Note: Descriptions are shown in the official language in which they were submitted.
34~
Back~r_ nd of the Invention
This invention relates to a process for the production of
polyesters from isophthalic acld or terephthalic acid. In particular,
this invention relates to a process for the product:ion oE unsaturated
polyesters from isophthalic acld or terephthalic acld, a polyol and an
unsaturated alLphatie polycarboxylie aeld.
~ len isophthalie aeid and terepllthallc aeid were sub-
stituted for phthalle anhydride in the production of polyesters, the
one-stage proeess ~Ised wlth phthalic anhydride was not as effeetive.
The art developed a two-stage process in which polyesters were pro-
duced from isophthalic acid or terephthalic acid, a polyhydric alcohol,
or polyol, and a saturated or unsaturated polycarboxylic acid. I
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One two-stage process is disclosed in U.S. Patent 2,904,533 (Carlson
et al.). In the first stage the isophthalic acid is polycondensed with all of
the glycol until essentially a zero acid number product mixture is obtained.
Then, this product mixture has an urls~turated acid, such as maleic acid or an-
S hydride, added to it until the desired acid number and unsaturated polyester
is obtained. This two-stage process was subsequently improved by conducting
the first stage reaction so most but not all of the water of esterification
; hat theoretically could be produced was removed from the first stage. Another
improvement on this two-stage process is the use of two dihydric alcohols of
different carbon atom content. This process is disclosed in l).S. Patent
3,196,131 (Mayer et al.). The higher boiling alcohol is charged to the first
tage along with the aromatic dicarboxylic acid such as isophthalic acid. The
unsaturated acid, the other dihydric alcohol and remaining first alcohol, if
lany, are charged to the second stage.
Another two-stage process is disclosed in U.S. Patent 3,345,339 (Par-
~er et al.). In the first stage a part of the polyol ingredient is reacted with
sophthalic acid or terephthalic acid in the presence of an esterification cata-
yst, a tin compound, and in the substantial absence of an alpha, beta-ethylen-
ically unsaturated polycarboxylic acid. In the second stage an alpha~ beta-
~0 ~thylenically unsaturated polycarboxylîc acid is reacted with the reaction
product mixture of the first stage.
¦ ~ All of these two-stage processes endeavor to increase the effective-
~ess of using isophthalic acid or terephthalic acid from that of a one-step pro-cess. In the two-stage process there is a serious disability over the one-
~tage process. The two-stage process takes from two to three times the number
~f hours to complete a polyester preparation as does the one-stage process. The
bove discussed patents purport to overcome this disadvantage in duration of
~rocessing time. The reduction in the duration of processing time effected by
the two-stage processes used in the prior art can be improved.
:IL11~38~2
The object of this invention is to provide a process that reduces the
processing time in the production of a polyester in a two-stage process from
isophthalic acid or terephthalic aci(l, a polyol and a saturatecl or unsaturatedaliphatic polycarboxylic acid.
Sumlllar,y of the Invention
The present invention is an improvement in the first stage polycon-
densation reaction of a two-stage process for the production of a polyester
from isophthalic acid or terephthalic acid, a polyol, and a saturated or un-
saturated aliphatic polycarboxylic acid. The isophthalic or terephthalic acid .,
0 is reacted with at least a theoretical amount of polyol in the first stage to
form a half-ester mixture of isophthalic or terephthalic acid and polyol. This
mixture is reacted with the saturated or unsaturated,aliphatic polycarboxylic
acid in the second stage to form the polyester. The theoretical amount of
polyol introduced in the first stage is approximately one equivalent of polyol
for each equivalent of acid needed to produce the polyester.
The improvement embodying the present invention is to decrease the
initial portion of polyol reacted with the isophthalic or terephthalic acid and
heat this mixture to a temperature of at least 190C., and then add the remain-
ing portion of the polyol to this heated mixture at such a rate tnat the ,
,0 temperature does not drop below the 190C.
