HK1064327A - Device for carrying out material exchange processes - Google Patents

Description

Apparatus for carrying out mass exchange processes

Technical Field

The invention relates to an industrial plant for carrying out mass exchange processes in high-viscosity liquids, in particular for concentrating and/or degassing polymer melts. The apparatus is based primarily on a vertically disposed container in which the high viscosity liquid to be treated is divided into a plurality of separate streams which flow under gravity into a liquid bath in the container.

Background

An important method of mass exchange for liquids is concentration and degassing of solutions, suspensions or melts. In particular, in the production of polymeric plastics, the problem arises that low molecular weight substances such as water or monomers are separated from the plastic melt, since these substances adversely affect the product quality or are even toxic.

For concentrating the polymer melt, according to the prior art, thin-film evaporators are frequently used, as described in documents DE3310676a1, DE4328013a1 and US 3630689. Disadvantages of such a device are the high investment costs and in particular the wear of the rotating parts of such a device.

Strand evaporators are also known, in which the polymer melt is divided in a vertically secured container by means of a nozzle plate into a plurality of individual strands or filaments which are separated in the free state and run parallel to one another from the top downwards through the container and converge again at the bottom of the container. Specifically, the polymer melt is divided on the top of the container into strands which taper gravitationally in the free state and which dip into the melt pool at the bottom of the container. Such devices are described in US2719776, US5024728 and US 4934433. The main disadvantage of the described devices is that they are only suitable for liquids which form filaments after leaving the nozzle plate as in the spinning process. A further disadvantage is that a longer residence time in the degassing chamber can only be achieved by means of a long descent path and a correspondingly large installation height.

In addition, document CA2168630 describes a process for the manufacture of polycarbonate, in which a mixture of monomers and prepolymers is dispersed onto a plurality of filaments arranged vertically in a reactor, the liquid mixture flowing down the filaments and simultaneously completing the polymerization. Specifically, the polymerization takes place in a thin stream of liquid surrounding the filaments; that is, a defined polymerization zone is formed in the reactor by means of vertically tensioned wires. This document does not mention polymer solutions which are finished by degassing.

Disclosure of Invention

The object of the invention is to develop an industrial plant for mass-exchange processes which ensures that the product remains in the gas space for a long time and for as short a residence time as possible, which is also suitable for high-viscosity liquids, wherein the formation of converging strands or threads as a result of foaming or bubble formation is disturbed or prevented.

This object is achieved, based on the above-described apparatus with a vertically disposed container, in that on the liquid supply devices in the container, parallel to the vertical plane, side-by-side wire loops are arranged, and on the top end of the container, at least one liquid supply device is arranged in each case for supplying a partial flow, which flows away downwards along the wire loops. Here, "parallel to the vertical plane" means that the plane of the wire loop coincides with the vertical plane, but a slight deviation is completely allowed. In the case of highly viscous, non-foaming liquids, the partial flow flowing off through the wire loop forms a liquid layer, whereas in the case of foaming liquids it forms a thin layer which extends partially or completely over the plane of the wire loop. In both cases, the flow boundary is defined by a wire loop and the flow is directed. On the top of the wire loop, liquid is continuously fed. On the bottom end, it drips again. The wire loop functions to stabilize and hold the thin liquid or thin layer in a flowing state, where a large number of phase interfaces have been provided for material exchange.

The invention relates to a device for carrying out mass transfer processes in high-viscosity liquids, in particular for concentrating and/or degassing polymer melts, comprising at least one vertically arranged container having a supply device for supplying the liquid to be treated, an outlet for volatile components and an outlet for the treated liquid, wherein the supply device has a distributor element having a plurality of openings for dividing the high-viscosity liquid to be treated into a plurality of individual streams, wherein a substantially vertically arranged thread loop is arranged in the region of the openings, over which the high-viscosity liquid flows away under the action of gravity.

The wire loops may have different shapes, such as square, rectangular or triangular. The wire loops are preferably bent from a steel wire having a thickness of 0.5mm-6mm and preferably a length (height) of 0.5mm-4mm depending on the field of application.

