BE878183A - PROCESS FOR THE PREPARATION OF POLYESTERS OF GLYCOLS AND DICARBOXYLIC ACIDS - Google Patents

Description

       

  DESCRIPTIVE MEMORY

  
in support of a request for

PATENT

  
for

  
"Process for the preparation of polyesters of glycols and dicarboxylic acids"

  
by

  
1) Mikhail Vladimirovich VISHNYAKOV,

  
Shelepikhninskaya naberezhnaya, 8, korpus 2, kv. 85, MOSCOW (U.R.S.S.),

  
2) Jury Efimovich NOSOVSKY,

  
Volzhsky bulvar, 43, kv. 44,

MOSCOW (U.R.S.S.),

  
3) Rema Samuilovich BARSHTEIN,

  
2 ulitsa Bebelya, 26, kv. 139,

MOSCOW (U.R.S.S.),

  
4) Vera Gavrilovna GORBUNOVA,

  
2 Pugachevskaya ulitsa, 8, korpus 5, kv. 10, MOSCOW (U.R.S.S.),

  
 <EMI ID = 1.1>

  
ulitsa Fryazevskaya, 35, korpus 1, kv. 36,

MOSCOW (U.R.S.S.),

  
6) Vladimir Lvovich SVERDLIK,

  
ulitsa Verkhnekrasnoselskaya, 34, kv. 55,

MOSCOW (U.R.S.S.),

  
7) Vladimir Sergeevich SCHERBAKOV,

  
ulitsa Lesnaya, 8, kv. 85,

REUTOV MOSKOVSKOI OBLASTI (U.R.S.S.).

  
The present invention relates to a process for the preparation of polyester glycols and dicarboxylic acids with a molecular weight of 600 to 8000 by transesterification of the dialkyl esters of dicarboxylic acids with glycols in the presence of a transesterification catalyst. The reaction products are mainly used as plasticizers for different polymers, preferably for chloro

  
 <EMI ID = 2.1>

  
are also used in putty rubbers intended for

  
the manufacture of cables, for the manufacture of linoleum, flexible hoses resistant to petrol and oils for tractors and cars, seals for refrigerators, etc.

  
Processes for preparing polyesters of glycols and dicarboxylic acids are widely described in the literature.

  
According to the USSR author's certificate N [deg.] 149 217, dasse C081 27/06, the preparation of polydiethylene glycol sebacate

  
there 0

  
is carried out at a temperature of 130 to 200 C and under atmospheric pressure in a flow of nitrogen.

  
A disadvantage of this process is the excessive duration

  
transesterification, as well as the high content of the final product in lower molecular weight compounds.

  
To eliminate the aforementioned drawbacks, polyesters are prepared in two stages (see V.V. Korshak,

  
S.V. Vinogradova "Polycondensation of balance", Moscow, Editions "Naouka", 1968, page 198).

  
According to the USSR author's certificate N [deg.] 311 930, class C08g 63/15, to obtain polydiethylene glycol adipate, at the first stage of the process, under a residual pressure of 150

  
at 200mm Hg, the temperature is gradually increased to 150-

  
0

  
180 C. The reaction is carried out under these conditions until the cessation of the release of the reaction by-product (butyl alcohol). Then the pressure in the system is lowered to a residual pressure of 15 to 20 mm of Hg and the reactions are completed under this pressure and at the temperature of 180

  
at 190 C.

  
One drawback of this process is the duration of its first stage, the rate of temperature rise being limited by the boiling points of the constituents of the reaction mixture under a given pressure and by the danger of sudden boiling. and effervescence with projections of the reaction mass.

  
To reach the high temperatures more quickly, a two-stage process for the preparation of polyesters is used, in which the first stage is carried out at atmospheric pressure, while the final stage is carried out under vacuum. According to Japanese Patent N [deg.] 35,797, class 26g 6,
1972, for the preparation of polyethylene glycol terephthalate by transesterification of dimethyl terephthalate with ethylene glycol, the first stage of the process is carried out

  
 <EMI ID = 3.1>

  
until the quantitative or almost quantitative release of the by-product of the reaction which is methyl alcohol. The se-

  
0 stage of the process takes place at a temperature of 275 to 285C and under a residual pressure of 0.3 to 0.05 mm Hg.

