DE2723549C2 - Process for the production of thermoplastic polyesters and polyamides by continuous polycondensation in the solid phase - Google Patents

Description

The invention relates to a process for the production of thermoplastic polyesters, in particular of Polyethylene terephthalate, and thermoplastic polyamides, especially of polyamide 6, by continuous polycondensation in the solid phase in the moving bed in a shaft reactor.

The in a polycondensation of polyesters and The heat input necessary for polyamides in the solid phase causes the granules used to stick together, which leads to a continuous reaction process is disturbed. To avoid such sticking, it is necessary to keep the granules in constant motion keep. Those already known procedures for the polycondensation of polymer particles in solid Phase in the moving bed do not meet this requirement.

For example, DD-PS 9346 describes a process according to which linear polyester, especially polyethylene terephthalate. in the solid phase at temperatures below the melting point be treated. For this purpose, the ground polyester is conveyed into a heated system and thereby into a high polymer form. According to the patent, this process should also without any difficulties can be operated continuously; an instruction, but in what way then the granular material heated, continuously conveyed through the system and in what way then caking of the granular Good things should be avoided, is not to be found in this patent specification.

From DE-OS 17 70 410 a method is known in which a solid polycondensation, called there method for increasing the molecular weight of the

to polymer granulate, is carried out in a shaft reactor. To do this, the continuous pouring of the polymer granulate with a stream of hot inert gas blown against it, with the Aim to bring the bulk material to the reaction temperature heat and at the same time remove the gaseous reaction products from the reaction chamber. To that To obtain the desired high molecular weight, Du- ^ hlaufzeiten are in this laid-open specification named up to 20 hours

From practice, however, it is known that under such working conditions, the polymer granules are strongly bonded together with shrinkage of the Bulking of the polymer granules occur, whereby on the one hand the uniform distribution of the inert gas flow mes over the pipe cross-section and on the other hand the "Plug flow" of the bed of polymer particles is disrupted. These undesirable phenomena are evidently also when carrying out the method according to the above-mentioned publication occurred; because on page 11th last paragraph, the The aforementioned patent application is stated: “Finally, it turned out that the The risk of sticking during post-condensation can be further reduced if the granulate is in front of it Leaving the 2nd stage quickly cools down to temperatures below 150 ° C by creating a Such a cooling zone evidently achieves a certain shock effect on the bulk layer so that possibly still adhering particles due to the to jump apart due to a sudden drop in temperature. "

Such a procedure only helps then.

if the bulk layer before cooling to 150 ° C actually hiked uniformly

In a number of other known practices, the

Adhesion of the bulk layer of the polymer granules avoided by being on the surface of the Polyester grains are applied before the solid polycondensation substances that cause the sticking together of the Prevent particles during heat treatment

so-called "antisticking agents" are supposed to. In the Literature for this purpose all possible inorganic substances in powder form Form, such as kaolin, clay. Silica gel. Metal oxides. Soot. various salts. Glass and also organi see substances proposed in solid and liquid form, but these substances all have the Disadvantage that they can not be completely removed after the solid polycondensation because they - if it are solid particles - in ζ Β. softened

μ polyester are pressed in. This will make the Properties of the end products manufactured, e.g. B. just the polyesters and polyamides, in particular their transparency, deteriorated.

In DE-OS 25 51982 a method

described, in which finely ground table salt is used as an anti-sticking substance. This substance has the advantage over other, water-insoluble substances that it is after

Solid polycondensation almost quantitatively by washing off the polyester grains with water again can be removed. Small amounts of table salt also limit the use of the sun manufactured polyester as packaging material for food due to the physiological harmlessness of table salt. A disadvantage of the However, the method described consists in that the polyester must be dried again before further processing.

Proposals are also known from the literature that Bonding occurring during the solid polycondensation of polymer particles on mechanical Eliminate or prevent ways. Slowly rotating, horizontal screw devices, Rotary tubes and tumble dryers recommended. However, such apparatus are very expensive and have an effect Unsolicited stirring and mixing processes that the Adversely affect the reaction time and thus result in uneven quality of the end products to have. In addition, this treatment produces dust-like abrasion with vigorous agitation, which also affects the homogeneity of the end product influences and can cause so-called "fish eyes".

It is also known that the necessary heat supply in the solid phase polycondensation in the Polymer particles cause the process of partial melting. This melting and the one with it connected great mobility of the existing macromolecules is probably on the one hand one Prerequisite for the rapid process of the polycondensation, the amorphous, molten ones in Jen Areas of the polymer particles instead. 'et, on the other hand As a result of this partial melting of the polymer particles, they also become alive Polymer particles in static layers. This act of sticking together the polymer particles is likely to explain that it is between point or line-shaped contacting polymer particles as a result of a dynamic equilibrium between the amorphous and the crystalline phase over time spherulites from one polymer particle to the other polymer particles form, whereby the individual polymer particles grow together. The polymer particles can be prevented from sticking together by moving the polymer particles against one another. With such a movement The aim is to identify the points of contact or lines of the To displace polymer particles at certain time intervals around the connecting the polymer particles To interrupt the crystal growth process, which then restores the polymer particles in a new position must begin. The ongoing disruption of this crystal growth process causes sticking of the polymer particles are interconnected.

With certain additives that are supposed to influence the properties of the end products, such as thermal stabilizers, additives to improve the colorability with Surface dyes, light stabilizers and other co-polymers tend to be in such thermoplastics Particularly suitable for gluing and must be used in the solid polycondensation even at relatively low levels Temperatures are constantly being moved slightly.

The invention is based on the object in a process for the production of polyesters and Polyamides carry out the polycondensation continuously in the solid phase in the moving bed without sticking.

The problem posed is achieved based on the generic type described at the outset, according to the invention in that the shaft reactor is inside in horizontal direction is equipped with wire mesh, which is at right angles to the reactor wall are arranged, and that the polymer granulate particles through the shaft reactor in the vertical direction of migrate up and down, where they have a migration speed of 0.3-1.5 m / h, with a Minimum dwell time of 10 minutes and one maximum Residence time of 3 h between two internals arranged in the horizontal direction.

The maximum distance between the wire mesh built into the shaft reactor in the horizontal direction is determined by the adhesion of the polymer particles, the reaction temperature and the migration speed of the polymer particles are determined. In the shaft reactor the wire mesh in the horizontal direction at a distance "on 100-1000 mm. especially at a distance of 200 - 500 mm, arranged

The mesh size in the built-in wire mesh depends on the size of the polymer granules Mesh sizes of 4-6 times the length of the polymer granules. In This area is then namely guaranteed that those furthest away from the wire netting and mi *, the wire netting Granules that do not come into direct contact can still be moved sufficiently well. Accordingly, the wire mesh in the shaft reactor has a mesh size of 10-30 mm. especially from 10-20 mm. on. From references (1) Holleman-Wilberg.

Chemistry textbook. Part 1, Inorganic Chemistry, 26th and 27th editions. Publisher Walter de Gruyter & Co. Berlin (1951), pages 234-235, and (2) Winnacker Küchler. Chemical Technology, Volume 2, Inorganic Technology II, Carl Hanser Verlag, Munich (1959), page 227.

is the use of reactors with PUtin nets for a completely different purpose, namely for the catalysis of the chemical conversion of a gas mixture, is known. Here the platinum nets are also in a horizontal direction and at right angles to the reactor wall

* 5 arranged, but in contrast to present invention, however, be very fine-meshed and made of the specified material. the Mesh sizes in (1) and (2) are approximately 0.12 and 0.25 mm, respectively.

The wire mesh should also be made in this way be that as little as possible is covered by the cross-section of the reactor. This means that the wire from which the wire mesh is made up should not be thicker than for reasons of strength Wire mesh is essential. In practice, this results in diameter for the Wire from OJ - 23 mm, preferably 03 - 1.0 mm.

In another embodiment, in the interior of the shaft reactor are run in the vertical direction Fenden wires attached star-shaped structures made of wire, the star-shaped structures in one Distance of 100-1000mm, especially in one At a distance of 200-500 mm, the star-shaped structures have a diameter of 20-100 mm and made of a wire, with a Diameters of 0.5-2.5 mm, in particular with a diameter of 1.0-1.5 mm, are formed. The described fixtures in the shaft breaker

can instead of · - ■ '.: round wires made of steel wires be constructed with a triangular profile. Likewise, the internals described can be used instead of round wires can be made from wires with a polygonal profile.

The wire mesh built into the shaft reactor in the horizontal direction can .. after be divided into a checkerboard, d. h that the individual wire mesh layer alternating fields with lesser and with a larger mesh width.

These individual fields are smaller and larger meshes with two consecutive ones Wire mesh layers also alternate, d. H. seen in the horizontal direction is from wire mesh layer to wire mesh layer the mesh size is smaller and larger

In these wire mesh fabrics, the mesh size is 10-30 mm in the smallest case and in the largest trap 20-50 mm. The thickness of the alternating wire mesh used for this Wires should be 0.5-2.5 mm, preferably 0.5-1.5 mm

In addition to the tendency of the polymer particles to stick together discussed at the beginning of the text of the description, this sticking tendency is increased under the action of pressure caused by a high bulk layer of the polymer granules on the lower layers. This then results in stable bonds that can fill the entire reaction space. Such structures then block the conical part of the shaft reactor and thus interrupt the continuous course of the reaction. It has been found in practice that, depending on the chemical composition of the polymer granules used, the reaction temperature, the size of the granules, the migration speed and the pressure ratio in the moving bed, a certain time elapses before irreversible adhesions occur. This time is, for example, polyethylene terephthalate in a 3-meter tube reactor of 500 mm in diameter at 240 ⁰ C. at a rate of 30 kg / h and a cylindrical shape of the pellets, 3 mm in length and 2 mm in diameter, about 25 min.

Under different reaction conditions, the following critical sticking points became apparent in the case of polyesters and polyamides determined:

Are the polyester granules in contact with each other in a time that is shorter than this critical 25 minutes, to the extent that the original, mostly punctiform contacts are canceled, then the process of the overgrowth of the Spherolites interrupted from one polymer particle to another polymer particle, urri thus the The formation of irreversible adhesions is prevented. The spherulites are then, however, in de; news.

ίο Contact position again in the critical time with the neighboring polymer particles will grow together if this process is not carried out by renewed agitation of the polymer particles are mutually disrupted.

In practice it has also proven to be advantageous to reduce the static pressure exerted on the upper bulk layer of the Polymer particles in the shaft reactor exerts on the lower layers of the polymer particles, so that the Contact of the polymer particles with one another becomes less intense. In this way the slope of the Particles also broken down to grow together

The advantages achieved by the process according to the invention are in particular that the production of thermoplastic polyesters and polyamides, in particular of polyethylene terephthalate and polyamide 6, made possible by continuous polycondensation in the solid phase in the moving bed of a shaft reactor good quality non-stick and tack-free polymer particles can be obtained.

example 1

material Reaction
temperature
in ⁰ C Critical
Bonding time
in minutes Pol> ethylene terephthalate 240 25th Polyethylene terephthalate 235 32 Polyethylene terephthalate
with 5% by weight diethylene
glycol 225 25th Polyethylene terephthalate
with 5% by weight isophthalic
acid 220 27 Polycaprolactam 185 40 Polycaprolactam.
heat stabilized 175 34

A cylindrical shaft reactor 3000 mm long and 300 mm in diameter, which at its lower The end is provided with a discharge cone, 30 kg of cylindrical polyethylene terephthalate granules per hour 3 mm in length and 2 mm in diameter fed continuously from above

The density of the precrystallized granules was 1383; the bulk weight of the granules in agitation Condition 0.76 kg / 1; the intrinsic viscosity was 0.53.

The shaft reactor was inside at intervals of 100 mm with a wire mesh of 16 mm mesh size with a wire thickness of 0.5 mm

The precrystallized granules migrated in the shaft reactor at a speed of 0.566 m / h from top to bottom, so that the granules passed a wire mesh every 10.5 minutes. After a Total residence time of 53 hours, the chips left the cylindrical part of the reactor and entered the discharge cone.

At the entrance to the shaft reactor there was a temperature of 220 ° C. At the bottom of the reactor nitrogen at a temperature of 2'tTC in an amount of 2kg per kg of polyethylene terephthalate blown against the bulk material, creating a temperature profile from the bottom to the top from 238-220 ° C.

A polycondensation of precrystallized elements took place in the reactor over a period of 100 hours Polyester granules carried out on a permanent basis; there were no operational disruptions on.

Polyäthylenterepiithalat-Granaüen obtained had an intrinsic viscosity of 9.8. No sticking was observed in the granules produced. The granulate could be processed into foils that did not show any “fish eyes”.

Comparative example

A shaft breaker, as described in example 1, were IO kg of polyethylene terephthalate granules per hour with the same properties as described in Example I ">, supplied.

The bulk of the granules migrated at a speed of 0.189 m / h in the reactor up down; the total residence time in the cylindrical part of the shaft reactor was about 16 in Hours.

After about 10 hours of operation of the reactor no more granules are discharged from the discharge cone, because both those in the discharge cone and the lower half of the cylindrical part of the Schachtrc- ι ■> actuator located cips were glued.

Comparative example 2

A shaft reactor as described in Example 1, but without wire mesh inserts as in the example: r < 1, was charged with 30 kg / h of polyethylene terephthalate, the shaft reactor initially with high polymer granules operated and brought into thermal equilibrium.

4 hours after low molecular weight polyethylene- -Ί terephthalate granules had been added to the reactor, it was found that no more More granules flow into the reactor. After the reactor had cooled down. was - starting on Discharge cone up to the inlet nozzle of the reactor in - found a compact, firmly glued bulk. The shaft reactor had to be mechanical be emptied.

Example 2

A cylindrical shaft reactor 12 m long and 1 m in diameter weighed 965.5 kg per hour Granules of a polyester whose dicarboxylic acid component consists of 95% terephthalic acid and 5% isophthalic acid exists, entered. The granules had a - »o cylindrical in shape and were 2.5 mm long and 1 mm thick. The density of the precrystallized granules was 1.32; the bulk weight in the moved state 0.82; the intrinsic viscosity was determined to be 0.41.

The shaft reactor was at intervals of 0.35 m with * 5 Wire mesh inserts with a mesh size of 10 mm and a wire thickness of 1 mm.

The granules migrated through the shaft reactor at a speed of 1.5 m / h so that they followed a layer of woven fabric w for about 15 minutes each time happened. The maximum residence time for the granules in this type of polyester was 27 minutes.

At the upper end of the shaft reactor a temperature of 215 ° C. prevailed at the lower end such of 220 ⁰ C. Due to the bulk layer of the granules has been kg from bottom to top through the reactor a hot nitrogen stream in an amount of 13/1 Kg polyester blown .

In the shaft reactor, the polycondensation reaction with the listed poly cster granules carried out without any noticeable agglutination or bonding.

The intrinsic viscosity of the obtained polyester was 1.02; Dust proportions were not found. Flawless films were blown from this polyester had no "fish eyes".

Example J

In a shaft reactor according to Example 2 was a corresponding solid polycondensation pro / .eß under Keeping all other conditions constant, as indicated in Example 2, operated so that the salt through from initially 965.5 kg / h per 4 hours gradually each 30 kg was reduced. At a throughput of 845 kg / h, granules stuck together in the discharge observed.

This specified throughput corresponds to one Dwell time of the polyester granules / wipe two wire cloths of approximately 27 minutes. For this The result of the experiment can be used to determine the maximum possible dwell time between two mesh fabric layers.

Example 4

A shaft reactor with a cylindrical length of 3000 mm and a diameter of 300 mm, which at its lower end has a discharge cone of 30 ° inclination and an annular distribution pipe for distributing the nitrogen after 1000 mm, measured from top to bottom, after 3000 mm. was provided at the lower end of the cylindrical part and after 300 mm in the discharge cone, and contained a wire mesh of 15 mm mesh size and 1 mm wire thickness at a distance of 300 mm, was per hour with 20 kg of cylindrical polyamide 6 pellets of 2 mm diameter and 2 mm length and a temperature of 100 ⁰ C charged.

The density of the pre-crystallized pellets was 1.14, the bulk density in the agitated state was 0.8 kg / l. the Pellets had a relative viscosity on entry into the moving bed reactor of 2.35 and a water content of 5% by weight.

Through the upper gas feed 40 Nm ^J h of nitrogen I3O ° C were introduced biases on the lower blowing 25 NMVH nitrogen of 185 ° C and in the discharge cone 40NmVh nitrogen of 2O ⁰ C. The nitrogen contained small amounts of water (less than 0.2 wt%) and less than 5 ppm oxygen.

The pellets left the cone of the Wanderbeu reactor with a temperature of about 10O ⁰ C and showed a relative viscosity of 3.22.

The product obtained in this way was spun without any problems into Endios threads, which are of good tire cord quality revealed.

Claims (4)

Patent claims: 1. Process for the production of thermoplastic polyesters, in particular polyethylene terephthalate, and thermoplastic polyamides, in particular of polyamide 6, through continuous polycondensation in the solid phase in the moving bed in a shaft reactor, characterized in that the shaft reactor inside in horizontal direction is equipped with wire mesh that is at right angles to the Reactor wall are arranged, and that the polymer granules. through the shaft reactor in migrate vertically from top to bottom, with a migration speed of 0.3-1.5 m / h, with a minimum dwell time of 10 min and a maximum residence time of 3 h between two internals arranged in the horizontal direction. 2. The method according to claim 1, characterized in that in the Schachircaktor the Wire mesh in the horizontal direction at a distance of 100-1000 mm, especially in a distance of 200 - 500 mm, are arranged. 3. The method according to claims J and 2, characterized in that in the shaft reactor the wire mesh has a mesh size of 10-30 mm, in particular a mesh size of If ¹ . - 20 mm. 4. The method according to claim 1, characterized in that in the interior of the shaft reactor in vertical wires are attached to star-shaped structures made of wire, the star-shaped structures at a distance of 100-1000 mm. especially at a distance of 200-500 mm. are arranged, the star-shaped structures have a diameter of 20-100 mm have and made of a wire with a diameter of 03-23 mm, in particular with 1.0-13 mm in diameter.