FR2525614A1 - PROCESS FOR THE PREPARATION OF HIGH MOLECULAR WEIGHT POLYESTER - Google Patents

Abstract

HIGHLY CONDENSED POLYETHYLENETEREPHTHALATE IS PREPARED BY A CONTINUOUS TWO-STAGE TREATMENT OF POLYETHYLENETEREPHTHALATE, MOST OFTEN IN AGGREGATE FORM (INTRINSIC VISCOSITY APPROXIMATELY 0.35). IN THE FIRST STAGE, WATER VAPOR IS INTRODUCED IN 3 IN PART 2 OF THE APPROPRIATE REACTOR AND IN THE SECOND STAGE THE SECONDARY CONDENSATION IS CARRIED OUT BY CONVENTIONAL METHODS. IN PART 7 OF THIS REACTOR, THUS SURPRISINGLY ELIMINATION OF UNWANTED ACETALDEHYDE IS OBTAINED IN 10 A HIGHLY CONDENSED POLYETHYLENETEREPHTHALATE WITH A CONSIDERABLY DECREASED ACETALDEHYDE CONTENT. USE OF THIS POLYETHYLENETEREPHTHALATE IN THE FOOD INDUSTRY IN PARTICULAR FOR MANUFACTURING BOTTLES.

Description

-1 - Process for the preparation of high molecular weight polyester

  The present invention relates to a method for

  continuous preparation of polyester, in particular

  lycondensates of (cyclo) aliphatic diol and dicarboxylic acid

  preferably aromatic boxyl, in particular poly-

  ethylene terephthalate. Polyesters with a high molecular weight, especially

  high molecular weight polyethylene terephthalate,

  that has undergone secondary condensation in the

  lide, are becoming more and more important today.

  Thus, for the preparation of bottles or containers

  in the food industry, polyethylene is used

  terephthalate which has undergone secondary condensation

  solid phase, in the form of granules.

  sign this polyethylene terephthalate by the expression "poly-

  ethylene terephthalate condensed a second time.

  Secondary condensation of polyethylene terephthalate

  solid phase is known (U.S. Patent 3,733,309).

  The main problem for this secondary condensation of polyethylene terephthalate is, however, the elimination

  highly volatile materials, in particular acetal

  hyde which is also present in the form of vinyl ester

  than chemically bound that physically dissolved.

  A condensed polyester a second time, containing

  volatile compounds of this kind and most often

  highly odorous, such as acetaldehyde,

  is unsuitable for use in the food industry.

  re, for example in the form of bottles.

  To remove, from polyester, these constituents

  For example, U.S. Patent No. 4,263,425 discloses a method of charging the polyethylene terephthalate to gas at 200 ° C. with inert gases, and the polyethylene terephthalate granules must then contain less than 25 ppm of catalyst.

  transesterification or 20 ppm phosphoric acid.

  2 - U.S. Patent No. 4,223,128 proposes the treatment of solid polyethylene terephthalate with air at about

2200 C.

  The processes according to these two U S patents however give condensed polyethyleneterephthalate one or two

  twelfth time, including the total content of acetaldehyde

  dissolved and chemically bound is still

  too much for what is being asked now.

  The authors of the present invention then

  surprisingly covered, a process for the preparation of high molecular weight polyester,

  by which the content of volatile constituents, in parti-

  the overall content of acetaldehyde physically

  under and chemically bound in this polyester, can be

  significantly decreased compared to the method of the prior art. The present invention therefore relates to a method for

  the continuous preparation of high molecular weight polyester

  in particular of polycondensates of diol (cyclo)

  aliphatic and preferably dicarboxylic acid

  with a content of volatile constituents, in particular

  particular with an overall acetaldehyde content

  dissolved and chemically bound, very low, by

  treatment in two stages of the polyester, in solid phase.

  This process is characterized in that the polyester, in a first stage, is treated with steam or with an inert gas or air containing water vapor at 100-2450 C, and then in a second stage, it is condensed a second time at normal pressure or under vacuum, at 200-2450 C, with an inert gas, for example from

nitrogen and / or air.

  The polyesters in question may consist of the following diols and dicarboxylic acids:

  Diols: alkylene glycols, in particular a, -alkyl

  glycols such as ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol and cyclohexane-1,4-dimethylol;

  or cycloalkanediols such as cyclohexane-1,4-diol.

  Dicarboxylic acids: terephthalic acids, iso

  phthalic, naphthalenedicarboxylic, as well as adipic acid, sebacic acid, etc. Of course, mixtures of diols and dicarboxylic acids and a small amount of alcohols

  and polyfunctional or carboxylic acids tri and po-

  lyfunctional agents for crosslinking may also be

used.

  Polyester of this kind, which is by far the most important, is polyethylene terephthalate and it will not

  exclusively question of it in what follows.

