Process for producing polycarbonate with reduced phosgene excess

Abstract

The present invention relates to a method for producing polycarbonates from at least one dihydroxydiarylalkane, phosgene, at least one catalyst and at least one chain terminator according to the phase boundary method, which method makes it possible to reduce the phosgene excess by specific energy input during dispersion of the aqueous and organic phases. Furthermore, this method produces polycarbonates with a low proportion of oligomers and a low proportion of two chain terminator carbonates.

Description

[Technical Field]

[0001] The present invention relates to a method for producing polycarbonate by an interfacial process from at least one dihydroxydialkylalkane, phosgene, at least one catalyst, and at least one chain terminator, which allows the use of a reduced phosgene excess by a defined energy input for dispersing the aqueous and organic phases. At the same time, the method according to the present invention provides polycarbonate having a low proportion of oligomers and a low proportion of di-chain terminator carbonate. The present invention also relates to the use of a defined energy input for dispersing the aqueous and organic phases in a method for producing polycarbonate by an interfacial process to reduce the phosgene excess. [Background technology]

[0002] The production of polycarbonates by the interfacial method has been previously described in [1], [2], [3] and finally in [4].

[0003] The interfacial method for producing polycarbonates is further described, for example, in US Pat. No. 5,629,399.

[0004] The process generally involves the phosgenation of the disodium salt of a bisphenol or a mixture of different bisphenols, initially in aqueous alkaline solution or suspension, in the presence of an inert organic solvent or solvent mixture, which forms a second organic phase in addition to the aqueous phase. The resulting oligocarbonate, which is primarily present in the organic phase, is condensed with a suitable catalyst to give a high molecular weight polycarbonate dissolved in the organic phase, the molecular weight of which can be controlled by suitable chain terminators (e.g., monofunctional phenols). The organic phase is finally separated, from which the polycarbonate is isolated through various processing steps.

[0005] Continuous processes for producing condensates using phosgene by interfacial methods, such as for producing aromatic polycarbonates, polyester carbonates, or their oligomers, generally have the disadvantage that, to promote the reaction and / or improve phase separation, more phosgene than is necessary for the product balance must be used. The excess phosgene is then decomposed during synthesis in the form of by-products, such as additional conventional salts or alkali metal carbonate compounds. Continuous interfacial processes for producing aromatic polycarbonates typically use an excess of phosgene of about 20 mol % relative to the added diphenoxide (see Non-Patent Document 3).

[0006] Reducing the phosgene excess can lead to undesirable side effects, such as poor separation of the dispersion after the last reaction step and therefore a high water content in the organic solution and / or a high residual monomer or chain terminator content in the wastewater. Various methods for reducing the phosgene excess have been discussed in the literature.

[0007] US Pat. No. 5,699,499 teaches that first combining the aqueous phase and the phosgene-containing organic phase in a tube and then introducing them into a tank reactor is beneficial to the phosgene yield of the process.

[0008] In the continuous interfacial process for producing polycarbonates known from Patent Document 3, an aqueous phase of diphenols and the required amount of alkali metal hydroxide is combined with a phosgene-containing organic phase in a tube using a static mixer. This process can only produce prepolymers with molecular weights of 4,000 g / mol to 12,000 g / mol.

[0009] It is clear from Patent Document 4 that a low phosgene excess can be achieved by separating the BPA solution streams. The disadvantage of this method is the high cost and complexity involved in metering the second BPA stream.

[0010] Patent Document 5 discloses a continuous process for producing polycarbonate, in which a disperser is used to disperse an organic phase and an aqueous phase. It is described here as being advantageous to use a disperser to produce an oil-in-water dispersion. For this purpose, this document generally describes a 2×e dispersion via a disperser. 6 W / m 3 ~5×e 9 W / m 3 , preferably 5 × e 6 W / m 3 ~1×e 9 W / m 3 In fact, the example in the document discloses an energy input of 1.2×e 6 W / m 3 The document discloses an energy input of 1000 kJ / 2000 kcal / g, and an oil-in-water dispersion is present. The energy input in the examples does not match the range of the generally disclosed energy input, and it is clear that the generally disclosed energy input is misrepresented in the specification. This document focuses only on reducing the phosgene content and does not provide many details about the properties of the resulting polycarbonate. In particular, it does not mention the proportion of oligomers in the polycarbonate, nor the content of double chain-stopper carbonates.

[0011] However, the properties of the resulting polycarbonate (PC) are affected by the proportion of oligomers in the PC and also by the proportion of di-chain terminator carbonate. According to the present invention, "di-chain terminator carbonate" is understood to mean a compound formed by reacting two chain terminator molecules with phosgene to form a carbonate. The properties of PC affected thereby include impact strength, glass transition temperature, and behavior at high temperatures. Low-molecular-weight compounds can also cause bleaching during CD production. It should also be noted that the formation of di-chain terminator carbonate results in the loss of the chain terminator required for the actual reaction and its viscosity control. Therefore, the higher the proportion of di-chain terminator in the polycarbonate, the greater the amount of chain terminator required, which is economically and environmentally unfavorable and makes viscosity control during the process more difficult. Therefore, it is desirable to keep the content of di-chain terminator carbonate as low as possible.

[0012] Double chain-stopper carbonates are produced by the reaction of phosgene with a chain-stopper. Therefore, it is common to add a chain-stopper to the reaction system only when the phosgene is fully converted. This can be achieved, for example, by using a multi-stage process that involves first producing oligomers in a first stage and then further condensing the oligomers in a second stage, or by adding the chain-stopper very late in the process, at a high conversion rate, i.e., when a relatively high molecular weight polycarbonate is produced. However, conventional theory suggests that adding a chain-stopper only at a high conversion rate increases the oligomer content in the resulting polycarbonate. It has been reported that a high oligomer content leads to brittleness in low-molecular-weight PCs, and that transesterification during extrusion can reduce the molecular weight, resulting in reduced impact strength. Therefore, in the prior art, processes are usually carried out to find a compromise between a high content of oligomers and a low content of two chain terminator carbonates in the polycarbonate, or between a low content of oligomers and a high content of two chain terminator carbonates.

[0013] Patent Document 6 describes the production of low-molecular-weight polycarbonates with narrow molecular weight distributions, i.e., low oligomer content. To achieve such a narrow distribution, one of these prior art documents proposes a two-stage process in which a phosgene-free bischloroformate having a degree of polymerization of 0 to 6 is capped, for example, with phenol, followed by condensation of the resulting capped bischloroformate with the addition of a catalyst and a base. Here, phenol is again added as a chain terminator to the bischloroformate solution once phosgene is no longer present in the solution. Patent Document 7 also relates to the production of polycarbonates with a low oligomer content. This document also begins with a bischloroformate having a degree of polymerization of 0 to 6. According to Example 2, this bischloroformate is first produced in a reaction with a large excess of phosgene (739.3 mmol of phosgene per 250 mmol of bisphenol A). Therefore, the unconverted phosgene is subsequently decomposed by the addition of NaOH. Only after this is the chain terminator pt-butylphenol added. This again means that the chain terminator is added to the reaction system once phosgene is no longer present.

[0014] US Patent No. 5,999,623 describes a two-stage process which involves first continuously reacting bisphenol A with an excess of phosgene. In a further step which follows, the organic and aqueous phases are separated, after which further bisphenol A and NaOH are added to the organic phase, thereby converting any remaining phosgene. Only afterwards are catalysts and chain terminators added.

