Process for preparing polycarbonate with reduced phosgene excess

Abstract

The present invention relates to a process for preparing polycarbonates from at least one dihydroxydiarylalkane, phosgene, at least one catalyst and at least one chain terminator by the phase interface process, wherein the process enables a reduced phosgene excess with a given energy input for dispersing the aqueous and organic phases. In addition, the process provides polycarbonates with a low oligomer fraction and a low di-chain terminator carbonate fraction.

Description

[0001] The present invention relates to a process for preparing polycarbonates from at least one dihydroxydiarylalkane, phosgene, at least one catalyst and at least one chain terminator by the interfacial process, wherein the process enables a reduced phosgene excess by a given energy input for dispersing the aqueous and organic phases. At the same time, the process according to the invention produces polycarbonates with a low oligomer fraction and a low di-chain terminator carbonate fraction. The invention also relates to the use of a given energy input for dispersing the aqueous and organic phases for reducing the phosgene excess in a process for preparing polycarbonates by the interfacial process.

[0002] The preparation of polycarbonates by the phase interface process has been described in the following literature: Schnell "Chemistry and Physics of Polycarbonates", Polymer Reviews, Volume 9, Interscience Publishers, New York, London, Sydney 1964, pages 33-70; 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)"; pages 75-90, D. Freitag, U. Grigo, PR Müller, N. Nouverne ', BAYER AG, "Polycarbonates" in Encyclopedia of Polymer Science and Engineering, Volume 11, Second Edition, 1988, pages 651-692 and finally Dres U. Grigo, K Kircher and PR Müller "Polycarbonate" in Becker / Braun, Kunststoff Handbuch, Volume 3 / 1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Crul Hanser Verlag Munich, Vienna 1992, pp. 118-145.

[0003] Furthermore, for example, EP-A 0 517 044 describes phase interface processes for preparing polycarbonates.

[0004] Here, the phosgenation of the disodium salt of a bisphenol or a mixture of different bisphenols, which has been previously placed in an alkaline aqueous solution or suspension, is usually carried out in the presence of an inert organic solvent or solvent mixture, which forms, in addition to the aqueous phase, a second organic phase. The oligocarbonates formed, which are present predominantly in the organic phase, are condensed with the aid of suitable catalysts to form high molecular weight polycarbonates dissolved in the organic phase, the molecular weight being controllable by suitable chain terminators (for example monofunctional phenols). Finally, the organic phase is separated and the polycarbonate is isolated therefrom by various processing steps.

[0005] The continuous method of preparing condensation products by using phosgene through the phase interface method, for example, preparing aromatic polycarbonates or polyester carbonates or their oligomers, usually has the following disadvantages, that is, more phosgene than the product balance required must be used to accelerate the reaction and / or improve phase separation. Then, the excess phosgene is decomposed in the form of by-products (for example, additional salt or alkali metal carbonate compounds) during the synthesis. The continuous phase interface method for preparing aromatic polycarbonates usually uses an excess of about 20 mol% of phosgene based on the added bisphenol salt (see D. Freitag, U. Grigo, PR Müller, N. Nouvertne', BAYER AG, "Polycarbonates" in Encyclopedia of Polymer Science and Engineering, Volume 11, Second Edition, 1988, pp. 651-692).

[0006] In the case of a reduction in the excess phosgene, undesirable side effects occur, such as poor separation of the dispersion after the last reaction step and thus an increased water content in the organic solution and / or an increased residual monomer or chain terminator content in the wastewater. Various methods for reducing the excess phosgene are discussed in the literature.

[0007] DE-A 2 725 967 discloses that it is advantageous for the phosgene yield of the process if the aqueous phase and the phosgene-comprising organic phase are first combined in a tube and then introduced into a tank reactor.

[0008] According to the continuous phase interface process for preparing polycarbonates known from EP-A-304 691, an aqueous phase from diphenols and the exact amount of alkali metal hydroxide is combined with an organic phase comprising phosgene in a tube using a static mixer. Only prepolymers with molecular weights of 4000 to 12000 g / mol can be prepared using this process.

[0009] EP 0 520 272 B1 discloses that a small excess of phosgene can be achieved by splitting the stream of the BPA solution. A disadvantage of this process is also the increased outlay and complexity of metering the second BPA stream.

[0010] DE 10 2008 012 613 A1 discloses a continuous process for preparing polycarbonate, in which a disperser is used to disperse the organic phase and the aqueous phase. It is described here as being advantageous to produce an oil-in-water dispersion by means of a disperser. For this purpose, the document generally discloses using a 2*e 6 W / m 3 to 5*e 9 W / m 3 , preferably 5*e 6 W / m 3 to 1 * e 9 W / m 3 In fact, the examples in this document disclose 1.2* e 6 W / m 3 energy input, whereby an oil-in-water dispersion is present. Since the energy input in the examples is not consistent with the generally disclosed energy input range, it is conceivable that the generally disclosed energy input in the specification is incorrectly stated. The document focuses only on reducing the phosgene content and rarely discusses the properties of the resulting polycarbonate. In particular, it does not mention either the oligomer ratio in the polycarbonate or the content of di-chain terminator carbonate.

[0011] However, the properties of the resulting polycarbonate (PC) are influenced by the proportion of oligomers and the proportion of di-chain terminator carbonates in the PC. According to the invention, the term "di-chain terminator carbonate" is understood to mean a compound which is produced by the reaction of two chain terminator molecules with phosgene to form a carbonate. The PC properties affected thereby include, in particular, impact toughness, glass transition temperature and performance at high temperatures. In addition, low molecular weight compounds can lead to bleaching during the preparation of the CD. It should also be noted that the chain terminator which is actually required for the reaction and its viscosity control is lost by the formation of di-chain terminator carbonates. Therefore, the higher the proportion of di-chain terminators in the polycarbonate, the higher the required amount of chain terminators, which is not very favorable economically and ecologically on the one hand and makes viscosity control in the process difficult on the other hand. It is therefore desirable to keep the content of di-chain terminator carbonate as low as possible.

[0012] The formation of di-chain terminator carbonate is carried out by the reaction of phosgene with a chain terminator. Therefore, the chain terminator is usually added to the reaction system only when the phosgene is completely converted. For example, this can be achieved by using a multi-stage process, in which oligomers are first prepared in the first stage, which are further condensed in the second stage, or the chain terminator is added very late in the process at a high conversion, i.e., when a polycarbonate of a larger molecular weight has been constructed. However, according to conventional theory, when the chain terminator is added only at a high conversion, the content of oligomers in the resulting polycarbonate increases. It has been described that a high oligomer ratio leads to brittle low molecular weight PC, which can lead to a decrease in molecular weight and a decrease in impact toughness during extrusion due to transesterification. Therefore, in the prior art, the method is usually carried out in such a way that a compromise is reached between a high oligomer content and a low di-chain terminator carbonate content in the polycarbonate or a low oligomer content and a high di-chain terminator carbonate content.

[0013] EP 0 408 924 A2 describes the preparation of low molecular weight polycarbonates with a narrow molecular weight distribution, i.e. a low oligomer fraction. In order to achieve this narrow distribution, the prior art proposes a two-stage process in which phosgene-free bischloroformates with a degree of polymerization of 0 to 6 are capped with, for example, phenol, and the resulting capped bischloroformates are subsequently condensed by adding a catalyst and a base. Here, phenol is added as a chain terminator to the bischloroformate solution at a point in time when no phosgene is (anymore) present in the solution. EP 0 289 826 A2 likewise relates to the preparation of polycarbonates with a low oligomer fraction. Here, too, starting from bischloroformates with a degree of polymerization of 0 to 6 is used. According to Example 2, the bischloroformate is prepared in a reaction that first uses a large excess of phosgene (739.3 mmol phosgene to 250 mmol bisphenol A). Therefore, the unreacted part of the phosgene is subsequently decomposed by adding NaOH. Only then is the chain terminator p-tert-butylphenol added. This means that here too, the chain terminator is added to the reaction system at a point in time at which phosgene is no longer present.

