Method for hydrolyzing (poly)carbonates

Abstract

The present invention relates to a process for the hydrolysis of carbonates, in particular polycarbonates, in the presence of at least one phase transfer catalyst. The process according to the invention makes it possible to recover valuable raw materials from carbonates, more particularly polycarbonates, produced on an industrial scale, after they have fulfilled their intended purpose of use, thus avoiding the loss of such raw materials, as occurs when they are disposed of by incineration or landfilling.

Description

[Technical field]

[0001] The present invention relates to a method for hydrolyzing carbonates, in particular polycarbonates, in the presence of at least one phase transfer catalyst. The method according to the invention makes it possible to recover valuable raw materials from industrially produced carbonates, in particular polycarbonates, after they have served their intended purpose, thus avoiding the loss of such raw materials, as occurs, for example, in the case of disposal by incineration or landfill. [Background technology]

[0002] Carbonates are versatile products. Polycarbonates in particular are used in a wide variety of applications in industry and in everyday life. They are known for their excellent property profile in terms of mechanical and optical properties, heat resistance and weathering stability. This property profile allows polycarbonates to be used in a very wide range of interior and exterior applications. This wide range of applications and the associated economic success also generate large amounts of polycarbonate waste (e.g. old houses, lamp covers, compact discs, etc.). Such polycarbonate waste must be redirected to a suitable use. The most technically feasible use is incineration, where the released heat of combustion is utilized in other processes, e.g. industrial processes. However, this does not close the raw material loop. Another use is the so-called "physical recycling", where polycarbonate waste is mechanically crushed and used to manufacture new products. This type of recycling has its natural limitations, so there have been ample attempts to recover the basic raw materials for polycarbonate production by reverse cleavage of polycarbonate bonds (so-called "chemical recycling"). The recovered raw materials generally contain bisphenols, especially bisphenol A. Depending on the type of chemical recycling, CO2 may also be recovered in addition to carbonate-containing compounds such as diphenyl carbonate or dimethyl carbonate.

[0003] The present invention relates to the hydrolysis of carbonates, in particular polycarbonates. This generally gives alcohols or diols and CO2 (depending on the type of starting compound to be cleaved). The term hydrolysis is known to the skilled artisan. According to the present invention, the term "hydrolysis" is understood in particular to refer to the cleavage of carbonate groups by water. In the "hydrolysis of polycarbonates", generally, a number of carbonate groups in the polymer chain, preferably substantially all of the carbonate groups, are cleaved by water. This does not generally prevent the presence of further solvents, for example alcohols, during hydrolysis. In this case, it is also possible that esters are at least partially formed as intermediates due to the initial presence of at least one alcohol (possibly the carbonate groups are cleaved directly by water). However, these esters will be re-cleaved by water under the conditions according to the invention. Thus, here too, a cleavage by water (not of the carbonate groups directly, but rather of the ester groups formed as intermediates) is effectively carried out. This cleavage of intermediate ester groups is preferably likewise encompassed by the term "hydrolysis". In another embodiment, this cleavage of intermediate ester groups is not encompassed by the term "hydrolysis" according to the present invention. Advantageously according to the invention, at least one organic solvent may be present in the hydrolysis. Said solvent can be fed simultaneously with and / or subsequently to the water of hydrolysis. It is preferred when this at least one organic solvent is selected from the group consisting of acetone, acetophenone, cyclohexanone, cyclopentanone, methyl ethyl ketone, methyl benzoate, cyclopropylene carbonate, cycloethylene carbonate, ethyl acetate, γ-butyrolactone, acetonitrile, tert-butyl methyl ether, chlorobenzene, o-dichlorobenzene, dichloromethane, chloroform, dibutyl ether, dimethylformamide, dimethyl sulfoxide, 1,4-dioxane, ethylene glycol dimethyl ether, methylene chloride, N-methyl-2-pyrrolidone, nitromethane, phenol, sulfolane, tetrahydrofuran, toluene and at least one alcohol. It is also possible to use any desired mixture.Likewise, it is preferred if these organic solvents are not present during hydrolysis. Particularly preferred is the case where at least one alcohol is present during hydrolysis. It will be understood that said alcohol is different from the hydrolysis product. In this case, the at least one alcohol is selected from the group consisting of methanol, ethanol, propanol, isopropanol, propane-1,3-diol, n-butanol, 2-butanol, isobutanol, tert-butanol, butane-1,4-diol, n-pentanol, 2-pentanol, 3-pentanol, isoamyl alcohol, 2-methyl-2-butanol, neopentanol, 2-methyl-1-butanol, 3-methyl-2-butanol, pentaerythritol, cyclopentanol, hexane-1-ol, hexane-2-ol, hexane-3-ol, 2-methylpentan-1-ol, 2-methylpentan-3 ... It is further preferred if the alcohol is selected from the group consisting of cyclohexanol, 2-methylpentan-3-ol, 4-methylpentan-1-ol, 4-methylpentan-2-ol, 3-methylpentan-1-ol, 3-methylpentan-2-ol, 3-methylpentan-3-ol, 2,2-dimethylbutan-1-ol, 3,3-dimethylbutan-1-ol, 3,3-dimethylbutan-2-ol, 2,3-dimethylbutan-1-ol, 2,3-dimethylbutan-2-ol, 2-ethylbutan-1-ol, 4-methylpentan-2-ol, cyclohexanol, phenol and 2-ethylhexanol. Any mixture of these alcohols may be used. It is very particularly preferred that in the hydrolysis of the process step (ii) according to the invention, in addition to the at least one alcohol, no further organic solvent is present, in particular none of the organic solvents indicated as preferred as described above.Thus, the only organic solvent present in process step (ii) is at least one alcohol, preferably methanol, ethanol, propanol, isopropanol, propane-1,3-diol, n-butanol, 2-butanol, isobutanol, tert-butanol, butane-1,4-diol, n-pentanol, 2-pentanol, 3-pentanol, isoamyl alcohol, 2-methyl-2-butanol, neopentanol, 2-methyl-1-butanol, 3-methyl-2-butanol, pentaerythritol, cyclopentanol, hexane-1-ol, hexane-2-ol, hexane-3-ol, 2-methylpentane-1-ol, 2-methylpentane-2-ol, 2-methylpentane-1 ... At least one alcohol selected from the group consisting of 2-methylpentan-2-ol, 2-methylpentan-3-ol, 4-methylpentan-1-ol, 4-methylpentan-2-ol, 3-methylpentan-1-ol, 3-methylpentan-2-ol, 3-methylpentan-3-ol, 2,2-dimethylbutan-1-ol, 3,3-dimethylbutan-1-ol, 3,3-dimethylbutan-2-ol, 2,3-dimethylbutan-1-ol, 2,3-dimethylbutan-2-ol, 2-ethylbutan-1-ol, 4-methylpentan-2-ol, cyclohexanol, phenol and 2-ethylhexanol. Of course, as the skilled artisan will recognize, there may be traces of organic solvent introduced via the reactants of process step (ii).

