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Claims  |
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We claim:
1. A polyisocyanurate form comprising the reaction product of an organic
polyisocyanate, a blowing agent, a trimerization catalyst, and a minor
amount of a polyol, wherein from about 5 to 100 weight percent of the
polyol comprises a polyester polyol mixture comprising the reaction
product obtained by
(a) digesting polyethylene terephthalate with a digesting medium comprising
a polycarboxylic acid component-containing polyol derived from a digesting
polycarboxylic acid component and a digesting polyol component to form a
digested polyol mixture and liberate ethylene glycol from said
polyethylene terephthalate, and
(b) distilling from said digested polyol mixture the amount of liberated
ethylene glycol sufficient for improved storage stability of the mixture.
2. A process for producing a polyisocyanurate foam comprising reacting
together under foam-forming conditions an organic polyisocyanate, a
blowing agent, a trimerization catalyst, and a minor amount of a polyol,
wherein from about 5 to 100 weight percent of the polyol comprises the
polyester polyol mixture of claim 1.
3. A polyurethane foam comprising the reaction product of an organic
polyisocyanate, a blowing agent, a catalyst and a polyol, wherein from
about 5 to 100 weight percent of the polyol comprises a polyester polyol
mixture comprising the reaction product obtained by
(a) digesting polyethylene terephthalate with a digesting medium comprising
a polycarboxylic acid component-containing polyol derived from a digesting
polycarboxylic acid component and a digesting polyol component to form a
digested polyol mixture and liberate ethylene glycol from said
polyethylene terephthalate, and
(b) distilling from said dispersed polyol mixture the amount of liberated
ethylene glycol sufficient for improved storage stability of the mixture.
4. A process for producing a polyurethane foam comprising reacting together
under foam-forming conditions an organic polyisocyanate, a blowing agent,
a catalyst and a polyol, wherein from about 5 to 100 weight percent of the
polyol comprises the polyester polyol mixture of claim 3.
5. A laminate comprising at least one facing sheet adhered to the
polyisocyanurate foam of claim 1.
6. A process for producing laminate comprising
(a) contacting at least one facing sheet with a polyisocyanurate
foam-forming mixture comprising an organic polyisocyanate, a blowing
agent, a trimerization catalyst and a minor amount of a polyol, wherein
from about 5 to 100 weight percent of the polyol comprises the polyester
polyol mixture of claim 13, and
(b) foaming said foam-forming mixture.
7. A laminate comprising at least one facing sheet adhered to the
polyurethane foam of claim 3.
8. A process for producing a laminate comprising
(a) contacting at least one facing sheet with a polyurethane foam-forming
mixture comprising an organic polyisocyanate, a blowing agent, a catalyst
and a polyol, wherein from about 5 to 100 weight percent of the polyol
comprises the polyester polyol mixture of claim 1, and
(b) foaming said foam-forming mixture.
9. The polyisocyanurate foam of claim 1 wherein said polycarboxylic acid
component-containing polyol includes at least one glycol which is
co-distillable with said liberated ethylene glycol, and said distillation
step (b) is conducted to distill from said digested polyol mixture the
amount of liberated ethylene glycol and co-distillable glycol sufficient
for improved storage stability of the mixture.
10. The polyisocyanurate foam of claim 9 wherein said distillation step (b)
is conducted rapidly at reduced temperature and pressure to prevent or
minimize the liberation of further ethylene glycol from said polyethylene
terephthalate during the distillation.
11. The polyisocyanurate foam of claim 10 wherein said digesting
polycarboxylic acid component has aromatic ring unit with two
##STR10##
on adjacent or alternate ring positions.
12. The polyisocyanurate foam of claim 11 wherein said digesting polyol
component is a member selected from the group consisting of diethylene
glycol, dipropylene glycol, mixture of said glycols and mixtures of said
glycols with at least one other oxyalkylene glycol.
13. The polyisocyanurate foam of claim 12 wherein said digesting
polycarboxylic acid component is a member selected from the group
consisting of phthalic anhydride, phthalic acid, isophthalic acid,
trimellitic anhydride, trimellitic acid, benzophenonetetracarboxylic
dianhydride, esters of said polycarboxylic acid components and mixtures
thereof.
