DD144674A1 - PROCESS FOR PREPARING POLYESTERS - Google Patents

Abstract

The invention relates to a process for the preparation of polyesters with glycols and dicarboxylic acids. The purpose of the invention is to shorten the process time and to improve the quality of the polyesters. According to the invention, a transesterification of dicarboxylic acid dialkyl esters with glycols takes place at between 150 and 250 ° C. The polyesters are used for example as plasticizers, in cable plastics, in the production of linoleum lying under 760 Torr pressure to 2 Torr residual pressure in the presence of a catalytic system consisting of an organometallic compound and activated carbon such that tetrabutoxytitanium as the organometallic compound at a tetrabutoxytitanium-to-weight ratio of 0.004: 1 to 0.05; 1, wherein the amount of the catalytic system, based on the weight of starting di-carboxylic acid dialkyl esters, is O, 2 to 10%. The weight ratio of tetrabutoxytitanium to activated carbon may also be 0.008; 1 to 0.009. In this case, 1.5 to 2.5% of the catalyst system, based on Dikarbonsauredialkylester applied.

Description

- </ - 2139

Process for the preparation of polyesters

Field of application of the invention

The invention relates to a process for preparing the polyesters of glycols and dicarboxylic acids by transesterification of dicarboxylic acid dialkyl esters with glycols The reaction products serve mainly as plasticizers for various polymers, preferably polyvinyl chloride, cellulose nitrate, hylcelluiose, gum and they are also used in cable plastics used in the manufacture of linoleum, oil and gasoline resistant fuel lines in tractors and cars, gaskets for refrigerators.

Characteristic of the known technical solutions

As is known, the preparation of polyesters by transesterification without a catalyst is virtually impossible.

As transesterification catalysts, for example, salts, oxides and alcoholates of manganese, zinc, cobalt, antimony, titanium, germanium and tin are used (see WW. Korschak, SW Vinogradova "Rawnovjesnaja polikondensatsija" ( ^fJ Gleichgewissttspolykondensation "), Moscow, -Hauka-Verlag, 1968 166), but these catalysts are insufficiently effective.

Trying to use a Zv.eikoinponentenkatalysator -au, in which the selected components reinforce each other

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showed no positive results (see LB Sokolov "Poiikonsatsionny metod sintesa polimerow" (polycondensation method for the synthesis of polymers), Moscow, Chimija-Verlag, 1966, p. 100) _β

Also known is a process for the preparation of polyesters with glycols and dicarboxylic acids by transesterification of Dikarbonsäuredialkylestern with glycols at a lying between 130 and 190 ⁰ C temperature below 200 to 10 Torr residual pressure in the presence of a catalytic system consisting of activated carbon mixed with zinc acetate or an organotin compound of the general formula

C ₄ H ₉ OOCR

.. Sn O ₄ H ₉ OOCR,

wherein R is C ^ IL ^ or CaH ,, α (see SJ- Zuirscheinschein No. 311 93Ο, class 0 08 g 63/16).

However, the synthesis of polyesters takes a relatively long time in the application of said catalytic systems, namely 15 to 17 h. In the case of the utilization of zinc acetate in a mixture with activated carbon also gives strong yellow to dark brown colored polyester. If cinnamic compounds in admixture with activated carbon serve as the catalyst, the resulting polyesters are unstable to hydrolytic degradation, and only the additional treatment with zinc acetate assures their storage stability.

   · ·. - 3 - '

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- 3 - Object of the invention

The aim of the present invention is to provide a process for the production of polyester with glycols and Dikarbonsä.uren, which allows to shorten the process time and to improve the quality of the final products.

Explanation of the essence of the invention

The invention has the object of selecting a suitable catalytic system in the process for preparing the polyesters of glycols and dicarboxylic acids by transesterification of Dikarbonsäuredialkylestern, which allows to shorten the process time and to improve the quality of the final products.

In accordance with the stated object or object, the invention consists in that a process for the preparation of the polyesters of glycols and dicarboxylic acids by transesterification of Dikarbonsäuredialkylestern with glycols at a lying between 150 and 25Ο ⁰ C temperature under a pressure of 760 Torr to 2 Torr residual pressure in the presence of a catalytically acting system consisting of an organometallic compound and activated carbon, is proposed in the invention as the organometallic compound tetrabutoxytitanium at a tetrabutoxytitanium activated carbon weight ratio of 0.004; 1 to 0 _s 5: 1 »preferably 0 _t 008s1 to 0.009: 1, with the amount of catalytic

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see system 0.2 to 10%, preferably 1.5 to 2.5 % by weight of starting Dikarbonsauredialkylestern is.