In a preferred apparatus, the distribution member is a perforated plate.

According to one variant, the dispensing element preferably comprises at least one horizontally arranged tube with downwardly and/or upwardly directed (i.e. counter to the liquid flow) openings for the outflow of the high-viscosity liquid.

For better cleaning, the wire loop is preferably releasably placed in the opening area of the dispenser.

Such a device is particularly advantageous in which one of the distribution members is formed by at least one horizontally arranged tube with an upwardly facing slot-shaped opening.

It is particularly preferred that these distribution pipes have an internal diameter of 10mm to 100 mm. The width of the slit of the opening is particularly preferably from 0.2mm to 10mm, and the length of the slit is particularly preferably from 10mm to 100 mm.

Another preferred variant of the device also allows for easy clarity, wherein the dispensing element comprises at least one horizontally arranged tube with slit-shaped openings facing upwards, in which the wire loops are suspended.

Such a device is particularly preferred, wherein two, three or more wire loops are each composed of a grid or wire mesh resembling a basket.

A particular advantage is achieved if, in a preferred embodiment of the device, more than two adjacent grids or wire meshes are connected to one another.

In order to increase the stability asynchronously, in a particularly preferred embodiment of the device, the wire loop can also be fixed on the container bottom.

In a preferred embodiment, the wire loop can be heated, in particular by means of a resistive heating device.

A further preferred variant of the apparatus is characterized in that the distributor is formed by a plurality of heat exchange tubes with openings, which heat exchange tubes are arranged vertically in and open into the vessel, and in that the wire loops are fixed to the bottom ends of the heat exchange tubes.

The area enclosed by a wire loop is preferably 0.5cm²-2500cm²。

A further preferred embodiment of the device is characterized in that the wire loop tapers in the direction of the liquid flow and ends in particular at an acute angle at the bottom end.

In order to achieve a better heat exchange, in a special embodiment of the invention, the container is designed to be heatable and/or coolable, and it has in particular an outer casing for electrical heating or for the circulation of a heat transfer medium.

Another alternative of the invention is that the wire loop is not fixed to a distribution tube, a distribution plate or a heat exchange tube as described above, but is placed on the bottom of the vessel by means of a suitable bracket, but the wire loop leads to the opening of the distribution tube, distribution plate or vertical heat exchange tube.

By means of the invention the following advantages are obtained compared to the devices known from the prior art.

The product can be allowed to stay in the gas space for a considerably longer time than in strand evaporators.

Furthermore, by a suitable choice of the geometry (in particular the length and the area) of the wire loops, the residence times can be varied within wide limits and the process requirements can be met.

Document CA2168630 describes vertically arranged wires for extending the residence time of the product in the reactor. Here, one thread is assigned to more than one product outlet. The product flows down over the vertical wires under the force of driving gravity. The sticking of the product to the surface of the wire causes shear stresses, especially in the case of high viscosity products, which are in the opposite direction to the direction of gravity. In this way, the mean residence time of the product can be extended compared to a free falling strand (as in strand evaporators).

The inventive device using wire loops or a wire web formed by connecting wire loops, which are not necessarily vertically continuous, locally or wholly, has the advantage over reactor devices using vertical filaments.

More than one vertical thread segment receives the product, such an arrangement making the distribution of the product on the thread more uniform by laminar flow effects.

Different product inlets wet the loop with product, due to the tapering of the loop (the downward facing wire is not exactly vertical). In this way, a significant homogenization is achieved when the feed is pulsed through a number of openings (in any case, the product feed is generally kept constant by a preceding pump).

By the preferred cross-wire connection (transverse to the force of gravity), an additional flow resistance for the product occurs (referred to as resistance value Cw or pressure loss value Cd). In particular, a grid which is tensioned transversely to the flow direction and has a certain packing density brings advantages with regard to the residence time which can be adjusted to the filament surface and the homogenization described.