14. The polyisocyanurate foam of claim 13 wherein said digesting
polycarboxylic acid component is a member selected from the group
consisting of phthalic anhydride, esters of phthalic anhydride and
mixtures thereof, and said digesting polyol component is diethylene
glycol.
15. The polyisocyanurate foam of claim 10 wherein substantially all of the
ethylene glycol formed in the digestion is distilled from said digested
polyol mixture, and additional polyol is optionally added after said
distillation step (b) to yield the desired equivalent weight of the
mixture.
16. The polyisocyanurate foam of claim 15 wherein said digesting
polycarboxylic acid component is a member selected from the group
consisting of phthalic anhydride, phthalic acid, isophthalic acid,
trimellitic anhydride, trimellitic acid, benzophenonetetracarboxylic
dianhydride, esters of said polycarboxylic acid components and mixtures
thereof, and said digesting polyol component is a member selected from the
group consisting of diethylene glycol, dipropylene glycol, mixtures of
said glycols and mixtures of said glycols with at least one other
oxyalkylene glycol.
17. The polyisocyanurate foam of claim 16 wherein said digesting
polycarboxylic acid component is pre-reacted with said digesting polyol
component before said digestion step (a).
18. The polyisocyanurate foam of claim 17 wherein in the digestion reaction
the ratio of equivalents of total polyol to equivalents of total acid is
1.5-10 to 1, the ratio of moles of said polyethylene terephthalate to
moles of said digesting polycarboxylic acid component is 1.0-10 to 1, and
the ratio of moles of said digesting polyol component to moles of ethylene
glycol in said polyethylene terephthalate is 1.8-2.5 to 1.
19. The polyisocyanurate foam of claim 18 wherein said polyester polyol
mixture has a viscosity in cps at 25.degree. C. of about 700 to 12,000, a
hydroxyl number of about 300 to 475, and an acid number of about 0.1 to
10.
20. The polyurethane foam of claim 3 wherein said polycarboxylic acid
component-containing polyol includes at least one glycol which is
co-distillable with said liberated ethylene glycol, and said distillation
step (b) is conducted to distill from said digested polyol mixture the
amount of liberated ethylene glycol and co-distillable glycol sufficient
for improved storage stability of the mixture.
21. The polyurethane foam of claim 20 wherein said distillation step (b) is
conducted rapidly at reduced temperature and pressure to prevent or
minimize the liberation of further ethylene glycol from said polyethylene
terephthalate during the distillation.
22. The polyurethane foam of claim 21 wherein said digesting polycarboxylic
acid component has aromatic ring units with
##STR11##
on adjacent or alternate ring positions.
23. The polyurethane foam of claim 22 wherein said digesting polyol
component is a member selected from the group consisting of diethylene
glycol, dipropylene glycol, mixtures of said glycols and mixtures of said
glycols with at least one other oxyalkylene glycol.
24. The polyurethane foam of claim 23 wherein said digesting polycarboxylic
acid component is a member selected from the group consisting of phthalic
anhydride, phthalic acid, isophthalic acid, trimellitic anhydride,
trimellitic acid, benzophenonetetracarboxylic dianhydride, esters of said
polycarboxylic acid components and mixtures thereof.
25. The polyurethane foam of claim 24 wherein said digesting polycarboxylic
acid component is a member selected from the group consisting of phthalic
anhydride, esters of phthalic anhydride and mixtures thereof, and said
digesting polyol component is diethylene glycol.
26. The polyurethane foam of claim 21 wherein substantially all of the
ethylene glycol formed in the digestion is distilled from said digested
polyol mixture, and additional polyol is optionally added after said
distillation step (b) to yield the desired equivalent weight of the
mixture.
27. The polyurethane foam of claim 26 wherein said digesting polycarboxylic
acid component is a member selected from the group consisting of phthalic
anhydride, phthalic acid, isophthalic acid, trimellitic anhydride,
trimellitic acid, benzophenonetetracarboxylic dianhydride, esters of said
polycarboxylic acid components and mixtures thereof, and said digesting
polyol component is a member selected from the group consisting of
diethylene glycol, dipropylene glycol, mixtures of said glycols and
mixtures of said glycols with at least one other oxyalkylene glycol.
