Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-02-28
2001-11-13
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06316678
ABSTRACT:
The present invention relates to a process for producing bis(4-hydroxy-aryl)alkanes of high purity from addition products of bis(4-hydroxy-aryl)alkanes and aromatic hydroxy compounds which are obtained by the acid-catalysed reaction of the aromatic hydroxy compounds with ketones.
The synthesis of bis(4-hydroxyaryl)alkanes by the acid-catalysed reaction of aromatic hydroxy compounds with ketones is known from U.S. Pat. No. 2,775,620 or EP-A 342 758 for example. As a rule, an addition product of the bis(4-hydroxyaryl)alkane and of the aromatic hydroxy compound which is used as a starting material is obtained as an intermediate, and is subsequently freed from the aromatic hydroxy compound by distillation. The most important example of large-scale industrial production is the production of bisphenol A, during which an addition product of bisphenol A (BPA) and phenol is obtained as an intermediate. Even after purification, by recrystallisation for example, this addition product still contains traces of acid (about 5 to 10.10
−6
mol acid/mol BPA) due to the acid-catalysed production route employed. On the separation of the phenol from bisphenol A, which is associated with an increase in temperature, these traces of acid result in the partial decomposition of the bisphenol and in the formation of by-products. The consequence of these decomposition reactions is an impairment of the purity and quality of colour of the bisphenol. This also has a negative effect on the quality of products produced from the bisphenols, such as epoxy resins, polyesters, polyester carbonates and polycarbonates, the consequences of which are problems of colour, poor transmission of light through transparent products, or pinholes in the surfaces of mouldings produced from these end products. Similar phenomena also occur during the production of other bis(4-hydroxyaryl)alkanes. Improving the thermal stability of bis(4-hydroxyaryl)alkanes and of the addition products thereof with aromatic hydroxy compounds is therefore of particular interest.
Various methods of stabilising bis(4-hydroxyaryl)alkanes have already become known. According to EP-A 374 692, hydroxycarboxylic acids or ammonium or alkali salts thereof are used as additives. According to EP-A 523 931, alkali salts of aliphatic carboxylic acids are added to the relevant addition product of a bis(4-hydroxyaryl)alkane and an aromatic hydroxy compound. U.S. Pat. No. 5,399,789 proposes the addition of amines in amounts of 1 to 1000 ppm to bis(4-hydroxyaryl)alkanes before the thermal work-up of the latter. A common feature of all these processes is that the addition of an excessive amount of basic substances results in the decomposition of the product during thermal work-up and during further thermal processing steps.
EP-A 469 689 describes a process in which the adsorptive effect of activated carbon is utilised in order to protect the bis(4-hydroxyaryl)alkane from cleavage processes in subsequent work-up stages. However, high throughputs of reaction mixture, particularly if the process if operated continuously, result in abrasion of the activated carbon to form very fine particles, even if activated carbon granules are used. These very fine particles can increasingly contaminate the final product and impair the quality of colour and purity thereof, even if very careful filtration is employed.
EP-A 559 372 describes a combination of an acidic and of a basic ion exchange resin which is operated in the form of a mixed bed. The mother liquor is passed through this bed, and is thus purified before it is added to the mixture of starting materials before the actual reaction. However, this process has the disadvantage that substances which promote decomposition and which are first formed in the course of the reaction are not removed and can thus continue to impair the quality of the product. Moreover, oligomers of these resins in dissolved form always enter the product stream and likewise impair the quality of the product.
The object of the present invention was to provide a process by which bis(4-hydroxyaryl)alkanes can be obtained with a reduced proportion of by-products. A process has now been identified in which a neutralising agent is deposited in very finely divided form on the bis(4-hydroxyaryl)alkane addition product. In one preferred embodiment of the process according to the invention, the metered addition of the neutralising agent is controlled depending on the isomer content of the product.
The present invention relates to a process for producing bis(4-hydroxyaryl)-alkanes, wherein an aqueous alkali hydroxide solution, e.g. aqueous NaOH, is fed as an aerosol via the gas phase to an addition product of a bis(4-hydroxyaryl)alkane and the aromatic hydroxy compound which is used as a starting material, which addition product is obtained by the acid-catalysed reaction of aromatic hydroxy compounds with ketones, and the addition product is subsequently freed from the aromatic hydroxy compound by distillation. In a preferred embodiment, the addition product is an addition product of bisphenol A and phenol.
In large-scale industrial processes, the neutralisation of traces of acid which are still present in the addition product due to the production conditions employed is extremely difficult, since only very small amounts of base are necessary and have to be uniformly distributed over the crystalline addition product. According to the present invention, this difficulty is overcome by depositing an aqueous alkali hydroxide solution as an aerosol on the addition product. The amount of alkali hydroxide which is deposited on the addition product is controlled via the concentration of the alkali hydroxide solution which is employed and which is deposited on the addition product. This concentration preferably ranges from 0.005 to 0.015 % by weight alkali hydroxide.
A further difficulty is the control of the neutralisation process, since it has hitherto not been technically possible to perform a pH measurement on the addition product in order to determine the neutral point. In one preferred embodiment of the invention, which is a continuous process for the production of bis(4-hydroxyaryl)alkanes, this problem is solved in that a constant mass flow of alkali hydroxide is fed to the addition product, which occurs in crystalline form and which is freed from mother liquor, the addition product is subsequently freed from the aromatic hydroxy compound which it contains, the content of by-products in the bis(4-hydroxyaryl)alkane obtained is determined by analysis, and if the content of defined by-products exceeds a predetermined threshold value the mass flow of alkali hydroxide is correspondingly readjusted. The content of by-products in the bis(4-hydroxyaryl)alkane obtained is preferably determined by gas chromatography or by high-pressure liquid chromatography. Determination of the by-products can also be effected on-line. The interval between control operations can thereby be shortened and variations in product composition can be minimised. The alkali hydroxide is preferably supplied as an aerosol of an aqueous alkali hydroxide solution and the mass flow of alkali hydroxide is controlled via the concentration of the alkali hydroxide solution. In one particularly preferred embodiment, dilute alkali hydroxide solution is used as the operating liquid of a water ring pump and an aerosol is thereby produced on the delivery side. The alkali hydroxide concentration in the aerosol can be controlled by a continuous, quantitatively controlled feed of water and alkali hydroxide solution and by the continuous removal of part of the operating liquid. In addition, the pump acts as a mixing unit and ensures homogeneous mixing throughout of the operating liquid.
The process according to the invention is suitable for producing bis(4-hydroxyaryl)alkanes which are based on ketones which comprise at least one aliphatic group on their carbonyl function. Examples thereof include acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, diethyl ketone, acetophenone, cyc
Fennhoff Gerhard
Heydenreich Frieder
Kuhling Steffen
Lanze Rolf
Neumann Rainer
Bayer Aktiengesellschaft
Gil Joseph C.
Preis Aron
Shippen Michael L.
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