[0004] Particularly preferred is the case where the amount of at least one organic solvent, in particular at least one alcohol, used is not excessively large relative to water. Particularly preferred is the case where the mass of at least one organic solvent, in particular at least one alcohol, is at most 15% of the mass of water, particularly preferably 0% to 10%, particularly preferably 1% to 7%, very particularly preferably 0% to 4%. Particularly preferred is the case where the above organic solvents, in particular alcohols, are used. In a particularly preferred embodiment, the total mass of organic solvents, in particular alcohols, during hydrolysis is at most 4%, particularly preferably at most 3%, more preferably at most 2%, very particularly preferably at most 1% of the mass of water.

[0005] Non-Patent Document 1 describes, inter alia, the alcoholysis (partly also understood as hydrolysis according to the preferred term of the present invention) of polycarbonate waste using a mixture of methanol, water and NaOH as catalyst. It is stated that the use of water is disadvantageous since, compared to the use of pure methanol, the mixture leads to a reduced selectivity, a lower yield and at the same time the loss of dimethyl carbonate as a by-product. Moreover, it was observed that the greater the amount of water used, the longer the reaction time required.

[0006] Non-Patent Document 2 describes the glycolysis of polycarbonate using sodium carbonate as a catalyst. The resulting bishydroxyalkyl ethers can be used as new starting products for the production of polyurethanes. However, they are not generally starting products for the new production of polycarbonates.

[0007] Non-Patent Document 3 describes the complete hydrolysis of polycarbonate using CeO2 as catalyst under hydrothermal conditions. Polycarbonate could not be cleaved using water alone in a pressure tube at 200 °C. Depolymerization was only achieved with the addition of a catalyst. However, the conditions described there are very harsh, which is ecologically and economically disadvantageous.

[0008] Example 7 of the document describes the depolymerization of polycarbonate using a mixture of water, tetrahydrofuran and KOH as catalyst in an autoclave at 120° C. Here too, the described conditions for the cleavage of carbonate groups can be ecologically and economically optimized.

[0009] In Non-Patent Document 4, Tsintzou et al. describe a method for alkaline hydrolysis of BPA-based polycarbonate by phase transfer catalysis under microwave irradiation. The process conditions described therein are relatively harsh. For example, a temperature of 160° C. is described. In a large industrial scale process, such harsh conditions are ecologically and economically rather undesirable. This document also teaches the use of superstoichiometric amounts of alkali metal hydroxide solutions. This leads to the formation of large amounts of polluted alkali metal salts, which would require disposal in the corresponding industrial context of the process.

[0010] Patent document 2 describes a method for hydrolyzing polycarbonate, in which sodium carbonate is used as a hydrolysis catalyst, and also describes a temperature of 120° C. to obtain a high depolymerization yield.

[0011] In Non-Patent Document 5, Iannone et al. describe the use of ionic liquids and ZnO nanoparticles as catalysts for the depolymerization of polycarbonate. In particular, Bu4NCl is used to stabilize the metal nanoparticles and prevent agglomeration, which is said to extend the catalyst life.

[0012] Of the processes of chemical recycling known from the literature, only a few are currently operated on a large industrial scale. This is mainly because the reaction conditions are less economical compared to using new, non-recycled starting products. In view of the generally increasing environmental awareness and the increasing efforts to configure industrial processes as sustainable as possible, both of which are in principle in favor of chemical recycling, this seems to indicate that chemical recycling of carbonate, and especially polycarbonate products, is still far from mature from a technical and economic point of view. For example, the efficiency of catalytic carbonate cleavage is a challenge. Conventional process approaches, which require high temperatures, are always accompanied by risks such as discoloration, formation of by-products, etc. This in turn results in the reuse of recovered raw materials being significantly hindered or even uneconomical. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] China Patent Application Publication No. 101407450 [Patent Document 2] International Publication No. 2020 / 257237 [Non-patent literature]

[0014] [Non-Patent Document 1] Green Chem., 2005, 7, 380-387 [Non-Patent Document 2] Green Chem 2007, 9, 38-43 [Non-Patent Document 3] Catalysis Communications 84 (2016) 93-97 [Non-Patent Document 4] Journal of Hazardous Materials vol. 241-242, 2021-09-23, pages 137-145 [Non-Patent Document 5] Journal of Molecular Catalysis A: Chemical vol. 426, pages 107-116 Summary of the Invention [Problem to be solved by the invention]

[0015] Therefore, further improvements are needed in the field of chemical recycling of carbonates, especially polycarbonates and / or polycarbonate products. In particular, it is desirable to provide a process in which the hydrolysis can be efficiently catalyzed and therefore preferably carried out at relatively low temperatures. Therefore, there was also a need to provide a method, especially hydrolysis, that allows the cleavage of carbonates, especially polycarbonates, on a large industrial scale. The post-treatment of the reaction products should preferably be simple. [Means for solving the problem]

[0016] At least one of the cited objects, preferably all of these objects, has been achieved by the present invention. Surprisingly, it has been found that the presence of at least one phase transfer catalyst allows high conversions to be obtained in the hydrolysis of carbonates, especially polycarbonates, under relatively mild conditions. This is understood to mean in particular that the presence of at least one phase transfer catalyst in the hydrolysis leads to a high yield of hydrolysis product. This allows relatively mild conditions to be adopted, so that the process according to the present invention is particularly suitable for large-scale industrial-scale processes. The process according to the present invention is therefore an ecologically and / or economically advantageous process. It has also been found that the hydrolysis product can be particularly easily worked up. This is particularly true when the amount of organic solvent in the system is limited.

