Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02284965 1999-09-29
ITW CASE 8492-60
INLINE SOLID STATE POLYMERIZATION OF PET
FLAKES FOR MANUFACTURING PLASTIC STRAP
CROSS-REFERENCE TO RELATED PATENT APPLICATION
This application is related to Canadian Patent File No. 2,227,952 filed
January 26, 1998, in the name of Donald Van Erden et al. and entitled INLINE
SOLID STATE POLYMERIZATION OF PET FLAKES FOR
MANUFACTURING PLASTIC STRAP.
FIELD OF THE INVENTION
The present invention relates generally to the solid
state polymerization (SSP) processing of polyethylene tereph-
thalate (PET) material, as well as the material produced by
such process, and more particularly to the solid state polym-
erization (SSP) processing of post-consumer and non-post-con-
sumer polyethylene terephthalate (PET) material, especially
for use in connection with the fabrication or manufacture of
high-performance strapping, as well as the high-performance
strapping produced by such process.
CA 02284965 2002-08-12
BACKGROUND OF THE INVENTION
Post-consumer polyethylene terephthalate (PE'I~), which is primarily provided
by or derived from plastic soft drink bottles, can be re4~dily obtained from
material recovery
facilities. Such material, however, exhibits relatively low and heterogeneous,
or a wide
distribution of, intrinsic viscosity (IV) values and in the bast, this
characteristic has prevented
such PET materials from being directly used to produce products, such as, for
example, high-
performance plastic strapping, which in fact require relatively high a.nd
homogeneous intrinsic
viscosity (IV) values. It was one of the discoveries of the invention
disclosed within the
aforenoted related Canadian Patent Application file Number 2,227,952 that such
heterogeneity, or relatively wide distribution, of the intrinsic viscosity
(IV) values of the PET
material did not in fact adversely affect the production of such high-
performance strapping
and the present invention further defines tyre intrinsic v.~isuosity (IV)
parameters or values of
the PET starting materials used in connection with the processing of such PET
materials into
high-performance plastic strapping.
1 S In accordance with prior art processing techniques, the PET material,
whether
past-consumer andlor non-post consumer material, was initially chopped into
flakes and
chunks and the flakes and chunks were. extruded into pellets. 'I~he chopped
PET materials had
a relatively low and wide range of IV values because the various soft drink
bottles, for
example, were manufactured by different companies using different materials
exhibiting
different IV values. 'rhe IV values were typically within the range of 0.60 -
0.80 dl/g. In
accordance with such prior art processing techniques, it was further believed
that in order to
make a high-performance product, such as. for example, high-performance
plastic strapping,
from such post-consumer PE'r materials, it was necessary that the mraterials
exhibit or achieve
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a relatively high and narrow range of IV values aftc;r the solid state
processing which
therefore required, as an initial step, the pellctizing of the flakes before
commencement of the
solid state polymerization. When the I'FT pellets are then subjected to solid
state
S polyrrterization (SSP), the pellets 'would have their 1V values raised and
exhibit a relatively
high and narrow range of IV values whereby such enhanced pellets could then be
used to
produce high-performance products, such as, l:or example, high-performance
strapping.
As noted hereinabove, irt accordance with the noted prior art processing
techniques, the prior art solid state polymerization (SSP) of the PET
materials commenced
with pellets of uniform geometry. Such prior art solid state polymerization
(SSP) of the
pellets, however, required an inordinate amount of tithe, that is,
approximately twelve to
nineteen hours, to complete in order to produce the desired scrapping and it
was not
appreciated, until the invention disclosed within the albrenoted Canadian
Patent Application
File No. 2,227,952, that a heterogeneous mixture of flakes and chunk-like PET
materials
1 S could undergo direct solid state polymerization, without necessarily being
initially pelletized,
to the same or higher average IV values as those of the prior art pellets and
in a significantly
faster manner, that is, upon the ardor of one-quarter the time required for
the solid state
polymerization of the pellet materials.