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Thus the present invention provides a t~o-stage process for the
production of polyesters wherein an aromatic polycarboxylic acid selected
from the group consisting oE isophthalic acid and terephthalic acid is reacted
in the first stage with a polyol to produce half-ester mixture which is reacted
with a saturated or unsaturated al:i.phatic polycarboxylic in the second stage
to produce the polyester, to reduce the processi.ng time in the first sta~e;
thereby reducing the processing time Eor the production of the polyester,
comprising:
a. contacting first portion of the polyol with the aromatic poly-
carboxylic acid in the first stage in an amount at least sufficient to
form an agitatable mixture with the aroma-tic polycarboxylic acid
but in an amount sli.ghtly less than the theoretical amount of polyol
needed to react with the isophthalic acid or terephthalic acid and
saturated or unsaturated aliphatic polycarboxylic acid,
b. heating the agitatable mixture to a temperature of at least 190 C
to 230 C, and
c. adding the remaining portion of the polyol to the heated agitatable
mixture in the first stage in such a manner that the temperature of the
heated agitatable mixture is maintained at a -tempera-ture of at least
190 C in order to produce a half-ester mixture.
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The improvelllent in such a first stage esterification comprises: con-
tacting a portion of the total amount of polyol with substantially all of the
isophthalic or terephthalic acid wherein said portion is sufficient to make an
agitatable mixture witil the isophthalic or terephthalic acid, heating the
agitatable mixture with agitation to a temperature of a-t least 190C. where thereaction of isophthalic or terephthalic acid with polyol to form a half-ester
mixture proceeds at a satisfactory rate, and adding the remaining portion of
the total amount of polyol to the heated agitatable mixture in such a manner
that the temperature of the heated agitatable mixture relnains at or above 190Cwhereby a half-ester mixture is obtained.
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An esterlfication catalyst or initiator may be added to the first stage
esterification reaction in order to reduce further the duration of processing
time of the polyester. Generally, the catalyst can be any tin, lead or lithium
catalyst or initiator or any other catalyst or initiator known ln the art
to catalyze or inLtLate the reaction oE isophthalic acid or terephthalic scid
and polyols. The reactLon of the remainlng port:Lon of polyol with the agitat-
able mixture may be accomplLshed by addlng the remaining portion continuously
or lncrementally. Also, the remaining portion of polyol may be heated and
added to the heated agitatable mixture.
All the isophthalic or terephathalic acid need not be contacted initial-
ly with the first portion of the total amount of polyol. A substantial amount
of the isophthalic or terephthalic acid should be contacted initially and the
remaining amount oE the isopthalic or terephthalic acid should be contacted
before the remaining portion of the total amount of polyol is added to the
heated agitatable mixture which already contains an amount of the half-ester.
The agitatable mixture is heated at ambient pressure to at least a
temperature of 190C. and maintained at least at this temperature while the
remaining portion oE polyol is added. However, the temperature can be as much
above 190C. as the esteriEication equipment will allow but the polyester resin
produced may have undesired characteristics if the temperature is too high.
Therefore, the temperature should not be above 230C. If a pressure other
than ambient pressure is used the temperature should still be at least 190C.
The term "poIyester" describes the polymer product whereln both of the
carboxylic acid groups of the d?acid of isophthalic acid or terephthalic acid
and the alipha~ic polycarboxylic acid added 1D the second stage have reacted
to form a polymer.
The term "half-ester mixture" describes the mixture obtained from the
reaction between the isophthalic acid or terephthalic acid and the polyol. This
mixture consists mainly of the ester wherein both of the carboxylic
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acid groups of the dlacid of Lsophthalic acid or terephthallc acid have reacted
with the polyol. The mixture may also contaln some :Lsophthalic and/or tere-
phthalic acid wherein only one carboxyl group is esterified with glycol, some
free glycol and trace amounts of other further reacted compounds.
The term "total amount of polyol" means an amount o~ polyol in a range
from at least the theoretlcal alllount, which 19 one equlvalent of polyol for
each equLvaLent oE acld to produce the polyester, up to an amount usually not
more than 125 percent of the theoretlcal amount. More of an excess may be used
but it would lessen the effectiveness of the process.
