Process for purifying a bisphenol

Abstract: A process for the purification of a crude bisphenol comprises the following steps: (1) preparing a mixture comprising from 35 to 70 percent of a crude bisphenol and from 65 to 30 percent of water, by the total weight of bisphenol and water, without the addition of a substantial amount of an organic solvent or an alkaline compound, at a pressure above atmospheric and a temperature above 100°C, (2) crystallizing bisphenol at a pressure below atmospheric, (3) separating crystalline bisphenol from the mother liquor, (4) dividing at least a portion of the mother liquor into a bisphenol-rich oil phase and a water-rich phase, (5) preparing a mixture comprising at least a portion of the bisphenol-rich oil phase, water and optionally an additional amount of crude bisphenol at a pressure above atmospheric and a temperature above 100°C, (6) cooling the mixture and crystallizing bisphenol; and (7) separating crystalline bisphenol from the mother liquor.

Description: The present invention relates to a process for the purification of bisphenols. Bisphenols are valuable compounds useful in the preparation of various polymers, such as epoxy resins or polycarbonates. High quality epoxy resins, and particularly polycarbonates, require especially pure bisphenols for use in their preparation. Bisphenols are prepared according to various known processes by the condensation reaction of an aldehyde or a ketone and a stoichiometric excess of a phenol in the presence of a catalyst. These known processes produce bisphenols and certain impurities including isomers, analogs and homologs, such as 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)propane (hereafter referred to as o,p-bisphenol isomer), 2,2,4-trimethyl-4-(4-hydroxyphenyl)chroman, trisphenol, polyphenol and unfavorably colored substances. Numerous processes exist for the purification of bisphenols in general and particularly for the purification of 2,2-bis(4-hydroxyphenyl)-propane (hereafter referred to as bisphenol A or the p,p'-isomer). U.S. Patent No. 3,919,330 discloses a purification process wherein crude bisphenol A crystals are dissolved in an organic solvent. Water is then added, the solution is cooled, bisphenol A crystallizes and the crystals are then separated by filtration or centrifugation. U.S. Patent No. 4,354,046 relates to a process for purifying bisphenol A wherein crude bisphenol A is mixed with toluene and a critical amount of water. The critical amount of water is 2 to 9 percent by weight based on the amount of crude bisphenol A. This mixture is heated to 80°C to 100°C to form a single liquid phase. The liquid phase is then cooled whereby bisphenol A crystallizes. However, some of the organic solvents which have been suggested for the purification of bisphenols are inflammable or toxic. A method which uses water as the crystallization medium for bisphenol A is disclosed in U.S. Patent No. 3,326,986. According to this patent, crude bisphenol A is mixed with water at a ratio of 0.5 to 2.0 parts, preferably 1.0 part of water per part by weight of crude bisphenol A. The mixture is heated to a temperature of about 100°C resulting in an aqueous phase and a liquid organic phase. The mixture is cooled slowly to crystallize bisphenol A. Any isomeric diphenols or other organic impurities remaining in the crystals are removed by washing with a chlorinated solvent, such as chloroform, methylene chloride, ethylene dichloride, propylene dichloride or chlorobenzene. However, the necessity to wash the crystalline bisphenol A with a chlorinated solvent for obtaining a sufficiently pure product is undesirable. In order to overcome the disadvantages of the method taught in U.S. Patent No. 3,326,986, U.S. Patent No. 4,461,915 suggests mixing water-crystallized bisphenol A in the presence of water with a water-immiscible organic solvent, such as toluene, agitating the mixture and forming three phases in the agitated mixture. The phase containing mainly the organic solvent is removed and purified bisphenol A is recovered from the remaining two phases. However, the usage of large amounts of an organic solvent, such as toluene for purification purposes, is undesirable. U.S. Patent No. 4,507,509 suggests a method of purifying bisphenol A by washing solid crude bisphenol A with an aqueous alkaline solution. The concentration of the base ranges from 0.1 to 25 weight percent of the crude bisphenol A. However, the use of an alkaline solution for washing purposes may affect the quality of the purified bisphenol A. U.S. Patent No. 4,740,635 discloses a process for crystallizing bisphenol