More specifically, it was believed that, in accordance with the teachings of
the
prior art, flakes with a wide distribution of IV values could hat be solid
stated directly and
must firstly be pelletized to a slate which is "suitable" for the production
of high performance
strapping. In this environment, the term "suitable" meant that the materials
not only exhibited
a relatively high average IV value, but in addition, the materials also
exhibited a relatively
narrow range of IV values. 'I-'he solid state polytnerizatic>n of the pellets
was intended to
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result in and did in fact result in, materials exhibiting a narrow IV value
range which those
skilled in the art believed was necessary in order to make a high-performance
product.
However, the resulting prior art strapping exhibited average I V values which
were not greater
than 0.90 dl/g. In contrast and contrary to the aforenoted teachings of the
prior art, it was
discovered that high-performance plastic strapping fabricated in accordance
with the
processing techniques disclosed within the aforenoted Canadian Patent
Application File
Number 2,227,952 exhibited average iV values which were greater than 0.90
dl/g. Therefore,
in accordance with the teachings of the invention embodied within the
aforenoted Canadian
Patent Application file Number 2,227,952, high-performance plastic strapping
could be
commercially manufactured in an economical manner using fl~,T materials,
having a relatively
wide distribution of I V values and as a result of undergoing solid state
polymerization directly
from flaked materials which do not have t~:~ be initially Iae:lletized.
'The prior art is also exemplified by the type of solid phase polymerization
processing as that disclosed within Knox, United States Patent 3,767,601,
wherein the solid
phase polymerization of waste PIT is disclosed without initially palletizing
the same.
However, again, as was true or characteristic of the aforenoted type of prior
art, the waste
PET film used as the starting materials in connection with the process
disclosed within the
Knox patent is gathered from a commercial production run c>f manufacturing PET
film and
is characterized by a relatively low and very narrow ranl;e o1' intrin.sic
viscosity (IV) values,
such as, for example, 0.50 - 0.55 dl/g. in accordance with the teachings of
the present
invention, however and contrary to the disclosure or teachings of Knox, the
initial starting
materials have a much wider distribution or diversity of IV values, such as,
for example,
within the range of 0.60 - 0.80 dl/g and as high as 0.90 dl/g and more
particularly, the
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difference in the intrinsic viscosity (IV) values between different ones or
types of starting
materials is at least, or greater than, ().~>5 dl/g, is probably at (east 0.10
dl/g and the
differential range of intrinsic viscosity (IV) values of the starting
materials can be 0.10 - 0.30
dl/g.
SUMMARY OF THE INVENTION
Accordingly, the present invention seeks to find versatile ways of reusing
post-
consumer and other forms of PET and therefore, tile present invention provides
a new and
improved inline solid state polymerization (SSP) process which increases the
IV values of
such PET materials such that I'ET flakes can be utilized for subsequent
processing of the
same into high-performance plastic strapping.
Further the present invention seeks to provide a new and improved solid state
polymerization (SSP) process, for processing PIT flakes into high-performance
plastic
strapping, whereby the solid state pc>Ivmerization of the flakes occurs faster
than similar
processing of prior art pellets.
Further still the present invention seeks to provide a new and improved solid
state polymerization (SSPI process, for processing fIT' hakes into high-
performance plastic
strapping, wherein, for example, entire post-consumer I'F,T soft-drink bottles
can be utilized,
including the relatively thick or chunk-like neck l7ortic>rxs thereof, as a
result of such neck
portions being rolled into thinner flake-like portions whiclo effectively
improves the geometry
of such portions so as to undergo more effective solid state polymerization
thereof.
Disclosed in a process of directly converting post-consumer PET flake
materials
to materials having relatively high average intrinsic viscosity (IV) values
whereby such
resulting materials are useful in connection with the f~'brication of
particularly desirable
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products, such as, for example, high-performance strapping. High performance
strapping
exhibits increased weld strength. Weld strength is critically important in
view of the fact that
weld strength is often the weak link in strapping products. A weld strength
value which is
equal to 50% of the tensile strength of' the strapping is considered normal
for conventional
or prior art high-performance strapping. As a result c>f the pro<;essing
techniques of the
present invention, however, the tensile strength and accordingly a
proportional percentage of
the weld strength, of the strapping produced has been able to be increased
approximately 30%
with respect to the conventional or prior art high-performance strapping.
