CH656391A5 - METHOD FOR PRODUCING HIGH MOLECULAR POLYESTERS. - Google Patents

Description

The present invention thus relates to a process for the continuous production of high molecular weight polyesters with a very low content of volatile An-10 parts, by two-stage treatment of polyesters from diols and dicarboxylic acids in the solid phase which may be crosslinked with tri- and polyfunctional alcohols or carboxylic acids. This process is characterized in that the polyesters are treated in a first stage with water vapor or an inert gas and / or air containing water vapor at 100-245 ° C and then in a second stage at 200-245 ° C with inert gas and / or air can be post-condensed at normal pressure or in vacuo.

Said polyesters can be composed of the following diol and dicar-20 acid components:

Diols: alkylene glycols, in particular α, co-alkylene glycols, such as ethylene, 1,3-propylene, 1,4-butylene glycol, also also cyclohexane-1,4-dimethylol, or cycloalkane diols, such as cyclo-hexane-1, 4-diol.

2s dicarboxylic acids: terephthalic acid, isophthalic acid, naphtha-lindicarboxylic acids, also adipic acid, sebacic acid etc.

Mixtures of diols and dicarboxylic acids and small amounts of trifunctional and polyfunctional alcohols or carboxylic acids are of course also suitable for crosslinking.

By far the most important polyester of this type is polyethylene terephthalate, and this will only be discussed below.

The removal of the physically dissolved acetaldehyde 35 is known to be determined by the diffusion processes of the acetaldehyde from the polyethylene terephthalate granules; on the other hand, as is known, in order to remove the chemically bound acetaldehyde, the vinyl ester groups in the polyethylene terephthalate first have to be converted into free acetaldehyde, which has not been completely achieved in the previously known processes. In the absence of water vapor, the vinyl ester groups cannot react completely.

Surprisingly, it has now been found that the presence of water vapor according to the method according to the invention enables the physically dissolved and chemically bound acetaldehyde to be removed almost quantitatively, without adverse effects on the polyester, in particular those in the form of granules.

A new analytical method was developed to determine the total content of the physically dissolved and chemically bound acetaldehyde.

With the new analytical method of determining the total content of physically dissolved and chemically bound acetaldehyde, the polyester sample is ground 55 (20-50 mesh), placed in a glass bottle with 10 times the amount of oxygen-free water and sealed with a Teflon-coated rubber septum. The bottle is then heated to 120 ° C for 17 hours. After the bottle has cooled, a sample of the aqueous solution is taken and analyzed for the content of acetaldehyde by head-space gas chromatography or the colorimetric method.

The new analytical method allows a quantitative determination of the physically dissolved and chemically bound acetaldehyde in the polyester.

Previously known analytical methods for determining the acetaldehyde content in the polyester have been described, for example, in DE-OS 28 34 161 and US Pat. No. 4,223,128.

3 656391

According to DE-OS 28 34 162, a sample of the ground

The procedure for a polyester in a glass flask with a rubber septum is as follows (see closed. The air contained in the flask is shown in FIG. 1):

Nitrogen replaced. Then the flask is heated for 90 minutes on granules of polyethylene-150 ° C. customary in the textile industry and a sample of the acetaldehyde-nitrogen-terephthalate (its total acetaldehyde content in the mixture after gas chromatography on acetaldehyde in the order of about 100) ppm is) is lysed by the filler. Opening 1 in the reactor part 2, in which the first stage is ahead. The method described in DE-OS 28 34 162 is the one in, initiated and falls by its own gravity in the US Pat. No. 4,233,128 acetaldehyde analysis described as a countercurrent of water vapor at 240 ° C down, similar. io The water vapor flows into reactor part 2 at 3,

The known acetaldehyde determination methods strip off the acetaldehyde and flow out again at 4. But this only part of the acetaldehyde in the polyester. This reactor part contains a closable opening 5 for the analysis of the two analyte samples for the purpose of analyzing the entire acetal method (the known and the newly developed maldehyde content).

