HK1037559A - Device and method for removing volatile components from polymer solutions - Google Patents

Description

Apparatus and method for removing volatile components from polymer solutions

The present invention relates to an apparatus and a process for removing volatile components from polymer solutions, in particular for evaporating volatile components from polymer solutions by indirect heat exchange. The apparatus has at least one container having an inlet for the polymer solution and an outlet for the volatile components and an outlet for the polymer solution after removal of the volatile components, a heat exchanger having a plurality of channels forming a heat exchange zone, wherein the length of the channels is 1.0 to 40cm, the height thereof is constant over the entire length thereof is 1.3 to 13mm, the width of the channels in the inlet zone is 1 to 10cm, and wherein the width of the channels from the inlet to the outlet is at least doubled.

The removal of volatile components from polymer solutions is the last step in many polymer production processes. The volatile component to be removed may be a solvent or an unpolymerized monomer. Depending on the size of the viscosity of the polymer solution, many different methods are known for removing volatile constituents from polymer solutions, wherein the temperature of the polymer solution is always heated above the evaporation temperature of the volatile constituents by means of a heat exchanger. As drying equipment, for example, thin film evaporators, extruders and indirect heat exchange equipment are disclosed.

When heating the polymer solution, it is important not to subject the polymer to thermal damage.

European publication EP-A-150225 describes an apparatus which functions by means of ｃA two-row heat exchanger bank. The heat exchanger group is provided with a plurality of rectangular channels. This device is mainly used for secondary heating or cooling during the reaction, but it is relatively expensive.

EP-B-226204 discloses a process and a heat exchanger for removing volatile constituents from polymer solutions containing at least 25% by weight of polymer. The polymer solution is heated in an indirect heat exchange zone consisting of a plurality of channels. The ratio of the area to the volume of the channels is substantially uniform and ranges from 0.158 to 1.97mm-1, from 1.27 to 12.7mm in height, from 2.54 to 10.16cm in width and from 1.27 to 30.48cm in length. The polymer solution is heated in the channel at a pressure of 2-200 bar to a temperature above the evaporation temperature of the volatile components but below the boiling point of the polymer. The residence time of the polymer solution in the channel is from 5 to 120 seconds. After heating, the polymer solution is sent to a chamber where at least 25% of the volatile components are evaporated from the solution. The process reduces thermal damage by reducing the residence time of the polymer at high temperatures. However, this process has the disadvantage that it is not possible to completely remove the solvent at once. In addition, polymer deposits can form on the outside of the heat exchanger block and over time carbonize and crack, contaminating the polymer after solvent removal.

EP-B-352727 discloses a process for removing volatile constituents from polymer solutions, in which the polymer solution is heated above the evaporation temperature of the volatile constituents in a plurality of parallel-arranged channels. The ratio of the heat exchange area to the product volume flow is at most about 80m²/m³H. Flow velocity in the channel being maximum0.5mm/s, the residence time of the polymer solution in the channel being from 120 to 200 seconds. This method also has the disadvantage that it is impossible to completely remove the solvent at once. In addition, polymer deposits can form on the outside of the heat exchanger block and over time carbonize and crack, contaminating the polymer after solvent removal.

It is therefore the object of the present invention to provide an apparatus and a process for removing volatile constituents from polymer solutions which do not have the disadvantages of the prior art.

This task can be accomplished by the device of independent claim 1.

The subject of the invention is an apparatus for removing volatile constituents from polymer solutions, having at least one container with an inlet for the polymer solution, an outlet for the volatile constituents and an outlet for the polymer solution from which the volatile constituents have been removed, and a heat exchanger disposed inside the vessel, the heat exchanger having a central polymer solution receiving zone connected to the vessel inlet, a product zone for receiving the treated polymer solution, a heat exchanger body with a plurality of channels forming the heat exchange zone and connecting the receiving zone to the product zone, a heating means for heating the heat exchanger body and the channels, characterised in that the length of the channel is from 1.0 to 40cm, the height is constant from 1.3 to 13mm over its entire length, the width of the channel in the inlet zone is from 1 to 10cm, and wherein the width of the channel from the inlet to the outlet to the product zone is at least doubled.