The term "agitatable mixture" means a mixture between substantially
all of the isophthalic acld or terephthallc acid and the flrst portLon of polyol
which is in an amount to allow mixing in convent:Lonal mixing equipment used in
the production of polyesters from lsophthatlic or terephthallc acid. The
agitatable mixture of isophthalic or terephthalic acid and first portion of
the total amount of polyol must be mixed in order to provide even temperatures
throughout the mlxture.
The term "acid" as used in the discussion oE the process of this
invention and i`n the appended claims includes the corresponding anhydrides
where such anhydrides exlst.
Detailed Description of the Invention
Throughout the remaining discussion of the process of this invention
the term "isophthalic acid" shall include the term "terephthalic acid" unless
otherwise expressly stated.
A problem in reducing the processing time in a two-state process for
the production of a polyester from isophthalic acid, at least a theoretical
amount of polyol, and a saturated or unsaturated aliphatic polycarboxylic acid
or anhydride is the ~lrs-t stage reaction rate. This esterifLcation reaction
rate is very slow until an adequate reaction temperature is obtained. Broadly9
a temperature of at least 190C. but preferably 195C. is the temperature
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around which the reaction should be conducted. ~e desieed reactlon temperature
in the range of 190-230C. and preferably in the range of 195-210C. appears
to be limited by the boiling point of the reaction mixture when all of the
total amount of polyol is contacted at once with all of the lsophthalic acid.
A reaction mixture of a portion of the total amount of polyol and isophthalic
ac:ld achleves the desire(l reactLon temperature more qulckly.
The total amotmt of polyol :Ls commonly ill the range of about 105 to
110 percent of the theoretical amount needed. The first portion of the total
amount of polyol i8 at least an amount that makes a substantial amount of the
isophthalic ac:Ld mixable or agi~atable with the liquid polyol. The amount of
polyol in the first portion should not exceed an amount slightly less than the
theoretical amount of polyol needed to react with the isophthalic acid and
saturated or unsaturated aliphatic carboxylic acid to form the polyester. The
closer the first portion comes to thls theoretical amount, the smaller the
amount of reduction in processing time. The amount of polyol in ~he first
portion of polyol is preferably in the range of 0.5 to 1.7 moles per mole of
isophthaIic acid and more preferably in the range of .8 1.4 moles per mole of
isophthalic aci`d. Also a solvent can be used to make the isoph~halic acid
more soluble in the polyol. If a solvent is used, it is preferably a non-
reactive solvent which forms an azeotrope with water. Typical of such a solvent
is xylene.
The amount of isophthalic aci~ with which the first portion of polyol
is contacted need not be all the isophthalic acid that is going to be reacted.
The amount of isophthalic acid need be only a substantial amount of the total
a unt of isophtl~alic acid to be reacted. This substantial amount is that
amount which will form an agitatable mixture of isophthalic acid and polyol withthe use of amounts of polyol that are less that the theoretical amount. This
amount is preferably in the range of 50 to 90-percent by weight of the total
amount of isophthalic acid to be used, which depends on the formulation for
the particular polyester desired.
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The agitatable mixture of isophthalic acid and first por-tion of polyol
is heated while being agitated to a temperature which is at least a temperature
of 190C. and is preferably in the range oF 195-210C. While the agitatable
reaction mixture is at this temperature, the remaining portion of the total
amount of polyol is added to the mixture in such a manner as not to reduce the
temperature below the temperature of 190C. and preferably 195C. This manner
may be performecl by adding the remaining portion of polyol at such a rate that
the temperature is not decreased~ The rate of addition may be accelerated by
heating the remaining portion of polyol before it is added to the heated
agitatable mixture to a temperature above ambient temperature but below the
¦boiling temperature of the polyol. This agitatable reaction mixture containing
¦the total amount of polyol continues to react to produce a half-ester mixture.
