Process for the production of crystalline adduct of bisphenol A and phenol

Abstract: High purity, crystalline adduct of bisphenol A and phenol is produced multi-stage crystallization of a phenolic slurry of bisphenol A with a crystal separation being interposed between each stage. The purity of the phenol solvent which is used to prepare the solutions for the crystallization stages is controlled so as to increase progressively. The crystalline adduct obtained in the final crystallization stage is washed with purified phenol.

Description: This invention relates to a process for the production of a crystalline adduct of bisphenol A and phenol and to an apparatus suitable for carrying out the process. One well known process for the production of bisphenol A (2,2-bis(4'-hydroxyphenyl)propane) includes reacting acetone with a stoichiometrically excess amount of phenol in the presence of an acid catalyst. With respect to the recovery of bisphenol A from the reaction product, a method is known in which the reaction product is cooled for the crystallization of a bisphenol A/phenol adduct and the resulting adduct is subsequently decomposed into bisphenol A and phenol (U.S. Patent No. 3,936,507). Since the purity and hue of bisphenol A recovered from a bisphenol A/phenol adduct depend largely upon the purity and hue of the adduct, it is highly desired to produce colourless, high purity crystals of the adduct. To attain this purpose, a method is proposed in which a solution of bisphenol A in phenol is subjected to a series of crystallization stages each of which is followed by separation of crystals and dissolution of which is followed by separation of crystals and dissolution of the separated crystals. With this method, it is possible to improve the purity of the adduct by increasing the number and/or the size of the crystallization towers. However, since the number and size of the adduct separators and their associated dissolving vessels are also increased with the increase of crystallization towers, the whole apparatus becomes undesirably large, complicated and inefficient. The crystallization of the adduct of bisphenol A and phenol is generally performed by feeding a solution of bisphenol A in phenol to a crystallization tower and cooling the solution in the tower to form a slurry of the adduct. The cooling is performed by continuously discharging part of the slurry from the tower, introducing the discharged slurry into a cooler and recycling the cooled slurry to the tower. This cooling method has a problem because it is difficult to control the size of the crystals of the adduct and because fine crystals of the adduct are apt to be produced. Because of their large surface area, the fine crystals of the adduct have a tendency to adsorb impurities. The present invention has been made with the foregoing problems of the conventional method in view. EP-A-332878 discloses a process for the production of a crystalline adduct of bisphenol A and phenol, in which a slurry of the adduct is separated in a first separation stage into a solid phase containing the adduct which is recovered, and a liquid phase containing phenol which is discharged, and then the separated solid phase is reslurried and the resulting slurry is separated in a second separation stage to recover the desired crystalline adduct. A part of the filtrate from the second separation stage is used for the reslurrying step and the remainder is recycled for use in the initial adduct-forming reaction or crystallisation stage. In both separation stages the separated solids are washed with washing phenol, the washings for the first separation stage being discharged while those from the second separation stage are used in the reslurrying. In accordance with the present invention there is provided a process for the production of a crystalline adduct of bisphenol A and phenol, comprising: (A) a first stage including the steps of: (A-a) feeding a solution of bisphenol A dissolved in phenol to a crystallization zone and cooling same to crystallize an adduct of bisphenol A and phenol and to obtain a slurry containing crystals of the adduct, (A-b) discharging said slurry from said crystallization zone and introducing same into a solid-liquid separating zone to separate said slurry into a solid phase containing crystals of the adduct and a liquid phase containing phenol, and (A-c) washing said solid phase with a washing liquid to obtain a washed solid phase and a used washing liquid; and (B) one or more, second to n-th stages following said first stage and each including the steps of: (B-a) dissolving the washed solid phase obtained in the immediately preceding stage into solvent phenol to obtain a solution, (B-b) feeding said solution obtained in step (B-a) to a crystallization zone and cooling same to crystallize an adduct of bisphenol A and phenol and to obtain a slurry containing crystals of the adduct, and (B-c) discharging said slurry obtained in step (B-b) from said crystallization zone and introducing same into a solid-liquid separating zone to separate said slurry into a solid phase containing crystals of the adduct and a liquid phase containing phenol, and (B-d) washing said solid phase obtained in step (B-c) with a washing liquid to obtain a washed solid phase and a used washing liquid; wherein said washing liquid used in said n-th stage is purified phenol, wherein said washed solid phase obtained in said n-th stage is recovered as a product adduct, wherein at least one of a portion of said used washing