
(polyethylene terephthalate) is preferably produced.
[0019] The following technical features emerge as crucial criteria
for a minimised hydrolysis:
[0020] 1. no pre-dewatering before the dryer,
[0021] 2. rapid discharge of the conveying water in the dryer
within <10 sec.,
[0022] 3. rapid removal of the surface water within 30 s to 2
minutes,
[0023] 4. low evaporation of residual water which has diffused into
the polymer structure with continuing drying and efficient
discharge thereof by means of dry preheated air in counterflow from
the subsequently connected collection silo,
[0024] 5. condensation of the water vapour/air mixture in a
subsequently connected spray condenser, the water of which is
removed from the conveying water circulation, cooled and returned
to the main circulation after filtration,
[0025] 6. control of the purging air with respect to quantity and
dew point, which should be between -10.degree. C. and -40.degree.
C., in the main drying for further removal of water and other
volatile by-products of the polyester.
[0026] The invention also relates to the granulate which is
produced according to the previously described method, preferably
made of PET. The granulate according to the invention which is
produced with the above-described method is characterised in
particular in that its polycondensation degree is less than 2%,
preferably less than 1.5%, relative to the polycondensation degree
of the highly viscous polyester resin. Further essential features
which characterise the granulate according to the invention are the
crystallisation degree of less than 38% (density measuring method),
a low-boiling proportion (e.g. AA, MDO etc.) of less than 1 ppm,
preferably 0.5 to 0.9 ppm, and also an excellent colour which,
according to specification, has a yellow value b* (CIELAB) of -1 to
-3. The granulate according to the invention is characterised in
addition in that its water proportion is less than 100 ppm and in
that the granulate particle weight is less than 25 g, preferably
<15 g. It is furthermore surprising that the produced granulate
has a very low content of acetaldehyde (AA content) of <0.8 ppm.
A further advantage of the granulate according to the invention is
that its specific surface is >1.4 m.sup.2/kg, preferably 1.6 to
1.8 m.sup.2/kg. The granulate according to the invention is hence
outstandingly suitable for all applications in the packaging
industry and, due to its low crystallinity, offers additional
advantages in bottle production which makes possible in particular
a low reheating temperature and consequently reduces the renewed
formation of low-boiling degradation products of the polyester and
increases the speed of the production of preforms. Also no "high
melts" in the preforms are established, which can be produced with
conventional methods during a solid phase condensation since, in
the new method, no increase in viscosity is effected because of the
described low-temperature treatment.
[0027] The invention then relates furthermore to a device for the
production of polyester granulate, preferably PET granulate, from a
highly viscous polyester melt with a polycondensation degree of 132
to 165. The device is characterised in particular in that the
pre-dryer is configured as an agitating centrifuge. In addition to
formation of the pre-dryer as an agitating centrifuge, it is
essential furthermore in the device that a specifically configured
drying/degassing device is used. The drying/degassing device of the
invention is characterised in particular in that it is configured
in the form of a vertical cylindrical container and in that the
container is subdivided into a zone of equal temperature and a
cooling zone.
[0028] The invention is described subsequently in more detail by
FIGS. 1 and 2.
[0029] FIG. 1 thereby shows a flow chart of the entire process
and
[0030] FIG. 2 shows the drying/degassing device.
[0031] The entire process is represented in FIG. 1. The course
relates to the production of PET.
[0032] The highly viscous melt (hiV) is pressed by means of a
metering pump 2 which can build up a pressure of >80 bar to 200
bar through a heated nozzle plate 3 (submerged granulation under at
least 1 bar excess pressure with a water inlet temperature of at
least 70.degree. C., preferably 80-95.degree. C.). A cutting blade
ring which runs close to the latter peels off the melt from each
hole of the nozzle plate, as a result of which round or oval grains
(pellets) are formed and solidify amorphously on the surface due to
an intensive water rinse. The water chamber is under slight excess
pressure and the liquid to solid ratio is between 8 and 12:1. The
pellet/water mixture passes via a short pipe and an agglomerate
separator 4 into the pre-dryer 5 which is configured as an
agitating centrifuge, the water separation taking place in the
lower region and the pellets emerging in the upper region.