28. The polyurethane foam of claim 27 wherein said digesting polycarboxylic
acid component is pre-reacted with said digesting polyol component before
said digestion step (a).
29. The polyurethane foam of claim 28 wherein in the digestion reaction the
ratio of equivalents of total polyol to equivalents of total acid is
1.5-10 to 1, the ratio of moles of said polyethylene terephthalate to
moles of said digesting polycarboxylic acid component is 1.0-10 to 1, and
the ratio of moles of said digesting polyol component to moles of ethylene
glycol in said polyurethane terephthalate is 1.8-2.4 to 1.
30. The polyurethane foam of claim 29 wherein said polyester polyol mixture
has a viscosity in cps at 25.degree. C. of about 700 to 12,000, a hydroxyl
number of about 300 to 475, and an acid number of about 0.2 to 10. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to polyester polyols which are obtained by digesting
scrap or recycled polyethylene terephthalate with polyols to form digested
polyol mixtures and distilling ethylene glycol from the digested mixtures.
The distilled polyols are useful in the preparation of cellular foam
materials, particularly polyisocyanurate and polyurethane foams.
2. Description of the Prior Art
The preparation of foams characterized by isocyanurate and urethane
linkages is well known in the art. Generally, these foams are prepared by
reacting an organic polyisocyanate with a polyol in the presence of a
blowing agent and a catalyst(s). Polyester polyols of many types can be
used as the polyol components in the production of these foams.
U.S. Pat. No. 4,039,487, for example, discloses the use of aromatic
polyester polyols to prepare polyisocyanurate foams. Although the foams of
this patent have good fire resistance and low smoke evolution upon
combustion, they have a relatively high friability. Furthermore, the
polyols are comparatively expensive to manufacture.
U.S. Pat. No. 4,092,276 also discloses the use of rather costly aromatic
polyester polyols in preparing polyisocyanurate foams. Another
disadvantage of these foams is that they do not have especially high
compressive strength. A further problem with using aromatic polyester
polyols, particularly those of low molecular weight, is that the polyols
tend to be solid at room temperature, or to be characterized by very high
viscosity and poor solubility in resin mixtures, thus making them
difficult to handle.
To remedy the above drawbacks, it has been proposed in U.S. Pat. No.
4,237,238 to use in the preparation of polyisocyanurate foams a minor
amount of a cheap by-product type of liquid polyol mixture which is
obtained by the transesterification, with a glycol of molecular weight
from about 60 to 400, of a dimethyl terephthalate esterified oxidate
reaction product residue. The polyisocyanurate foams produced are
disclosed to be characterized by a high degree of fire resistance with low
smoke evolution on combustion, a low foam friability and reasonably good
compressive strength. U.S. Pat. No. 4,411,949 discloses cellular foams of
exceptional quality producible by employing a polyol mixture derived from
a by-product of dimethyl terephthalate production which has a
substantially higher content of dimethyl terephthalate than the residue
used in U.S. Pat. No. 4,237,238.
Another source of aromatic polyester polyols is available through the
recovery of polyester wastes. High molecular weight polyesters of
terephthalic acid and aliphatic dihydric alcohols are well known in the
art. These high molecular weight polyesters, especially polyethylene
terephthalate (PET), are used commercially for the manufacture of
packaging film, fibers, electrical insulators, molded articles, such as
PET beverage bottles, etc. The various manufacturing processes
unfortunately generate considerable waste as the polyester is processed
into commercial form. Also, the tremendous quantities of spent consumer
goods containing the polyester constitute a huge supply of scrap polyester
material.
There is a growing awareness of the need for energy conservation and the
utilization of recyclable materials. It is realized that the judicious use
of plastics can contribute significantly to energy savings. The industry
has long recognized that recycling waste polyalkylene terephthalate would
conserve raw materials, improve process economics, and eliminate the
problem of waste disposal. Numerous processes have been proposed for
recovering useful products from waste or scrap polyalkylene terephthalate
by reducing or digesting the high molecular weight polymer to short-chain
fragments. These short-chain fragments have been used principally in the
production of additional polyester materials.
The use of a polyalkylene terephthalate digestion product in flexible
polyurethane foam is described in U.S. Pat. No. 4,048,104. In this patent,
the digestion product is employed to prepare polyisocyanate prepolymers,
and not as a polyol ingredient in the manufacture of flexible polyurethane
foam.