liquid and a portion of said liquid phase obtained in each of said second to n-th stages is recycled to step (B-a) thereof as at least part of said solvent phenol, wherein at least one of a portion of said used washing liquid and a portion of said liquid phase obtained in each of said second to n-th stages is recycled to step (B-d) of the preceding stage thereof as at least part of said washing liquid, wherein the purity of the solvent phenol used in each of said second to n-th stages is controlled so that the content of impurities in the solvent phenol used in one stage of said second to n-th stages is greater than that of the stage immediately following said one stage, and wherein the purity of the washing liquid used in each of said second to n-th stages is controlled so that the content of impurities in the washing liquid used in one stage of said second to n-th stages is greater than that of the stage immediately following said one stage. The present invention will now be described in greater detail below with reference to the accompanying drawing which is a flow diagram of an apparatus suitable for carrying out a preferred embodiment of the process according to the present invention. In the following description, bisphenol A is referred to as BPA for brevity. Referring now to the drawing, designated as A-1 through A-3 are first through third crystallization zones, respectively, as B-1 are first through third solid/liquid separation zones, respectively, and as C-1 and C-2 are first and second dissolution zones, respectively. A raw material solution of BPA dissolved in phenol is fed through a line 87 to the first crystallization zone A-1 where the solution is cooled to crystallize an adduct of BPA and phenol and to obtain a first slurry containing crystals of the adduct. The first slurry is discharged from the first crystallization zone A-1 and is introduced through a line 82 into the first solid-liquid separating zone B-1 where the slurry is separated into a first solid phase containing crystals of the adduct and a first liquid phase containing phenol. The first liquid phase is discharged from the separating zone B-1 through a line F-1 and is introduced, optionally after being treated for the reduction of the amount of impurities, into a reaction zone (not shown) in which acetone is reacted with phenol to form BPA. The first solid phase is washed with a second liquid phase, described hereinafter, and the waste washing liquid is fed through a line E-1 to the reaction zone. The first solid phase thus washed is fed through a line D-1 to the first dissolution zone C-1 where it is dissolved in a waste washing liquid supplied from the second solid-liquid separation zone B-2 through a line E-2 to obtain a second solution. The second solution is fed through a line 83 to the second crystallization zone A-2 where the second solution is cooled to crystallize an adduct of BPA and phenol and to obtain a second slurry containing crystals of the adduct. The second slurry is discharged from the second crystallization zone A-2 and is introduced through a line 84 into the second solid-liquid separating zone B-2 where the slurry is separated into a second solid phase containing crystals of the adduct and a second liquid phase containing phenol. The second liquid phase is discharged from the separating zone B-2 and is introduced through a line F-2 into the first solid-liquid separation zone B-1 for washing the first solid phase as described previously. The second solid phase is washed with a third liquid phase, described hereinafter, and the waste washing liquid is fed through the line E-2 to the first dissolution zone C-1 and is used for dissolving the first solid phase, as described previously. The second solid phase thus washed is fed through a line D-2 to the second dissolution zone C-2 where it is dissolved in a waste washing liquid supplied from the third solid-liquid separation zone B-3 to obtain a third solution. The third solution is fed through a line 85 to the third crystallization zone A-3 where the solution is cooled to crystallize an adduct of BPA and phenol and to obtain a third slurry containing crystals of the adduct. The third slurry is discharged from the third crystallization zone A-3 and is introduced through a line 86 into the third solid-liquid separating zone B-3 where the slurry is separated into a third solid phase containing crystals of the adduct and a third liquid phase containing phenol. The third liquid phase is discharged from the separating zone B-3 and is introduced through the line F-3 into the second solid-liquid separation zone B-2 for washing the second solid phase as described previously. The third solid phase is washed with purified phenol, described hereinafter, and the waste washing liquid is fed through a line E-3 to the second dissolution zone C-2 to dissolve the second solid phase as described previously. The third solid phase thus washed is recovered through a line D-3 as product. As the phenol to be used for washing the third solid phase, phenol having APHA colour of 15 or less may be used. Generally available phenol contains an impurity, such as benzofuran and derivatives thereof and aromatic aldehydes and derivatives thereof, which is responsible for the colouring of BPA. Preferably there is used, as the purified phenol, purified phenol obtained by a method including the steps of (a) providing raw material phenol which contains impurity, such as mentioned immediately above, capable of forming a high boiling point material