A wherein water is added to a mixture of a phenol-free mixture of bisphenol A, 0.5 to 15 weight percent diphenol isomers and impurities. The ratio of water to the crude bisphenol A mixture is between 1:1 and 3:1, preferably between 1.5:1 and 2.5:1. Water and the crude bisphenol A mixture are heated to a temperature of 95°C to 105°C at ambient pressure to melt all the solid material. Then it is adiabatically cooled, while stirring, by reducing the pressure. The temperature is brought down to below 90°C, preferably to a temperature of from 55°C to 75°C. The crystallized bisphenol A may be washed to further increase its purity. Unfortunately, the maximum purity of the crystallized bisphenol A, even after several washing operations, does not exceed 99.2 percent. U.S. Patent No. 4,927,973 discloses a process for the continuous purification of crude bisphenol wherein, in a first step, a single liquid phase is formed which comprises a hot mixture of crude bisphenol and water in a weight ratio of 75 to 85 percent of crude bisphenol to 15 to 25 percent of water. In a second step, this mixture is continuously fed together with a stream of warm water to a first crystallization zone at a temperature sufficient to maintain a bisphenol-rich liquid phase, a water-rich phase and a crystalline phase comprising 70 to 95 percent of the total bisphenol in the mixture. When the mixture in the second step comprises 15 to 20 weight percent of bisphenol and 80 to 85 weight percent of water, the temperature in the second step is 99°C to 101°C. The three-phase mixture is passed to a second crystallization zone operated at 85°C to 97°C until 90 to 99 percent of the total bisphenol is crystallized. Bisphenol of very high purity is recovered, however, in the described process the bisphenol used as a starting material already has a high purity. The total amount of impurities less phenol according to the examples in the U.S. patent is only about 330 ppm, however, the total amount of impurities in the bisphenol prior to the purification process is only 1700 ppm. Single crystals and coarse agglomerates are said to be obtained in the process. However, the presence of coarse agglomerates is undesirable because they generally include mother liquor with impurities. Furthermore, the presence of agglomerates reduces the washing efficiency when the recovered crystals are washed. U.S. Patent No. 4,533,764 discloses a process for removing occluded organic solvent from bisphenol crystals. The crystals are placed in water which is maintained at a temperature of 100°C or above to produce a molten water-bisphenol phase. According to the Examples the weight ratio between water and bisphenol A is 3.4:1 or 4:1 respectively. The water-bisphenol phase separates from the excess water, and the solvent occluded by the bisphenol crystals can diffuse into the water phase from where it can be flash distilled. After the flash distillation the temperature of the bisphenol-water phase is reduced to allow the bisphenol to separate from the water and to crystallize. The described process is very useful for removing organic solvents which can be distilled off. However, the described process is less useful for removing impurities which have a similar or higher boiling point than the desired bisphenol. U.S. Patent No. 4,141,924 discloses a process for purifying a crude crystalline aromatic compound, such as bisphenol A, wherein a dispersion of the liquified crude material in an aqueous liquid is formed by agitating the mixture at ambient pressure and at a temperature sufficient to melt the crude material. Agitation is then reduced to permit formation of three phases: a solid crystalline phase, an aqueous liquid phase and a mother liquor phase. According to one example, bisphenol A of high purity and a relatively high yield is obtained; however, in this example chlorobenzene is used as a solvent. The use of such an organic solvent is not very desirable. U.S. Patent No. 4,861,919 describes the purification of aromatic compounds, such as bisphenol A, by a countercurrent multi-stage water crystallization wherein the crystals are melted by the addition of heat and water prior to each crystallization step. The temperature in each crystallizer is selected depending on the desired purity of the compound to be crystallized. The temperature in the first crystallizer is relatively low, preferably about 70°C. Bisphenol A of a high yield, but of relatively low purity, is recovered from the first crystallizer. The obtained crystals are washed and melted at progressively higher temperatures in order to obtain a higher degree of