[0015] In both of the above cases, an excess amount of phosgene is initially used, which is then destroyed again. This is uneconomical because not all of the phosgene is used in the actual reaction. Furthermore, it is not sustainable from an environmental point of view because the previously produced product is destroyed "unused." Furthermore, in the described process, a new solution must be produced after the production of bischloroformate, which involves corresponding costs and complexity. This particularly results in the described process being unable to be carried out as a continuous process. Therefore, additional, corrosion-resistant equipment is required, which involves additional residence time of highly corrosive materials. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] European Patent Application Publication No. 0517044 [Patent Document 2] German Patent Application Publication No. 2725967 [Patent Document 3] European Patent Application Publication No. 304691 [Patent Document 4] European Patent No. 0520272 [Patent Document 5] German Patent Application Publication No. 102008012613 [Patent Document 6] European Patent Application Publication No. 0408924 [Patent Document 7] European Patent Application Publication No. 0289826 [Patent Document 8] European Patent Application Publication No. 0640639 [Non-patent literature]

[0017] [Non-Patent Document 1] Schnell, "Chemistry and Physics of Polycarbonates", Polymer Reviews, volume 9, Interscience Publishers, New York, London, Sydney 1964, pp. 33-70 [Non-patent document 2] DC Prevorsek, BT Debona and Y. Kesten, Corporate Research Center, Allied Chemical Corporation, Morristown, New Jersey 07960: "Synthesis of Poly(ester Carbonate) Copolymers" in Journal of Polymer Science, Polymer Chemistry Edition, vol. 18, (1980); pp. 75-90 [Non-patent document 3] D. Freitag, U. Grigo, PR Mueller, N. Nouverne', BAYER AG, "Polycarbonates" in Encyclopedia of Polymer Science and Engineering, volume 11, second edition, 1988, pp. 651-692 [Non-patent document 4] Dres U. Grigo, K. Kircher and PR Mueller “Polycarbonate” in Becker / Braun, Kunststoff Handbuch, volume 3 / 1, Polycarbonates, Polyacetals, Polyesters, Cellulose esters, Crul Hanser Verlag Munich, Vienna 1992, pp. 118-145 Summary of the Invention [Problem to be solved by the invention]

[0018] Therefore, it is an object of the present invention to provide a method for producing polycarbonate by an interfacial process, which overcomes at least one of the drawbacks of the prior art. A particular object of the present invention is to provide a method for producing polycarbonate by an interfacial process, in which the amount of excess phosgene can be reduced. In addition, it is desirable to obtain polycarbonate having a low oligomer content and therefore a narrow molecular weight distribution, preferably at the same time. It is also desirable that the method provide polycarbonate having a low content of two chain terminator carbonates, preferably at the same time. A particular object of the present invention is to provide a method for producing polycarbonate by an interfacial process, which obtains polycarbonate containing both a low proportion of oligomers and two chain terminator carbonates. [Means for solving the problem]

[0019] The present invention has achieved at least one, and preferably all, of the above-mentioned objectives. Surprisingly, it has been found that the use of a defined energy input in dispersing the aqueous and organic phases can reduce the amount of excess phosgene. This results in economic savings, since a smaller excess amount of phosgene is required. At the same time, it has been surprisingly found that, as a result of the high conversion of the phosgene produced, the phosgenation, oligomerization, and hydrolysis reactions of the at least one dihydroxydiarylalkane can be separated. This preferably means that, as a result of the high phosgene conversion, the addition of at least one chain terminator to the reaction system can be carried out earlier. This particularly means that the addition of the chain terminator to the reaction system can be carried out even when phosgene is still present in the reaction system. Thus, the chain terminator can be introduced into the reaction system at a very early stage. Here, "very early stage" is understood to mean that only oligomeric compounds having an average degree of polymerization of at least 1 unit and at most 5 or 6 units are present from the reaction of the at least one dihydroxydiarylalkane with phosgene. The resulting polycarbonate surprisingly has a low proportion of double chain terminator carbonate, despite the introduction of a chain terminator into a phosgene-containing system. At the same time, the resulting polycarbonate has a narrow molecular weight distribution and, therefore, a low proportion of oligomers. The resulting polycarbonate therefore also has the improved properties described above, which are due to the low proportion of double chain terminator carbonate and the low proportion of oligomers. The process according to the present invention is more economical and environmentally friendly than the processes described in the prior art. First, the process according to the present invention not only allows for a reduction in the amount of excess phosgene, but also allows for a reduction in the amount of chain terminator required, due to the lower loss caused by the formation of double chain terminator carbonate.

[0020] The present invention therefore provides a method for producing polycarbonates by an interfacial process from at least one dihydroxydiarylalkane, phosgene, at least one catalyst and at least one chain terminator, comprising the following steps: (a) forming a dispersion from an organic phase and an aqueous phase by continuously dispersing the organic phase in the aqueous phase or the aqueous phase in the organic phase in a disperser, wherein the organic phase comprises at least one solvent suitable for polycarbonates and at least a portion of the phosgene, and the aqueous phase comprises at least one dihydroxydiarylalkane, water, and 1.8 mol to 2.2 mol, preferably 1.95 mol to 2.05 mol, of an aqueous alkali metal hydroxide solution per mol of dihydroxydiarylalkane; (b) adding at least one chain terminator to the dispersion from step (a); (c) adding at least one catalyst to the mixture resulting from step (b); Including, The energy input by the disperser in step (a) is 2.5 x e 6 W / m 3 ~5.0×e 7 W / m 3 , preferably 3.0 × e 6 W / m 3 ~4.0×e 7 W / m 3 , particularly preferably 1.0 × e 7 W / m 3 ~3.5×e 7 W / m 3 The present invention provides a method, characterized in that:

[0021] Those skilled in the art will appreciate that 1.22 g / cm at 25°C 3 Based on the density of the PC solution, convert J / kg to W / m 3The terms homogenization and dispersion are known to those skilled in the art. The term "homogenization" is preferably understood to mean that the concentration of the individual components of the composition within any desired volume element of the aqueous or organic phase is substantially the same, and preferably achieved. The term "substantially" is preferably understood to mean a difference of 5% or less, preferably 3% or less, and particularly preferably 1% or less, in the concentration of the individual components of the composition within any desired volume element. Unlike dispersion, for homogenization, it is further preferred that the phase interface between the aqueous and organic phases is as small as possible. Furthermore, the term "dispersion" is preferably understood to mean the formation of an emulsion from the aqueous and organic phases, preferably in the absence of an emulsifier, although the aqueous and organic phases may also contain additional components for producing polycarbonates. Examples of such emulsions are oil-in-water dispersions or water-in-oil dispersions. Homogenization differs from dispersion in that, for homogenization, there is preferably no concentration gradient of all dissolved substances within either phase, and the phase interface between the phases is as small as possible.

[0022] According to the present invention, it has been found that the phosgene excess can be further effectively reduced only in a certain range of energy input, and those skilled in the art can calculate the corresponding energy input once the reactor is specified.

[0023] According to the invention, the energy input determined is an average value. This means that higher or lower values ​​of the energy input are preferably not excluded. These may optionally occur only for short periods of time. According to the invention, the average value is preferably formed over the entire reactor system. Thus, the energy input at relevant edge zones or internal structures is also included in the calculation.

[0024] Dispersion of an organic phase into an aqueous phase or an aqueous phase into an organic phase using a disperser can produce an oil-in-water (OW) dispersion or a water-in-oil (WO) dispersion, where oil is understood to mean the organic phase. However, according to the present invention, it is preferred that process step (a) comprises producing a water-in-oil dispersion. This has been found to be advantageous for low contents of oligomers and double chain-stopper carbonates in the polycarbonate. The organic phase is preferably continuously dispersed in the aqueous phase using a disperser.

[0025] An oil-in-water dispersion is by definition one in which water forms the external (continuous) phase and oil forms the internal (dispersed) phase, i.e., oil droplets are dispersed in water. A water-in-oil dispersion is therefore one in which oil forms the external phase and water forms the internal phase.

[0026] The method according to the invention is preferably characterized in that it comprises one or more steps of adding an aqueous alkali metal hydroxide solution. The term "addition" is preferably understood to mean an active step of additional addition. It is also possible, in particular, to initially dissolve at least one dihydroxyarylalkane in the aqueous alkali metal hydroxide solution before feeding it to the reaction system. According to the invention, such an initial step is preferably not the addition of an aqueous alkali metal hydroxide solution. However, it is further preferred to understand that any addition of an aqueous alkali metal hydroxide solution (whether or not accompanied by at least one dihydroxyarylalkane) after this initial step of dissolving at least one dihydroxyarylalkane constitutes the addition of an aqueous alkali metal hydroxide solution.