[0014] EP 0 640 639 A2 describes a two-stage process in which bisphenol A is firstly continuously converted with excess phosgene. In a further step, the organic phase and the aqueous phase are then separated, with further bisphenol A and NaOH then being added to the organic phase, whereby any phosgene still present is reacted completely. The catalyst and chain terminator are then added.

[0015] In all the above cases, an excess of phosgene is first used and then destroyed again. This is uneconomical on the one hand, because not all phosgene is used for the actual reaction. However, on the other hand, from an ecological point of view, this is also unsustainable, because the previously manufactured product would be "unused" to be destroyed. In addition, the described method requires the preparation of a new solution after the preparation of the bischloroformate, which is associated with corresponding costs and complexity. This especially causes the described method to be unable to be easily implemented as a continuous method. In this case, additional corrosion-resistant equipment will be required, with the residence time of additional highly corrosive materials.

[0016] The object of the present invention is therefore to provide a process for preparing polycarbonates by the phase interface process, in which at least one disadvantage of the prior art is improved. In particular, the object of the present invention is to provide a process for preparing polycarbonates by the phase interface process, in which the phosgene excess can be reduced. In addition, it is preferably simultaneously desirable to obtain polycarbonates with a low oligomer proportion and thus a narrow molecular weight distribution. It is also preferably simultaneously desirable to provide polycarbonates with a low di-chain terminator carbonate content by this process. In particular, the object of the present invention is to provide a process for preparing polycarbonates by the phase interface process, which provides polycarbonates with a low oligomer and di-chain terminator carbonate proportion.

[0017] At least one, preferably all of the above-mentioned objects are achieved by the present invention. Surprisingly, it has been found that the phosgene excess can be reduced by using a given energy input when dispersing the aqueous phase and the organic phase. This leads to economic savings on the one hand, because less excess phosgene is required. At the same time, it has been surprisingly found that due to the high phosgene conversion rate produced, the reactions of phosgenation, oligomerization and saponification of the at least one dihydroxydiaryl alkane can be separated. This preferably means that due to the high phosgene conversion rate, the at least one chain terminator can be added to the reaction system earlier. This means in particular that the addition of the chain terminator to the reaction system can also be carried out at a time point when phosgene is still present in the reaction system. The chain terminator can therefore be introduced into the reaction system at a very early time point. Here, "very early" means that only oligomeric compounds from the reaction of at least one dihydroxydiaryl alkane with phosgene are present, which have an average degree of polymerization of at least one unit and at most five or six units. Surprisingly, despite the fact that the chain terminator is introduced into the system containing phosgene, the resulting polycarbonate has a low di-chain terminator carbonate ratio. At the same time, the resulting polycarbonates have a narrow molecular weight distribution and therefore a low oligomer ratio. The resulting polycarbonates therefore also have the improved properties already described due to the low di-chain terminator carbonate ratio and the low oligomer ratio. The process according to the invention is more economical and more ecological than the processes described in the prior art. On the one hand, the phosgene excess can be reduced with the process according to the invention. Likewise, the required amount of chain terminator can be reduced, since the losses due to the formation of di-chain terminator carbonate are less.

[0018] Therefore, according to the present invention, there is provided a process for preparing polycarbonate from at least one dihydroxydiarylalkane, phosgene, at least one catalyst and at least one chain terminator by a phase interface process, comprising the following steps:

[0019] (a) producing a dispersion from an organic phase and an aqueous phase by dispersing the organic phase in the aqueous phase or the aqueous phase in the organic phase continuously in a disperser, wherein the organic phase comprises at least one solvent suitable for polycarbonate and at least a portion of phosgene, and the aqueous phase comprises the 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 mole of dihydroxydiarylalkane,

[0020] (b) adding at least one chain terminator to the dispersion from step (a), and

[0021] (c) adding at least one catalyst to the mixture obtained from step (b),

[0022] It is characterized in that

[0023] The energy input through the disperser in step (a) is 2.5 * e 6 W / m 3 to 5.0 * e 7 W / m 3 , preferably 3.0* e 6 W / m 3 to 4.0*e 7 W / m 3 , particularly preferably 1.0 * e 7 W / m 3 to 3.5 * e 7 W / m 3 .

[0024] The density of the PC solution at 25°C is 1.22 g / cm 3 , a person skilled in the art can convert J / kg to W / m 3 . The terms homogenization and dispersion are known to those skilled in the art. The term "homogenization" is preferably understood to mean that a state is sought, preferably achieved, in which the concentrations of the individual components of the composition in any volume element of the aqueous phase or the organic phase are substantially the same. Here, the term "substantially" is preferably understood to mean that the concentration deviations of the individual components of the composition in any volume element are at most 5%, preferably at most 3%, particularly preferably at most 1%. Here, in contrast to dispersion, for homogenization it is also preferred that the phase interface between the aqueous phase and the organic phase is as small as possible. Similarly, the term "dispersion" is preferably understood to mean that an emulsion is formed from an aqueous phase and an organic phase, preferably in the absence of an emulsifier, wherein the aqueous phase and the organic phase may also contain other components for the preparation of polycarbonate. Examples of such emulsions are water-in-oil or water-in-oil dispersions. Therefore, the difference between homogenization and dispersion is preferably that in the case of homogenization there is no concentration gradient of any dissolved substance in any phase and in this case the phase interface between the phases is as small as possible.

[0025] According to the invention, it has been shown that only within certain energy input ranges can the phosgene excess be successfully reduced further. Here, the person skilled in the art is able to calculate the corresponding energy input when predetermining the reactor.

[0026] According to the invention, the energy inputs given are average values. This means that preferably higher or lower values ​​for the energy input are not excluded. These may also optionally occur only briefly. According to the invention, the average value is preferably formed over the entire reactor system. Therefore, the energy inputs of the corresponding edge regions or internal components are also taken into account.

[0027] In the case of dispersing the organic phase in the aqueous phase or the aqueous phase in the organic phase by means of a disperser, an oil-in-water (ow) dispersion or a water-in-oil dispersion (wo) can be produced, wherein oil is to be understood as meaning the organic phase. However, it is preferred according to the invention to produce a water-in-oil dispersion in process step (a). This has proven to be advantageous for low oligomer and di-chain terminator carbonate contents in the polycarbonate. The organic phase is preferably dispersed continuously into the aqueous phase by means of a disperser.

[0028] By definition, an oil-in-water dispersion is one in which water forms the outer (continuous) phase and oil forms the inner (dispersed) phase, i.e., oil droplets are distributed in the water. Thus, a water-in-oil dispersion is one in which oil forms the outer phase and water forms the inner phase.

[0029] Preferably, the method according to the invention is characterized in that it comprises the step of adding an aqueous alkali metal hydroxide solution at least once. Here, the expression "addition" preferably refers to an active step of additional addition. In particular, it is also possible that the at least one dihydroxyaryl alkane is first dissolved in an aqueous alkali metal hydroxide solution before it is supplied 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 that, after this initial step of dissolving the at least one dihydroxyaryl alkane, any addition of an aqueous alkali metal hydroxide solution (whether with or without the at least one dihydroxyaryl alkane) is understood as the addition of an aqueous alkali metal hydroxide solution.

[0030] The step of adding the aqueous alkali metal hydroxide solution is an exothermic reaction. According to the invention, it is preferably carried out in a temperature range of -5°C to 100°C, particularly preferably 15°C to 80°C, very particularly preferably 25 to 65°C, wherein depending on the solvent or solvent mixture, it is optionally necessary to work under overpressure. Depending on the reactor used, it is possible to work under different pressures. For example, it is possible to preferably work under a pressure of 0.5 to 20 bar (absolute).

[0031] It has proven to be particularly advantageous here if the process according to the invention is characterized in that the addition of at least one chain terminator to the reaction system in process step (b) is carried out temporally before the first addition of the at least one addition of an aqueous alkali metal hydroxide solution.

[0032] It is clear to the person skilled in the art that, although in principle it is possible to add an aqueous alkali metal hydroxide solution before adding the at least one chain terminator, it has been demonstrated according to the invention that this amount must not be too high, since otherwise the degree of polymerization of the reaction product R becomes too high. This means that the person skilled in the art can only add so much aqueous alkali metal hydroxide solution before adding the at least one chain terminator as to ensure that the preferred properties of the reaction product R according to the invention are maintained.