[0017] The present invention relates to a process for hydrolyzing a carbonate, preferably a polycarbonate, comprising the steps of: (i) providing a carbonate, at least one hydrolysis catalyst, and water, wherein the at least one hydrolysis catalyst comprises a salt of an oxoacid of an element of Group 5, 6, 14, or 15 of the Periodic Table of the Elements, and the pK of the anion of the salt is greater than or equal to 1.0; B a value in the range of 0.1 to 7.0; (ii) conducting hydrolysis by contacting the components from step (i) to obtain at least one hydrolysis product and carbon dioxide; Including, The process according to the invention now provides a process characterised in that in step (ii) at least one phase transfer catalyst is present, wherein the at least one phase transfer catalyst comprises a charged organic molecule.

[0018] The term "carbonate" in the context of the present invention denotes a compound containing one, at least one or more carbonate groups. Carbonate group is understood to mean the functional group RO-(C=O)-OR, where the two radicals R can in each case be identical or different. This term particularly preferably denotes a compound containing at least one carbonate group. However, to describe the different reaction products, a distinction is often made between carbonates and polycarbonates, although according to the present invention a carbonate can easily also be a polycarbonate. Carbonates very particularly preferably contain only one carbonate group.

[0019] The term "polycarbonate" in the context of the present invention refers to a polymer having a plurality of carbonate groups. The carbonate groups are present in the polymer backbone. This is understood to mean that the polycarbonate preferably comprises repeat units of the type ...-(RO-(C=O)-O-)-.... The term polycarbonate is understood to mean both homopolycarbonates and copolycarbonates. Polycarbonates may be linear or branched, as is well known. The skilled person is equally aware that in particular polycarbonate products use mixtures of different polycarbonates. The term polycarbonate therefore also encompasses any desired mixture of such polycarbonates. Polycarbonates may in particular also include so-called post-consumer polycarbonates, a term well known to the skilled person. Post-consumer polycarbonates in particular relate to molded polycarbonate parts made of polycarbonate compositions, which have already been used for their intended purpose and are now destined for disposal. The polycarbonate composition may also contain correspondingly relevant additives and blend partners, which may need to be separated by known methods from the actual polycarbonate before carrying out the process according to the invention.

[0020] The "water" used in step (i) is preferably used in a superstoichiometric amount. This is understood to mean that the water is used in an amount theoretically sufficient to hydrolyze all the carbonate bonds of the (poly)carbonate to obtain a hydrolysis product with liberated carbon dioxide. The water is preferably deoxygenated by inert gas saturation (e.g. nitrogen, argon and / or helium). The water used can in principle be any optically transparent water, for example filtered river water or well water. It is preferable to use demineralized water. In general, the demineralized water used exhibits a conductivity of less than 20 μS / cm, preferably less than 12 μS / cm, which is determined according to DIN EN 27888 together with DIN 50930-6.

[0021] The term "hydrolysis catalyst" is known to the person skilled in the art. Such hydrolysis catalysts are in particular capable of reducing the activation energy of hydrolysis of carbonates, in particular polycarbonates (compared to the activation energy of hydrolysis of carbonates without the addition of catalytically active compounds). Thus, the hydrolysis catalyst is preferably capable of adding water to the carbonyl functions of the carbonate esters. In some cases, the hydrolysis catalyst may be identical to the phase transfer catalyst according to the invention. The invention also encompasses embodiments in which, in addition to the hydrolysis activity, the hydrolysis catalyst also has a certain activity as a phase transfer catalyst. The activity / magnitude of activity can be determined via the absolute amount by which it reduces the activation energy of hydrolysis. In the case of an added activity as a phase transfer catalyst, the hydrolysis catalyst also has the ability to overcome the phase interface itself more easily (see below for the magnitude of activity of phase interface catalysts). However, in this case, the main activity of the catalyst is in hydrolysis catalysis, so that this catalyst is preferably included in the term hydrolysis catalyst. It is also possible to use a mixture of different hydrolysis catalysts. Some or only one of the catalysts from this mixture may furthermore have inferior or equally good phase transfer catalytic properties. However, the process according to the invention preferably uses at least one hydrolysis catalyst and at the same time at least one phase transfer catalyst, however, at least one catalyst may also have a certain activity as the other catalyst.

[0022] The term "phase transfer catalyst" is known to those skilled in the art. A phase transfer catalyst is a substance that allows the passage of a reactant to a chemical reaction, in particular through the interface of two immiscible phases, to the phase in which the chemical reaction takes place. The transferred reactant exhibits increased reactivity towards the intended reaction, in particular due to a change in solubility, an increased concentration and a greater proximity to the other reactant(s) compared to the situation without the phase transfer catalyst. In the absence of such a phase transfer catalyst, the intended reaction generally takes place only slowly, if at all. This also makes it possible to measure the magnitude of the activity of the phase transfer catalyst. The activity and / or the magnitude of the activity of the phase transfer catalyst can particularly preferably be determined by comparing the yields obtained in the reaction at the same time and at the same temperature with and without the phase transfer catalyst. The skilled person generally uses the corresponding phase prism here. According to the invention, the phase transfer catalyst particularly mediates the passage of water into carbonates, in particular polycarbonates, which are generally insoluble in water. The phase transfer catalyst simultaneously mediates the passage of the resulting hydrolysis product (alcohol or diol) into the surrounding water.

[0023] According to the present invention, the hydrolysis catalyst is a salt and the phase transfer catalyst is a charged organic molecule. Surprisingly, it has been found that the use of a charged catalyst allows the hydrolysis to be carried out in high yields under particularly mild process conditions. Without wishing to be bound by a particular theory, it is believed that ion pairing (such as salt metathesis) makes the phase transfer catalysis particularly efficient and makes the hydrolysis catalysis more and more efficient. This is due in particular to the fact that according to the present invention, the hydrolysis catalyst is at least partially chemically bound to the phase transfer catalyst, and therefore achieves particularly good solubility in the different phases of the reaction mixture.

