METHOD FOR PRODUCING A POLYCARBONATE USING A STRIPPING DEVICE

Abstract

A method is described for producing a polycarbonate by reacting one or more diaryl carbonates with one or more aromatic hydroxy compounds, which are first mixed in a mixing device and enter, as a raw material mixture, a raw material mixture container to subsequently react in one or more reactors under reduced pressure and increased temperature to form polycarbonate, wherein the mixture of diaryl carbonate and aromatic hydroxy compound is subjected to a purification by an inert gas in a countercurrent process, in a stripping device, before entering the raw material mixture container. The present invention also relates to a stripping device which is particularly suitable for purifying a raw material mixture stream, and to the use of such a stripping device in a method for producing polycarbonate.

Claims

1. A process for producing a polycarbonate by reaction of one or more diaryl carbonates with one or more aromatic hydroxy compounds, wherein diaryl carbonate and aromatic hydroxy compound are first mixed in a mixing device and enter, as a raw material mixture, a raw material mixture container to subsequently react in one or more reactors under reduced pressure and increased temperature to form polycarbonate, wherein the mixture of diaryl carbonate and aromatic hydroxy compound passes through a stripping device in which the raw material mixture is purified by a gas in a countercurrent process before entering the raw material mixture container.

2. The process according to claim 1, characterized in that the purification of the raw material stream in the stripping device takes place under reduced pressure, in particular under a pressure of less than 700 mbar a, more preferably under a pressure of less than 600 mbar a, still more preferably under a pressure of less than 100 mbar a, and most preferably under a pressure of less than 60 mbar a, in particular between 50 mbar a and 10 mbar a.

3. The process according to claim 1 or 2, characterized in that one or more inert gases are used as the gas.

4. The process according to one of the preceding claims, characterized in that nitrogen is used as the gas.

5. The process according to one of the preceding claims, characterized in that the ratio of liquid to gaseous mass flow, expressed in kg/h, in the stripping device is greater than 100, preferably greater than 1,000, more preferably greater than 2,500 and more preferably between 3,000 and 113,000.

6. The process according to at least one of the preceding claims, characterized in that the stripping device has a column zone with structured packings.

7. The process according to at least one of the preceding claims, characterized in that the stripping device has a preheating zone which is downstream with respect to the column zone in the direction of the raw material mixture stream.

8. The process according to at least one of the preceding claims, characterized in that the column zone of the stripping device is heated.

9. The process according to at least one of the preceding claims, characterized in that the gas is introduced into the stripping device via the raw material mixture container.

10. The process according to at least one of the preceding claims, characterized in that dihydroxydiarylalkanes of the formula HOZOH, wherein Z is a divalent organic residue having 6 to 30 carbon atoms, which contains one or more aromatic groups, are used as the aromatic hydroxy compound.

11. The process according to at least one of the preceding claims, characterized in that di-(C.sub.6 to C.sub.14 aryl) carbonic acid esters are used as the diaryl carbonate.

12. The process according to at least one of the preceding claims, characterized in that bisphenol A is used as aromatic hydroxy compound and diphenyl carbonate is used as diaryl carbonate.

13. A stripping device, in particular for the purification of a raw material mixture stream by a gas in a countercurrent process in a process for the production of polycarbonate, wherein the stripping device comprises a column zone with structured packings and a preheating zone for preheating the gas.

14. The stripping device according to claim 13, characterized in that the column zone is heated.

15. The stripping device according to claim 13 or 14, characterized in that the stripping device is designed so that it can be connected and sealed vacuum-tight via weld lip seals.

16. The stripping device according to claims 13 to 15, characterized in that the housing and the structured packings in the column zone are made of stainless steel 904L or of higher quality.

17. Use of a stripping device according to at least one of the claims 13-16 in a process for producing polycarbonate.

Description

[0034] In a preferred embodiment, the process of the invention is designed so that the purification of the raw material stream in the stripping device takes place under reduced pressure, in particular under a pressure of less than 700 mbar a; more preferably less than 600 mbar a; still more preferably under a pressure of less than 100 mbar a; and most preferably under a pressure of less than 60 mbar a; in particular between 50 mbar a and 10 mbar a.

[0035] In a preferred embodiment, the method according to the invention is designed such that one or more inert gases are used as the gas.

[0036] In a particularly preferred embodiment, the method according to the invention is designed such that nitrogen is used as the gas.

[0037] However, other inert substances may be used as well, singly or in combination, such as CO.sub.2, argon, helium. In addition, it is conceivable to heat or to cool the gas stream before feeding it into the container. It is also possible to treat the gas stream after exiting the container and to recirculate it. The gaseous stream can be varied according to the expected contamination and/or the liquid flow, or the throughput of the plant.

[0038] In a preferred embodiment, the method according to the invention is designed so that purifying the raw material stream in the stripping device takes place under elevated temperature; in particular above a temperature of 85? C.; preferably above a temperature of 120? C.; still more preferably above a temperature of 145? C. and most preferably at a temperature between 150? C. and 165? C.

[0039] In a preferred embodiment, the method according to the invention is designed so that purifying the raw material stream in the stripping device takes place under increased temperature and reduced pressure, especially at a temperature between 150? C. and 165? C. and at a pressure of between 50 mbar a and 10 mbar a.

[0040] In a preferred embodiment, the process according to the invention is designed such that the ratio of liquid to gaseous mass flow, expressed in kg/h, in the stripping device is greater than 100, preferably greater than 1,000, more preferably greater than 2,500 and still more preferably between 3,000 and 113,000.

[0041] However, the skilled person should further consider that not only does a relationship between the liquid stream and the gas stream exist, but also between the impurities in the liquid stream and the gas stream, which, therefore, can affect the gas flow.

