Organic compounds -- part of the class 532-570 series – Organic compounds – Carbonate esters
Reexamination Certificate
2002-08-21
2004-05-11
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbonate esters
C502S213000
Reexamination Certificate
active
06734319
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process and more particularly to a process for separating off impurities from reaction solutions.
SUMMARY OF THE INVENTION
A process for the separation a substantially adduct-free diaryl carbonate from reaction solution is disclosed. The process entails obtaining a solution that contains diaryl carbonate, catalyst system components and an aromatic solvent, lowering the temperature of the solution, optionally in the presence of a nucleating agent, to produce a crystallization product, and washing the crystallization product with an anhydrous wash solution to remove catalyst residues and impurities.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,239,106 disclosed the separation of diphenyl carbonate (DPC) from catalyst-containing reaction solutions by crystallization of the 1:1 adduct of DPC with phenol, comprising 30.5 wt. % phenol and 69.5 wt. % diphenyl carbonate, with the aid of suspension crystallization. A disadvantage of this process that it is limited to a narrow concentration range in order to be able to isolate the 1:1 adduct in a sufficiently high yield, i.e. diphenyl carbonate concentrations of at least 50 wt. % to 70 wt. % in the reaction solution.
In order still to be able to process the resulting suspensions by filtration techniques, at least a two-stage procedure requiring expensive equipment is necessary.
Furthermore, the catalyst system in this process may not be separated off completely, since the crystals filtered off are still contaminated by adhering mother liquor and inclusions of mother liquor. During subsequent working up of the 1:1 adduct by distillation, these catalyst constituents which have not been separated off have an adverse effect due to catalysis of by-product formation and DPC decomposition. The proposed washing of the crystallization product with a mixture of 9% water and 91% phenol (see column 3, lines 14-18) reduces the yield by the dissolving of large portions of the 1:1 adduct.
This treatment moreover leads to an increase in the water content of the adduct crystals, resulting in DPC losses by hydrolysis in the subsequent distillation columns, i.e. for DPC isolation and for separating water off from the wash solution used. Furthermore, essential process parameters, e.g. relating to the nature of the reactor, the temperature program, stirrer geometry, stirrer output etc., are not disclosed in U.S. Pat. No. 5,239,106.
In order to process reaction solutions where the DPC content is less than 50 wt. % by this process, concentration by distillation is essential, with the disadvantages described above of distillation in the presence of catalyst constituents. In addition, exposure of the reaction solution to heat leads to a deactivation of the catalyst system, which requires an expensive fresh feed of the catalyst components into the process. All these disadvantages described make the process inflexible and unattractive and obstruct industrial realization.
EP-A 0 687 666 described a process for the purification of diphenyl carbonate by fractional melt crystallization of highly concentrated reaction solutions in the temperature range of 45-85° C. The diphenyl carbonate purities which may be achieved are between 97.5 and 99.5%. A disadvantage of this process is the limitation to reaction solutions with a diaryl carbonate content of greater than 70 wt. %. Reaction solutions with diaryl carbonate contents below 70 wt. % may not be processed by this process and would therefore have to be concentrated to the required contents, for example by distillation. During this exposure to heat, the catalyst system causes side reactions and is thereby deactivated itself. For these reasons the process is uneconomical and cumbersome for reaction solutions with diphenyl carbonate contents below 70 wt. %.
There is therefore interest in discovering a gentle method which allows catalyst components to be recovered in a high yield and to be recycled into the reaction without significant deactivation of the catalyst system and under economical conditions which may be realized and reproduced industrially, from solutions which comprise the hydroxyaromatic compound employed and diaryl carbonate in various compositions.
DETAILED DESCRIPTION OF THE INVENTION
It has now been found, surprisingly, that the disadvantages described may be overcome if the reaction mixture is crystallized in an aromatic solvent. In a completely surprising manner, substantially adduct-free diaryl carbonate may be obtained by this procedure even at diaryl carbonate concentrations below 70 wt. %. The crystallization may be carried out very efficiently at moderate crystallization start and end temperatures. Thermal damage of the catalyst system therefore does not take place by this process, which reduces deactivation of the catalyst to a minimum. By the combination of a crystallization and a washing of the crystals, the catalyst constituents may surprisingly be separated off almost completely. The mother liquor comprising catalyst constituents may then be recycled again into the reactor or worked up. The invention accordingly relates to a method for separating off the catalyst system and substantially adduct-free diaryl carbonate, wherein the catalyst systems may include a platinum metal catalyst, a cocatalyst, a bromide salt and a base, from reaction solutions which comprise aromatic carbonates of the formula (I)
R—O—CO—O—R (I)
in which R denotes a substituted or unsubstituted C
6
-C
24
-aryl, and at least one aromatic hydroxy compound of the formula (II)
R—O—H (II)
wherein R has the above mentioned meaning, comprising
a) obtaining a solution that contains hydroxy an aromatic compound, diaryl carbonate and catalyst system in an aromatic solvent,
b) lowering the temperature of the solution, optionally introducing seeding materials, to bring about crystallization to produce a crystallization product and mother liquor that contains the catalyst system,
c) separating the catalyst-containing mother liquor from the crystallization product, and optionally
d) recycling the mother liquor for the preparation of a diaryl carbonate or working up the mother liquor, and (optionally)
e) washing the crystallization product to remove the catalyst system.
Embodiments which utilize the parameters, compounds, definitions and explanations mentioned as preferred, particularly preferred or very particularly preferred are preferred, particularly preferred or very particularly preferred.
However, the definitions, parameters, compounds and explanations mentioned above generally or mentioned in preferred ranges may also be combined as desired with one another, that is to say between the particular ranges and preferred ranges.
The catalyst system includes at least one noble metal of group VIIIB, preferably palladium. It may be added in various forms in the process according to the invention. Palladium may be employed in metallic form, e.g. as palladium black or on a support, such as Pd/C, Pd/Al
2
O
3
or Pd/SiO
2
, or preferably in the form of palladium compounds of oxidation levels 0 and +2, such as, for example, palladium(II) acetylacetonate, halides, carboxylates of C
2
-C
18
-carboxylic acids, dicarboxylates, such as oxalate, nitrate, sulfate or oxides, or palladium complexes which may comprise, for example, carbon monoxide, olefins, amines, nitriles, phosphorus compounds and halides. Palladium bromide and palladium acetylacetonate are particularly preferred.
The amount of catalyst present is not limited in the process according to the invention. Preferably, catalyst is added in an amount such that the concentration of the metal in the reaction mixture is 1 to 3,000 ppm, and concentrations of 5 to 500 ppm are particularly preferred.
A metal of groups III A, III B, IV A, IV B, V B, I B, II B, VI B or VII B, of the rare earth metals (atomic numbers 58-71) or of the iron group of the periodic table of the elements (Mendeleev), optionally also mixtures thereof, is present as a metal salt acting as a cocatalyst for the process according to the
Fischer Peter
Hansen Sven Michael
Reisinger Claus-Peter
Wirges Hans-Peter
Gil Joseph C.
McKane Joseph K.
Preis Aron
Saeed Kamal
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