DE1520976A1 - Process for the production of polyesters - Google Patents

Description

DR. E. WIEGAND

MONKS DIUi-ING. W. NIEMANN

HAMBURG PATCNTANWXLTI

MÖNCHEN 15, July 21, 1961 NUSSBAUMSTRASSE 10 • TELEPHONE: 55547 «

1520978

10686/61 7 / Hei

Teikoku Jinzo Kenahi Kabushiki Kaisha, Osaka (Japan)

Process for the production of polyesters.

The invention relates to a method of manufacture of polyesters. The invention relates in particular to a process for the production of fiber and film-forming high molecular weight linear polyesters, the recurring basic units of which are formed by alkylene terephthalates.

So far, polyalkylene terephthalates are industrially after conventional method of ester interchange reaction (transesterification reaction) has been manufactured. So is polyalkylene terephthalate after

909 0 8 6/1546

BATH ORIGINAL

the conventional process generated via a first working stage in which an ester exchange reaction between a dialkyl terephthalate and an excess amount, namely more than 2.2 moles of an alkylene glycol under atmospheric pressure at a temperature of 150 ° - 220 ° C and in particular 180 ° - 200 ⁰ C is brought about for the production of bis (u / -hydroxyalkyl) terephthalate or its oligomers (first product) and, via the second stage, a polycondensation of the first product at a high temperature and at reduced pressure, in which excess amounts of the alkylene glycol were expelled . According to this process, however, a detour step must be carried out, namely the esterification of a terephthalic acid with an aliphatic alcohol for conversion into a dialkyl terephthalate. So if it is possible to produce the high molecular weight polyesters without the detour via this dialkyl terephthalate by direct reaction of a terephthalic acid with an alkylene glycol to produce bis (u / -hydroxyalkyl) esters or their oligomers, the economic advantage would be very considerable. In the following, this method will be abbreviated as the direct esterification process in the description for the sake of simplicity *

A feature of the invention resides in the application of difeser direct esterification method for specifying a process for the production of fiber- and film-forming, .high molecular weight, linear polyesters, their repeating basic units

909886/1545

BATH ORIGINAL

are formed by alkylene terephthalate latex, namely by linear polyesters, which in terms of quality are in no way more achleous than the products manufactured using the ester exchange process

The high molecular weight linear polyesters mentioned, their Recurring basic units formed by alkylene terephthalate include the polyesters with recurring Alkylene terephthalate units from a terephthalic acid and an alkylene glycol and polyester made from a terephthalic acid and an alkylene glycol in which up to 10 percent of the terephthalic acid and / or the alkylene glycol is used by other difunctional acids or dihydric alcohols are replaced, but the intrinsic molecular viscosity of the polyesters is at least 0.35 in both cases, in both cases Cases are fiber and film-forming high molecular weight linear polyester.

As is known, the direct esterification process must be used Production of polyesters necessarily to a heterogeneous Lead to reaction, since a terephthalic acid is only slightly soluble in the alkylene glycol used j has accordingly the complete implementation of the reaction takes a very long time Takes time even when a large excess of alkylene glycol is used. For example, in the UK Patent specification 578 079 describes that even when using about 4.5 moles of ethylene glycol ala alkylene glycol per 1 hol of terephthalic acid the reaction 72 hours at one

909886/1545

BATH ORIGINAL

Reaction temperature of 200 ° 0 required. To carry out the reaction in the direct esterification process in a time that makes the ^v out industrially applicable, it is, as shown in British Patent '777 628, therefore necessary to apply a Übersohußmenge of alkylene glycol as that in the EsterauB-exchange agreements with above atmospheric pressure (as it is not used in the ester exchange process) and at a temperature above the normal boiling point of the alkylene glycol used.