[0024] Process step (i) according to the invention comprises providing a carbonate, preferably a polycarbonate, at least one hydrolysis catalyst and water. This does not exclude the presence of other chemicals in process step (i). Process step (i) may in particular comprise providing at least one organic solvent, in particular at least one alcohol. Similarly, it is also preferred that in the hydrolysis of process step (ii) at least one organic solvent, particularly preferably at least one alcohol, is present. Very particularly preferred is when the organic solvent is at least one organic solvent selected from the group consisting of acetone, acetophenone, cyclohexanone, cyclopentanone, methyl ethyl ketone, methyl benzoate, cyclopropylene carbonate, cycloethylene carbonate, ethyl acetate, γ-butyrolactone, acetonitrile, tert-butyl methyl ether, chlorobenzene, o-dichlorobenzene, dichloromethane, chloroform, dibutyl ether, dimethylformamide, dimethyl sulfoxide, 1,4-dioxane, ethylene glycol dimethyl ether, methylene chloride, N-methyl-2-pyrrolidone, nitromethane, phenol, sulfolane, tetrahydrofuran, toluene and alcohol. If alcohol is present, this alcohol is preferably water-soluble. Very particularly preferred is when the at least one alcohol is from the group of alcohols mentioned in the definition of the term "hydrolysis" according to the present invention. Likewise preferred is when at least one organic solvent, in particular at least one alcohol, is used in the amounts mentioned therein. As mentioned above, it is preferred according to the invention if at most 15% by weight of the water present in process step (ii) is an organic solvent, particularly preferably 0% to 10%, very particularly preferably 1% to 7%, likewise preferably 0% to 4%. In one embodiment, "organic solvent" preferably does not comprise alcohol in this context. In another embodiment, "organic solvent" comprises an alcohol, particularly preferably an alcohol as mentioned above.Very particular preference is given to the organic solvent being selected from the group consisting of acetone, acetophenone, cyclohexanone, cyclopentanone, methyl ethyl ketone, methyl benzoate, cyclopropylene carbonate, cycloethylene carbonate, ethyl acetate, γ-butyrolactone, acetonitrile, tert-butyl methyl ether, chlorobenzene, o-dichlorobenzene, dichloromethane, chloroform, dibutyl ether, dimethylformamide, dimethylsulfoxide, 1,4-dioxane, ethylene glycol dimethyl ether, methylene chloride, N-methyl-2-pyrrolidone, nitromethane, phenol, sulfolane, tetrahydrofuran, toluene and at least one alcohol. Likewise, it is preferred if the organic solvent is selected from the group consisting of acetone, acetophenone, cyclohexanone, cyclopentanone, methyl ethyl ketone, methyl benzoate, cyclopropylene carbonate, cycloethylene carbonate, ethyl acetate, γ-butyrolactone, acetonitrile, tert-butyl methyl ether, chlorobenzene, o-dichlorobenzene, dichloromethane, chloroform, dibutyl ether, dimethylformamide, dimethylsulfoxide, 1,4-dioxane, ethylene glycol dimethyl ether, methylene chloride, N-methyl-2-pyrrolidone, nitromethane, phenol, sulfolane, tetrahydrofuran and toluene. At most 15% by weight of the water present in process step (ii) is organic solvent, but it is preferred if at least one alcohol is present in the hydrolysis of process step (ii). This is understood to mean that, preferably, the hydrolysis may also be carried out in the presence of an alcohol, optionally in the presence of a further organic solvent, but the total mass of this alcohol and / or organic solvent is limited to at most 15%, particularly preferably 0% to 10%, very particularly preferably 1% to 7%, likewise preferably 0% to 4% of the mass of water present in process step (ii). It has been found that limiting the amount of organic solvent in process step (ii) according to the invention facilitates the work-up of the product obtained. A phase transfer catalyst may also already be provided in step (i).

[0025] It has proven to be advantageous, especially when the carbonate is a polycarbonate, to previously grind the polycarbonate, preferably mechanically. As known to those skilled in the art, this increases the surface area of ​​the solid and thus the activity of the hydrolysis that takes place. This is also particularly useful when used polycarbonate is involved. Grinding may be carried out by commonly used methods such as pressure grinding, impact grinding, friction grinding, cutting grinding and impact grinding. The carbonate / polycarbonate can in particular be subjected to mill grinding. Mill grinding can also be carried out in particular using a cryomill. It is preferred when the polycarbonate is ground to have an average particle size of less than 1 mm, preferably less than 0.5 mm, particularly preferably less than 50 μm, very particularly preferably less than 10 μm.

[0026] In process step (ii), the components from step (i) are optionally contacted with the addition of at least one phase transfer catalyst if not already provided in step (i). This allows and thus performs the actual hydrolysis reaction. According to the present invention, process steps (i) and (ii) may optionally not be clearly separated from each other. Conversely, process steps (i) and (ii) may also be performed at different locations. Thus, for example, it is conceivable that the carbonate, particularly preferably the pulverized polycarbonate, is loaded into a suitable transport vehicle, for example a silo vehicle, for further transport to process step (ii). At the site of hydrolysis (process step (ii)), the carbonate is loaded into a reactor intended for hydrolysis.

[0027] The contacting of the components from step (i) is preferably carried out with the introduction of mixing energy. This can be done by methods known to those skilled in the art. Increasing surface renewal is known to affect the hydrolysis rate.

[0028] The hydrolysis can be carried out in any reactor known for such purposes in the art, with autoclaves, stirred tanks (stirred reactors) and tubular reactors being particularly suitable as hydrolysis reactors.

[0029] The hydrolysis is preferably carried out in the absence of oxygen, i.e. the reaction is carried out in an inert gas atmosphere, in particular a nitrogen, argon or helium atmosphere, and it is particularly advantageous if the water used is freed of oxygen by inert gas saturation.

[0030] The process according to the invention is preferably characterized in that process step (ii) is carried out at temperatures between 50° C. and 180° C., particularly preferably between 70° C. and 130° C., very particularly preferably between 80° C. and 115° C., optionally under reflux or in a closed system. The process according to the invention in particular makes it possible to achieve low temperatures for the hydrolysis, in particular lower temperatures than in the prior art. This has ecological and economic advantages. This also results in the formation of less by-products. For a particular selection, it is clear to the skilled person what optimal conditions should be selected during the reaction: water should not evaporate. Conversely, it is also possible to achieve higher temperatures if the process is operated in a closed system, for example an autoclave. However, there are no special pressure requirements for this reaction. Likewise, it can also be carried out at ambient pressure or at slightly reduced pressure (in particular with a lower pressure limit of 200 mbar (absolute), preferably 900 mbar (absolute)), which facilitates the removal of the carbon dioxide formed. Likewise, a slight pressure increase, in particular up to 1.8 bar (absolute), is also possible.