[0042] In a particularly preferred embodiment, the method according to the invention is designed such that the stripping device comprises a column zone with structured packings.

[0043] The structured packings in the column zone increase the contact area between liquid and gaseous stream, thus increasing the efficiency of the purification.

[0044] In a particularly preferred embodiment, the process according to the invention is designed so that the stripping device includes a preheating zone, which is downstream with respect to the column zone in the direction of the raw material mixture stream.

[0045] Such a preheating zone downstream of the column zone, has the advantage that a preheating of the gas stream takes place before the gas stream in the column zone comes into intense contact with the liquid raw material stream. By virtue of the fact that the stripping device is typically operated under vacuum and that a strong relaxation of the gas stream, typically nitrogen, occurs, in relation to the pressure of the gas in the supply line, such a preheating zone can significantly enhance the efficiency of the purification process, since overly excessive cooling of the expanded gas is avoided.

[0046] In a particularly preferred embodiment, the method according to the invention is designed such that the column zone of the stripping device is heated. Heating of the column zone can also enhance the efficiency of the purification process.

[0047] In a preferred embodiment, the method according to the invention is designed such that the gas is introduced into the stripping device via the raw material mixture container. It has been shown that feeding the gas stream via the raw material mixture container leads to particularly good results, since contact between the raw material stream and the gas stream will occur downstream of the stripping device; this leads to a certain purifying effect and, moreover, causes preheating of the gas stream.

[0048] In a preferred embodiment, the process according to the invention is designed such that dihydroxydiarylalkanes of the formula HOZOH are used as the aromatic hydroxy compound, wherein Z is a divalent organic residue having 6 to 30 carbon atoms which contains one or more aromatic groups.

[0049] In a preferred embodiment, the process according to the invention is designed such that di-(C.sub.6 to C.sub.14 aryl) carbonic acid esters are used as the diaryl carbonate.

[0050] In a preferred embodiment, the process according to the invention is designed such that bisphenol A is used as aromatic hydroxy compound and diphenyl carbonate as the diaryl carbonate.

[0051] In a preferred embodiment, the inventive method is designed such that the mixing device for mixing the raw material streams, consists of a so-called static mixer as part of a tubing.

[0052] In addition, in a particularly preferred embodiment, the method according to the invention can be designed such that the mixing device for mixing the raw material streams, consists of a raw material mixing container in which the raw material streams are fed and mixed continuously or batchwise.

[0053] In addition, the present invention also relates to a stripping device, in particular for purifying a raw material mixture stream by a gas in the countercurrent process in a process for producing polycarbonate, wherein the stripping device has a column zone with structured packings and a preheating zone for preheating the gas.

[0054] Such a stripping device can, in particular, be used for use in a process for the preparation of polycarbonate.

[0055] The stripping device typically has a height to diameter ratio of greater than one. Ideally, the stripping device is insulated and heated. The heating can be carried out by a double jacket, with thermal oil or steam heating or by an electric trace heating. The specific installations can be designed as pipes, as packings, as trays or as gauze packings. Ideally, structured gauze packings are used. In addition, heating elements may be part of the installations.

[0056] In a particularly preferred embodiment, the stripping device according to the invention is designed such that it can be connected via weld lip seals and sealed in a vacuum-tight manner.

[0057] It has been found that the connection of the stripping device via weld lip seals provides advantages compared to the graphite seals commonly used. This is particularly the case as the stripping device is typically operated under vacuum.

[0058] In a preferred embodiment, the stripping device according to the invention is designed so that the housing and structured packings in the column zone are made of stainless steel 904L, or of higher quality. The use of stainless steel, in particular 904L or of higher quality, results in increased durability of the stripping device and prevention of corrosion and reduction of discoloration of the raw material.

[0059] The implementation of the invention is not limited to a single purification of the liquid raw material stream. Of course, it is also conceivable to circulate the raw material mixture continuously, or batchwise, from the following raw material container via the container.

[0060] FIG. 1 shows a schematic representation of the method according to the invention. The schematic representation shows the principle of countercurrent purification in a column zone of the stripping device.

TABLE-US-00001 FIG. 1 No. description 40 diaryl carbonate component 41 aromatic hydroxyl component 42 gaseous countercurrent component 43 raw material stream 44 exhaust gas stream 45 countercurrent column

[0061] A particularly preferred embodiment of the method according to the invention is shown in FIG. 2:

TABLE-US-00002 FIG. 2 No. description 50 bisphenol A production 51 diphenyl carbonate production 52 bisphenol A raw material container 53 diphenyl carbonate raw material container 54 mixing device 55 countercurrent column 56 vacuum system 57 nitrogen supply 58 raw material mixture container 59 raw material pump 60 first reaction system

[0062] The individual raw material streams are fed from the respective production plant (50) and (51) into storage containers (52) and (53). The raw material streams fed from the storage containers are then combined in a specific molar ratio and mixed with a mixing device (54). The raw material mixture is then fed into the stripping device (55). At the same time, nitrogen from the nitrogen supply (57) is fed in countercurrent from below into the stripping device (55). Impurities accumulate in the nitrogen stream by contact with the liquid countercurrent. The enriched gas stream leaves the stripping device at the head and is forwarded to the vacuum system (56). The purified raw material stream exits at the bottom of the stripping device (55) into a raw material mixture container (58). The raw material mixture is fed to the first reaction system (60) by means of raw material pump (59).

[0063] FIG. 3 shows a particularly preferred embodiment of the method according to the invention, in which the stripping device has a preheating zone and the gas in the form of nitrogen is introduced via the raw material mixture container.