As in this reaction, in contrast to the esterification of a terephthalic acid using a monovalent If alcohol, a dihydric alcohol is used, the reaction does not proceed in one direction, of course Bonder is from side reactions like the formation of Xther bonds of the alkylene glycols. If this is a product of degradation the first stage is subjected to polycondensation without prior separation of the by-products in the second stage, the orientation of the molecules of the high molecular weight linear polyester obtained as a result of the By-products built into the molecules are irregular dae leads to a reduction in the expansion point of the polyester. Mainly as a result of installing the Xtfaerbindungen occurring lowering of the softening point reduces the Resistance to light, weather resistance and the Ojsyd & tlonibe * durability of the polymer as well as the washing and usage

909386/154 5

properties of the fibers produced by Däraua; it is therefore • Required, a polymer with the highest possible expansion point cut out to marketable, usable polyester to obtain..

öemäß the invention has been found as a result of TJnterauchungen on the Beaktionsbedingungen that may lead to an increase of the softening point of the polymer, that when carrying out a ^v eresterungsreaktion at a temperature of 210 ° - 290 ⁰ O and insbeedndere 220 ° 26O ⁰ O under pressure and when using an amount * of at least 1.0 mole but less than 2.0 moles of alkylene glycol per 1 mole of terephthalic acid, the high molecular weight polyesters obtained have higher softening points than if at least 2 moles of alkylene glycol per 1 mole of terephthalic acid are reacted with one another.

The following example 1 illustrates the influence different amounts of ethylene glycol, used as Alkylene glycol per 1 mol of terephthalic acid on the softening points of the polymers obtained * '

The indications "parts" in the examples mean Gfewiohtsteile-f the basic molar viscosity / JL / iat the value which ^{would like to sow at 35 Q} O with the polyester obtained when dissolved in a solvent mixture of equal parts by volume (II) of phenol and tetrachloride «

example 1

A car * equipped with a distillation column. SÖ9886 / t545

BATH ORIGINAL

klav was each charged with 120 parts of terephthalic acid and various amounts of ethylene glycol, as shown in Table 1. The air in the system was replaced by nitrogen gas, which was kept closed until the overpressure reached 2.2 kg / cm the mixture was heated under Hühren to 240 ⁰ C. The internal pressure, which rose together with the increase in temperature, was set to a constant value by means of a valve opening. The water formed by the reaction was sequentially removed from the system through the distillation column. When the water had been distilled off, the pressure was reduced to 1.0 kg / cm and the reaction was continued for 20 minutes Parts of "phosphoric acid were added and the mixture was heated to 270 ⁰ O with stirring. The polycondensation reaction was terminated flat for 30 minutes under atmospheric pressure, 30 minutes under about 20 mm Hg and .9.0 minutes under about 0.1 mm Hg; The results of these studies are shown in Table I,

909886/1545

Table I.

Try amount of
Mr. Ethylene glycol
(Parts)

Molar ratio

Time required - Gmndmolare softening color

span for the Vi sko si ta "ta counting point (° CT

Esterification reaction, (min)

O
(O
CO
OO

1
2
3
4th
.5
6th
7th

58.2
67.2
80.7
89.6

135

179

448

1.3 1.5 1.8 2.0 3.0 4.0 10.0 185 175 150 150 150 150 100

0.72 259.9 III 0.75 259.5 II 0.73 258.9 II 0.76 257.2 III 0.78 253.0 III 0.72 251.5 III 0.76 234.7 IV

cn

■ ο co

CD

Figure 1 shows the results according to Example 1 in curve a; it shows that increases considerably with "'Verringerung- ■ the comparable' wendeten- amount of ethylene glycol, the softening point and that is slow in the area of a molar ratio of ethylene glycol to terephthalic acid ■ below 2.0 the increase. ---- -

Since a terephthalic acid is only slightly soluble in an alkylene glycol in the direct esterification method, thought it has hitherto been known that with the direct esterification method, of course a larger excess of alkylene glycol should be used than with the ester exchange method.

According to the inventors' studies, however, contrary to the conventional view and as shown in Table I above, it has been found that in the direct esterification process, even if a small amount, namely 1-2 moles, alkylene glycol is reacted per 1 mole of terephthalic acid, if adhered a temperature of at least 210 ⁰ C üie esterification reaction proceeds smoothly; at the same time, a polyester having an unusually high softening point is obtained, and the formation of by-products which cause disruption of the crystal state of the polymer is remarkably reduced.