[0031] The hydrolysis is generally complete within a period of from 1.0 h to 48 h, preferably from 1.5 h to 24 h, particularly preferably from 2.0 h to 20 h, very particularly preferably from 2.5 h to 19.0 h and exceptionally preferably from 3.0 h to 18.0 h, i.e. after this reaction time very little, if any, further reaction takes place.

[0032] The process according to the invention may also be practiced in accordance with the present invention, in which at least one hydrolysis catalyst comprises a salt of an oxoacid of an element of group 5, 6, 14 or 15 of the Periodic Table of the Elements, the pK of the anion of which is BThe process according to the invention is also characterised in that the at least one hydrolysis catalyst comprises a salt of an oxoacid of an element of group 5, 6, 14 or 15 of the Periodic Table of the Elements, the pK of the anion of the salt being in the range of 0.1 to 11.0, preferably 0.25 to 10.80, particularly preferably 0.50 to 10.60. B The hydrolysis of carbonate bonds is characterized by a low to moderate pK value of 0.1 to 7.0, preferably 0.25 to 6.95, particularly preferably 0.50 to 6.85. B It has been found that even a catalytic scale is possible using the described anionic compounds with a value, even without using them stoichiometrically. As already mentioned above, the hydrolysis catalysts are capable of adding water onto the carbonyl functions of the carbonate esters. The hydrolysis catalysts consist of at least one anion and at least one cation.

[0033] With regard to salts of oxoacids of elements of groups 5, 6, 14 or 15 of the periodic table (hereinafter oxoacid salts for short), for the purposes of the present invention, it is not necessary that the oxoacids themselves be stable and isolatable compounds. Thus, for example, a carbonate salt can be derived formally from "carbonic acid, "H2CO3"", and the fact that it is not isolatable in pure form does not prevent this and does not depart from the scope of the present invention.

[0034] pK in the context of the present invention B The value is the pK in an "ideally dilute" aqueous solution. B value, i.e., the pK value at which the interaction between the cation and anion of the salt of an oxoacid is negligible in the temperature range of 23°C to 25°C. B pK is understood to mean the value of the acid-base pair pK. Here, the following formula, known for the corresponding acid-base pair, is applicable with sufficient accuracy: A +pK B = 14.00. As a result, for example, the pK of all hydroxides (regardless of counterion) B The value is, for purposes of the present invention, equal to 0.00 and is therefore not within the present invention's range of 0.1 to 7.0.A values ​​and therefore the pK values ​​of those salts B Value (pK A +pK B =14.00) are also known from the literature. In particular, reference is made to the standard text "Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils: Lehrbuch der anorganischen Chemie, 101st edition, De Gruyter", where many pK values ​​of oxo acids are given in the chapter on the corresponding elements. A Values ​​are specified: e.g., orthophosphate, pK of the third dissociation step A = 12.3 (p. 771); orthosilicic acid, pK of the second dissociation step A =11.7 (page 923), "carbonic acid", pK of the second dissociation step A =10.3 (page 862).

[0035] If literature values ​​are not available, pK B The value is determined in the context of the present invention by acid-base titration, which is the base constant (K B ) is analytically determined and pK B The titration is carried out by calculating the value of the base constant K. Such procedures for acid-base titration are known to those skilled in the art. See the relevant technical literature: Gerhart Jander, Karl Friedrich Jahr, Gerhard Schulze, Juergen Simon (Ed.): Massanalyse. Theorie und Praxis der Titrationen mit chemischen und physikalischen Indikationen, 16th edition, Walter de Gruyter, Berlin 2003, pages 67 to 128. B is calculated using the formula for hydroxide ion concentration given in the chapter "Sehr schwache Saeuren und Basen" (pages 86 and 87). B Solving for gives: K B=[c 2 (OH - )-K W ] / c0(B) (I) In the formula, c(OH - ) is the concentration of hydroxide ions determined by titration with acid, K W is the ionic product of water (10 -14 Mol 2 / l 2 ) and c0(B) is the starting concentration of the base (=anion of the oxoacid), i.e. the concentration calculated from the starting weight. In many cases, the pK according to the invention is in the range of 0.10 to 6.00. B In the lower region of the range, the effect of autoprotolysis of water is very small, so the simplified formula: K B =c 2 (OH - ) / c0(B) (II) It is also possible to carry out the calculation using the formula (I), and in case of doubt, the exact formula (I) is important for the purposes of the present invention. For the purposes of the present invention, the titration is carried out with phenolphthalein and 0.1 N hydrochloric acid.

[0036] According to the invention, at least one hydrolysis catalyst comprises a salt of an oxoacid of an element of group 5, 6, 14 or 15 of the periodic table of the elements. The anion of the hydrolysis catalyst comprises, and preferably consists of, at least one central metal, transition metal or nonmetallic atom coordinated by three or more oxygen atoms, at least one of which has a negative formal charge. The central metal, transition metal or nonmetallic atom is preferably carbon, silicon, phosphorus, vanadium, molybdenum or tungsten. Particularly preferred is when the anion is in the form of carbonate, silicate, silanolate, phosphate, phosphite, vanadate, molybdate and tungstate. Particularly preferred is when the salt of the oxoacid is an anion selected from: - Orthovanadate (VO4 3- ), - Carbonate (CO3 2- ), - Orthophosphate (PO4 3- ), - Diphosphate (P2O74- ), - Triphosphate (P3O9 5- ), - Tetraphosphate (P4O 11 6- ), - Metaphosphate ([(PO3) - ] n ), - Alkyl phosphate (RPO3 2- where R is an alkyl radical having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms; - Phosphite (HPO4 2- ), - Arylphosphonates (ArPO3 2- where Ar is an aryl radical, in particular phenyl; - Hydrogen orthosilicate (HSiO4 3- ), - Metasilicate ([SiO3 2- ] n ), - Hydrogen metasilicate ([HSiO3 - ] n ), - Dihydrogen orthosilicate (H2SiO4 2- ), - Trihydrogen orthosilicate (H3SiO4 - ), - Alkylsilanolate (R x SiO 4-x (4-x)- where R is an alkyl radical having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, and x is 1, 2 or 3, preferably 1 or 2, particularly preferably 1), or - Arylsilanolate (Ar x SiO 4-x (4-x)- in which Ar represents an aryl radical, in particular phenyl, and x is 1, 2 or 3, preferably 1 or 2, particularly preferably 1, - Tungstate (WO4 2- ), - Polytungstate (WO 168- ;W7O 24 6- ;W 10 O 32 4- ;H2W 12 O 40 6- ;H2W 12 O 42 10- ), - Molybdate (MoO4 2- ), - Polymolybdate (Mo2O7 2- ;Mo7O 24 6- ;Mo8O 26 4- ;Mo 36 O 112 (H2O) 16 8- ).