purity. Crystals of extremely high purity may be achieved by this process. However, the process has to be conducted very carefully because the repeated melting of the crystals increases the risk of partial degradation or cracking of the product. Due to the various disadvantages of the known processes, it is still desirable to provide a new process for the purification of a crude bisphenol. The present invention relates to a process for the purification of a crude bisphenol which comprises the steps of: (1) preparing a mixture comprising from 35 to 70 parts by weight of a crude bisphenol and from 65 to 30 parts by weight of water, without the addition of a substantial amount of an organic solvent or an alkaline compound, at a pressure above atmospheric and a temperature above 100°C, (2) crystallizing bisphenol at a pressure below atmospheric, (3) separating crystalline bisphenol from the mother liquor, (4) dividing at least a portion of the mother liquor into a bisphenol-rich oil phase and a water-rich phase, (5) preparing a mixture comprising at least a portion of the bisphenol-rich oil phase, water and optionally an additional amount of crude bisphenol at a pressure above atmospheric and a temperature above 100°C, (6) cooling the mixture and crystallizing bisphenol and (7) separating crystalline bisphenol from the mother liquor. The drawing is a schematic process flow diagram of a preferred embodiment of the process of the present invention. Crude bisphenol, which is purified according to the process of the present invention, is the reaction product of a phenolic compound with a carbonyl compound. The phenolic compound can be any compound containing one or more hydroxyl groups linked to a carbon of the aromatic group. Suitable phenolic compounds include, for example, phenol and substituted phenols, the naphthols, phenanthrol, their homologues and analogues. Suitable phenolic compounds include those containing one or more phenolic groups in each nucleus as well as polynuclear compounds. Preferred phenolic compounds are those of Formula (I) wherein: R 1 , R 2 and R 3 independently of one another represent hydrogen, halogen, preferably chlorine or bromine, C 1-8 -alkyl, C 5-6 -cycloalkyl, C 5-10 -aryl, preferably phenyl, or C 7-12 -aralkyl, preferably phenyl-C 1-4 -alkyl, more preferably benzyl. Preferred examples of the compounds of Formula (I) are phenol, cresols, xylenols, such as 2,6-dimethylphenol or 3,5-dimethylphenol, chlorophenols, dichlorophenols, 2-isopropyl-5-methyl-phenol, 5-isopropyl-2-methyl-phenol, 2-methyl-6-ethylphenol, 2,4-dimethyl-3-ethylphenol, 4-ethylphenol, 2-ethyl-4-methylphenol, 2,3,6-trimethylphenol, 2-methyl-4-tertiary-butylphenol, 2,4-ditertiary-butyl-phenol, 4-methyl-2-tertiary-butylphenol, 2-tertiary-butyl-4-methylphenol, 2,3,5,6-tetramethylphenols, 2,6-ditertiary-butylphenol, 3,5-diethylphenol, 2-methyl-3,5-diethylphenol, o-phenylphenol or p-phenylphenol. The carbonyl compound employed for producing the bisphenol can be a ketone or an aldehyde. Preferred carbonyl compounds are those of the following formula: wherein: R 4 is an aliphatic, cycloaliphatic, aromatic or heterocyclic radical, and R 5 is hydrogen or an aliphatic, cycloaliphatic, aromatic or heterocyclic radical; or R 4 and R 5 together represent a divalent aliphatic or aromatic group. Preferred groups R 4 and R 5 are C 1-8 -alkyl, C 5-6 -cycloalkyl, C 5-10 -aryl, preferably phenyl, or C 7-12 -aralkyl, preferably phenyl-C 1-4 -alkyl, more preferably benzyl. These groups are optionally halogenated. When R 4 and R 5 together represent a divalent aliphatic group, the group preferably is -(R 6 CR 7 ) n - wherein R 6 and R 7 in each occurrence individually selectable are hydrogen or C 1-6 -alkyl, such as methyl or ethyl, and n is an integer from 4 to 7, preferably 4 or 5. Examples of suitable ketones include, for example, acetone, 1,3-dichloroacetone, methyl ethyl ketone, diethyl ketone, dibutyl ketone, methyl isobutyl ketone, cyclohexanone, fluorenone, preferably 9-fluorenone, propionylphenone, methyl amyl ketone, mesityl oxide, cyclopentanone or acetophenone. Examples of suitable aldehydes include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and benzaldehyde. The process of the present invention is particularly suitable for the purification of bisphenol A, which is the reaction product of acetone and phenol. However, the process of the present invention is not limited thereto. Preferably, the purity of the crude bisphenol which is further purified according to the process of the present invention is 92 percent or more, more preferably 95 percent or more, most preferably 97.5 percent or more. Preferably the purity of the crude bisphenol is up to 99.9 percent, more preferably up to 99.7 percent, most preferably up to 99.5 percent. Preferably, the phenol content in the crude bisphenol is not more that 0.1 percent, more preferably not more than 0.05 percent, based on the total weight of the crude bisphenol. The production of a crude bisphenol of such purity is well known in the art. The impurities which may be removed by the purification process of the present invention are those which are formed during the production of the desired bisphenol compound. These congeneric impurities typically include, for example, isomers and homologs of the desired bisphenol compound. For example, when bisphenol A is the desired compound, the impurities may include a variety of by-products, such as 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)propane, 2,2,4-trimethyl-4-(4-hydroxyphenyl)chroman, trishydroxyphenyl compounds, such as 4,4'-(4-hydroxy-m-phenylenediisopropylidene)diphenyl, polyphenols, isopropenylphenol, spiro biindanes and other by-products resulting from the reaction of phenol with acetone. In step (1) of the process of the present invention a mixture is prepared which comprises from 35 to 70 percent, preferably from 40 to 60 percent, more preferably from 50 to 55 percent of crude bisphenol and from 30 to 65 percent, preferably from 40 to 60 percent, more preferably from 45 to 50 percent of water, based on the total weight of bisphenol and water. The bisphenol can be preheated and partially or entirely molten before it is mixed with water. When bisphenol is preheated, it is preferably heated to a temperature of from 155 to 240°C, more preferably from 170°C to 205°C. Water can also be preheated before it is mixed with bisphenol. When water is preheated, it is preferably heated to a temperature of from 45°C to 105°C, more preferably from 80°C to 99°C. The mixture is prepared at a pressure above atmospheric, preferably at a pressure of up to 5 bar, and a temperature above 100°C, preferably at a temperature of up to 150°C. The preferred pressure is from 1.5 to 5 bar, more preferably from 2.5 to 5 bar, most preferably from 3.5 to 4 bar. The temperature preferably is from 110°C to 150°C, more preferably from 120°C to 130°C. Preferably, distilled or deionized water is used for preparing the mixture of crude bisphenol and water. In order to reduce the water consumption in step (1), generally up to 90 percent, preferably from 50 to 80 percent of the volume of water used in step (1) may be recycled water originating from steps (4) and/or (7) described further below. No substantial amount of an organic solvent or an alkaline compound is added. This means that no more than 5 percent, preferably no more than 2 percent, more preferably no more than 1 percent of an organic solvent is added, based on the weight of the crude bisphenol, if an organic solvent is added at all. Most preferably, no organic solvent is added. Furthermore, no more than 0.3 percent, preferably no more than 0.15 percent, more preferably no more than 0.05 percent of an alkaline compound is added, based on the weight of the crude bisphenol, if an alkaline compound is added at all. Most preferably, no alkaline compound is added. In step (2) of the process of the present invention the pressure is reduced to below atmospheric, preferably to an absolute pressure of from 640 to 920 mbar, more preferably from 700 to 900 mbar, most preferably from 720 to 860 mbar. When lowering the pressure, the hot mixture resulting from step (1) is preferably cooled to a temperature of from 80°C to 100°C, more preferably from 88°C to 98°C, most preferably from 92°C to 97°C. The cooling is preferably conducted adiabatically. The freezing point of the bisphenol depends on the percentage of impurities present. The presence of the o,p-bisphenol isomer and other impurities decreases the freezing point of the composition being crystallized. At the freezing point crystalline bisphenol and two liquid phases, that is a bisphenol-rich liquid phase and a water-rich phase, coexist in equilibrium. In step (3) of the process of the present invention crystalline bisphenol is separated from the mother liquor. The bisphenol crystals can be recovered by techniques known in the art, such as filtration or centrifugation, preferably at atmospheric pressure. The temperature in step (3) generally is from 80°C to 110°C, preferably from 92°C to 105°C, more preferably from 95°C to 102°C. The recovered crystals can be washed with a washing liquor, such as water, organic solvents or mixtures of water and organic solvents. Distilled or deionized water is the preferred washing liquor. Washing with an organic solvent is not necessary. The washing liquor generally has a temperature of from 70 to 105°C, preferably from 85°C to 100°C. The amount of the washing liquor preferably is from 10 to 80 percent, more preferably from 20 to 60 percent, most preferably from 25 to 45 percent, based on the weight of the bisphenol crystals. In step (4) of the process of the present invention at least a portion of the mother liquor is divided into a bisphenol-rich oil phase and a water-rich phase. Generally at least 50 percent, preferably at least 75 percent, more preferably at least 90 percent of the total volume and most preferably substantially the entire volume of the mother liquor is separated into two phases. The two phases can be separated by known means, such as decantation or centrifugation. The temperature in step (4) generally is from 60°C to 105°C, preferably from 72°C to 98°C, more preferably from 80°C to 95°C. Step (4) is advantageously conducted at atmospheric pressure although a pressure above or below atmospheric is also useful. The resulting bisphenol-rich oil phase generally contains more than 50 percent, preferably more than 78 percent, more preferably more than 94 percent of the total weight of bisphenol present in the mother liquor. The resulting water-rich phase generally contains more than 50 percent, preferably more than 62 percent, more preferably more than 72 percent of the total weight of water present in the mother liquor. The entire amount or a part of the water-rich phase can be disposed of or recycled to steps (1) and/or (5). In step (5) of the process of the present invention a mixture is prepared which comprises at least a portion of the bisphenol-rich oil phase, water and optionally an additional amount of crude bisphenol. Prior to mixing, the bisphenol-rich oil phase preferably has a temperature of from 60°C to 105°C, more preferably from 72°C to 98°C, most preferably from 80°C to 95°C. Water can be preheated before it is mixed with the bisphenol-rich phase. When water is preheated, it is preferably heated to a temperature of from 85°C to 105°C, more preferably from 95°C to 102°C. If crude bisphenol is mixed with the bisphenol-rich oil phase, the crude bisphenol can be preheated and partially or entirely molten before it is mixed with the other components. When crude bisphenol is preheated, it is preferably heated to a temperature of from 155°C to 240°C, more preferably from 170°C to 205°C. Generally at least 50 percent, preferably at least 75 percent, more preferably at least 90 percent of the total volume and most preferably substantially the entire volume of the bisphenol-rich oil phase which has been recovered in step (4) is used in step (5) of the process of the present invention. The mixture preferably comprises from 25 to 100, more preferably from 25 to 90, most preferably from 60 to 70 weight parts of the bisphenol-rich oil phase, from 0 to 75, preferably from 10 to 75, more preferably from 30 to 40 weight parts of crude bisphenol and from 65 to 200, preferably from 80 to 150, more preferably from 100 to 125 weight parts of water. The mixture is prepared at a pressure above atmospheric, preferably at a pressure of up to 5 bar, and a temperature above 100°C, preferably at a temperature of up to 150°C. The preferred pressure is from 1.5 to 5 bar, more preferably from 2.1 to 4.5 bar, most preferably from 2.5 to 3 bar. The temperature preferably is from 110°C to 140°C, more preferably from 115°C to 125°C. Preferably, distilled or deionized water is used for preparing the mixture. In order to reduce the water consumption in step (5), generally up to 90 percent, preferably from 50 to 80 percent of the volume of water used in step (5) may be recycled water originating from steps (4) and/or (7). Generally no substantial amount of an organic solvent or an alkaline compound is added to the mixture. The term "no substantial amount" as used herein has the meaning as described above in step (1). In step (6) of the process of the present invention the mixture is cooled and bisphenol A crystallizes. The mixture is preferably cooled to a temperature of from 70°C to 98°C, more preferably from 80°C to 95°C, most preferably from 85°C to 92°C. The cooling is preferably conducted adiabatically. The cooling and crystallization is conducted in a crystallizer. Preferably, the pressure in the crystallizer is reduced to below atmospheric, preferably to an absolute pressure of from 420 to 920 mbar, more preferably from 560 to 900 mbar, most preferably from 700 to 880 mbar. The amount of impurities present in the mixture, comprising bisphenol-rich phase, water and optionally crude bisphenol, is not critical as long as the solubility of these impurities in the water is not exceeded. In step (7) of the process of the present invention crystalline bisphenol is separated from the mother liquor. The bisphenol crystals can be recovered by techniques known in the art, such as filtration or centrifugation. The temperature and the pressure in step (7) are generally about the same as in step (3). The recovered crystals can be washed with washing liquor, such as water, organic solvents or mixtures of water and organic solvents. Distilled or deionized water is the preferred washing liquor. Washing with an organic solvent is not necessary. The washing liquor generally has a temperature of from 70°C to 105°C, preferably from 85°C to 100°C. The amount of the washing liquor preferably is from 10 to 80 percent, more preferably from 20 to 60 percent, most preferably from 25 to 45 percent, based on the weight of the bisphenol crystals. The entire amount or a part of the mother liquor left after the separation of crystalline bisphenol can be disposed of or recycled to steps (1) and/or (5). The process of the present invention is preferably conducted continuously although it can also be conducted in batches. According to the process of the present invention bisphenol of high purity and high yield is obtained. At least according to the preferred embodiments of the process of the present invention a yield of purified bisphenol of from 82 to 95 percent is achieved, based on the weight of the crude bisphenol, and the purity of the purified bisphenol generally is at least 99.7 percent. Crystalline bisphenol having very large and firm crystals is obtained. The crystallization process of the bisphenol can be controlled very well. The use of an organic solvent or of an alkaline compound is not necessary in the process of the present invention. In the case of bisphenol A the o,p-bisphenol isomer can be separated from the desired p,p-bisphenol to a very large degree. Furthermore, applicants have found that the above-mentioned advantages are even achieved when running the purification process continuously on a large scale. A preferred embodiment of the present invention is described with reference to the drawing. It is to be understood that the drawing represents only one preferred embodiment of the process of the present invention and is not to be construed as limiting the scope of the invention. A feed stream 11 of crude bisphenol and a feed stream 12 of water are continuously fed into a first mixer 1. In mixer 1 the two feed streams are mixed under conditions described above in step (1). The hot mixture is fed via line 13 into a first crystallizer 3 wherein the crystallization of bisphenol is conducted as described above in step (2). The obtained suspension is continuously fed via line 14 into a separator 6, such as a filter, centrifuge or decanter, wherein crystalline bisphenol is separated from the mother liquor and washed as described in step (3) above. The crystalline bisphenol is removed from the separator via line 16, dried and collected in a storage device 8, such as a hopper. The mother liquor is removed from the separator via line 15 and fed into a liquid/oil separating device wherein, in step (4), it is divided into a bisphenol-rich oil phase and a water-rich phase. The bisphenol-rich oil phase is continuously fed into a second mixer 2 via line 17. Crude bisphenol is optionally fed via line 21 and water is fed via line 22 into the second mixer 2. The mentioned feed streams are mixed under the conditions described above in step (5). The hot mixture is fed via line 23 into a second crystallizer 4 wherein the crystallization of bisphenol is conducted as described above in step (6). The obtained suspension is continuously fed via line 24 into a separator 7 wherein crystalline bisphenol is separated from the mother liquor and washed as described in step (7) above. The crystalline bisphenol is removed from the separator via line 26, dried and collected in storage device 8. The mother liquor is removed from the separator via line 25. The present invention is further illustrated by the following example which should not be construed to limit the scope of the present invention. Unless otherwise indicated, all parts and percentages are by weight. The example refers to the drawing. Example A feed stream 11 of 2100 parts/hour of crude bisphenol A consisting of molten p,p-isomer of 98 percent purity of a temperature of 190°C and a feed stream 12 of 2100 parts/hour of deionized water of a temperature of 96°C were continuously fed into a first mixer 1. The resulting pressure of the mixture was about 3.8 bar and the temperature about 125°C. The hot mixture was injected via line 13 into a first crystallizer 3. It was worked adiabatically at 95°C and an absolute pressure of 810 mbar. The obtained suspension was continuously fed via line 14 into a separator 6 wherein crystalline bisphenol was separated from the mother liquor. The bisphenol crystals were washed in the separator with hot deionized water having a temperature of 99°C in a ratio of water:crystals of 1:3. About 1675 parts/hour of purified crystalline bisphenol were removed from the separator via line 16 and after drying collected in a storage device 8. The crystals had an o,p-isomer concentration of less than 0.20 percent. The mother liquor was removed from the separator via line 15 and fed into a liquid/oil separating device 5 where it was separated into a bisphenol-rich oil phase and a water-rich phase. About 425 parts/hour of bisphenol-rich oil phase were continuously fed into a second mixer 2 via line 17. 200 parts/hour of molten crude bisphenol A of a temperature of 190°C were fed via line 21 and 700 parts/hour of deionized water of a temperature of 96°C were fed via line 22 into the second mixer 2. The resulting pressure of the mixture was about 3.2 bar and the temperature about 115°C. The hot mixture was injected via line 23 into a second crystallizer 4. It was worked adiabatically at 91°C and an absolute pressure of 770 mbar. The obtained suspension was continuously fed via line 24 into a separator 7 wherein crystalline bisphenol was separated from the mother liquor which was removed from the separator via line 25. The bisphenol crystals were washed in the centrifuge with hot deionized water having a temperature of 99°C in a ratio of water:crystals of 1:3. About 375 parts/hour of purified crystalline bisphenol were removed from the separator via line 26 and after drying collected in a storage device 8. The crystals had an o,p-isomer concentration of less than 0.20 percent. The overall yield of the purified bisphenol A crystals, after both crystallization steps, was 89 percent, based on the weight of the crude bisphenol A prior to purification.

Claims: A process for the purification of a crude bisphenol which comprises the steps of (1) preparing a mixture comprising from 35 to 70 parts by weight of a crude bisphenol and from 65 to 30 parts by weight of water, without the addition of more than 5 percent of organic solvent or more than 0.3 percent of an alkaline compound based on the weight of the crude bisphenol, at a pressure above atmospheric and a temperature above 100°C, (2) crystallizing bisphenol at a pressure below atmospheric, (3) separating crystalline bisphenol from the mother liquor, (4) dividing at least a portion of the mother liquor into a bisphenol-rich oil phase and a water-rich phase, (5) preparing a mixture comprising at least a portion of the bisphenol-rich oil phase, water and optionally an additional amount of crude bisphenol at a pressure above atmospheric and a temperature above 100°C, (6) cooling the mixture and crystallizing bisphenol; and (7) separating crystalline bisphenol from the mother liquor. The process of Claim 1 wherein the pressure in step (1) is from 1.5 to 5 bar. The process of Claim 1 or 2 wherein the temperature in step (1) is from 110°C to 150°C. The process of any one of Claims 1 to 3 wherein, in step (2), the mixture is cooled to a temperature of from 80°C to 100°C. The process of any one of Claims 1 to 4 wherein the mixture prepared in step (5) comprises from 25 to 100 parts by weight of the bisphenol-rich oil phase and from 75 to 0 parts by weight of additional crude bisphenol. The process of Claim 5 wherein the mixture prepared in step (5) comprises from 65 to 200 parts by weight of water. The process of any one of Claims 1 to 6 wherein the pressure in step (5) is from 2.1 to 4.5 bar. The process of any one of Claims 1 to 7 wherein in step (6) the mixture is cooled to a temperature of from 70°C to 98°C. The process of any one of Claims 1 to 8 wherein, in step (6), the pressure is decreased to an absolute pressure of from 420 to 920 mbar. The process of any one of Claims 1 to 9 wherein separated crystalline bisphenol is washed with water at a temperature of from 70°C to 100°C.

Inventors: GRESSMANN JOCHEN, KRAEHLING KARL, PATRASCU EMIL, GRESSMANN, JOCHEN, KRAEHLING, KARL, PATRASCU, EMIL
Applicants: DOW DEUTSCHLAND INC, DOW DEUTSCHLAND INC.
Application year: 1995
Main classification: C07C37
IPC codes: C07C39, C07C37