CTenerally, when
the tensile strength is increased, percentage joint strength decreases,
however, the process of
the present invention not only retains joint strength, but actually increases
percentage joint
strength. 'The process of the present invention not only produces strapping
which exhibits at
least a 50% joint strength value, but can produce strapping which exhibits a
joint strength
value as high as 80%. 'these characteristics of the manufactured strapping
help clarify what
is meant in the art as "high performance" strapping.
The invention in one broad aspect comprehends a process for making a
polyethylene terephthalate (PET) material. comprising the steps oh collecting
diverse PET
material having a wide distribution of tntrmstc vtscostty (IV) values within
the range of 0.60
to 0.90 dl/g and wherein the difference in the IV values of the collected PET
material is at
least 0.05 dl/g, co-mingling the collected I'E'f material and reforming the co-
mingled PET
material into a single heterogeneous IV batch mixture of' IaI:T' material
comprised substantially
of a plurality of non-uniform flake-like and chunk-like pieces and directly
subjecting the
single heterogeneous 1V batch mixture of PET material to solid state
polymerization (SSP)
so as to form a heterogeneous PET material having an average IV value of at
least 0.85 dl/g.
More particularly the inventive process begins by obtaining post-consumer and
non-post-consumer material containing PE'l'. These materials may be obtained,
for example,
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from strapping or material recovery facilities and the materials have a
relatively wide
distribution or diversity of initial IV values, such as, fir example, within
the range of 0.60
dl/g to 0.80 dl/g and as high as 0.90 dl/g and more particularly, the
difference in the intrinsic
viscosity (IV) values between different ones or types of starting materials is
at least, or greater
than, 0.05 dl/g, is probably at least 0.10 dl'g and can be within the range of
0.10 - 0.30 dl/g.
The PET materials usually contain a variety of impurities, such as., for
example, PVC.
The PVC and PET materials arc then chopped into a heterogeneous mixture of
flakes and chunks and the PET and PVC flakes and chunks are preheated within a
dryer or
preheater so as to undergo a preheating stage at a temperature level of
approximately 270 -
350°F and for a time period of approximately 3.S - 4 hours. As a result
of such preheating
process step, the PET materials are dried in view of molecular water having
been removed
therefrom and the PVC flakes and chunks are brov~ned. ~fhe 1E'1' and browned
PVC
materials are discharged from the dryer «r preheater and conveyed through a
pair of flattening
rolls which generally do not disturb or alfcc°t the flake pieces but
flatten the chunk pieces into
a more flake-like state. The browned PVC:' flakes or flake-like chunks are
removed through
means of suitable color-sensitive camera ~:~pparatus or equipment.
Subsequently, the PET
flakes, from which the PVC flakes have now been removed, are now ready to
enter the first
stage of solid state polymerization and accordingly, the PET flakes are placed
into a hopper
and heated in the absence of oxygen and in the presence of nitrogen until they
reach a
temperature level of between 420°l' and 4,0°F.
After undergoing the first stage of solid state polymerization for
approximately
one hour or more, the flakes are ready to enter the second stage of solid
state polymerization
and accordingly, the heated flake mixture is removed from the hopper and
placed within a bin
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in the absence of oxygen and in the presence of n itragerr. The flakes are
heated to a
temperature level of appraximately 425°F and remain in the bin for a
time period of
approximately four hours.
Once the flakes have completed the first and second stages of solid state
polymerization, the LV value of the resulting PET material has been increased
to at least 0.90
dl/g and to as high as 1.50 dl/g, with the average l V value being
approximately 0.95 dl/g.