[0037] Among the above, the particularly preferred anion is WO4 2- , VO4 3- , CO3 2- , HPO4 2- , MoO4 2- , HSiO4 3- , RSiO3 3- where R is an alkyl radical having 1 to 10 carbon atoms or PO4 3- A particularly preferred anion is PO4 3- It is.

[0038] Likewise, it is also preferred to use only one salt of an oxoacid as catalyst, and not a mixture. It is even more preferred if no other hydrolysis catalyst not mentioned above is used in this reaction. It has proven advantageous to use the salt of an oxoacid in an amount such that its weight represents 0.10% to 20%, preferably 1.0% to 15%, particularly preferably 5.0% to 10% of the weight of the carbonate, in particular polycarbonate, to be reacted.

[0039] According to the invention, it is preferred if the cation of the salt is selected from alkali metal ions, alkaline earth metal ions and quaternary ammonium ions. It is particularly preferred if the salt is a sodium or potassium salt or a quaternary ammonium ion, particularly preferably a sodium or potassium salt. This preference applies in particular if the hydrolysis catalyst comprises the above-mentioned preferred anions.

[0040] According to the present invention, the at least one phase transfer catalyst comprises a charged organic molecule. It is particularly preferred when the at least one phase transfer catalyst is a cationic surfactant. At least in this case, the hydrolysis catalyst and the phase transfer catalyst are clearly distinguished by their chemical structures.

[0041] Particularly preferred is when the phase transfer catalyst is selected from quaternary ammonium salts or quaternary phosphonium salts that contain an organic radical and a counterion. Particularly preferred is a quaternary ammonium salt with an organic radical and a counterion. The organic radical is preferably methyl, benzyl, butyl, octyl, hexadecyl or stearyl. The counterion is preferably chloride, bromide, sulfate, chlorate or triflate. Particularly preferred is at least one phase transfer catalyst selected from the group consisting of trimethylbenzylammonium chloride, tetrabutylammonium chloride, dimethyldistearylammonium chloride, tetraphenylphosphonium chloride, hexadecyltributylphosphonium chloride and methyltrioctylphosphonium chloride, very particularly preferred is tetrabutylammonium chloride.

[0042] It will be understood that the phase transfer catalyst may also have a certain activity as a hydrolysis catalyst (see above). The catalyst / catalysts may also be formed in situ. As an example, a phase transfer catalyst may be formed by the following reaction, which then simultaneously contains as an anion a salt of an oxoacid of an element of group 5, 6, 14 or 15 of the periodic table of the elements, and thus exhibits hydrolysis activity: H3PO4+3R4NOH→PO4(R4N)3+3H2O

[0043] Such embodiments are preferably encompassed by the present invention. In another embodiment, the in situ formation of the catalyst is not encompassed.

[0044] Likewise, it is preferred to use only one phase transfer catalyst rather than a mixture, and it is even more preferred if the reaction does not use another phase transfer catalyst not mentioned above.

[0045] Preference is given to the process according to the invention, characterized in that the phase transfer catalyst is used in a molar ratio to the hydrolysis catalyst of 0.5 to 1.5:1, particularly preferably 0.75 to 1.25:1 and very particularly preferably 1.1 to 1.3:1. It is particularly preferred when the salt of an oxoacid is used in a mass amount of 0.10% to 20%, preferably 1.0% to 15%, particularly preferably 5.0% to 10% of the mass of the carbonate, in particular polycarbonate, to be reacted.

[0046] Similarly, it is also preferable that the hydrolysis catalyst and / or phase transfer catalyst is used in an amount of 0.005 to 0.15 molar equivalents per 1 molar equivalent of the carbonate.

[0047] It is particularly preferred to use a mass ratio of water (used in total) to carbonate, particularly polycarbonate, of 0.05:1.00 to 30.00:1.00, particularly preferably 0.10:1.00 to 25.00:1.00.

[0048] The process according to the invention is preferably characterized in that the hydrolysis product obtained in step (ii) contains at least one hydroxyl group. Depending on the reaction conditions, the hydrolysis may also form other products. However, it is preferred that the hydrolysis product contains at least one hydroxyl group. According to the invention, this is understood to mean that by-products may still continue to be formed. However, the hydrolysis product having at least one hydroxyl group is the main product. The skilled person can optimize the reaction conditions of the process according to the invention so that the yield and / or purity of this main product is maximized. However, in this case, the hydrolysis product may still contain small amounts of by-products. Similarly, depending on whether carbonates, biscarbonates, etc. or polycarbonates are hydrolyzed, it will be understood that the hydrolysis product may contain more than one hydroxyl group, in particular two hydroxyl groups.

[0049] The method according to the invention preferably further comprises the following step (iii): (iii) separating the at least one hydrolysis product from at least the hydrolysis catalyst and the phase transfer catalyst.

[0050] This step (iii) is intended in particular to separate and / or purify the hydrolysis product obtained. This then allows it to be sent to further chemical reactions, in particular for the synthesis of new materials intended for use, such as new polycarbonates. The hydrolysis product can also be separated from any remaining water in step (iii). This has proven to be advantageous when the amount of organic solvent in process step (ii) is limited (see above). In this case, process step (iii) can be carried out particularly efficiently. This allows in particular a better separation of the aqueous phase with the phase transfer catalyst and the hydrolysis catalyst and the hydrolysis product. Process step (iii) is preferably carried out by the addition of water. This is understood to mean that this water is actively added. It is therefore preferably different from the water provided in process step (i). It is preferred when the phase transfer catalyst and the electrocatalyst are dissolved in water (only one catalyst if the catalysts are identical). The hydrolysis product is insoluble in water. This allows a purer hydrolysis product to be obtained, as known to those skilled in the art. The hydrolysis product can be subjected to further purification steps.

[0051] However, it is equally possible to carry out extraction in process step (iii). The hydrolysis product is extracted with at least one organic solvent. Suitable organic solvents are aliphatic hydrocarbons, cycloaliphatic hydrocarbons, aromatic hydrocarbons, halogen-substituted aliphatic hydrocarbons, halogen-substituted cycloaliphatic hydrocarbons, halogen-substituted aromatic hydrocarbons, and mixtures of two or more of the abovementioned organic solvents.