The channel preferably has a rectangular cross-section, the width of the channel being three times as large at the outlet as at the inlet, wherein the enlargement of the channel is continuous, but can be performed according to any profile.

In a preferred embodiment, the channel expands in a parabolic shape.

It is also preferred that the width of the channel in the device is kept constant at least until half its length and then expands to at least twice the width, wherein the width is continuous but can follow any profile, in particular a non-linear curve. The shape of the channel can be adapted to the temperature, the width of the channel remaining constant in the region where the polymer solution is heated, and the width of the channel expanding only when the temperature of the polymer solution is higher than the evaporation temperature of the volatile component, so that the gas can escape from the solution well in the channel.

In a further embodiment, not only the width but also the height of the channel preferably widens towards the outlet.

The heat exchanger of the apparatus of the invention preferably has at least 100 such channels. It is particularly preferred to have 200 to 100000 channels in the heat exchanger.

In a preferred embodiment, the heat exchanger is cylindrical, so that the channel also surrounds the receiving region in cylindrical form. The outlets of the heat exchanger channels are preferably arranged such that the sides of the individual channels and/or their upper and lower sides are directly connected, so that no areas are present between the outlets of the channels where polymer material can be deposited. This applies both to the cylindrical configuration and to the other configurations that should be.

In another preferred embodiment of the apparatus, the heat exchanger body has a particular rectangular parallelepiped shape and is located below the receiving zone.

In a preferred arrangement the heat exchanger body is formed by a number of plates arranged in a plane one above the other or in parallel, wherein the plates in a plane are spaced apart from each other with a spacing forming with the side walls of the plane the width of the channel, and the thickness of the plates determines the height of the channel.

In a further preferred arrangement, the heat exchanger body is formed by a plurality of plates arranged in a planar manner one above the other or in parallel, which plates are separated from one another by spacer supports, wherein the spacing and the side faces of the spacer supports form the width of the channel, and the thickness of the spacer supports determines the height of the channel.

The device is preferably produced wholly or partially, in particular with parts which come into contact with the polymer, from an iron-depleted metal material which contains up to 10% by weight, preferably up to 5% by weight, of iron.

The iron-depleted material is preferably tantalum or an iron-depleted nickel alloy, in particular selected from: alloy59 (2.4605), inconel 686(2.4606), alloy-B2, alloy-B3, alloy-B4, nickel-based alloy C-22, nickel-based alloy-C276, nickel-based alloy-C4, and in particular alloy 59.

The heat exchanger has any heating means known to the skilled person for heating the channel above the evaporation temperature of the volatile components. Such as a resistance heater or a network of pipes for conveying a heat exchange fluid.

The channels in the heat exchanger body are preferably inclined over their entire length at an angle to the horizontal, so that the outlet is low and can be arranged in particular vertically. In this case, the receiving area is located above the channel.

The heating means of the heat exchanger are preferably constituted by a plurality of lines, arranged transversely to the channels by means of plates or plates, in which the heat exchange fluid circulates.

Another subject of the invention is a process for removing volatile constituents from a polymer solution containing at least 40% by weight of polymer, using the apparatus of the invention, wherein the process comprises:

A) the polymer solution is passed into a receiving zone at a pressure of from 1 to 100 bar absolute,

B) flowing the polymer solution in a channel of a heat exchanger and heating to a temperature above the evaporation temperature of the volatile components of the polymer solution but below the boiling point or decomposition temperature of the polymer, wherein the residence time of the polymer solution in the channel is from 5 to 120 seconds,

C) discharging the volatile components separated from the polymer solution through an outlet, and

D) the polymer after removal of the volatile components is discharged.

The apparatus and method of the present invention can be used to remove volatile components from sensitive solids in general, and particularly from thermoplastic polymers, elastomers, silicone polymers and high molecular weight lubricating oils and the like.

However, the process of the invention is preferably used for degassing thermoplastic polymers. The polymers include all plastics which are flowable under the influence of pressure and temperature. Such as polystyrene, polycarbonate, polyphenyl, polyurethane, polyamide, polyester, polyacrylate, polymethacrylate, and the like. The invention is particularly suitable for degassing polycarbonates.

The volatile component can be either unpolymerized monomer or a solvent. For example, a solvent frequently used in the preparation of thermoplastics is methylene chloride or a mixture of methylene chloride and chlorobenzene.

The polymer solution contains at least 40% by weight of polymer. The viscosity of the polymer solution in the molten state is generally from 0.5 to 200 Pas.

In the process, the polymer solution is pressed into the channel, flows through the channel of the heat exchanger and is heated to a temperature of between 250 and 350 bar, in particular at an absolute pressure of 1.5 to 50 bar, in particular at an absolute pressure of 2 to 5 bar. The pressure at the outlet of the channels is preferably lower than the saturation pressure of the volatile component at the corresponding temperature. The pressure in the product zone is preferably less than or equal to 105Pa, in particular from 3000Pa to 105 Pa.

The pressure before and after the passage, the temperature in the passage and the shape of the passage are preferably chosen such that the volatile components are completely separated from the polymer in the passage.

The pressure in the receiving zone and the temperature in the channel are in particular selected such that at least 95%, in particular at least 98%, preferably at least 99.5%, particularly preferably at least 99.8%, of the volatile constituents of the polymer solution evaporate in the channel.

The residence time of the polymer solution in the passage is generally from 5 to 120 seconds, preferably from 80 to 120 seconds. The flow rate of the polymer solution is in particular from 0.0001 to 0.01mm/sPreferably 0.001 to 0.005 mm/s. The ratio of the heat exchange surface of the channels to the volume flow of the polymer solution is from 5 to 75, preferably from 15 to 50m²/m³/h。

The invention is further explained below with the aid of the figures. This description is intended to be illustrative only and not to limit the invention.

FIG. 1 is a longitudinal view of an apparatus of the present invention.

Figure 2 shows a preferred configuration of the channel width.

Fig. 3 is a cross-sectional view of one plane of the heat exchanger.

Fig. 4 shows the arrangement of the heat exchanger planes in a section through a part of the heat exchanger.

Figure 5 shows a partial section of a heat exchanger of the device according to the invention consisting of plates placed one above the other.

FIG. 6 is a longitudinal view of an apparatus of the present invention comprised of vertically disposed channels.

Fig. 7 is a longitudinal view along the line a-a in fig. 6, showing the flow of the heat exchange medium through the tubes 13 in a simplified manner.

Examples

The apparatus of the present invention is shown in fig. 1. All components are machined from alloy59 or have a coating of alloy 59. The device has a double-skin housing 16. The upper part of the apparatus has a polymer solution inlet 1 and a volatile component outlet 3. The polymer freed of volatile components is discharged in the lower part via outlet 2 by means of pump 24. The inlet 1 is temperature regulated by a heat exchange medium.

The heat exchanger 31 is located inside the double-walled enclosure 16 and has a central receiving area 21 for receiving the polymer solution to be degassed. The receiving area 21 is connected to the inlet 1. Around the receiving zone 21 there are 200 channels 14 (see fig. 2) which extend from the receiving zone 21 up to the periphery of the heat exchanger 31 and open in a parabolic shape at the outlet 32 to the product zone 18.

The polymer solution is fed from inlet 1 into receiving zone 21 by means of a conventional pump (not shown). In order to distribute the polymer solution evenly in the respective channels, a cylindrical drainer 10 is centrally located in the receiving area 21. In addition, the heat exchanger has means for heating the channels above the temperature at which the volatile components evaporate. The means are a number of tubes 13 located at the periphery and inside the heat exchanger, which communicate with each other via an annular chamber 17. The pipe 13 communicates at the upper part with the annular chamber 11, into which hot heat exchange oil is fed through the channel 4. The heat transfer oil is discharged from the heat exchanger through an outlet 5. The tubes 13 are held together by end plates. The housing 16 of the device may be heated by a heat exchanger fluid.

Figure 2 shows the channels of the apparatus of the invention in cross-section. The inlet 23 has a rectangular cross-section with a height of 2mm and a width of 10 mm. The channel length is 110 mm. The width of the channel was constant at 10mm at the first 60 mm. Thereafter it expands gradually, reaching a width of 40mm at the outlet 32. The interior of the side walls 25 and 26 of the channel are parabolic.

Figure 3 shows how the channels 14 of the present invention are arranged in an annular configuration around the receiving zone 21. The tube 13 is fixed in the spacer bracket 20 through the hole 22.