  The elimination of acetaldehyde physically

  sub is in a known manner determined by the phenomenon of

  diffusion of acetaldehyde out of the polyethylene granulate

  lènetéréphtalate; on the contrary and as is known, to remove chemically bound acetaldehyde, the vinyl ester groups in the polyethylene terephthalate must first be converted into free acetaldehyde, which was not achieved completely in the methods known hitherto. the absence of water vapor,

  the vinyl ester groups can not react fully

  ment. Surprisingly, the inventors have discovered that in the presence of water vapor, according to the

  according to the invention, the physical acetaldehyde

  dissolved and chemically bound could be eliminated almost quantitatively from the polyester granulate without

  have an adverse influence on it.

  To determine the overall content of the acetal

  hyde physically dissolved and chemically bound, we put

  to the point a new method of analysis.

  During the new method of determination of the overall content of physically dissolved and chemically bound acetaldehyde, the polyester sample is ground (20-50 mesh) in a glass vial with ten times the amount of free water. of oxygen added thereto, and this vial is closed with a tfion-coated rubber septum. The vial is then heated for 17 hours at C. After cooling the vial, a sample of the aqueous solution is taken and analyzed. to obtain the acetaldehyde content by gas chromatography using the headspace technique or by

the colorimetric method.

  The new analytical method allows a determination of physically dissolved and chemically bound acetaldehyde

in the polyester.

  The methods of analysis known until now for dosing

  acetaldehyde in the polyester, are described, for example

  in the published German patent application DE-OS 28 34 161 and in the U.S. Patent No. 4,223,128

  DE-OS 28 34 162, a ground polyester sample is

  closed in a glass balloon fitted with a rubber septum

  The air trapped in the flask is replaced by nitrogen. Next, the flask is heated for 90 minutes at 150 ° C, and a sample of the acetaldehyde / nitrogen mixture is analyzed by gas chromatography.

on acetaldehyde.

  The method described in the German patent application

  DE-OS 28 34 162, is similar to that of the analysis of

  acetaldehyde described in U.S. Patent No. 4,233,128.

  However, methods for the determination of acetaldehyde

  of known, only seize a part of the acetaldehyde in the polyester So as part of a comparison

  of the two methods of analysis, (the known method and the

  new thode developed here) acetaldehyde is

  in a granulate (HOECHSTM 81 E) from a bottle in

  commercial ethylene terephthalate by the methods of

  lysis, and an acetaldehyde content of 2.6 ppm was found, which is consistent with the

  the firm (acetaldehyde <2 ppm, max 3).

  Then the same granulate is determined according to the new - previously described method of analysis of acetaldehyde,

  and there is an overall acetaldehyde content of 9.4 ppm.

  Therefore, the present invention preferably relates to a process for the continuous preparation of high molecular weight polyethylene terephthalate having

  an overall content of dissolved and bound acetaldehyde

  less than 3 ppm, by treatment in two stages of this poly-

  ethyleneterephthalate, in the solid phase, which initially

  has an intrinsic viscosity of at least 0.35, and

  advantageously in the form of granulate.

  is characterized by the fact that the polyethylenetere-

  phthalate is treated, in a first stage, with water vapor or with an inert gas and / or air containing water vapor at 100-2450 C, then, in a second stage,

  is condensed a second time at 200-2450 C with an inert gas.

te and / or air.

  The first stage is then continued preferably

  until the total content of physical acetaldehyde

  dissolved and chemically bound is less than 20, preferably less than 10, ie less than 5 ppm,

  at the end of this stage, what can be determined by

  samples at the appropriate places on the

  and analyzing these samples according to the new

  of analysis previously described.

  In the first stage, it is advantageous to use

  be pure water vapor; but we can also use

  mix a mixture of water vapor and air and / or inert gas. The second stage is carried out as usual under an atmosphere of inert gas and / or air (preferably a

  inert gas, in particular nitrogen).

  As apparatus, use is advantageously made of conventional reactors, the first and second stages being carried out either in a single reactor (reactor with

  two zones) or in a reactor consisting of two

  for the two stages In general, the reactions

  In this case, in the first part of the reactor (see direction of the reaction), the steam is introduced <optionally mixed with the inert gas and / or with air). each time at the temperature mentioned. In a preferred embodiment, the process according to the invention is carried out as follows

  (see single figure): granulate from polyethylene

  conventional terephthalate in the textile industry (whose overall acetaldehyde content is about 100 ppm) is introduced through the filling opening 1 in the

  part 2 of the reactor in which the first

  of, then down by gravity downwards in the direction of

  milk steam stream at 2400 C Water vapor

  arrives by 3 in part 2 of the reactor, extracts the acne

  talehyde, and spring by 4 This part of the reactor

  has a slidable opening 5 for taking samples

  for the purpose of analysis of the overall acetal-

  dehyde. Then, the granulate advantageously passes through an airlock 6 and then enters the second part 7 of the reactor where the secondary condensation takes place. This is carried out according to the usual methods in the countercurrent of inert gas and / or air. of the reactor comprises an inlet 8 and an outlet 9 for the inert gas and / or air and an outlet 10 advantageously designed in

form of lock for the final product.

