HK1043108A - Method for producing diaryl carbonates - Google Patents

Description

Process for producing diaryl carbonate

It is known that organic carbonates are prepared by reacting aromatic hydroxy compounds with carbon monoxide in the presence of noble metal catalysts (DE-OS 2738437). Palladium is preferably used as the noble metal. Co-catalysts (e.g. manganese or cobalt salts), bases, quaternary salts, various quinones or hydroquinones and drying agents may also be added, where the operation may be carried out in a solvent, preferably dichloromethane.

When an aromatic dihydroxy compound is reacted with carbon monoxide and oxygen, 1 mole of water is produced per 1 mole of carbonate unit formed, and this water, if left in the reaction system, hydrolyzes the organic carbonate which has been formed, so that only a low space-time yield is obtained without effective separation of water, and in addition, water deactivates the catalyst system. However, the reactivation of deactivated catalysts is industrially very costly and the replacement of deactivated catalysts with fresh catalysts is costly, on the basis of which it is necessary to employ methods for the effective removal of water for the economic significance of the process.

DE-OS 2738437 proposes separating water by adding molecular sieves, but molecular sieves are unattractive for process technology utilization, since efficient separation of water from the liquid phase requires large amounts of molecular sieves (100-500% excess) and, for their regeneration, requires a high industrial outlay.

US-a 5,498,724 uses a process in which water formed during the reaction is stripped off with excess reaction gas, which may contain from 0 to 30% by volume of an inert gas capable of forming an azeotrope with water. Inert organic solvents may also be present in the reaction mixture. However, in this process, large gas operations must be used to completely remove the water, a minimum water content of over 500ppm can be achieved, and relatively large amounts of aromatic hydroxy compounds are also carried over during the removal of the water and must be separated from the gas stream.

It has now surprisingly been found that the addition of an inert organic solvent to the reaction mixture which under the reaction conditions forms an azeotrope with water, and in turn makes it possible to remove the azeotrope from the reaction mixture, thereby adjusting the water content in the reaction mixture to significantly below 500ppm, preferably even below 250ppm, with the amount of gas being much less than with stripping alone. In this way considerable cost savings can be achieved in large scale process reactions.

The subject of the present invention is therefore a process for the preparation of

R-O-CO-O-R (I), process for preparing aromatic carbonates in which

R is substituted or unsubstituted C₆-C₁₂Aryl, preferably substituted or unsubstituted phenyl, particularly preferably unsubstituted phenyl.

Through type is

R-O-H (II), wherein R is as defined above, with carbon monoxide and oxygen in the presence of a platinum group metal catalyst, a cocatalyst, a base, and optionally a quaternary salt and an inert organic solvent, wherein the organic solvent forms an azeotrope with the water of reaction under the reaction conditions and the azeotrope is removed from the reaction mixture.

In a preferred embodiment, the removal of water from the reaction mixture which forms an azeotrope with the solvent is facilitated by stripping with excess reaction gas, it being important here that more than 5% by volume of the solvent is removed from the reaction mixture as an azeotrope. In a preferred embodiment, the removal of the azeotrope from the reaction mixture is facilitated by the excess of the reaction gas. Under pure stripping conditions (DE-OS 4403075), no azeotrope is formed with the inert solvent and at the same time no azeotrope is removed from the reaction mixture, while the amount of conversion is significantly less.

The process according to the invention for the production of carbonic esters is carried out at a reaction temperature of from 30 to 200 ℃, preferably from 50 to 150 ℃, particularly preferably from 60 to 130 ℃ and at from 1 to 100 bar, preferably from 1 to 50 bar, particularly preferably from 1 to 10 bar. The temperature and total pressure are selected so that under the reaction conditions an azeotrope is formed and partially removed from the reaction mixture.

As inert organic solvents there may be used halogenated hydrocarbons which boil at a suitable temperature and form azeotropes with water and aromatic solvents, such as chlorobenzene, dichlorobenzene, fluorobenzene, benzene, anisole, dichloromethane or 1, 2-dichloroethane, if desired mixtures thereof, particularly preferably chlorobenzene is added, the reaction mixture containing an inert solvent in a proportion of from 1 to 99%, preferably from 20 to 98%, particularly preferably from 40 to 98%.

