EP1678236A1

EP1678236A1 - Tower reactor and use thereof for the continuous production of high molecular weight polyesters

Info

Publication number: EP1678236A1
Application number: EP04791054A
Authority: EP
Inventors: Eike Schulz Van Endert; Christian Atlas
Original assignee: Uhde Inventa Fischer GmbH
Current assignee: Uhde Inventa Fischer GmbH
Priority date: 2003-10-31
Filing date: 2004-10-29
Publication date: 2006-07-12
Also published as: CN1867607A; DE10351085A1; RU2275236C2; KR100948229B1; CN100491439C; KR20060094532A; RU2004110060A; US7608225B2; WO2005042615A1; US20070116615A1

Abstract

The invention relates to a tower reactor and use thereof for the continuous production of high molecular weight polyesters, such as for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polynaphthalene terephthalate (PEN), polytrimethylene terephthalate (PTT) and/or polyesters of other dicarboxylic acids and diols, including copolymers thereof. The above is a single-stage tower reactor.

Description

Tower reactor and its use for the continuous production of high molecular weight polyester

The invention relates to a tower reactor and its use for the production of high molecular weight polyesters such as Polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polynaphthalene terephthalate (PEN), polytrimethylene terephthalate (PTT) and / or polyesters of other dicarboxylic acids and diols including their copolymers. It is a single-stage tower reactor.

Processes for the continuous production of polyesters are known from the prior art, in which multi-stage reactor systems are used which consist of three to five different reaction vessels connected to one another. In these processes, the polyester is formed in several reaction stages, which are usually designed as stirred tanks, which are spatially separated from one another. running: esterification, transesterification, precondensation, polycondensation and polyesterification. The reaction conditions for the esterification are at temperatures between 200 and 280 ° C and pressures between 0 and 4 bar, while the conditions for the transesterification are usually at atmospheric pressures and at temperatures between 150 and 240 ° C, depending on the starting substances of the diols. Low temperatures and low pressures are desirable for the processes in order to avoid undesired side reactions.

For example, DE 35 44 551 A1 discloses a process for the continuous production of high molecular weight polybutylene terephthalate, in which the process is carried out under atmospheric pressure.

In all the processes known from the prior art, it is important to meet the following conditions:

I) Appropriate process control and design of the devices to avoid undesirable side reactions.

II) Removal of by-products as quickly as possible, e.g. Water, methanol, THF and acetaldehyde, which shifts the reaction equilibrium to the right and the main reaction takes place primarily.

III) Gentle treatment, i.e. short residence time at minimum reaction temperature.

IV) Optimally coordinated pressure reduction or temperature increase by the greatest possible progress to achieve the esterification / transesterification and the polycondensation / polyesterification.

V) High surface formation to improve the reaction kinetics.

These tasks can only be insufficiently achieved by a plurality of stirred reactors connected in series, which are usually used for these processes in accordance with the prior art. This can e.g. the quality of the product or the amount of unwanted by-products as well as the yield are adversely affected, which, in addition to other disadvantages, such as energy consumption, maintenance requirements and investment, severely impairs the economics of the process.

Furthermore, DE 101 55 419 discloses a process for producing high molecular weight polyester and an apparatus for carrying out this process, the individual reaction zones being integrated in a single reactor vessel.

Based on these disadvantages of the prior art, it was an object of the present invention

To provide a reactor in which the individual reaction stages can be carried out and, compared to the prior art, a faster reaction procedure and a gentler production of the reaction products is made possible.

This object is achieved by the generic tower reactor with the characterizing features of claim 1 and its use with the features of claim 31. The further dependent claims show advantageous developments. According to the invention, a tower reactor for the continuous production of high molecular weight polyester is provided, which has reaction zones for the simultaneous esterification and / or transesterification and precondensation. The individual reaction zones are combined in a tower reactor and can be connected to at least one reactor for polycondensation in the solid and / or liquid phase.

The tower reactor is constructed as follows: In the upper third, the tower reactor is designed in the form of a hydrocyclone with an attached heat exchanger and has a feed for the paste, the slurry and / or the liquid raw material mixture. The area of the tower reactor below the hydrocyclone is designed in the form of a downdraft cascade. This cascade is connected via a suitable inlet pipe to the lower part of the tower reactor, which is designed in the form of a single- or multi-stage falling film zone with pre-relaxation.

This construction method has various advantages. In this way, the product flow from the entire tower reactor can be ensured by gravimetric flow without the use of a pump. Long external pressure lines for the transport of the monomer into the reactor are also superfluous. Further advantages relate to the fact that there is no heating of the upper reactor cover, which leads to corresponding cost savings, and that the reaction vapor can be partially used to heat the reaction product in the hydrocyclone. There is also a uniform pressure drop across the entire reactor in the pressure reactor. This means that the wall material thickness can be reduced. The hydrocyclone preferably has a vapor connector and is connected to a heat exchanger in the upper part of the tower reactor. This makes it possible to lead the product in a natural or forced cycle through the heat exchanger into the hydrocyclone.

In an advantageous embodiment, the heat exchanger has a separate gas fireplace which leads to an upper part of the cyclone.

The cascade preferably has at least two, particularly preferably four, reaction cups. A stirring unit can be integrated in at least one cascade area to support the input of diol or additives. Alternatively, the additive can also be added to a product drain pipe of the penultimate cup via an injection lance, which ensures an optimal distribution of the same in the product mass.

The pressure line is preferably designed as a double jacket line, which continues inside the first head cup as a heating coil. The pressure line can be equipped with a volume feed pump and static mixing elements or a mixing pump.

The hydrocyclone preferably has a gas inlet in its conical area.

In an advantageous embodiment, one of the head cups in the vapor area also has an inert gas inlet. The reaction gases and / or foreign gases are preferably passed from reaction zone to reaction zone in cocurrent by means of submerged feeds the reaction liquid passed, creating a pressure drop between the cups. The reaction mass is fed centrally to the next cup by means of a likewise submerged tube.

Preferably, the pre-relaxation zone to the falling film zone also has the form of a hydrocyclone, which supports the flash effect and ensures adequate separation of the liquid / gas phases and generates a further pressure gradation.

The product is fed from the pre-expansion zone to the falling film zone by suitably designing the process from it in the concentric outer area of the falling film zones and the product is evenly distributed over alleys in the tube field.

It is also preferred that the falling film zone has at least one tube field. An inlet cylinder is assigned to each pipe in the pipe field, which ensures uniform wetting of the inside of the pipe, which is equipped with overlapping, non-axial slots on the circumference, a constant fill level is generated above the pipe rows due to the loss of slot pressure, and a maximum overflow with jagged Krone has, the slots being designed in such a way that differences in viscosity only cause negligible changes in the fill level, but a proportional change from fill level to liquid throughput.

It is also preferred that the length of the falling film tubes is dimensioned such that total wetting takes place.

The diameter of the falling film tubes is preferably larger than the largest reaction vapor bubble that occurs selected. The reaction vapors are carried out in cocurrent with the product flowing downwards.

The falling film tube field can preferably also be used for heat transfer.

The entire tower reactor is preferably equipped with a jacket for heating with organic heating media in vapor form.

The tower reactor preferably has a plate bottom valve designed as a feed with a special plate. The feed of the raw mixture is arranged centrally in the spherical bottom below the heat exchanger. This has the advantage that the plate of the bottom valve creates a baffle plate effect, which enables a uniform turbulent distribution of the raw mixture with the reaction mixture.

The tower reactor preferably has static mixing elements to improve the mixing of the raw mixture into the reaction mixture. The mixing of the raw mixture into the reaction mixture is improved by the complete or partial filling of the heat exchanger tubes. The result of this is that the reaction can be accelerated due to the higher mass exchange and the reaction product is spared due to the improved heat exchange (lower wall temperature).

The raw mixture entering the lower part of the external heat exchanger is subjected to intensive mixing into the liquid reaction mixture. The ratio of the circulating reaction mixture to the raw mixture entered is in the range from 100: 1 to 300: 1, so that satisfactory mixing is ensured by the dilution if a 100% mixture is assumed. A three-dimensional statistical mixing element is particularly preferably used, which generates a large number of diagonal cross-flows with simultaneous axial flow before the reaction mixture enters the heat exchanger. Problems such as streaking of the raw mixture in the reaction mixture can thus be ruled out, so that an inhomogeneous reaction in the heat exchanger which would disturb the natural circulation can be hindered. Sedimentation of a raw material component, which can lead to process disturbances over time, can also be avoided in this way. These problems of mechanical mixing can be eliminated by means of commercially available stirring elements or mixing pumps, but these have the disadvantage that a further element requiring maintenance is part of the reactor, which requires electrical power and thus reduces the economic efficiency of the process. In this context, the use of a three-dimensional static mixing element has proven to be particularly advantageous. With this, a radial distribution of reaction mixture and raw mixture with simultaneous axial upward movement can take place, ie there is intensive mixing of the components and thus a uniform reaction. In a particularly preferred embodiment, the three-dimensional static mixing element consists of cross-shaped, perforated sheet metal sections, the inclination of which is adjusted in such a way that the impact pressure loss is only a few mmWWS / m. The ratio of the axial height to the heat exchanger diameter is preferably between 0.2: 1 to 0.5: 1. This ratio is important in order to disturb the natural circulation as little as possible.

Defined packing types can also be used for the mixing. These guarantee but often only a limited, local axial mixing.

Another variant of the mixing is realized by folded layer packs, as are often used in distillation columns. Good results can also be achieved with this, particularly with regard to the crosswise and diagonal flow, the axial leakage flow and the low pressure loss.

The heat exchanger preferably has two areas, a product room and a heating room, and a separating device for the horizontal separation of these two areas, the height of the separating device being at least 1D (D = diameter of the heat exchanger tubes) and the separated areas of the heat exchanger having a rotated offset of 0 to 1D.

The individual heat exchanger areas preferably have a different pipe division.

In an advantageous development, the vapor spaces have adhesion-reducing coatings. For example, adhesion-reducing organochemicals and inorganic chemistries can be used as coatings in the thin-film process (up to 10 µm) at a high application temperature of up to 350 ° C. With this surface treatment, the susceptibility to contamination of the polymeric reaction masses can be reduced.

In a further advantageous embodiment, all heat exchange surfaces in the individual zones are equipped for liquid heat carriers for process-relevant temperature and heat quantity distribution. The reactor according to the invention can be used to carry out a process for the continuous production of high molecular weight polyesters, based on the esterification of dicarboxylic acids and / or transesterification of dicarboxylic acid esters with diols in the presence of catalysts with simultaneous formation of a prepolymer and its polycondensation to give high molecular weight polyesters. The following steps characterize the procedure:

al) A paste and / or a slurry of the dicarboxylic acids and the diol is produced, a molar ratio of diol to dicarboxylic acid being maintained from 0.8 to 1.8. At the same time the temperature is kept between 20 and 90 ° C and the pressure between 0.1 and 1 bar.

a2) As an alternative to al), a dicarboxylic acid ester can be melted and mixed with the diol in a molar ratio of diol to dicarboxylic acid ester of 1.2 to 1.8 at a temperature of 145 to 165 ° C.

b) The products from a1) and / or a2) are continuously fed to a tower reactor. The esterification or transesterification to precondensation then takes place continuously, simultaneously and without interruption in the tower reactor, the following reaction conditions being maintained: bl) The products from a1) and / or a2) are subjected to a temperature treatment at 170 to 270 ° C. and pressures of 0. Subjected to 3 to 3 bar. At the same time, a portion of the catalyst (s) is added while the reaction vapors are removed from the reaction mixture in situ the .

b2) The product obtained from bl) is continuously transferred into a pipe section and the pressure is kept between 1 and 10 bar, the temperature between 200 and 280 ° C. In this reaction step, 0.03 to 0.3 mol of diol are fed in simultaneously.

b3) The product from b2) is continuously transferred to a third zone, a reduced pressure of 0.1 to 2 bar and a temperature between 230 to 280 ° C. being maintained. In this third stage 0.02 to 0.2 mol of diol and a portion of the and / or the catalyst (s) are fed.

b4) The product from b3) is subjected to a further reaction, the pressure being kept between 0.01 and 0.1 bar and the temperature between 240 and 280 ° C.

b5) The reaction product water from the esterification or methanol from the transesterification, the by-products and excess diol from reaction steps bl) and b3) to b5) are removed and the diol is returned to the individual process stages after purification.

cl) The prepolymer obtained from b4) is continuously processed into the polymer in a conventional polycondensation apparatus at temperatures between 240 and 290 ° C. and pressures between 0.0002 to 0.003 bar.

c2) As an alternative to cl), it is also possible to freeze the pre-polymer, process it into pellets and subject it to post-condensation in the solid phase at temperatures between 160 and 230 ° C under inert gas.

The new process enables parallel, uninterrupted transesterification / esterification and precondensation of dicarboxylic acids and their esters with diols in a single tower reactor. This enables the mechanical and procedural integration of several process stages for polyester synthesis for the first time.

The gaseous by-products formed in stage b1) and the excess diol are preferably separated off by means of a hydrocyclone in the "statu nascendi". The rapid removal of lower-boiling reaction gases is of great importance with regard to minimizing the formation of by-products by cars The content of by-products in the reaction mass is determined on the basis of the partial pressures of these products by the reaction pressure and the existing static product heights: the higher the total pressure, the higher the by-product formation. The formation as a hydrocyclone with an external heat exchanger is therefore due the resulting thermosiphon circulation is decisive for a short dwell time of the by-products in the reaction mass with increasing static product height and because immediate effective degassing in the hydrocyclone and in the heat exchanger is ensured.

When carrying out an esterification, a temperature between 200 and 270 ° C. and a pressure between 0.3 and 3 bar are preferred in step bl) respected. If, on the other hand, a transesterification is carried out, step b1) is carried out at a temperature between 170 and 200 ° C. and at a pressure between 0.3 and 1 bar.

In step b2), when an esterification is carried out, the pressure is preferably kept between 2 and 6 bar, the residence time between 1 and 5 min and the temperature is preferably kept between 220 and 280 ° C. and particularly preferably between 230 and 250 ° C. If, on the other hand, a transesterification is carried out, the pressure in stage b2) is preferably in the range between 2 and 5 bar, the residence time between 1 and 4 min and the temperature in the range between 200 and 240 ° C., particularly preferably between 210 to Kept at 230 ° C.

In an advantageous development of the method, in step b3) the reaction product continuously fed from step b2) is passed over a falling flow cascade, with a 20 to

60 mbar falling pressure and a temperature rising by 5 to 20 ° C per shell. The esterification produces a precondensate with 5 to 20 repetition units with a conversion between 97 and 99.5%. In contrast, the transesterification turnover is between 98.5 and 99.8%.

In addition to the normal process gas, a dry inert gas and / or superheated process gas is preferably fed into at least the first shell under the reaction mass surfaces. This will separate the by-products by "dragging", i.e. Saturation of gases, supported. At the same time, the internal mixing of the reaction mass is promoted.

The dwell time in the individual shells is moves in a range between 5 and 15 min.

In a further advantageous development of the method, the product is supplied centrally in the shells. The product runs on the outer edge of the

Shells distributed evenly over the outer wall, which is used for accelerated degassing, and is then brought together again centrally.

Step b4) is designed as a falling film zone with pretensioning and is preferably carried out at a temperature between 245 and 270 ° C. and a residence time between 4 and 30 minutes and a pressure between 0.01 and 0.05 bar. This creates a precondensate with 10 to 40 repetition units with a conversion of 99.8%.

After leaving one or more falling film zone (s), the reaction product is preferably brought together by a heated cone, a gas-liquid separation being carried out in its central region by means of a spoiler.

The diol 1, butanediol, ethanediol or propanediol is preferably used. The process is also suitable for cyclohexane dimethanol. Terephthalic acid is preferably used as the dicarboxylic acid. In the transesterification, dimethyl terephthalate (DMT) is preferably used as the dicarboxylic acid ester. The known tin, antimony, germanium, manganese, calcium and / or titanium metals etc. are preferably used as catalysts, in particular as their organic compounds. The catalysts can also be accommodated in a porous carrier substance in order to develop a targeted effect. The subject according to the invention is to be explained in more detail with reference to the following figures and the example, without restricting it to these statements.

1 shows a first variant of a tower reactor according to the invention,

2 shows a second variant of a tower reactor according to the invention,

3 shows a reaction cup with foam brake 13 and vapor-liquid separation,

4 shows various embodiments of the tubes of the tube field,

5 shows various embodiments of the cylindrical inlet pipes,

Fig. 6 shows an embodiment of the process of the second film reaction zone, and

Fig. 7 shows an embodiment of the tube sheets in the form of a spherical cap.

Fig. 1 shows the schematic structure of a tower reactor. A slurry of the dicarboxylic acid with the diol or the molten dicarboxylic acid ester and the diol are injected into the reaction mass under pressure in the lower region of a heat exchanger 5 attached to the tower reactor, and by suitable design of the injection nozzle 3 it mixes optimally with the one in the lower part - The reaction product comes. A catalyst that is used for some polyester is partial, be fed. The heat exchanger ensures that the mixture is heated to the reaction boiling point. The boiling reaction mixture passes through a short connecting line which tangentially opens into a hydrocyclone 2 for further reaction. For the rapid removal of reaction gas from the reaction mass, the majority of these gases are passed from the heat exchanger into the gas space of the cyclone via a separate line, a steam chimney 6.

In the hydrocyclone 2, further degassing takes place as the reaction continues. The reacted product returns to the heat exchanger 5 via a short connecting line at the base of the cyclone, so that a natural circulation is created. The entire reaction gas is removed from the vapor space of the hydrocyclone 2 above the reaction mass.

For particularly sensitive products, such as in the production of PBT, cyclization of butanediol creates the undesirable tetrahydrofuran (THF). The formation is enhanced by the presence of water, which is formed, for example, during the esterification. In this case, a preheated, unsaturated entraining gas or superheated process vapors can advantageously be introduced in the lower region of the cyclone, thereby accelerating the removal of, in particular water, methanol, acetaldehyde or tetrahydrofuran from the reaction mass.

The reactor has a pressure line for the product, into which the diol is intimately mixed with the reaction mass via static mixing elements. Depending on the product, a pressure of up to 10 bar can be set using a pressure control valve. Alternatively, the mixing and the pressure can also be Target mixing pump are generated.

By introducing the diol under pressure, a spontaneous reaction with the carboxyl or methoxy groups is initiated, which takes place in the time range from 1 to 5 minutes and is complete after relaxation to atmospheric or subatmospheric pressure. The reaction time is set in that part of the pressure line is arranged in the form of a heating coil in the uppermost reaction cup of the tower reactor. The double jacket ensures that the reaction mass, cooled by expansion, is brought back to the reaction temperature.

The relaxed reaction mass is then passed through a downflow cascade 7, which consists of at least 2, preferably 4 to 5, reaction shells equipped with heating coils, into which the product flows centrally and submerged below the surface. The reaction gas, on the other hand, is passed through the reaction mass separately from the respective overlying shell by means of likewise submerged tubes. This results in a differential pressure, which preferably has the effect of lowering the pressure from shell to shell from top to bottom.

The product from the second to umpth bowl runs on the outer wall, which acts as an additional evaporation surface, each bowl into a conically shaped collector, the drain of which is located at the lowest point of the cone. The collector also contains the immersion tubes that feed the reaction gas into the next bowl. The dishes are preferably laid out for a residence time of 5 to 10 minutes in order to achieve the desired reaction progress. To control the reaction temperature, in addition to a gentle increase of 2 to 10 ° C per bowl, each bowl is equipped with heating coils.

It follows from the arrangement that the reaction gas is conducted in cocurrent with the product flow, the gas bubbling through the reaction mass and ensuring optimum mixing on the one hand, and on the other hand not reaching its saturation limit due to the pressure drop with simultaneous temperature increase and thus remaining receptive for newly forming reaction gas (drag effect). Another important effect of the downflow cascade described is that the initially present low-boiling short-chain oligomers of the product with the reaction gas are returned to the reaction mass and continue to participate in the reaction there. Bubble formation also promotes the speed of the reaction by introducing the gas into the reaction mass, by additional surface formation and by contact with the gaseous diol.

This is not the case, for example, with stirred cascades and thus reduces the yield and causes faults in the subsequent capacitors and vacuum devices.

If necessary for the mixing in of additional additives or diol, an obliquely positioned stirrer 10 can be arranged in the last bowl, which supports the mixing of the vapor bubbles.

The reaction mass is then brought through a suitable feeder for renewed expansion in a hydrocyclone-like arrangement which, like the previous shells, is equipped with heating coils for temperature adjustment. The gas / liquid Separation takes place on the surface, with suitable baffles ensuring that the reaction mass runs evenly over the jagged outer edge of the shell, unaffected by the reaction gas bubbles that form. The reaction mass running on the periphery is collected on a tube plate - also on its periphery - and is distributed with the help of so-called. "Alleys" evenly on the floor.

The tube sheet is part of a straight tube bundle 9, which also serves for film formation on the inner tube surfaces and for heat exchange. An inlet cylinder 11 (cf. FIG. 5) is assigned to each tube in the bundle. This is designed with a series of non-axial, overlapping slots with a particularly balanced geometry on its periphery. The geometry is set so that

- a minimum level is maintained for all pipes for uniform liquid distribution, only small level differences occur for a certain viscosity spectrum,

Changes in throughput result in a proportional change in level and the inner pipe surface is evenly wetted over the entire pipe length,

- The upper edge of the inlet cylinder 11 serves as an emergency overflow and is equipped with a serrated crown.

The tube diameter is selected so that it is larger than the largest possible reaction gas bubble. The reaction steam is co-current with the descending product film. The ratio of pipe length to pipe diameter should be between 10 and 25 and the surface of the falling film pipes must be adapted to the wettability of the product. The product emerges as a film and / or strands on the underside of the falling film tubes, is brought together by conical collector plates which let the gas flow through, and is fed to a second falling film reaction zone on the periphery. This is basically the same as the first zone, but takes into account the increased viscosities by taking appropriate measures on the inlet cylinders 11, distributing the pipes and length of the module.

Below the module is a device for bringing the melt together, which contains a central tube in the center for carrying out the reaction gases and the product. The product running off on the device, preferably on the wall, is separated from the gas stream by a spoiler device 12 (cf. FIG. 6), which is deflected and removed in the gas space of the integrated prepolymer collector. The collected prepolymer is discharged from the collector after a calming and post-reaction time of 5 to 15 minutes on the reactor floor and can now be subjected to further treatment, e.g. granulation with subsequent solid phase post-condensation or melt phase post-condensation.

For certain products, the possibility is provided to return a partial stream of the prepolymer into the lower falling film module and to mix it with the preliminary product from the upper falling film module, so that the reaction time can be advantageously extended in a simple manner. The outer shell of the reactor is equipped with a heating jacket, which is preferably provided for heating as an active insulation, with a synthetic heat transfer vapor. The temperature profile required for the reaction is generated zone by zone with the aid of the inner heating surfaces, essentially using a liquid heat transfer oil. The reaction gases from the different zones are discharged through conventional devices such as condensers, columns and vacuum systems, the diol with small amounts of oligomer essentially being returned to the process.

FIG. 2 shows a further variant of the tower reactor, which has the essential elements as in FIG. 1.

In this variant of the tower reactor, however, a special mixing pump is used instead of the pressure control valve and the static mixing elements. In this variant, too, the use of an obliquely positioned stirrer for mixing in additional additives and diols is dispensed with.

Fig. 3 shows an embodiment of the reaction cup with foam brakes and vapor-liquid separation. The reaction cup shown here has a foam brake 13 and an adjustable, serrated overflow 14. The liquid is led through the reaction gases and can run off via the central liquid drain (dip tube) 15, which serves to generate the differential pressure. At the same time, the reaction cup has a closable drainage opening 16, which consists of a bore hole with a conical extension, into which a conical closure with an additional temperature-resistant sealing element is inserted. leads is. The actuation takes place from the outside with the aid of a double vacuum-sealed rod 17. Furthermore, the reaction cups have heating tubes 18. The AH ratio _/ ^ is preferably between 2 and 10, the flow velocity W is between 1 and 5 m / s and Wl between 0.05 and 0.3 m / s.

4 shows the distribution of the melt on the distributor floors from the periphery with the aid of lanes 19 in the tube field 20, which ensure a distribution deviation of a maximum of 30%, i. H. the throughput difference between two pipes with maximum distance is not higher than 30%. Three different versions are shown for the formation of the gases.

5 shows various embodiments of the cylindrical inlet pipes 11 for the film-producing pipes in order to achieve an optimal film flow. The tine angle of the overflow can be between 45 and 90 ° C and the tine height between 5 and 20 mm. The ratio of the distance between the holes s to the diameter d of an s

Bore V = ^~ is between 1.5 and 2.5.

Depending on the course of the chemical reaction and the resulting physical values, the gap / hole geometry is determined using a suitable differential equation, whereby a minimum level, which is necessary for optimal distribution, is maintained.

6 shows an embodiment of the sequence of the second film reaction zone in the form of a spoiler 21. The product from this zone already has a melt viscosity that has film and fiber-forming properties. The exit of such a melt from a tube can then already take the form of an elastic hose. When a gas passes through, in this case the reaction gas, there is a risk that this film tube will be torn open and that flat parts of it will enter the downstream condensation and vacuum systems with the gas stream. This would lead to unpleasant malfunctions and losses. According to the invention, this problem was solved by bundling the polymer stream, which then only flows through the tube in strands, with the simultaneous release of gas passage areas with the aid of the spoiler 21.

Fig. 7 shows a variant of the tube sheets in the form of a spherical cap. To support the uniform supply of the peripheral tubes and the subsequent tubes of the tube mirror up to the central tubes, the tube sheets can be designed in the form of a spherical cap, by means of which a targeted height difference in the liquid level is generated. This eliminates the distribution non-uniformity caused by the mass difference and pressure loss of the mass on the floor and ensures that all pipes are evenly loaded on the floor. ΔH corresponds to the natural decrease in level in the flow from the outside, ie from the reactor wall 22, to the inside. example

1. A paste of the reactants PTA and diol or the liquid carboxyester and diol at a temperature of 150 ° C. with molar ratios between 0.8 and 1.8 are injected into a first chamber with the temperature of 20-90 ° C. Existing monomer / prepolymer reaction mass is intensively mixed in the heat exchanger with product recirculated from the hydrocyclone and at least one catalyst.

2. Degassing by removing the by-products in a range between 30 and 90%, preferably 40 and 60% "in situ" during the passage through the heat exchanger which leads the reaction vapors into the hydrocyclone via a 'chimney' channel (gas / liquid Separation).

3. The reaction mass is further degassed in a connected hydrocyclone at pressures between 500 and 3000 hPa.

4. Inject a carrier gas at the bottom of the hydro cyclone for further improved removal of

By-products. Any inert medium or one of the purified gaseous by-products (superheated) can be used as the carrier gas.

5. Transfer the reaction mass through an under

Pressure tube and simultaneous addition of parts of the diol to the mass in amounts between 0.03 to 0.5 mol / mol acid or dimethyl ester, preferably between 0.1 and 0.3 mol / mol acid or dimethyl ester, for an immediate reduction of the carboxyl groups or an exchange of ester end groups between see 20-80%, preferably 40-60% of the acid or ester end groups present in the hydrocyclone.

6. Transfer of the reaction mass into a first tray in order to remove the by-products previously formed and to heat the reaction mass again in the container by means of the heating jacket of the tube under pressure.

7. The product is passed through at least two or a plurality of steam-stirred integrated trays with a residence time of between 5 and 15 minutes, the temperature increasing continuously in steps of 1 to 20 ° C. and the pressure increasing continuously by 5 to 50 hPa per tray. le is reduced. The vapors generated by continuing the reaction are in an unsaturated gaseous state and are introduced below the liquid surface of the following bowl, while the product flows into the following container in a liquid-tight manner. The vapors promote the removal of the reaction side products by intensive mixing with the primary product. In addition, dried inert gas or process gas can be admitted into the first shell in order to further improve the progress of the reaction by saturating steam and gas. The available reaction progress is between 10 and 40% for the simultaneous reactions between carboxyl and hydroxyl groups as well as ester end groups.

8. The product is transferred to another flash tank, in which the pressure is 1/5 to 1/50 lower than in the last steam-stirred tank and the reaction temperature is raised by 2 to 20 ° C. The resulting polyesters have a chain length of 5-20, preferably between 10 and 15 Repeat units with sales of more than 99.5%.

9. Flow of the polyester through at least one highly surface-active tube field in which each partial product quantity is exposed uniformly to the temperature and surface, resulting in a prepolymer which preferably has between 20 and 35 repetition units and a conversion of 99.8%. The superheated reaction gases are led downward in cocurrent with the polymer films and absorb any new gaseous by-product of the polymer films. This arrangement enables the method to be carried out under the above conditions in a period between 5 and 30, preferably 8 and 16, minutes.

10. To balance the molecular distribution, the product remains in the system for between 2 and 10 minutes.

11. The polymer is transferred to a polycondensation reactor, in which a PG of 80-150 is achieved. A suitable reactor is described for example in US 5,779,986 and EP 0 719 582.

12. Alternatively, the product pumped off after 2 to 10 minutes can be processed into granules, which can then be further heat-treated in the solid state in order to obtain a polymer with a PG of 90-200.

Both polymers manufactured according to items 1-11 as well as items 1-10 and item 12 are excellently suitable for fiber-forming processes, as a resin for bottle applications, especially for "still water", and for film-forming and technical plastic applications. Among other things, they stand out due to an improved yellowness level by up to 2.5 points according to CIELAB (b * value) and an improved whiteness level (L * value) by up to 5 points.

These analyzes suggest, among other things to the fact that, compared to the polymers produced in conventional processes and equipment, it is polyester of high purity.

Compared to the prior art, the device according to the invention therefore represents a new concept which is advanced in its features.

Claims

claims

1. Tower reactor comprising reaction zones for the simultaneous esterification and / or transesterification and precondensation, the individual reaction zones being connected to one another and combined in the tower reactor, so that the at least one tower reactor is constructed as follows:

In the upper third, the tower reactor is designed in the form of a hydrocyclone (2) with attached heat exchanger (5) and has a feed (3) for the paste, slurry and / or liquid raw material mixture, the area of the tower reactor below the hydrocyclone (2 ) is designed in the form of a downdraft cascade (7); - The cascade (7) is connected via a line to the lower part of the tower reactor in the form of a single or multi-stage falling film zone (9) with pre-relaxation (8).

2. Tower reactor according to claim 1, characterized in that the hydrocyclone (2) has a vapor connector and is connected to a heat exchanger (5), so that the product in the natural or forced circulation via the heat exchanger (5) into the hydrocyclone (2) can be performed.

3. Tower reactor according to at least one of claims 1 or 2, characterized in that the heat exchanger (5) has a separate gas fireplace (6) which leads into an upper part of the cyclone (2).

4. Tower reactor according to at least one of claims 1 to 3, characterized in that the cascade (7) has at least two cups, preferably four reaction cups.

5. Tower reactor according to claim 4, characterized in that a stirring unit (10) for mixing in additives is integrated in at least one cascade area.

6. Tower reactor according to claim 4, characterized in that the penultimate cascade has a drain pipe on which an injection lance for the supply of additives is arranged.

7. tower reactor according to at least one of claims 1 to 6, characterized in that the pressure line (4) is designed as a double jacket line, which continues inside the first head cascade as a heating coil.

8. tower reactor according to at least one of claims 1 to 7, characterized in that the pressure line (4) with a volume conveyor and static see mixing elements or a mixing pump is equipped.

9. Tower reactor according to at least one of claims 1 to 8, characterized in that the hydrocyclone has a gas inlet in the cone area.

10. Tower reactor according to at least one of claims 1 to 9, characterized in that one of the reaction cups (7) in the vapor area has an inert gas inlet.

11. Tower reactor according to at least one of claims 1 to 10, characterized in that the pre-expansion zone (8) to the falling film part has the shape of a hydrocyclone.

12. Tower reactor according to at least one of claims 1 to 11, characterized in that the pre-expansion zone is equipped with at least one further pressure reducing chamber.

13. Tower reactor according to at least one of claims 1 to 12, characterized in that the at least one falling film zone (9) has a tube field.

14. Tower reactor according to at least one of claims 1 to 13, characterized in that an inlet cylinder (11) is assigned to each tube of the tube fields, which ensures uniform wetting of the tube inner sides, this being equipped with overlapping, non-axial slots on the circumference, Due to the loss in slot pressure, a constant fill level is generated above the rows of pipes and has a maximum overflow with a serrated crown, the slots are designed so that differences in viscosity do not cause a change in the fill level, but a proportional change from fill level to liquid flow rate.

15. Tower reactor according to at least one of claims 13 or 14, characterized in that the tube field has lanes for distributing the melt.

16. Tower reactor according to at least one of claims 13 to 15, characterized in that the tubes have a cold-rolled, drawn surface "m" according to EN ISO 1127 with a surface roughness R _a = 0.4 to 0.6 or R _t = 4 to 6 µm.

17. Tower reactor according to at least one of claims 13 to 16, characterized in that the tube sheets (9) are designed in the form of a spherical cap.

18. Tower reactor according to at least one of claims 13 to 17, characterized in that the length of the tubes of the falling film zone is dimensioned and the inner surfaces have a structure that total wetting takes place depending on the product viscosity (L: D> 10 <25 ).

19. Tower reactor according to at least one of claims 13 to 18, characterized in that the diameter of the tubes of the falling film zone is chosen to be larger than the largest reaction vapor bubble that occurs and that the reaction vapors are conducted in cocurrent with the downward flowing product.

20. Tower reactor according to at least one of claims 1 to 19, characterized in that the door reactor has submersed feeds for the reaction gases and / or foreign gas from reaction cup to reaction cup for passage in cocurrent through the reaction liquid, with a pressure drop between each cup.

21. Tower reactor according to at least one of claims 1 to 20, characterized in that the entire tower reactor is equipped with a jacket for heating with organic heating medium in vapor form.

22. Tower reactor according to at least one of claims 1 to 21, characterized in that all heat exchange surfaces in the individual zones are equipped for liquid heat transfer media for process-relevant temperature and heat quantity distribution.

23. Tower reactor according to at least one of claims 1 to 22, characterized in that the tower reactor has a plate-bottom valve (3) with a flow-defining shape, with which the raw materials are supplied centrally from below.

24. Tower reactor according to at least one of claims 1 to 23, characterized in that the heat exchanger (5) static mixing elements for improved mixing of the raw mixture into the reaction mixture.

25. Tower reactor according to at least one of the preceding claims, characterized in that the heat exchanger (5) has a three-dimensional static mixing element for generating diagonal cross currents with simultaneous axial flow.

26. Tower reactor according to claim 25, characterized in that the three-dimensional static mixing element has crosswise and diagonally executed sheet metal sections with supporting and holding frames in the direction of flow.

27. Tower reactor according to claim 26, characterized in that the sheet metal sections are perforated, wave-like and / or folded, i.e. are pleated.

28. Tower reactor according to at least one of claims 1 to 27, characterized in that the heat exchanger (5) has a boiler room and a product room and at least one separating device for the horizontal separation of the boiler room and product room, the height of the separating device being at least the diameter of the Corresponds to heat exchanger tubes and the separate heat exchanger areas have a rotated offset which corresponds at most to the diameter of the heat exchanger tubes.

29. Tower reactor according to claim 28, characterized in that the individual separate heat exchanger areas have a different pipe pitch.

30. Tower reactor according to at least one of claims 1 to 29, characterized in that the vapor spaces are coated to reduce adhesion.

31. Use of the device according to at least one of claims 1 to 30 for the continuous production of high molecular weight polyesters by esterification of dicarboxylic acids and / or transesterification of dicarboxylic acid esters with diols in the presence of catalysts to form a prepolymer and its polycondensation to form the high molecular weight polyester.