Fig. 4 is a longitudinal view of a plurality of channel faces stacked one above the other. The channel 14 is formed by a number of spacer brackets 20 and plates 19 placed one above the other, through which the tubes 13 pass and fix the spacer brackets and plates in their position. The arrangement shown here is suitable for devices with vertical channels. The receiving zone 21 is located above the channel entrance 23.

In the solution shown in fig. 5, the heat exchanger body 32 is formed by a holder 37 of plates 36 placed one above the other. The plates 36 are spaced apart from each other in the bracket 37, thereby defining the width of the channel 14. The height of the channels is determined by the thickness of the plate 36.

The mode of operation of the apparatus according to the invention is explained below with reference to fig. 1. After the polymer solution to be treated is introduced into the receiving zone 21, the solution passes through the channel 14 where it is heated and the volatile components are removed. At the end 32 of the channel 14, the degassed polymer falls by gravity to the product zone 18 of the shell 16 and is discharged by the apparatus of the invention via the pipe 2 by means of the pump 24. The volatile components are withdrawn through outlet 3. The channel 14 is heated by a heat exchange liquid circulating through lines 4, 13 and 5.

In the variant of the apparatus illustrated in fig. 6, the support of the vertically placed rectangular plates 19 and the spacing brackets 20 (see fig. 4) is maintained by a set of lines 13, the lines 13 being connected at the ends by elbows (not shown) forming a line system. The line system is connected to the inlet pipe 4 and the outlet 5 so as to pass the heat exchange oil (see fig. 7).

The polymer solution is fed into the apparatus through inlet 1 (fig. 6), passes through the receiving zone 21 of the belt drain 10 and is distributed into the channel 14. The solution flows down the channel 14 and the volatile components are removed by heating. The polymer melt exits the channel 14 and drops to a product zone 18 for further processing. The polymer is discharged from line 2 by means of a pump 24.

Test examples

In this example, a 75% by weight polycarbonate solution containing 24% by weight chlorobenzene and 1% by weight dichloromethane was concentrated in the apparatus described in FIG. 1. The polycarbonate solution was pressed into the channel 14 under a pressure of 3000hPa, where it was heated to 300 ℃. The pressure in the product zone after channel 14 was 40hPa and the residence time of the polymer in channel 14 was 100 seconds. The channel is 1cm wide at the inlet 23 and 3cm wide at the outlet 32, widening after half the channel length as in fig. 2. All parts in contact with the product were made of Alloy 59. The pressures at the channel inlet 23 and outlet 32 and the shape of the channels are chosen such that the volatile components are completely or at least almost completely degassed within the channels. The degassed polycarbonate contained only 400ppm of chlorobenzene (solvent).

Claims (20)

1. Apparatus for removing volatile components from a polymer solution, the apparatus comprising at least

A container (30) having a polymer solution inlet (1), a volatile component outlet (3) and a polymer solution discharge port (2) from which volatile components have been removed;

and a heat exchanger (31) disposed inside the vessel (30), the heat exchanger having a central receiving zone (21) for the polymer solution connected to the inlet of the vessel, a product zone (18) for receiving the treated polymer solution;

a heat exchanger body (32) having a plurality of channels (14) forming heat transfer zones and connecting the receiving zone to the product zone;

a heating device (13) for heating a heat exchanger body (32) and a channel, characterized in that the length of the channel (14) is 1.0 to 40cm, the height is constant over its entire length between 1.3 and 13mm, the width of the channel (14) in the receiving zone (21) in the inlet zone is 1 to 10cm, wherein the width of the channel (14) from the inlet (23) to the outlet (32) to the product zone (18) is at least doubled.

2. An apparatus as claimed in claim 1, characterized in that the width of the channel (14) is at least tripled from the inlet (23) to the outlet (32) to the product zone (18).

3. The apparatus as claimed in claim 1 or 2, characterized in that the width of the channel (14) remains constant between the inlet (23) and at least half its length, expanding to at least twice, preferably at least three times, its width in the other regions up to the length of the outlet (32) to the product zone (18).

4. Device according to one of claims 1 to 3, characterized in that the width of the channel (14) between the inlet (23) and the outlet (32) to the product area (18) is non-linear, in particular expanding in a parabolic shape.