  
One drawback of this process is the long duration of its first stage, which is 72 hours. It has been successful in reducing the duration of the transesterification by applying the process in a stream of inert gas. Thus according to the patent of the United States of America N [deg.] 3 386 960, class 260-75, we prepare

  
polyethylene glycol terephthalate carrying the mixture

  
0

  
initial reaction up to the temperature of 217 C in a slow flow of nitrogen under atmospheric pressure. Then the pressure is lowered to 1 mm Hg in order to remove the excess glycol and the operations are completed for 2 hours at a

  
0

  
temperature of 280 C and under said residual pressure.

  
According to Japanese Patent N [deg.] 40,711, class 26g 6, 1971,

  
the preparation of polyethylene glycol terephthalate is carried out

  
0

  
in a stream of nitrogen at a temperature of 180 to 210 C and under atmospheric pressure. The second stage of the process is carried out.

  
0

  
by bringing the temperature to 280 C and lowering the pressure to 0.1mm Hg.

  
The implementation of the process for preparing polyesters of glycols and dicarboxylic acids in a flow of

  
inert gas makes it possible to improve the conditions for elimination of the reaction by-product (of the aliphatic monoalcohol) and to reduce to a certain extent the duration of the first phase of the process. However, in this case, there is a sudden increase in losses of raw materials and by-product of the reaction, because of the difficulty of their condensation and their trapping from the flow of inert gaseous effluents. Thus, according to Japanese Patent N [deg.] 40,711, class 26g 6, during transesterification it is necessary to use more than a double excess of glycol relative to the stoichiometric amount.

  
An industrial process for the preparation of polyesters of glycols and of dicarboxylic acids is widely known by transesterification of the dialectic esters of dicarboxylic acids with glycols in the presence of a transesterification catalyst, the process taking place, first at a temperature of

  
[deg.]

  
 <EMI ID = 4.1>

  
final Pf equal to 150 - 1mm Hg, after which the transesterification is carried out at the same temperature and under the final pressure Pf until the completion of the operations.

  
The disadvantages of this known process are due to the excessive duration of the transesterification, to the losses of raw materials (glycol) in the by-product of the reaction (aliphatic monoalcohol) discharged from the cycle. The change in the composition of the reaction mass due to the loss of glycol in the distilled alcohol leads to the production of final products with a molecular weight lower by 1.3 to 3 times

  
at nominal molecular weight. In addition, in some cases

  
end products with an unsatisfactory coloring are obtained
(this coloring following the scale with iron-copper-cobalt corresponding to N [deg.] 30).

  
The products obtained are characterized by excessive acidity (for example 2.2 milligrams of KOH / gram).

  
The object of the present invention is to eliminate the aforementioned drawbacks.

  
We therefore proposed to solve the following problem:

  
in a process for the preparation of polyesters of glycols and dicarboxylic acids by transesterification of dialkyl esters of dicarboxylic acids with glycols, creating a regime for lowering the initial pressure Po to the final pressure Pf which would allow reduce the duration of transesterification, lower consumption standards for raw materials and improve the quality of final products.

  
The solution to said problem consists in a process for preparing polyesters of glycols and dicarboxylic acids by transesterification of dialkyl esters of dicarboxylic acids with glycols in the presence of a transesterification catalyst, by applying the process first to a temple-

  
0

  
 <EMI ID = 5.1>

  
final pressure Pf of 150 to 1 mm of Hg, then carrying out the transesterification at the same temperature and under the same final pressure Pf, according to the invention the reduction in the

  
 <EMI ID = 6.1>

  
according to the following relation:

  

 <EMI ID = 7.1>


  
P being the current pressure (mm of Hg);

  
Po being the initial pressure (mm of Hg);

  
 <EMI ID = 8.1>

  
B, C being empirical coefficients having the following values:

  
B = 466 to 2080, C = 226 to 1440

  
 <EMI ID = 9.1>

  
quickly that / according to the relationship indicated, a considerable foaming, boiling and projections of the reaction mass result. If the reduction in the initial pressure is slower, the duration of the operations increases due to the slow evacuation of the reaction by-product.
(aliphatic monoalcohol) outside the reaction zone.