[0027] This step of adding an aqueous alkali metal hydroxide solution is an exothermic reaction. According to the invention, this step is preferably carried out at a temperature range of from -5°C to 100°C, particularly preferably from 15°C to 80°C, and very particularly preferably from 25°C to 65°C, and may be carried out under positive pressure depending on the solvent or solvent mixture. Depending on the reactor used, different pressures may be used. For example, a pressure of from 0.5 bar (absolute) to 20 bar (absolute) may be preferably used.

[0028] The method according to the present invention comprises: It has proven particularly advantageous if the addition of at least one chain terminator to the reaction system in process step (b) is carried out at a point prior to the first of the one or more additions of the aqueous alkali metal hydroxide solution.

[0029] It is obvious to those skilled in the art that, in principle, an aqueous alkali metal hydroxide solution can be added before the addition of at least one chain terminator. However, it has been found in accordance with the present invention that this amount should not be too high, since otherwise the degree of polymerization of the reaction product R would be too high. This means that, before the addition of at least one chain terminator, those skilled in the art can add only an amount of aqueous alkali metal hydroxide solution that still ensures that the requirements for the reaction product R according to the present invention are met.

[0030] The process according to the invention can be used to reduce the phosgene excess. It is preferred if in process step (a) there is an excess of phosgene of 3 mol% to 20 mol%, preferably 4 mol% to 10 mol%, particularly preferably 5 mol% to 9 mol%, and very particularly preferably 6 mol% to 8 mol%, based on the total amount of dihydroxydiarylalkanes used. According to the invention, the mol% is calculated as follows: moles of phosgene / (sum of moles of all phenolic OH groups / 2). The sum of all phenolic groups is, for example, made up of dihydroxydiarylalkanes having two OH groups, chain terminators having one OH group, and / or, optionally, branching agents having, for example, three OH groups.

[0031] As mentioned above, according to the present invention, the presence of an aqueous alkali metal hydroxide solution in step (a) is preferably not understood to mean the addition of an aqueous alkali metal hydroxide solution. This is an aqueous alkali metal hydroxide solution, preferably an aqueous sodium hydroxide solution, used to dissolve BPA in the aqueous phase. During the phosgenation step (a), it is preferable to have as little free aqueous alkali metal hydroxide solution as possible to avoid hydrolysis of phosgene to sodium carbonate (i.e., loss of phosgene). Therefore, in step (a) of the present invention, 1.80 mol to 2.20 mol, preferably 1.95 mol to 2.05 mol, of an aqueous alkali metal hydroxide solution is used per mol of dihydroxydiarylalkane.

[0032] The organic phase comprises one or more solvents.

[0033] Suitable solvents are aromatic and / or aliphatic chlorinated hydrocarbons, preferably dichloromethane, trichloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, and chlorobenzene, and mixtures thereof. However, aromatic hydrocarbons, such as benzene, toluene, m- / p- / o-xylene, or aromatic ethers, such as anisole, can also be used alone, in admixture, or in addition to or in admixture with chlorinated hydrocarbons, with dichloromethane and chlorobenzene and mixtures thereof being preferred. Another embodiment of the process according to the invention uses a solvent that does not dissolve polycarbonate but merely swells it. Therefore, it is also possible to use a non-solvent for polycarbonate in combination with the solvent. Solvents soluble in the aqueous phase, such as tetrahydrofuran, 1,3- or 1,4-dioxane, or 1,3-dioxolane, can also be used as solvents when the solvent partner forms a second organic phase.

[0034] Suitable dihydroxydiarylalkanes (also referred to above and below specifically as diphenols) have the general formula: HO-Z-OH where Z is a divalent organic radical having 6 to 30 carbon atoms containing one or more aromatic groups. Examples of such compounds that can be used in the method according to the invention are dihydroxydiarylalkanes, such as hydroquinone, resorcinol, dihydroxydiphenyl, bis(hydroxyphenyl)alkanes, bis(hydroxyphenyl)cycloalkanes, bis(hydroxyphenyl)sulfides, bis(hydroxyphenyl)ethers, bis(hydroxyphenyl)ketones, bis(hydroxyphenyl)sulfones, bis(hydroxyphenyl)sulfoxides, 4,4'-bis(hydroxyphenyl)diisopropylbenzene, and alkylated, ring-alkylated, and ring-halogenated compounds thereof.

[0035] Preferred dihydroxydiarylalkanes are 4,4'-dihydroxydiphenyl, 2,2-bis(4-hydroxyphenyl)-1-phenylpropane, 1,1-bis(4-hydroxyphenyl)phenylethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A (BPA)), 2,4-bis(4-hydroxyphenyl)-2-methylbutane, 1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene (bisphenol M), 2,2-bis(3-methyl-4-hydroxyphenyl)propane, bis(3,5- These are 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)methane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, bis(3,5-dimethyl-4-hydroxyphenyl)sulfone, 2,4-bis(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane, 1,3-bis[2-(3,5-dimethyl-4-hydroxyphenyl)-2-propyl]benzene, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC).

[0036] Particularly preferred dihydroxydiarylalkanes are 4,4'-dihydroxydiphenyl, 1,1-bis(4-hydroxyphenyl)phenylethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A (BPA)), 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC).

[0037] These and further suitable dihydroxydiarylalkanes are described, for example, in U.S. Pat. Nos. 2,999,835, 3,148,172, 2,991,273, 3,271,367, 4,982,014, and 2,999,846, DE-A-1,570,703, DE-A-2,063,050, DE-A-2,036,052, DE-A-2,211,956, and DE-A-3,832,396, FR-A-1,561,518, H. Schnell, "Chemistry and Physics of Polycarbonates", Interscience Publishers, New York 1964, pp. 28 ff., 102 ff., monographs, and D.G. Legrand, J.T. Bendler, "Handbook of Polycarbonate Science and Technology", Marcel Dekker, New York This is described in the monograph, 2000, p. 72 et seq.

[0038] According to the invention, polycarbonates are understood to mean both homopolycarbonates and copolycarbonates. In the case of the inventive production of homopolycarbonates, only one dihydroxydiarylalkane is used, while in the case of the inventive production of copolycarbonates, two or more dihydroxydiarylalkanes are used, it being understood that the dihydroxydiarylalkanes used, as well as all other chemicals and auxiliaries added to the synthesis, may be contaminated with impurities resulting from their own synthesis, handling and storage, although it is desirable to use the purest possible raw materials.

[0039] In the context of the present invention, aqueous alkali metal hydroxide solution is understood to mean preferably aqueous sodium hydroxide solution, potassium hydroxide solution or mixtures thereof, particularly preferably aqueous sodium hydroxide solution.