The PET flakes, having the enhanced I V values, can then be extruded through a
suitable
extruder so as to produce high-performance strapping. 'fire strapping produced
by means of
the process of the present invention, that is, utilizing I'ET flakes which
have been directly
subjected to solid state polymerization, which have not necessarily been
subjected to
intermediate pelletization and which have resulted in material having an
enhanced average IV
value of approximately 0.95 dl/g and a wide distribution of 1V values within
the range of 0.90
dl/g to 1.50 dl/g, is therefore able to comprise high-performance strapping
which exhibits
good tensile strength, weld strength and joint str=ength characteristics. In
addition, the solid
state polymerization process to which the flakes of~ the present invention are
subjected only
requires a fractional amount of time that was previously required in
connection with the prior
art processing of the PET material pellets. As a result of such faster
processing times
experienced or facilitated by the present invention, increased residence times
of the flakes
within the SSP processing may be implemented so as to economically produce
materials of
even greater IV values and performance characteristics, that is, the tensile
and weld strength
properties thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
Various other aspects, features and attendant advantages of the present
invention
will be more fully appreciated from the following detailed description when
considered
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in connection with the accompanying drawings in which like
reference characters designate like or corresponding parts
throughout the several views, and wherein:
FIGURES lA-1C comprise a flow chart showing the var-
y ious steps of the PET flake process of the present invention;
FIGURE 2 is a flow chart of a nitrogen cycle por-
tion, of the solid state polymerization (SSP) stage of the
process of the present invention, including the use of a guard
bed for HCl removal; and
10 FIGURE 3 is a graph showing the relationship between
the amount of PET material and the intrinsic viscosity (IV)
for a starting material and various resulting materials pro-
duced under different conditions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
15 Referring now to the drawings, and more particularly
to FIGURE 1A thereof, post-consumer and non-post-consumer
polyethylene terephthalate (PET) materials are collected from
any one or more of various different sources, including, for
example, material recovery facilities, and the materials are
20 co-mingled into a heterogeneous mixture. In addition to con-
taining or comprising polyethylene terephthalate (PET) materi-
als, the mixture also usually contains various other materi-
als, or impurities such as, for example, PVC, polypropylene,
polyethylene, paper, and the like, which are not desirable for
25 use within the solid state polymerization (SSP) processing of
the PET materials in accordance with the present invention.
Accordingly, the heterogeneous mixture of the majority post-
consumer PET materials and the minority post-consumer PVC ma-
terials and other impurities are firstly chopped into flakes
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and chunks so as to render such constituents or components suitable for
further processing
in accordance with the subsequent processing steps characteristic of the
present invention.
The flakes and chunks are respectively derived, for example, from wall
portions and neck
portions of plastic soft drink bottles, with the neck or chunk portions being
thicker and denser
than the wall or flake portions. T'he materials are then subjected to a
flotation segregation
process which serves to separate the polyethylene, polypropylene and any paper
material from
the PET materials as a result of' bulk density techniques whereby the
polyethylene,
polypropylene and paper material components float to the top of the flotation
apparatus while
the PET materials sink to the bottom of the flotation a.pparaius.
The 1'ET materials prepared in accordance with the foregoing process steps
initially have a substantially wide intrinsic viscosity (1V) value range which
in fact extends
from a relatively low 1V value of approximately 0.60 dl/g to a relatively high
IV value of
approximately 0.80 dl/g, with the average initial I V value being
approximately 0.70 dl/g as
shown by curve A in I'IGURF: 3. The reaxson for this relatively wide range of
IV values is
due, for example, to the fact that different plastic sofVt drink bottles are
manufactured by
different bottle manufacturers using different plastic materials. It is .also
to be appreciated still
further that the initial mixture of PET materials can have IV values which may
differ from
those noted hereinabove depending upon the particular s«urce of the materials.
It is possible,
for example, to use recycled materials. other than plastic soft drink bottles,
which are
characterized by relatively low IV values, or alternatively, to use recycled
high performance
strapping made either by prior art processes or by the process of the present
invention
whereby such strapping may exhibit average IV values of U.90 dl/g or higher.
In any case,
it is to be appreciated that the initial materials can be and usually are,
quite diverse and
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comprise materials wherein the intrinsic viscosity (1 V ) values differ from
each other by at
least 0.05 dl/g and can differ in IV values by as much as, at least, or up to,
0.10 - 0.30 dl/g,
or in other words, between 0.10 and 0. i0 dl/g. It is to be appreciated
further that in
accordance with the various teachings of the present invention, it is possible
to produce, from
a heterogeneous mixture having a relatively wide or broad distribution of IV
values of, for
example, 0.60 - 0.80 dl/g and as high as 0.90 dllg and characterized further
by a relatively
low average IV value of, for example, 0.7~J dl/g, r°esultant materials
which have a relatively
wide or broad distribution oh IV values, such as, for example 0.70 dl/g to
1.50 dl/g and
characterized by a relatively high average 1V value oi~, for example, 0.X5
dl/g as illustrated
by means of curve B shown in FIC?IIRI:~ ~.