having a boiling point of higher than 185°C when heated at a temperature higher than the melting point of phenol, (b) contacting the raw material phenol with a strong-acid ion exchange resin at such a temperature as to convert at least part of the impurity into the high boiling point material and to obtain treated phenol, and (c) distilling the treated phenol at a temperature of 185°C or less to separate phenol as distillate from the high boiling point material. The raw material phenol is preferably selected from (A) phenol for industrial use, (B) phenol separated from a reaction product of phenol and acetone, (C) phenol separated from a crystallization product of BPA-containing phenol and (D) phenol used for washing a crystalline adduct. The raw material phenol preferably has a purity of at least 95% by weight, more preferably at least 97% by weight. Commercially available phenol of an industrial use grade with a purity of 95% or more may be suitably used as the above phenol (A). After completion of the reaction of acetone with phenol, the product is generally subjected to a separation treatment for removing a part of unreacted phenol therefrom. The phenol thus recovered may be used as raw material phenol (B). The product obtained by reaction of acetone with phenol is treated to form a crystalline adduct of BPA and phenol. Crystallization is generally performed at a temperature of about 41-80°C. After crystallization, the mixture is subjected to solid-liquid separation to separate the mixture into a crystalline adduct and a mother liquor. Generally, such crystallization and solid-liquid separation is repeated several times. Thus, phenol is recovered as a mother liquor in each of the solid-liquid separation stages. Such recovered phenol may be used as raw material phenol (C). The phenol recovered in the initial crystallization and separation step is preferably used. Phenol which has been used for washing the crystalline adduct is recovered. Such phenol may be suitably reused, after being purified, for washing the adduct. Thus, phenol recovered in the washing step may be used as raw material phenol (D). The raw material phenol (B)-(D) may be one recovered in any BPA/phenol adduct production processes. The purification of above raw material phenol (A)-(D) is performed as follows. The raw material phenol is first contacted with a strong-acid ion exchange resin, generally a sulfonic acid-type ion exchange resin, such as a sulfonated styrene-divinylbenzene copolymer, a sulfonated, crosslinked styrene polymer, a phenol-formaldehyde-sulfonic acid resin or a benzene-formaldehyde-sulfonic acid resin. The ion exchange resin has a crosslinked structure and is insoluble in water. Known sulfonic acid-type ion exchange resins are of a gel-type or a microporous-type. While both types of the ion exchange resins may be used for the purpose of the present invention, the use of a gel-type ion exchange resin is advisable because the activity thereof remains unchanged during use. The gel-type ion exchange resin generally has a degree of crosslinking (the amount of the crosslinking agent contained in the resin) of 10% by weight or less, preferably 5% by weight or less. Illustrative of suitable commercially available, gel-type ion exchange resins are Amberlite, Amberlyst (both manufactured by Rohm & Haas Company) and DIAION (manufactured by Mitsubishi Kasei, Inc.). The contact of the raw material phenol with the ion exchange resin may be carried out by passing the raw material phenol through a fixed layer of the ion exchange packed in a tower or by stirring a mixture of the phenol and the ion exchange resin in a vessel. The contact is generally performed at 45-150°C, preferably 50-100°C for 5-200 minutes, preferably 15-60 minutes. It is preferred that the raw material phenol have a water content of 0.5% by weight or less, more preferably 0.1% by weight or less, for reasons of improved impurity removing effect. The removal of moisture from the raw material phenol may be effected by azeotropic distillation using a suitable known azeotrope agent. By the contact with the ion exchange resin, the impurities such as benzofuran and derivatives thereof and aromatic aldehydes and derivatives thereof contained in the raw material phenol are converted into high boiling point substances with the ion exchange resin serving as a catalyst. The raw material phenol which has been treated with the strong-acid ion exchange resin is then distilled to obtain purified phenol as a distillate, with high boiling point impurities formed in the previous treatment with the ion exchange resin being separated as distillation residues. The distillation is performed under conditions so that the high boiling point impurities are not contained in the distillate. To achieve this purpose, it is preferable to perform the distillation at a temperature of 185°C or less. At a temperature higher than 185°C, the high boiling point impurities tend to be decomposed and to contaminate the distillate. While the distillation may be carried out at any desired pressure, a reduced pressure of 50-600 Torr is preferably used. The thus obtained purified phenol has an APHA colour of 10 or less so that it does not adversely affect the hue of BPA when used for washing the adduct of BPA and phenol. The illustrated embodiment of the invention uses three crystallization zones. However, the number of the crystallization zones is not limited to only three but generally can be "n" which is two or more. The liquid phase obtained in one