[0040] The aqueous phase in the interfacial method for producing polycarbonate contains an aqueous alkali metal hydroxide solution, one or more dihydroxydiarylalkanes, and water, calculated as free dihydroxydiarylalkanes rather than as alkali metal salts. The concentration of this aqueous solution with respect to the total amount of dihydroxydiarylalkanes is preferably 1% to 30% by weight, particularly preferably 3% to 25% by weight, and very preferably 15% to 18% by weight, based on the total weight of the aqueous phase. The alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide, used to dissolve the dihydroxydiarylalkane can be used in solid form or as the corresponding aqueous alkali metal hydroxide solution. The concentration of the aqueous alkali metal hydroxide solution is determined according to the target concentration of the desired dihydroxydiarylalkane solution, but is generally 5% to 25% by weight, preferably 5% to 10% by weight, based on 100% by weight of the aqueous alkali metal hydroxide solution, or a more concentrated solution that is subsequently diluted with water. In the method involving subsequent dilution, an aqueous alkali metal hydroxide solution, optionally at a temperature adjusted, is used, having a concentration of 15% to 75% by weight, preferably 25% to 55% by weight. The alkali metal content per mole of dihydroxydiarylalkane depends on the structure of the dihydroxydiarylalkane, but is generally 1.5 to 2.5 mol alkali metal / mol dihydroxydiarylalkane, preferably 1.8 to 2.2 mol alkali metal / mol dihydroxydiarylalkane, and particularly preferably 1.85 to 2.15 mol alkali metal, very particularly preferably 2.00 mol alkali metal, in the particularly preferred case where bisphenol A is used as the only dihydroxydiarylalkane. If two or more dihydroxydiarylalkanes are used, they can be dissolved together.However, since the solubility of dihydroxydiarylalkanes is highly dependent on the amount of alkali metal used, it may be advantageous to dissolve two solutions, each containing one dihydroxydiarylalkane, in the appropriate aqueous alkali metal hydroxide solution, rather than one solution containing two dihydroxydiarylalkanes, and then separately measure these solutions to the correct mixing ratio. Furthermore, it may be advantageous to dissolve the dihydroxydiarylalkane(s) in a diluted aqueous dihydroxydiarylalkane solution containing additional alkali metal, rather than in an aqueous alkali metal hydroxide solution. The dissolution process may proceed from solid dihydroxydiarylalkane, typically in flake or prill form, or from molten dihydroxydiarylalkane. The alkali metal hydroxide / aqueous alkali metal hydroxide solution used, in the case of sodium hydroxide or aqueous sodium hydroxide, may be produced, for example, by the amalgam process or the so-called membrane process. Both methods have been used for a long time and are well known to those skilled in the art. When aqueous sodium hydroxide is used, it is preferably produced by the membrane process.

[0041] In such aqueous solutions and / or phases, the dihydroxydiarylalkane(s) are completely or partly in the form of the corresponding alkali metal / dialkali metal salts.

[0042] The optional actual metered addition of dihydroxydiarylalkane(s) after or during the introduction of phosgene can be carried out as long as phosgene or its direct derivative chlorocarboxylic acid ester is present in the reaction solution.

[0043] The organic phase in step (a) contains not only at least one solvent but also at least phosgene. The organic phase already contains all or part of the required phosgene before the mixture is formed. Preferably, the organic phase contains the total amount of phosgene required, including the excess amount of phosgene used, before the mixture is formed. Phosgene can be introduced into the organic phase in gaseous or liquid form.

[0044] The addition of at least one chain terminator to the reaction system of step (a) is carried out in step (b). The reaction system of step (a) preferably still contains unconverted phosgene. The at least one chain terminator is usually monofunctional. The at least one chain terminator is preferably selected from the group consisting of phenol, alkylphenol, and its chlorocarbonate or acid chloride of monocarboxylic acid, preferably selected from phenol, tert-butylphenol, isooctylphenol, and cumylphenol. Any desired mixture of the listed chain terminators can be used.

[0045] In a particularly preferred embodiment of the process according to the invention, phenol is used as a chain terminator. In step (b), phenol is preferably used in the form of a solution comprising at least one organic solvent and phenol at a concentration of 5% to 40% by weight, preferably 10% to 25% by weight. In this embodiment, the aqueous phase is preferably adjusted to a pH of 11.3 to 11.6 at the end of the reaction (i.e., step (b)). The addition of phenol and the adjustment of the pH to 11.3 to 11.6 are preferably carried out before the addition of the catalyst.

[0046] In another preferred embodiment of the process according to the present invention, p-tert-butylphenol is used as a chain terminator. The p-tert-butylphenol in step (b) is preferably used in the form of a solution containing at least one organic solvent and p-tert-butylphenol at a concentration of 2% to 25% by weight, preferably 3% to 15% by weight. In this embodiment, the aqueous phase is preferably adjusted to a pH of 11.5 to 11.8 at the end of the reaction (i.e., step (b)). The addition of p-tert-butylphenol and the adjustment of the pH to 11.5 to 11.8 are preferably carried out before the addition of the catalyst.

[0047] In step (b), one or more branching agents or a mixture of branching agents may optionally be added to the synthesis. However, such branching agents are preferably added before the chain terminator(s). Such branching agents are very particularly preferably added to the aqueous phase in process step (a) together with a solution of at least one dihydroxydiarylalkane. Branching agents used include, for example, trisphenols, quaterphenols, chlorides of tri- or tetracarboxylic acids, or polyphenols, or mixtures of acid chlorides.

[0048] Examples of compounds having three or more phenolic hydroxyl groups that are suitable as branching agents are phloroglucinol, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)hept-2-ene, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptane, 1,3,5-tri(4-hydroxyphenyl)benzene, 1,1,1-tri(4-hydroxyphenyl)ethane, tri(4-hydroxyphenyl)phenylmethane, 2,2-bis[4,4-bis(4-hydroxyphenyl)cyclohexyl]propane, 2,4-bis(4-hydroxyphenyl-2-isopropyl)phenol, and tetra(4-hydroxyphenyl)methane.

[0049] Other examples of trifunctional compounds suitable as branching agents include 2,4-dihydroxybenzoic acid, trimesic acid, cyanuryl chloride, and 3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole. Particularly preferred branching agents are 3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole and 1,1,1-tri(4-hydroxyphenyl)ethane.

[0050] It has been found to be advantageous if at least one addition of aqueous alkali metal hydroxide solution is carried out while the dispersion is still an oil-in-water dispersion.Addition of aqueous alkali metal hydroxide solution to a water-in-oil emulsion generally results in a non-ideal molecular weight distribution.Because at least one chain terminator is preferably added in advance, this also means that at least one chain terminator is preferably added to the oil-in-water dispersion.According to the present invention, it is possible to change the dispersion from a water-in-oil dispersion to an oil-in-water dispersion during the process.

[0051] The method according to the present invention comprises: (c) adding at least one catalyst to the mixture resulting from step (b); Further includes:

[0052] It is preferred if at least one catalyst is selected from the group consisting of tertiary amines, organic phosphines, and any desired mixtures. Very particularly preferably, at least one catalyst is a tertiary amine or a mixture of at least two tertiary amines.

[0053] The tertiary amine is also preferably triethylamine, tributylamine, trioctylamine, N-ethylpiperidine, N-methylpiperidine, or Ni / n-propylpiperidine, which compounds are described in the literature as typical interfacial catalysts, are commercially available, and are well known to those skilled in the art. The catalysts can also be added to the synthesis individually, as a mixture, or simultaneously or successively, optionally before phosgenation, but are preferably metered in after the introduction of phosgene. The metering of one or more catalysts can be carried out as a pure substance, in an inert solvent, preferably the solvent of the organic phase in the polycarbonate synthesis or one of the solvents, or as an aqueous solution. When a tertiary amine is used as the catalyst, its metering can be carried out, for example, as an ammonium salt with an acid, preferably a mineral acid, in particular hydrochloric acid, in an aqueous solution. When two or more catalysts are used, or when metering in portions of the total amount of catalyst, it is understood that different metering modes at different locations or different times can be used. The total amount of catalyst used is preferably 0.001 mol % to 10 mol %, more preferably 0.01 mol % to 8 mol %, particularly preferably 0.05 mol % to 5 mol %, based on the number of moles of dihydroxydiarylalkane used.

[0054] Dispersing machines are known to those skilled in the art in principle.According to the present invention, it is preferred that at least one nozzle, pipe baffle, static mixer, pump and / or jet dispersing machine is used as the dispersing machine in process step (a).In particular, jet dispersing machines are preferred, as they allow the preferred direction of metered addition.Dispersing machines suitable for the context of the present invention are described, for example, in EP-A-1368407 and EP-A-1599520.

[0055] Suitable nozzles are, for example, slot nozzles, annular slot nozzles, orifice nozzles, Lefos nozzles or smooth jet nozzles. A person skilled in the art can use his knowledge in the art to select the nozzle openings such that the energy input according to the invention is obtained.