The precise curves and material results or characteristics will of course
depend
upon the initial input material characteristics and the particular processing
parameters and
accordingly, curves C and D of FIGURE 3 illustrate other resultant materials
having relatively
1 S wide distributions of I V values with, however, different average IV
values, the different
materials being produced as a result of diiTerent process residence times. It
is therefore to
be appreciated that in accordance with the processing techniques and
parameters characteristic
of the present invention, resulting solid state polymerized (SSI') material,
having an average
IV value of, for example, approximately t).80 - 0.85 dl/g and useful or
suitable for fabricating
high-performance strapping exhibiting currently or conventionally acceptable
quality and
performance characteristics, can in fact be fabricated merely by reducing the
residence time
of the materials within the process. Accordingly, still further and quite
advantageously, high-
performance strapping exhibiting conventionally acceptable average IV values
and tensile
strength and weld strength characteristics, can be manufactured faster and
more economically
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when ultra-high-performance strapping, which can also be manufactured in
accordance with
the various processing techniques characteristic of the present invention and
having an average
IV value of, for example, 1.15 dl/g, are not in fact required for particular
applications.
Accordingly, with continued reference being made to FIGURE 1A, after the
polypropylene, polyethylene and paper materials or impurities have been
segregated from the
charge or batch materials, the PET and 1'V('. flake materials are placed
within a suitable
preheater tank or dryer so as to undergo a pre-heating stage. In the preheater
tank or dryer,
the P>=:T and 1'VC flake materials are heated to a temperature level of
approximately 2?0°F
- 352°F and for a time period of approximately _3.5 tcs .4.0 hours.
rhhe purpose of the pre-
heating stage is essentially to dry the flake materials so as to remove
molecular water
therefrom and to also brown the PVC m~iterials. 'l h~; pre-heated. materials,
including the
browned PVC materials, are then removed from the preheater tank or dryer and
conveyed
toward a pair of flattening rolls.
The flattening rolls permit the wall flake portions to f>ass through the nip
of the
flattening rolls in a generally undisturbed state. however. the neck chunk
portions are
flattened. By flattening the relatively thick neck chunk portions, the
geometry of such
portions is altered such that such flattened neck chunk portions now resemble
the wall flake
portions. When the rolled or flattened neck chunk portions are subsequently
heated to a solid
stating temperature of approximately 420 - 430°F, it has been found
that they tend to reform
themselves back into their original shape or configuration, however, as a
result of the
processing of such materials in accordance with the teachings of the present
invention, when
such materials are heated to approximately 420 - 430°I~ during the:
solid stating thereof and
when they tend to reform themselves back to their original shape or
configuration, they do
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so with many cracks and splits being formed within such mater-
ial pieces. These cracks and splits therefore reduce the dis-
tance from any point within the piece to a surface region
thereof, and therefore, these reformed, cracked or split, ori-
ginally chunk-type neck pieces solid state substantially like
the original flake-type wall pieces.
After flattening, the flakes and flattened chunks
are conveyed along a conveyor belt and are studied by highly
sensitive cameras for color. The cameras are able to isolate
the browned PVC flakes. The positions of the browned PVC
flakes are then identified and an air blast or other suitable
means are actuated so as to discharge the browned PVC flakes
from the conveyor belt and into a discharge bin. At this point
in the process, the material has been purified of the unwanted
PVC flakes and consists of substantially solely PET flakes.
The browned PVC flakes are weighed and correlated with the
weight of the preheated PET flakes, as well as compared with
the weight of the entire original sample of PET and PVC flakes
that went through the preheater, whereby it can be determined
if substantially all of the PVC material has been removed from
the batch of PET flake materials to be processed further in
accordance with the solid stating techniques of the present
invention.
It is important to remove the PVC flakes from the
batch of materials to be solid stated so as to prevent the
production of hydrochloric acid (HC1) which tends to damage
the equipment or apparatus used in connection with the solid
state polymerization processing. In addition, if PVC is pre-
sent within the materials undergoing the solid state polym-
erization, brown streaks will be present within the extruded
film or material which then, in turn, appears within the pro-
duced strapping. Still further, the presence of PVC material
may also lead to clogging of the melt filtration components of
the extruder, and PVC also tends to lower the intrinsic vis-
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cosity (IV1 values of the flakes undergoing the solid state
polymerization.