The majority of the solvent which is carried over in the removal of water can be separated off from the water by separating means which are present in the azeotrope-containing offgas, for example partial condensers, distillation columns with trays or packings and other apparatuses known to the expert, and fed back into the reactor, the azeotrope which has been separated off being separated off or destroyed by extraction, freezing or distillation according to the current technology.

The portion of the dissolved gas which escapes with the azeotrope can, after the separation, in a preferred embodiment be returned to the reactor circulation gas, and the educts (e.g. phenol), solvent, products and water which are carried over from the gas mixture fed to the circulation, if appropriate compressed before the separation, can be separated according to the current technology, for example by adsorption, absorption or preferably by condensation. The amount of reaction gas consisting of carbon monoxide, oxygen and inert gas necessary for the reaction is in the range from 1 to 10000 Nl per liter of reaction solution, preferably from 5 to 5000 Nl per liter of reaction solution and particularly preferably from 10 to 1000 Nl per liter of reaction solution, the gas mixture to be recirculated being produced during the removal of water taking into account the CO and O contained therein₂Included within the volume.

The composition of the reaction gases carbon monoxide and oxygen can vary within a wide concentration range, but practical CO: O₂Molar ratios (based on CO) of 1 to (0.001 to 1.0), preferably 1 to (0.01 to 0.5) and particularly preferably 1 to (0.02 to 0.3) at which the partial oxygen pressure is sufficient to achieve high space-time yields while at the same time achieving high space-time yieldsAvoidance of explosive CO/O₂A gas mixture.

All raw compounds may be contaminated with impurities during their manufacture and storage, but should be handled with chemicals that are as clean as possible in order to obtain the desired pure end product. No special purity requirement is provided for reaction gas, and the synthetic gas can be used as a CO gas source and air can be used as O₂The support, but care should be taken not to introduce catalyst poisons, such as sulfur or compounds thereof, pure CO and pure oxygen being employed in a preferred embodiment of the process of the invention.

Examples of aromatic hydroxy compounds which can be reacted according to the invention are phenol, o-, m-or p-cresol, o-, m-or p-chlorophenol, o-, m-or p-ethylphenol, o-, m-or p-propylphenol, o-, m-or p-methoxyphenol, 2, 6-dimethylphenol, 2, 4-dimethylphenol, 3, 4-dimethylphenol, 1-naphthol, 2-naphthol and bisphenol A, preferably phenol. In general, the substituent of such aromatic hydroxy compound means C having 1 or 2 substitutions₁-C₄Alkyl radical, C₁-C₄-alkylhydroxy, fluoro, chloro or bromo.

Bases which can be added in the process of the invention are Alkali metal hydroxides, Alkali metal salts or quaternary salts of weak acids, such as Alkali metal tert-butoxide (Alkali-tert. -butyrate) or Alkali metal salts or quaternary salts of aromatic hydroxy compounds of the formula (II), in which R is still in the sense indicated above, very particularly preferably Alkali metal salts or quaternary salts of aromatic hydroxy compounds of the formula (II) are those which should react to form organic carbonates, for example tetrabutylammonium phenolate, which may be lithium-, sodium-, potassium-, rubidium-or caesium salts, preferably lithium-, sodium-and potassium phenolate, particularly preferably potassium phenolate.

The base is added in catalytic amounts, the ratio of platinum group metal, such as palladium, to base being chosen preferably in the range from 0.1 to 500, preferably from 0.3 to 200, particularly preferably from 0.9 to 130, equivalents of base per gram atom of, for example, platinum group metal, such as palladium.

According to the inventionThe process is suitably carried out with a platinum group metal catalyst consisting of at least one group VIII noble metal, preferably palladium. In the process of the invention, the palladium can be added in different forms, either in the form of the metal or preferably in the form of palladium compounds having oxidation numbers 0 and +2, for example palladium (II) -acetylacetonate, -halides, -C₂-C₁₈Carboxylates, -nitrates, oxides of carboxylic acids or palladium complexes which may contain, for example, olefins, amines, phosphorus compounds and halides, palladium bromide and palladium acetylacetonate being particularly preferred.