[0056] The pressure used may be preferably 0.001 MPa to 1 MPa, particularly preferably 0.001 MPa to 0.5 MPa.

[0057] In a preferred embodiment of the process according to the invention, a disperser is used, in which the organic and aqueous phases are preferably fed to the pre-disperser separately from each other and / or only one of these phases is fed to the pre-disperser by means of only one pump in each case. The pressure of these pumps is preferably below 2.5 MPa, preferably between 0.001 MPa and 0.5 MPa. The pre-disperser preferably produces a water-in-oil dispersion.

[0058] Suitable nozzles as pre-dispersers include any desired nozzles, such as slot nozzles, annular slot nozzles, orifice nozzles, Lefos nozzles, or smooth jet nozzles, and jet dispersers. Suitable nozzles as homogenizing nozzles also include any desired nozzles, such as slot nozzles, annular slot nozzles, orifice nozzles, Lefos nozzles, or smooth jet nozzles, and jet dispersers.

[0059] In a more preferred embodiment, a rotary disperser such as that described in EP 2090605 can be used. The pre-disperser is preferably followed by the disperser used in the present invention. The energy input specified by the present invention is carried out here.

[0060] The process according to the invention is carried out as a continuous process. Thus, the entire reaction, i.e., the reaction and further condensation, can be carried out in a stirred tank, a tubular reactor, a pumped-circulation reactor, or a stirred tank cascade, or a combination thereof. The use of such mixing devices ensures that the aqueous and organic phases are ideally demixed only when the synthesis mixture is completely reacted, i.e., when the hydrolyzable chlorine of phosgene or chlorocarbonate is no longer present. In a preferred embodiment of the process according to the invention, the disperser in process step (a) is followed by a flow reactor. This arrangement makes it particularly advantageous to achieve extremely short residence times of the passing mixture of less than 0.5 seconds. In a further preferred embodiment of the process according to the invention, a recirculation reactor follows.

[0061] The recirculation reactor used is preferably a tank reactor having a recirculation loop and a recirculation rate of 5 to 15 times, preferably 7.5 to 10 times, the throughput rate. The residence time of the reaction mixture in this reactor is preferably 2 to 20 minutes, particularly preferably 2 to 5 minutes.

[0062] In a further preferred embodiment of the process according to the invention, the recycle reactor is followed by a further residence time reactor. The residence time of the reaction mixture in the recycle reactor and in the residence time reactor is in each case preferably from 2 to 20 minutes.

[0063] In a preferred aspect of the present invention, the continuous process according to the present invention, in all of the above-described embodiments and preferred aspects, is characterized in that in process step (b), at least one chain terminator is introduced into a reaction system comprising at least one dihydroxydiarylalkane, phosgene, and the reaction product R of the at least one dihydroxydiarylalkane and phosgene at a time when the reaction product R is a mixture of compounds having an average degree of polymerization of at least one unit and at most six units formed from the at least one dihydroxydiarylalkane by reaction with phosgene. At the time of addition of the at least one chain terminator, the reaction system comprises at least one dihydroxydiarylalkane, phosgene, and the reaction product R. The reaction system may also comprise at least one catalyst at this time, although this is not preferred. At the time of addition of the at least one chain terminator, the reaction system preferably comprises, and very particularly preferably consists of, the at least one dihydroxydiarylalkane, phosgene, the reaction product R, and the solvent necessary for carrying out the interfacial process. The solvent is preferably an aqueous alkali metal hydroxide solution and at least one organic solvent.

[0064] As mentioned above, according to the present invention, the chain terminator is preferably introduced into the reaction system "early," which is defined according to the present invention as the point when the reaction product R is a mixture of compounds having an average degree of polymerization of at least 1 unit and at most 6 units.

[0065] The term "degree of polymerization" is known to those skilled in the art. The degree of polymerization preferably indicates the number of units in the oligomeric reaction product R formed from at least one dihydroxydiarylalkane by reaction with phosgene. The reported degree of polymerization is an average value. This means that the degree of polymerization is preferably determined by the number-average molar mass M n This is because it is determined based on the M nand the molar mass of the repeating units (units formed from at least one dihydroxydiarylalkane by reaction with phosgene; preferably units represented by general chemical formula (I)). On the other hand, according to the present invention, the number-average molar mass M n is preferably determined by gel permeation chromatography (GPC). It is particularly preferred that this mass be determined by GPC according to DIN 55672-1:2016-03, calibrated against bisphenol A polycarbonate standards using dichloromethane as the eluent. According to the invention, it is very particularly preferred that the molecular weights Mw (weight average), Mn (number average), and Mv (viscosity average) be determined by gel permeation chromatography according to DIN 55672-1:2007-08 using BPA polycarbonate calibration. Calibration was carried out using linear polycarbonates of known molar mass distribution (e.g., from PSS Polymer Standards Service GmbH, Germany). Method 2301-0257502-09D (German version, 2009) from Currenta GmbH & Co. OHG, Leverkusen was used. Dichloromethane was used as the eluent. The column combination consisted of cross-linked styrene-divinylbenzene resin. The GPC may comprise one or more commercially available GPC columns connected in series for size-exclusion chromatography, selected to allow sufficient separation of polymer molar masses, particularly those of aromatic polycarbonates with weight-average molar masses Mw ranging from 2,000 g / mol to 100,000 g / mol. The analytical column typically has a diameter of 7.5 mm and a length of 300 mm. The particle size of the column material ranges from 3 μm to 20 μm. The concentration of the solution analyzed was 0.2 wt%. The flow rate was adjusted to 1.0 ml / min, and the solution temperature was 30°C. Detection was performed using a refractive index (RI) detector.

[0066] The process according to the invention is further preferably characterized in that the compounds of the mixture of reaction products R are of the general chemical formula (I): [ka] (In the formula, R1 and R2 independently of one another represent H, C1-C18 alkyl, C1-C18 alkoxy, halogen, for example Cl or Br, or in each case optionally substituted aryl or aralkyl, preferably H or C1-C12 alkyl, particularly preferably H or C1-C8 alkyl, very particularly preferably H or methyl, R3 represents H, (C=O)-Cl or (C=O)-OH; R4 represents OH or Cl; X represents a single bond, -SO2-, -CO-, -O-, -S-, C1-C6 alkylene, C2-C5 alkylidene, or C5-C6 cycloalkylidene, which may be substituted with C1-C6 alkyl, preferably methyl or ethyl, or represents a C6-C12 arylene, which may be fused to a further aromatic ring optionally containing a heteroatom; n represents the degree of polymerization and therefore the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene and may have a value on average of 1 to 6, preferably 1 to 5, particularly preferably 1 to 4, very particularly preferably 1 to 3).

[0067] According to the present invention, it is also possible that the reaction product R may be in a partially hydrolyzed form. The chlorine of the chloroformate group is liberated and a carbonate is formed. However, according to the present invention, this side reaction is undesirable. This means that the reaction product R is a mixture containing this type of hydrolysis product. However, this is less preferred. The compounds of the mixture of reaction product R are preferably: R1 and R2 each independently of one another represent H or C1-C12 alkyl, particularly preferably H or C1-C8 alkyl, very particularly preferably H or methyl, R3 represents H or (C=O)-Cl; R4 represents Cl; X represents a single bond, C1-C6 alkylene, C2-C5 alkylidene or C5-C6 cycloalkylidene, which may be substituted with methyl or ethyl; It is represented by the general chemical formula (I), in which n represents the degree of polymerization and therefore the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene and can have a value on average of 1 to 6, preferably 1 to 5, particularly preferably 1 to 4, very particularly preferably 1 to 3.

[0068] The compounds of the mixture of reaction products R are very particularly preferably R1 and R2 each independently represent H or methyl; R3 represents H or (C=O)-Cl; R4 represents OH; X represents isopropylidene or 3,3,5-trimethylcyclohexylidene; It is represented by the general chemical formula (I), in which n represents the degree of polymerization and therefore the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene and can have a value on average of 1 to 6, preferably 1 to 5, particularly preferably 1 to 4, very particularly preferably 1 to 3.