¦The esterification reaction was taking place since the first portion of polyol
¦was contacted with the isophthalic acid and the resulting agitatable mixture
¦was heated to the adequate reaction temperature of at least 190C. The ester-
¦ification reaction continues until the reaction is complete as indicated by the¦acid number of the half-ester mixture. If the final desired acid number of the
half-ester mixture is reached before all of the remaining portion of polyol is
added, the excess polyol that is left may be used as a coolant. The coolant
would aid in cooling the half-ester mixture before the addition of aliphatic
polycarboxylic acid. The half-ester mixture produced is composed of isophthalic
acid and polyol and has an acid number of less than 90 miligrams of potassium
hydroxide to neutralize 1 gram of the half-ester mixture.
This half-ester mixture is reacted with an aliphatic polycarboxylic
acid in the second stage. The aliphatic polycarboxylic acid may be saturated
or unsaturated but is preferably unsaturated. This second stage is conducted
in any manner known to those skilled in the art of two-stage polyester produc-
tion processes. The product from the second stage is the polyester having a
desired acid number.
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The polyester produced by the improved process of this invention can
be prepared from those polyols or a mixture of those polyols utilized in con-
ventional processes. These polyols include: ethylene glycol, propylene glycol,
butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol,
neopentyl glycol, trimethylene glycol, polyethylene glycol, polypropylene
glycol, ~ 1,5-pentanediol, trimethylolethane, trimethylolpropane,
CJlycerol, 1,2,6-hexanetriol, pentaerythritol, sorbitol, mannitol, methyl glyco-side, and the like. Other polyols including unsaturated polyols may be used
alone or in addition to the above mentioned polyols. This list of polyols is
¦ exemplary of the polyol that may be used, and the list is not exhaustive. Typi-
cally, the total amount of polyol up to 125~ of theoretical is used but even
greater excesses may be utilized if desired.
l The aliphatic polycarboxylic acid used in the production of the poly-
¦ ester by the improved process of this invention may be any of the polycarboxylic
¦ acids conventionally used. Examples of such polycarboxylic acids include:
maleic acid, fumaric acid, itaconic acid, citraconic acid, glutaconic acid,
mesaconic acid. Other polycarboxylic acids including saturated polycarboxylic
¦ acids may be used in addition to the above-mentioned acids. -
l The polyester may be produced by the process of this invention with
¦ even a greater reduction in processing time when an esteriFication catalyst orI I mixture of esterification catalysts is us~d in the first stage. Catalysts known
by those skilled in the art to be effective in the esterification reaction of
¦ the first stage include inorganic salts and organic compounds of tin, lead or
lithium. Examples of inorganic tin salts include: stannous salts, such as
¦ stannous halides, like stannous bromide, stannous chloride, stannous fluoride,stannous iodide, stannous oxychloride; and other stannous salts, like stannous
hydroxide, stannous sulfate, stannous oxide, stannous acetate; and stannic
salts, such as stannic chloride, stannic bromide, stannic fluoride, and stannic
oxychloride; and stannous acylates; and stannous alkoxides. Examples of
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organic tin compounds include dialkyltin salts of carboxyllc acid, like
dibutyltin diacetate, dibutyltin dil~lrate and dibutyltin maleate; and
dialkyltin chlorldes, like dibutylLin oxide; and trialkyltin hydroxides,
like tributyltin hydroxitle an~l trimethyltin hydroxlde. These catalysts
are effectLve in amounts of nbout 0.0l percerlt by welght to about 2.0
percellt by weigh~ of the total welgllt oE tlle charge ln the tirst stage.
~llgher quantLtie~s of catalysts can be usecl lf desired. Other catalysts
known to those skilled in the art that may be used in the improved pro-
cess of ~his inventlon are tetrabutyl zlrconium and zirconium naphthonate.
In the preferred embodiment of the process of this invention
isophthalic acid and not terephthallc acld ls used as the aromatlc poly-
carboxyllc acld to be esterified. Propylene glycol is the preferred
polyol used ln the lmproved process of this inventlon. The total amount
of propylene glycol is a theoretlcal amount of around 2 moles of
propylene glycol per mole of lsophthalic acid and maleic acid. The pre-
ferred catalyst is dibutyltin oxide in an amount of around 0.2 percent
by weight of total weight charged to the first stage. The production
of the polyester i5 conducted in the presence of an inert gas at
atmospheric pressure.