The limit amounts of the described catalytic system, based on the weight of starting dialkyl dicarboxylates, depend on the duration of the process, the color of the available polyesters and their resistance to hydrolytic degradation. The use of the catalytic system in an amount of more than 10%, based on the weight of starting diesters, for example, leads to a significant deterioration in the color of polyesters (via No. 5 on the Fe-Gu-Co scale), while the Reduction of the amount of the catalytic system to less than 0.2%, based on the weight of starting diesters, the extension of the duration of the process and the reduction of the degree of completion of the process (ie, the reduction of the degree of conversion) result.

By using the catalytic system of the invention, consisting of tetrabutoxytitanium and activated carbon, the process time can be shortened by 1.5 to 3 times. In this case, when using the catalytic system according to the invention virtually non-dyed polyester can be produced. The color of them is Nos. 2 to 3 according to the Fe-Cu-Co scale. The polyesters, synthesized in the presence of the catalytic system of the invention, have a sufficiently high storage stability (acid numbers of polyesters after the Smonatigen storage at 98 % moisture does not exceed 2 mg KOH / g).

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Polyesters of glycols and dicarboxylic acids are obtained by reacting Dikarbonsauredialkylestern or mixtures thereof with glycols or mixtures thereof. As the starting s-diltarboxylic dialkyl ester, various esters of aliphatic and aromatic acids such as adipic acid, sebacic and phthalic acids and aliphatic monohydric alcohols, for example of methyl and butyl alcohol can be used. As glycols can be used for example ethylene glycol, diethylene glycol, butanediol (1,4) -2,2-dimethyl-1i3-propanediol (Feopentylglykol). The synthesis is carried out at a temperature between 150 and 250 ⁰ C temperature at a pressure of 760 Torr to 2 Torr residual pressure ·

Embodiment Example

For a better understanding of the present invention, examples of its specific embodiment will be given.

example 1

300 g (1.16 mol) of dibasic adipate, 92.4 g (0.87 mol), are introduced into a three-necked flask of glass provided with rectification column, system of cooling systems and initial charge of butyl alcohol, which is by-produced during the reaction. Diethylenglykoi, 0.01 g of tetrabutoxytitanium and 0.59 g of activated carbon. Tetrabutoxytitanium is active to charcoal vae 0.017 to 1. The amount of catalytic system, based on the weight of adipic acid dibutyl ester, is 0.2%. Then you switch the agitator

At between 180 and 190 ⁰ C

and the heating on. At between 180 and 190 ⁰ C

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lying temperature, the pressure in the system is lowered to 560 to 460 Torr residual pressure. As the distillation of butyl alcohol is attenuated, the residual pressure drops to 20 to 10 torr while the temperature gradually rises to 200 ^° C. The transesterification is carried out under the conditions mentioned until the distillation of butyl alcohol is completed and the hydroxyl number reaches 0.05 % . The synthesis time is between 5 and 5 * 5 h.

Table 1 below gives the characteristics of the polyester prepared according to Example 1 and the characteristics which the same polyester according to the standard requirements should have.

Table 1

Characteristics of polyester

according to Example 1

according to standard requirements 1st grade top variety

Hydroxyl number, %

Acid number, mg KOH / g

Flashpoint, C

Color number according to the Fe-Cu-Co-scale

0.05

0.52

Density at 25 ^° C., g / cm ³ 1.11 viscosity at 25 ^° C., cp 400

200

No. 3

at most 0,35 0,3

at most 2 2

1.097-1.115 1.1-1.225 200-350 250-400

at least at least

180 195 maximum no more than No. 4 No. 3

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& ν .. 7 -

Example 2

In a three-necked flask made of glass, equipped with rectification, system of cooling systems and template for butyl alcohol, which is obtained during the reaction, 300 g (1.16 Hol) "adipic acid dibutyl ester, 92.4 g (0.87 mol) of diethylene glycol, 0 , 12 g of tetrabutoxytitanium and 29 ₍ 88 g of activated carbon.) Tetrabutoxytitanium behaves as activated charcoal as 0.004 to 1. The amount of catalytic system based on the weight of adipic acid dibutyl ester is 10 %, then the stirrer and heating are switched on a temperature of 195 ⁰ C, which has the reaction mixture, the pressure in the system at 560 to 4-60 Torr residual pressure is lowered attenuated in proportion as the distillation of butyl alcohol v;. ird, the residual pressure drops to 20 to 10 Torr while the temperature gradually increases to 210 ^° C. The transesterification is carried out under the conditions indicated until the distillation of butyl alcohol is completed and the hydroxyl number reaches 0.1 % .