[0069] The use of bisphenol A as dihydroxydiarylalkane in the process according to the invention preferably results in an average molar mass Mn (number average) ranging from 352 g / mol (BPA with two chlorocarbonate end groups) to 1623 g / mol (n=average 6), depending on the nature of the end groups R3 and / or R4 (OH or Cl) in the general chemical formula (I). Particular preference is given to molar masses below 1000 g / mol.

[0070] It has been found to be advantageous if the at least one chain terminator is first thoroughly mixed before it can react.The at least one chain terminator is preferably uniformly distributed.This can be achieved, for example, by using a static mixer after adding the at least one chain terminator and before it reacts.

[0071] It has also been found to be advantageous if the at least one chain terminator is fed to the reaction system as an organic phase rather than as an aqueous phase.

[0072] However, it has proven advantageous to add the at least one chain terminator at a pH of 8 to 11, preferably 9 to 10. At higher pH values ​​(above 11), it has been found that the distribution of the at least one chain terminator between the organic and aqueous phases is unfavorable. In this case, a large proportion is present in the aqueous phase and is unable to react with the chloroformate end groups. Therefore, according to the present invention, it is preferred that the process according to the present invention does not involve the addition of an aqueous alkali metal hydroxide solution before the addition of the at least one chain terminator. This is particularly evident when the at least one chain terminator contains a phenol. For this reason, it is advantageous to add the aqueous alkali metal hydroxide solution only after the addition of the at least one chain terminator.

[0073] Despite the small phosgene excess, the process according to the invention allows for good phase separation at the end of the reaction, achieving both a low water content in the organic phase and a low residual monomer content in the aqueous phase, while also avoiding contamination of the product with catalyst components.

[0074] The workup involves allowing the reacted, at least two-phase reaction mixture, which contains at most trace amounts of chlorocarbonates, preferably less than 2 ppm, to stand and undergo phase separation. The alkaline aqueous phase is optionally recycled as aqueous phase in the polycarbonate synthesis in whole or in part, or sent to a wastewater workup, where fractions of the solvent and catalyst are separated and optionally recycled to the polycarbonate synthesis. In another workup variant, separation of organic impurities, in particular solvent and polymer residues, and optional adjustment to a specific pH, for example by adding sodium hydroxide solution, is followed by separation of salts, which may be sent, for example, to chloralkali electrolysis, and the aqueous phase can optionally be returned to the polycarbonate synthesis.

[0075] The organic phase containing the polycarbonate may then be purified by a variety of methods known to those skilled in the art to remove alkali metal, ionic, or catalytic contaminants.

[0076] After one or more precipitation processes, optionally via settling tanks, stirred tanks, coalescers or separators and / or combinations of these means (optionally using active or passive mixing devices, and possibly adding water in each or several separation steps), the organic phase generally still contains a portion of the catalyst(s) as well as a portion of the alkaline aqueous phase in fine droplets. After this rough separation of the alkaline aqueous phase, the organic phase can be washed one or more times with dilute acid, mineral acid, carboxylic acid, hydroxycarboxylic acid, and / or sulfonic acid. Aqueous mineral acids, particularly hydrochloric acid, phosphorous acid, phosphoric acid, or mixtures of these acids, are preferred. The concentration of these acids should preferably be between 0.001% and 50% by weight, preferably between 0.01% and 5% by weight. The organic phase can further be repeatedly washed with demineralized or distilled water. After each washing step, separation of the organic phase, optionally dispersed with a portion of the aqueous phase, is carried out using a settling tank, a stirred tank, a coalescer or separator, and / or a combination of these means, and washing water between washing steps can optionally be added using an active or passive mixing device. An acid, preferably dissolved in the solvent used in the polymer solution, can optionally be added during or after these washing steps. It is preferred to use hydrogen chloride gas, phosphoric acid, or phosphorous acid, which can optionally also be used as a mixture. After the final separation step, the purified polycarbonate solution thus obtained should preferably contain no more than 5% by weight of water, preferably less than 1% by weight, and very particularly preferably less than 0.5% by weight.

[0077] Isolation of the polycarbonate from the solution can be achieved by evaporating the solvent using temperature, vacuum, or heated entrained gas. Other isolation methods include, for example, crystallization and precipitation.

[0078] Concentration of the polycarbonate solution, and optionally further isolation of the polycarbonate, is carried out by distillative removal of the solvent, optionally by heating and expansion, which is called the "flash process." Such processes are known to those skilled in the art and are described, for example, in "Thermal Separation Processes," VCH Verlagsanstalt 1988, p. 114. If a heated carrier gas is instead sprayed with the solution to be concentrated, this is called "spray evaporation / spray drying," and is described, for example, by Vauck, "Grundoperationen chemischer Verfahrenstechnik," Deutscher Verlag für Grundstoffindustrie 2000, 11th edition, p. 690. All of these processes are described in patent literature and textbooks and are well known to those skilled in the art.

[0079] Highly concentrated polycarbonate melts can be obtained by thermal solvent removal (distillative removal) or by the more technically efficient flash process. In the flash process, polymer solutions are repeatedly heated under slight positive pressure to temperatures above their boiling point at atmospheric pressure, and then these solutions, superheated to atmospheric pressure, are decompressed in a vessel at lower pressure, e.g., atmospheric pressure. It can be advantageous to not have too many concentration stages, or in other words, superheated temperature stages, but rather to choose a two- to four-stage process.

[0080] From the highly concentrated polycarbonate melt thus obtained, the solvent residues can be removed by means of vented extruders (see, for example, BE-A-866991, EP-A-0411510, U.S. Pat. No. 4,980,105, DE-A-3332065), thin-film evaporators (see, for example, EP-A-0267025), falling-film evaporators, strand evaporators, foam evaporators (see, for example, U.S. Pat. No. 2012 / 015763), or by friction compression. The solvent can be removed by compaction (see, for example, EP-A-0 460 450), optionally with the addition of further entraining agents such as nitrogen or carbon dioxide, or by using a vacuum (see, for example, EP-A-0 03996, EP-A-0 256 003, U.S. Pat. No. 4,423,207), or alternatively by subsequent crystallization (see, for example, DE-A-3,429,960) and / or by baking out the solvent residues in the solid phase (see, for example, U.S. Pat. No. 3,986,269, DE-A-2,053,876). These processes and the apparatus required therefor are described in the literature and are well known to those skilled in the art.

[0081] Polycarbonate granules can be obtained, if possible, by direct spinning of the melt followed by granulation, or by using discharge extruders from which they are spun in air or in a liquid (usually water). If an extruder is used, the polycarbonate melt can be mixed with additives upstream of the extruder, optionally using a static mixer or via side extruders of the extruder.

[0082] Alternatively, the polycarbonate solution may be spray-evaporated. During spraying, the optionally heated polycarbonate solution is jetted into a container under negative pressure or into a container under atmospheric pressure using a nozzle together with a heated carrier gas, such as nitrogen, argon, or steam. In either case, depending on the concentration of the polymer solution, a polymer powder (dilute) or flakes (concentrated) is obtained, from which the last residues of solvent may need to be removed as described above. Granules can then be obtained by compounding extruders followed by spinning. Here, too, the additives described above can be added to peripheral equipment or the extruder itself. Due to the low poured density of the powders and flakes, polymer powders often require a compaction step before extrusion.

[0083] The addition of a non-solvent to the polycarbonate allows the polymer to be largely extracted from the washed, optionally further concentrated, polycarbonate solution. The non-solvent acts as a precipitant. It is advantageous to add a small amount of the non-solvent first, optionally allowing a waiting period between the addition of each portion of the non-solvent. It is also advantageous to use different non-solvents. Precipitants used include, for example, aliphatic or alicyclic hydrocarbons, especially heptane, isooctane, or cyclohexane; alcohols, such as methanol, ethanol, or isopropanol; ketones, such as acetone, or mixtures thereof. During precipitation, the polymer solution is generally slowly added to the precipitant. The polycarbonate thus obtained is processed into granules as described in spray evaporation, and optionally additives are added.