U.S. Pat. No. 4,223,068 discloses the manufacture of rigid polyurethane
foam wherein 5 to 30 percent of the weight of the organic polyol used in
the manufacture is a digestion product of polyalkylene terephthalate
residues or scraps digested with organic polyols. The preparation of
isocyanurate modified polyurethane foams utilizing a digestion product of
polyalkylene terephthalate scrap dissolved in one or more organic polyols
is described in U. S. Pat. No. 4,417,001. While these foams are
characterized by desirable physical properties, deficiencies have been
encountered in the fluidity and storage stability of polyol digestion
products disclosed for use in preparing the foams. These deficiencies lead
to inefficiency in the foam production.
One solution to the instability of the digestion products is to employ
certain polycarboxylic acid components in the digestion of the scrap
polyalkylene terephthalate, such as polyethylene terephthalate (PET), as
disclosed in U.S. patent application Ser. No. 582,348, filed Feb. 22,
1984. However, cellular foams synthesized from the resulting improved
digestion products have been found to be inferior in certain properties,
e.g., foam density and thermal insulation capacity, to the generally
acceptable foams of above-mentioned U.S. Pat. No. 4,411,949. It would be
desirable if PET scrap could be utilized to produce an inexpensive polyol
mixture having a good shelf stability for extended periods of time and the
capacity to yield foamed products characterized by a broad range of
desirable properties.
OBJECTS OF THE INVENTION
It is accordingly an object of the present invention to provide a storage
stable polyol composition for use in preparing polymeric foam materials,
particularly polyurethane and polyisocyanurate foams, of reduced
friability, high thermal stability and compressive strength, and suitable
density and reactivity, and a method of producing the polyol composition.
It is another object of the present invention to provide improved cellular
foams, especially polyisocyanurate and polyurethane foams, having a
combination of advantageous properties, including a reduced friability,
and high thermal resistance, compressive strength and insulation
properties, and an improved method of producing the foams.
It is an additional object of the present invention to provide a polyol
mixture having good storage stability, low viscosity, and a controllable
equivalent weight for use in producing polyurethane and polyisocyanurate
foams.
It is yet another object of the present invention to provide a polyol
mixture for admixture with blowing agents to form compatible premixes for
the preparation of polyurethane and polyisocyanurate foams.
It is still another object of the present invention to produce an improved
polyisocyanurate foam material characterized by a high degree of fire
resistance with low smoke evolution and flame spread on combustion, and
the formation of a protective char over unburnt foam upon combustion.
It is a further object of the present invention to provide polyisocyanurate
foams which are characterized by a high conversion to trimer.
It is a still further object of the present invention to provide closed
cell polyisocyanurate and polyurethane foam materials which can be used in
building panels which are highly insulating, thermally resistant, low in
friability, soundproof and self-supporting.
These and other objects and advantages of the present invention will become
more apparent by reference to the following detailed description and
drawings wherein:
FIG. 1 is a side schematic representation of an apparatus suitable for
producing a cellular foam material in accordance with the present
invention.
FIG. 2 is a cross-sectional view of a laminated building panel having one
facing sheet; and
FIG. 3 is a cross-sectional view of a laminated building panel having two
facing sheets.
DESCRIPTION OF THE INVENTION
The above objects have been achieved and the drawbacks of the prior art
have been overcome by the development of an improved polyester polyol,
which is prepared by digesting polyethylene terephthalate (PET) with an
organic polyol and distilling off ethylene glycol (EG) formed during the
digestion reaction. Preferably, substantially all the liberated EG is
distilled from the digested polyol mixture. The distillation of the
invention is advantageously carried out to strip off EG formed in the
depolymerization of the PET but to prevent re-equilibration of the
digested PET with formation of more EG. This prevention or minimization of
EG formation during distillation is accomplished by suitably selecting the
distillation conditions, such as by rapidly conducting the distillation at
reduced temperature and pressure in an appropriate device, e.g., a wiped
film evaporator.
Accordingly, this invention relates to a process for preparing a polyol
mixture by
(1) depolymerizing PET with a polyol digesting medium to form a digested
polyol mixture containing EG, and
(2) distilling from the digested polyol mixture at least a portion and
preferably substantially all of the EG formed in the depolymerization
while preventing or minimizing the formation of further EG during the
distillation.
The digestion of the PET is carried out under normal depolymerization
conditions well known and described in the prior art. In a preferred
embodiment, the digesting medium includes at least one glycol which is
co-distillable with the EG. Advantageously, the quantity of digesting
components is sufficient to produce a digested polyol having a desirably
low equivalent weight, such as below about 120, before the distillation
step. The distillation is carried out to strip off the amount of EG which
will yield a polyol mixture having a prolonged storage stability and
predetermined equivalent weight, and, when the digesting medium includes a
distillable glycol, the portion of this distillable glycol which, in
conjunction with the distilled EG, produces the polyol mixture having a
prolonged storage stability and the desired equivalent weight.
The PET to be digested is available in the form of films, fibers, and
shaped articles. In addition, PET is available as sludges which are
obtained as cleanup by-products from PET manufacturing plants. The
molecular weight of such PET material is at least about 15,000 and ranges
upward to 100,000 or more. Lower molecular weight oligomers of PET also
can be used.
According to the present invention the PET is depolymerized or degraded
with digesting polyols which can be aliphatic, cycloaliphatic, aromatic,
araliphatic and/or heterocyclic, and are preferably selected from the
group consisting of diols and triols. Low molecular weight polyols such as
aliphatic dihydric alcohols having from 2 to 16 carbon atoms are highly
satisfactory. The molecular weight of the digesting polyol advantageously
ranges from about 60 to about 500. Examples of suitable polyols include
alkylene glycols and glycol ethers, such as ethylene, oxydiethylene,
propylene, oxydipropylene, butylene, pentylene, hexylene, and
octamethylene glycols, and isomeric forms thereof, and the polyoxyalkylene
glycols such as polyoxyethylene and polyoxypropylene glycols,
1,4-bis-hydroxymethyl cyclohexane, dimethylol dicyclopentadiene,
1,3-cyclohexanediol, 1,4-cyclohexanediol, and in general
hydroxy-terminated ethers, esters or mixed ether esters having a molecular
weight of about 500 or less. The digesting polyols may, of course, be used
as mixtures of two or more polyols. The polyols may include substituents
which are inert in the digestion reaction, for example, chlorine and
bromine substituents. Especially suitable polyols are oxyalkylene glycols,
such as diethylene glycol, dipropylene glycol, triethylene glycol,
tripropylene glycol, tetraethylene glycol, tetrapropylene glycol,
trimethylene glycol and tetramethylene glycol.
In a preferred embodiment of the invention, the digesting medium contains a
polycarboxyic acid component. The polybasic-carboxylic acid component may
be aliphatic, cycloaliphatic, aromatic, araliphatic and/or heterocyclic
and may be substituted, for example, with halogen atoms and/or may be
unsaturated. The following are mentioned as examples: succinic acid,
glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid,
citric acid, 1,4-cyclohexanedicarboxylic acid, trimellitic acid,
tetrahydrophthalic acid anhydride, hexahydrophthalic acid anhydride,
endomethylene tetrahydrophthalic acid anhydride, glutaric acid anhydride,
phthalic anhydride, isophthalic acid, terephthalic acid,
benzophenonetetracarboxylic acid dianhydride, maleic acid, maleic acid
anhydride, fumaric acid, and dimeric and trimeric fatty acids. Aromatic
carboxylic acid compounds are particularly useful constituents of the
digesting medium.
An especially satisfactory digested polyol mixture is obtained by digesting
PET with a preferred polycarboxylic acid component-containing polyol, the
polycarboxylic acid component having ring units with two
##STR1##
on adjacent (or ortho) or alternate (or meta) ring positions, the ring
unit content of the polycarboxylic acid component being sufficient for
improved storage stability of the digestion product. A preferred digesting
polyol of the invention contains o-phthalic, isophthalic and/or
trimellitic acid residues. By o-phthalic, isophthalic and trimellitic acid
residues are meant the groups
##STR2##
respectively.