The synthesis lasts 10 h.

In the following, Table 2 indicates the characteristics of the polyester prepared according to Example 2 and the characteristics which the same polyester should have according to the standard requirements.

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Table 2

Characteristics of polyester according to example 1 according to standard requirements top variety Hydroxyl number, % 0.1 1st grade at the most at the most 0.3 * Acid number, mg KOH / g 0.2 0.35 at the most at the most 2 Density at 25 ^° C., g / cm ³ 1,109 2 1.1 to 1.125 Viscosity at 25 ^° C., cP 298 1.097 to 1 * 115 250-400 Flash point, ⁰ C 195 200-350 at least at least 195 Color number after the No. 2 180 at the most Fe-Cu-Go "scale at the most No. 3 Example 3 No, 4

A three-neck flask made of glass, equipped with rectification column, system of cooling systems and template for butyl alcohol, accumulating during the reaction, brings 300 g (1.16 mol) of adipidyl dibutyl ester, 92.4 g (0.87 mol) of diethylene glycol, 0.13 S of tetrabutoxytitanium and 14.87 g of activated carbon. Tetrahutoxytitanium behaves as activated charcoal as 0.0087 to 1 * The amount of catalytic system based on the weight of adipic acid dibutyl ester is 5 %, then the stirrer and heating are switched on. At a temperature of 180 ⁰ O, which has the reaction mixture, the pressure in the system drops to 560 to 46o Torr Resdruck from. As the distillation of butyl alcohol decreases,

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is weak, the residual pressure is lowered to 20 to 10 Torr, while the temperature gradually increases to 210 ⁰ G. The transesterification is carried out under the specified conditions until the distillation of butyl alcohol is completed and the hydroxyl number reaches 0.07%. The synthesis lasts 7h. ,

Below, Table 3 gives the characteristics of the polyester prepared according to Example 3 and the characteristics which the same polyester should have according to the standard requirements.

Table 3

according to characteristics of polyester

according to standard requirements

Game 1 1st grade top variety

Hydroxyl number, % acid number, mg KOH / g

25 ⁰

Density at 25 ^° C., g / ce viscosity at 25 ^° C., cP flash point, ⁰ ° C.

Color number according to the Fe-Ou-Co scale

0.07 at most

, 0.35 0.3

0.21 at most

2 2

1,115 1.097-1.115 1.1-1.25

200-350 250-400

200 at least at least

180 195

No 2 at most

No. 4 No. 3

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Bejspiel 4

In a three-necked flask made of glass, equipped with Re bifizierkolonne, system of cooling systems and initial charge of butyl alcohol, accumulating during the reaction, brings 135 g (0.52 mol) of dibutyl adipate, 165 g (0.52 mol) of dibutyl sebacate, 92.4 g (0.87 mol) of diethylene glycol, 0.05 g of tetrabutoxytitanium and 6 g of activated carbon. Tetrabutoxytitanium reacts to activated carbon ve 0.0083 to 1e The amount of catalytic system, based on the total weight of starting diesters, is 2%. Then you switch on the agitator and the heating. At a temperature of 180 ⁰ C, which has the reaction mixture, the pressure in the system is lowered to 560 to 460 Torr Eestdruck. In proportion as the distillation of butyl alcohol is weakened, the residual pressure, the temperature of the reaction mixture is lowered to 20 to 10 Torr from? Iährend gradually to 200 ° to 210 ⁰ C increases. The transesterification is carried out under the specified conditions until the distillation of butyl alcohol is completed and the hydroxyl number reaches 0.25 % . The synthesis lasts 9h,

By way of illustration, Table 4 gives the characteristics of the polyester prepared according to Example 4 and the characteristics which the same polyester should have according to the standard requirements.