[0084] In another method, the precipitated and crystallized product or amorphously solidified product is crystallized into a finely divided form and further condensed to higher molecular weight by evaporation of one or more non-solvents for the polycarbonate, simultaneously heating below the glass transition temperature, optionally in the presence of oligomers with different end groups (phenolic and chain terminator-terminated), which is called solid-phase condensation.

[0085] Additives can be added to increase shelf life or color stability (stabilizers), to facilitate processing (e.g., mold release agents, flow promoters, antistatic agents), or to tailor the properties of the polymer to specific needs (impact modifiers, e.g., rubber; flame retardants, colorants, glass fibers).

[0086] These additives can be added to the polymer melt either alone or in any mixture, together with or in a mixture of different additives. This can be done directly during the isolation of the polymer or after melting the granules in a so-called compounding process. These additives or their mixtures can be added to the polymer melt as solids, preferably as powders, or as melts. Another aspect of metered addition is the use of masterbatches or mixtures of masterbatches of additives or additive mixtures.

[0087] Suitable additives are described, for example, in "Additives for Plastics Handbook", John Murphy, Elsevier, Oxford 1999, and in "Plastics Additives Handbook", Hans Zweifel, Hanser, Munich 2001.

[0088] A further aspect of the present invention is to provide a method for reducing the amount of excess phosgene in the production of polycarbonate by an interfacial process by adding 2.5×e 6 W / m 3 ~5.0×e 7 W / m 3 , preferably 3.0 × e6 W / m 3 ~4.0×e 7 W / m 3 , particularly preferably 1.0 × e 7 W / m 3 ~3.5×e 7 W / m 3 The present invention provides a process for producing a polycarbonate having an energy input of 100 wt. % or more, wherein the organic phase comprises at least one solvent suitable for polycarbonate and at least a portion of the phosgene, and the aqueous phase comprises at least one dihydroxydiarylalkane, water, and 1.8 to 2.2 mol, preferably 1.95 to 2.05 mol, of an aqueous alkali metal hydroxide solution per mol of dihydroxydiarylalkane, and optionally at least one chain terminator. As described above, the use of this specific energy input preferably also simultaneously results in a reduction in the oligomer content in the resulting polycarbonate. Similarly, the use of this specific energy input preferably also simultaneously results in a reduction in the content of di-chain terminator carbonates in the resulting polycarbonate.

[0089] More preferably, the energy input is carried out via a disperser. Suitable dispersers have been described above. It is also preferred if the process for producing polycarbonate by the interfacial method is carried out continuously. It has proven particularly advantageous that suitable dispersers can be easily installed and / or retrofitted into existing plants. More preferably, in the use according to the invention, an excess of phosgene of 3 mol% to 20 mol%, preferably 4 mol% to 10 mol%, particularly preferably 5 mol% to 9 mol%, based on the total dihydroxydiarylalkanes used, is used.

[0090] The following examples are intended to be illustrative of the present invention and are not to be construed as limiting. [Brief explanation of the drawings]

[0091] [Figure 1]Information about Figure 1: Solid line: original GPC, normalized to area = 1 Dotted line: Schulz-Flory distribution adjusted so that its maximum coincides with the maximum of the GPC Dashed line: difference between the two curves (solid and dotted) The percentage of oligomers is obtained from the integration of the difference curves from 500 g / mol to 5000 g / mol. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0092] The molecular weight distribution and average values ​​Mn (number average) and Mw (weight average) were determined by gel permeation chromatography (GPC) using a Waters "Mixed Bed" column with methylene chloride as the eluent (BPA homopolycarbonate standard with Mw 31000 g / mol).

[0093] In addition to the standing evaluation, the deviation of the GPC from the ideal Schulz-Flory distribution was also measured. This was done by first normalizing the GPC and determining the area under the solid line in the diagram in Figure 1. This area was normalized to 1. Furthermore, the Schulz-Flory (SF) distribution was adjusted so that both the maximum height and molecular weight matched those of the measured distribution (dotted line in Figure 1). The difference between the measured and adjusted SF distributions gives the difference distribution (dashed line in Figure 1). Here, the Schulz-Flory distribution is narrower, and therefore the difference distribution is positive (excluding measurement imprecision). At its maximum, the difference based on this method is zero, resulting in a distribution of difference divided into low and high molecular weight fractions (see also Figure 1).

[0094] It is known from the prior art that a high oligomer content is detrimental to product quality. However, this generally only refers to the total content of low molecular weight compounds below a certain threshold, or to the content soluble in acetone. This has the drawback of capturing the unavoidable oligomer content, which also varies depending on the type of polycarbonate (viscosity, Mn). The method of the present invention modifies this correlation and determines only the process-specific oligomer content.

[0095] In the following, 2,2'-bis(4-hydroxyphenyl)propane (bisphenol A, BPA) was used as the dihydroxydiarylalkane, and the organic phase solvent was a mixture of approximately 50% by weight methylene chloride and 50% by weight monochlorobenzene. All examples produced polycarbonates with the specified weight average molecular weights, as determined by GPC (Waters "Mixed Bed" column, in methylene chloride, using a BPA homopolycarbonate standard with a Mw of 31,000 g / mol).

[0096] Example 1: Reduction of excess phosgene A series of laboratory tests were carried out using a pump and stirred reactor combination. In all experiments, 70.1 g / h of gaseous phosgene was dissolved in 772 g / h of organic solvent (1:1 methylene chloride / chlorobenzene) at -7 °C in a T-piece. The amount of solvent required to obtain a final 15 wt. % polycarbonate solution was calculated. The continuously supplied phosgene solution was contacted in a further T-piece with 912 g / h of a 15 wt. % alkaline aqueous BPA solution (2 mol NaOH per mol BPA) preheated to 30 °C. This aqueous BPA solution was dispersed in the aqueous phosgene solution using a stainless steel filter (pore size 60 μm) as a predisperser. In all cases, a water-in-oil dispersion was obtained. The energy input reported in Table 1 was then generated by a rotor pump.

[0097] The reaction mixture was passed through a Fink HMR040 mixing pump thermostated at 25°C, resulting in maximum possible conversion of phosgene at the end of the reaction pump, but still present. In Examples 1a, 1c, and 1d, 3.29 g / h of p-tert-butylphenol as a chain terminator was added downstream of this pump as a 3% by weight solution in the same solvent mixture added above. In a further HMR040 pump at 25°C, the reaction mixture was reacted with 53.95 g / h of 32% by weight aqueous sodium hydroxide solution, resulting in a pH of approximately 11.5 at the end of the reaction system. In Comparative Example 1b, 3.29 g / h of p-tert-butylphenol as a chain terminator was added as a 3% by weight solution in the same solvent mixture as above.

[0098] Two stirred tanks, each equipped with a gear pump from Ismatec, were used in each case. The metered addition of 0.679 g / h of catalyst (10% by weight of N-ethylpiperidine dissolved in chlorobenzene) in a T-piece in a Teflon hose was carried out between the two stirred tanks (and the gear pump).

[0099] A total of 156 g of polycarbonate in organic solution was continuously obtained and, together with the aqueous phase from the reaction, was sent to a phase separation vessel for separation of the phases. The polycarbonate solution was washed with 10 wt % HCl and dried at normal pressure and room temperature.

[0100] Table 1 summarizes the results obtained in Example 1.

[0101] [Table 1]

[0102] Example 1a shows that a high energy input in process step (a) results in a polycarbonate with a low content of oligomers and two chain terminator carbonates. In Example 1b, the chain terminators were added later.

[0103] Examples 1c and 1d of the present invention demonstrate that the excess phosgene can be reduced at high energy inputs, while at the same time obtaining polycarbonates with good or even improved oligomer and di-chain terminator carbonate contents. In Example 1b, NaOH is added earlier than the chain terminator, while the chain terminator is added early enough that phosgene is still presumably remaining in the reaction system.