The PET flakes are now ready for the first stage of
the solid state polymerization process. It is known that the
different thickness characteristics or dimensions of different
products or materials affects the time required to solid state
the materials to a predetermined IV value, and as noted in the
aforenoted related parent patent application, the relatively
thicker neck or chunk portions are slower to solid state than
the relatively thinner wall or flake portions. The first stage
of solid state polymerization comprises increasing the temper-
ature of the charge or batch of PET materials, and in view of
the fact that the chunk portions or materials have been previ-
ously, in effect, converted to flake portions or materials as
a result of the flattening or rolling process, the time re-
quired for processing the wall or flake portions or materials
is relatively short whereby enhanced processing efficiency,
comprising the processing flow-through of the flake or wall
portions of the materials, is able to be achieved. More par-
ticularly, the PET flakes are deposited within a hopper which
comprises an oxygen-free environment within which nitrogen gas
is disbursed. The temperature of the materials is elevated to
approximately 420°F-430°F. The flakes are continuously depos-
ited into the hopper, and they continuously move through the
hopper from the top of the hopper to the bottom of the hopper,
during which time the materials experience a slight increase
in their IV values. In accordance with one embodiment or ex
ample of practicing the present invention process, this first
stage of solid state polymerization takes approximately one
hour.
The heated PET flakes are now ready for the second
stage of solid state polymerization. Accordingly, the flakes
are removed from the preheating hopper and are continuously
deposited into a bin. The heated PET flakes are retained with-
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in the bin for a processing time period of approximately four hours during
which time the
flakes travel from the top of the bin to the bottom of the bin and the
temperature level within
the bin is in the range of i80°F to 425°lv in accordance with a
nitrogen cycle which will be
explained more fully hereinafter. As a result of such processing, thc;
intrinsic viscosity (IV)
value of the PET flakes, which was initially within the range of approximately
0.60 dl/g to
0.80 dl/g, but could be as high as 0.90 dl/g, increases substantially to an
average IV value of
approximately 0.95 dl/g and with a wide distribution ot' I V values ranging
from approximately
0.70 dllg to 1.5 dllg as shown, for example, by .means of curve I3 in FIGURE
~. The heated,
high intrinsic viscosity flakes may then be removed from the bin and fed
directly to an
extruder from which high-performance strapping, having an IV value of at least
0.9U dl/g,
may be manufactured.
During the solid state polymerization process, various volatile organic
compounds are formed. For example, ethylene glycol is a by-product generated
from
the polyester, acetaldehyde is a decomposition by-product of ethylene glycol
and hydrochloric
acid (ICI) is generated as a result of the heating c~f the polyvinyl chloride
(PVC).
The nitrogen cycle is utilized within the second stage of solid state
polymerization so as
to, in effect, rid the system or process of such contaminants. As more fully
illustrated in
FI(:~URE 2, the nitrogen cycle comprises supplying pure nitrogen to the bottom
of the bin and
aspirating the contaminants from the top of the bin. 'rhe nitrogen travels
upwardly through
the bin and through the flakes and in so doing, the nitrogen lowers the
partial pressure within
the system and permits the contaminants to vaporize whereby the acetaldehyde,
ethylene
glycol and hydrochloric acid (HCl) are effectively extracted and entrained
within the nitrogen.
The nitrogen supplied or used within the: nitrogen cycle may either be
continuously supplied
pure nitrogen or nitrogen which has been derived from the cycle and purified
of
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the contaminants. If the latter option is chosen, the same ni-
trogen can of course be reused which renders the process much
more economical.