It is clear that this method has a merit by only a small amount of the alkylene glycol used in the reaction needed v / ird. The theoretical amount of alkylene glycol, the formation of high molecular weight linear poly-

90 3 δ 8 6/1545

estern is necessary, is calculated in moles equal to the • amount of terephthalic acid; what is added beyond this amount, is, is distilled off and recovered in the polycondensation process of the second stage; the regained Alkylene glycol must be used for the purpose of further use be subjected to a cleaning stage. Accordingly, the reduction in the amount of alkylene glycol required for the direct esterification reaction is required, very favorable from the viewpoint of lowering manufacturing costs .:

Another, emerging from Example 1 advantage of the invention is that even when reducing the Amount of ethylene glycol the time required for the esterification reaction * does not change very much; In fact the esterification takes place completely in the same time, even if the amount of ethylene glycol per 1 mole of terephthalic acid is reduced from 4 moles to 1.8 moles o

Although, according to previous knowledge, a large change in the response time with a small change in the amount of Glycol would be expected is within the scope of the present invention. applied range of the very small amount of glycol to all expectations such a tendency has not been observed at all "

The reason why the temperature of the esterification reaction in the process of the invention to 210 ° - 290 ⁰ O and insfee-

909886/1546

- ίο -

is particularly limited to 220 ° -26O ⁰ C, is that 'at a temperature below 210 ⁰ C a long period of time is necessary for the completion of the esterification reaction and the industrial implementation of the invention is difficult. In contrast, when the temperature exceeds 29o C ^0, the polyester obtained are colored by thermal decomposition of alkylene glycol.

According to the invention it was also found that it is possible in the described reaction of 1-2 moles of alkylene glycol per 1 mole of terephthalic acid at a temperature of 210 ° -29O ⁰ C by adding certain types of metals or metal compounds, the amount of the in first stage carried out esterification reaction to reduce by-products formed. Accordingly, polyesters with extremely high softening points can be obtained in this Pail without the need to purify the first esterification products. they are also quite excellent in terms of color.

As such, metals or metal compounds used according to the invention are called selenium: the metals lithium, sodium, potassium, rubidium, gaesium, magnesium, calcium, strontium and barium; Oxides, alcoholates, hydrides, salts of inorganic acids such as halides, carbonates, arsenates,

909886/1545.

BATH ORIGINAL

Antimonates ,,,. Acuminates, borates, etc., salts of organic, aliphatic or aromatic acids such as acetates, oxalates, benzoates, terephthalates, etc., and chelate compounds formed by reaction with acetylacetone, salicylaldehyde, etc. _, both one of the metals mentioned and zinc, lead Cobalt and Manganese The reason why these metallic compounds influence the reaction effectively is seen in the effect of the metals of these metallic compounds; any compounds can therefore be used, except those whose anions associated with metals have an unfavorable influence on the reaction exercise, such as the Sulfatec

So far, the catalysts for the direct esterification have been hydrogen chloride, p-toluenesulfonic acid and camphor sulfonic acid has been proposed. The use of these compounds is, however, in terms of color and color Softening point of the polycondensates obtained is undesirable «

Although sulfuric acid or sulphates often the speed accelerate the esterification of low molecular weight substances, they have the disadvantage of deteriorating the color and noticeably increasing the softening point of a polycondensate decrease c

As clearly shown in Example 3, they work metals or metallic compounds mentioned as inhibitors or inhibitors for those to be attributed to alkylene glycol Side reactions, especially with regard to the

9 0 9 8 8 6/1545

BATHROOM ^{0R16 INAL}

Formation of ether bonds, and thereby improve the color and the crystallization state of the polycondensate obtained; on the other hand, they hardly act as esterification catalysts. ° , -