  
The preparation of the polyesters according to the invention allows:

  
1. reduce the duration of operations by 1.5 to 2 times by creating optimal conditions for the elimination of the reaction by-product (aliphatic monoalcohol) from the reaction zone, and therefore shifting the balance of the process in the required direction.

  
2. reduce the consumption standards for raw materials by reducing the loss of glycol in the reaction by-product (aliphatic monoalcohol) which is removed from the cycle.

  
3. to improve the quality of the final products and in particular to increase their viscosity, to improve their coloration, (coloration according to the scale with iron-copper-cobalt corresponding to N [deg.] 3) and to lower l acid number up to 0.8 milligrams of KOH per gram, thanks to the reduction in the residence time of the reaction mass at high temperatures.

  
The present invention can be carried out in particular in a unit composed of a boiler apparatus with an agitator having a jacket or a coil for heating or cooling, a rectification column and a system for condensing the vapors expelled by distillation.

  
To prepare the polyester, the starting reagents - glycol and a dialkyl ester of acid are placed in the reactor.

  
 <EMI ID = 10.1>

  
Then the reaction mixture is brought under stirring to

  
 <EMI ID = 11.1>

  
residual pressure of 200 mm Hg depending on the nature of the reactants and the catalyst. After 0.5 to 3 hours after

  
 <EMI ID = 12.1>

  
a final pressure PF of 150 to 1 mm of Hg in accordance with the relationship indicated in the above. The lowering of the pressure in the system in accordance with said relationship can be achieved in particular by means of an automatic regulation system comprising a vacuum gauge, a programmed sensor, a regulator and a valve in the vacuum piping.

  
 <EMI ID = 13.1>

  
reaction mass having the required hydroxyl number.

  
The mixture of glycol vapors and the reaction byproduct that is the aliphatic monoalcohol, distilled off during the transesterification, arrives in a rectification column where it is separated into glycol and alcohol. The glycol leaving the boiler of the rectification column is continuously recycled, while the alcohol, after its condensation, is partially recycled as reflux from the column, the remaining part of the alcohol being removed from the cycle.

  
In the process which is the subject of the invention, it is

  
 <EMI ID = 14.1>

  
dicarboxylic acids various esters of aliphatic and aromatic acids, in particular adipic, sebacic, phthalic acids, and aliphatic monoalcohols, in particular methyl alcohol, butyl alcohol. Among the glycols, ethylene glycol, diethylene glycol, propylene glycol-1,2 can be used in particular. As catalyst, any transesterification catalyst can be used, in particular tetrabutoxytitane, zinc acetate, n-dibutyl-dicaprylate-tin, a mixture of acetate

  
zinc and activated carbon, a mixture of n-dibutyldicaprylate tin and activated carbon.

  
Other characteristics and advantages of the present invention will be better understood on reading the description

  
 <EMI ID = 15.1>

  
limiting.

Example 1.

  
In a periodically running unit comprising an apparatus

  
boiler with a capacity of 3.2 m with agitator, heating coil and cooling jacket, a rectification column with filling body, with a height of 7 m, a condensation and trapping system for the vapors expelled by distillation, and collectors for the distilled products, the polypropylene glycol adipate is obtained by transesterification of dibutyl adipate with propylene glycol-1,2 in the presence of an active zinc acetate catalytic system.