[0052] It will be understood by those skilled in the art that separation of the hydrolysis products from at least the hydrolysis catalyst and the phase transfer catalyst need not necessarily proceed completely, in the sense that all of the hydrolysis products are separated from all of the hydrolysis catalyst and / or all of the phase transfer catalyst.

[0053] As mentioned above, the carbonate used in the process according to the invention is particularly preferably a polycarbonate. The polycarbonate may be an aliphatic or aromatic polycarbonate. Preferably, the polycarbonate is an aromatic polycarbonate. Particularly preferred are polycarbonates made on the basis of bisphenols. Even more preferred are polycarbonates comprising one or more monomer units of formula (4): [ka] During the ceremony, R 7 and R 8 are, independently of each other, H, C1 to C 18 -Alkyl, C1-C 18 -alkoxy, halogen such as Cl or Br, or aryl or aralkyl, each of which is optionally substituted, preferably H or C1-C 12 alkyl, particularly preferably H or C1-C8-alkyl, very particularly preferably H or methyl, Y is a single bond, -SO2-, -CO-, -O-, -S-, C1-C6-alkylene or C2-C5-alkylidene, or a C6-C6 alkylene optionally fused to a further heteroatom-containing aromatic ring. 12 -Arylene.

[0054] The monomer unit(s) of general formula (4) are introduced into the polycarbonate or copolycarbonate via one or more corresponding diphenols of general formula (4a): [ka] In the formula, R 7 , R 8 and Y are each as defined above in relation to formula (4).

[0055] Examples of diphenols of formula (4a) include hydroquinone, resorcinol, dihydroxybiphenyls, bis(hydroxyphenyl)alkanes, bis(hydroxyphenyl)sulfides, bis(hydroxyphenyl)ethers, bis(hydroxyphenyl)ketones, bis(hydroxyphenyl)sulfones, bis(hydroxyphenyl)sulfoxides, α,α'-bis(hydroxyphenyl)diisopropylbenzene and their ring-alkylated and also ring-halogenated compounds, and α,ω-bis(hydroxyphenyl)polysiloxanes.

[0056] Very particular preference is given to using compounds of the general formula (4b): [ka] In the formula, R 11 is H, linear or branched C1-C 10 -alkyl, preferably linear or branched C1-C6-alkyl, particularly preferably linear or branched C1-C4-alkyl, very particularly preferably H or C1-alkyl (methyl), In the formula, R 12 is a linear or branched C1-C 10 -alkyl, preferably linear or branched C1-C6-alkyl, particularly preferably linear or branched C1-C4-alkyl, very particularly preferably C1-alkyl(methyl).

[0057] In this case, in particular the diphenol (4c) is very particularly preferred. [ka]

[0058] The diphenols of general formula (4a) can be used alone or in mixtures with one another. They are either known from the literature or can be prepared by literature processes (see, for example, HJ Buysch et al., Ullmann's Encyclopedia of Industrial Chemistry, VCH, New York 1991, 5th ed., vol. 19, p. 348).

[0059] If the polycarbonate is a copolycarbonate, it is particularly preferred if this copolycarbonate comprises at least one unit of formula (1a), formula (1b), formula (1c), formula (1d), or any desired mixture of formula (1a), formula (1b), formula (1c) and formula (1d): [ka] During the ceremony, R 1 is hydrogen or a C1- to C4-alkyl radical, preferably hydrogen, R 2 is a C1- to C4-alkyl radical, preferably a methyl radical, n is 0, 1, 2 or 3, preferably 3; R 3 is a C1- to C4-alkyl radical, an aralkyl radical or an aryl radical, preferably a methyl radical or a phenyl radical, most preferably a methyl radical.

[0060] It is particularly preferred if the copolycarbonate further comprises units of formula (4) above.

[0061] For copolycarbonate, R 1 represents hydrogen or a C1- to C4-alkyl radical, preferably hydrogen, R 2 It is particularly preferred if the copolycarbonate comprises at least one unit of formula (1a) in which R is a C1- to C4-alkyl radical, preferably a methyl radical, and n is 0, 1, 2 or 3, preferably 3. 1 is hydrogen and R2 Particularly preferred is the case where the diphenols contain units of formula (1a) in which n is methyl and n is 3. Such units (1a) are derived from 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC). Some of the diphenols of formula (1a) used to prepare the copolycarbonates are known in the literature (DE-A-3918406).

[0062] It is clear to those skilled in the art that the hydrolysis product obtained according to the present invention may contain the above-mentioned dihydroxy compounds, especially bisphenols.The hydrolysis product obtained according to the present invention is preferably represented by formula (4a), formula (4b) and formula (4c).It is also conceivable that the hydrolysis product is represented by the corresponding dihydroxy compound of formula (1a), formula (1b), formula (1c) or formula (1d).It is clear to those skilled in the art that different hydrolysis products can be obtained correspondingly when copolycarbonates are concerned.

[0063] A further aspect of the present invention is (ia) carrying out a method of hydrolysis of a polycarbonate according to the above process according to the invention, in any preferred form or combination of choices (with the restriction that the carbonate is a polycarbonate), to obtain at least a dihydroxy compound as hydrolysis product; (iia) separating the dihydroxy compound as the hydrolysis product from step (ia) from at least the hydrolysis catalyst and the phase transfer catalyst; (iiia) reacting the separated dihydroxy compound of step (iia) with phosgene in a phase interface process; or (iiib) reacting the separated dihydroxy compound of step (iia) with a diaryl carbonate in a melt transesterification process; The present invention provides a method for producing a polycarbonate, comprising:

[0064] This process makes it possible, in particular, to return polycarbonates that have already been utilized, such as used polycarbonates, first to their constituent parts and then to use the resulting hydrolysis products to manufacture new polycarbonates.

[0065] In this case, process step (iia) is a preferred form of carrying out process step (iii) already described in detail in the preferred embodiment above.

[0066] In particular, a further work-up of the obtained hydrolysis product may be carried out after process step (iia), which work-up should result in the purification of the hydrolysis product in order to be able to use it in process steps (iiia) or (iiib).In particular, a recrystallization of the hydrolysis product is possible, for example in a manner known to the skilled person.