In the digestion of PET with a polycarboxylic acid component-containing
polyol, the digesting medium may comprise a polyol and a polycarboxylic
acid or acid derivative, such as an anhydride or ester of the
polycarboxylic acid. Since the digesting polycarboxylic acid component is
converted to a polyester either before or at the beginning of the
digestion process, the polycarboxylic acid component-containing polyol
used in depolymerizing the PET can be defined as the reaction product of a
mixture of digesting polycarboxylic acid and polyol components. The
ingredients can be introduced in various ways in the digesting process.
For example, all ingredients can be charged at the same time to the
reacting vessel and thereupon reacted together. In a preferred method, the
polycarboxylic acid or acid derivative is pre-reacted with a polyol to
form a polyester polyol, and then the PET is digested by the preformed
polyester polyol. In an alternative method, the PET first is reacted with
a polyol, and the polycarboxylic acid or acid derivative thereof
subsequently is added to the reactor and the reaction continued to
completion. Various mixtures of digesting reactants, such as mixtures of
diols, like diethylene glycol, dipropylene glycol, triethylene glycol,
tripropylene glycol, tetraethylene glycol, tetrapropylene glycol,
trimethylene glycol and tetramethylene glycol, and polyester polyols, like
reaction products of mixtures of phthalic anhydride and said diols, can be
introduced together to the reactor.
Advantageously, at least enough of a polycarboxylic acid component having
the above-described ring residues with ortho or meta
##STR3##
is included in the digesting medium for storage stability improvement of
the resulting digestion product. The acid compounds containing the ring
residues may be aromatic, cycloaliphatic, araliphatic and/or heterocyclic
compounds, and preferably are aromatic. In addition to the two requisite
##STR4##
the acid compounds may have additional
##STR5##
or --OH groups, and further may include substituents which are inert in
the digestion reaction, for example, chlorine and bromine substituents.
Compounds having more than one such ring residue, such as
benzophenonetetracarboxylic dianhydride, can also be used.
Polycarboxylic acids or acid derivatives introduced in the digestion or
depolymerization will be converted to esters during the process.
Alternatively, the acids or acid derivatives can be pre-reacted to form
esters and these esters then introduced in the depolymerization.
Examples of ring residue-containing acid compounds are phthalic anhydride,
isophthalic acid, trimellitic anhydride, tetrahydrophthalic anhydride,
tetrachlorophthalic anhydride, benzophenonetetracarboxylic dianhydride,
tetrabromophthalic anhydride,
1,4,5,6,7,7-hexachloro-5-norbornene-2,3-dicarboxylic anhydride, and
1,8-naphthalic anhydride. The ring residue-containing acid compounds may
be used in the depolymerization in conjunction with the other
polybasic-carboxylic acid components mentioned above.
The digestion of the PET is conveniently carried out in the temperature
range from about 150.degree. to 290.degree. C., preferably 190.degree. to
235.degree. C. Illustratively, the digestion or depolymerization can be
conducted in the absence of a liquid reaction medium composed of material
other than the digesting ingredients. The reaction suitably is performed
under a flow of nitrogen and at atmospheric subatmospheric or
superatmospheric pressure for a period from about one hour to about ten
hours. The stripping of EG and of distillable glycol(s) to produce the
desired equivalent weight can be accomplished during and after the
reaction. The digestion reaction can be carried out as a batch process or
continuously, and is normally catalyzed. Generally, enough
depolymerization or transesterification catalyst is added to the reaction
mixture to suitably promote the reaction. Any conventional
transesterification catalyst (single compound or mixture of compounds) can
be used.
Some PET materials contain dispersed solids which can be catalyst particles
(left over from the processing by which the terephthalate was produced);
or may be pigments or other foreign substances. Such dispersed solids may
remain in the digestion product, so long as they are substantially inert
in the subsequent preparation of rigid polymeric foam. Although the
digested polyol mixture of the invention generally can be employed without
being filtered, it is often desirable to filter this mixture prior to its
subsequent utilization in foam preparations.
In the broadest aspects of this invention, the digested polyol mixture
prepared by reaction of the PET and polycarboxylic acid-containing polyol
is distilled to strip off the EG derived from the PET and the other
distillable glycols without regard to minimizing the formation of further
EG, such as at a temperature of about 200.degree.-300.degree. C., a
pressure of about 0.1 to 20 atmospheres, and a distillation time of about
1 to 10 hours. The amount of EG removed by the distillation may vary
widely, such as from about 1% by weight of the digested polyol mixture up
to the total amount of EG contributed by the PET, and preferably is
sufficient to bring about significant improvement in the mixture's storage
stability.