thode) a commercially available polyethylene terephthalate bottle. The granulate then advantageously passes through a green particle (HOECHST M81E) according to the known lock 6 and then enters the second reactor part 7, analyzed for acetaldehyde using an analytical method and in which the post-condensation takes place. The same will

Acetaldehyde content of 2.6 ppm found, which is therefore the same with the usual methods in countercurrent of inert gas

Company information agrees (acetaldehyde, ppm ^ 2, max. And / or air carried out. This reactor part 7 contains a

3). Then the same granulate was tested for acetaldehyde according to the new analytical method described above for inlet 8 and outlet 9 for the inert gas and / or air, and an outlet which was expediently designed as a lock was tested, and a total acetaldehyde content of 9.4 ppm 10 for the end product.

found. Post-condensed polyethylene terephthalate is thus obtained

According to the present invention, preferably with a total content of physically dissolved and high molecular weight polyethylene terephthalate with a total mixed acetaldehyde of less than 3 ppm and content of dissolved and bound acetaldehyde below with an intrinsic viscosity of normally at least

3 ppm, through two-stage treatment of solid polyethylene 0.7 ml / g, which could not be expected without

lenterephthalate which is an initial intrinsic viscosity weight increasing extension of the post-condensation time,

of at least 0.35 ml / g and expediently in graphite. In addition, all of the acetaldehyde is present in the nulate form, produced continuously. The method according to the invention becomes much more effective (almost quantitative

granulated polyethylene terephthalate can be removed in a first stage with tiv) than this according to the usual

Water vapor or a water vapor-containing inert gas method was the case. This gives polyethylene terephthalate

and / or air at 100-245 ° C and then in a thalate, which thanks to its high condensation

second stage at 200-245 ° C with inert gas and / or degrees of air and the virtually complete absence of post-condensed. 35 acetaldehyde (and other volatile substances)

The first stage is preferably extended until it is used in the food industry, in particular until the total content of physically dissolved and suitable for the production of bottles and foils.

chemically bound acetaldehyde at the end of this stage. The following examples illustrate the invention, less than 20, advantageously less than 10 ppm, which can be obtained by taking the sample at the corresponding position on the 40th .

Equipment and analysis of this sample according to the above. e (mi a ej described new analysis method can determine 50 kg per hour P ° lyathylene terephthalate granules (m-

described new analysis meta. trinsic viscosity 0.668 ml / g; Total acetaldehyde content

In the first stage, pure water vapor (76 ppm) is expediently used (FIG. 1) through inlet 1 in the upper one; but it is also possible to introduce a mixture of water reactor part 2. The reactor part is under counter steam and air and / or inert gas to be used. flow of water vapor at a temperature of 240 ° C,

As usual, the second stage takes place under inert gas and / which flows in at 3 and flows out at 4.

or air (preferably inert gas, especially nitrogen). The granulate then passes through the lock 6 and

The equipment used is suitably the customary flows into the reactor part 7, which is

Reactors, the first and second stage either in a stream of 240 ° C. The nitrogen flows out at 8 in a single reactor (two-zone reactor) or in one and at 9. The granulate is then used in the as

The reactor is drawn off from two separate parts for the outlet 10 designed for the two stages from the lock.

be performed. In general, the two-part. A post-condensed polyethylene terephthalate

Reactors better proven. Here, in the (in reaction lat granules with the in the table below)

seen direction) first part of the reactor the water vapor (opposite properties, thanks to which it is very good for the le-

optionally in a mixture with inert gas and / or air) in each case in the food industry, in particular for the production of the temperature mentioned. Bottles.