solid-liquid separation zone may be used as at least part of the washing liquid for washing the solid phase obtained in the stage which immediately precedes the one separation zone. If desired, a part of the waste washing liquid obtained in the one separation zone may be used in conjunction with the liquid phase of the one separation zone for washing the solid phase of the immediately preceding separation zone. Further, the waste washing liquid obtained in one solid-liquid separation zone may be used as at least part of the solvent for dissolving the solid phase obtained in the stage which immediately precedes the one separation zone. If desired, a part of the liquid phase obtained in the one separation zone may be used in conjunction with the waste washing liquid of the one separation zone for dissolving the solid phase of the immediately preceding separation zone. In the process of this invention, the purity of the solvent phenol to be used for dissolving the solid phase obtained in one solid-liquid separation zone is higher than the solvent used for dissolving the solid phase obtained in the adjacent separation zone located upstream of the one separation zone. Further, the purity of the washing liquid used for washing the solid phase obtained in one solid-liquid separation zone is higher than the washing liquid used for washing the solid phase obtained in the adjacent separation zone located upstream of the one separation zone. Therefore, the content of impurities in the slurry in one crystallization zone is smaller than that in the slurry of any upstream crystallization zone. The term "impurities" used immediately above is intended to refer to by-products produced during the reaction of phenol with acetone and include, for example, isomers of BPA, chroman and derivatives thereof. In the process of this invention, the adduct is subjected to washing with purified phenol in the downstream end, n-th stage only. Nonetheless, the product crystalline adduct has a high purity. The following Examples and Reference Example will further illustrate the present invention. "Percentages" are by weight. The APHA number referred to in the examples is measured in accordance with the method specified in ASTM D 1686, Standard Test Method for Color of Solid Aromatic Hydrocarbons and Related Materials in the Molten State". Reference Example Raw material phenol (water content: 0.1%) was contacted with a sulfonic acid-type cation exchange resin (Amberlite IR-118H + , manufactured by Rohm & Haas Company) at 80°C for 50 minutes. The thus treated phenol was then distilled at a distillation tower bottom temperature of 175°C, a tower top pressure of 560 Torr to obtain purified phenol whose APHA colour was 5. Acetone was reacted with phenol in the presence of an acid catalyst to obtain a mixture containing BPA and phenol. The mixture was then cooled to 50°C to obtain 3000 g of a first slurry containing 20% of a crystalline adduct of BPA and phenol. The first slurry was suction filtered at 50°C to obtain a first solid phase and 2250 g of a first mother liquor (A-ML). The first solid phase was washed with 600 g of the above purified phenol to obtain a first washed adduct and 580 g of a first waste washing liquid (B-WW). The first washed adduct was dissolved into 1310 g of the above purified phenol and recrystallized at 50°C to obtain a second slurry containing 20% of a crystalline adduct of BPA and phenol. The second slurry was suction filtered at 50°C to obtain a second solid phase and 1430 g of a second mother liquor (C-ML). The second solid phase was washed with 600 g of the above purified phenol to obtain a second washed adduct and 580 g of a second waste washing liquid (D-WW). The second washed adduct was again washed with 600 g of the above purified phenol to obtain a third washed adduct and 580 g of a third waste washing liquid (E-WW). The third washed adduct was found to have APHA colour of 5 and an impurity content of 100 ppm by weight. Example 1 Acetone was reacted with phenol in the presence of an acid catalyst to obtain a mixture containing BPA and phenol. The mixture was then cooled to 50°C to obtain 3000 g of a first slurry containing 20% of a crystalline adduct of BPA and phenol. The first slurry was suction filtered at 50°C to obtain a first solid phase and a first mother liquor. The first solid phase was washed with 700 g of C-ML obtained in the above Reference Example to obtain a first washed adduct and a first waste washing liquid. The first washed adduct was dissolved into a mixture of 730 g of C-ML and 580 g of D-WW, both of which were obtained in the above Reference Example, and recrystallized at 50°C to obtain a second slurry containing 20% of a crystalline adduct of BPA and phenol. The second slurry was suction filtered at 50°C to obtain a second solid phase and a second mother liquor. The second solid phase was washed with 580 g of E-WW in the above Reference Example to obtain a second washed adduct and a second waste washing liquid. The second washed adduct was again washed with 600 g of the purified phenol obtained in the above Reference Example to obtain a third washed adduct and a third waste washing liquid. The third washed adduct was found to have APHA colour of 5 and an impurity content of 100 ppm by weight. From the results of Example 1 and the Reference Example, it is appreciated that the product obtained in Example 1 has the same quality as that in the Reference Example, in spite of the fact that purified phenol is used only in the final washing step.