The wire grids in the transverse direction of the product inlet flow can also be used in a multi-layer overlapping manner, thereby creating a high degree of flexibility in the design of the desired flow resistance. In the case of high-viscosity products, the grid is mostly coarse-meshed. However, the grid is also effective for low viscosity liquids, if the envelope density of the wire is low, the beam stream impinging on the screen surface in a pause vertically expands and leaves the screen surface with an almost constant throughput.

The interconnection of the wire loops (bars) additionally results in a considerably higher mechanical stability compared to devices using simply suspended wires.

A device is therefore preferred which is characterized in that below the opening there are also provided one or more wire grids arranged substantially horizontally and vertically.

A small residence time range is obtained due to the prescribed laminar flow of the high-viscosity medium in the wire loop. This means that all liquid volumes in the apparatus will undergo the same thermodynamic process. This has a higher consistency of product quality, especially for heat sensitive products.

Compared to the known devices, a large phase interface has been provided for the mass exchange in the gas space.

The apparatus of the invention is suitable for degassing foamed and non-foamed polymers. In the case of degassing foamed polymers, the advantages of film degassing are combined with those of foam degassing in terms of degassing efficiency.

The total surface area of the wire loops made of metal is small and thus the risk of the product being damaged by undesired chemical reactions on the metal surface, such as cracking processes, is greatly reduced.

The apparatus for realizing the apparatus according to the invention is less expensive than the known apparatus.

The main field of application of the invention is, as mentioned above, the concentration and degassing of high-viscosity polymer melts and in particular polymer melts with a viscosity of 0.01pa.s to 40000pa.s, but also well-defined chemical and concentration reactions between the liquid layer in the wire loop and the surrounding gas space containing the reaction gas components.

A further subject matter of the present invention is therefore the use of a device according to the invention for concentrating and degassing highly viscous liquids and in particular for concentrating and/or degassing polymer solutions or melts thereof, and particularly preferably polycarbonate solutions or melts thereof, and the use of such a device for carrying out chemical reactions and in particular concentration reactions between a liquid layer in a wire loop and an ambient gas space containing reactive gas components.

Drawings

The invention is described in detail below, by way of example, but not by way of limitation, with reference to the accompanying drawings, in which:

figure 1 shows a principle design of a material exchange device by means of a wire loop,

figure 2 shows a dispensing tube with liquid openings and a wire loop belonging to the opening,

figures 3a, 3b show the arrangement of the wire loops at the nozzle plate in longitudinal section (figure 3a) and in cross-section (figure 3b),

fig. 4a, 4b show in longitudinal section (fig. 4a) and in cross-section (fig. 4b) the arrangement of wire loops on vertically arranged heat exchange tubes, each tube being provided with a wire loop,

FIGS. 5a and 5b show, in longitudinal section (FIG. 5a) and in cross-section (FIG. 5b), the arrangement of wire loops on vertically disposed heat exchange tubes, one wire loop for each two adjacent heat exchange tubes,

figures 6a-6c show different embodiments of basket structures consisting of wire loops,

fig. 7 shows the arrangement of wire loops on a vertically arranged heat exchange tube, wherein the wire loops constitute a wire web,

figure 8 shows an arrangement of two additionally arranged horizontal grate bars,

fig. 9 shows the arrangement of wire loops on a vertically disposed heat exchange tube, wherein the wire loop ends are connected away from the opening,

figure 10a shows the structure of figure 9 from below,

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

Detailed Description

Example 1

According to fig. 1, in a vertically disposed degassing container 1, four wire loops 2 are provided, which likewise extend in the vertical direction. The thread loop 2 is fixed to a horizontally extending, here tubular, dispensing element 3. The dispensing member 3 is connected to a supply device 4. The degassed product is removed at the reservoir 5 of the container 1 by means of a gear pump 6. The residual steam produced during degassing is removed via the pipe connection 7. By means of the pipe connection 7, a predetermined reduced pressure can be set in the container 1. The container 1 may be heated by an electric heating device (not shown).

Fig. 2 shows how the wire loop 2 is fixed to the dispensing tube 3. They are suspended over a slit-shaped opening 8 provided over the upper half of the dispensing tube 3 in such a way that the slit-shaped opening 8 extends over the entire width of the wire loop in the longitudinal direction, so that the wire loop receives the liquid product to be degassed over its entire width. The slot-shaped openings 8 are directed upwards in a semicircular manner, so that the liquid product can flow around the tubes 3 and the tube surfaces are flushed with the liquid product. The advantage of this arrangement is that the liquid product residence time is extended. The liquid product residence time can be further extended by increasing the tube diameter. At the same time, the pressure gradient in the tube is thereby reduced and the flow through the slit-shaped opening 8 is thus homogenized. The inner diameter of the tube 3 is 16 mm. The slot width is for example 3mm, while the slot length is approximately 27 mm. At the bottom end above the liquid pool, the wire rings 2 are tapered. In one variant, the tips of adjacent loops 2 are connected by a soldered wire 13.

Example 2

In another evaporator configuration (top and side view) as shown in fig. 3, the distribution member for the incoming liquid product consists of a nozzle plate 9 with openings 10. The wire loop 2 is fixed, e.g. soldered or welded, on the bottom side of the nozzle plate 9. The liquid product is fed through a feed pipe 11 which covers the entire cross-section of the nozzle plate 9. The supply pipe 11 can also be designed in the form of a heat exchanger pipe.

Example 3

The distribution member as described in examples 1 and 2 can also be designed in this way. As shown in fig. 4, 5, the liquid product is sent to the wire loop 12 through heat exchange tubes 12 arranged vertically inside the vessel 1. In the embodiment shown in fig. 4, the wire loops 12 are respectively arranged at the heat exchange tube 12 outlets, i.e. in this case the heat exchange tubes directly serve as supports for the wire loops 2. For greater stability, at its bottom end, the loops 2 are connected in a grid-like manner by transverse bars 13 (see top view). In contrast, in the variant embodiment shown in fig. 5, the thread loops 2 are arranged on two adjacent heat exchange tubes 12, respectively, so that liquid is fed into one thread loop 2 by two liquid feed mechanisms, respectively. In this embodiment, the sharply narrowed loop ends are connected by a cross-bar 13.

In all the examples described above, the wire loop 2 is bent from a 1.5mm thick steel wire and it is 1.5 meters long. As shown, a triangle-like shape, wherein the triangle apex is located at the base end, has proven particularly advantageous; i.e. the wire loop tapers from top to bottom in the direction of liquid flow. According to the variant shown in fig. 6a-6c and fig. 7, the wire loop 2 can also be formed in such a way that a plurality of wire loops are grouped into a basket structure 14 (fig. 6a-6c) or a grate structure (fig. 7), which enclose a half space. Wire meshes can also be used to create such spatial structures.

In operation, the mass flow (metering) of the liquid product supplied to the apparatus is regulated in such a way that a defined laminar flow is formed in the region enclosed by a wire loop (wire loop plane). The liquid product fed on the top end through the openings 8, 10 in the distribution member or through the separate tube 12 is evenly distributed onto the plane of the wire loop. Here, the steel wire acts as a boundary and as a flow guide in the flow. It goes without saying that in the basket structure shown in fig. 6a-6c, the liquid product fills only the meshes and does not fill the inner space of the basket structure or the grate structure.

At the bottom end of the wire loop, the degassed liquid product is dropped into a liquid sump at the bottom of the vessel. Surprisingly, even in the case of foamed polymer melts, such laminar flows (laminar flows) form, whereby the technical prerequisites for a combined mode of laminar degassing and foaming degassing are established, whereby a very high degassing efficiency is obtained. The foaming of the polymer melt in the degassing vessel can be achieved in particular in that the total pressure in the vessel is reduced to a pressure which is less than the vapor pressure of the volatile constituents to be removed from the polymer. A further possibility for foaming and improving the degassing consists in adding an entraining agent to the polymer before it enters the vessel, the entraining agent being dispersed into the melt, for example by means of a static mixer.

Example 4

Fig. 9, 10a and 10b show another construction of the evaporator in which vertical heat exchange tubes 12 further apart from each other are connected at their openings to the ends of wire loops. Thus, in the polymer treatment, the liquid flow is further evaporated in the evaporator and the flux fluctuations are compensated.

If two further bars 15 are provided below the wire loop 2, as shown in fig. 8, the flow can be further homogenized. The wire grid 15, when bent approximately towards the centre as shown, also allows to direct the product flow to a position immediately above the product outlet 6.

Claims (17)

1. Device for carrying out mass transfer processes in high-viscosity liquids, in particular for concentrating and/or degassing polymer melts, comprising at least one vertically positioned container (1), which container (1) has a supply device (4) for supplying the liquid to be treated, an outlet (7) for volatile constituents and an outlet (6) for the treated liquid, wherein the supply device (4) is provided with a distributor element (3) having a plurality of openings (8, 10) for dividing the high-viscosity liquid to be treated into a plurality of individual streams, characterized in that in the region of the openings (8, 10) a substantially vertically arranged thread loop (2) is arranged, over which the high-viscosity liquid flows away under the influence of gravity.

2. The apparatus of claim 1, wherein the dispensing member is a perforated plate.

3. The apparatus as claimed in claim 1 or 2, characterized in that the distribution member (3) comprises at least one horizontally arranged tube (3), which tube (3) has a downwardly and/or upwardly directed opening (8).

4. Device according to one of claims 1 to 3, characterized in that the loop (2) of the thread is detachably arranged in the region of the opening (8, 10) of the dispensing element (3, 9).

5. The apparatus as claimed in claim 3 or 4, characterised in that the distribution member comprises at least one horizontally arranged tube (3) with an upwardly directed slot-shaped opening (8).

6. Device according to claim 5, characterized in that the distribution member comprises at least one horizontally arranged tube (3) with upwardly facing slot-shaped 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 connected like a basket grid (14) or a wire mesh, respectively.

8. Device according to claim 7, characterized in that more than two adjacent grids (14) or wire meshes are connected.

9. Device according to one of claims 1 to 8, characterized in that the thread loop (2) is also fixed to the bottom of the container.

10. Device as claimed in one of the claims 1 to 9, characterized in that the wire loop can be heated, in particular by means of a resistive heating means.

11. The apparatus as claimed in one of claims 1 to 10, characterized in that the distribution member (3, 9) is formed by a plurality of heat exchange tubes (12) with openings (8), which heat exchange tubes (12) are arranged vertically in the vessel (1) and open into the vessel (1), the wire loops (2) being fixed to the bottom ends of said heat exchange tubes.

12. The apparatus of any of claims 1 to 11, wherein the area enclosed by a loop is 0.5cm²-2500cm²。

13. Device according to one of claims 1 to 12, characterized in that the wire loop (2) tapers in the direction of the liquid flow and ends in particular at an acute angle at the bottom end.

14. Device according to one of claims 1 to 13, characterized in that the container (1) is designed to be heatable and/or coolable, and in particular has an outer casing for electrical heating or for the circulation of a heat transfer medium.

15. Device according to one of claims 1 to 14, characterized in that the upper ends of the wire loops (2) are placed on different openings (8, 10) and in particular on openings that are distant without close proximity.

16. Device according to one of claims 1 to 15, characterized in that below the openings (8, 10) one or more wire meshes (15) are additionally provided, which are arranged essentially horizontally one above the other.

17. Use of a device according to one of claims 1 to 16 for the concentration and degassing of high-viscosity liquids, in particular for the concentration and/or degassing of polymer solutions or melts thereof, and particularly preferably polycarbonate solutions or melts thereof, and for carrying out chemical reactions, in particular concentration reactions, between a liquid layer in a wire loop and a surrounding gas space containing reactive gas components.