The amount of the platinum group metal catalyst added in the process of the present invention is not limited, and the amount is preferably added so that the metal concentration in the reaction mass is 1 to 3000ppm, particularly preferably 5 to 500 ppm.

In the process of the invention, the co-catalyst used is a metal of groups IIIA, IIIB, IVA, IVB, VB, IB, IIB, VIB, VIIB of the periodic Table of the elements Mendeleev, a rare earth metal (with an atomic number of 58 to 71) or an iron group, if desired also a mixture thereof, the added metal being able to exhibit different oxidation valences. The addition of Mn, Cu, Co, V, Zn, Ce and Mo is preferred, and the method of the present invention is exemplified by, but not limited to, manganese (II), manganese (III), copper (I), copper (II), cobalt (III), vanadium (IV). The metals may be present, for example, as halides, oxides, C₂-C₆Carboxylates, diketonates and nitrates of carboxylic acids and also as complexes containing, for example, carbon monoxide, olefins, amines, phosphorus compounds and halides, with particular preference for Mn, Cu, Mo and Ce, and very particular preference is given to using manganese compounds, in particular manganese (II) and manganese (III) complexes, very particular preference being given to manganese (II) acetylacetonate or manganese (III) acetylacetonate salts, in the process according to the invention.

The cocatalyst can also be formed in situ and is added in such an amount that its concentration in the reaction mixture is between 0.0001 and 20% by weight, preferably in a concentration range of 0.005 to 5% by weight, particularly preferably 0.01 to 2% by weight.

The quaternary salts added within the scope of the invention may be, for example, substituted with organic radicalsAmmonium-, Guanidinium-, phosphonium or sulfonium salts, if desired in mixtures. Suitable for incorporation into the process of the invention are those having an organic substituent C₆-to C₁₀-aryl, C₇-to C₁₂-aralkyl and/or C₁To C₂₀Alkyl ammonium, guanidinium, phosphonium and sulfonium salts and as anions halides, tetrafluoroborates or hexafluorophosphates, it being preferred in the process according to the invention to add salts with C₆-to C₁₀-aryl, C₇-to C₁₂-aralkyl and/or C₁To C₂₀Ammonium salts of alkyl groups and halides as anions, particularly preferably tetrabutylammonium bromide and tetrabutylphosphonium bromide, such quaternary salts being added, for example, in amounts of from 0.1 to 20% by weight, preferably from 0.5 to 15% by weight and particularly preferably from 1 to 5% by weight, based on the weight of the reaction mixture.

When using bases such as tetrabutylammonium phenolate containing quaternary cations, the amount of quaternary ammonium salts such as tetrabutylammonium bromide can be reduced accordingly, and the total amount of quaternary salt anions added, if desired, can also be adjusted by adding further salts of the anions such as potassium bromide.

In a further embodiment, the platinum group metal or the platinum group metal and the cocatalyst are supported on a heterogeneous support, and instead of a homogeneous catalyst system, a heterogeneous catalyst in the form of a powder or a shaped body is used. The other components of the catalyst system, such as the base, the quaternary compound and, if desired, the cocatalyst, are dissolved in the reaction solution in a homogeneous phase, the amount of platinum group metal in the total weight of the heterogeneous catalyst being from 0.01 to 15% by weight, preferably from 0.05 to 10% by weight, based on the platinum group metal.

The co-catalyst on the catalyst support is prepared using at least one metal compound of the above-mentioned type.

The amount of cocatalyst added, calculated as metal, is from 0.01 to 15% by weight, preferably from 0.05 to 10% by weight, based on the total weight of the heterogeneous catalyst.

Suitable catalyst supports are one or more oxides of the metals of the V, Mn, Ti, Cu, Zr, La, rare earths (atomic numbers 58 to 71), not only chemically pure but also mixtures and iron and cobalt oxides, nickel, aluminum, silicon and magnesium oxides, zeolites and activated carbon. If the supported catalyst is added in the form of a powder, a suitable stirrer is provided for the stirring vessel used or a bubble column reactor is used in order to mix it with the reaction components.