Claims: A process for the production of a crystalline adduct of bisphenol A and phenol, comprising: (A) a first stage including the steps of: (A-a) feeding a solution of bisphenol A dissolved in phenol to a crystallization zone and cooling same to crystallize an adduct of bisphenol A and phenol and to obtain a slurry containing crystals of the adduct, (A-b) discharging said slurry from said crystallization zone and introducing same into a solid-liquid separating zone to separate said slurry into a solid phase containing crystals of the adduct and a liquid phase containing phenol, and (A-c) washing said solid phase with a washing liquid to obtain a washed solid phase and a used washing liquid; and (B) one or more, second to n-th stages following said first stage and each including the steps of: (B-a) dissolving the washed solid phase obtained in the immediately preceding stage into solvent phenol to obtain a solution, (B-b) feeding said solution obtained in step (B-a) to a crystallization zone and cooling same to crystallize an adduct of bisphenol A and phenol and to obtain a slurry containing crystals of the adduct, and (B-c) discharging said slurry obtained in step (B-b) from said crystallization zone and introducing same into a solid-liquid separating zone to separate said slurry into a solid phase containing crystals of the adduct and a liquid phase containing phenol, and (B-d) washing said solid phase obtained in step (B-c) with a washing liquid to obtain a washed solid phase and a used washing liquid; wherein said washing liquid used in said n-th stage is purified phenol, wherein said washed solid phase obtained in said n-th stage is recovered as a product adduct, wherein at least one of a portion of said used washing liquid and a portion of said liquid phase obtained in each of said second to n-th stages is recycled to step (B-a) thereof as at least part of said solvent phenol, wherein at least one of a portion of said used washing liquid and a portion of said liquid phase obtained in each of said second to n-th stages is recycled to step (B-d) of the preceding stage thereof as at least part of said washing liquid, wherein the purity of the solvent phenol used in each of said second to n-th stages is controlled so that the content of impurities in the solvent phenol used in one stage of said second to n-th stages is greater than that of the stage immediately following said one stage, and wherein the purity of the washing liquid used in each of said second to n-th stages is controlled so that the content of impurities in the washing liquid used in one stage of said second to n-th stages is greater than that of the stage immediately following said one stage. A process according to Claim 1, wherein n is 3.

Inventors: ASAOKA SACHIO, KAMEDA TAKAO, KOUZAKI TAKESHI, MAEJIMA TETSUO, MORIYA NOBUO, NISHIJIMA HIROAKI, ONDA NOBUHIRO, SAKASHITA KOUJI, SHIMODA KEIJI, YASUI MAKOTO, ASAOKA, SACHIO, KAMEDA, TAKAO, KOUZAKI, TAKESHI, MAEJIMA, TETSUO, MORIYA, NOBUO, NISHIJIMA, HIROAKI, ONDA, NOBUHIRO, SAKASHITA, KOUJI, SHIMODA, KEIJI, YASUI, MAKOTO
Applicants: CHIYODA CHEM ENG CONSTRUCT CO, CHIYODA CORPORATION
Application year: 1992
Main classification: C07C39
IPC codes: C07C37