.- 11 -

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Table 4

according to

Characteristics of Polyester Example 1

according to standard requirements e variety

top variety

Hydroxyl number, %

0.25

Acid number, mg KOH / g 0.32

Density at 25 ⁰ C, g / cm ³ 1.079 Viscosity at 25 ⁰ G, cP 587 Flash point, ⁰ C

Color number according to the Fe-Ou-Co-Slcala

221

No.

at the most at the most 0.35 0.3 over 2 at most 2 1.07 to 1.1 1.08 to 1.1 400-550 450-600 at least at least 200 220. at the most at the most No. 5 No. 4

At game 5

The process vdrd performed in a plant comprising a vertical cylindrical stainless steel reactor

the steel of 3.2 m capacity, provided with Propellermisdi device and located inside coil for heating and cooling of the reaction mixture, a Eektifizierkoionne _s cooling systems and templates for butyl alcohol, accumulating during the reaction contains.

The reactor is charged with 1600 kg of dibutyl adipate, 430 kg of diethylene glycol, 0.3 g of tetrabutoxytitanium and 30 kg of activated carbon. Tetrabutoxytitanium behaves as activated carbon as 0.01 to 1. The amount of the catalytic system, based

- 12 -

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-. 12 -

on the weight of dibutyl adipate, is 1.89%. After completion of the feed, the reaction mixture is heated to between 180 and 190 ⁰ C lying temperature. At this temperature and atmospheric pressure (760 torr), distillative distillation of the butyl alcohol obtained during the reaction begins, which is reduced at the rate of approximately 30 % conversion. Then, the pressure in the system is gradually lowered to 4-0 to 30 Torr residual pressure and carries out the reaction at said Sestdruck and lying between 180 and 190 ⁰ O temperature until the distillation of butyl alcohol is terminated and the hydroxyl value 0.15 % reached. The synthesis takes 12 h.

Table 5 below gives the characteristics of the polyester prepared according to Example 5 and the characteristics which the same polyester according to the standard requirements should have.

Table 5

Characteristics of polyester

according to Example 1

according to standard requirements

1st grade

top variety

Hydroxyl number, %

Acid number, mg KOH / g

0 * 15

0.56

Density at 25 ⁰ G, g / cm ³ 1.1 Viscosity at 25 ⁰ C, cP 276

Flash point, 0

Color number according to the Fe-Cu-Co scale ·

195

No. 3

at the most at most

0.35 0.3 at most 2 at most 2

1.097-1.115 1.1-1.125 2OO-35O 250 ^ 400

at least at least 180 195 at the most at the most No. 4 No. 3 - 13 -

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- 13 Example 6

The process is carried out in a plant similar to that described in Example 5.

The reactor is charged with 700 kg of dibutyl adipate, 852 kg of dibutyl sebacate, 448 kg of diethylene glycol, 0.3 kg of tetrabutoxytitanium and 30 kg of activated carbon. Tetrabutoxytitanium behaves to activated carbon such as O ₈ OI: 1, The amount of the catalytic system, based on the total weight of the starting diesters, is 1.95% · After completion Beschikkung the reaction mixture is heated at a temperature 180-190 ⁰ C temperature , At this temperature and the atmospheric pressure, the distilling off of the incurred during the reaction butyl alcohols. As the distillation is attenuated, the pressure in the system is gradually reduced to 40 to 30 Torr residual pressure. The transesterification is carried out at the said residual pressure and a temperature of 180 to 190 ⁰ C until the distillation of Butylalkohoi is completed and the hydroxyl number of the reaction mixture reaches 0.1%. The synthesis lasts 11 h.

In the following, Table 6 gives the characteristics of the polyester prepared according to Example 6 and the characteristics which the same polyester should have according to the standard requirements.

- 14 -

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Table δ

Characteristics of polyester

according to Example 1

according to standard requirements 1 «variety top variety

Hydroxyl number, %

Acid number, mg KOH / g

Color number according to the Pe-Ou-Oo scale

0.1

1.0

Density at 25 ⁰ G, g / ciP 1.08 Viscosity at 25 ⁰ C ₁ cP 518 Flash point, ⁰ C 220

No.

at the most at most

0.35 0.3

at most 2 at most 2

1.07-1.1 1.08-1 _t 1 "

