EP4010401A1

EP4010401A1 - Process for the preparation of a polycarbonate

Info

Publication number: EP4010401A1
Application number: EP20746680.6A
Authority: EP
Inventors: Pedro DESCHAMPS; Siemen BANCK
Original assignee: Covestro Intellectual Property GmbH and Co KG
Current assignee: Covestro Intellectual Property GmbH and Co KG
Priority date: 2019-08-08
Filing date: 2020-08-03
Publication date: 2022-06-15
Also published as: WO2021023690A1; CN114222774A; KR20220045150A

Abstract

The present inventions relates to a melt transesterification process for producing a polycarbonate from a dihydroxyaryl compound and a diaryl carbonate. The process according to the invention is characterized in that the rate of the reaction between the dihydroxyaryl compound with the diaryl carbonate is monitored and controlled. Especially the rate of the reaction between the dihydroxyaryl compound with the diaryl carbonate is monitored and – in case that the rate of reaction drops below a predefined value – the rate of reaction is increased again.

Description

Process for the preparation of a polycarbonate

The present invention relates to a melt transesterification process for producing a polycarbonate from a dihydroxy aryl compound and a diaryl carbonate. The process according to the invention is characterized in that the rate of the reaction between the dihydroxyaryl compound with the diaryl carbonate is monitored and controlled. Especially the rate of the reaction between the dihydroxyaryl compound with the diaryl carbonate is monitored and - in case that the rate of reaction drops below a predefined value - the rate of reaction is increased again.

Both polycarbonates and production thereof by the melt transesterification process are known in the prior art.

In the production of polycarbonate by melt transesterification, a dihydroxyaryl compound is reacted with a diaryl carbonate in which, in the context of a transesterification reaction, a monohydroxyaryl compound is eliminated from the diaryl carbonate. The condensation leads initially to the formation of low molecular weight polycarbonate oligomers, which react further by continued elimination of the monohydroxyaryl compound to give high molecular weight polycarbonate (reaction scheme (I)). The progress of the reaction can be promoted by the use of suitable catalysts.

The production of aromatic polycarbonates by the melt transesterification process is known and described for example in "Schnell", Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney 1964, in D.C. Prevorsek, B.T. Debona and Y. Kersten, Corporate Research Center, Allied Chemical Corporation, Moristown, New Jersey 07960, "Synthesis of Poly(ester)carbonate Copolymers" in Journal of Polymer Science, Polymer Chemistry Edition, Vol. 18, 75-90 (1980), in D. Freitag, U. Grigo, P.R. Miiller, N. Nouvertne, BAYER AG, “Polycarbonates” in Encyclopedia of Polymer Science and Engineering, Vol. 11, Second Edition, 1988, pages 648-718, and finally in Dres. U. Grigo, K. Kircher and P.R. Miiller "Polycarbonate" in Becker/Braun, Kunststoff-Handbuch, Volume 3/1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Carl Hanser Verlag Munich, Vienna 1992, pages 117-299.

Industrially very important is the production of high molecular weight polycarbonate from 2,2- bis(4-hydroxyphenyl)propane (also abbreviated to bisphenol A or BPA) and diphenyl carbonate (also abbreviated to DPC). Polycarbonates in the context of the present invention include not only homopolycarbonates but also copolycarbonates and/or polyestercarbonates; the polycarbonates may be linear or branched in known fashion. According to the invention, it is also possible to use mixtures of polycarbonates.

The thermoplastic polycarbonates including the thermoplastic aromatic polyestercarbonates have average molecular weights M„ (determined by measuring the relative solution viscosity at 25 °C in CH2CI2 and a concentration of 0.5 g per 100 ml of CH2CI2) of 20 000 g/mol to 32 000 g/mol, preferably of 23000 g/mol to 31 000 g/mol, in particular of 24000 g/mol to 31 000 g/mol.

A portion, up to 80 mol%, preferably from 20 mol% to 50 mol%, of the carbonate groups in the polycarbonates used in accordance with the invention may have been replaced by aromatic dicarboxylic ester groups. Such polycarbonates, which contain both acid radicals of carbonic acid and acid radicals of aromatic dicarboxylic acids incorporated into the molecular chain, are referred to as aromatic polyestercarbonates. In the context of the present invention, they are covered by the umbrella term of thermoplastic aromatic polycarbonates.

The polycarbonates are prepared in a known manner from dihydroxy aryl compounds, carbonic acid derivatives, optionally chain terminators and optionally branching agents, and the polyester carbonates are prepared by replacing a portion of the carbonic acid derivatives with aromatic dicarboxylic acids or derivatives of the dicarboxylic acids, to a degree according to the extent to which carbonate structural units in the aromatic polycarbonates are to be replaced by aromatic dicarboxylic ester structural units. The dihydroxyaryl compound or dihydroxyaryl compounds respectively and the carbonic acid derivate or carbonic acid derivates respectively used as starting compounds collectively also are referred to as monomer or monomers respectively.

Dihydroxyaryl compounds suitable for producing polycarbonates include those of formula (1)

HO-Z-OH (1), in which

Z is an aromatic radical which has 6 to 30 carbon atoms and may contain one or more aromatic rings, may be substituted and may contain aliphatic or cycloaliphatic radicals or alkylaryls or heteroatoms as bridging elements.

Preferably, Z in formula (1) is a radical of the formula (2) in which

R⁶ and R⁷ are independently H, Ci- to Cis-alkyl-, Ci- to Cis-alkoxy, halogen such as Cl or Br or in each case optionally substituted aryl- or aralkyl, preferably H or Ci- to Cu- alkyl, more preferably H or Ci - to Cs-alkyl and most preferably H or methyl, and

X represents a single bond, -SO₂-, -CO-, -0-, -S-, Ci- to CValkylcnc, C₂- to Cs-alkylidene or C₅- to G.-cycloalkylidcnc which may be substituted by Ci- to Ce-alkyl, preferably methyl or ethyl, or else represents Ce- to Ci2-arylene which may optionally be fused to further aromatic rings containing heteroatoms.

It is preferable when X represents a single bond, Ci- to Cs-alkylene, C2- to Cs-alkylidene, C5- to V cycloalkylidene, -0-, -SO-, -CO-, -S-, -SO2- or a radical of formula (2a)

Examples of dihydroxyaryl compounds are: dihydroxybenzenes, dihydroxydiphenyls, bis(hydroxyphenyl)alkanes, bis(hydroxyphenyl)cycloalkanes, bis(hydroxyphenyl)aryls, bis(hydroxyphenyl) ethers, bis(hydroxyphenyl) ketones, bis(hydroxyphenyl) sulfides, bis(hydroxyphenyl) sulfones, bis(hydroxyphenyl) sulfoxides, 1,1'- bis(hydroxyphenyl)diisopropylbenzenes and the ring-alkylated and ring-halogenated compounds thereof.

Dihydroxyaryl compounds suitable for producing the polycarbonates for use in accordance with the invention are for example hydroquinone, resorcinol, dihydroxydiphenyl, bis(hydroxyphenyl)alkanes, bis(hydroxyphenyl)cycloalkanes, bis(hydroxyphenyl) sulfides, bis(hydroxyphenyl) ethers, bis(hydroxyphenyl) ketones, bis(hydroxyphenyl) sulfones, bis(hydroxyphenyl) sulfoxides, a,a'-bis(hydroxyphenyl)diisopropylbenzenes and the alkylated, ring-alkylated and ring-halogenated compounds thereof.

Preferred dihydroxyaryl compounds are 4,4’ -dihydroxydiphenyl, 2,2-bis(4-hydroxyphenyl)-l- phenylpropane, l,l-bis(4-hydroxyphenyl)phenylethane, 2,2-bis(4-hydroxyphenyl)propane (BPA), 2,4-bis(4-hydroxyphenyl)-2-methylbutane, l,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, l,3-bis[2-(3,5- dimethyl-4-hydroxyphenyl)-2-propyl]benzene and l,l-bis(4-hydroxyphenyl)-3,3,5- trimethylcyclohexane (also abbreivated to bisphenol TMC), or one of the bisphenols of the formulas (3) to (5) wherein R‘ in each case means Ci-C4-alkyl, aralkyl or aryl, preferably means methyl oder phenyl.

Particularly preferred dihydroxyaryl compounds are 4,4’-dihydroxydiphenyl, l,l-bis(4- hydroxyphenyl)phenylethane, 2,2-bis(4-hydroxyphenyl)propane (BPA), 2,2-bis(3,5-dimethyl-4- hydroxyphenyl)propane, l,l-bis(4-hydroxyphenyl)cyclohexane and l,l-bis(4-hydroxyphenyl)- 3,3,5-trimethylcyclohexane (TMC), or one of the bisphenols of the formulas (3) to (5) wherein R‘ in each case means Ci-C4-alkyl, aralkyl or aryl, preferably means methyl oder phenyl.

These and further suitable dihydroxyaryl compounds are described, for example, in US 2 999 835 A, US 3 148 172 A, US 2 991 273 A, US 3 271 367 A, US 4 982 014 A and US 2 999 846 A, in German published specifications DE 1 570 703 A, DE 2 063 050 A, DE 2 036 052 A, DE 2 211 956 A and DE 3 832 396 A, in French patent specification FR 1 561 518 Al, in the monograph “H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964, p. 28 ff.; p.102 ff.”, and in “D.G. Legrand, J.T. Bendler, Handbook of Polycarbonate Science and Technology, Marcel Dekker New York 2000, pp. 72ff.” In the case of the homopolycarbonates, only one dihydroxyaryl compound is used; in the case of copolycarbonates, two or more dihydroxyaryl compounds are used. The dihydroxyaryl compounds employed, similarly to all other chemicals and assistants added to the synthesis, may be contaminated with the contaminants from their own synthesis, handling and storage. However, it is desirable to work with the purest possible raw materials.

Any branching agents or branching agent mixtures to be used are added to the synthesis in the same manner. Compounds typically used are trisphenols, quaterphenols or acyl chlorides of tri- or tetracarboxylic acids, or else mixtures of the polyphenols or of the acyl chlorides.

Some of the compounds having three or more than three phenolic hydroxyl groups that are usable as branching agents are, for example, phloroglucinol, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)hept- 2-ene, 4, 6-dimethyl -2, 4, 6-tri(4-hydroxyphenyl)heptane, l,3,5-tris(4-hydroxyphenyl)benzene, 1,1,1- tri(4-hydroxyphenyl)ethane, tris(4-hydroxyphenyl)phenylmethane, 2,2-bis[4,4-bis(4- hydroxyphenyl)cyclohexyl]propane, 2,4-bis(4-hydroxyphenylisopropyl)phenol, tetra(4- hydroxyphenyl)methane.

Some of the other trifunctional compounds are 2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and 3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.

Preferred branching agents are 3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole and 1,1,1 -tri(4-hydroxyphenyl)ethane.

The amount of branching agents for optional use is from 0.05 mol% to 2 mol%, in turn based on moles of dihydroxyaryl compounds used in each case, in which the branching agents are initially charged with the dihydroxyaryl compounds.

All of these measures for producing polycarbonates are familiar to those skilled in the art.

Aromatic dicarboxylic acids suitable for the production of the polyestercarbonates are, for example, orthophthalic acid, terephthalic acid, isophthalic acid, tert-butylisophthalic acid, 3,3'- diphenyldicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4-benzophenonedicarboxylic acid, 3,4'-benzophenonedicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-diphenyl sulfone dicarboxylic acid, 2,2-bis(4-carboxyphenyl)propane, trimethyl-3-phenylindane-4,5'-dicarboxylic acid.

Among the aromatic dicarboxylic acids, particular preference is given to using terephthalic acid and/or isophthalic acid.

Derivatives of dicarboxylic acids include dicarbonyl dihalides and dialkyl dicarboxylates, in particular dicarbonyl dichlorides and dimethyl dicarboxylates. The carbonate groups are replaced essentially stoichiometricahy and also quantitatively by the aromatic dicarboxylic ester groups, and so the molar ratio of the coreactants is also reflected in the finished polyester carbonate. The aromatic dicarboxylic ester groups can be incorporated either randomly or in blocks.

Diarylcarbonates which may be used for producing polycarbonates by the melt transesterification process are di-CVCw-aryl esters, preferably diesters of phenol or substituted phenols, i.e. diphenyl carbonate or bissalicyl carbonate for example. The diaryl carbonates are used in amounts of 1.01 to 1.30 mol, preferably 1.02 to 1.15 mol, based on 1 mol of dihydroxyaryl compound.

The fully reacted at least biphasic reaction mixture, containing at most only traces (< 2 ppm) of chlorocarbonic acid aryl esters, is allowed to settle out for the phase separation. The aqueous alkaline phase (reaction wastewater) is separated off and the organic phase is extracted with dilute hydrochloric acid and water. The combined water phases are fed to the wastewater workup where solvent and catalyst fractions are separated off by stripping or extraction and are recycled. Subsequently, after adjusting to a certain pH of 6 to 8, for example by addition of hydrochloric acid, the organic impurities potentially still remaining, such as monophenol for example, are removed by treatment with activated carbon and the water phases are fed to chloralkali electrolysis.

In another variant of the workup, the reaction wastewater is not combined with the wash phases but, after stripping or extraction to remove solvents and catalyst residues, is adjusted to a certain pH of, for example, 6 to 8, by addition of hydrochloric acid for example, and after removing the organic impurities still remaining, such as monophenol for example, by treatment with activated carbon, is fed to chloralkali electrolysis.

After removing the solvent and catalyst fractions by stripping or extraction, the wash phases can optionally be fed again to the synthesis.

The diaryl carbonates are prepared according to the prior art by reacting monophenols and a carbonyl halide in an inert solvent in the presence of alkali metal and a nitrogen catalyst by the phase interfacial process, with formation of alkali metal halide, e.g. NaCl. The carbonyl halide can be a carbonyl dihalide in this case, preferably phosgene, or diphosgene or triphosgene; particular preference is given to phosgene. Optimizations of the method by improving the mixing and maintaining a narrow temperature and pH profile and isolation of the diaryl carbonate are described in EP 1 219589 Al, EP 1 216981 A2, EP 1 216982 A2 and EP 784048 Al.

Particularly suitable monophenols for preparing diaryl carbonates in step c) are phenols of formula

(6)

OH

R (6), in which

R is hydrogen, halogen or a branched or unbranched Ci- to C9-alkyl radical or alkoxycarbonyl radical.

Preference is therefore given to phenol, alkylphenols such as cresols, p-tert-butylphenol, p- cumylphenol, p-n-octylphenol, p-isooctylphenol, p-n-nonylphenol and p-isononylphenol, halophenols such as p-chlorophenol, 2,4-dichlorophenol, p-bromophenol and 2,4,6-tribromophenol, and also methyl salicylate. Particular preference is given to phenol.

The alkali used to form the phenolate can be an alkali metal hydroxide solution from the series: hydroxides of Na, K, Li, preference being given to aqueous sodium hydroxide solution, and is used in the novel method preferably as a 10 to 55% by weight solution.

The preparation of the diaryl carbonates can be accelerated by catalysts such as tertiary amines, N- alkylpiperidines or onium salts. Preference is given to using tributylamine, triethylamine and N- ethylpiperidine.

The amine catalyst used can be open-chain or cyclic, particular preference being given to triethylamine and ethylpiperidine. The catalyst is preferably used as a 1 to 55% by weight solution.

Onium salts are understood here to mean compounds such as NR₄X, where R may be an alkyl and/or aryl radical and/or an H and X is an anion.

The carbonyl halide, especially phosgene, may be used in liquid or gaseous form or dissolved in an inert solvent.

The preparation of phosgene from carbon monoxide and chlorine is known per se, for example in EP 881 986 B1 or EP 1 640 341 A2. Carbon monoxide is converted by reacting carbon monoxide with chlorine to give phosgene, for example over an activated carbon catalyst. However, it is also possible to use alternative catalysts. Reference can be made here to the prior art (e.g. DE 3327274 Al; GB 583 477 A; WO 97/30932 Al; WO 96/16898 Al; US 6,713,035 Bl). On an industrial scale, phosgene is predominantly produced by reacting carbon monoxide with chlorine, preferably over activated carbon as catalyst. The highly exothermic gas phase reaction takes place at temperatures of at least 100°C up to a maximum of 600°C, generally in tube bundle reactors. The heat of reaction can be removed in different ways, for example by a liquid heat exchange medium such as described for example in WO 03/072237 Al, or by evaporative cooling via a secondary circuit with simultaneous use of the heat of reaction for vapour generation, such as is disclosed in US 4,764,308 A for example. Preference is given to using activated carbon as catalyst, in which the activated carbon comprises a total sulfur content of less than 1 % by weight, especially less than 0.5% by weight, based on the total weight of the catalyst. Furthermore, the production of phosgene is carried out preferably at temperatures less than or equal to 300°C and furthermore the production of phosgene is combined with the generation of vapour. In addition, the catalyst preferably has a specific surface area of greater than 10 m²/g.

In the process for producing a polycarbonate from a dihydroxyaryl compound, especially BPA, or two or more dihydroxyaryl compounds, especially a mixture of BPA and bisphenol TMC or a mixture of BPA and one of the bisphenols of the formulas (3) to (5) wherein R‘ in each case means Ci-C4-alkyl, aralkyl or aryl, preferably means methyl or phenyl, and a diaryl carbonate, especially DPC, by the melt transesterification process a stream of a liquid dihydroxyaryl compound or a stream of a mixture of the two or more liquid dihydroxyaryl compounds and a stream of a liquid diarylcarbonate are conducted into a mixing tank in which the dihydroxyaryl compound or the two or more dihydroxyaryl compounds and the diarylcarbonate are mixed. The mixing may be conducted by a stirrer e.g. In the mixing tank no noteworthy reaction between dihydroxyaryl compound or the two or more dihydroxyaryl compounds and the diarylcarbonate takes place. Hereinafter, both the “dihydroxyaryl compound” and the “two or more dihydroxyaryl compounds” are referred to as “dihydroxyaryl compound”.

The liquid mixture of the dihydroxyaryl compound and the diarylcarbonate then is conducted through a pipeline whereby a catalyst - usually dissolved in phenol - is added and fed into a reaction vessel in which the mixture is heated towards the reaction temperature. Further substances may be added at this stage, too. The reaction temperature is from 180 °C to 220 °C, preferably 190 °C to 210 °C, most preferably about 190 °C, for the production of a polycarbonate from 2,2-bis-(4- hydroxyphenyl)-propan (BPA) and diphenylcarbonat (DPC). At residence times of 15 to 90 min, preferably 30 to 60 min, a reaction equilibrium is set without the formed monohydroxyaryl compound, e.g. phenol in case that DPC is used as diarylcarbonate, being removed. The reaction may be conducted at atmospheric pressure but also may be conducted at overpressure.

The relative solution viscosity of the resultant oligocarbonate, which is likewise in the form of a melt under the conditions in the production, is increased with rising temperatures and falling pressures in suitable apparatuses and devices by removal of the monohydroxyaryl compound eliminated, for example phenol, until the desired relative solution viscosity of the oligocarbonate has been attained. By choice of the ratio of the dihydroxyaryl compound to the diaryl carbonate, by the rate of loss of the diaryl carbonate via the vapours that results from choice of the procedure and of the production plant for preparation of the oligocarbonate, and by any catalysts added, the desired relative solution viscosity can be established. With regard to the manner of, the apparatuses in which and the way in which the melt transesterification process is executed, there is no limitation and restriction, provided that the apparatuses chosen and the procedure chosen enable a melt transesterification with appropriately rapid removal of the monohydroxyaryl compound eliminated and enable the establishment of a particular desired relative solution viscosity.

Moreover, there is no limitation and restriction with regard to the temperatures, pressures or the catalysts used in order to conduct the melt transesterification reaction between the dihydroxyaryl compound and the diaryl carbonate. Any condition is possible provided that the temperatures, pressures and catalysts chosen enable a melt transesterification with correspondingly rapid removal of the monohydroxyaryl compound eliminated and enable the establishment of a particular desired relative solution viscosity.

The monohydroxyaryl compound eliminated is removed by at least one evaporator stage, preferably by multiple evaporator stages. Devices, apparatuses and reactors suitable as evaporator stage are, in accordance with the process sequence, heat exchangers, flash apparatuses, for example flash evaporators, vacuum chambers, separators, columns, evaporators, stirred vessels and reactors or other purchasable apparatuses which provide the necessary residence time at selected temperatures and pressures. The devices chosen must enable the necessary input of heat and be constructed such that they are able to cope with the continuously increasing relative solution viscosities.

All devices, apparatuses and reactors are connected to one another by pumps, pipelines or valves. The pipelines between ah the devices, apparatuses and reactors should of course be as short as possible and the curvature of the conduits should be kept as low as possible in order to avoid unnecessarily prolonged residence times. At the same time, the external, i.e. technical, boundary conditions and requirements for assemblies of chemical production plants should be observed.

The melt is expanded here in a first stage into a first evaporator stage, the pressure of which is set to 100 to 400 mbar absolute, preferably to 150 to 300 mbar absolute, and then heated directly back to the inlet temperature at the same pressure in a suitable device. In the flash operation, the monohydroxyaryl compound formed, for example phenol in the case of use of diphenyl carbonate as diaryl carbonate, is evaporated together with unconverted monomers still present. After a residence time of 5 to 30 min in a bottoms reservoir, optionally with pumped circulation, at the same pressure and the same temperature, the reaction mixture, in a second stage, is preferably expanded into a second evaporator stage, the pressure of which is 50 to 200 mbar absolute, preferably 80 to 150 mbar absolute, and directly thereafter heated in a suitable apparatus at the same pressure to a temperature of 190°C to 250°C, preferably 210°C to 240°C, more preferably 210°C to 230°C. Here too, the hydroxyaryl compound formed is evaporated together with unconverted monomers still present. After a residence time of 5 to 30 min in a bottoms reservoir, optionally with pumped circulation, at the same pressure and the same temperature, the reaction mixture, in a third stage, is preferably expanded into a third evaporator stage, the pressure of which is 30 to 150 mbar absolute, preferably 50 to 120 mbar absolute, and directly thereafter heated in a suitable apparatus at the same pressure to a temperature of 220°C to 280°C, preferably 240°C to 270°C, more preferably 240°C to 260°C. Here too, the hydroxyaryl compound formed is evaporated together with unconverted monomers still present. After a residence time of 5 to 20 min in a bottoms reservoir, optionally with pumped circulation, at the same pressure and the same temperature, the reaction mixture, in a fourth stage, is preferably expanded into a fourth evaporator stage, the pressure of which is 5 to 100 mbar absolute, preferably 15 to 100 mbar absolute, more preferably 20 to 80 mbar absolute, and directly thereafter heated in a suitable apparatus at the same pressure to a temperature of 250°C to 300°C, preferably 260°C to 290°C, more preferably 260°C to 280°C. Here too, the hydroxyaryl compound formed is evaporated together with monomers still present. The evaporator stages are also called flash stages.

The number of these evaporator stages, 4 here by way of example, may vary between 2 and 6, but just one evaporator stage is also possible. The temperatures and pressures should be adjusted appropriately when the number of stages is altered in order to obtain comparable results. The relative solution viscosity of the oligocarbonate attained in these stages is in the range from 1.04 to 1.18, preferably from 1.05 to 1.12, more preferably from 1.06 to 1.10.