[0067] The implementation of process step (iiia) is known to those skilled in the art. For example, in the phase interface process, the hydrolysis products, e.g. bisphenols, and optionally branching agents, can be dissolved in an aqueous alkali solution and reacted with phosgene, optionally dissolved in a solvent, in a two-phase mixture of an aqueous alkali solution, an organic solvent and a catalyst, preferably an amine compound. The reaction can also be carried out in a multi-stage mode. Such processes for producing polycarbonates are in principle known as two-phase interface processes and are described, for example, in H. Schnell, Chemistry and Physics of Polycarbonates, Polymer Reviews, vol. 9, Interscience Publishers, New York 1964 p. 33 ff. and Polymer Reviews, vol. 10, "Condensation Polymers by Interfacial and Solution Methods", Paul W. Morgan, Interscience Publishers, New York 1965, chapter VIII, p. 325, and therefore the prerequisites are well known to those skilled in the art.

[0068] Alternatively, process step (iiib) is also known to those skilled in the art. The melt transesterification process is described, for example, in Encyclopedia of Polymer Science, vol. 10 (1969), Chemistry and Physics of Polycarbonates, Polymer Reviews, H. Schnell, vol. 9, John Wiley and Sons, Inc. (1964), and German Patent No. 1031512. In the melt transesterification process, hydrolysis products such as bisphenols are transesterified with diaryl carbonate in the melt using a suitable catalyst and any other additives. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0069] Obtaining bisphenol A (BPA) by hydrolysis of polycarbonate (PC) 51 mg of freeze-ground polycarbonate (PC, 0.19 mmol, with Mn of 46500 g / mol (GPC, BHT); initially 3 mm granules, 1.00 eq.) or 0.19 mmol of DiCPC were initially charged into a pressure tube with a volume of 9 ml. This was followed by addition of the hydrolysis catalyst (0.1 eq.) listed in the table and, optionally, tetrabutylammonium chloride (BuNCl) as a phase transfer catalyst. * H2O (0.1 equiv.) was added. Finally, 1 ml of distilled water was added to the mixture. The vessel was sealed and heated with stirring for 17 hours. The mixture was mixed with a few milliliters of tetrahydrofuran (THF) to dissolve the reaction product. The resulting conversion was analyzed by proton magnetic resonance spectroscopy (NMR) using dimethylsulfoxide-d6 as the solvent. 1 H-NMR) The PC signals from 7.31 ppm to 7.22 ppm were integrated as a reference for monitoring the conversion.

[0070] 1H-NMR(400 MHz, DMSO-d6): δ 6.99 - 6.88(m, 4 H, BPA), 6.66 - 6.57(m, 4 H, BPA), 3.59(tq, J= 5.9, 1.7 Hz, THF), 3.54(s, H2O), 2.50(p, DMSO), 1.75(td, J = 5.9, 5.0, 2.5 Hz, THF), 1.50(s, 6H, BPA).

[0071] The results are summarized in Table 1:

[0072] TIFF2024540158000006.tif197170

[0073] As is evident from the table, the hydrolysis of DiCPC and also of polycarbonate is not successful without the presence of a phase transfer catalyst.

Claims

1. 1. A method for hydrolyzing a carbonate, comprising: (i) providing a carbonate, at least one hydrolysis catalyst, and water, wherein the at least one hydrolysis catalyst comprises a salt of an oxoacid of an element of Group 5, 6, 14, or 15 of the Periodic Table of the Elements, and the pK of the anion of the salt is Ｂ a value ranging from 0.1 to 7.0; (ii) conducting said hydrolysis by contacting the components from step (i) to obtain at least one hydrolysis product and carbon dioxide; Including, A method characterized in that in step (ii) at least one phase transfer catalyst is present, wherein said at least one phase transfer catalyst comprises a charged organic molecule.

2. 2. The process according to claim 1, characterized in that the hydrolysis product obtained in step (ii) contains at least one hydroxyl group.

3. The following step (iii): (iii) separating the at least one hydrolysis product from at least the hydrolysis catalyst and the phase transfer catalyst; The method of claim 2 further comprising:

4. 4. A process according to any one of claims 1 to 3, characterized in that process step (ii) is carried out at a temperature between 50°C and 180°C, optionally under reflux or in a closed system.

5. 4. A process according to any one of claims 1 to 3, characterized in that in the hydrolysis of process step (ii) at least one alcohol is present.

6. 4. The process according to any one of claims 1 to 3, characterized in that at most 15% by weight of the water present in process step (ii) is organic solvent.

7. The anion of the salt contained in the at least one hydrolysis catalyst is WO ４ ２－ , V.O. ４ ３－ , CO ３ ２－ , H.P.O. ４ ２－ , MoO ４ ２－ , HSiO ４ ３－ , RSiO ３ ３－ where R is an alkyl radical having 1 to 10 carbon atoms, or PO ４ ３－ The method according to any one of claims 1 to 3, characterized in that it comprises:

8. 4. The method according to claim 1, wherein the cation of the salt contained in the at least one hydrolysis catalyst is selected from alkali metal ions and alkaline earth metal ions.

9. 4. The method according to claim 1, wherein said at least one phase transfer catalyst is a cationic surfactant.

10. 10. The process of claim 9, wherein the at least one phase transfer catalyst is selected from the group consisting of trimethylbenzylammonium chloride, tetrabutylammonium chloride, dimethyldistearylammonium chloride, tetraphenylphosphonium chloride, hexadecyltributylphosphonium chloride, and methyltrioctylphosphonium chloride.

11. 6. The method according to claim 5, characterized in that the salt of the oxoacid is used in an amount of from 0.10% to 20% by weight of the carbonate, in particular of the polycarbonate.

12. 4. The method according to claim 1, wherein the carbonate is a polycarbonate.

13. (ia) carrying out the method for hydrolyzing polycarbonate according to claim 12 to obtain at least a dihydroxy compound as a hydrolysis product; (iia) separating the dihydroxy compound as a hydrolysis product from step (ia) from at least the hydrolysis catalyst and the phase transfer catalyst; (iiia) reacting the dihydroxy compound as the isolated hydrolysis product of step (iia) with phosgene in a phase interface process; or (iiib) reacting the dihydroxy compound as the isolated hydrolysis product of step (iia) with a diaryl carbonate in a melt transesterification process; A method for producing polycarbonate, comprising: