DE102011082769A1 - Method and device for degassing a PET plastic melt in an extrusion plant - Google Patents

Abstract

Method and device for degassing a PET plastic melt through which a gas mixture (1) by means of a vacuum device (2) sucked from the PET plastic melt and a gas inlet (3) of a gas cleaning device (4) is supplied. The gas mixture (1) is brought into contact with a hygroscopic washing liquid (5) within the gas cleaning device (4). By means of the vacuum device (2), which is connected to a gas outlet (6) of the gas purification device (4), a negative pressure of less than 50 mbar, preferably in the range 1 mbar-15 mbar absolute generated at the gas inlet (3). The hygroscopic scrubbing liquid (5) is brought into contact with the gas mixture (1) within the gas scrubber (4) in such a way that the volume flow of the gas mixture (1) at the gas outlet (6) is at least 60%, preferably 75%, due to absorption of the water components. -90% compared to the volume flow of the gas mixture (1) is reduced at the gas inlet (3).

Description

Technical area

The present invention relates to a method and an apparatus for degassing a PET plastic melt in an extrusion plant.

State of the art

In the manufacture of articles of PET (= polyethylene terephthalate), e.g. a PET film, extruders are used to melt a plastic granulate and feed it to an extrusion die. The temperatures of the melt are in the range between 200 ° C and 300 ° C.

In order to achieve the best possible quality of the products that are made from the plastic melt, this may contain only low levels of moisture. In addition, volatile decomposition products of the plastic, e.g. Oligomeric or undesirable additive components are kept away from the final product. It is therefore desirable to extract water vapor, hydrocarbons and other sublimation-capable components from the melt in the extruder area.

For this purpose, systems are used in the prior art, which consist essentially of a melt trap, a gas cleaning device and a vacuum device.

In prior art gas purification equipment, e.g. condensable impurities e.g. Oligomers condensed from a mixture of water vapor, hydrocarbons and air. Such devices are also used to absorb gaseous contaminants from such a gas mixture in a washing liquid or to filter solid components of such aspirated gas mixtures and / or dissolve in a washing liquid.

Such a gas cleaning system with washing liquid, but without a vacuum device, discloses, for example, the US 20080207868 A1 (see there 7 ). The scrubbing liquid used is ethylene glycol. In this scrubber, organic material and also certain amounts of water are condensed out and removed by the glycol. To dry the gas, this is additionally fed to the scrubber a drying device.

A gas purifier with integrated filter and condenser shows the DE 10 2008 031 834 A1 , This system has the disadvantage that the filter must be soiled quickly and then cleaned or replaced. The degassing process must be interrupted.

In the WO 2009/065384 A2 It is proposed to cool the gas mixture in the degassing to temperatures below 10 ° C. As a result, components sublimated in the gas mixture resorb on the surfaces of the cooling elements to solid particles, which entails cleaning processes in which there is a risk that the vacuum will be interrupted.

In the degassing of PET plastic melts, however, is generally worked with suppression, which are in the range of less than 30 mbar absolute.

The negative pressure is required so that the undesirable components can be removed with high efficiency from the PET melt. However, the negative pressure in the gas purification system resulting from the suction has the consequence that water vapor condenses out only at very low temperatures, namely in the range below normal room temperatures. Therefore, the oligomer-purified gas mixture leaving a prior art gas purification plant still contains a relatively high level of water vapor. This amount of steam and the possibly contained therein impurities must be processed smoothly by the connected to the gas cleaning vacuum device, which entails considerable technical effort.

Typical water contents of PET plastic granulate, which is melted in an extruder, are in the range 500 ppmW-4000 ppmW; in practice even higher values occur. This water content must be reduced by the degassing of the melt in order to achieve a perfect quality of the end products made of PET.

The object of the present invention is to extract a high proportion of water from a PET plastic melt with the aid of a gas cleaning device which is operated under reduced pressure.

Description of the invention

The object is achieved by a method and a device according to the independent claims.

Here, a laden with moisture gas mixture of water vapor, air and hydrocarbons or oligomers is sucked from a PET plastic melt and placed in a gas cleaning device with a hygroscopic washing liquid in contact. In this case, components of the PET plastic melt (for example water and oligomer proportions) which are contained in the gas mixture are absorbed or absorbed by the hygroscopic washing liquid and removed via a liquid outlet. The purified gas mixture is passed from the gas purifier to a vacuum device. The invention is characterized in that at a gas inlet of the gas cleaning device, a negative pressure of less than 50 mbar, preferably 1-15 mbar absolute is present and that the hygroscopic washing liquid is brought into contact with the gas flow in such a way that by absorption of the water components of the flow of the gas mixture within the gas cleaning device is reduced by at least 60%.

This process is preferably carried out according to the operating principle of an absorption column in which the washing liquid drops dropwise in countercurrent to an ascending gas mixture down or is sprayed through spray nozzles into the gas mixture.

The remaining reduced and purified volume flow of the gas mixture is passed on via a gas outlet from the gas cleaning device to the vacuum device on. This can work with smaller sized vacuum pumps than usual in the art. As a rule, no special precautions need to be taken to protect the vacuum pumps from deposits, e.g. Oligomer condensate, protect.

For a person skilled in the art, it is obvious to pass the gas stream sucked from the PET melt before entering the gas purification device also via a so-called melt trap, in which possibly entrained liquid melt constituent is collected.

It is also obvious to control the negative pressure at the gas inlet in such a way that any existing pressure losses between a degassing opening of the plastic melt-filled extruder and the gas inlet of the gas purification device are compensated. For the expert it comes in the degassing of plastic melts on it to produce directly at the melt a negative pressure of a certain size.

In the course of the process, it is further obvious that impurities in the form of particles, e.g. remove condensed oligomers by filtration from the discharged washing liquid outside the gas purification plant.

Particularly advantageous is the use of glycol as a hygroscopic washing liquid. However, other hygroscopic liquids are also useful which can accommodate not only water but also oligomer components from the gas mixture (e.g., glycerin).

In an advantageous embodiment of the invention, the hygroscopic absorption or washing liquid is renewed discontinuously. The washing liquid is taken alternately from several reservoirs and returned to this. When certain water concentrations in the washing liquid are exceeded, they must be renewed or regenerated in the process sequence. For this purpose, it is advantageous to switch over at certain time intervals or when reaching a certain water concentration in the washing liquid from one reservoir to a second. The respectively unused reservoir can then be replaced or refilled. A separate filtration of the contaminated washing liquid in the ongoing process is not essential in this case.

Furthermore, it is also conceivable to continuously regenerate the hygroscopic scrubbing liquid, ie to recycle it, for example in a regeneration plant.

A further advantageous process procedure therefore provides that in the continuous regeneration of the washing liquid undesirable constituents - such as water and oligomers - are separated by distillation or rectification of the washing liquid - eg glycol; if necessary, a pre-filtration is still required to remove the solid components from the washing liquid.

The method of the invention may e.g. be carried out with triethylene glycol (TEG) as absorption or washing liquid, because this has a particularly high water absorption capacity. However, it is also possible to use diethylene glycol (DET).

A particularly advantageous method embodiment results from the fact that the regeneration of the glycol takes place in a regeneration plant, which is used in the process sequence of a PET polycondensation plant. In such plants, preferably monoethylene glycol (MEG) is used. Such regeneration devices for glycol in combination with PET polycondensation are known in principle to the person skilled in the art; so for example from the US 3367847 A1 or the US 5413681 A1 ,

Against this background, it is particularly advantageous if the entire gas cleaning device is designed for the use of washing liquid in the form of a glycol which is used in large quantities in PET polycondensation - e.g. Monoethylene glycol (MEG).

An apparatus according to the present invention comprises a gas purifier and a vacuum device. About the gas cleaning device, a gas mixture is sucked by means of the vacuum device from a PET plastic melt. The device is designed so that the inventive method can be carried out with it. By means of the vacuum device is therefore at the gas inlet of the gas cleaning device, a negative pressure of less than 50 mbar, preferably in the range 1-15 mbar absolutely generated. Furthermore, the gas cleaning device is designed such that by contact between the hygroscopic washing liquid and the gas mixture by absorbing the water components, the volume flow of the gas mixture at the gas outlet is reduced by at least 60% compared to the volume flow of the gas mixture at the gas inlet. Preferred is a process control with a volume flow reduction of 75% -90%. This creates the advantages described above in the design of the vacuum system.

Particularly preferred is the use of an absorption column as a gas cleaning device, which is designed for the flow through the gas mixture with glycol as the absorption and washing liquid. The operating principle of the absorption column is that the washing liquid is passed in countercurrent to an ascending gas mixture. The liquid is distributed dropwise over a reaction zone or sprayed through spray nozzles in the gas mixture.

An embodiment of the device according to the invention is characterized in that the gas cleaning device is connected to a plurality of storage containers for hygroscopic washing liquid. The washing liquid is alternately removed from these reservoirs and traceable in this. There is a device with which, with an increase in the volume flow of the gas mixture, which is passed on to the vacuum device, the washing liquid circuit from one reservoir to another reservoir is switchable. In this way, a container can be filled or replaced with fresh washing liquid while the other is available for the running process. The switching is expediently carried out when exceeding a predetermined size of the volume flow of the gas mixture, which is passed on to the vacuum device on.

A further embodiment results from the fact that the device is combined with a device for the continuous regeneration of the washing liquid.

It has proven to be particularly advantageous to use this facilities for rectification. This is, for example, a rectification column in which an ascending vapor stream and a descending liquid stream are in constant heat and mass transfer at the phase boundary between vapor and liquid.

In connection with the device according to the invention, a particularly advantageous embodiment results from the use of glycol as a hygroscopic washing liquid in combination with a regeneration plant which is used for the regeneration of glycol in the course of a PET polycondensation plant. In this way, no separate regeneration system is required for the degassing, but it is used an already used for another process plant with.

Brief description of the drawings

1 Simplified representation of an embodiment of the device according to the invention with two storage containers

2 Schematic representation of components of an absorption column, which in the apparatus according to 1 can be used

3 Simplified representation of an embodiment of the device with rectification column

4 Simplified illustration of an embodiment of the device in combination with a polycondensation system

Advantageous embodiments of the invention

1 shows an extruder 15 with a degassing opening 14 , which has a pipe system with a melt trap 13 and the gas inlet 3 a gas purification device 4 connected is. The gas purification device 4 has a gas outlet 6 that with a vacuum device 2 connected is. Furthermore, the gas purification device 4 a fluid inlet 24 and a liquid outlet 26 on. The liquid inlet 24 is over a cooler 18 with outlets of storage tanks 8th and 9 connected. The liquid outlet 26 is about a pump 17 with inputs of the reservoir 8th and 9 connected. The reservoir 8th and 9 are with hygroscopic washing liquid 5 filled. In the present example, monoethylene glycol is used for this purpose. The glycol cycle between the gas purifier 4 and the storage containers 8th and 9 is by means of a switching device 10 between reservoir 8th and reservoir 9 switchable. The switching device 10 is electrical with a sensor device 16 connected in the supply line to the vacuum device 2 is arranged. The switching device 10 is set so that when exceeding a certain size of the volume flow of the gas mixture 1 is automatically switched. It is also conceivable the output of a signal to the operator who makes the switch manually or at least the replacement of the reservoir with saturated washing liquid 5 , in the present case glycol, makes or refills it.

The system according to 1 works as follows:
A gas mixture 1 is sucked from a PET plastic melt, which is in the extruder 15 located. By applying a negative pressure at high temperatures, moisture and oligomer components from the molten plastic become the gas mixture 1 transferred. The gas mixture 1 gets over the melt trap 13 directed to retain any entrained liquid melt components. The gas mixture 1 is in the gas purification device 4 with the glycol 5 brought into contact. This happens in countercurrent between gas mixture 1 and the glycol 5 , These are by the glycol 5 Components of PET plastic melt in the gas mixture 1 contained, and taken over a liquid outlet 26 along with the glycol 5 dissipated. The purified gas mixture 1 is from the gas purifier 4 over the gas outlet 6 to the vacuum device 2 passed on. The vacuum device is designed in the present embodiment, that at the vent 14 a negative pressure of 1 mbar-15 mbar can be set absolutely. The level of the necessary negative pressure depends on the composition or additive and the temperature of the melt. The negative pressure loss due to the system parts between the degassing opening 14 and gas inlet 3 is to be considered accordingly.

In order to carry out the described method particularly advantageously, the gas cleaning device 4 as absorption column 7 formed in which the absorption or washing liquid 5 in a stream of drops in countercurrent to the rising gas mixture 1 falls down. Due to the high absorption of water in the glycol 5 is the volume flow of the gas mixture 1 reduced in the present example by about 75%. 2 shows further details of an embodiment of such an absorption column 7 , The gas mixture 1 is from the gas inlet 3 over a support grid 23 in a reaction path 20 sucked. The support grid 23 has a lattice-like structure on which a variety of reaction bodies 21 stacked on top of each other. These consist of perforated metallic rings or cylinders which serve to increase the surface area through which the contact between the washing or absorption liquid 5 and the gas mixture 1 takes place. The washing liquid - the glycol 5 - gets over the fluid inlet 24 in the upper part of the column 7 fed. It gets there to a pot-like liquid distributor 22 that cares for the liquid 5 over the entire diameter of the column 7 As evenly dripped down as possible, while the gas mixture 1 can flow up unhindered as possible.

The drained glycol enriched with water and other ingredients 5 collects in a column swamp 19 from where it comes from the liquid outlet 26 is derived. In the column swamp 19 is a level gauge 25 appropriate. This is connected in a manner not shown with a control device of the entire device. Should be in the column bottom 19 Setting too high a liquid level, the excess liquid is a not shown valve and another pump 5 specifically from the bottom of the column 19 derived without interrupting the vacuum in the absorption column.

The procedure is otherwise such that the glycol 5 except for the water components in the gas purifier 4 the oligomer ingredients and other undesirable components from the extracted gas mixture 1 absorbs and dissipates to the outside. It has been shown that it is necessary for the uptake of hydrocarbons from the gas mixture 1 advantageous is the temperature of the gas mixture 1 by contact with the dropwise supplied glycol 5 for example, 150 ° C when entering the absorption column 7 to reduce to about 23 ° C. This allows the oligomers and other undesirable components within the absorption column 7 largely from the gas mixture 1 into the liquid 5 condense or be dissolved or absorbed in it. At the mentioned temperature within the absorption column 7 To achieve, there is a cooling of the supplied Gylcols 5 over the radiator 18 , In addition, a metering of the mass flow of the liquid 5 attached to the volume flow of the gas mixture 1 is adjusted. The cycle of the washing liquid 5 between storage tanks 8th . 9 and absorption column 7 is controlled by the pump 17 and the vacuum inside the absorption column 7 certainly.

It has been shown that the gas mixture purified according to the invention 1 , that of the vacuum system 2 is fed only a small amount of water vapor contains. The residual moisture (for example 10%) depends on the degree of saturation of the washing liquid 5 , the proportion of air and the temperature in the gas mixture 1 from.

The following Table 1 shows some process parameters for a process that can be carried out with the device described above: Diameter absorption column 0.25 m Length of the reaction path 1,6 m Mass flow of PET in the extruder 400 kg / h Water contained in the PET 3000 ppmW Volume percent air in the gas 10% Operating pressure at the gas inlet 0.005 bar Temperature at the gas inlet 150 ° C Amount of water to be separated 1.1 kg / h Speed gas mixture 3 m / s Water concentration in absorption liquid 1% Temperature at the liquid inlet 20 ° C Volume flow at the gas inlet 520 m ³ / h Water mass flow at the gas inlet 1.2 kg / h Volume flow at the gas outlet 91 m ³ / h Residual moisture at the gas outlet 10% Mass flow absorption liquid 40 kg / h Temperature at the liquid outlet 23 ° C

The absorption liquid glycol 5 is in the embodiment according to 1 alternately from several storage containers 8th and 9 taken and returned to this. When certain water concentrations in the glycol are exceeded 5 this is in the process of the glycol cycle from the reservoir 8th on the second reservoir 9 switched, since no water from the glycol 5 more is recorded. This limit is usually reached at water concentrations of about 5% in glycol.

Switching during operation is done by means of a switching device 10 , This consists of a number of electrically controllable valves in the supply and discharge of the two reservoir 8th . 9 , The switching device 10 is from the sensor device 16 activated. The sensor device 16 measures in the present example a pressure increase in the supply line of the vacuum device 2 , This increase in pressure is the result of an increased volume flow of the gas mixture 1 and the associated reduced negative pressure generation by the vacuum device 2 , The increase in the volume flow of the gas mixture 1 is the result of a reduced removal of water from the gas mixture 1 by already strongly water-enriched glycol 5 , Of course, there are other principles for controlling the switching device 10 conceivable - eg a direct measurement of the volume flow of the gas mixture 1 or a measurement of the water concentration in the glycol 5 eg by increasing the volume flow of the glycol 5 as a result of water absorption.

For example, the process starts with a water concentration in the glycol 5 of 0.1% and the absorption column 7 is as long as from the first reservoir 8th fed until the water concentration in the glycol has reached 5%. Then it's on with fresh glycol 5 filled second reservoir 9 switched. Subsequently, the glycol 5 in the storage container 8th renewed, so that the process can continue until the water concentration in the reservoir 9 has reached the 5% mark, resulting in a renewed switch to storage tank 8th leads. The components, via the gas mixture 1 or over the fluid circuit of the glycol 5 with the interior of the gas purification plant 4 Pressure connected are adapted to the operation with vacuum accordingly.

An alternative to the discontinuous exchange of the glycol 5 represents a process in which this continuously in a regeneration plant 300 . 401 cleaned and freed of water.

For this purpose, a rectification column is in a particularly advantageous manner 300 used. A device for degassing a PET melt for carrying out this process variant is shown schematically in FIG 3 shown. The area where the gas mixture 1 cleaned and the water components in the glycol 5 be absorbed is analogous to the device according to the 1 and 2 built up. It only lacks the second reservoir 9 and the switching device 10 , Instead, it is a rectification column 300 present to the water-saturated glycol 305 , the column sump of the gas purification plant 4 leaves, the water withdraws. The glycol 305 is done by means of a pump 307 into the cycle of the rectification plant 300 pumped. A filter device 308 makes sure that the glycol 305 also the Oligomerbestandteile and possibly other solids are withdrawn. The glycol purified in this way 305 becomes the rectification column 300 over a heater 309 supplied with a temperature at which the saturated with water glycol 305 begins to boil. In the lower part of the rectification column 300 there is another heating element 310 , This ensures that the liquid, largely anhydrous glycol 305 in the column swamp 19 the rectification column 300 is kept constantly at its boiling point. In the temperature control of the two heaters 309 respectively. 310 It should be noted that water-saturated glycol has a lower boiling point than anhydrous glycol.

At the top of the rectification column 300 becomes water vapor 301 dissipated. This is via a capacitor with adjustable temperature 302 passed and the condensed water is in a container 303 collected. The water is then via a flow meter, not shown, with adjustable flow valve in exactly metered mass flow through the water return 306 fed again to the rectification column. Water surplus in the tank 303 is over a tank overflow 304 derived and thus the glycol cycle 5 . 305 permanently withdrawn. The excess of regenerated glycol 305 in the column bottom of the rectification column 300 is in a container 311 collected. Due to the negative pressure in the area of the gas purification plant 4 becomes the regenerated glycol 305 from the container 311 into the cycle of the gas purification plant 4 sucked. It is through a cooler 312 passed the heated glycol 305 cooled to room temperature.

4 shows schematically simplified the device according to the invention for degassing in a particularly advantageous combination with a PET polycondensation system 400 , The production of PET is glycol 5 as one of the starting materials by means of a pump 404 from the reservoir 408 taken. The second source of terephthalic acid 406 is fed separately. The with the polycondensation plant 400 produced PET raw material 402 is further processed into granules and can the entrance 11 of the extruder 15 be supplied. In the extruder 15 If necessary, additives or recycled material are added before the melt melts the extruder 15 at the exit 12 leaves in the direction of an extrusion die. Excess or contaminated glycol formed in the PET condensation process 403 becomes a regeneration plant 401 fed. About the pump 407 becomes contaminated or water-saturated glycol 405 from the gas purification plant 4 also the regeneration plant 401 fed. The container 408 is constantly running with purified glycol from the Regenieranlage 401 provided. As in the polycondensation plant 400 but constantly Glycol is consumed for the production of PET, must additionally fresh glycol 410 be supplied from the outside.

Such regeneration plants for polycondensation plants generally have process stages, which also solid components of the glycol 403 respectively. 405 remove. These solid components and the water are after separation / separation from the glycol 403 . 405 remove from the regeneration plant. The facilities are in 4 not shown. A separate filtration of the contaminated washing liquid 405 before the supply to the regeneration plant 401 is usually no longer required.

The determination of an increase of the water content in the hygroscopic washing liquid 5 . 305 . 405 If necessary, in the devices according to the 3 and 4 in the same way as in the embodiment according to 1 , With increasing saturation of the washing liquid 5 . 305 . 405 with water takes the volume flow of the gas mixture 1 at the gas outlet 6 to. This increase is due to a pressure measurement by means of a sensor device 16 between gas outlet 6 and vacuum system 2 detected. From the sensor device 16 an electrical signal is sent to a display or to a switching device 10 passed on, for a switching or distribution of fluid circuits 5 . 305 . 405 provides.

LIST OF REFERENCE NUMBERS

1

 mixture of gases

2

 vacuum equipment

3

 gas input

4

 Gas cleaning device

5

 washing liquid

6

 gas output

7

 absorption column

8, 9

 reservoir

10

 switchover

11

 Raw material input extruder

12

 Melt outlet extruder

13

 melt case

14

 Degassing extruder

15

 extruder

16

 sensor device

17

 Pump in the drain of the washing liquid

18

 Cooler in the inlet of the washing liquid

19

 Column sump absorption column

20

 reaction section

21

 reaction bodies

22

 liquid distributor

23

 support grid

24

 liquid inlet

25

 level indicator

26

 liquid output

300

 rectification column

301

 Steam outlet rectification

302

 capacitor

303

 Collection container water

304

 Overflow of water

305

 Glycol feed rectification

306

 Water return rectification

307

 Pump in glycol feed for rectification

308

 Glycolfilteranlage

309

 Glycol heating inlet

310

 Glycol heating column sump rectification

311

 Collection container glycol

312

 Cooler in the glycol return

400

 PET polycondensation

401

 regeneration system

402

 PET raw material output

403

 Glycol effluent from polycondensation

404

 Pump for glycol feed polycondensation

405

 Glycol effluent from absorption column

406

 Feed terephthalic acid

407

 Pump for glycol feed Regenerating system

408

 Reservoir glycol polycondensation

409

 Feed fresh glycol polycondensation

410

Glycol discharge from regeneration plant

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 20080207868 A1 [0006]
• DE 102008031834 A1 [0007]
• WO 2009/065384 A2 [0008]
• US 3367847 A1 [0025]
• US 5413681 A1 [0025]

Claims (16)

Method for degassing a PET plastic melt in which a gas mixture ( 1 ) by means of a vacuum device ( 2 ) sucked from the PET plastic melt and a gas inlet ( 3 ) a gas purification device ( 4 ) is fed and in which the gas mixture ( 1 ) within the gas purification device ( 4 ) with a hygroscopic washing liquid ( 5 ) is brought into contact, characterized in that by means of the vacuum device ( 2 ) with a gas outlet ( 6 ) of the gas purification device ( 4 ), at the gas inlet ( 3 ) a negative pressure of less than 50 mbar, preferably in the range 1-15 mbar absolute is generated and that the hygroscopic washing liquid ( 5 ) with the gas mixture ( 1 ) is brought into contact in such a way that by absorption of the water constituents of the volume flow of the gas mixture ( 1 ) at the gas outlet ( 6 ) by at least 60%, preferably by 75% -90%, relative to the volume flow of the gas mixture ( 1 ) at the gas inlet ( 3 ) is reduced. A method according to claim 1, characterized in that as a gas purification plant ( 4 ) an absorption column ( 7 ) is used. Method according to claim 1 or 2, characterized in that the hygroscopic washing liquid ( 5 ) is renewed discontinuously or continuously regenerated. A method according to claim 3, characterized in that for the discontinuous renewal of the hygroscopic washing liquid ( 5 ) alternately from several storage containers ( 8th . 9 ) and returned to this. A method according to claim 4, characterized in that when exceeding a predetermined size of the volume flow of the gas mixture ( 1 ) at the gas outlet ( 6 ) the washing liquid circuit ( 5 ) from a storage container ( 8th ) to another reservoir ( 9 ) is switched. A method according to claim 3, characterized in that for the continuous regeneration of the hygroscopic washing liquid ( 5 ) a rectification plant ( 300 ) is used. Method according to one of the preceding claims, characterized in that as a hygroscopic washing liquid ( 5 ) a glycol is used. A method according to claim 3, characterized in that as a hygroscopic washing liquid ( 5 ) a glycol, and that the regeneration of the glycol ( 5 ) in a regeneration plant ( 401 ) used for the regeneration of the glycol ( 403 ) in the process flow of a PET polycondensation plant ( 400 ) is used. Device for degassing a PET plastic melt with a gas cleaning device ( 4 ) with a gas inlet ( 3 ) and with a gas outlet ( 6 ) and with a vacuum device ( 2 ) connected to the gas outlet ( 6 ), wherein the gas purification device ( 4 ) is designed such that therein a gas mixture ( 1 ) with a hygroscopic washing liquid ( 5 ) is brought into contact, characterized in that by means of the vacuum device ( 2 ) at the gas inlet ( 3 ), a negative pressure of less than 50 mbar, preferably in the range 1-15 mbar is absolutely producible and that the gas cleaning device ( 4 ) is formed such that by contact between the hygroscopic washing liquid ( 5 ) and the gas mixture ( 1 ) by absorption of the water components of the volume flow of the gas mixture ( 1 ) at the gas outlet ( 6 ) by at least 60%, preferably by 75% -90%, relative to the volume flow of the gas mixture ( 1 ) at the gas inlet ( 3 ) is reducible. Apparatus according to claim 9, characterized in that the gas purification device ( 4 ) as absorption column ( 7 ) is trained. Apparatus according to claim 9 or 10, characterized in that the gas purification device ( 4 ) in such a way with several storage containers ( 8th . 9 ) for the hygroscopic washing liquid ( 5 ), that the hygroscopic washing liquid ( 5 ) alternately from these storage containers ( 8th . 9 ) Removable and is traceable to this. Apparatus according to claim 11, characterized in that a sensor device ( 16 ) is present, with the exceeding of a predetermined size of the volume flow of the gas mixture ( 1 ) connected to the vacuum device ( 2 ) is passed on, recognizable and that a switching device is present, with the switching of the washing liquid circuit ( 5 ) from a storage container ( 8th ) to another reservoir ( 9 ) is feasible. Device according to one of claims 9 or 10, characterized in that a device ( 300 . 401 ) for the continuous regeneration of the hygroscopic washing liquid ( 305 . 405 . 403 ) is available. Apparatus according to claim 13, characterized in that the means for regenerating as a rectification column ( 300 ) is trained. Device according to one of the preceding claims, characterized in that the device for glycol as a hygroscopic washing liquid ( 5 ) is trained. Apparatus according to claim 13, characterized in that the device to the use of glycol as a hygroscopic washing liquid ( 5 ) and that the device for continuous regeneration is used as a regeneration device ( 401 ) in the glycol cycle ( 410 . 403 ) of a PET polycondensation plant ( 400 ) is trained.

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