~11 of the isophthalic acid is added to a suitable reaction
vessel for carrying out condensation reactions. This vessel may be con-
structed of stainless steel or it may be a glass-lined kettle which ls
insulated to prevent heat loss. The vessel should be equipped with an
agitator, heating and cooling coils, a temperature measuring device,
vapor removal equipment for continuous removal of water of esterifi-
cation, and may include vapor columns designed to minimize loss of low
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boiling polyols. The vessel also contains an inert gas inlet for con-
ducting the reaction in an inert atmosphere ofnitrogen. The first
portion of total amount of propylene glycol is added to this vessel which
contains all tile isophthalic acid to be reacted. The amount of propylene
glycol in th:Ls
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first portion is in the ranye of 0.8-1.4 moles per mole of isophthalic acid but
most preferably in the ran~e oF 0.9-1.0 mole per mole of isophthalic acid. The
resultin(J mixture is quite thick but it can be agitated and it becomes more
fluid when the temperature is increased.
This resulting atJitatable mixture of isophthal;c acid and first portior
of propylene glycol ;s a9itated and heat:ed to a temperature of at least 190C.
and preferably in the range of 195C.-210C. at ambient pressure. This temper-
ature is quickly and easily obtained. When the temperature reaches about 198C.
the remaining portion of the total amount of propylene glycol is added to the
nixture of isophthalic acid and first portion of propylene glycol. This
¦addition is at the fastest practical rate while maintaining a minimum temperatur~
of at least 190C. and preferably 195C. Upon completion of the addition of the
remaining portion oF propylene glycol, the first stage reaction is continued to
ompletion which is indicated by the acid number of the product. The product
f the first stage is a half-ester mixture of isophthalic acid and propylene
lycol which has an acid number of less than 90 milligrams and preferably in
he range of 20-gO milligrams of potassium hydroxide to neutralize 1 gram of
alf-ester mixture.
The vessel containing the half-ester mixture is cooled to around
150C. and maleic anhydride is added. The maleic anhydride is the preferred
liphatic polycarboxylic acid. The vessel is heated to a temperature of around
~00C. and held at this temperature for the duration of the polyesterification
~eaction. The duration depends on the desired acid number in the final product.
~fter the desired acid number is obtained, the reactor is cooled. The product
2~ from the second stage is the unsaturated polyester.
The unsaturated polyesters produced by the improved process of this
invention can be thinned in a suitable reactive monomer in a manner known to
those skilled in the art.
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;
For a better understanding of the inven-~ion reference should be had
to the following examples. In the followiny examples the term isophthalic acid
does not i ncl ude the term terephthalic acid.
Il trative Example #1
For the purposes of comparison unsaturated polyester was prepared from
isophthalic acid, propylene glycol and maleic anhydride according to a conven-
tional two-stage process. All of the propylene glycol, which was a theoretical
amount of two moles of propylene glycol to one mole of isophthalic acid considering the one mole of maleic anhydride to be added to form the polyester, was
added to the isophthalic acid. A weight percent amount of 36.5% of propylene
glycol was added to 39.9 wt. % of isophthalic acid, based on a total weight of
the components, for the final unsaturated polyester. This mixture was heated
to the adequate reaction temperature of 200C. and held until the acid number
of the half-ester mixture produced decreased to 25-30 milligrams. The mixture
was cooled and 23.6 wt. % of maleic anhydride was added to produce the unsat-
urated polyester. The yield was 96.7% of the theoretical yield. The first
stage processing time was 11-1/4 hours.
