EP1713752A1

EP1713752A1 - Production of bisphenol a with a reduced isomer formation

Info

Publication number: EP1713752A1
Application number: EP05706966A
Authority: EP
Inventors: Rainer Neumann; Ulrich Blaschke; Stefan Westernacher
Original assignee: Bayer MaterialScience AG
Current assignee: Covestro Deutschland AG
Priority date: 2004-02-05
Filing date: 2005-01-22
Publication date: 2006-10-25
Also published as: US20050176918A1; SG152282A1; WO2005075396A1; KR20060130169A; CN100516011C; DE102004005724A1; RU2006131515A; RU2402521C2; CN1918097A; JP2007520502A; TW200536876A; JP4874125B2

Abstract

The invention relates to a method for producing bisphenol A, according to which phenol and acetone are brought up to temperatures of between 48 and 54 °C prior to the reaction.

Description

Production of bisphenol A with reduced isomer formation

The present application relates to a process for the preparation of bisphenol A, in which the mixture comprising phenol and acetone is brought to a temperature of 48 to 54 ° C.

Bisphenols as condensation products of phenols and carbonyl compounds are starting materials or intermediates for the production of a large number of commercial products. The condensation product from the reaction between phenol and acetone, 2,2-bis (4-hydroxyphenyl) propane (bisphenol A, BPA) is of particular technical importance. BPA serves as a starting material for the production of various types of polymeric materials such as polyarylates, polyether imides, polysulfones and modified phenol-formaldehyde resins. Preferred areas of application are in the production of epoxy resins and polycarbonates.

Technically relevant production methods for BPA are known and are based on the acid-catalyzed reaction of phenol with acetone, a phenol-acetone ratio of greater than 5: 1 being preferably set in the reaction. The reaction usually takes place in continuous operation and in general at temperatures from 45 to 110 ° C., preferably at 50 to 80 ° C., as described in DE-A-1 99 57 602. Homogeneous as well as heterogeneous Bronsted or Lewis acids can be used as acidic catalysts, for example strong mineral acids such as hydrochloric or sulfuric acid. Gel-shaped or macroporous sulfonated crosslinked polystyrene resins (acidic ion exchangers) are preferably used. Divinylbenzene is normally used as the crosslinker, but others such as divinylbiphenyl can also be used. In addition to the catalyst, a cocatalyst can be used. These are usually thiols that have at least one SH function. The cocatalyst can either be dissolved homogeneously in the reaction solution or, in the case of the acidic ion exchangers, can be fixed on the catalyst itself. Homogeneous cocatalysts are, for example, mercaptopropionic acid, hydrogen sulfide, alkyl sulfides such as ethyl sulfide and similar compounds. Fixed cocatalysts are ammoalkylthiols and pyridylalkylthiols, which are ionically bound to the catalyst, whereby the SH function can be protected and is only released to the catalyst during or after fixation. Likewise, the cocatalyst can be covalently bound to the catalyst as alkyl or aryl thiol.

When phenol is reacted with acetone in the presence of acidic catalysts, a product mixture is formed which, in addition to unreacted phenol and optionally acetone, contains primarily BPA and water. In addition, typical by-products of the condensation reaction occur in small amounts, for example 2- (4-hydroxyphenyl) -2- (2-hydroxyphenyl) propane (o, p-BPA), substituted indanes, hydroxyphenyl indanols, hydroxyphenyl chromanes, spirobisin dane, substituted rndenols, substituted xanthenes and higher condensed compounds with three or more phenyl rings in the molecular backbone. In addition, self-condensation of the acetone and reaction with impurities in the raw materials can result in the formation of further secondary components such as anisole, mesityl oxide, mesitylene and diacetone alcohol.

For economic and technical reasons, the reaction is usually carried out in such a way that 100% conversion of the acetone is not achieved and 0.1 to 0.6% by weight of acetone are still present in the reactor outlet.

The by-products mentioned, such as water, but also the unreacted starting materials, such as phenol and acetone, impair the suitability of BPA for the production of polymers and must be removed by suitable processes. In particular for the production of polycarbonate, high purity requirements are placed on the raw material BPA.

A processing and purification method of BPA is carried out by separating BPA from the reaction mixture in the form of an approximately equimolar crystalline adduct with phenol by cooling the reaction mixture with crystallization of the BPA-phenol adduct in a suspension crystallization. The BPA-phenol adduct crystals are then separated from the liquid phase by a suitable apparatus for solid-liquid separation, such as rotary filters or centrifuges, and sent for further purification.

Adduct crystals obtained in this way typically have a purity of> 99% by weight of BPA, based on the sum of BPA and the secondary components, with a phenol content of approximately 40% by weight. By washing with suitable solutions, which typically contain one or more components from the group consisting of acetone, water, phenol, BPA and secondary components, the adduct crystals can be freed from impurities adhering to the surface.

The liquid stream (mother liquor) obtained in the solid-liquid separation contains phenol, BPA, water formed in the reaction, unreacted acetone and is enriched in the secondary components typically obtained in the production of BPA. This mother liquor stream is usually returned to the reaction unit. In order to maintain the catalytic activity of the acidic ion exchanger, water previously formed is removed by distillation, wherein any acetone still present is also removed from the mother liquor. The dewatered reaction stream thus obtained is supplemented by phenol, acetone and optionally cocatalyst and returned to the reaction unit. The phenol can also be added in whole or in part before dewatering. Alternatively, water and acetone can also be removed by distillation before the suspension crystallization of the BPA-phenol adduct is carried out. In the distillation steps mentioned, a portion of the phenol present in the reaction solution can also be separated off by distillation. The problem with such a recycle mode is that by-products from BPA production are enriched in the recycle stream and lead to the deactivation of the catalyst system and to poorer product qualities. In order to avoid excessive accumulation of secondary components in the circulating stream, a partial amount of the circulating stream is removed from the process chain as so-called BPA resin - if necessary after partial or complete distillative recovery of phenol.

In addition, part or all of the circulating stream after the solid-liquid separation and before or after the separation of water and residual acetone can be passed through a rearrangement unit filled with an acidic ion exchanger. This unit is generally operated at higher temperatures than the reaction unit. In this rearrangement unit, under the prevailing conditions, some of the secondary components of the BPA production present in the recycle stream are isomerized to BPA, so that the overall yield of BPA can be increased.

To further recover secondary components, the resin can also be subjected to a thermal, acidic or basic catalyzed cleavage. The phenol released and, if appropriate, also isopropenylphenol can be separated off by distillation and returned to the reaction.

The BPA-phenol adduct crystals obtained after the above-described suspension crystallization of the reaction solution and solid-liquid separation are passed on to further purification steps, with the separation of phenol and possibly a reduction in the concentration of secondary components being achieved.

The BPA-phenol adduct crystals can be recrystallized for further purification from phenol, organic solvents, water or mixtures of the solvents mentioned, which may also contain BPA and its isomers, according to a suspension crystallization. The phenol present in the adduct crystals can also be removed in whole or in part by the choice of suitable solvents. Any phenol remaining in the BPA after recrystallization is then completely separated off by suitable distillative, desorptive or extractive methods.

Alternatively, the phenol can also be removed from the BPA-phenol adduct crystals by means of a melting process.

After the phenol has been separated off, a bisphenol A melt is obtained which can be used without prior solidification for the production of polycarbonate by the transesterification process (melt polycarbonate). The bisphenol A melt can also by known Processes, such as, for example, after the test procedure or by desquamation, are solidified for sale or recycling. Furthermore, the melt can be dissolved in sodium hydroxide solution and used for the production of polycarbonate by the phase interface process. If appropriate, the phenol-free bisphenol A can be subjected to a purification step such as melt crystallization, distillation and / or recrystallization from phenol, water or an organic solvent such as toluene or mixtures of these substances before further processing.

In the process described, the content of secondary components, the so-called isomers, plays a decisive role in the quality of the bisphenol. These so-called isomers (indanes, chromanes, trisphenols, o, p-BPA etc.) influence the crystallization of bisphenol A from the reaction solution. Their influence increases with increasing content in the reaction solution. In order to nevertheless achieve a sufficient quality in the crystallization, parts of the circuit stream, the so-called BPA resin, must be removed from the circuit, as already described above. It is of economic interest to keep the amount discharged as small as possible, since phenol and acetone as bisphenol A and isomers are lost here. The processes known to the person skilled in the art, such as rearrangement and resin splitting, enable part of the raw materials to be recovered, but this is associated with energy expenditure and additional investment costs.

The object of the present invention was therefore to provide a process for the preparation of bisphenol A, in which the formation of isomers during the reaction is reduced, and a high purity of bisphenol A is achieved after the crystallization and filtration in the end product and thus the discharged amount from the cycle stream, the so-called BPA resin, can be kept low.

It has now been found that this problem can be solved by a special reaction procedure.

The invention relates to a process for the preparation of bisphenol A, in which

a) phenol and acetone are mixed together, and

b) the mixture containing phenol and acetone is heated to a temperature in the range from 48 to 54 ° C. and then

c) the mixture containing phenol and acetone is brought into contact with an acidic ion exchanger as a catalyst at this temperature, and d) the mixture containing phenol and acetone is converted to bisphenol A.

An essential feature of the process according to the invention is that the mixture comprising phenol and acetone in step b) is heated to a temperature of 48 to 54 ° C., preferably 50-53 ° C., particularly preferably 51.5 to 52.5 ° C. before the reaction becomes.

The acidic ion exchanger is preferably used in step c) in combination with a cocatalyst. These are usually thiols that have at least one SH function. The cocatalyst can either be dissolved homogeneously in the reaction solution or, in the case of the acidic ion exchangers, can be fixed on the catalyst itself. Homogeneous cocatalysts are, for example, mercaptopropionic acid, hydrogen sulfide, alkyl sulfides such as ethyl sulfide and similar compounds. Fixed cocatalysts are aminoalkylthiols and pyridylalkylthiols which are ionically bound to the catalyst, where the SH function can be protected and is only released to the catalyst during or after fixation. Likewise, the cocatalyst can be covalently bound to the catalyst as alkyl or aryl thiol.

The mixture containing phenol and acetone may also contain other substances. For example, in addition to p, p-bisphenol A itself, the so-called isomers can also be contained, which are contained in the recycled partial stream of the mother liquor, which originates from the crystallization and filtration of the BPA-phenol adduct. These are the compounds known to the person skilled in the art, such as, for example, o, p-bisphenol A, o, o-bisphenol A, trisphenols, (hydroxyphenyl) chromanes, (hydroxyphenyl) indanes, (substituted) indanes, (substituted) indenols, ( substituted) spirobisindanes, isopropenlyphenol and its di- and oligomers, (substituted) xanthenes, as well as other highly condensed compounds with three or more phenyl rings in the molecular structure. In addition, further substituted phenols, anisoles, methanol, mesityl oxide, mesitylene, diacetone alcohol and water, degradation products of the catalyst and of the cocatalyst and impurities from the raw materials can also be present in the recirculated partial stream.

By cooling the mixture containing phenol and acetone from the otherwise usual 55 to 60 ° C to 48 to 54 ° C, the starting temperature of the reaction is ultimately lowered to a temperature in the range from 48 to 54 ° C. This makes the formation of isomers during the reaction on the acidic ion exchanger more selective with regard to p, p-bisphenol A, the desired main product. At the same time, the amount to be discharged from the recirculated partial stream of the mother liquor, which originates from the crystallization and filtration of the BPA-phenol adduct crystals, i.e. ultimately the amount of BPA resin to be discharged, in order to keep the content of by-products, the so-called isomers, in the reactor constant on one for performing the crystallization and maintain the purity of the final product at an acceptable level. Due to the lower discharge, less bisphenol resin is obtained as a residue. Thus the amount of BPA resin is a direct indication of the isomer formation in the reaction. By reducing the reactor inlet temperature, the amount of resin can be reduced by up to 50%, which represents great economic savings with the same product quality.

The reaction is preferably carried out in such a way that a reactor temperature of 77 ° C. is not exceeded. Adiabatic reaction control is preferred. In practice, this usually leads to the highest temperature occurring at the outlet of the reactor. The reactor outlet temperature is then the highest temperature that occurs in the reactor. Adiabatic reaction control also includes a reaction control in which the reactor jacket is slightly heated from the outside in order to avoid crystallization in wall areas.

The low temperature at the start of the reaction, at which a high concentration of acetone is still present, in particular reduces the acetone's own condensation and the formation of chromanes, indanes and other by-products of bisphenol A production known to the person skilled in the art.

In order to obtain a bisphenol of sufficient quality and to be able to carry out the crystallization and filtration of the bisphenol A-phenol adduct crystals without any problems, the content of the so-called isomers of 100 g / l in the reaction mixture after the reaction should not be exceeded if possible. A content of the so-called isomers of 60 to 100 g / l is preferably set in the reaction mixture at the reactor outlet. The discharge of the substream from the recycled mother liquor, which originates from the crystallization and filtration of the BPA-phenol adduct crystals, can be reduced in quantity by the process according to the invention without exceeding the limit of 100 g / l of the so-called isomers in the product mixture at the reactor outlet , A process is therefore preferred in which a product mixture is obtained in step d), from which a bisphenol A-phenol adduct is then crystallized out and filtered off and bisphenol A is produced therefrom, and in which the mother liquor formed during the crystallization and filtration is partially is recycled into the mixture of phenol and acetone in step a), a partial stream being discharged from the recycled mother liquor and this partial stream in quantitative terms, taking into account the phenol present, less than 6% by weight, based on the amount of bisphenol A produced accounts. The amount of the diverted mother liquor is therefore less than 6% by weight, based on the amount of bisphenol A produced, if all components contained in the substream except phenol are taken into account Partial stream to be discharged from the mother liquor can easily be determined by the expert using standard analysis methods.

In the process according to the invention, too, the amount of BPA resin ultimately obtained can be further reduced by measures known to the person skilled in the art, such as, for example, rearrangement and resin cleavage.

The formation of h danen, indenols and spirobisindanes is particularly favored by high temperatures. Formula (I) and (H) exemplify indane, formula (IS) exemplifies an indenol and formula (IV) exemplifies a spirobisindane.

(l) (II)

It is known that isomers such as o, p-BPA can still be rearranged during the reaction, but indanes, spirobisindanes and lhdenols cannot. Their formation in the reaction must therefore be avoided particularly and as far as possible and their concentration in the reaction mixture must be kept low.

It has been shown that the content of such indanes, spirobisindanes and indenols in the product mixture at the reactor outlet can be reduced to below 15 g / l by the process according to the invention.

After crystallization and filtration of the BPA-phenol adduct, subsequent washing with phenol and distillative and / or desorptive separation of the phenol, a BPA in a purity of greater than 99.5% by weight of p, p-bisphenol A can be obtained by the process according to the invention can be produced without additional purification by primary crystallization being necessary. The bisphenol A produced by the process according to the invention can be reacted with phosgene by the phase interface process or with diaryl carbonates, preferably diphenyl carbonate, to polycarbonate by the melt process.

Example 1

A reactor loaded with 100 m ^{3 of} phenol-moist acidic ion exchanger Lewatit SC104 is reacted from top to bottom with a reaction solution consisting of 4% by weight acetone, 6% by weight isomers, 7% by weight bisphenol A, 0.05% by weight. Drive through water, 300 ppm mercaptopropionic acid and the rest of the phenol (approx. 83% by weight) at a throughput of 30 t / h. This corresponds to a bisphenol A production of 4.2 t / h. The reactor inlet temperature is adjusted to 52 ° C. The reactor outlet temperature is 75 ° C. With this setting, the amount of the diverted partial stream of the mother liquor is 5.1% by weight, based on the amount of bisphenol A produced, if all components contained in the partial stream except phenol are taken into account. The content of indanes, spirobisindanes and indenols is about this Operating mode in total at 12 g / 1 in the reactor outlet.

Example 2 (comparative example)

Experimental procedure as in Example 1, but the reactor inlet temperature is now 56 ° C and the reactor outlet temperature is 79 ° C. With this setting, the discharged partial stream of the mother liquor is 8% by weight, based on the amount of bisphenol A produced, if all components contained in the partial stream except phenol are taken into account. The content of indanes, spirobisindanes and indenols is in this mode of operation Total at 19 g / 1 in the reactor outlet.

Claims

Patentansprflche

1. Process for the preparation of bisphenol A, in which a) phenol and acetone are mixed with one another, and b) the mixture comprising phenol and acetone is heated to a temperature in the range from 48 to 54 ° C., and then c) the mixture is contained Phenol and acetone are brought into contact with an acidic ion exchanger as catalyst at this temperature, and d) the mixture containing phenol and acetone is converted to bisphenol A.

2. The method according to claim 1, wherein the acidic ion exchanger in step c) is used in combination with a cocatalyst.

3. The method according to any one of claims 1 or 2, wherein the temperature of the reaction in step d) does not exceed 77 ° C.

4. The method according to any one of claims 1 to 3, in which the reaction in step d) is carried out adiabatically.

5. The method according to any one of claims 1 to 4, in which a product mixture is obtained in step d), from which a bisphenol A-phenol adduct is then crystallized and filtered and bisphenol A is prepared therefrom, and in which the crystallization and filtration of the resulting mother liquor is partly returned to the mixture of phenol and acetone in step a), a partial stream being discharged from the recycled mother liquor and this partial stream being less than 6% by weight, based on the amount, of phenol not taking account of the phenol present bisphenol A produced.

6. The method according to any one of claims 1 to 5, wherein the content of indanes, spirobisindanes and indenols in the product mixture obtained in step d) is less than 15 g / 1 based on the product mixture.

7. A process for the preparation of polycarbonate, in which bisphenol A is prepared according to one of claims 1 to 6 and is then reacted with phosgene according to the interfacial process or with diphenyl carbonate according to the melt process to polycarbonate.