  
1.550 kg of dibutyl adipate are placed in the reactor,
420 kg of 1,2-propylene glycol, 16 kg of zinc acetate, 32 kg

  
activated carbon. Once the charge has been put in place, water vapor is admitted into the reactor coils and the reaction mass is reheated under the pressure of 760 mm Hg. After 50 minutes the temperature

  
0

  
of the reaction mass reaches 185 ° C., and operations are then carried out at this temperature. After 1.5 hours after the start of heating, the pressure in the system begins to reduce in accordance with the relationship:

  

 <EMI ID = 16.1>


  
 <EMI ID = 17.1>

  
the residual pressure Pf in the system is 20 mm Hg. The operations are continued under this same pressure for a further 8 hours until the hydroxyl number of the reaction mass is 0.3%. Total duration of operations
(from the start of reheating until obtaining the finished product) is 15 hours.

  
During all the synthesis operations we admit in

  
 <EMI ID = 18.1>

  
product (butyl alcohol), continuously removed by distillation from the reactor, in a rectification column where this mixture is

  
 <EMI ID = 19.1>

  
both the boiler of the rectification column is continuously recycled while the butyl alcohol, after its condensation, is partly recycled as reflux in the column, the remaining amount of alcohol being removed from the cycle.

  
By way of comparison, a similar synthesis is carried out using known technology. The synthesis is carried out as described in the above, with the only difference that it is carried out under atmospheric pressure (760 mm of Hg) at temperature.

  
o

  
of 185 C until an 80% conversion is reached. Then the pressure in the system is lowered for 60 minutes to 20 mm Hg and the operations are continued under

  
o

  
the indicated pressure and at the temperature of 185 C until

  
that the hydroxyl number of the reaction mass reaches 0.3%. The duration of the first stage (under atmospheric pressure) is 23 hours, the duration of the second stage under the residual pressure of 20 mm Hg is 6 hours. To compare the quality of the polyesters obtained by the process according to the invention and by the known process, samples of the two operations are drawn off and their qualitative analysis is carried out. The results of the analysis are shown in Table 1.

Example 2.

  
 <EMI ID = 20.1> of polydiethylene glycol by transesterification of dibutyl adipate with diethylene glycol in the presence of a catalytic system zinc acetate-activated carbon. 1600 kg of dibutyl adipate, 510 kg of diethylene glycol, 16 kg of zinc acetate, 32 kg of activated carbon are placed in the reactor. After the introduction of the load, the pressure in the system is lowered to 200 mm Hg, and the heating of the reaction mass is started. After 0.5 h after the start of

  
0

  
reheating to the temperature of 150 ° C., the pressure in the system begins to drop in accordance with the relation:

  

 <EMI ID = 21.1>


  
 <EMI ID = 22.1>

  
After 3 hours, the pressure in the system is 1 mm from

  
o

  
Hg. The operations are continued at the temperature of 150 ° C. and under the residual pressure indicated for 17 hours until the hydroxyl number of the reaction mass is 0.45%.

  
The total duration of the process is 20.5 hours.

  
By way of comparison, a similar synthesis is carried out according to the known process. This synthesis is carried out as indicated in the above, with the only difference that

  
0

  
leads it to a temperature of 150 ° C. and under the residual pressure of 200 mm of Hg until a conversion of
90%. Then, for 30 minutes, the pressure is lowered to 1 mm of Hg and the operations are continued under this same pressure

  
0

  
and at a temperature of 150 ° C until the hydroxyl number of the reaction mass is 0.45%. The total duration of the process is 27 hours.

  
To compare the quality of the polyesters obtained by the process according to the invention and by the known process, samples are drawn in the two operations and their qualitative analysis is carried out. The results of the analysis are shown in Table 1.

Example 3.

  
 <EMI ID = 23.1>

  
catalytic n-dibutyldicaprylate-tin-activated carbon. 1600 kg of dibutyl ate, 470 kg of diethylene glycol, 1.42 kg of n-dibutyldicaprilat-tin, 40 kg of activated carbon are placed in the reactor. Once the charge has been put in place, the reaction mass is started under atmospheric pressure. After 1.2 h the temperature reaches

  
o

  
200 C, and then the operations are carried out at this temperature. Two hours after the start of heating, we begin to lower the pressure in the system in accordance with the relation:

  