[0033] It was shown here that, in contrast to the conventional
method, it is important to move the liquid to solid ratio towards
"zero" within a few seconds dwell time in the pre-dryer 5, i.e. in
the lower fifth of the same, to remove the water as completely as
possible, in order, on the one hand, to minimise further heat
withdrawal from the pellets by the water and, on the other hand, to
minimise the surface water film on the pellets such that, as a
result of the evaporating water, neither hydrolysis nor
supercooling of the pellets from the operating range of 120.degree.
C. to 180.degree. C. occurs. It was found at the same time that the
ratio of pellets to evaporated water in kg/kg should be only within
narrow limits of 100:1 to 20:1 in order to avoid the described
disadvantageous results.
[0034] These premises underlay the new dryer configuration. In
particular the input region of the liquor is configured such that
the agitating/conveying spirals which are configured in the form of
an open screw, obtain additional conducting elements in the form of
a blade or turbine agitator.
[0035] As a result, the fluid mass of the liquor is moved towards
the periphery of the agitator and can thus be discharged without
effort and extremely rapidly through the cylindrical, perforated
centrifuge groove there, perforation size and number requiring to
be considered. Furthermore for separation of the surface water, a
reduction in layer thickness is undertaken in that the bis dato
cylindrical centrifuge groove is configured conically at the top,
as a result of which the centrifugal forces increase continuously
and correspondingly the layer thickness of the water on the pellets
reduces. The centrifugal/conveying agitator is constantly adapted
to the increase in diameter so that the layer thickness (cake)
reduces with ever increasing diameter. The spacing of the
agitator/conveying blades to the screen groove also plays a
significant role in maximum water separation. Both water and the
forming vapour can thus be discharged easily externally through the
screen cone. A further advantage of the cone is the increased
availability of screen surface which facilitates the passage of
water and vapour. It has been shown that a cone-base/basic area
diameter of 0.75 to 0.6 produces the best effect for water
separation with simultaneous minimisation of the vapour
formation.
[0036] Astonishingly it was found also that the first
crystallisation takes place already in the pre-dryer 5 at <10%.
Repeated tests gave the result that then no more agglomeration than
is otherwise normal for PET could be established. The necessity for
a further crystallisation, e.g. on a vibrating trough, is therefore
no longer required. A simple, insulated classifying screen 6 for
separating excess lengths suffices to accomplish the further course
of diffusion and drying of low-boiling components of the PET.
[0037] An injection condenser 9 should be mentioned as a further
essential element which optimises the water balance of the casting
water circulation so that fewer sludge losses and water losses of
the water being treated in an expensive manner by reverse osmosis
result.
[0038] The injection condenser 9 is connected subsequently directly
to the pre-dryer 5 in order to reduce the unavoidably produced
water vapour in the dryer to less than 1/10. It emerged from the
mass/energy balance that for example with a pellet throughput of
12,000 kg/h, a vapour quantity of 600 kg/h was produced. From this,
530 kg/h was now able to be recovered. Since the injection
condenser is disposed in the side flow of the main casting water
circulation, the temperature control of the latter, which is of
great significance during "die-face-cutting", could therefore be
achieved at the same time.
[0039] In order reliably to avoid increased hydrolysis, it was
shown astonishingly that purging with dry air preheated to
140.degree. C. to 180.degree. C. (heater 10) through the subsequent
collecting vessel 7 and by conducting this airflow in the opposite
direction to the pellet flow through the classifying screen 6 and
the pre-dryer 5, the moisture of which is adjusted to approx.
+10.degree. C. dew point, is necessary for a uniformly
crystallising and pre-dried product which corresponds to the
demands with respect to quality. For this purpose, the air quantity
flowing into the collecting vessel 7 is controlled as a function of
the dew point at the inlet of the air into the dryer 5 such that a
residual moisture of the pellets of <200 ppm, preferably >100
ppm, is achieved at the outlet. The transfer of the hot chips into
a delay silo 8 is then effected by means of the same preheated dry
air, a "high-density" conveyance being preferred, which conveys the
spherical granulate gently into the silo.
[0040] Astonishingly, it was shown that further drying at this time
counteracts further degassing of the pellets of low-boiling
components. It was found that the small quantities of water present
in the polyester structure have an entraining effect for the
low-boiling components, which are less by a power, acetaldehyde,
methyldioxolane and other degradation products of PE, and hence the
accelerated expulsion of these materials can be controlled with the
help of the residual water component. A temporal reduction in the
gas evolution procedure by approx. 30% to 40% relative to
conventional methods was found.
[0041] The degassing part of the silo 8 is subjected to a flow of
cold air, this having a controlled dew point between -10.degree. C.
and -40.degree. C. The quantity of air is thereby set via a
controller 15 such that the by-products which diffuse out of the
pellets and are gaseous under the mentioned temperature conditions
are discharged. The ratio of pellet quantity to air quantity is set
optimally at 5 to 25. The supply of air is effected for instance at
room temperature but below the permissible pellet course
temperature of 50.degree. C., the distribution of the air being
disposed below a chips/water tubular heat exchanger which is
integrated in the silo in order to cool the chips to packaging
temperature. The air inlet itself is configured by means of a
double cone. The chip cooler ensures further improvement of the
distribution of the small quantity of air which bubbles through the
pellet column in counterflow. Because of the small quantity of air
which has a low enthalpy in relation to the mass of the pellets, a
temperature equilibrium is set in the silo 8 which does not impede
the temperature-control process. Even a few decimetres above the
chip cooler, the temperature of the chip column is in equilibrium
with the provided temperature profile of the degassing.
[0042] Advantageously, the purging/conveying air is produced by a
Konti air dryer system. As an energy-saving variant, the exhaust
air of the silo can also be used for purging the collecting
container and pre-dryer and also for the conveying air and for
regeneration of the air dryer system.
[0043] FIG. 2 shows in enlarged representation and in section the
configuration of the delay/degassing silo 8. The delay/degassing
silo 8 is thereby configured in the form of a perpendicular
cylindrical housing. The delay/degassing silo 8 is thereby
subdivided into two zones and in fact into one zone of equal
temperature 9 and into a cooling zone 10. The heat exchanger of the
cooling zone is thereby configured as a tube bundle 15 with
machining which is free of dead surfaces on its upper side. It is
thereby essential in the case of the delay/degassing silo 8 that
the free surface of the heat exchanger tubes relative to the
container surface is dimensioned at 1:4 to 1:6 and the L/D ratio of
the heat exchanger is at least 1.2:1. The introduction of the dry
air below the tube bundle of the heat exchanger is thereby
implemented through an annular gap which is produced by a double
cone. On the upper side of the container a hot gas outlet 16 is
provided. In order to monitor the temperature profile, the
delay/degassing silo 8 can have at least 3 measuring points over
the entire cylinder height which preferably can be disposed
centrally close to the central line of the container (not
illustrated). A further characteristic of the delay/degassing silo
8 is that the cylindrical part of the container is equipped with
active insulation, e.g. electrical heating, half pipe coil
jackets.
[0044] Without further elaboration, it is believed that one skilled
in the art can, using the preceding description, utilize the
present invention to its fullest extent. The preceding preferred
specific embodiments are, therefore, to be construed as merely
illustrative, and not limitative of the remainder of the disclosure
in any way whatsoever.
[0045] In the foregoing and in the examples, all temperatures are
set forth uncorrected in degrees Celsius and, all parts and
percentages are by weight, unless otherwise indicated.
[0046] The entire disclosures of all applications, patents and
publications, cited herein and of corresponding German application
No. 10 2007 040 135.5, filed Aug. 24, 2007, and U.S. Provisional
Application Ser. No. 60/957,806, filed Aug. 24, 2007, are
incorporated by reference herein.
[0047] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
[0048] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *