DE10144233A1 - Device for carrying out mass transfer processes - Google Patents

Abstract

The invention relates to a device for carrying out mass transfer processes in the case of highly viscous liquids, in particular for evaporating and / or degassing polymer melts, comprising at least one vertically standing container (1) with a feed (4) for the liquid to be treated, an outlet (7) for volatile components and an outlet (6) for the treated liquid, the feed (4) having a distributor element (3) with a multiplicity of openings (8, 10) for dividing the highly viscous liquid to be treated into a plurality of individual streams, characterized in that in the area of the openings (8, 10) substantially vertically arranged wire loops (2) are attached, on which the highly viscous liquid flows away under the action of gravity.

Description

The invention relates to a process engineering apparatus for performing Mass transfer processes for highly viscous liquids, especially for one vaporization and degassing of polymer melts. The apparatus is essentially based on a vertical container, in which the highly viscous to be treated Liquid is divided into a large number of individual streams, under the action gravity flow into the sump of the container.

Evaporation and removal are important processes for the exchange of substances in liquids gases from solutions, dispersions or melts. Especially with the manufacturer development of polymeric plastics, the problem occurs, low molecular weight substances such. B. Separate water or monomers from the plastic melt, as such substances have an adverse impact on product quality or e.g. T. even toxic are.

For the evaporation of polymer melts are often used in the prior art fig thin film evaporator used, as described in the documents DE 33 10 676 A1, DE 43 28 013 A1 and US 3 630 689 are described. The disadvantages of such Machines are in the relatively high investment costs and especially in ver wear of rotating parts of such machines.

Also known are strand evaporators in which the polymer melt is in one vertically standing container in a variety of A by means of a perforated nozzle plate individual strands or threads are divided, which in free fall are separated and parallel to each other flow through the container from top to bottom and again at the bottom of the container be brought together. The polymer melt is in at the head of the container Separated strands that taper in free fall under the influence of gravity and immerse in the melt sump at the bottom of the container. Such apparatus are described in patents US 2,719,776, US 5,024,728 and US 4,934,433  ben. A fundamental disadvantage of the apparatus described is that these are only suitable for liquids that are similar after exiting the nozzle plate form long threads independently as in a spinning process. Another disadvantage is that a longer residence time in the degassing room can only be achieved with the help of a very long drop distance and correspondingly large apparatus height can.

Furthermore, CA 2 168 630 describes a process for the production of poly carbonate described in which a mixture of monomers and prepolymer distributed a plurality of individual wires arranged vertically in a reactor along which the liquid mixture runs down and out polymerized. The polymerization therefore takes place in a thin, enveloping the wire the fluid line instead; d. H. through the vertically stretched wires in Reactor defined a defined polymerization zone. Via the degassing machine Polymer solutions do not describe anything in the document.

The invention has for its object a process engineering apparatus for To develop mass transfer processes that have a long product retention time in the gas space guaranteed while maintaining the narrowest possible residence time spectrum and is also suitable for highly viscous liquids in which the formation of coherent strands or threads through foam or bubble formation is disturbed or prevented.

This task is based on the device described at the beginning a vertically standing container, according to the invention solved in that the Liquid supply in the container essentially parallel to the vertical plane wire loops are arranged side by side, at the upper end of each min at least a liquid supply is provided for feeding a partial flow, that flows down along the wire loop. "Parallel to the vertical plane" means in this case that the wire loop plane coincides with the vertical plane, however, slight deviations can easily be tolerated. The  In the case of a highly viscous, partial stream flowing off via the wire loop forms non-foaming liquid a liquid lamella and in the case of a foaming liquid a thin layer that is partially or entirely over the wire extends loop level. In both cases, the fluid from the wire loop limited and managed. The liquid becomes continuous at the upper end of the wire loop fed slowly. At the lower end it drips again. The wire loop causes the thin liquid layer or lamella to flow when flowing is bilized and maintained, with large phase interfaces for the substance exchange will be provided.

The invention relates to a device for carrying out material Exchange processes for highly viscous liquids, especially for evaporation and / or degassing polymer melts, consisting of at least one vertically standing container with a feed for the liquid to be treated, a Outlet for volatile components and an outlet for the treated liquid speed, the supply with a distributor element with a large number of openings Solutions for dividing the highly viscous liquid to be treated into one Large number of individual streams, characterized in that in the area of the public openings are arranged substantially vertically arranged wire loops which the highly viscous liquid drains away under the effect of gravity.

The wire loops can have a different geometry, e.g. B. squares, Form rectangles or triangles as a shape. The wire loops are preferably made of a 0.5 to 6 mm thick steel wire and bent depending on the application preferably offers a length (height) of 0.5 to 4 m.

In a preferred device, the distributor member is a perforated plate.

According to one variant, the distributor member preferably has at least one hori zonally arranged pipe which is directed downwards and / or upwards (i.e. counter to the  Flow direction of the liquid) directed openings for the exit of the highly viscous liquid.

The wire loops are preferably for improved cleaning in the area of the Openings in the distributor element are detachably attached.

A device in which the distributor element consists of at least one device is particularly advantageous a horizontally arranged tube, the slit-shaped, upward has openings.

The distribution pipes particularly preferably have an inside diameter of 10-100 mm. The slot width of the openings is particularly preferably 0.2-10 mm and the slot length is particularly preferably 10-100 mm.

Another preferred variant of the device can also be cleaned more easily, in which the distributor element consists of at least one horizontally arranged tube exists, the slot-shaped, upward openings into which the Wire loops are attached.

A device is particularly preferred in which two, three or more of each Wire loops combined into a basket-like grid or wire mesh are.

There are also particular advantages if, in a preferred embodiment, the Device two or more adjacent grids or wire mesh with each other are connected.

To further increase the stability, in a particularly preferred embodiment tion of the device, the wire loops must also be attached to the bottom of the container.  

In a preferred embodiment, the wire loops can be, in particular, by means of electrical resistance heating, be heated.

Another preferred variant of the device is characterized in that the distribution organs from vertically arranged in the container, into the container Ending the heat exchanger tubes are formed with openings at the lower end the wire loops are attached.

The area enclosed by a wire loop is preferably 0.5 cm ² to 2500 cm ² .

Another preferred embodiment of the device is characterized in that that the wire loops taper in the direction of flow of the liquid and especially in particular, terminate it at an acute angle at its lower end.

For the purpose of improved heat exchange is in a special training the device of the container can be heated and / or cooled. In particular the container has a casing for an electric heater or for the Passage of a heat transfer medium.

Another alternative of the invention is that the wire loops are not on a distributor pipe or a distributor plate or on the heat exchanger pipes be attached as described above, but by means of an appropriate holder tion on the bottom of the tank are attached to the openings of the distribution pipes or distributor plate or the vertical heat exchanger tubes.

With the invention, the advantages shown below compared to devices known from the prior art are achieved:
Compared to a strand evaporator, considerably longer product retention times can be achieved in the gas space.

By choosing the geometry of the wire loops (especially length and area!) the residence time can also vary within wide limits and depending on the process fish requirements are adjusted.

CA 2 168 630 describes vertically arranged wires for extension described the product residence time in a reactor. A wire is one or assigned to several product outlets. By driving gravity the product runs down on the vertical wires. Through product liability Shear stresses develop on the wire surface, particularly in the case of highly viscous ones Counteract products of gravity. This means that the average product ver because of the length of time compared to the freely falling thread (as with the strand evaporator) become.

Compared to the reactor device with a simple vertical wire, the device according to the invention has a wire loop or wire mesh, which, for. B. results from partial or complete connections of the wire loops that are not necessarily strictly vertical throughout, various advantages:
The wire loops are often loaded with a polymer foam that does not enter the degassing tank evenly; rather, the individual product openings are subject to fluctuations in throughput. A vertical wire can barely absorb these product pulsations, which means that the product quality at the discharge also fluctuates considerably. A simple wire loop smoothes out these fluctuations in several ways. Furthermore, the product retention time distribution and the average product retention time can be set much more flexibly. The advantages are:

• - By an arrangement in which more than one vertical wire section is a pro product supply, the product flow on the wires becomes even the lamella effect.  
• - By tapering the wire loops (the wires pointing down are not exactly aligned vertically) different product entry openings Wet a wire loop with product. This results in a Significant equalization with pulsating feed from the individual openings (The product supply is usually integral through an upstream pump constant).
• - Through the preferred cross connections of the wires (across the gravity) creates additional flow resistance for the product (known as Resistance coefficient Cw or pressure loss coefficient Cd). In particular through a Grid stretched across the flow direction with a certain Packing density results in advantages with regard to adjustable product retention time related to the wire surface and the described equalization.

Wire mesh across the product flow can also be stacked in several layers can be used horizontally several times, which gives a high degree of flexibility the desired flow resistance results. For highly viscous products the grid can usually be coarse-meshed. However, the grille also works with niedervis free liquids when the packing density of the wires is tight: a bundled one The beam that intermittently strikes a sieve surface becomes spatial expanded and leave the screen area with approximately constant throughput.

The networking of the wire loops with one another (grid) results in counter over the known device with simple hanging wires also one much higher mechanical stability.

A device which is characterized in that underneath the openings one or more one above the other essentially horizontally arranged wire mesh are provided.  

Also preferred is a variant of the device in which the upper ends the wire loops on different ones, especially on distant ones, not directly side by side openings are attached.

Due to the defined layer flow of highly viscous media into the wire a narrow dwell time range is achieved. This means everyone Liquid volume elements in the apparatus are approximately the same thermodynamic go through mixing process. This has a higher uniformity in the product quality, especially of thermally sensitive products.

For the mass transfer in the gas space compared to the known devices provided a large phase interface.

The apparatus according to the invention is for the degassing of both foaming and of non-foaming polymers. When degassing foaming Polymers can take advantage of a thin in terms of degassing effectiveness layer degassing can be combined with the advantages of foam degassing.

The total surface of the metal wire loops is comparative low, so the risk of product damage from undesirable chemical Reactions on the metal surfaces (e.g. cracking processes) is greatly reduced.

The outlay on equipment for realizing the devices according to the invention is comparatively less compared to the known devices.

As already described, the main fields of application of the invention are evaporation fung and the degassing of highly viscous polymer melts, especially in one Viscosity range from 0.01-40000 Pa.s, but also targeted chemical reactions between the layer of liquid in the wire loop and the surrounding gas space containing a reactive gas component and condensation reactions.  

Another object of the invention is therefore the use of the invention device for evaporating and degassing highly viscous liquids, especially for evaporation and / or degassing of polymer solutions or - melt, particularly preferably of polycarbonate solutions or melts, and the use to carry out chemical reactions between the liquid layer in the wire loop and the surrounding gas space, which is a reactive Contains gas component, as well as for condensation reactions.

The invention is explained below with reference to the figures by the examples which however, do not constitute a limitation of the invention, explained further.

Show it:

Fig. 1 shows the basic design of a mass transfer apparatus with built-in wire loops

Fig. 2 is a manifold with liquid openings and the openings assigned wire loops

Fig. 3a, b the arrangement of the wire loops on a nozzle plate in longitudinal section (Fig. 3a) and cross section (Fig. 3b)

Fig. 4a, b an arrangement of wire loops in longitudinal section ( Fig. 4a) and cross section ( Fig. 4b) on vertically standing heat exchanger tubes, each wire being assigned a wire loop

Fig. 5a, b an arrangement of wire loops in longitudinal section ( Fig. 5a) and cross section ( Fig. 5b) on vertically standing heat exchanger tubes, with two adjacent heat exchanger tubes being assigned a wire loop

FIGS. 6a-6c show different embodiments of loops formed from wire basket-like structures

Fig. 7 shows an arrangement of wire loops on vertical heat exchanger tubes, the wire loops forming a wire mesh

Fig. 8 shows an arrangement of two additionally attached horizontal grids

Fig. 9 shows an arrangement of wire loops on vertically standing heat exchanger tubes, wherein the ends of the wire loops connect remote openings

Schematically seen Fig. 10a, the arrangement of FIG. 9 Angle

Fig. 10b shows an enlarged detail of Fig. 10a.

Examples example 1

Referring to FIG. 1 are located precisely if arranged vertically extending wire loops 2 in a vertically standing degassing tank 1 four. The wire loops 2 are attached to a horizontally extending distributor member 3 , which is designed here as a tube. The distributor pipe 3 is connected to a product feed 4 . The degassed product is discharged at the sump 5 of the container 1 using a gear pump 6 . The vapors formed during the degassing are drawn off through the nozzle 7 . About the nozzle 7 can be set in the container 1 before a given reduced pressure. The container 1 can be heated with electrical heating (not shown).

From Fig. 2 it can be seen how the wire loops 2 are attached to the manifold 3 . They are suspended in slot-shaped openings 8 attached to the upper half of the distributor pipe 3 in such a way that the slot-shaped opening 8 extends in the longitudinal direction over the entire width of the wire loop, so that the wire loop strikes with a product liquid to be degassed over its full width becomes. The slots 8 are oriented in a semicircular shape so that the product liquid can flow around the pipes 3 and the pipe surfaces are washed by the product. An advantage of this arrangement is that the residence time of the product liquid is increased. A further increase in the residence time of the product liquid can be achieved by increasing the pipe diameter. At the same time, the pressure gradient in the tube is thereby reduced and the throughput in the slot-shaped openings 8 is thus more uniform. The tubes 3 have an inner diameter of 16 mm. The slot width is z. B. 3 mm and the slot length about 27 mm. The wire loops 2 taper to a point at their lower ends above the swamp. In one variant, the pointed ends of adjacent wire loops 2 are connected to one another by a welded-on wire 13 .

Example 2

In another evaporator arrangement according to FIG. 3 (side view and top view), the distributor element for supplying the product liquid consists of a nozzle plate 9 with openings 10 . The wire loops 2 are attached to the underside of the nozzle plate 9 , e.g. B. welded or soldered. The product liquid is supplied via a feed line 11 covering the entire cross section of the nozzle plate 9 . The feed line 11 can also be designed as a heat exchanger tube.

Example 3

The distributor member as in Examples 1 and 2 can also be formed in the following manner. As shown in Fig. 4 and 5, the product liquid of a wire loop 2 is fed by vertically in the container 1 disposed heat exchanger tubes 12. In the embodiment according to FIG. 4, the wire loops 2 are each attached to the outlet of the heat exchanger tubes 12 ; ie in this case the heat exchanger tubes serve directly as a holder for the wire loops 2 . At their lower end, the wire loops 2 are connected in a grid-like manner by transverse webs 13 for stability reasons (see also plan view). In the variant of the embodiment according to FIG. 5, on the other hand, the wire loops 2 are each attached to two adjacent heat exchanger tubes 12 , so that the liquid is fed into a wire loop 2 via two liquid feeds. In this embodiment, too, the pointed ends of the wire loops are interconnected by transverse webs 13 .

The wire loops 2 are bent from a 1.5 mm thick steel wire in all the examples mentioned above and have a length (height of the loop) of 1.5 m. As shown in the figures, a triangle-like shape has proven particularly useful, the apex of the triangle being at the lower end; ie the wire loop tapers from top to bottom in the direction of flow of the liquid. According to the variants shown in FIGS. 6a to 6c and FIG. 7, the wire loops 2 can also be designed such that several wire loops 2 form a basket structure 14 (FIGS . 6a to 6c) or lattice structure ( FIG. 7) are set, which includes a half space. Wire meshes can also be used to produce such spatial structures.

During operation, the volume flow of the product liquid supplied to the apparatus (metering) is set so that a defined layer flow forms in the area enclosed by a wire loop (wire loop level). The liquid supplied at the upper end through the openings 8 and 10 in the distributor element or through the individual tubes 12 is distributed evenly over the wire loops. The wire acts as a limitation and fluidic guide element. It goes without saying that the basket structures according to FIGS. 6a-6c, the liquid product only the loops and not the interior of the basket or grid structure filling.

At the lower end of the wire loop, the degassed product liquid drips into the Sump from the bottom of the tank. Surprisingly, this stratified flow forms (Film flow) even with a foaming polymer melt, so that the ver technical driving requirements for a combined film and show day Solution are given, whereby a particularly high degassing effectiveness is achieved. The foaming of the polymer melt in the degassing container can thereby be targeted achieved that the total pressure in the container is below the vapor pressure of the the polymer volatile component to be removed is lowered. Another Possibility of foaming and improving the degassing effectiveness is that the polymer entrainer before entering the container be added, the z. B. with the help of a static mixer in the melt be dispersed.  

Example 4

Figs. 9, 10a and 10b describe a different arrangement of the evaporator in the further away from each other, vertical heat exchanger tubes 12 at their voltages Publ with the ends of the wire loops are connected. This further attenuates the product flow within the evaporator during the treatment of polymers and flow pulsations are compensated.

If two additional grids 15 are attached below the wire loops 2 , as shown in FIG. 8, the product flow is further homogenized. In the grids 15 which are somewhat sagging towards the center, a certain guidance of the product flow to a point directly above the product discharge 6 is additionally made possible.

Claims (17)

1. Device for carrying out mass transfer processes in the case of highly viscous liquids, in particular for evaporating and / or degassing poly melt, consisting of at least one vertically standing container ( 1 ) with a feed ( 4 ) for the liquid to be treated, an outlet ( 7 ) for volatile components and an outlet ( 6 ) for the treated liquid, the feed ( 4 ) having a distributor element ( 3 ) with a large number of openings ( 8 , 10 ) for dividing the highly viscous liquid to be treated into a plurality of individual streams, characterized in that in the area of the openings ( 8 , 10 ) substantially vertically arranged wire loops ( 2 ) are attached, on which the highly viscous liquid flows away under the action of gravity. 2. Device according to claim 1, characterized in that the distributor organ is a perforated plate. 3. Device according to claim 1 or 2, characterized in that the United divider member ( 3 ) has at least one horizontally arranged tube ( 3 ) which has downward and / or upward openings ( 8 ). 4. Device according to one of claims 1 to 3, characterized in that the wire loops ( 2 ) in the region of the openings ( 8 , 10 ) in the distributor member ( 3 , 9 ) are detachably attached. 5. Apparatus according to claim 3 or 4, characterized in that the United divider organ consists of at least one horizontally arranged tube ( 3 ) which has slot-shaped, upward openings ( 8 ). 6. The device according to claim 5, characterized in that the distributor organ consists of at least one horizontally arranged tube ( 3 ) which has slot-shaped, upwardly directed openings ( 8 ) into which the wire loops ( 2 ) are suspended. 7. Device according to one of claims 1 to 6, characterized in that two, three or more of the wire loops ( 2 ) are combined to form a basket-like grid ( 14 ) or wire mesh. 8. The device according to claim 7, characterized in that two or more adjacent grids ( 14 ) or wire mesh are interconnected. 9. Device according to one of claims 1 to 8, characterized in that the wire loops ( 2 ) are additionally fastened to the container bottom. 10. Device according to one of claims 1 to 9, characterized in that the wire loops in particular by means of electrical resistance heating are heated. 11. Device according to one of claims 1 to 10, characterized in that the distributor elements (3, 9) are formed of arranged in the container (1) vertically in the container (1) opening out heat exchange tubes (12) having openings (8), at the lower end of the wire loops ( 2 ) are attached. 12. Device according to one of claims 1 to 11, characterized in that the area enclosed by a wire loop is 0.5 cm ² to 2500 cm ² . 13. Device according to one of claims 1 to 12, characterized in that the wire loops ( 2 ) taper in the direction of flow of the liquid and in particular at their lower end with an acute angle. 14. Device according to one of claims 1 to 13, characterized in that the container ( 1 ) is heatable and / or coolable, in particular has a casing for an electrical heater or for the passage of a heat transfer medium. 15. The device according to one of claims 1 to 14, characterized in that the upper ends of the wire loops ( 2 ) are attached to different, in particular at distant openings ( 8 , 10 ) which are not arranged directly next to one another. 16. Device according to one of claims 1 to 15, characterized in that below the openings ( 8 , 10 ) additionally one or more wire meshes ( 15 ) arranged one above the other essentially horizontally are provided. 17. Use of the device according to one of claims 1 to 16 for one vaping and degassing highly viscous liquids, especially for Evaporation and / or degassing of polymer solutions or melts, particularly preferred of polycarbonate solutions or melts and the Use to carry out chemical reactions between the liquid layer in the wire loop and the surrounding gas space, the one contains reactive gas component, as well as for condensation reactions.