[0033] The process according to the invention can be used to reduce the phosgene excess. It is preferred that in process step (a) there is an excess of phosgene of 3 to 20 mol %, preferably 4 to 10 mol %, particularly preferably 5 to 9 mol %, very particularly preferably 6 to 8 mol %, relative to the sum of the dihydroxydiarylalkanes used. According to the invention, the mol % is calculated as follows: mol phosgene / (mol sum of all phenolic OH groups / 2). The sum of all phenolic groups is composed, for example, of dihydroxydiarylalkanes having 2 OH groups, chain terminators having 1 OH group and / or branching agents optionally having, for example, 3 OH groups.

[0034] As mentioned above, according to the present invention, the presence of an aqueous alkali metal hydroxide solution in step (a) is preferably not to be understood as the addition of an aqueous alkali metal hydroxide solution. This is an aqueous alkali metal hydroxide solution, preferably an aqueous sodium hydroxide solution, which is used to dissolve the BPA in the aqueous phase. During the phosgenation step (a), preferably as little free alkali metal hydroxide solution as possible is provided in order to avoid saponification of phosgene to sodium carbonate (i.e. phosgene loss). Therefore, according to the present invention, in step (a), 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.

[0035] The organic phase comprises one or more solvents.

[0036] 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 additionally or in admixture with chlorinated hydrocarbons; dichloromethane and chlorobenzene and mixtures thereof are preferred. According to another embodiment of the method of the invention, a solvent is used which does not dissolve but only swells the polycarbonate. Therefore, a non-solvent for polycarbonate can also be used in combination with the solvent. Wherein, if the solvent participant forms a second organic phase, a solvent soluble in the aqueous phase such as tetrahydrofuran, 1,3- or 1,4-dioxane or 1,3-dioxolane can also be used as a solvent.

[0037] Suitable dihydroxydiarylalkanes - also referred to above and below inter alia as diphenols - are those of the general formula

[0038] HO-Z-OH

[0039] wherein Z is a divalent organic radical having 6 to 30 carbon atoms, which comprises one or more aromatic groups. Examples of such compounds which can be used in the process according to the invention are dihydroxydiarylalkanes, such as hydroquinone, resorcinol, dihydroxybiphenyl, 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.

[0040] Preferred dihydroxydiarylalkanes are 4,4'-dihydroxybiphenyl, 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-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)cyclohexyne and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC).

[0041] Particularly preferred dihydroxydiarylalkanes are 4,4′-dihydroxybiphenyl, 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).

[0042] These and other suitable dihydroxydiarylalkanes are described, for example, in US-A 2 999 835, US-A 3,148,172 US-A 2,991,273, US-A 3 271 367, US-A 4,982,014 and US-A 2,999,846, in the German open-access literature: 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, in French patent document FR-A 1 561 518, in H. Schnell's monograph, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964, page 28 and following pages; page 102 pp. 72 and following, in DG Legrand, JT Bendler, Handbook of Polycarbonate Science and Technology, Marcel Dekker New York 2000, p. 72 and following.

[0043] According to the invention, polycarbonate is understood to mean both homopolycarbonates and copolycarbonates. In the case of the preparation of homopolycarbonates according to the invention, only one dihydroxydiarylalkane is used, in the case of the preparation of copolycarbonates according to the invention, a plurality of dihydroxydiarylalkane are used, wherein of course the dihydroxydiarylalkane used and all other chemicals and auxiliaries added to the synthesis may be contaminated with impurities originating from the synthesis itself, handling and storage, although it is desirable to work with raw materials that are as clean as possible.

[0044] In the context of the present invention, aqueous alkali metal hydroxide solution is preferably understood to mean aqueous sodium hydroxide solution, aqueous potassium hydroxide solution or mixtures thereof, particularly preferably aqueous sodium hydroxide solution.

[0045] The aqueous phase in the phase interface method for preparing polycarbonate comprises an aqueous alkali metal hydroxide solution, one or more dihydroxydiaryl alkanes and water, wherein the concentration of the aqueous solution in terms of the total dihydroxydiaryl alkanes, not as alkali metal salts but as free dihydroxydiaryl alkanes, is preferably 1 to 30% by weight, particularly preferably 3 to 25% by weight, and very particularly preferably 15 to 18% by weight, based on the total weight of the aqueous phase. The alkali metal hydroxide used to dissolve the dihydroxydiaryl alkanes, such as sodium hydroxide or potassium hydroxide, 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 by the target concentration of the dihydroxydiaryl alkane solution sought, but is generally 5 to 25% by weight, preferably 5 to 10% by weight, based on 100% of the aqueous alkali metal hydroxide solution, or more concentrated, and then diluted with water. In the method with subsequent dilution, an optionally tempered aqueous alkali metal hydroxide solution is used, and its concentration is 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 generally ranges from 1.5 mol alkali metal / mol dihydroxydiarylalkane to 2.5 mol alkali metal / mol dihydroxydiarylalkane, preferably from 1.8 to 2.2 mol alkali metal / mol dihydroxydiarylalkane, and in the particularly preferred case of using bisphenol A as the only dihydroxydiarylalkane, from 1.85 to 2.15 mol alkali metal, very particularly preferably 2.00 mol alkali metal. If more than one dihydroxydiarylalkane is used, they can be dissolved together. However, since the solubility of the dihydroxydiarylalkane depends very strongly on the amount of alkali metal used, it may be advantageous to have, instead of one solution with two dihydroxydiarylalkane, two solutions each with one dihydroxydiarylalkane dissolved in a suitable aqueous alkali metal hydroxide solution, which are then metered separately to form the correct mixing ratio. It may also be advantageous that the one or more dihydroxydiarylalkanes are not dissolved in an alkali metal hydroxide aqueous solution but in a dihydroxydiarylalkanes solution of dilution equipped with an additional alkali metal. The dissolution process can proceed from solid dihydroxydiarylalkanes, mostly in the form of flakes or particles, or from molten dihydroxydiarylalkanes. In the case of sodium hydroxide or sodium hydroxide aqueous solution, the alkali metal hydroxide or alkali metal hydroxide aqueous solution used can be prepared, for example, by amalgam method or so-called membrane method. These two methods have long been used and are familiar to those skilled in the art. In the case of sodium hydroxide aqueous solution, those prepared by membrane method are preferably used.

[0046] In this aqueous solution and / or aqueous phase, the one or more dihydroxydiarylalkanes are present completely or partly in the form of the corresponding alkali metal salts or dialkali metal salts.

[0047] As long as phosgene or its direct subsequent products, chlorocarbonates, are present in the reaction solution, the optional metering of the dihydroxydiarylalkane can be carried out after or during the introduction of the phosgene.

[0048] The organic phase of step (a) contains at least phosgene in addition to at least one solvent. Here, before the mixture is produced, the organic phase already contains the required phosgene in whole or in part. Preferably, before the mixture is produced, the organic phase already contains all the required phosgene, including the excess of phosgene used. Phosgene can be introduced into the organic phase in gaseous or liquid form.

[0049] In step (b), at least one chain terminator is added to the reaction system of step (a). In this case, the reaction system of step (a) preferably contains unconverted phosgene. The at least one chain terminator is usually monofunctional. Preferably, the at least one chain terminator is selected from phenol, alkylphenols and their chlorocarbonates or acid chlorides of monocarboxylic acids, preferably from phenol, tert-butylphenol and isooctylphenol, cumylphenol. Any mixtures of the chain terminators can be used.

[0050] In a particularly preferred embodiment of the process according to the invention, phenol is used as chain terminator. Preferably, phenol is used in step (b) in the form of a solution comprising at least one organic solvent and phenol in 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 value of 11.3 to 11.6 at the end of the reaction (i.e. in step (b)). The addition of phenol and the adjustment of the pH value to 11.3 to 11.6 are preferably carried out before the addition of the catalyst.