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Example #2
A first portion of 7,310 kg of propylene glycol WdS added to 11~402 kg ~
of isophthalic acid. This gave a mixture having a 1.4/1.0 moler ratio of pro- ~;
pylene glycol to isophthalic acid. This mixture was agitated and heated to
198C. The remaining portion of propylene glycol, 3,132 kg equival~nt to 0.6
moles per mole of isophthalic acid, was added to the heated agitatable mixture
in 2-3/4 hours, thus, holding the reaction temperature at 198C. The reaction
; 25 was continued until the half-ester mixture had an acid number of 25 to 30
milligrams at 200C. without the use of a catalyst. The half-ester mixture
which contained the esterification product of propylene glycol and isophthalic
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13~42
acid was cooled. Then maleic anhydride in an amount of 6,732 kg was added.
This combination of half-ester mixture and maleic anhydride was heated to a
temperature of around 200C. This temperature is maintained until the desired
acid number of th~ unsaturate~ polyester was achieved. Then the temperature
was decreased and the product, an unsaturated polyester resin, was removed.
The first stage processing time was 7-1/2 hours. This is a processing time
savings of 40% compared to the conventional process in Illustrative Example #1.
Example #3
A first portion of propylene glycol equaling 4,61~ kg was added to
` 10 7,279 kg of isophthalic acid. The resulting mixture had a moler ratio of 1.4/
1.0 propylene glycol to isophthalic acid. An amount of dibutyl tin oxide of
57 kg or 0.2 wt. %, based on the total we;ght of components in the charge to
the first stage, was added to the mixture. The mixture was agitated and heated
t~ 185C. at which temperature the mixture became more fluid. An additional
amount of 3,919 kg of isophthalic acid was added to the mixture. This addition
brought the moler ratio of propylene glycol to isophthalic acid to 0.9/1.0 in
the mixture. The mixture was agitated and heated to 198C. and the balance of
the propylene glycol, 6,152 kg (1.20 moles/mole of isophthalic acid), was added
in 2-3/4 hours thus maintaining the reaction temperature at 198C. This additic n
of the balance of the propylene glycol was at such a rate that the temperature
of the reaction did not decrease below 198C. This addition consisted of
dribbling the remaining portion of the propylene glycol into the heated,
agitated mixture from a weigh tank.
After the addition of all of the balance of propylene glycol the mix-
ture was held at 200C. until the acid number decreased to 25 to 30 milligrams
and the half-ester mixture was cooled to a temperature of around 150C. Maleic
anhydride in an amount of 6,732 kg was added and the combination of half-ester
mixture and maleic anhydride was heated to a temperature of around 200C. The
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temperature is held until the desired acid number product is obtained. Then
the reactor vessel was cooled and the unsaturated polyester removed. The first
stage processing time was 7-1/2 hours.
¦ Table I sumlllarizes the first stage processing time results of several
iruns conductecl by the two-step glycol addition of the improved process of thisinvention and a conventional two-stage process. The conventional two-stage
process runs are for the purpose of comparison. The conventional runs were
conducted in a similar manner as Illustrative Example #1 and a few of the con-
ventional runs were performed with a dibutyl tin oxide catalyst. The runs
according to the improved process of this invention were conducted in a manner
similar to Example #2 with and without the use of a catalyst. The results
indicated that the improved process of this invention, even without the use of
a catalyst, improves the processing time of a two-step process better than the
use of a catalyst in a conventional two-step process.
Z
Table I
Processing Tlme Comparison
% ~t.Processing Time
Run ~ Process Used DBT0* ~ , hrs.
1 Convent;onal None 12
2 Conventional None 11
3 Conventional None 9
4 Conventional None 9
2-Step Glycol None 7-1/2
Addit;on
6 Conventional 0.1 10
7 2-Step Glycol 0.1 6
Addition
8 Conventional 0.2 10
9 2-Step Glycol 0.2 4
Addition
2-Step Glycol 0.2 4
Addition
* Dibutyltin oxide.
According to the provisions of the patent statutes, I have explained
the principle9 preferred construction and mode of operation of my invention and
have illustrated and described what I now consider to represent its best embodi-ment. However, I desire to have it understood that within the scope of the
appended claims, the invention may be practiced otherwise than as specifically
illustrated and described.
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