A-OO-550 450-600

at least 200 220 at least

no more than no. 5 no. 4 at the most

Example 7

A glass three-necked flask equipped with rectification column, system of cooling equipment and template for butyl alcohol, which is obtained during the reaction, is charged with 300 g (1.16 mol) of dibutyl mipinate, 90.7 g (0.87 mol) of 2,2-dibutyl Dimethyl-1,3-propanediol, 0.05 g of tetrabutoxytitanium and 6 g of activated carbon. Tetrabutoxytitanium behaves as active carbon as 0.0083 ² ^ 1 · The amount of the catalytic system, based on the weight of dibutyl adipate, is 2 % · Then the agitator and the heating are switched on. At between 170 and 180 ⁰ C lying temperature of the reaction mixture, the pressure in the system is lowered to 660 to 560 Torr residual pressure. To the extent that the Destilla

- 15 -

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f 39 $ 6

Butyl alcohol is attenuated, the residual pressure drops to 20 to 10 Torr, while the temperature gradually increases to 200 ⁰ C. The transesterification is carried out under the conditions indicated until the distillation of butyl alcohol is completed and the hydroxyl number reaches 0.17 % . The synthesis lasts 8h.

Comparatively, a similar synthesis was carried out except that the catalytic system was a zinc acetate-activated carbon mixture (SU-Authors No. 311 930). The synthesis time was 17 h.

The characteristics of polyester prepared according to Example 7 and according to the SU-certificate Fr. 311 930 are given in Table 7.

Table 7

according to the SU-copyright characteristics of polyester, _{Np #} ^

Hydroxyl number, % 0.17 0.2

Acid number, mg KOH / g 0.43 1.2

Density at 25 ⁰ Ct g / cm ³ 1.093 1.091

Viscosity at 25 ⁰ O, cP 3 ^ 5. 328

Flash point, ⁰ O 197 192 Color number after the

Fe-Cu-Oo scale 2 '13

Put into a three-necked flask of glass _t rectified »

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- 16 -

column, system of refrigerators and template for butyl alcohol, resulting during the reaction, bring 300 g (1.16 mol) of dibutyl adipate, 45.6 g (0.4-3 mol) Diethylengiykol, 26.7 g (0.43 mol ) Ethylene glycol, 0.03 g tetrabutoxytitanium and 3.17 g activated carbon. Tetrabutoxytitanium behaves as activated charcoal as 0.0095 to 1. Di © Amount of the catalytic system, based on the weight of dibutyl adipate, is 8 %. After completion of the feed, the pressure in the system is lowered to 560 to 460 Torr and the reaction mixture is brought to a temperature heated by 150 ⁰ G. As the distillation of butyl alcohol is weakened, the temperature of the reaction mixture rises to 250 G while the residual pressure gradually drops to 10 to 2 Torr. The transesterification process takes place under the conditions indicated until the distillation of butyl alcohol is completed and the hydroixyl number of the reaction mixture reaches 0.17 % . The synthesis lasts 7 h.

The result is a polyester with the following characteristics:

Hydroxyl number, % 0.17

Acid number, mg KOH / g 0.32

Density at 25 ⁰ G, g / cm ³ 1.099

Viscosity at 25 ⁰ G, cP 382

Flash point, ⁰ G 194

Color number according to the Fe-Gu-Go scale. No., 3

Example 9.

In a three-necked flask made of glass, vershai with. Rectification column, system of cooling equipment and template for

- 17 -

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- 17 -

Butyl alcohol, accumulating during the reaction, are introduced 300 g (1.16 mol) of dibutyl adipate, 53. 4 g (0.86 mol) Efehylenglykol, 0.02 g of tetrabutoxytitanium and 1.48 g of activated carbon. Tetrabutoxytitanium behaves as activated carbon as 0.014 to 1 ". The amount of catalytic system based on the weight of dibutyl adipate is 0.5 %. After completion of Beschik-. kung the pressure in the system is lowered to 560 to 460 Torr and the reaction mixture heated to 160 ⁰ G. As the distillation of butyl alcohol is weakened, the residual pressure in the system drops to 2 Torr, while the temperature to 250 ⁰ G. increases. The transesterification is carried out under the conditions specified until the distillation of butyl alcohol is completed and the hydroxyl number of the salt solution reaches 0.15 % . The synthesis lasts 8 h.