[0051] In another preferred embodiment of the process according to the invention, p-tert-butylphenol is used as chain terminator. Preference is given to using p-tert-butylphenol in the form of a solution in step (b), the solution comprising at least one organic solvent and a concentration of 2 to 25% by weight, preferably 3 to 15% by weight, of p-tert-butylphenol. In this embodiment, the aqueous phase is preferably adjusted to a pH value of 11.5 to 11.8 at the end of the reaction (i.e. in step (b)). Addition of p-tert-butylphenol and adjustment of the pH value to 11.5 to 11.8 are preferably carried out before the addition of the catalyst.

[0052] In step (b), one or more branching agents or a mixture of branching agents can optionally be added to the synthesis. However, such branching agents are preferably added before the one or more chain terminators. Such branching agents are very particularly preferably added in process step (a) together with the aqueous phase and the solution of at least one dihydroxydiarylalkane. As branching agents, for example, triphenols, tetraphenols, acid chlorides of tri- or tetracarboxylic acids or mixtures of polyphenols or acid chlorides are used.

[0053] Examples of compounds having three or more phenolic hydroxyl groups which are suitable as branching agents are phloroglucinol, 4,6-dimethyl-2,4,6-tris-(4-hydroxyphenyl)hept-2-ene, 4,6-dimethyl-2,4,6-tris-(4-hydroxyphenyl)heptane, 1,3,5-tris-(4-hydroxyphenyl)benzene, 1,1,1-tris-(4-hydroxyphenyl)ethane, tris-(4-hydroxyphenyl)phenylmethane, 2,2-bis-[4,4-bis-(4-hydroxyphenyl)cyclohexyl]propane, 2,4-bis-(4-hydroxyphenyl-2-isopropyl)phenol, tetrakis-(4-hydroxyphenyl)methane.

[0054] Examples of other trifunctional compounds suitable as branching agents are 2,4-dihydroxybenzoic acid, trimesic acid, cyanuric 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-tris-(4-hydroxyphenyl)ethane.

[0055] It has proven to be advantageous to carry out the at least one addition of the aqueous alkali metal hydroxide solution while the dispersion is still an oil-in-water dispersion. The addition of an aqueous alkali metal hydroxide solution to a water-in-oil emulsion generally results in an undesirable molecular weight distribution. Since at least one chain terminator is preferably added beforehand, this also means that at least one chain terminator is preferably also added to the oil-in-water dispersion. According to the invention, the dispersion can be converted from a water-in-oil dispersion to an oil-in-water dispersion during the process.

[0056] The method according to the present invention further comprises the following steps

[0057] (c) adding at least one catalyst to the mixture obtained from step (b).

[0058] It is preferred that the at least one catalyst is selected from tertiary amines, organic phosphines and any desired mixtures. The at least one catalyst is very particularly preferably a tertiary amine or a mixture of at least two tertiary amines.

[0059] The tertiary amine is likewise preferably triethylamine, tributylamine, trioctylamine, N-ethylpiperidine, N-methylpiperidine or N-iso / n-propylpiperidine; these compounds are described in the literature as typical interfacial catalysts, are commercially available and are familiar to those skilled in the art. The catalysts can be added to the synthesis individually, mixed or simultaneously or successively, optionally also before phosgenation, but preferably metered in after the introduction of phosgene. The metered addition of one or more catalysts can be carried out in substance, in an inert solvent, preferably in the solvent or one of the solvents of the organic phase in the polycarbonate synthesis, or as an aqueous solution. In the case of using a tertiary amine as a catalyst, its metered addition can be carried out, for example, in an aqueous solution as its ammonium salt with an acid, preferably an inorganic acid, especially hydrochloric acid. When using a plurality of catalysts or metering a portion of the total amount of the catalyst, of course, different metering methods can also be used at different locations or at different times. The total amount of catalyst used, based on mol % of dihydroxydiarylalkane used, is preferably 0.001 to 10 mol %, preferably 0.01 to 8 mol %, particularly preferably 0.05 to 5 mol %.

[0060] Dispersers are in principle known to those skilled in the art. According to the present invention, it is preferred to use at least one nozzle, perforated plate, static mixer, pump and / or jet disperser as the disperser in method step (a). Here, particularly preferred are jet dispersers that allow a preferred direction of metering. Suitable dispersers within the scope of the present invention are described, for example, in EP-A 1 368 407 and EP-A 1 599 520.

[0061] Suitable nozzles are, for example, slit nozzles, annular slit nozzles, orifice nozzles, Raffles nozzles or smooth jet nozzles. A person skilled in the art can use his or her expert knowledge to select the opening of the nozzle so that the energy input according to the invention occurs.

[0062] The pressure used may preferably be 0.001 to 1 MPa, particularly preferably 0.001 to 0.5 MPa.

[0063] In a preferred embodiment of the process according to the invention, a disperser is used in which the organic phase and the aqueous phase are preferably fed separately from one another and / or only one of the phases is fed into the predisperser by means of a respective pump. The pressure of these pumps is preferably each at most 2.5 MPa, preferably 0.001 to 0.5 MPa. The predisperser preferably produces a water-in-oil dispersion.

[0064] Suitable predispersers are all arbitrary nozzles, such as slit nozzles, annular slit nozzles, orifice nozzles, Raffles nozzles or smooth jet nozzles and jet dispersers. Suitable homogenizing nozzles are likewise all arbitrary nozzles, such as slit nozzles, annular slit nozzles, orifice nozzles, Raffles nozzles or smooth jet nozzles and jet dispersers.

[0065] In another preferred embodiment, a rotary disperser as described in EP B1 2090605 can be used. The predisperser is then followed by the disperser used according to the invention. The energy input given according to the invention is carried out here.

[0066] The implementation of the method according to the invention is carried out continuously. Therefore, the entire reaction, i.e. conversion and further condensation, can be carried out in a stirred tank, a tubular reactor, a circulating pump reactor or a stirred tank cascade or a combination thereof, wherein by using the already mentioned mixing device, it can be ensured that the aqueous phase and the organic phase are demixed as far as possible when the synthetic mixture is completely reacted, i.e. no longer containing saponifiable chlorine of phosgene or chlorocarbonate. In a preferred embodiment of the method of the invention, the disperser in the method step (a) is followed by a flow tube. With this arrangement, it is particularly advantageous to achieve an extremely short residence time of less than 0.5 seconds for the mixture implemented. In another preferred embodiment of the method of the invention, a circulating pump reactor is then provided.

[0067] Preferably, a tank reactor with a circulation pump loop and a circulation pump rate of 5 to 15 times, preferably 7.5 to 10 times, the flow rate is used as the circulation pump reactor. Preferably, the residence time of the reaction mixture in this reactor is 2 to 20 minutes, particularly preferably 2 to 5 minutes.

[0068] In another preferred embodiment of the process according to the invention, the circulation pump reactor is followed by a further residence reactor.Preferably, the residence time of the reaction mixture in the circulation pump reactor and in the residence reactor is each from 2 to 20 minutes.

[0069] In a preferred aspect of the present invention, the continuous process according to the invention in all the above-mentioned embodiments and preferred embodiments is characterized in that in process step (b) at least one chain terminator is introduced into a reaction system comprising at least the at least one dihydroxydiaryl alkane, phosgene and the reaction product R obtained from the at least one dihydroxydiaryl alkane and phosgene at a time point at which the reaction product R is a mixture of compounds and these compounds have an average degree of polymerization of at least one unit and at most six units, which are formed by the reaction of the at least one dihydroxydiaryl alkane with phosgene. Here, the reaction system at the time of adding the at least one chain terminator comprises at least the at least one dihydroxydiaryl alkane, phosgene and the reaction product R. At this time point, at least one catalyst may also be included. However, this is not preferred. The reaction system at the time of adding the at least one chain terminator preferably comprises at least one dihydroxydiaryl alkane, phosgene, the reaction product R and the solvent required for carrying out the phase interface process, and very particularly preferably consists of it. Preferably, this involves an aqueous alkali metal hydroxide solution and at least one organic solvent.

[0070] As mentioned above, it is therefore preferred according to the invention to introduce the chain terminator "early" into the reaction system. According to the invention, this point in time is defined by the reaction product R being a mixture of compounds, wherein these compounds have an average degree of polymerization of at least one unit and at most six units.