5. The apparatus as claimed in one of claims 1 to 4, characterized in that the heat exchanger (31) has more than 100, preferably 200 to 100000 passages.

6. An apparatus as claimed in any one of claims 1 to 5, characterized in that the heat exchanger body (32) is cylindrical and surrounds the receiving zone (21).

7. The apparatus as claimed in one of claims 1 to 5, characterized in that the heat exchanger body (32) has a rectangular parallelepiped shape and is located below the receiving region (21).

8. Apparatus according to claims 1 to 7, characterized in that the heat exchanger body (32) is formed by a number of plates (36) arranged one above the other or in parallel in planes (37), wherein the plates (36) in one plane (37) are spaced apart from each other with a spacing from the side walls of the plane defining the width of the channel (14), and the thickness of the plates (36) determines the height of the channel (14).

9. Apparatus according to claims 1 to 7, characterized in that the heat exchanger body (32) is formed by a number of plates (19) arranged one above the other or in parallel in planes (37), which plates (19) are separated from each other by spacing brackets (20), wherein the spacing and the sides of the spacing brackets (20) form the width of the channel (14), and the thickness of the spacing brackets (20) determines the height of the channel (14).

10. The apparatus as claimed in claims 1 to 9, characterized in that the channels (14) in the heat exchanger body (32) are inclined at an angle to the horizontal, preferably over the entire length, so that the outlet (32) is low, in particular vertically arranged.

11. Apparatus according to claims 1 to 10, characterized in that the heating means (13) of the heat exchanger are constituted by a plurality of lines (13) arranged transversely to the channels (14) by means of plates (36) or plates (19) in which the heat exchange fluid circulates.

12. Device according to claims 1 to 11, characterized in that the device is preferably wholly or partly, in particular the parts in contact with the polymer, machined from an iron-depleted metal material containing up to 10% by weight, preferably up to 5% by weight, of iron.

13. The plant as claimed in claims 1 to 12, characterized in that the iron-depleted material is preferably tantalum or an iron-depleted nickel alloy, in particular selected from the group consisting of: alloy59 (2.4605), inconel 686(2.4606), alloy-B2, alloy-B3, alloy-B4, nickel-based alloy C-22, nickel-based alloy-C276, nickel-based alloy-C4, and in particular alloy 59.

14. A process for removing volatile components from a polymer solution containing at least 40% by weight of polymer using an apparatus according to claims 1 to 13, wherein the process comprises:

A) the polymer solution is passed into a receiving zone (21) at a pressure of 1 to 100 bar absolute,

B) the polymer solution is caused to flow in the channels (14) of a heat exchanger (31) and is heated to a temperature above the evaporation temperature of the volatile components of the polymer solution but below the boiling point or decomposition temperature of the polymer, wherein the residence time in the channels of the polymer solution is between 5 and 120 seconds,

C) the volatile constituents separated from the polymer solution are discharged via an outlet (3), and

D) the polymer after removal of the volatile components is discharged.

15. The method as claimed in claim 14, wherein the polymer is a thermoplastic polymer, preferably polystyrene, polycarbonate, polystyrene, polyurethane, polyamide, polyester, polyacrylate, polymethacrylate, or a copolymer of the aforementioned polymers, in particular polycarbonate, or an elastomeric or silicone polymer.

16. A process according to claim 14 or 15, characterized in that the volatile component is a polymer solvent or an unpolymerised monomer.

17. The method as claimed in one of claims 14 to 16, characterized in that the pressure in the receiving zone (21) and the temperature in the channel (14) are selected such that the volatile constituents of the polymer solution evaporate in the channel by at least 95%, preferably by at least 98%, particularly preferably by at least 99.5%.

18. A method as claimed in any one of claims 14 to 17, characterized in that the temperature in the channel (14) is 250 to 350 ℃.

19. A method as claimed in any one of claims 14 to 18, characterized in that the pressure in the receiving zone (21) at the inlet (23) of the channel (14) is 1.5 to 50 bar absolute, preferably 2 to 5 bar absolute.

20. The process as claimed in one of claims 14 to 19, characterized in that the pressure in the product zone (18) is less than or greater than 105Pa, in particular from 3000Pa to 105 Pa.