In a preferred embodiment of the invention, the distillation is performed
after the depolymerization and conducted rapidly to prevent
re-equilibration with formation of more EG. The distillation is preferably
conducted at a temperature from about 100.degree. to 300.degree. C., more
preferably about 120.degree. to 180.degree. C,; at a pressure from about
0.1 mm. to 760 mm., more preferably about 0.5 mm. to 50 mm.; and a
distillation time of less than 60, more preferably less than 15, minutes.
This rapid stripping can reduce the EG content to less than 5, preferably
less than 0.5, weight % of the polyol mixture. Although the removal of EG
can be accomplished by various distillation apparatuses provided the
process design minimizes the possibility of re-equilibration, a wiped film
evaporator is particularly effective for rapid distillation of the glycols
without re-equilibration. A wiped film evaporator operated at a jacket
temperature of about 120.degree. to 140.degree. C., a pressure of about
0.5 to 5 mm. Hg, and a contact time of less than 5 minutes has been found
very effective.
The process of the invention may be efficiently conducted with recycling of
the glycols distilled from the digested polyol mixture back to the
depolymerization reaction mixture. This accomplishes an economical
recycling and reuse of the distilled glycols and thereby avoids the need
to otherwise recover them and find other uses or disposed of them.
In a preferred embodiment of the invention, the depolymerization is
initiated by reacting the PET, which is composed of repeating ethylene
glycol (EG) and terephthalatic acid (TPA) molecules connected by ester
linkages; with a polyol, such as diethylene glycol (DEG) and/or
dipropylene glycol (DPG), in the presence of a catalyst, such as
tetrabutyl titanate, until a solution of the PET is obtained. Then the
acid component, such as phthalic anhydride (PA), or an ester thereof, such
as the product of a catalyzed esterification reaction between PA and DEG
and/or DPG, is added and the depolymerization is completed. In another
preferred embodiment of the invention, the PET is added to a mixture of a
polyol and a polyester polyol derived from the acid component, and the
depolymerization is carried out. The proportions of PET to polyol to acid
or derivative thereof may be varied to a considerable degree in accordance
with the product desired. At all events, sufficient polyol and acid
component should be used to form a polyester polyol having long-term
storage stability and capable of efficiently polymerizing with organic
polyisocyanates in the formation of rigid foams.
In the depolymerization of PET with DEG as the digesting glycol and PA as
the digesting acid, the sum of DEG and PET moles represents the total
glycol while the sum of PA and PET moles gives the total acid. In the case
of PET, one repeat unit
##STR6##
represents one EG mole and one terephthalic acid mole and weighs 192
g/unit. For generation of high molecular weight polyester (10,000-30,000
mw), the glycol to acid ratio must approach 1. For glycolysis of the high
molecular weight PET, the reaction must be reversed; therefore, a large
stoichiometric excess of glycol to acid is utilized. The heat and
catalyst-induced reequilibration reaction produces low molecular weight
oligomers (300-600 mw) of PA and terephthalate glycols and liberates a
portion of the EG from the PET chain. The unincorporated DEG functions as
a solvent.
Suitable proportions of reactants in the digestion may be as follows:
Equivalents of total polyol (digesting polyol, preferably DEG, +EG) to
total acid (TPA+digesting polycarboxylic acid component, preferably
PA)=1.5-10, preferably 2.1-4, to 1
Moles of PET to digesting polycarboxylic acid component, preferably
PA=1.0-10, preferably 1.5-8, to 1
Moles of digesting polyol, preferably DEG, to EG=1.8-2.5 to 1.
Since the storage stability of the polyol digestion product is enhanced by
the presence of the ring unit-containing polycarboxylic acid component in
the digesting medium, much lower PET:polycarboxylic acid component mole
ratios, with an accompanying increase, if desired, in the amount of
digesting polyol to maintain the equivalent weight, may of course be
employed. However, the cost of the digestion product increases with
increasing content of the stabilizing acid component. In an especially
preferred digestion product from a commercial standpoint, the molar
proportions | | |