656 391

4th

table

1st stage

2nd stage

example

Steam treatment 1 (

Granulate analysis

Post-condensation

Granulate analysis on

No.

after water vapor

End of postconditions

treatment

station

Entry

Stay

Total salary

Entry

Stay

Total housing

intrinsic

temperature time of

Acetaldehyde temperature time of

Acetal viscosity

of the water

Granules

Granule dehyd ml / g

steamy tes

tes

2)

° C

Minutes ppm

° C

Minutes ppm

1

240

15

4.0

240

240

0.4

0.810

2nd

230

15

4.5

230

360

0.6

0.822

3rd

220

15

5.0

230

360

0.7

0.837

4th

190

120

4.5

230

360

0.6

0.845

5

160

120

17.5

235

300

1.92

0.896

63)

190

120

4.5

235

360

0.45

0.830

74)

240

360

4.4

0.860

11 mass of water vapor / mass of granulate = 0.5 kg / kg

2) 0.5 g sample in 100 ml mixture of phenol and 1,1,2,2-tetrachloroethane (in a mutual weight ratio of 1: 1) measured at 20 ° C

3) In this experiment, 10% by volume of air was added to the water vapor

4) Comparative example, without steam treatment.

C.

1 sheet of drawings

Claims (3)

656391 PATENT CLAIMS 1. A process for the continuous production of high molecular weight polyesters with a very low content of volatile components, by two-stage treatment of polyesters from diols and dicarboxylic acids in the solid phase, optionally crosslinked with tri- and polyfunctional alcohols or carboxylic acids, characterized in that the polyesters in a first stage with water vapor or an inert gas and / or air containing water vapor, treated at 100-245 ° C and then in a second stage at 200-245 ° C with inert gas and / or air at normal pressure or in a vacuum. 2. A process for the continuous production of high molecular weight polyethylene terephthalate according to claim 1 with a total content of physically dissolved and chemically bound acetaldehyde below 3 ppm, by two-stage treatment of polyethylene terephthalate, which has an initial intrinsic viscosity of at least 0.35 ml / g, in the solid phase , characterized in that this polyethylene terephthalate is treated in a first stage with water vapor or water vapor containing inert gas and / or air at 100-245 ° C and then in a second stage at 200-245 ° C with an inert gas and / or air . 3. A process for the production of high molecular weight polyethylene terephthalate according to claim 2, characterized in that in the first stage a steam treatment is carried out until the total acetaldehyde content in the polyethylene terephthalate at the end of this stage is less than 20, preferably less than 10 ppm . High molecular polyester, especially high molecular, i.e. Polyethylene terephthalate post-condensed in the solid phase is becoming increasingly important these days. So used in the production of bottles or containers in the food industry, in the solid phase post-condensed polyethylene terephthalate in the form of granules. The post-condensation of polyethylene terephthalate in the solid phase is known per se (US Pat. No. 3,733,309). The main problem in the post-condensation of polyethylene terephthalate, however, is the removal of the volatile substances, in particular the acetaldehyde, which is both a chemically bound vinyl ester and is physically dissolved. A post-condensed polyester containing such volatile and usually also odor-intensive compounds, such as acetaldehyde in particular, is for use in the food industry, e.g. not suitable as bottles. Various methods have been proposed to remove these volatile components from the polyester. For example, US Pat. No. 4,263,425 describes fumigation of polyethylene terephthalate at 200-220 ° C. with inert gases, and the polyethylene terephthalate granulate must contain less than 25 ppm transesterification catalyst or 20 ppm phosphoric acid. U.S. Patent 4,223,128 describes the treatment of solid polyethylene terephthalate with Luftbeica. 180-220 ° C suggested. However, the methods according to these two US patents provide post-condensed polyethylene terephthalate, the total content of physically dissolved and chemically bound acetaldehyde is still too high for today's requirements. It has now surprisingly become a continuous one Process for the production of high molecular weight polyester found by means of which the volatile constituents, in particular the total content of physically dissolved and chemically bound acetaldehyde in these polyesters, 5 can be considerably reduced compared to the previous processes.