The oligocarbonate now obtained in this way, in the form of a melt, after a residence time of 5 to 20 min in a bottoms reservoir, optionally with pumped circulation, at the same pressure and the same temperature as in the fourth stage, is conveyed into at least one further reactor, for example a disk or cage reactor, as the last evaporator stage and subjected to further condensation at 250°C to 310°C, preferably 250°C to 290°C, more preferably 250°C to 280°C, at pressures of 1 to 15 mbar absolute, preferably 2 to 10 mbar absolute, with residence times of 30 to 90 min, preferably 30 to 60 min. The oligocarbonate then attains a relative solution viscosity of 1.13 to 1.18, preferably of 1.14 to 1.16.

Apart from the reactors already mentioned, the evaporator stages may also be selected from the group comprising stirred tanks, thin-film evaporators, falling-film evaporators, stirred tank cascades, extruders, kneaders, high-viscosity reactors according to EP460466A1, and high- viscosity disk reactors.

The oligocarbonate is then processed further to give a polycarbonate. For this purpose, the oligocarbonate is guided into a reactor or a series of at least two reactors suitable for condensation of the oligocarbonate to the polycarbonate. This reactor is/these reactors are also referred to as polycondensation reactor(s). The reactor(s) are independently selected from the group comprising cage reactors, high-viscosity reactors according to EP460466A1, disk reactors, high-viscosity disk reactors, extrusion machines such as single-shaft, twin-shaft, ring or planetary roll extruders and polymer kneaders, and thin-film evaporators. The twin-shaft extruder may, for example, be a twin- shaft extruder from Readco Kurimoto LLC.

Preference is given to using reactors suitable for the processing of high-viscosity materials, which provide a sufficient residence time with good mixing and subject the oligocarbonates and the polycarbonates formed therefrom to the requisite vacuum. The viscosities of such high-viscosity materials are typically in the range from 1 to 10000 Pas, measured with the commercial viscometers known to those skilled in the art, for example capillary, plate-cone or plate-plate viscometers. The patent literature describes numerous reactors that basically fulfil these demands and can be used in accordance with the invention. For example, it is possible to use reactors according to EP460466A1, EP528210A1, EP638354A1, EP715881A2, EP715882A2,

EP798093A2 or those according to EP329092A1, according to EP517068A1, or EP1436073A1 and those according to EP222599A2. Especially preferably, a reactor according to EP460466A1 is used, which cleans itself by kinematic means.

The second or last one of the at least two reactors reactors may be designed, for example, as a twin- shaft extruder or as a disk or cage reactor, for example as a high-viscosity reactor according to EP460466A1 in which the oligocarbonate can be condensed up to give a polycarbonate having a desired final relative solution viscosity. The temperatures are 270°C to 330°C, preferably 280°C to 320°C, more preferably 280°C to 310°C, and the pressure is 0.01 to 3 mbar, preferably 0.2 to 2 mbar, with residence times of 60 to 180 min, preferably 75 to 150 min. This desired final relative solution viscosity is greater than 1.18 and is preferably from 1.181 to 1.40, more preferably 1.181 to 1.36, most preferably 1.181 to 1.34. The vapours from all the process stages are directly led off, collected and processed. This processing is generally effected by distillation in order to achieve high purities of the substances recovered. This can be effected, for example, according to EP1221454A1. Recovery and isolation of the eliminated monohydroxyaryl compound in ultrapure form is an obvious aim from an economic and environmental point of view. The monohydroxyaryl compound can be used directly for preparation of a dihydroxyaryl compound or a diaryl carbonate.

It is a feature of the disk or cage reactors that they provide a very large, constantly renewing surface under reduced pressure with high residence times. The disk or cage reactors have a geometric shape in accordance with the melt viscosities of the products. Suitable examples are reactors as described in EP460466A1 and EP1253163A1, or twin-shaft reactors as described in WO99/28370A1.

The oligocarbonates and the polycarbonates formed therefrom can be guided through mixing elements for better mixing. For example, it is possible to use a static or dynamic mixer, for example in the secondary strand for improved mixing-in of one or more coreactants. Both the oligocarbonates and the polycarbonates formed therefrom are in the form of a melt under the conditions in the preparation.

If a high-viscosity reactor is used, for example a high-viscosity reactor according to EP460466A1, the polycarbonate is discharged from the high-viscosity reactor preferably using a single-shaft extruder, a twin-shaft extruder or a gear pump. If appropriate, additives are also supplied and mixed in. The additives may, for example, be production auxiliaries, UV stabilizers, colorants, for example pigments, fillers, flame retardants, demoulding agents, antistats, flow improvers, thermal stabilizers or processing stabilizers.

The additives may be conventional polymer additives, for example those described in EP-A 0 839 623, WO-A 96/15102, EP-A 0 500 496 or “Plastics Additives Handbook”, Hans Zweifel, 5th Edition 2000, Hanser Verlag, Munich.

Production auxiliaries used may, for example, be alkyl phosphates, e.g. mono-, di- and trihexyl phosphate, triisooctyl phosphate and trinonyl phosphate. The alkyl phosphate used is preferably triisooctyl phosphate (tris-2-ethylhexyl phosphate). It is also possible to use mixtures of various mono-, di- and trialkyl phosphates.

Demoulding agents may be based, for example, on a fatty acid ester, preferably a stearic ester, especially preferably based on pentaerythritol. In addition, it is possible to use pentaerythritol tetrastearate (PETS) and/or glycerol monostearate (GMS). Additives likewi e mean ultraviolet absorbers. Suitable ultraviolet absorbers are compounds having the lowest possible transmittance below 400 nm and the highest possible transmittance above 400 nm. Such compounds and the preparation thereof are known from the literature and are described, for example, in EP-A 0 839 623, WO-A 96/15102 and EP-A 0 500 496. Particularly suitable ultraviolet absorbers are benzotriazoles, triazines, benzophenones and/or arylated cyanoacrylates. The following ultraviolet absorbers are especially suitable, for example: hydroxybenzotriazoles such as 2-(3',5'-bis(l,l-dimethylbenzyl)-2'-hydroxyphenyl)benzotriazole (Tinuvin® 234, BASF AG Ludwigshafen), 2-(2'-hydroxy-5'-(tert-octyl)phenyl)benzotriazole (Tinuvin® 329, BASF AG Ludwigshafen), bis(3-(2H-benztriazolyl)-2-hydroxy-5-tert-octyl)methane, (Tinuvin® 360, BASF AG Fudwigshafen), BASF AG Fudwigshafen 2-(4,6-diphenyl-l,3,5-triazin-2-yl)-5- (hexyloxy)phenol (Tinuvin® 1577, BASF AG Fudwigshafen), and the benzophenones 2,4- dihydroxybenzophenone (Chimasorb® 22, BASF AG Fudwigshafen) and 2-hydroxy-4- (octyloxy)benzophenone (Chimassorb® 81, BASF AG Fudwigshafen), 2-propenoic acid, 2-cyano- 3, 3 -diphenyl-, 2,2-bis[[(2-cyano-l-oxo-3,3-diphenyl-2-propenyl)oxy]-methyl]-l,3-propanediyl ester (9CI) (Uvinul® 3030, BASF AG Fudwigshafen), 2-[2-hydroxy-4-(2-ethylhexyl)oxy]phenyl- 4,6-di(4-phenyl)phenyl-l,3,5-triazine (CGX UVA 006, BASF AG Fudwigshafen) or tetraethyl 2,2'-(l,4-phenylenedimethylidene)bismalonate (Hostavin® B-Cap, Clariant AG).

It is also possible to use mixtures of these ultraviolet absorbers.

Thermal stabilizers or processing stabilizers used may be phosphites and phosphonites, and also phosphines. Examples include triphenyl phosphite, diphenyl alkyl phosphite, phenyl dialkyl phosphite, tris(nonylphenyl) phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythritol diphosphite, tris(2,4-di-tert-butylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, bis(2,4-dicumylphenyl) pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite, diisodecyloxy pentaerythritol diphosphite, bis(2,4-di-tert-butyl-6-methylphenyl) pentaerythritol diphosphite, bis(2,4,6-tris(tert-butylphenyl)) pentaerythritol diphosphite, tristearyl sorbitol triphosphite, tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenylenediphosphonite, 6-isooctyloxy-

2.4.8.10-tetra-tert-butyl-12H-dibenzo[d,g]-l,3,2-dioxaphosphocine, bis(2,4-di-tert-butyl-6- methylphenyl) methyl phosphite, bis(2,4-di-tert-butyl-6-methylphenyl) ethyl phosphite, 6-fluoro-

2.4.8.10-tetra-tert-butyl-12-methyldibenzo[d,g]-l,3.2-dioxaphosphocine, 2,2',2"- nitrilo[triethyltris(3,3',5,5'-tetra-tert-butyl-l,r-biphenyl-2,2'-diyl) phosphite], 2-ethylhexyl(3,3',5,5'- tetra-tert-butyl-l,l'-biphenyl-2,2'-diyl) phosphite, 5-butyl-5-ethyl-2-(2,4,6-tri-tert-butylphenoxy)- 1 ,3,2-dioxaphosphirane, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, triphenylphosphine (TPP), trialky lphenylphosphine, bisdiphenylphosphinoe thane or a trinaphthylphosphine. Especially preferably, triphenylphosphine (TPP), Irgafos® 168 (tris(2,4-di- tert-butylphenyl) phosphite) and tris(nonylphenyl) phosphite or mixtures thereof are used. It is also possible to use phenolic antioxidants such as alkylated monophenols, alkylated thioalkylphenols, hydroquinones and alkylated hydroquinones. Particular preference is given to using Irganox® 1010 (pentaerythritol 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate; CAS: 6683-19-8) and Irganox 1076® (2,6-di-tert-butyl-4-(octadecanoxycarbonylethyl)phenol).

The additives can be mixed in in the discharge unit or in a downstream static mixer. The polycarbonate is shaped by means of one or more nozzles and comminuted with a pelletizing device according to prior art.

It is also possible to use a combination of machines mentioned above. For example, additives can be mixed in using a twin-shaft extruder which is then combined with the abovementioned high- viscosity reactor.

The polycarbonates obtained by the melt transesterification process according to the invention can be subjected to a further workup. This workup may, for example, be a filtration or a depth filtration, wherein a melt of the polycarbonate obtained in each case is passed through filter media composed of fibre web or sinter material. In addition, the melt of the polycarbonate obtained in each case can be provided with additives, for example via side extruders. The additives may be the substances mentioned above. Preferably, one or more production auxiliaries or inhibitors can be added at the end of the process.

The oligocarbonates and the polycarbonates formed therefrom are generally conveyed by means of gear pumps, screws of a wide variety of designs or positive displacement pumps of a specific design.

Particularly suitable materials for manufacture of the apparatuses, reactors, pipelines, pumps and fittings are stainless steels of the Cr Ni (Mo) 18/10 type, for example 1.4571, 1.4404 or 1.4541 (nomenclature according to EN 10027-2; see Stahlschlussel [Key to Steel] 2001, publisher: Stahlschliissel Wegst GmbH, Th-Heuss-Strasse 36, D-71672 Marbach) for components with relatively low hardness demands, and 1.4112, 1.4313 or 1.4418 for components with elevated hardness demands and Ni-base alloys of the C type, for example 2.4605 or 2.4610 (Stahlschlussel 2001, publisher: Stahlschlussel Wegst GmbH, Th-Heuss-Strasse 36, D-71672 Marbach). The stainless steels are utilized up to process temperatures of about 290°C, and the Ni-base alloys at process temperatures above about 290°C.

Polycarbonates that can be prepared by means of the process according to the invention are preferably selected from the group comprising unbranched homopolycarbonates based on bisphenol A, branched polycarbonates or copolycarbonates, preferably selected from the group comprising block copolycarbonates, for example a siloxane-based block copolycarbonate or a polyester-based block copolycarbonate, polyestercarbonates or polycarbonates that are formed from a diaryl carbonate, for example diphenyl carbonate, and at least two different bisphenols, for example bisphenol A and bisphenol TMC or bisphenol A and one of the bisphenols of the general formulae (3) to (5) elucidated further down.

It is known in the state of the art that the reaction rate of the formation of oligocarbonates or polycarbonates respectively from a reaction mixture comprising a dihydroxyaryl compound and a diaryl carbonate by the melt transesterification process may drop due to numerous reasons. These reasons may be e.g. a poor quality of the raw materials, wrong catalyst dosing, poor activity of the catalyst because e.g. of deactivation or poor quality of the catalyst, wrong ratio between the amount of the dihydroxyaryl compound and the amount of the diaryl carbonate.

In the meaning of the present invention the term “reaction rate of the formation of oligocarbonates or polycarbonates respectively from a dihydroxyaryl compound and a diaryl carbonate by the melt transesterification process” means the increase in molecular weight of the oligocarbonates or polycarbonates formed by the reaction of a dihydroxyaryl compound and a diaryl carbonate due to molecular chain elongation per time unit. Due to the above explained reaction scheme (I), the increase in molecular weight of the oligocarbonates or polycarbonates formed by the reaction of a dihydroxyaryl compound and a diaryl carbonate due to molecular chain elongation per time unit corresponds to the formation of a monohydroxyaryl compound per time unit.

However, the state of the art does not provide a simple solution to monitor and to control the reaction rate of the formation of oligocarbonates or polycarbonates respectively from a dihydroxyaryl compound and a diaryl carbonate by the melt transesterification process reliably. This may result in large amounts of polycarbonate which does not meet the required specification and thus is not saleable. Further, in case of a too high viscosity, the production apparatuses may be damaged, too.

US 6,399,739 B1 discloses a method of preparing polycarbonate from a diaryl carbonate and a dihydroxy aromatic compound wherein the process is controlled by measuring the viscosity of the product polycarbonate.

KR 100354801 B1 also discloses a process for the production of polycarbonate by a transesterification process which is controlled by the value of the viscosity of the polycarbonate.

However, the value of a measured viscosity is susceptible to mistakes since the value of the measured viscosity is influenced strongly by temperature or by-products contained in the polycarbonate. So the control of the processes disclosed in US 6,399,739 B1 or KR 100354801 B1 susceptible to this mistakes too and therefore not reliable. Further, the control of the processes disclosed in US 6,399,739 B1 or KR 100354801 B1 need sophisticated control devices and therefore are not simple. Therefore it is an object of the present invention to provide a melt transesterification process for producing a polycarbonate from a dihydroxyaryl compound and a diaryl carbonate in which the reaction rate of the reaction between the dihydroxyaryl compound with the diaryl carbonate can be monitored and controlled simply and reliably. Especially the reaction rate of the reaction between the dihydroxyaryl compound with the diaryl carbonate shall be monitored simply and reliably and - in case that the reaction rate drops below a predefined value - the reaction rate shall be increased again. By means of this melt transesterification process a required molecular weight and/or a required relative solution viscosity of the obtained polycarbonate shall be kept.

Surprisingly, the object of the invention is achieved by a process according to claim 1. Especially the object is achieved by a melt transesterification process for producing a polycarbonate comprising at least the following steps:

(a) Providing an amount of a starting material comprising an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate and an amount of a catalyst in a specified ratio;

(b) Mixing the amount of the dihydroxyaryl compound and the amount of the diaryl carbonate and the amount of the catalyst;

(c) Reacting the dihydroxyaryl compound and the diaryl carbonate to form an oligocarbonate and a monohydroxyaryl compound;

(d) Determining a measured value correlating to the amount of the monohydroxyaryl compound formed;

(e) Comparing the measured value correlating to the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I):

(f) Making a decision based on of the result of the comparison of step (e) whether reaction rate is too low or not too low; and then: (g) Taking measures to increase the reaction rate again in case the reaction rate is too low. or

(h) Taking no measures in case the reaction rate is not too low.

In the meaning of the present invention the term “the reaction rate is too low” means that the reaction rate is less than 90 % of the desired reaction rate. It is clear for one skilled in the art that the desired reaction rate depends on the characteristics of the production plant and other characteristics of the reaction in a technical implementation, e.g. the throughput rate of the production plant. Preferably, term “the reaction rate is too low” means that the reaction rate is less than 95 % of the desired reaction rate. Consequently, “the reaction rate is not too low” when the reaction rate is at least 90 % of the desired reaction rate, preferably at least 95 % of the desired reaction rate.

According to the invention this drop of the reaction rate may be detected first at the outlet of a polycondensation reactor or of a series of coupled polycondensation reactors which follows or follow the last one of the at least one evaporator stages. A series of coupled polycondensation reactors comprises at least two polycondensation reactors in sequence. The polycondensation reactor or the reactors of a series of coupled polycondensation reactors may be selected from a rotating disc reactor according to EP460466A1 or a cage reactor e.g. as explained above already.

In case of a drop of the reaction rate the value of the relative solution viscosity will be too low. In case of an oligocarbonate or polycarbonate respectively which is formed from BPA and DPC only and in case of only one polycondensation reactor the relative solution viscosity at the outlet of the reactor shall reach, depending on the actual specification, a specific value which represents the required solution viscosity and is selected from a value from 1.06 to 1.36 and in case of a series of at least two coupled polycondensation reactors the relative solution viscosity at the outlet of the first reactor shall reach, depending on the actual specification, a specific value which represents the required solution viscosity and is selected from a value from 1.06 to 1.22 and the relative solution viscosity at the outlet of the last of the series of coupled reactors shall reach, depending on the actual specification, a specific value which represents the required solution viscosity and is selected from a value from 1.15 to 1.36. However, it is clear for one skilled in the art that in case of a series of coupled reactors the relative solution viscosity at the outlet of the first reactor always in lower than the relative solution viscosity at the outlet of the last one of a series of coupled reactors.

Due to the drop of the reaction rate the relative solution viscosity is reduced in such a way that - in regard to the specific value which represents the required solution viscosity according to the actual specification at the outlet of each reactor and especially in regard to the specific value which represents the required solution viscosity according to the actual specification at the outlet of the last reactor - this or these aforementioned specific required value or values is or are not achieved. With such a oligocarbonate or polycarbonate respectively it is not possible anymore to produce a polycarbonate which meets the required specification concerning relative solution viscosity and OH end group concentration (the OH end group concentration is determined by infrared spectrometry at a IR-band at 3582 cm ¹ wherein the net absorption is multiplied with a factor which is established from a set of calibration samples).

In an alternative embodiment of the invention this drop of the reaction rate may be detected first at the outlet of the first one of the at least one evaporator stage.

Preferably, in step (a), in case that only one dihydroxyaryl compound is used, the dihydroxyaryl compound is BPA preferably. In case that only two dihydroxyaryl compounds are used, preferably one of the bisphenols is BPA and the other bisphenol is selected from the group consisting of bisphenol TMC or one of the bisphenols of the formulas (3) to (5) wherein R‘ in each case means Ci-C4-alkyl, aralkyl or aryl, preferably means methyl or phenyl. Preferably, in step (b), the molar ratio of the amount of the dihydroxyaryl compound and the amount of the diaryl carbonate is from 1.0:1.3 to 1.0:1.0, preferably from to 1.0:1.2 to 1.0:1.03;

Preferably, in step (c), the oligocarbonate obtained is further converted in a polycarbonate by chain elongation.

Preferably, in step (d), the determination of a measured value correlating to the amount of a monohydroxy aryl compound formed is conducted as follows:

(d) Determining the amount of the monohydroxyaryl compound formed.

Further preferably, in step (d), the determination of a measured value correlating to the amount of the monohydroxyaryl compound formed is conducted by means of a computer running a software being a computer program product designed to determine a measured value correlating to the amount of the monohydroxyaryl compound formed or the determination the amount of the monohydroxyaryl compound formed is conducted by a human operator.

Furthermore preferably, in step (d), the determination of the amount of a monohydroxyaryl compound formed is conducted as follows:

(d(a)l) Determining the mass going out of the mixing vessel towards the first evaporator stage,

(d(a)2) Determining the mass of liquids directly after the first evaporator stage,

(d(a)3) Determining the amount of a monohydroxyaryl compound formed by the following equation: n(monohydroxaryl compound formed)= ki * (1 - (mass measured in step (d(a)2)

/ mass measured in step (d(a)l))), wherein n(monohydroxyaryl compound) is the molar amount of the monohydroxyaryl compound and ki is an empirical value with whose help it is possible to calculate the molar amount of a monohydroxyaryl compound formed by the quotient of flow measured in step (d(a)2) and the flow measured in step (d(a)l);

(d(b)l) Measuring the mass going into the first evaporator stage,

(d(b)2) Measuring the position of a degassing control valve of the first evaporator stage,

(d(b)3) Determining the amount of a monohydroxy aryl compound formed by the following equation: n(monohydroxyaryl compound formed) = * position measured in step

(d(b)2) / mass measured in step (d(b)l); wherein n(monohydroxyaryl compound formed) is the molar amount of the monohydroxyaryl compound and is an empirical value with whose help it is possible to calculate the molar amount of a monohydroxyaryl compound formed by the quotient of flow measured in step (d(b)2) and the flow measured in step (d(b)l); or (d(c)) Determining the torque of a rotating part of the polycondensation reactor or of one reactor of a series of coupled polycondensation reactors.

In step d(a)l or step d(b)l the mass is measured as mass flow via inline flow measurement preferably when the process for producing a polycarbonate is a continuous process.

The empirical values ki and k e.g. take into account that the amount of the monohydroxyl compound which is determined may have to be adjusted due to underestimation because of e.g. incomplete determination of the amount or due to overestimation because of e.g. monohydroxyl compound being comprised in the starting material already. Since each kind of plant or specific reaction or required molecular weight or relative solution viscosity is different the empirical values ki and k have to be determined individually and will be different for each kind of plant or specific reaction or required molecular weight or relative solution viscosity. However, one skilled in the art knows how to determine these empirical values ki and k e.g. by measurement series.

Preferably, in step (d(a)3) or step (d(b)3) the determination of the amount of the monohydroxyaryl compound formed is conducted by an automated system, e.g. by means of a computer running a software being a computer program product designed to determine the amount of the monohydroxyaryl compound formed.

Alternatively, in step (d(a)3) or step (d(b)3) the determination the amount of the monohydroxyaryl compound formed may be conducted by a human operator. Such a human operator may be assisted by the automated systems explained above.

Alternatively to determining the amount of the monohydroxyaryl compound formed according to steps (d(a)l) to (d(a)3) or (d(b)l) to (d(b)3) and then comparing the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I), in a step (d(c)) the torque of a rotating part of the polycondensation reactor or of one reactor of a series of coupled polycondensation reactors can be determined for example, the rotating part being in close contact to the oligocarbonate or polycarbonate respectively. In case that the torque decreases under a certain limit, the reaction rate is not sufficient anymore. Also in this alternative embodiment, the determination of the torque of a rotating part of the polycondensation reactor or of one reactor of a series of coupled polycondensation reactors may be conducted by an automated system, which may also comprise a computer and a software being a computer program product designed to determine the torque of a rotating part of the polycondensation reactor or of one reactor of the a series of coupled polycondensation reactors, or a human operator, which may be assisted by an automated system.

Preferably, in step (e), the comparison of the measured value correlating to the amount of the monohydroxyaryl compound formed with the sum of the amounts of the dihydroxyaryl compound and of the diaryl carbonate is conducted as follows:

(e) Comparing the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I):

Further preferably, in step (e), the comparison of the measured value correlating to the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I) is conducted by means of a computer running a software being a computer program product designed to compare the measured value correlating to the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I) or the comparison of the measured value correlating to the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I) is conducted by a human operator.

Furthermore preferably, in step (e), the comparison of the amount of the monohydroxyaryl compound formed with the sum of the amounts of the dihydroxyaryl compound and of the diaryl carbonate is conducted as follows: (e) Determining the ratio R_a between the molar amount of the monohydroxyaryl compound formed and the amount of the monohydroxyaryl compound which can be formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I):

R_a = n(monohydroxyaryl compound formed) / n(monohydroxyarylaryl compound maximum) wherein n(monohydroxyaryl compound) is the molar amount of the monohydroxyaryl compound formed and n(monohydroxyarylaryl compound maximum) is the molar amount of the monohydroxyaryl compound which can be formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I):

Concerning the full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I) one skilled in the art knows how calculate this amount. He or she will also take into account possible impurities of the starting material, characteristics of the production plant, required molecular weight or relative solution viscosity or other characteristics of the reaction in a technical implementation.

Preferably, in step (e) the determination the ratio R_a is conducted by an automated system, e.g. by means of a computer running a software being a computer program product designed to determine the ratio R_a. The computer and the computer program product may be the same as used in step (d(b)3) or step (d(b)3), i.e. the computer and the computer program product both determines the amount of a monohydroxyaryl compound formed and the ratio R_a.

Alternatively, in step (e) the determination the ratio R_a is conducted by a human operator. Such a human operator may be assisted by the automated systems explained above.

Preferably, in step (f) the decision whether reaction rate is too low or not is made by an automated system, e.g. by means of a computer running a software being a computer program product designed to make the decision or an analogous setting unit, e.g a switch or a cascade of switches, or a gauge indicating at least the ranges “too low” and “not too low”. The gauge may be the position of the degassing control valve, e.g.

The computer and the computer program product may be the same as used in step (d(b)3) or step (d(b)3) or in step (e), i.e. the computer and the computer program product may determine the amount of a monohydroxyaryl compound formed and the ratio R_a and make the decision according to step (f).

Alternatively, in step (f) the decision whether reaction rate is too low or not is made by a human operator. Such a human operator may be assisted by the automated system explained above.

Anyway, if the outcome of the decision process is that the reaction rate is too low, an alarm can be triggered.

Preferably, in step (g), the measures to increase the reaction rate again may be the following:

(gl) Adjusting the ratio between the amount of the dihydroxyaryl compound and the amount of the diaryl carbonate in step (b) according to the outcome of the decision in step (f), or

(g2) Increasing the amount of catalyst or both adjusting the ratio between the amount of the dihydroxyaryl compound and the amount of the diaryl carbonate in step (b) according to the outcome of the decision in step (f) and increasing the amount of catalyst, or

(g3) Adjusting the pressure in the first reactor after the mixing vessel, according to the outcome of the decision in step (f), or (g4) adjusting the amount of NaOH in raw materials, according to the outcome of the decision in step (f).

Preferably, the adjustment is conducted when the reaction rate drops below a predefined value. This predefined value may be set differently for each kind of plant or specific reaction or required molecular weight or relative solution viscosity of the polycarbonate which shall be obtained.

Preferably, in step (g) the adjustment may be conducted by an automated system, e.g. mechanical devices.

These mechanical devices may be controlled by a computer running a software being a computer program product designed to control the mechanical devices in accordance with the decision in step (f). The computer and the computer program product may be the same as used in step (d(b)3) or step (d(b)3) or in step (e) or in step (f), i.e. the computer and the computer program product may determine the amount of a monohydroxyaryl compound formed and the ratio R_a and make the decision according to step (f) and control the mechanical devices conducting the adjustment according to step (g).

Alternatively, these mechanical devices may be controlled by a switch or a cascade of switches being able to control the mechanical devices in accordance with the decision in step (f). The switch or the cascade of switches may be the same switch or cascade of switches which is or are used in step (f), i.e. the switch or the cascade of switches both make the decision according to step (f) and control the mechanical devices conducting the adjustment according to step (g). Of course, the switch or the cascade of switches may be controlled by a computer running a software being a computer program product designed to control a switch or a cascade of switches, too.

Alternatively, these mechanical devices may be controlled by a human operator. Such a human operator may be assisted by a computer running a computer program product as explained above or a switch or a cascade of switches as explained above.

The present invention may be applied to a discontinuous or a continuous melt transesterification process for producing a polycarbonate, preferably to a continuous melt transesterification process for producing a polycarbonate.

The present invention provides a melt transesterification process for producing a polycarbonate from a dihydroxyaryl compound and a diaryl carbonate in which the reaction rate of the reaction between the dihydroxyaryl compound with the diaryl carbonate can be monitored and controlled. Especially the reaction rate of the reaction between the dihydroxyaryl compound with the diaryl carbonate can be monitored and - in case that the reaction rate drops below a predefined value - the reaction rate can be increased again. By means of this melt transesterification process a required molecular weight or relative solution viscosity of the obtained polycarbonate can be kept.

The present invention may also include a device that is set up for carrying out and/or controlling the process described above, or comprises the respective means for carrying out and/or controlling the steps the process described above.

Means of this device may comprise hardware and/or software components. The means may for example comprise at least one memory with program instructions of a computer program product and at least one processor designed for executing program instructions from the at least one memory. Accordingly, it is also intended according to the present invention that a device which comprises at least one processor and at least one memory with program instructions is understood as disclosed, wherein the at least one memory and the program instructions are set up to act together with the at least one processor in making the output module or the sensor module carry out and/or control the process according to the invention.

As an alternative or in addition, the means of the device may also comprise one or more sensors and/or one or more communication interfaces.

A communication interface is intended to be understood as meaning for example a wireless communication interface and/or a wire -bound communication interface.

A wireless communication interface is for example a communication interface according to a wireless communication technology. An example of a wireless communication technology is a local radio network technology such as Radio Frequency Identification (RFID) and/or Near Field Communication (NFC) and/or Bluetooth (for example Bluetooth Version 2.1 and/or 4.0) and/or Wireless Local Area Network (WLAN). RFID and NFC are for example specified according to the ISO standards 18000, 11784/11785 and the ISO/IEC standard 14443-A and 15693. WLAN is for example specified in the standards of the IEEE-802.11 family. Another example of a wireless communication technology is a trans-regional radio network technology, such as for example a mobile radio technology, for example the Global System for Mobile Communications (GSM) and/or Universal Mobile Telecommunications System (UMTS) and/or Long Term Evolution (LTE). The GSM, UMTS und LTE specifications are maintained and developed by the 3rd Generation Partnership Project (3GPP).

A wire -bound communication interface is for example a communication interface according to a wire-bound communication technology. Examples of a wire -bound communication technology are a Local Area Network (LAN) and/or a bus system, for example a Controller Area Network bus (CAN bus) and/or a Universal Serial Bus (USB). A CAN bus is for example specified according to the ISO standard ISO 11898. LAN is for example specified in the standards of the IEEE-802.3 family. It goes without saying that the output module and/or the sensor module may also comprise other means not mentioned here.

Furthermore, according to the present invention a computer program product is disclosed, comprising program instructions which are designed to make a device carry out and/or control the process described above when the computer program product is executed by a processor.

Also disclosed is a computer-readable storage medium which contains a computer program product according to the present invention. A computer-readable storage medium may for example be designed as a magnetic, electrical, electromagnetic, optical and/or other storage medium. Such a computer-readable storage medium is preferably physical (that is to say "tangible"), for example is designed as a data carrier device. Such a data carrier device is for example portable or permanently installed in a device. Examples of such a data carrier device are volatile or nonvolatile memories with random access (RAM) such as for example NOR flash memories or with sequential access such as NAND flash memories and/or memories with read-only access (ROM) or read and write access. Computer-readable is intended to be understood for example as meaning that the storage medium can be read from and/or written to by a computer or a server device, for example by a processor.

The term open-loop control is understood in the context of the present invention as meaning generally an influencing of one or more process parameters by way of one or more devices. Such open-loop control is included by a closed-loop control in dependence on the result of a comparison between an actual value and a setpoint value, wherein for example a process parameter controlled in an open-loop manner has in turn influence on a further iteration of the process parameter controlled in such a way in a closed-loop manner.

The present invention may also include a system which comprises one or more devices that are together designed and/or set up for carrying out one or more of the process described above. The system comprises for example detecting means for detecting a mass flow or position of a degassing control valve in the production plant, determining means for determining an estimated value that is indicative of a viscosity, e.g. the relative solution viscosity, wherein the determination is based at least partially on the detected position of a degassing control valve and at least partially on a temperature dependence of a viscous behaviour of the oligocarbonate or polycarbonate respectively, and determining means for determining a viscosity value indicative of the viscous behaviour of the oligocarbonate or polycarbonate, wherein the determination is based at least partially on at least one correction factor, e.g. one of the empirical values ki or k₂ or k₃, that is indicative of a state of process, and wherein the state of the process is determined at least partially by at least one prevailing process parameter. In the case of a further embodiment of the system, outputting means for outputting the at least one item of control information determined are provided. This allows a communication between devices of the system that work together in a control loop. Consequently, for example, first an item of control information may be determined by a determining means, then output by the outputting means, to then be transmitted to a closed-loop control device.

In the case of a further embodiment of the system, a closed-loop control device is provided, set up for carrying out an open-loop and/or closed-loop control of the one or more devices, wherein the open-loop and/or closed-loop control is based at least partially on the at least one item of control information determined.

The term closed-loop control device is understood as meaning in particular a device that is set up in a control loop for connection between at least one means for detecting a pressure value and at least one open-loop control device of at least one device of the system. Preferably, such an open-loop control device is set up for influencing a process parameter, for example as described in step (g), e.g step (gl) or step (g2) or step (g3) or step (g4). The control device comprises means for calculating, storing, comparing, and transmitting information.

Therefore, a further subject of the present invention is a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out steps (a) to (g) of the process according to the present invention.

Especially, the computer program product comprises instructions which, when the program is executed by a computer, cause the computer to carry out the following steps:

(A) Controlling the provision of an amount of a starting material comprising an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate and an amount of a catalyst;

(B) Controlling the mixing of the amount of the dihydroxyaryl compound and the amount of the diaryl carbonate and the amount of the catalyst;

(C) Controlling the reaction of the dihydroxyaryl compound and the diaryl carbonate to form an oligocarbonate and a monohydroxyaryl compound;

(E) Comparing the measured value correlating to the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate (F) Making a decision based on of the result of the comparison of step (e) whether reaction rate is too low or not too low; and then:

(G) Taking measures to increase the reaction rate again in case the reaction rate is too low; or (H) Taking no measures in case the reaction rate is not too low.

Figure 1 shall give an example of a possible embodiment of the invention. However, the invention shall not be reduced to this embodiment.

1 Step (a),

2 Step (b),

3 Step (c),

4 Step (d),

5 Step (e),

6 Step (f),

7 Step (g),

8 Step (f),

9 Decision path “too low”,

10 Decision path “not too low”.

Claims

1. Melt transesterification process for producing a polycarbonate comprising at least the following steps:

(e) Comparing the measured value correlating to the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound land an amount of a diaryl carbonate according to reaction scheme (I):

(f) Making a decision based on of the result of the comparison of step (e) whether reaction rate is less than 90 % of the desired reaction rate or not less than 90 % of the desired reaction rate; and then:

(g) Taking measures to increase the reaction rate again in case the reaction rate is less than 90 % of the desired reaction rate. or (h) Taking no measures in case the reaction rate is not less than 90 % of the desired reaction rate.

2. Melt transesterification process according to claim 1, wherein, in step (d), the determination of a measured value correlating to the amount of a monohydroxyaryl compound formed is conducted as follows:

(d) Determining the amount of the monohydroxyaryl compound formed.;

3. Melt transesterification process according to claim 1, wherein, in step (e), the comparison of the measured value correlating to the amount of the monohydroxyaryl compound formed with the sum of the amounts of the dihydroxyaryl compound and of the diaryl carbonate is conducted as follows:

4. Melt transesterification process according to claim 2, wherein, in step (d), the determination of the amount of a monohydroxyaryl compound formed is conducted as follows:

/ mass measured in step (d(a)l))), wherein n(monohydroxyaryl compound) is the molar amount of the monohydroxyaryl compound and ki is an empirical value with whose help it is possible to calculate the molar amount of a monohydroxyaryl compound formed by the quotient of flow measured in step (d(a)2) and the flow measured in step (d(a)l); or

(d(b)l) Measuring the mass going into the first evaporator stage,

(d(b)3) Determining the amount of a monohydroxyaryl compound formed by the following equation: n(monohydroxyaryl compound formed) = ]_¾ * position measured in step

(d(b)2) / mass measured in step (d(b)l); wherein n(monohydroxyaryl compound formed) is the molar amount of the monohydroxyaryl compound and ]_¾ is an empirical value with whose help it is possible to calculate the molar amount of a monohydroxyaryl compound formed by the quotient of flow measured in step (d(b)2) and the flow measured in step (d(b)l) or

(d(c)) Determining the torque of a rotating part of the polycondensation reactor or of one reactor of a series of coupled polycondensation reactors.

5. Melt transesterification process according to claim 3, wherein, in step (e), the comparison of the amount of the monohydroxyaryl compound formed with the sum of the amounts of the dihydroxy aryl compound and of the diaryl carbonate is conducted as follows:

Determining the ratio R_a between the molar amount of the monohydroxyaryl compound formed and the amount of the monohydroxyaryl compound which can be formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I): R_a = n(monohydroxyaryl compound formed) / n(monohydroxyarylaryl compound maximum).

6. Melt transesterification process as claimed in any of claims 1 to 5, wherein, in step (g), the measures to increase the reaction rate again may be the following:

(g3) Adjusting the pressure in the first reactor after the mixing vessel, according to the outcome of the decision in step (f), or

(g4) adjusting the amount of NaOH in raw materials, according to the outcome of the decision in step (f).

7. Melt transesterification process as claimed in any of claims 1 to 6, wherein the process is conducted continuously.

8. Melt transesterification process as claimed in any of claims 1 to 7, wherein, in step (d) the determination of a measured value correlating to the amount of the monohydroxyaryl compound formed is conducted by means of a computer running a software being a computer program product designed to determine a measured value correlating to the amount of the monohydroxyaryl compound formed or the determination the amount of the monohydroxyaryl compound formed is conducted by a human operator.

9. Melt transesterification process as claimed in any of claims 1 to 8, wherein, in step (e) the comparison of the measured value correlating to the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I) is conducted by means of a computer running a software being a computer program product designed to compare the measured value correlating to the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I) or the comparison of the measured value correlating to the amount of the monohydroxyaryl compound formed with the amount of the monohydroxyaryl compound which is formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to a full conversion of the dihydroxyaryl compound to a monohydroxyaryl compound formed in the reaction of an amount of a dihydroxyaryl compound and an amount of a diaryl carbonate according to reaction scheme (I) is conducted by a human operator.

10. Melt transesterification process as claimed in any of claims 1 to 9, wherein, in step (e) the determination the ratio R_a is conducted by means of a computer running a software being a computer program product designed to determine the ratio R_a. or the determination the ratio R_a is conducted by a human operator.

11. Melt transesterification process as claimed in any of claims 1 to 10, wherein, in step (f), the decision whether reaction rate is less than 90 % of the desired reaction rate or not less than 90 % of the desired reaction rate is made by means of a computer running a software being a computer program product designed to make the decision or an analogous setting unit or by a human operator.

12. Melt transesterification process as claimed in any of claims 1 to 11, wherein, in step (g), the adjustment may be conducted by an automated system or by a human operator.

13. Computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out steps (a) to (h) of the melt transesterification process as claimed in any of claims 1 to 12.

14. Computer program product according to claim 13, comprising instructions which, when the program is executed by a computer, cause the computer to carry out the following steps:

(G) Taking measures to increase the reaction rate again in case the reaction rate is less than 90 % of the desired reaction rate; or

(H) Taking no measures in case the reaction rate is not less than 90 % of the desired reaction rate.