The result is a polyester with the following characteristics:

Hydroxyl number, % 0.15

Acid number, mg KOH / g 0.36

Density at 40 ⁰ C, g / cm- ^ 1,085

Viscosity at 240 ^° C., cP 206

Flash point, ⁰ G 198

Color number according to the Fe-Gu-Cο-scale Hr. 4

At game 10

In a three-necked flask made of glass, equipped with rectification columns, system of cooling systems and template for butyl alcohol, accumulating during the reaction, brings 3OO g

- 18 -

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- 18 -

(1.16 mol) of dibutyl adipate, 79.2 g (0.88 mol) of 1,4-butanediol, 0.3 g of tetrabutoxytitanium and 6 g of activated carbon. Tetrabutoxytitanium behaves to activated carbon as 0.05 to 1 · -The amount of catalytic! Systems, based on the weight of dibutyl adipate, is 2.1%. After completion of the feed the reaction material is heated to 180 ⁰ G. At the indicated temperature and atmospheric pressure (760 Torr), the distillation of butyl alcohol begins. As the distillation of butyl alcohol is weakened, the pressure in the system is reduced to 5 Torr. The temperature gradually increases to 230 ° C. The transesterification takes place under the said conditions until the distillation of butyl alcohol is stopped and the hydroxyl number of the Eeaktionsgutes reached 0.08 % The synthesis lasts 6h.

The result is a polyester with the following characteristics:

Hydroxyl number, % . '0.08

Acid number, ng KOH / g. 0.52.

Density at 40 ⁰ O, g / cm ³ 1.080

Viscosity at 40 ^° C., cP 182

Flash point, - ⁰ C 212

Color number according to the Fe-Cu-Co-scale No. 4

The comparison of the examples given with the method described in the SU-copyright No. 311 93Ο shows that the utilization of the tetrabutoxytitanium-activated carbon mixture as a catalytic system allows the process time

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21396

- 19 -

to shorten 1.5 to 3 times compared to the catalytic systems Ziinkazetat activated carbon and DibutylzinndikaprilatrAktivkohle.

In the case of using the catalytic system according to the invention, the positive synergistic effect of the catalytic action is sharply pronounced. This is confirmed by the fact that when the activated carbon in admixture with tetrabutoxytitanium is used, the rate constant of the reaction is increased by 1.5 to 2 times over that in the presence of tetrabutoxytitanium as a catalyst. If one uses the activated carbon in a mixture with the other compounds such as zinc acetate or Dibutylzinndikaprylat (SU-copyright No. 311 930) as a catalytic system, however, the reaction rate constant compared to the reaction rate constant in the presence of zinc acetate or dibutyltin dicaprylate alone is reduced.

Table 8 shows the comparatively Geschindigkeitskonstanten the transesterification of dibutyl adipate with diethylene glycol at a temperature of 1? 0 ⁰ C in the presence of known catalytic systems, used for the production of industrial locations of polyesters, of the individual components of the given applied katalytischen.Systeme and in the presence of catalytic system according to the invention.

- 20 -

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- 20 -

Table 8 speed 7.1 Catalytic system Amount relative constant (Z ") x 10 Diesterge- _{at 1? 0} o ^ _W layer, -i mol% ^{1 1} .miiT 8.3 qualitative composition 0.33 1.1 (the process takes up to 70 % conversion) zinc acetate 0.066 5.0 Dibutylzinndikaprylat 2 activated carbon 0.33 4.8 fZinkazetat 0.66 (Activated carbon 0.066 5.3 Dibutyltin dicaprylate 2 7.5 (Activated carbon 0,025 tetrabutoxytitanium 0,025 10.1 ( Tetrabutoxytitanium 2 (Activated carbon 0.1 f tetrabutoxytitanium 2 fAktivkkohle

- 21 -

Claims (2)

.25. 1. 1980 IP G 08 G / 213 966 & 6 - 21 invention claim 1 · Process for the preparation of polyesters with glycols and dicarboxylic acids by transesterification of Dikarbonsäuredialkylestern with glycols at a lying between 150 and 250 ⁰ C temperature below 760 Torr pressure to 2 Torr residual pressure in the presence of a catalytically evaporating system consisting of an organometallic compound and activated carbon, characterized in that tetrabutoxy titanium serves as the organometallic compound at a tetrabutoxytitanium activated carbon weight ratio of 0.004: 1 to 0.05 J 1, wherein the amount of the catalytic system, based on the weight of starting dialkyl dicarboxylates, is 0.2 to 10 % . A method according to item 1, characterized in that a catalytic system consisting of tetrabutoxytitanium and activated carbon at a weight ratio of 0.008: 1 to 0.009: 1 is used, wherein the amount of the catalytic system, based on the weight of Dicarbonsauredialkylestern, 1.5 to 2.5 % .