When the supported catalyst powder is used as a suspension in a stirrer or a bubble column, the amount of the supported catalyst powder is from 0.001 to 50% by weight, preferably from 0.01 to 20% by weight, particularly preferably from 0.1 to 10% by weight, based on the amount of the aromatic hydroxy compound charged.

In a preferred embodiment, the heterogeneous supported catalyst is added in fixed form to a stirred vessel, a bubble column, a trickle bed reactor or a series of these reactors, without the supported catalyst at all having to be separated.

Suitable reactors for the process according to the invention using homogeneous or heterogeneous catalysts are stirred vessels, pressure vessels and bubble columns, which can be used individually or in cascade, the reactors in the series being 2 to 15, preferably 2 to 10, particularly preferably 2 to 5, reactors connected in series.

The stirred vessel used according to the invention is equipped with a suitable stirrer for mixing the reaction components. Such stirrers are well known to the skilled worker and there may be mentioned disk-, impeller-, propeller-, turbine-, MIG-and Intermig-stirrers, tubular stirrers and other hollow stirring types. Preferred are those which allow efficient mixing of gas and liquid, such as hollow tube jet mixers, propeller mixers, and the like.

The process according to the invention can be used in the following manner as a bubble column: simple bubble columns, bubble columns with internals such as with parallel compartments, cascade bubble columns with sieve plates or single-orifice plates, packed bubble columns, bubble columns with static mixers, pulsed sieve plate bubble columns, loop reactors (Schlaufenreaktoren) such as airlift loop reactors, downflow loop reactors, jet loop reactors, open jet reactors, nozzle jet reactors, liquid immersion jet bubble columns, downflow/upflow bubble columns and other bubble reactors familiar to the skilled worker. (chem.Ing.Tech.51(1979) Nr.3, p.208-216; W.D.Deckwer, Reaktiontechnik in Blasexulen, Otto Salle Verlag 1985).

In a preferred embodiment, bubble column reactors and bubble column-cascade reactors, such as cascade bubble columns and loop reactors, which allow efficient mixing of the gas and liquid are used, and distributors and redispersion means are provided along the axial direction of the bubble column reactor to ensure thorough mixing of the liquid phase and the reaction gas, and, as fixed redispersion means, single-well plates, perforated plates, sieve plates and other internals known to the skilled worker. In order to disperse the reaction gases initially in the liquid phase during the addition, they can be carried out by customary apparatus, for example perforated sinter plates, perforated plates, sieve plates, immersion tubes, nozzles, ring injectors and other fine-dispersing apparatus familiar to the expert.

The process according to the invention can be carried out in various variants, one of which is a batch operation in which CO and O are introduced₂The introduction into the reaction mixture can be effected via a bubble stirrer (Begasungsruhrer), for example in the case of stirred tanks, or via other known gas distribution members. After the optimum conversion has been reached, the reaction mixture is removed from the reactor and, if necessary, worked up in the reactor. In the case of the supported catalysts in powder form, they are separated from the reaction mixture by filtration, sedimentation or centrifugation.

The supported catalysts used in the batch tests can be reused without purification if necessary with the same charge, and the supported catalysts used in the continuous operation can be retained in the reactor for a long time and can be regenerated if necessary.

The preferred mode is a continuous mode of operation with a single reactor or a cascade of multiple reactors, where the immobilized heterogeneous catalyst is used, it can remain in the reactor for a long time and can be regenerated in situ if necessary.

Examples

Example 1

0.3 mmol of palladium bromide, 22 mmol of tetrabutylammonium bromide and 20 g of phenol are placed in 90 ml of chlorobenzene and dissolved in a 250 ml autoclave with a stirrer, a cooler and a cold trap connected thereto, carbon monoxide (3 l/h) is introduced at 90 ℃ for 30 minutes, after which 2.2 mmol of manganese (III) acetylacetonate and 10.4 mmol of tetrabutylammonium phenolate and 10 ml of chlorobenzo are introduced at a rate of 80 Nl/h at a total pressure of 3 bar and 110 ℃ into a gas mixture of carbon monoxide and oxygen (95: 5% by volume) to start the reaction. Hourly samples were taken from the reaction mixture for gas chromatography and the analysis showed that after 1 hour 11.4% diphenyl carbonate had been present in the reaction mixture and after 2 hours a total of 14.6% diphenyl carbonate had been present. In the cold trap, 12 g of chlorobenzene/water suspension condensed off and the water content of the reaction mixture after the end of the test was less than 250 ppm.

Example 2

0.15 mmol of palladium bromide, 11 mmol of tetrabutylammonium bromide and 10 g of phenol were placed in 90 ml of chlorobenzene and dissolved in a 250 ml autoclave with a stirrer, a cooler and a cold trap connected thereto, carbon monoxide (3 l/h) was introduced at 90 ℃ for 30 minutes, after which 1.1 mmol of manganese (III) acetylacetonate and 5.2 mmol of potassium phenoxide and 10 ml of chlorobenzene were added and a gas mixture of carbon monoxide and oxygen (95: 5% by volume) was introduced at a rate of 80 Nl/h at a total pressure of 5 bar and 125 ℃ to start the reaction. Samples were taken from the reaction mixture every half hour for gas chromatography and the analysis showed that after half an hour 5.4% diphenyl carbonate was present in the reaction mixture and after 1 hour a total of 7.2% diphenyl carbonate was present, 10 g of chlorobenzene/water suspension condensed in the cold trap and the water content of the reaction mixture after the end of the test was less than 250 ppm.

Example 3 (comparative example)

0.15 mmol of palladium bromide, 11 mmol of tetrabutylammonium bromide and 10 g of phenol were placed in 90 ml of chlorobenzene and placed in a 250 ml autoclave with a stirrer, a cooler and a cold trap connected thereto, carbon monoxide (3 l/h) was introduced at 90 ℃ for 30 minutes and dissolved, after which 1.1 mmol of manganese (III) acetylacetonate and 5.2 mmol of potassium phenoxide and 10 ml of chlorobenzene were added and a gas mixture of carbon monoxide and oxygen (95: 5 vol%) was introduced at a rate of 80 Nl/h at a total pressure of 10 bar and a temperature of 125 ℃ to start the reaction: samples were taken from the reaction mixture every half hour and analyzed by gas chromatography, and the analysis showed that after half an hour, 0.9% diphenyl carbonate was present in the reaction mixture and after 1 hour, a total of 1.2% diphenyl carbonate was present, less than 2 g of water was condensed in the cold trap, and the water content in the reaction mixture after the end of the reaction was greater than 500 ppm. The controlled pressure and temperature correspond to the pure stripping conditions, since virtually no azeotrope escapes from the reaction mixture, which in direct comparison with example 2 demonstrates the effect of removing the azeotrope from the reaction mixture.

Claims (10)

1. A process for the preparation of an aromatic carbonate of the formula R-O-CO-O-R (I) in which

R is substituted or unsubstituted C₆-C₁₂Aryl, preferably substituted or unsubstituted phenyl, particularly preferably unsubstituted phenyl,

wherein, by means of an aromatic hydroxy compound of the formula R-O-H (II), in which R has the meaning indicated above,

with carbon monoxide and oxygen in the presence of a platinum group metal catalyst, a cocatalyst, a base and, if desired, a quaternary salt and an inert organic solvent, wherein the inert organic solvent forms an azeotrope with the water of reaction under the reaction conditions and the azeotrope is removed from the reaction mixture.

2. The process of claim 1 wherein the removal of azeotropes from the reaction mixture is facilitated by excess reaction gas.

3. A process as claimed in claim 1 or 2, wherein an aromatic solvent is used as inert organic solvent.

4. A process as claimed in claim 3, wherein chlorobenzene is used as inert organic solvent.

5. A process according to claim 1 or 2, wherein a halogenated hydrocarbon is used as inert organic solvent.

6. A process as claimed in claim 5, wherein 1, 2-dichloroethane is used as solvent.

7. A process according to any one of claims 1 to 6, wherein an alkali metal or quaternary salt of a weak acid is used as base.

8. A process as claimed in claim 7, wherein potassium phenoxide is used as base.

9. A process as claimed in claim 7, wherein potassium tert-butoxide is used as base.

10. A process as claimed in any of claims 1 to 6, wherein an alkali metal hydroxide is used as the base.