|Title of Invention||
PROCESS FOR REMOVING CONTAMINANTS FROM POLYETHYLENE TEREPHTHALATE
|Abstract||A process for removing contaminants from PET components by mixing ethanediol with the PET feedstock at a temperature about the boiling point of ethanediol and for a time sufficient to convert the polyethylene terephthate components to polyethylene terephthate polymers which are soluble in the ethanediol and form bis(hydroxyethyl) terephthalate and produce a product mixture thereof containing insoluble materials. The soluble polyethylene terephthate polymers, bis(hydroxyethyl) terephthalate and ethanediol are recovered form the product mixture.|
|Full Text||A METHOD FOR THE DECONTAMINATION
OF POLYETHYLENE TEREPHTHALATE
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional
Application No. 60/450,537 filed February 27, 2003.
FIELD OF THE INVENTION
The invention relates a method for the decontamination of polyethylene terephthalate
BACKGROUND OF THE INVENTION
PET is a thermoplastic polyester that can be formed from 1,2-dihydroxyethane
("ethanediol") and terephthalic acid by direct esterification to form bis (hydroxy ethyl)
terephthalate ester ("BHT") which is then polymerized by catalyzed ester exchange
to useful polymers.
Traditionally, PET has been used extensively because it can be offered as an
oriented film or fiber, has high tenacity, good electrical resistance and low moisture
absorption together with a melting point of approximately 265°C. PET has been
found to be particularly valuable for the manufacture of bottles for containing
carbonated drinks where the bottle must have good tensile strength to resist
explosion, and low mass for convenient transport and use. The extensive use of
polyethylene terephthalate bottles has given rise to the need to recycle the PET
Methods for the removal of contaminants from PET are disclosed in United States
Patent No. 5,602,187, the contents of which are hereby incorporated by reference in
their entirety. The methods disclosed in this patent all required a first pretreatment
step to embrittle the PET components of the composition. Thereafter, the embrittled
components are further treated so as to allow the contaminants to be removed. In
particular, the PET was first embrittled in ethanediol then crushed and foreign
plastics which remain uncrushed removed. The crushed crumb may be separated
from paper fiber and glue by hindered settling.
This embrittlement step requires substantial time, manpower and expense to
obtained the finished product.
The rise in the usage of PET bottles has caused a decrease in the usage of polyvinyl
chloride (PVC) bottles as they are more expensive and are difficult to recycle. This
development has markedly increased the PET content of the available recycled
plastic bottle feedstock. Additionally, improvements in sorting technology now
provides feedstock PET having lower contamination levels then the earlier
feedstocks. Further, improvements in washing technology has resulted in reduction
of potentially harmful contamination in such feedstocks.
As a result, a need exists for an improvement in the method for removal of
contaminants from the PET feedstock to take advantage of the above noted
advantages provided by these new technologies.
SUMMARY OF THE INVENTION
I have discovered a new process for removing contaminants from PET components
which substantially reduces the costs, time and manpower requirements of the prior
known processes. More particularly, I have found that one can do away with the
step of embrittleling the PET components and proceed to direct conversion of these
components to soluble materials and still obtain a removal of contaminants as good
as that achieved with the embrittlement step. As a result, the embrittleing step which
was heretofore thought necessary can thereby be avoided resulting in a substantial
reduction in costs, equipment and time in converting the PET so that it can be
This is achieved by the inventive process which comprises:
mixing ethanediol with the PET feedstock at a temperature about the boiling point of
ethanediol and for a time period sufficient to convert the polyethylene terephthate
components to polyethylene terephthate polymers-which are soluble in the
ethanediol and form bis(hydroxyethyl) terephtalate and produce a product mixture
thereof with insoluble materials, and then recovering the soluble polyethylene
terephthate polymers, bis(hydroxyethyl) terephthalate and ethanediol from the
DETAILED DESCRIPTION OF THE INVENTION
Accordingly the invention provides a process for removing contaminants from PET
components by depolymerising PET comprising the following steps:
a) transesterifying material containing PET by reacting with ethanediol, typically
under pressure and with a mixture of PET oligomers having chain lengths of about
200 units and are in the form of solid flake at a temperature at or near the boiling
point of ethanediol at the reactor pressure to convert the PET to oligomers having
about 1 to Srepeat units and a maximum mass fraction of about 3. Generally, the
pressure of the reactor is in the range from about 0.8 to 5 bar absolute pressure.