  According to the process according to the present invention,

  a condensed polyethylene terephthalate is obtained

  times, having an overall content of phthalic acetaldehyde

  sily and chemically bound lower than 3 ppm and having an intrinsic viscosity of at least 0.7, which was quite unexpected. Surprisingly,

  obtained by this new process, a polyethylene terephthalate

  the desired and desired intrinsic viscosity, so that, surprisingly, it is not necessary to prolong the duration in a significant manner.

  Secondary condensation is also achieved

  all the acetaldehyde with much more efficiency (almost quantitatively), by the process according to the present invention, than was possible with the

  methods so far. Thus, we obtain a poly-

  ethylene terephthalate according to the present invention, which

  its properties, can be used in the food industry

  in particular is suitable for the manufacture of bottles and sheets, thanks to its high degree of

  condensation mentioned above and the practical absence of

  acetaldehyde <and other volatile substances

tiles).

  The present invention is illustrated by the examples

  descriptive and non-limiting plots below.

Example 1 to 7 (with table)

  Input 1 is introduced into the upper part of

  2 of the reactor 50 kg / h of polyethylenate granulate

  phthalate (intrinsic viscosity 0.668, total acetaldehyde content 76 ppm) (single figure) This part of the reactor is under a countercurrent of water vapor having a temperature of 2400 C, vapor which enters by 3 and

go out by 4.

  The granulate then passes through the airlock 6 and flows

  in part 7 of the reactor which is 240 ° C under a

  Nitrogen flow Nitrogen enters here by 8 and leaves by

  Then, the aggregate is extracted through the output 10

in the form of airlock.

  A condensed polyethylene terephthalate granulate is obtained a second time, with the properties indicated in the table below, by means of which this granulate

  very suitable for the food industry, especially

  special for the manufacture of bottles.

BOARD

  1st stage 2nd stage Steam treatment 1) Secondary condensation Analytical results Tpa Rsuttsanl of the aggregate at the end Exem Tempera-Duration of the analytical results of the condensation of the grains of the granulars

No the steam of the lat after

  of water to steam Steam Temperature Glo Viscosity

  the entrance water raid at the entrance stay of the bale intrins-

  Aggregate content of acetaldehyde granulate acetaldehyde hyde C minutes ppm C Minutes ppm 2)

1 240 15 4.0 240 240 0.4 0.810

2 230 15 4.5 230 360 0.6 0.822

3 220 15 5.0 230 360 0.7 0.837

4 190 120 4.5 230 360 0.6 0.845

160 120 17.5 235 300 1.92 0.896

6) 190 120 4.5 235 360 0.45 0.830

_

7 4) 240 360 4.4 0.860

  1) Mass of water vapor / Mass of granulate = 0.5 kg / kg 2) Sample of 0.5 g in 100 ml of a mixture of phenol and 1,1,2,2-tetrachloroethane (in one respective weight ratio of 1: 1), measured at 20 C 3) For this test 10% by volume of air was added to the water vapor

  4) Comparative example, without treatment with water vapor.

o Co i t '> Lnl -9-

Claims (3)

  1. Process for the continuous preparation of   high molecular weight lyester, in particular poly-   diol (cyclo) aliphatic and dicarboxylic acid condensates   preferably a very aromatic xyl, with a very low content of very volatile constituents, by treatment in two stages of the solid phase polyester, characterized in that the polyester is treated in a first stage with water vapor or inert gases or air containing water vapor at 100-245 C and then condensed a second time, in a second stage, at 200-245 C with an inert gas and / or air under normal or vacuum pressure.   2 Process for the continuous preparation of   high molecular weight lyethyleneterephthalate having a   overall content of physically dissolved acetaldehyde and   bound less than 3 ppm, by two-fold treatment   this polyethylene terephthalate which has a viscosity   initial intrinsic stability of at least 0.35, in the solid phase, characterized in that this polyethylene terephthalate is treated in a first stage with water vapor or an inert gas or air containing steam of water to   -245 C then is condensed a second time, in a second   Stage X, at 200-245 C with an inert gas and / or air.   3. Method according to claim 2 e characterized in that the treatment with water vapor (first stage) is carried out until the overall acetaldehyde content in the polyethylene terephthalate at the end of   this stage is less than 20, preferably less than at 10 ppm.