The contaminants can be removed from the nitrogen in
5 accordance with any one of several different techniques or
processes. One way is through the desiccant process formulated
by BEPEX ~. Another means is through removal of waste prod-
ucts by the catalytic oxygen process developed by BUHLER ~ . A
still further manner for removing hydrochloric acid (HC1) from
10 the nitrogen cycle is through the use of a lime bag filter ap-
paratus which eliminates the HC1 from the flow of gas. Yet an-
other manner in which to remove the HC1 from the nitrogen cyc-
le is to conduct the gas through a water spray whereby the HC1
is absorbed in the water slurry. A further endeavor may com-
15 prise the use of a guard bed of basic material as will be dis-
cussed more fully hereinafter.
The removal of the contaminants, and in particular,
the removal of the HCl, is important for several reasons. Dur-
ing the second stage of the solid state polymerization, the
20 amount of HCl that is emitted is relatively small, however,
the presence of the HCl may nevertheless cause problems within
at least two areas or regions of the apparatus and process of
the present invention, that is, in connection with catalytic
activity, and also in connection with corrosion, especially
25 when liquid water is or may also be present. HC1 is known to
deactivate a platinum catalyst, although the amount of such
deactivation, as might be encountered during practice of the
present invention process, is not precisely known. Increased
temperature can offset some of the catalyst deactivation but
30 at an increased risk of sintering, that is, permanent deacti-
vation, of the catalyst. Increasing the size of the catalyst
bed is also an option for offsetting lower catalyst activity,
however, this option increases catalyst costs, drops the
pressure within the system, and may require additional blower
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capacity. In connection with the corrosion problems, liquid
water tends to absorb HC1 from the passing gas stream and con-
centrate the same to levels where corrosion rates become prob-
lematic. This condition appears to exist at a location after
the condenser which cools the process stream and before the
absorbent bed.
In accordance then with various embodiments envi-
sioned by the teachings of the present invention, as more spe-
cifically illustrated in FIGURE 2, and as noted briefly here-
inbefore, the problems of catalytic deactivation and corrosion
due to HC1 reactions may be eliminated by removing the HCl
from the process of the present invention as soon as possible
by utilizing a guard bed of basic material. Such a guard bed
may be added to the BUHLER ~ line just before the catalyst
bed, or alternatively, may be incorporated within the bag
house filter assembly just after the solid state fluidized
bed. In accordance with another embodiment, the guard bed may
be placed after the bag house filter assembly so as to avoid
plugging the same with PET particles. In accordance with still
another embodiment, the relatively simpler BEPEX ~ design
omits the catalyst bed, so consequently, the guard bed can be
placed immediately after the solid state fluidized bed or in
the bag house filter assembly. In accordance with techniques
employed in connection with placing the guard bed within the
bag house filter assembly, the bag house filter can be coated
with a basic solid, such as, for example, calcium oxide, lime,
caustic soda, or bicarbonate, so as to neutralize the acid. In
this case, the conventional filter bags would be replaced by
those of the present invention. Still yet alternatively, the
guard bed may also take the form of a spray chamber which
sprays water or bicarbonate.
With reference continuing to be made to FIGURE 2,
suitable monitors may also be incorporated within the process-
ing line or system for detecting the levels of HCl present
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CA 02284965 1999-09-29
within the system or the various processing components there-
of. The levels of HCl could occasionally rise due to the pre-
sence of PVC material within the solid state fluidized bed. A
simple HC1 monitor can comprise a small fluid stream of known
5 flow rate into a scrubber-bubbler attached to an automated
titration unit, and the consumption of bases or basic materi-
als so as to maintain constant pH values would constitute a
simple yet direct way to measure HCl levels.
Due to the fact that steel or even stainless steel
is likely to corrode at excessive rates when liquid water is
in the presence of HC1 or C12, the apparatus of the present
invention may be constructed from alternatively viable con-
struction materials, such as, for example, CPPC, PP, or a
steel having a corrosion-resistant coating. The 13x molecular
15 sieves used in the BEPEX ~ desiccant process are also known
to degrade in the presence of acids. Accordingly, a larger bed
may have to be used so as to compensate for the lost drying
capacity. The deterioration of the sieves may also produce
powdered sieves. If this happens, the powder could be carried
20 into the PET production materials and/or accumulate within the
lower end of the desiccant vessel and thereby impede gas flow.