The suitable amount of these inhibitors to be used per part by weight of terephthalic acid or per part by weight of terephthalic acid and another bifunctional acid is 0.001 - 0.5% by weight for alkali and alkaline earth metal compounds, $ 0.001 - 0.2% by weight for zinc compounds and $ 0.001 for lead compounds. 0.04% by weight, for manganese compounds 0.001 - 0.5% by weight. and for cobalt compounds 0.001-0.1 wt. ^c / o. The reason why the amount of the compounds to be added as a side reaction inhibitors is different depending on their type is that these metal compounds precipitate under the conditions of drastic esterification according to the method according to the invention as a result of chemical changes, if, for example, at least 0 , 05 $ lead acetate is used, this creates an opaque clouding of the polycondensate. This phenomenon illustrates the great difference compared to the cases where such compounds are added as ester exchange catalysts in the production of polyesters according to -c the ester interchange process. For example, the American patent specification 2,641,59-2 describes that advantageously up to 0.15 % By weight of cobalt acetate per dimethyl terephthalate can be used; in the direct esterification process according to the

9OSü86 / 15 45

however, finding is the use of such a large amount «Of cobalt acetate undesirable, as it is during the course of the esterification reaction to the deposition of a conspicuous Amount of a deep gray precipitate.

If the esterification products of the first stage a Polycondensation are subjected to the second stage according to the invention, it is possible to use compounds of antimony, Germanium, titanium, aluminum, silicon, etc., which are used as polycondensation catalysts are known to add; Furthermore, phosphorus compounds can be used as color stabilizers are known to be added together »

In the process of the invention, for the purpose of a quality modification of the high molecular weight linear polyesters obtained, up to 10 mol. <? >> of terephthalic acid can be replaced by other aromatic and aliphatic difunctional acids including dibasic acid and also oxycarboxylic acids. For example, up to 10 mol Terephthalic acid can be replaced by an aliphatic dibasic acid such as oxalic acid, glutaric acid, adipic acid, sebacic acid, hexahydroterephthalic acid, etc. ₀ by an aromatic dibasic acid such as isophthalic acid, kaphthalenedicarboxylic acid, sulfonyldibenzoic acid, 5-dibenzoic acid, -diphenoxy-5-phenoxyethoxy acid, p-phenoxyethoxy-5-phenoxy-5-phenoxyethoxy acid -Phenoxyisophthalic acid, 5-lauryloxyisophthalic acid, alkyl-diphenylphosphinate-p, p ¹ -dicarboxylic acid, 5- (sodium sulfo) -isophthalic acid, etc. "or by an aromatic oxy acid such as p-hydroxyben-

9 0 988 6/1 SUB "

BATH ORIGINAL

zoic acid and p- (ß-hydroxyeth'oxyv) benzoic acid.

The main thing is an alkylene glycol such as ethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol and decamethylene glycol or mixtures of these compounds as the dihydric alcohol in the process of the invention used; however, up to 10 moles .. $ of the divalent Alcohol can be replaced by other dioxy compounds such as 1,4-cyclohexanedimethanol, 2,2,4,4-tetramethyl-eyclobutane diol- (l, 3), l, 4-bis - ((3-hydroxyethoxy) benzene etc. Also is it is possible to use the same direct esterification process to produce high molecular weight linear polyesters, all of them Alkylene glycol is replaced by a different from alkylene glycol dioxy compound.

In the following, the method of the invention is further illustrated by means of examples, but the invention is in no way limited to these embodiments,

Example 2 '

In this example calcium acetate was used as an inhibitor for Side reactions used; the change in the softening point when the molar ratio of Ethylene glycol was gradually changed to terephthalic acid as shown in Table II; the results are compiled in the same table. In this example the same esterification and the same polycondensation took place carried out as in Example 1 with the exception that 0.06 part of calcium acetate monohydrate was added prior to the first stage esterification reaction.

90 9886/15 45

Table II

attempt

Mr.

Amount of ethylene glycol t ropes)

Holares ■ relationship

Time span required for the esterification reaction

(min)

Base molar softening viscosity number point ( ⁰ C)

colour

58.2
67.2
71.7
80.7
89.6

155
17-9
269
448

1.3 1.5 1.6

1.8 2.0 3.0 4.0 6.0 10.0

180 170 160 150 150 150 150 120 100

0.71
0.71
0.69
0.71
0.67
0.70
Ό, 70
0.74
0.75

261.8

261.9 261.8 261.5 261.0 259.4 258.2 256.0 252.3

I I I I

I 't I

ί ·

II

CD CO

cn

The results of Example 2 are illustrated in curve b of Figure 1, in which the earlier Results of Example 1 had been shown. How out the curve b of Figure 1 can be seen, rose in this case, exactly as in Example 1, also in connection with decreasing molar ratio of ethylene glycol to terephthalic acid the softening point at and when the molar ratio was decreased from ethylene glycol to terephthalic acid to less than 2.0, the softening point reached its highest position. The fact that the softening points are each with the same molar value deserves attention Ratio of the softening point achieved with the addition of an inhibitor is consistently higher than that achieved without addition, -te Softening point.

From the comparison of Examples I and 2 it is also clear to see that the addition of a side reaction inhibitor resulted in a remarkable improvement in the color of the resulting Polyester is achieved «■

In the examples, the degree of coloration indicated by Roman numerals in the "Color" column is the value "b" according to HUlTTER, measured with the color difference meter, and classified as follows:

I b <2.0

: 3, o

'4.0

II 2 , 0 <: b III 3 b IV 4th b

903886/1545 BAD Oft / _G , _WAL

The bo obtained polycondensate of water brighter iarbe 'with a% Weichun: gspunkt of about 262 ⁰ G is no better or worse than a polycondensate which is prepared by the Esteraustausehverfahren "From an industrial point of view, this fact means in conjunction-with the fact that the amount of glycol required is less than in the ester interchange process that, according to the invention, it has been possible to make the direct esterification process superior to the ester interchange process.

The following examples show the resulting polycondensates, as they do with the addition of various auxiliaries as side reaction inhibitors.

Example 5

The esterification products prepared in the first stage are processed in the same way as in Example 1 obtained except that 400 parts of terephthalic acid and various amounts of ethylene glycol and a side reaction inhibitor according to Table III were used. To each of these, 0.13 parts of antimony trioxide was added. 0.25 part of triphenyl phosphite was added; each mixture was subjected to the same procedure as in Example 1 of the polycondensation subject. The results are presented in Table III.

909886/154

■ ^: .B attempt
No, Inhibitor Added
lot
(Parts) Table III Needed
Period of time
for the Ver
esterification
(min) G-round mola
re viscose
property number Expansion
chungs
Point
( ⁰ C) 3? work D.
O
33
Ω
Z 'ι
2
3 Lithium acetate
Dihydrate
dtOo
Lithium carbonate 0.13
0.13
0.09 Molar Ver
ratio of
ethylene glycol
kol to Tereph-
thalsare 125
137
127 0.72
0.73
0.69 258.5
262.0
261.6 HHH 4th Lithium hydroxide 0., 03 4.0
1.5
1.8 127 0.74 260.9 I. 5 Lithium fluoride 0.03 1.8 131 0.71 261.5 I. co 6th
7th Lithium hydride
Rubidium carbonate 0.01
0.29 1.8 131
134 0.67
0.63 261.7
259.6 I.
II
ι 0 9 8 8 6 8th Oeasium carbonate 0.39 1.8
1.8 130 0.79 260.2 I.
I. 9 Sodium acetate 0.10 1.8 174 0.67 261.3 II σ cn 10 Potassium hydroxide 0.13 1.3 172 0.67 261.5 ¹¹ cn 11 Zinc acetate dihydrate 0.18 1.3 146 0.70 256.4 I. 12th Zinc acetate dihydrate 0.18 4.0 153 0.68 259.8 X · 1.5

03 attempt
Ur. Inhibitor added
Henge
(Parts) 0.18 Table III Needed
Period of time
fd Ver
esterification
(min) Basal molars
Viscosity
number -Erwei-
ching Dye
« O
Q 13th Zinc borate 0.18 Molar Ver
ratio of
Ethylene glycol
kol to Tereph
thalic acid 155 0.72 259.2 ι ■ I. 14th Zinc benzoate ' 0.09 1.8 153 0.75 259.5 I. ft 15th Zinc oxide 0.23 1.8 148 0.69 258.1 I. 16 Zinc acetylacetonate 0.08 1.8 149 0.72 259.3 I. 17th Lead metaborate 0.05 1.8. 152 0.72 258.5 I:. _ι . co
O 18th Lead monoxide 0.05 1.8. 150 0.74 257.4 I ' cc
nc 19th dto. 0.29
0.29 4.0 156 0.75 259.8 IN THE
VD to
co 2ü
21 Kangan Acetate Tetrahy
drat
dto. 0.45 1.5 148
153 0.64
0.68 256.6
260.9 I-
I.
I. —A
cn 22nd Manganars enate 0.23 4.0
1.5 156 0.69 259.5 II 23 Manganese oxalate Cobalt II Acetate Tetra 0.15
hydrate
dto «, 0.15 1.8 155 0.71 260.8 I. . * 24
25th 1.8 145
150 0.69
0.70 256.0
259.3 I.
I. 4.0
1.5 • * 5209 •

attempt
No. Inhibitor Added
lot
(Parts) Table III Needed
Period of time
fd Ver
esterification
(min) Basal molars
Viscosity
number Expansion
chungs
Point
( ⁰ G) colour 26th f cobalt II acetate
iTetrahydrate
/ Zinc borate 0.04
0.18 Molar Ver
ratio of
Ethylene glycol
kol to Tereph
thalic acid 155 0.67 259.1 I. . 27 Cobalt II chloride 0.20 1.8 150 0.71 '258.7 I. ²⁸ Calcium benzoate 0.40 1.8 153 0.71 261.7 I. co
. · ■ - ο 29
30th Calcium aluminate
Caleium antimonate 0.19
0.47 1.8 157
151 0.73
0.68 261.3
261.7 I.
II 9 8 8 6 / 31 Calcium 0 ^ 048 1.8
1.8 150 0.65 261.9 I. cn 32 \ Calcium acetate
J lithium acetate
(^ Dihydrate 0.21
0.06 1.8 139 0.70 262.2 I. in 33 ΛGalcium acetate
1 zinc acetate
• 0.21
0.09 1.8 147 0.69
• 261.3 I. t
D.
O
33
O 1.8

Table III

Attempt no.

Inhibitor

Added Molar Ver Needed Basic mola. Expansion lot ratio of Period of time re viscose chungs (Parts) Ethylene glycol. f.d. Ver .. act s number Point kol to Tereph esterification thalic acid (min)

colour

Calcium acetate

0.21

1.8

149

0.69

260.7

to BAD OF 35 / Cobalt-II-acetate-
/ Tetrahydrate 0.04 1.8 153 • 0.65 260.3 II CO
CO Q 36 Strontium acetate 0.26 1.8 155 0.68 261.8 I. 37 Magnesium metaborate 0.30 1.8 157 0.64 261.7 III cn
cn Barium acetate mono-
hydrate 0.20

NJ CD CO

cn

15209/6

Example 4 ^J

The esterification and the polycondensation were carried out in the same way as in Example 1; the amount of terephthalic acid, the amount of ethyl englylcol, the type the difunctional acid used as modifier or the dihydric alcohol and the type and amount of a side reaction inhibitor were specified in the table IV chosen way. The properties of the obtained Polycondensates are shown in Table IV »

909886/1545

Table IV

Try terephthalic ethylene modification inhibitor No. acid (parts) glycol medium (parts) (parts)

(Parts) Zeitspan- basic mo- widening color ne fdVer- lare vis · * - ches- · esterification, .kosltäts- point (min); number ^ ( ⁰ C)

CD O CC

1 361 270 Is ophthalic acid
38.6 Manganese acetate
0.29 Zinc carbonate
0.35 148 2 259 , 270 Sebacic acid
'48.2 baso zinc carbon
nat-tetrahy-
drat
0.35 152 3 400 255 Tetramethyl
lenglycol
21.7 Calcium acetate
0.21 145 4th 400 270 1,4-bis (hydroxy calcium acetate
ethoxy) benzene 0.21
24.1 150 5 400 270 P- (ß-eyaroxy-
ethoxy) benzoin
acid 150

388

400

270

270

19.5

5-benzyloxy-lithium acetate isophthalic acid Dihydrate

19.5

135

Di- (ß-hydroxyethyl) zinc acetate 147

-phenoxyethylphos- 0.18

phonate

21.7 235.3 I.

0.65 234.5 I.

>, 70 242 ,:

1.68 248.2 I.

0.65 246.9 I.

0.62 252.6 II

0.67 250.3 I.

Example 5

120 parts of terephthalic acid, 156 parts of 1,4-cyclohexane-dimethanol (about 65 $ Trans) and 0.027 parts of lithium carbonate were reacted with stirring at a temperature of 24-CP-250 ° C. in an autoclave equipped with a distillation column, the pressure was reduced maintained in the same procedure as in Example 1 at about 4.5 kg / cm (overpressure). After 90 minutes, the distillation of the water ceased. The reaction mixture was transferred to a polycondensation autoclave and 0.06 part of tetraisopropyl titanate was added. The temperature was increased to about 27O ⁰ O, and the excess glycol has been expelled. The reaction mixture was then subjected to the same negative pressure as in Example 1 and the temperature was increased to 300 ° C. over a period of 1.5 hours. The l'olycondensate obtained in this way had a softening point of 285 ° C. and a pale white color - (HUIiEBR'.S b was 2.2).

Since a terephthalic acid is sparingly soluble in an alkylene glycol, the direct esterification method has hitherto been used assumed that in this case an excess is necessary Amount of alkylene glycol to be used compared to the ester interchange method; ale consequence of during the Side reaction products of an alkylene glycol formed in the reaction continued to have the polycondensate obtained by the direct esterification method compared to the product the ester interchange method, usually a disturbed crisis

903886/1545 _ßAn

SAD

- 25 -ν

.stallized state and showed a low softening point. Therefore, in spite of its property as a theoretically preferable process, the direct esterification process was unsuitable for the practical production of the polyesters having high softening points. Accordingly, for the purpose of improving the softening point of a polyester obtained by the direct esterification process, an experience had previously been proposed, for example in American patents 2,877,262 and 2,855,432, according to which 1 mole of terephthalic acid with at least 4 moles and in particular 9-10 moles of ethylene glycol is reacted under pressure; Here, an esterification product is produced in the first stage, the main component of which is bis ((3-hydroxyethyl) .- terephthalate; the product is purified by recrystallization using water to remove the side reaction products; then the purified esterification product in the second stage subjected to polycondensation; in this way, a polyester is obtained with a high softening point, since in the above-described ^v experienced a large amount xlthylenglykol, which is considerably more expensive than methanol, must be used and moreover the product obtained in the first stage in the esterification bis. - (ß-hydroxyethyl) -terephthalate polycondenses immediately when heated, but the industrially most economical purification method by distillation cannot be used according to this process

/9.09-886/154 5 ^'BAD

Purification of the bis ((3-hydroxyethyl) terephthalate only the arduous Recrystallization process used. Furthermore, in this case, as the ethylene glycol is in the form a dilute aqueous solution is obtained, the recovery of Äthylenglyko.ls from the recrystallization filtrate very costly »Accordingly, the direct esterification process in connection with this purification of the in The esterification product obtained in the first stage is not suitable for a conventional ester interchange process with respect to process superior to manufacturing costs.

However, since, as has been described in detail, according to the invention, such a purification step is perfect is unnecessary and, moreover, a water-white polyester having a high softening point can be obtained now the advantages of the direct esterification process come into their own.

909886/1545 ^ ° ^R ' ^G ' ^NAL

Claims (2)

Claims. 1.) Process for the production of linear polyesters Reaction of a dihydric alcohol with an acid component from the group of terephthalic acid and mixtures of Terephthalic acid with any other than terephthalic acid difunctional acid, in which the difunctional acid in. an amount less than 10 moles of the total acid component is contained, characterized in that the reaction is carried out at a temperature between 210 ° and 290 ° C and that the dihydric alcohol with the acid component in a ratio of 1 - 2 moles of alcohol 1 mole of acid component is reacted. 2.) Method according to claim 1, characterized in that that the reaction between dihydric alcohol and acid component in the presence of a side reaction inhibitor is carried out, with a substance from the Group lithium, sodium, potassium, rubidium, cesium, magnesium, calcium and barium «, the oxides, alcoholates, hydrides, organic and inorganic salts of these metals as well as of zinc, lead, cobalt and manganese as well as complex salts of metals is used. L e r s e i t e