[0104] Addition of a chain terminator at a time when no phosgene remains in the reaction system means that the reaction product R will, on average, have a higher average molecular weight, and therefore a higher proportion of oligomers is to be expected.

[0105] Example 2 The equipment used for the individual process steps was as follows: Process step (A): A disperser in the form of a perforated-plate nozzle, predisperser (with a perforated plate having a thickness of 2.35 mm and 5 holes each having a diameter of 2.5 mm, with a pressure drop of 0.2 bar at a flow rate of 5.2 m / s), a residence time in the predispersion space of 26 ms (in Examples 2a and 2b, the aqueous phase was dispersed in the organic phase by the predisperser, and in Comparative Example 2c, the organic phase was dispersed in the aqueous phase by the predisperser), and subsequent dispersion (Comparative Example 2c, which is particularly In Example 1 of Patent Document 5, the perforated plate is 2.35 mm thick and has a further perforated plate with 18 holes, each 1.5 mm in diameter, resulting in a pressure drop of 0.8 bar at a flow rate of 8.9 m / s; and in Examples 2a and 2b of the present invention, the perforated plate is 2.35 mm thick and has a further perforated plate with 18 holes, each 1.0 mm in diameter, resulting in a pressure drop of 0.8 bar at a flow rate of 8.9 m / s), whereby one liquid is dispersed into the other. Process step (B): A residence time reactor with a residence time of 0.2 seconds at 600 kg / h (bisphenol solution). Process step (C): A recirculating reactor with a metering point (for example for NaOH), a pump, a heat exchanger, an overflow vessel, a T-shaped take-off point with a volume of 140 l and equipped with a pH probe and a conductivity probe; redispersion occurs on entry into the recirculating reactor. In Example 2a, a chain terminator is added to the recirculating reactor. Process step (D): A delivery pump with upstream metering points for the chain terminator (in Example 2b and Comparative Example 2c, a chain terminator is added here; in Example 2a, nothing is added here) and for the NaOH solution, a static mixer in between, and downstream of this a helical-tube reactor (first dwell reactor) with a mixing zone and a dwell zone and a total volume of 60 l, and downstream of this a further helical-tube reactor (second dwell reactor) with a total volume of 80 l and a metering point for the catalyst at the beginning of the reactor. Subsequent phase separation: Separation vessel (4.15 m at 50% fill level) 3 size).

[0106] In process step (A) the following material flows were used: In Examples 2a and 2b, 500 kg / h of aqueous bisphenol solution (15% by weight of a mixture of bisphenol A and bisphenol TMC relative to the total weight of the solution, 2.13 mol NaOH / mol bisphenol solution) (the phosgene stream and the solvent mixture stream (see below) were metered corresponding to the reduced bisphenol stream), or In Comparative Example 2c, 600 kg / h of aqueous bisphenol solution (15% by weight of bisphenol A relative to the total weight of the solution, 2.13 mol NaOH / mol bisphenol solution) 44.6 kg / h of phosgene 520 kg / h of a solvent mixture consisting of 54% by weight of methylene chloride and 46% by weight of chlorobenzene

[0107] No additional material streams were used in process steps (B) and (C).

[0108] In process step (D), the following material streams were additionally used upstream of the first retention reactor: 17.8 kg / h of t-butylphenol solution (20 wt. % in a solvent mixture of 54 wt. % methylene chloride and 46 wt. % chlorobenzene) 35 kg / h of aqueous NaOH solution containing 32% by weight of NaOH

[0109] In process step (D), the following material streams were additionally used in the second retention reactor: 22.7 kg / h of catalyst solution (3 wt. % solution, ethylpiperidine in a solvent mixture of 54 wt. % methylene chloride and 46 wt. % chlorobenzene)

[0110] The temperature in the recycle reactor was 35° C. (downstream of the heat exchanger) to 38° C. (upstream of the heat exchanger). The temperature in the helical tubular reactor in process step (D) was in each case 37° C., and the temperature in the separation vessel was 35° C.

[0111] The dispersion direction was set so that the organic phase was dispersed in the aqueous phase.

[0112] Table 2 summarizes the results obtained.

[0113] [Table 2]

[0114] In Examples 2a and 2b, a 19% excess of phosgene was used. In Comparative Example 2c, a 15% excess of phosgene was used. Because the bisphenol solutions in the Comparative Examples had different compositions than those in the Inventive Examples, adjustments to the excess of phosgene were necessary.

[0115] Nevertheless, it is clear that the energy inputs disclosed in the examples of Patent Document 5 result in polycarbonates with a relatively high oligomer content. By increasing the energy input (Inventive Examples 2a and 2b), this proportion can be reduced while maintaining an acceptable double chain terminator carbonate content. In Inventive Examples 2a and 2b, the different energy inputs resulted in the presence of a water-in-oil dispersion in process step (a), while in Comparative Example 2c, an oil-in-water dispersion was present.

[0116] In these examples too it is clear that this point of addition of the chain terminator entails additional advantages in terms of the content of oligomers and di-chain terminator carbonates.

Claims

1. A continuous process for producing polycarbonates by an interfacial process from at least one dihydroxydiarylalkane, phosgene, at least one catalyst, and at least one chain terminator, comprising the steps of: (a) forming a dispersion from an organic phase and an aqueous phase by continuously dispersing the organic phase in the aqueous phase or the aqueous phase in the organic phase in a disperser, wherein the organic phase comprises at least one solvent suitable for the polycarbonate and at least a portion of the phosgene, and the aqueous phase comprises the at least one dihydroxydiarylalkane, water, and 1.8 mol to 2.2 mol of an aqueous alkali metal hydroxide solution per mol of dihydroxydiarylalkane; (b) adding at least one chain terminator to the dispersion from step (a); (c) adding at least one catalyst to the mixture resulting from step (b); The energy input by the disperser in step (a) is 2.5 x e ６ W / m ３ ~5.0 x e ７ W / m ３ A continuous process characterized in that:

2. 10. The continuous process of claim 1, wherein the process includes one or more steps of adding an aqueous alkali metal hydroxide solution.

3. 3. The continuous process of claim 2, wherein the addition of the at least one chain terminator to the reaction system in process step (b) occurs at a point prior to the first of the one or more additions of the aqueous alkali metal hydroxide solution.

4. 4. A continuous process according to claim 1, characterized in that in process step (a) there is present an excess of phosgene of from 3 mol % to 20 mol %, relative to the sum of the dihydroxydiarylalkanes used.

5. 5. A continuous process according to claim 1, characterized in that as disperser in process step (a) at least one nozzle, pipe baffle, static mixer, pump and / or jet disperser is used.

6. 6. The continuous process according to claim 1 , wherein in process step (b), the at least one chain terminator is introduced into the reaction system comprising at least the at least one dihydroxydiarylalkane, phosgene, and the reaction product R of the at least one dihydroxydiarylalkane and phosgene at a time when the reaction product R is a mixture of compounds which, on average, have a degree of polymerization of at least 1 unit and at most 6 units formed from the at least one dihydroxydiarylalkane by reaction with phosgene.

7. To reduce the amount of excess phosgene when producing polycarbonate by the interfacial method, 2.5 x e to a system containing an organic phase and an aqueous phase ６ W / m ３ ~5.0 x e ７ W / m ３ Utilizing an energy input of the organic phase comprises at least one solvent suitable for the polycarbonate and at least a portion of the phosgene; The aqueous phase comprises at least one dihydroxydiarylalkane, water, and 1.8 to 2.2 mol of an aqueous alkali metal hydroxide solution per 1 mol of dihydroxydiarylalkane.

8. 8. Use according to claim 7, characterized in that the energy input is via a disperser.

9. 9. Use according to claim 7 or 8, characterized in that the process for producing polycarbonate by the interfacial method is carried out continuously.

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