In order to prevent this from occurring, a section of the pro-
duction facility or plant could be provided with suitable fil-
ters so as to filter out the generated powder materials and
25 thereby prevent PET contamination with the same, and easily
accessible access ports could be provided within the bottom
regions of the apparatus whereby cleaning of the facility is
readily facilitated. In accordance with still another embodi-
ment, the nitrogen may be drenched, as the same passes through
30 the fluidized bed, with by-pass desiccant fumes. In any case,
once the nitrogen has been purified of its contaminants by any
one of the foregoing processes, the purified nitrogen can be
conducted back into the bottom of the bin so as to undergo an-
other nitrogen cycle.
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CA 02284965 1999-09-29
The process can be conducted either as a batch pro-
cess or as a continuous process. One of the important factors
in connection with the process of the present invention is
that the nitrogen gas removes volatile polymerization reaction
S products, including ethylene glycol and other impurities,
which can cause undesirable secondary reactions. If, for ex-
ample, more than twenty parts per million of PVC is still con-
tained within the flakes after the preheater stage, the flakes
will produce HC1 and degrade the desiccant which is used to
10 purify the nitrogen used in the second stage of the solid
state polymerization (SSP) process. As such, the desiccant
would have to be replaced more than once per year due to the
reactions between the HCl and the desiccant.
As briefly noted hereinabove, after the flakes have
15 passed through the hopper and bin structures of the first and
second stages, respectively, of the solid state polymerization
process, the flake products are removed from the bin of the
second stage of the solid stage polymerization process and di-
rectly fed in a hot state to the feed hopper of the extruder
20 from which the high-performance strapping is to be produced.
The feeding of the hot flake products or materials directly
from the solid state polymerization second stage bin to the
strap-producing extruder is economically advantageous in that
such processing conserves significant heat within the polymer
25 materials and accordingly reduces the power requirements per
pound of polymer to be extruded.
The degree of uniformity of the product resulting
from the process of the present invention is surprising in
view of the variety and relatively wide range of the intrinsic
30 viscosity (IV) values of the initial materials. In addition,
heating and solid state polymerization of the PET flakes pro-
ceeds readily, rapidly, and without any substantial problems,
such as, for example, agglomeration of the polymers, sticking
of the polymers to the processing equipment, or degradation of
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CA 02284965 1999-09-29
the polymers, as is often the case with pellets. An unexpected
result achieved by means of the process of the present inven-
tion is the production of a product which has a relatively
high average IV value and which was obtained using materials
5 having a wide range of relatively low initial IV values. Stat-
ed alternatively, an initially narrow range of IV values is
not in fact required in either the initial materials which
will undergo the solid state polymerization process and which
will be used to manufacture strapping, or in the final strap-
10 ping itself so as to obtain high quality, high-performance
plastic strapping.
Thus, it may be seen that the solid state polymeri-
zation process of the present invention advantageously leads
to the production of high-performance strapping in an econom-
15 ically desirable manner from both material flow-through and
production downtime points of view, although obviously, many
modifications and variations of the present invention are pos-
sible in light of the above teachings. For example, the pre-
cise operating or procedural parameters of the process of the
20 present invention may be altered somewhat in order to achieve
desired intrinsic viscosity (IV) values. Intrinsic viscosity
increases with increased amounts of nitrogen gas, with in-
creased temperature levels within the solid state polymeriza-
tion stages, as well as with increased residence times within
25 the solid state polymerization stages. It has also been deter-
mined that preheating the flakes to reaction temperature lev-
els reduces the size of the bin necessary to effect solid
state polymerization. In addition, it has been further deter-
mined that relatively thin flakes exhibit increased IV values
30 much faster than pellets or relatively thick chunks, and they
obtain high IV values, and most significantly or importantly,
flakes, unlike pellets or chunks, are most desirable in view
of the fact that the flakes do not become sticky or cause ag-
glomeration either in the first or second stage of the solid
35 state polymerization_ Oxygen is not added during either the
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CA 02284965 1999-09-29
preheat or solid state polymerization stages because the
presence of oxygen will degrade and color the polymers, and
nitrogen is the preferred gas to be used in the solid state
polymerization process because it does not lead to the adverse
5 effects that would be caused by oxygen, and because it is
economical and readily available. It is therefore to be
understood that within the scope of the appended claims, the
present invention may be practiced otherwise than as
specifically described herein.
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