[0071] The term "degree of polymerization" is known to the person skilled in the art. The degree of polymerization preferably gives the number of units in the oligomeric reaction product R formed by reaction of at least one dihydroxydiarylalkane with phosgene. The data for the degree of polymerization are average values. This is because the degree of polymerization is preferably determined by the number-average molar mass Mn. The quotient of the Mn of the oligomer / polymer and the molar mass of the repeating unit (unit formed by reaction of at least one dihydroxydiarylalkane with phosgene; preferably a unit represented by the general chemical formula (I)) is thus formed. According to the invention, the number-average molar mass Mn is in turn preferably determined by gel permeation chromatography (GPC). Particularly preferably, it is determined by means of GPC in accordance with DIN 55672-1: 2016-03, using dichloromethane as eluent, calibrated relative to a bisphenol A polycarbonate standard. According to the invention, it is very particularly preferred that the molecular weights Mw (weight average), Mn (number average) and Mv (viscosity average) are determined by means of gel permeation chromatography in accordance with DIN 55672-1: 2007-08, using BPA polycarbonate calibration. The calibration is performed with a linear polycarbonate of known molar mass distribution (e.g. from PSS Polymer Standards Service GmbH, Germany). Here, the method 2301-0257502-09D (German version 2009) of Currenta GmbH & Co. OHG, Leverkusen is used. Dichloromethane is used as eluent. The column combination consists of a crosslinked styrene-divinylbenzene resin. The GPC may include one or more commercially available GPC columns for size exclusion chromatography in series, which are selected so as to be able to fully separate the molar mass of the polymer, in particular the molar mass of aromatic polycarbonates with a weight-average molar mass Mw of 2000 to 100000 g / mol. The diameter of the analytical column is usually 7.5 mm and the length is 300 mm. The particle size range of the column material is 3 µm to 20 µm. The concentration of the solution under investigation is 0.2% by weight. The flow rate is set at 1.0 ml / min and the solution temperature is 30 ° C. Detection is performed with the aid of a refractive index (RI) detector.

[0072] Preferably, the method according to the present invention is further characterized in that the compounds of the mixture of reaction products R are represented by the general chemical formula (I):

[0073]

[0074] in

[0075] R1 and R2 are each independently H, C1- to C18-alkyl, C1- to C18-alkoxy, halogen such as Cl or Br or each optionally substituted aryl or aralkyl, preferably H or C1- to C12-alkyl, particularly preferably H or C1- to C8-alkyl and very particularly preferably H or methyl,

[0076] R3 is H, (C=O)-Cl or (C=O)-OH,

[0077] R4 is OH or Cl,

[0078] X is a single bond, -SO2-, -CO-, -O-, -S-, C1- to C6-alkylene, C2- to C5-alkylidene or C5- to C6-cycloalkylidene, which may be substituted by C1- to C6-alkyl, preferably methyl or ethyl, and furthermore is C6- to C12-arylene, which may optionally be fused to further aromatic rings containing heteroatoms, and

[0079] n is the degree of polymerization, thus the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene, and can have values ​​of 1 to 6, preferably 1 to 5, particularly preferably 1 to 4 and very particularly preferably 1 to 3 on average.

[0080] According to the invention, it is also possible that the reaction product R can also be present in a partially saponified state. Here, the chlorine of the chloroformate group dissociates and forms a carbonate. However, according to the invention, this side reaction is undesirable. This means that the reaction product R is a mixture containing such saponification products. However, this is less preferred. Preferably, the compound of the mixture of reaction products R is represented by the general chemical formula (I), where

[0081] R1 and R2 are each independently H or C1 to C12-alkyl, particularly preferably H or C1- to C8-alkyl and very particularly preferably H or methyl,

[0082] R3 is H or (C=O)-Cl,

[0083] R4 is Cl,

[0084] X is a single bond, a C1- to C6-alkylene group, a C2- to C5-alkylidene group or a C5- to C6-cycloalkylidene group, which may be substituted with a methyl group or an ethyl group, and

[0085] n is the degree of polymerization, thus the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene, and can have values ​​of 1 to 6, preferably 1 to 5, particularly preferably 1 to 4 and very particularly preferably 1 to 3 on average.

[0086] Very particularly preferably, the compounds of the mixture of reaction products R are represented by the general chemical formula (I), wherein

[0087] R1 and R2 are each independently H or methyl,

[0088] R3 is H or (C=O)-Cl,

[0089] R4 is OH,

[0090] X is isopropylidene or 3,3,5-trimethylcyclohexylidene, and

[0091] n is the degree of polymerization, thus the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene, and can have values ​​of 1 to 6, preferably 1 to 5, particularly preferably 1 to 4 and very particularly preferably 1 to 3 on average.

[0092] If bisphenol A is used as dihydroxydiarylalkane in the process according to the invention, then, depending on the type of the end groups R3 and / or R4 (OH or Cl) of the general chemical formula (I), an average molar mass Mn (number average) preferably in the range of 352 g / mol (BPA with two chlorocarbonate end groups) to 1623 g / mol (n = value of 6 on average) is obtained. In particular, molar masses below 1000 g / mol are preferred.

[0093] It has been found to be advantageous that the at least one chain terminator is first mixed well before it can react. The at least one chain terminator is preferably evenly distributed. This can be done, for example, by using a static mixer after adding the at least one chain terminator and before it reacts.

[0094] It has likewise been found to be advantageous to feed the at least one chain terminator into the reaction system as an organic phase rather than as an aqueous phase.

[0095] However, it has proven to be advantageous to add the at least one chain terminator at a pH value of 8-11, preferably 9-10. It has been shown that at higher pH values ​​(>=11), the distribution of the at least one chain terminator between the organic phase and the aqueous phase becomes unfavorable. In this case, the majority is found in the aqueous phase, where it cannot react with the chloroformate end groups. It is therefore preferred according to the invention that, in the process according to the invention, no aqueous alkali metal hydroxide solution is added before the addition of the at least one chain terminator. This is particularly advantageous if the at least one chain terminator comprises 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.

[0096] Despite the low excess of phosgene, the process according to the invention enables good phase separation at the end of the reaction and low water content in both the organic phase and the aqueous phase. In addition, the incorporation of catalyst components into the product is avoided.

[0097] For work-up, the fully reacted at least two-phase reaction mixture, which still contains traces of chlorocarbonate at most, preferably less than 2 ppm, can be allowed to settle for phase separation. The alkaline aqueous phase is optionally fully or partially fed back to the polycarbonate synthesis as aqueous phase or fed to wastewater work-up, where solvent and catalyst components are separated and optionally fed back to the polycarbonate synthesis. In another variant of the work-up, after separation of organic impurities, in particular solvent and polymer residues, and optionally after adjustment to a specific pH value, for example by adding aqueous sodium hydroxide solution, salts are separated, which can be fed, for example, to chloralkali electrolysis, while the aqueous phase is optionally fed back to the polycarbonate synthesis.

[0098] The organic phase comprising the polycarbonate can then be purified in various ways known to those skilled in the art in order to remove contaminants of the alkali, ionic or catalytic type.

[0099] Even after one or more sedimentation processes, optionally assisted by running a settling kettle, a stirred kettle, a coalescer or a separator or a combination of these measures - wherein optionally in each or some separation steps, water can be metered in using an active or passive mixing device - the organic phase usually still contains a certain proportion of alkaline water in the form of fine droplets and one or more catalysts. After the crude separation of the alkaline water phase, the organic phase can be washed once or multiple times with dilute acid, mineral acid, carboxylic acid, hydroxycarboxylic acid and / or sulfonic acid. Preferred aqueous inorganic acids, particularly hydrochloric acid, phosphorous acid, phosphoric acid or a mixture of these acids. The concentration of these acids should preferably be in the range of 0.001 to 50% by weight, preferably 0.01 to 5% by weight. In addition, the organic phase can be repeatedly washed with desalted water or distilled water. The separation of the organic phase optionally dispersed with a part of the aqueous phase after each washing step is carried out by means of a settling kettle, a stirred kettle, a coalescer or a separator or a combination of these measures, wherein the washing water can be metered in using an active or passive mixing device between the washing steps. Between these washing steps or even after the washing, an acid can optionally be added, preferably dissolved in the solvent on which the polymer solution is based. Preferably, hydrogen chloride gas, phosphoric acid or phosphorous acid are used here, which can optionally also be used as a mixture. The purified polycarbonate solution obtained in this way should preferably contain not more than 5% by weight, preferably less than 1% by weight and very particularly preferably less than 0.5% by weight of water after the last separation process.

[0100] The polycarbonate can be isolated from the solution by evaporating the solvent with the aid of temperature, vacuum or heated entrained gas. Other isolation methods are, for example, crystallization and precipitation.

[0101] If the concentration of the polycarbonate solution and possibly also the isolation of the polycarbonate is carried out by distillative removal of the solvent, optionally by overheating and decompression, this is referred to as a "flash process". This method is known to the person skilled in the art and is described, for example, in "Thermische Trennverfahren", VCH Verlagsanstalt 1988, page 114. If instead of this a heated carrier gas is sprayed together with the solution to be evaporated, this is referred to as "spray evaporation / spray drying", which is described, for example, in Vauck, "Grundoperationen chemischer Verfahrenstechnik", Deutscher Verlag für Grundstoffindustrie 2000, 11th edition, page 690. All these methods are described in the patent literature and textbooks and are familiar to the person skilled in the art.

[0102] In the case of solvent removal by temperature (distillative removal) or the technically more efficient flash process, highly concentrated polycarbonate melts are obtained. In the flash process, polymer solutions are repeatedly heated under slight overpressure to a temperature above the boiling point at normal pressure, and these solutions, which are superheated relative to normal pressure, are then depressurized into a vessel with a lower pressure, for example normal pressure. It can be advantageous here not to allow the concentration phase, or in other words the overheating temperature phase, to become too large, but rather to preferably choose a two- to four-stage process.

[0103] Solvent residues can be removed from the highly concentrated polycarbonate melt thus obtained directly from the melt using a vented extruder (see, for example, BE-A 866 991, EP-A 0 411 510, US-A 4 980 105, DE-A 33 32 065), a thin-film evaporator (see, for example, EP-A 0 267 025), a falling-film evaporator, a strand evaporator, a foam evaporator (see, for example, US 2012 / 015763 A1) or by friction compaction (see, for example, EP-A 0 460 450), optionally also with addition of entrainers such as nitrogen or carbon dioxide, or using a vacuum (see, for example, EP-A 0 039 96, EP-A 0 256 003, US-A 4 423 207), or also by subsequent crystallization (see, for example, DE-A 34 29 960) and / or heating of solvent residues in the solid phase (see, for example, US-A 3 986 269, DE-A 20 53 876). These processes and the equipment required for them are also described in the literature and are familiar to those skilled in the art.

[0104] Polycarbonate pellets can be obtained - if possible - by direct spinning of the melt and subsequent pelletization or by spinning in air or under a liquid (usually water) using an extruder. If an extruder is used, the polycarbonate melt can be mixed with additives before the extruder, optionally using a static mixer or by a side extruder in the extruder.

[0105] Alternatively, the polycarbonate solution can be subjected to spray evaporation. During spraying, the polycarbonate solution is optionally evaporated into a container with negative pressure after heating, or evaporated into a container with normal pressure by means of a nozzle together with a heated carrier gas such as nitrogen, argon or water vapor. In both cases, depending on the concentration of the polymer solution, a powder (diluted) or flake (concentrated) of the polymer is obtained, from which the final residue of the solvent must also be removed as above. Subsequently, pellets can be obtained by means of a mixing extruder and subsequent spinning. Additives can also be added here in peripheral equipment or in the extruder itself, as described above. Due to the low bulk density of powders and flakes, it may usually be necessary to implement a compacting step to the polymer powder before extrusion.

[0106] By adding a non-solvent for polycarbonate, a large amount of polymer can be precipitated from the washed and optionally concentrated polycarbonate solution. Here, the non-solvent serves as a precipitant. Advantageously, a small amount of non-solvent is first added, and optionally a waiting time is inserted between the addition batches of non-solvent. In addition, it may be advantageous to use different non-solvents. For example, aliphatic or alicyclic hydrocarbons, particularly heptane, isooctane or cyclohexane, alcohols such as methanol, ethanol or isopropanol, ketones such as acetone, or mixtures of these are used as precipitants. During precipitation, the polymer solution is usually slowly added to the precipitant. The polycarbonate thus obtained is processed into pellets as described under spray evaporation, and optionally an additive is added.

[0107] According to other methods, the precipitated and crystallized product in particulate form or the amorphous solidified product is converted by evaporation of one or more non-solvents for the polycarbonate while heating below the glass transition temperature to crystallize and further condense to higher molecular weight. If oligomers optionally with different end groups (phenolic and chain terminator ends) are involved, this is called solid phase condensation.

[0108] Additives are added to extend the service life or improve color stability (stabilizers), to simplify processing (e.g. release agents, flow aids, antistatic agents) or to match the polymer properties to specific loads (impact modifiers, e.g. rubber; flame retardants, colorants, glass fibers).

[0109] These additives can be added to the polymer melt individually or in any desired mixture, together or in a variety of different mixtures. This can be done directly during the separation of the polymer or in a so-called mixing step after the pellets have been melted. Here, the additives or their mixtures can be added to the polymer melt as a solid, preferably as a powder, or as a melt. Another type of metered addition is the use of masterbatches or masterbatch mixtures of additives or additive mixtures.

[0110] Suitable additives are described, for example, in "Additives for Plastics Handbook, John Murphy, Elsevier, Oxford 1999", in "Plastics Additives Handbook, Hans Zweifel, Hanser, Munich 2001".

[0111] Another aspect of the present invention relates to converting 2.5 * e 6 W / m 3 to 5.0 * e 7 W / m 3 , preferably 3.0 * e 6 W / m 3 to 4.0*e 7 W / m 3 , particularly preferably 1.0 * e 7 W / m 3 to 3.5 * e 7 W / m 3 The invention relates to a method for reducing the excess of phosgene in the preparation of polycarbonates by the phase interface process by a system comprising an organic phase and an aqueous phase, 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, 1.8 mol to 2.2 mol, preferably 1.95 mol to 2.05 mol of aqueous alkali metal hydroxide per mole of dihydroxydiarylalkane and optionally at least one chain terminator. As described above, the use of this specific energy input also preferably simultaneously leads to a reduction in the proportion of oligomers in the resulting polycarbonate. Likewise, the use of this specific energy input also preferably simultaneously leads to a reduction in the content of di-chain terminator carbonate in the resulting polycarbonate.

[0112] It is also preferred that the energy input is carried out by a disperser. Suitable dispersers have been described above. It is also preferred that the method for preparing polycarbonate by the phase interface method is carried out continuously. It has been proven to be particularly advantageous that a suitable disperser can be simply installed and / or retrofitted into an already existing device. In the use according to the invention, it is also preferred to use a phosgene excess of 3 to 20 mol%, preferably 4 to 10 mol%, particularly preferably 5 to 9 mol%, relative to the sum of the dihydroxydiaryl alkanes used. The following examples are used to illustrate the present invention by way of example and should not be construed as limiting.

[0113] Explanation of Figure 1:

[0114] Solid line: original GPC, normalized so that area = 1

[0115] Dotted line: Schulz Flory distribution, adjusted so that the maximum coincides with the GPC maximum

[0116] Dashed line: Difference between two curves (solid and dotted)

[0117] The oligomer ratio was obtained by integrating the difference curve between 500 and 5000 g / mol. Example

[0118] The molecular weight distribution and the average values ​​Mn (number average) and Mw (weight average) were determined by means of gel permeation chromatography (GPC). Instrument: Waters "Mixed Bed" column) with dichloromethane as eluent (using a BPA homopolycarbonate standard with a Mw of 31,000 g / mol).