b) Admixing a adsorbent with the product from the transesterification step
capable of absorbing dyes and other contaminants in the mixture. Absorbents such
as activated carbon and activated clay are preferred. The amount of absorbent may
be varied depending on the level of contamination of the starting material. For
example, for starting flake material that is relatively clear, on could use about 0.2%
of active carbon and clay, respectively. However, this can be increased for flake the
included high loads of PVC and amber PET. Typically, the adsorbent is mixed in
and stirred for about 15 to 30 minutes;
c) a filtration aid is then admixed into the mixture of product and adsorbent and
this mixture is subjected to pressure filtration. A clean decontaminated filtrate is
Previously decontamination of post consumer PET by a "tertiary" or chemical
process required the removal of PVC to below 1% content, where hydrogen chloride
generated by thermal decomposition of the PVC can be then be adsorbed onto
active carbon and so limit the production of color by reactions of the hydrogen
The invention is illustrated by the following non-limiting example.
1500 Ib of clean post consumer flake (that had been washed in hot water then
passed through a float/sink tank to separate flotable labels and polyolefin caps etc.)
was transferred to a jacketed stirred pressure reactor and 1000 Ib of ethanediol
added. The temperature was increased to 210 °C and the pressure allowed to
increase to 2 bar with reflux. After two hours the PET had reacted with the ethanediol
to give a mainly dissolved mass of oligomers of PET. The temperature of the mass
was cooled from about 210 to 170-180. °C by adding an additional 1000 Ib of
ethanediol, which also reduced the viscosity. 15 Ib of activated carbon and 15 Ib of
activated clay were then added with continuing stirring.
At the same time, a pressure leaf filter (Amafilter 42V-160) was prepared by
suspending 100b of coarse diatomite in 3000 Ib of ethanediol at 180 °C and rapidly
depositing a layer of compact diatomite on the filter leaves. The ethanediol was
removed by introducing hot nitrogen gas under pressure to dry the filter cake. 15 Ib
of fine diatomite was then added to the reactor and the contents passed through the
filter to separate the adsorbents with the colors, glue and undissolved pigments and
foreign plastics such as, PVC and polyolefins, that were not transesterified,. The
filtrate recovered was free of particulate.
Since modifications to the steps described are various and obvious to those skilled in
this art it is to be understood that this invention is not limited to the particular
1. A process for removing contaminants from polyethylene terephthalate
(PET) without the formation of embrittled PET during the process
characterized in that the process consists essentially of:
(a) mixing ethanediol with unembrittled polyethylene terephthalate which contains contaminants at a temperature about the boiling point of ethanediol for a time sufficient to convert the polyethylene terephthalate components to polyethylene terephthalate polymers which are soluble in the ethanediol and form bis (hydroxyethyl) terephthalate and produce a product mixture thereof with insoluble material; and
(b) recovering the soluble polyethylene terephthalate polymers and bis (hydroxyethyl) terephthalate and ethanediol from the mixture.
2. The process as claimed in claim 1 wherein the soluble polyethylene terephthalate polymers and ethanediol are recovered from the product mixture by filtration.
3. The process as claimed in claim 2 wherein the filtration is high pressure filtration, the range of the said pressure is 0.5 to 8.0 bar.
4. The process as claimed in claim 2 which optionally comprises adding to the product mixture prior to filtration a material selected from the group consisting of activated carbons, activated clays and mixtures thereof.
5. The process as claimed in claim 1 wherein the polyethylene terephthalate is converted to oligomers having 1 to 5 repeat units.
6. The process as claimed in claim 1 wherein the soluble polyethylene terephthalate polymers and ethanediol are recovered from the product mixture by density separation.
7. The process as claimed in claim 1 wherein the polyethylene terephthalate is in the form of post consumer polyethylene terephthalate.
|Indian Patent Application Number||3778/DELNP/2005|
|PG Journal Number||31/2009|
|Date of Filing||25-Aug-2005|
|Name of Patentee||PETRECYCLE PTY LTD.|
|Applicant Address||LEVEL 1, 230 BALACLAVA ROAD, CAULFIELD, VICTORIA 3061, AUSTRALIA.|
|PCT International Classification Number||C08J 11/24|
|PCT International Application Number||PCT/IB2004/004448|
|PCT International Filing date||2004-02-27|