 <EMI ID = 24.1>


  
 <EMI ID = 25.1>

  
continues operations under this pressure and at temperature

  
o

  
200 C until the hydroxyl number of the reaction mass is 0.3%.

  
By way of comparison, a similar synthesis is carried out according to the known method. The synthesis is carried out as described above, with the only difference that it is carried out at the

  
0

  
temperature of 200 C and under atmospheric pressure until a conversion of 95% is obtained. Then we lower for
60 limits the pressure in the system up to 10 mm Hg and continues operations under this pressure and at temperature

  
0

  
200 C until the hydroxyl number of the reaction mass becomes 0.3%.

  
To compare the quality of the polyesters obtained by the processes according to the invention and known, the samples are drawn off in the two operations and their qualitative analysis is carried out. The results of the analysis are collated in Table 1.

Example 4.

  
In the unit described in Example 1, polyethylene glycol phthalate is obtained by transesterification of dimethyl phthalate with ethylene glycol in the presence of a catalyst, tetrabutoxytitane.

  
1,700 kg of dimethyl phthalate are placed in the reactor,
410 kg of ethylene glycol and 2.21 kg of tetrabutoxytitanium. After placing the reagents, the pressure in the

  
 <EMI ID = 26.1>

  
reaction mass. After 1.5 hours, the temperature reaches 250 ° C. and the operations are then carried out at this temperature. After 3 hours after the start of heating, the pressure in the system begins to decrease in accordance with the relationship:

  

 <EMI ID = 27.1>


  
 <EMI ID = 28.1>

  
After four hours, the residual pressure in the system is 150 mm Hg. Then the operations are carried out under this

  
0

  
pressure and at the temperature of 250 C until the hydroxyl number of the reaction mass is equal to 0.3%.

  
By way of comparison, the synthesis is carried out according to known technology. The synthesis is carried out as described above, with the only difference that the temperature is

  
o

  
250 C and the residual pressure, 600 mm Hg, until a conversion of 85% is obtained. Then for 45 minutes,

  
the pressure in the system is reduced to 150 mm Hg and

  
operations are continued under the indicated residual pressure

  
0

  
and at a temperature of 250 ° C until the hydroxyl number of the reaction mass is 0.3%.

  
For the comparison of the quality of the polyesters obtained by the process according to the invention and by the known process, samples are drawn in both cases for which a qualitative analysis is carried out.

  
The results of this analysis are collated in the table
 <EMI ID = 29.1>
 <EMI ID = 30.1>
 In addition to determining the qualitative characteristics of the final products, the total duration of the operations was noted in each example (from the start of reheating until the final product was obtained), the quantity of aliphatic monoalcohol evacuated from the cycle was measured. rectification, as well as the glycol content of said monoalcohol.

  
The results are summarized in Table 2.

Table 2

  

 <EMI ID = 31.1>


  
Thus, the implementation of the process for preparing polyesters in accordance with the present invention makes it possible to reduce the duration of the process by 1.5 to 2 times, to reduce the

  
 <EMI ID = 32.1>

  
a final product of imposed molecular mass, of improved coloration and with an acid index of less than 2 milligrams of KOH per gram.

  
Of course, the invention is in no way limited to the modes of. described embodiment which have been given only by way of example. In particular, it includes all the means constituting technical equivalents of the means described, as well as their combinations, if these are carried out according to the spirit and implemented in the context of the claims which follow.


    

Claims (2)

1 mm Hg, after which the transesterification is carried out at the same temperature and under said final pressure Pf, characterized <EMI ID = 34.1> <EMI ID = 35.1> P being the current pressure (mm of Hg); <EMI ID = 36.1> B and C being empirical coefficients of the following values: B = 466 to 2080, C = 226 to 1440. 1. Process for the preparation of polyesters of glycols and dicarbo & y acids by transesterification of dialkyl esters of dicarboxylic acids with glycols in the presence of a transesterification catalyst, said transesterification o being carried out first at a temperature of 150 to 250 C and under <EMI ID = 33.1> 2. Polyesters of glycols and dicarboxylic acids, characterized in that they are obtained by transesterification in accordance with the process according to claim 1. <EMI ID = 37.1>