[0119] In addition to the standing evaluation, the deviation of the GPC from the ideal Schulz-Flory distribution is determined. For this purpose, the GPC is first normalized so that the area under the solid line of the curve in Figure 1 is obtained. This area is normalized to 1. Furthermore, the Schulz-Flory (SF) distribution is adjusted so that its maximum values ​​in terms of height and molecular weight correspond to the measured distribution (dotted line in Figure 1). The difference between the measured and adjusted SF distribution gives the difference distribution (dashed line in Figure 1). In the present case, the Schulz-Flory distribution is narrow, so that the difference distribution is positive (except for measurement inaccuracies). Due to this method, the difference at the maximum is zero, so that the difference distribution is resolved into a low molecular weight fraction and a high molecular weight fraction (see also Figure 1 for this).

[0120] It is known from the prior art that a high oligomer fraction is detrimental to product quality. However, here usually only the total fraction of low molecular weight compounds below a certain limit or the fraction soluble in acetone is taken into account. This has the disadvantage that the unavoidable oligomer fraction is also taken into account, which also varies with the type of polycarbonate (viscosity, Mn). The method according to the invention corrects this dependency and only determines the method-specific oligomer fraction.

[0121] 2,2'-bis-(4-hydroxyphenyl)propane (bisphenol A, BPA) was used as the dihydroxydiarylalkane, and the solvent of the organic phase was a mixture of about 50% by weight of dichloromethane and 50% by weight of monochlorobenzene. In all examples, polycarbonates with the indicated weight-average molecular weights were prepared, as measured by GPC (Waters "Mixed Bed" column, in dichloromethane, with a BPA homopolycarbonate standard with a Mw of 31,000 g / mol).

[0122] Example 1: Reducing excess phosgene

[0123] Continuous laboratory experiments were carried out in a combination of pump and stirred reactor. In all experiments, 70.1 g / h of gaseous phosgene were dissolved in 772 g / h of organic solvent (1:1 dichloromethane / chlorobenzene) at -7°C in a T-tube. The amount of solvent was calculated so that a 15% by weight polycarbonate solution was finally obtained. The continuously fed phosgene solution was contacted in another T-tube with 912 g / h of a 15% by weight alkaline BPA aqueous solution (2 mol NaOH / mol BPA), which had been preheated to 30°C. The BPA solution was dispersed in the phosgene solution through a stainless steel filter as a predispersor (pore size 60 μm). In all cases, a water-in-oil dispersion was obtained. The energy input given in Table 1 was then generated by a rotary pump.

[0124] The reaction mixture was directed to a Fink HMR040 mixing pump thermostated at 25°C, so that the phosgene was as completely reacted as possible at the end of the reaction pump but was still present. Examples 1a, 1c and 1d 3.29 g / h of p-tert-butylphenol as a 3% by weight solution as chain terminator were metered into the same solvent mixture as above, and the reaction mixture was further reacted with 53.95 g / h of 32% by weight aqueous sodium hydroxide solution at 25° C. in another HMR040 pump to a pH value of about 11.5 at the end of the reaction system. Example 1b Here, 3.29 g / h of p-tert-butylphenol as a 3% by weight solution were added as chain terminator to the same solvent mixture as above.

[0125] Next came two stirred tanks from Ismatec with a gear pump each. 0.679 g / h of catalyst (10% by weight of N-ethylpiperidine dissolved in chlorobenzene) was metered in between the two stirred tanks (and gear pumps) in a T-piece in a Teflon hose.

[0126] A total of 156 g of polycarbonate in organic solution were obtained continuously and passed together with the aqueous phase from the reaction into a phase separation vessel in order to separate it. The polycarbonate solution was washed with 10% by weight HCl and dried at normal pressure and room temperature.

[0127] Table 1 summarizes the results obtained in Example 1:

[0128] Table 1

[0129] Energy input Phosgene excess Mn 0 T Device Diff. id. MGV (PC) Di-chain terminator carbonate (PC) CO3 Mn (PC) Mw (PC) <![CDATA[W / m 3 ]]> % g / mol ℃ area% ppm weight% g / mol g / mol Example 1a <![CDATA[3.00 * e 7 ]]> 16.2 750 35 2.72 < 50 0.65 10580 26980 Example 1b <![CDATA[3.00 * e 7 ]]> 16.2 3470 35 8.10 < 50 0.65 7870 26160 Example 1c <![CDATA[3.00 * e 7 ]]> 9.5 660 25 2.78 < 50 0.38 9800 26200 Example 1d <![CDATA[3.00 * e 7 ]]> 7 730 25 2.50 < 50 0.33 9990 25300

[0130] Mn0: Molecular weight when chain terminator is added

[0131] Diff. id. MGV (PC): difference distribution; see explanation above.

[0132] Example 1a shows that polycarbonates low in oligomers and di-chain terminator carbonate can be obtained by high energy input in process step (a). In Example 1b, the chain terminator is added subsequently.

[0133] Examples 1c and 1d according to the invention show that, in addition, the phosgene excess can be reduced at high energy input. At the same time, polycarbonates with good or even improved oligomer and di-chain terminator carbonate contents are obtained. In Example 1b, the addition of NaOH takes place temporally before the addition of the chain terminator. However, the addition of the chain terminator takes place so early that it is assumed that phosgene is still present in the reaction system.

[0134] Adding the chain terminator at a point in time when phosgene is no longer present in the reaction system means that the reaction products R have an even higher molecular weight on average. An even higher proportion of oligomers can thus be expected.

[0135] Example 2

[0136] Use as equipment for various method steps:

[0137] Process step (A): Disperser in the form of an orifice plate nozzle with pre-dispersion (orifice plate with 5 holes, each with a diameter of 2.5 mm, a thickness of 2.35 mm, a pressure drop of 0.2 bar at a flow rate of 5.2 m / s), a residence time in the pre-dispersion space of 26 ms (in Examples 2a and 2b, the aqueous phase was dispersed in the organic phase via a pre-disperser; in Comparative Example 2c, the organic phase was dispersed in the aqueous phase via a pre-disperser) and subsequent dispersion (with another orifice plate with 18 holes, each with a diameter of 1.5 mm, a thickness of 2.35 mm, a pressure drop of 0.8 bar at a flow rate of 8.9 m / s in Comparative Example 2c (which corresponds to Example 1 of DE102008012613 A1; with another perforated plate having 18 holes, each with a diameter of 1.0 mm, a thickness of 2.35 mm, and a pressure drop of 0.8 bar at a flow rate of 8.9 m / s in Examples 2a and 2b according to the invention), through which one liquid is dispersed in another.

[0138] Process step (B): Residence time Reactor with a residence time of 0.2 s at 600 kg / h (bisphenol solution).

[0139] Process step (C): Circulation pump reactor with metering point (e.g. for NaOH), pump, heat exchanger, overflow container and T-shaped withdrawal point, volume 140 l, equipped with pH probe and conductivity probe; redispersion is carried out on entry into the circulation pump reactor; In example 2a, the chain terminator is added to the circulation pump reactor.

[0140] Process step (D): a discharge pump with upstream metering points for chain terminator (in Example 2b and Comparative Example 2c, chain terminator is added here; in Example 2a, nothing is added here) and NaOH solution, a static mixer in between, a serpentine reactor with mixing zone and residence zone and a total volume of 60 liters (first residence reactor) downstream, and a further serpentine reactor (second residence reactor) downstream thereof with a metering point for the catalyst at the beginning of the reactor and a total volume of 80 liters.

[0141] Subsequent phase separation: Separation vessel (size 4.15 m 3 , fill level is 50%).

[0142] The following material streams are used in process step (A):

[0143] In Examples 2a and 2b, 500 kg / h of aqueous bisphenol solution (15% by weight mixture of bisphenol A and bisphenol TMC, based on the total weight of the solution, 2.13 mol NaOH / mol bisphenol solution) (the phosgene stream and the stream of the solvent mixture (see below) are adjusted accordingly to the reduced bisphenol stream)

[0144] or

[0145] In comparative example 2c, 600 kg / h of bisphenol aqueous solution (15% by weight of bisphenol A, based on the total weight of the solution, 2.13 mol NaOH / mol bisphenol solution)

[0146] 44.6 kg / h phosgene

[0147] 520 kg / h of a solvent mixture of 54% by weight of dichloromethane and 46% by weight of chlorobenzene

[0148] In process steps (B) and (C) no further material streams are additionally used.

[0149] In process step (D), the following material stream is additionally used upstream of the first residence reactor:

[0150] 17.8 kg / h tert-butylphenol solution (20% by weight in a solvent mixture of 54% by weight of dichloromethane and 46% by weight of chlorobenzene)

[0151] 35 kg / h NaOH aqueous solution with 32 wt. % NaOH

[0152] In process step (D), the following streams are additionally used in the second residence reactor:

[0153] 22.7 kg / h catalyst solution (3% by weight solution of ethylpiperidine in a solvent mixture of 54% by weight of dichloromethane and 46% by weight of chlorobenzene).

[0154] The temperature in the circulation pump reactor was 35° C. (after the heat exchanger) to 38° C. (before the heat exchanger). The temperature in the coil reactor in process step (D) was in each case 37° C., and the temperature in the separation vessel was 35° C.

[0155] The dispersion direction is set such that the organic phase is dispersed in the aqueous phase.

[0156] Table 2 summarizes the obtained results.

[0157] Table 2

[0158] Energy input dispersion Mn Loop T Device Diff. id. MGV Di-chain terminator carbonate (PC) CO3 Mn (PC) Mw (PC) <![CDATA[W / m 3 ]]> g / mol ℃ area% ppm weight% g / mol g / mol Example 2a <![CDATA[4.2 * and 6 ]]> wo < 900* 60 3.50 200 0.75 12020 31650 Example 2b <![CDATA[4.2 * and 6 ]]> wo 2320 60 5.00 < 20 0.76 10240 29026 Comparative Example 2c <![CDATA[1.2 * and 6 ]]> ow 2210 50* 6.20 < 50 0.64 8750 24450

[0159] *Estimated value

[0160] MnLoop: molecular weight when chain terminator is added

[0161] Diff. id. MGV (PC): difference distribution; see explanation above.

[0162] In Examples 2a and 2b, a 19% phosgene excess was used. In Comparative Example 2c, a 15% phosgene excess was used. Since the bisphenol solutions of the comparative examples had a different composition than the examples according to the invention, the phosgene excess needed to be adjusted.

[0163] However, it can be seen that polycarbonates with a relatively high oligomer content are obtained with the energy input disclosed in the examples of DE 10 2008 012 613 A1. By increasing the energy input (according to examples 2a and 2b of the invention), this ratio can be reduced while maintaining an acceptable di-chain terminator carbonate content. Due to the different energy inputs, in examples 2a and 2b of the invention, a water-in-oil dispersion is present in process step (a), while in comparative example 2c an oil-in-water dispersion is present.

[0164] It can also be seen in these examples that the time of addition of the chain terminator brings further advantages with regard to the content of oligomers and di-chain terminator carbonate.

Claims

1. A continuous process for preparing polycarbonate from at least one dihydroxydiarylalkane, phosgene, at least one catalyst and at least one chain terminator by a phase interface process, comprising the following steps (a) producing 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 polycarbonate and at least a portion of phosgene, and the aqueous phase comprises at least one dihydroxydiarylalkane, water and 1.8 mol to 2.2 mol of an aqueous solution of an alkali metal hydroxide per mole of dihydroxydiarylalkane, (b) adding at least one chain terminator to the dispersion from step (a), and (c) adding at least one catalyst to the mixture obtained from step (b), It is characterized in that The energy input through the disperser in step (a) is 2.5*e 6 W / m 3 To 4.0*e 7 W / m 3 , wherein the method comprises the step of adding an aqueous solution of an alkali metal hydroxide one or more times and the addition of at least one chain terminator to the reaction system in method step (b) is performed at a time point before the first addition of the one or more additions of an aqueous solution of an alkali metal hydroxide.

2. The continuous process according to claim 1, wherein in step (a), the aqueous phase comprises 1.95 to 2.05 mol of an aqueous solution of an alkali metal hydroxide per mol of dihydroxydiarylalkane.

3. The continuous process according to claim 1, wherein the energy input by the disperser in step (a) is 3.0*e 6 W / m 3 To 4.0*e 7 W / m 3 .

4. The continuous process according to claim 1, wherein the energy input by the disperser in step (a) is 1.0*e 7 W / m 3 To 3.5*e 7 W / m 3 .

5. The continuous method according to any one of claims 1 to 4, characterized in that In process step (a) a water-in-oil dispersion is produced.

6. The continuous process according to any one of claims 1 to 4, characterized in that In process step (a), an excess of phosgene of 3 to 20 mol % is present, relative to the sum of the dihydroxydiarylalkanes used.

7. The continuous process according to any one of claims 1 to 4, characterized in that In process step (a), an excess of phosgene of 4 to 10 mol % is present, relative to the sum of the dihydroxydiarylalkanes used.

8. The continuous process according to any one of claims 1 to 4, characterized in that In process step (a), there is an excess of phosgene of 5 to 9 mol %, relative to the sum of the dihydroxydiarylalkanes used.

9. The continuous process according to any one of claims 1 to 4, characterized in that The at least one catalyst is selected from tertiary amines and organic phosphines.

10. The continuous process according to any one of claims 1 to 4, characterized in that The at least one chain terminator is selected from phenol, alkylphenols and their chlorocarbonates or acid chlorides of monocarboxylic acids.

11. The continuous method according to claim 10, characterized in that The at least one chain terminator is selected from phenol, tert-butylphenol and isooctylphenol, cumylphenol.

12. The continuous process according to any one of claims 1 to 4, characterized in that The at least one dihydroxydiaryl alkane is selected from 4,4'-dihydroxybiphenyl, 1,1-bis-(4-hydroxyphenyl)phenylethane, 2,2-bis-(4-hydroxyphenyl)propane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)propane, 1,1-bis-(4-hydroxyphenyl)cyclohexane, 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and any mixture thereof.

13. The continuous process according to any one of claims 1 to 4, characterized in that As disperser in process step (a) at least one perforated plate, static mixer, pump and / or jet disperser is used.

14. The continuous process according to claim 13, wherein the jet disperser is a nozzle.

15. The continuous process according to any one of claims 1 to 4, characterized in that In process step (b), 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 obtained from the at least one dihydroxydiarylalkane and phosgene at a time point at which the reaction product R is a mixture of compounds and these compounds have an average degree of polymerization of at least one unit and at most six units, the units being formed from the at least one dihydroxydiarylalkane by reaction with phosgene.

16. The continuous method according to claim 15, characterized in that The compounds of the mixture of reaction products R are represented by the general chemical formula (I): in R1 and R2 are each independently H, C1- to C18-alkyl, C1- to C18-alkoxy, halogen or are each optionally substituted aryl or aralkyl, R3 is H, (C=O)-Cl or (C=O)-OH, R4 is OH or Cl, X is a single bond, -SO2-, -CO-, -O-, -S-, C1- to C6-alkylene, C2- to C5-alkylidene or C5- to C6-cycloalkylidene, furthermore C6- to C12-arylene, optionally fused to further aromatic rings containing heteroatoms, and n is the degree of polymerization, thus the number of units formed from at least one dihydroxydiarylalkane by reaction with phosgene, and has a value of 1 to 6 on average.

17. The continuous process according to claim 16, wherein R1 and R2 are each independently of one another H or C1- to C12-alkyl.

18. The continuous process according to claim 16, wherein R1 and R2 are each independently of one another H or C1- to C8-alkyl.

19. The continuous process according to claim 16, wherein R1 and R2 are each independently H or methyl.

20. The continuous process of claim 16, wherein the halogen is Cl or Br.

21. The continuous process according to claim 16, wherein X is a single bond, -SO2-, -CO-, -O-, -S-, a C1- to C6-alkylene group, a C2- to C5-alkylidene group or a C5- to C6-cycloalkylidene group, which is substituted by a C1- to C6-alkyl group.

22. The continuous process according to claim 16, wherein X is a single bond, -SO2-, -CO-, -O-, -S-, a C1- to C6-alkylene group, a C2- to C5-alkylidene group or a C5- to C6-cycloalkylidene group, which is substituted with a methyl group or an ethyl group.

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