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

Abstract: A crystalline adduct of bisphenol A and phenol is produced by crystallization of a phenolic slurry of bisphenol A. The crystallization of the slurry is performed by continuously discharging a portion of the slurry from the crystallization zone into a plurality of cooling zones and then recycling the cooled slurry to the crystallization zone. The cooling zones are connected in parallel and they are operated so that at any one time one of the cooling zones can be cleaned of deposits of crystalline adduct without stopping the process. An apparatus having a plurality of coolers and suitable for effecting the above crystallization process is also disclosed.

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 colorless, 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 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. In accordance with the present invention there is provided a process for the production of a crystalline adduct of bisphenol A and phenol, comprising the steps of: providing a crystallization zone and a plurality of cooling zones connected in parallel with each other and each having a cooling surface adapted to cool a liquid upon contact therewith; feeding a solution of bisphenol A dissolved in phenol to the crystallization zone and cooling same to crystallize an adduct of bisphenol A and phenol and to obtain a slurry containing crystals of the adduct; discharging the slurry from the crystallization zone; introducing a portion of the slurry discharged from the crystallization zone to all of the cooling zones except one cooling zone whose cooling surface bears deposits of crystals of the adduct to cool the slurry introduced thereinto with the simultaneous formation of crystals of the adduct part of which deposit on the cooling surfaces thereof; recycling the cooled slurry to the crystallization zone so that the slurry in the crystallization zone is cooled; recovering the crystals from the slurry discharged from the crystallization zone; and removing the deposits from the cooling surface of the one cooling zone. The present invention also provides an apparatus carrying out a process for the production of a crystalline adduct of bisphenol A and phenol in accordance with this invention, comprising: a crystallization tower containing a slurry of crystals of an adduct of bisphenol A and phenol dispersed in phenol and having a recycling port and a discharge port; a plurality of coolers each having an inlet port and an outlet port; first conduit means extending between the discharge port of the crystallization tower and the inlet port of each of the coolers; second conduit means extending between the recycling port of the crystallization tower and the outlet port of each of the coolers; and pump means operable to continuously discharge part of the slurry from the crystallization tower, to pass the discharged slurry through the plurality of coolers with a selected one of the plurality of coolers being prevented from being fed with the discharged slurry and to return the discharged slurry after passage through the coolers to the recycling port, whereby the slurry within the crystallization tower is cooled with the recycled slurry which has been passed through the coolers to cause the crystals to grow. Yet further, the present invention also provides a crystallization device for use in a process for the production of a crystalline adduct of bisphenol A and phenol in accordance with this invention, comprising: a first crystallization tower for containing a slurry of crystals of an adduct of bisphenol A and phenol dispersed in phenol and having a recycling port, a discharge port and a feed port; a feed conduit connected to the feed port of the first crystallization tower for feeding a liquid mixture of bisphenol A and phenol; a second crystallization tower containing a slurry of crystals of an adduct of bisphenol A and phenol dispersed in phenol and having a recycling port, a discharge port and a feed port; a first group of two or more coolers each having inlet and outlet ports; a second group of two or more coolers each having inlet and outlet ports; a common cooler having inlet and outlet ports; feed conduit means extending between the discharge port of the first crystallization tower and the feed port of the second crystallization tower and having feed pump means for feeding a portion of the slurry in the first crystallization tower into the second crystallization tower through the feed conduit means; first introduction conduit means extending between the discharge port of the first crystallization tower and the inlet port of each of the coolers of the first group; first recycling conduit means extending between the recycling port of the first crystallization tower and the outlet port of each of the coolers of the first group; second introduction conduit means extending between the discharge port of the second crystallization tower and the inlet port of each of the coolers of the second group; second recycling conduit means extending between the recycling port of the second crystallization tower and the outlet port of each of the coolers of the second group; a recovery conduit in communication with the discharge port of the second crystallization port for discharging part of the slurry from the second crystallization tower therethrough for recovery; common introduction conduit means for communicating the inlet port of the common cooler with the discharge port of each of the first and second crystallization towers; common recycling conduit means for communicating the outlet port of the common cooler with the recycling port of each of the first and second crystallization towers; first pump means operable to continuously discharge part of the slurry from the first crystallization tower, to pass the discharged slurry through the first group of coolers and to return the discharged slurry after the passage of the coolers to the recycling port of the first crystallization tower; second pump means operable to continuously discharge part of the slurry from the second crystallization tower, to pass the discharged slurry through the second group of coolers and to return the discharged slurry after the passage of the coolers to the recycling port of the second crystallization tower; third pump means operable to continuously discharge part of the slurry from the first or second crystallization tower, to pass the discharged slurry through the common cooler and to return the discharged slurry after the passage of the common cooler to the recycling port of the first or second crystallization tower; and controlling means to control the operations of the first, second and third pump means so that selected one of the common cooler and first and second groups of cooler is prevented from being fed with the discharged slurry, whereby the slurry within each of the first and second crystallization towers is cooled with the recycled slurry which has been passed through the coolers to cause the crystals in each of the first and second crystallization towers to grow. The present invention will now be described in 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, the apparatus shown has two, first and second crystallization towers A and B which are connected in series by lines 102 and 104. The reference numerals 113 and 114 denote coolers associated with the first crystallization tower A while the reference numerals 116 and 117 denote coolers associated with the second crystallization tower B. Designated as 115 is a common cooler which is used as a substitute for one of the coolers 113, 114, 116 and 117. A raw material feed of a solution of BPA dissolved in phenol is continuously introduced through a line 101 to a lower part of the first crystallization tower A where the feed solution is cooled to a predetermined temperature so that BPA is crystallized as an adduct of phenol to form a slurry containing seed crystals of the adduct. Part of the slurry is discharged from the tower through the line 102 and a portion of the discharged slurry is fed through a pump 120 and the line 104 to the second crystallization tower B. In the tower B, the slurry is further cooled so that the crystals of the adduct grow. Part of the slurry is discharged from the tower B through a line 105 and a portion of the discharged slurry is recovered through a line 107. The slurry product thus recovered is introduced into a solid-liquid separator to obtain the adduct crystals. For the purpose of effecting the cooling in the first and second crystallization towers A and B, portions of the slurries discharged from the towers A and B are introduced into selected two of the coolers 113-117 and recycled to the towers A and B through lines 103 and 106, respectively. More particularly, a portion of the slurry discharged from the first crystallization tower A is fed to selected two of the coolers 113-115 by operation of selected two of pumps 123-125 and recycled to the tower A through the line 103. The temperature within the tower A depends upon the temperatures and feed rates of the liquids introduced through the lines 101 and 103. The crystallization of the adduct proceeds until the saturation concentration at that temperature within the tower A is reached. Similarly, a portion of the slurry discharged from the second crystallization tower B is fed to selected two of the coolers 115-117 by operation of selected two of pumps 125-127 and recycled to the tower B through the line 106. The temperature within the tower B depends upon the temperatures and feed rates of the liquids introduced through the lines 104 and 106. The crystallization of the adduct proceeds until the saturation concentration at that temperature within the tower B is reached. Means including valves are provided and periodically switched so that selected four of the coolers 113-117 are used for the cooling of the towers A and B, with the remaining cooler being subjected to a cleaning treatment. An example of the sequence of the operation of the coolers 113-117 is given in Table 1 below. Operation Mode Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 Cooler 113 A - A A A Cooler 114 A A A - A Cooler 115 - A B A B Cooler 116 B B - B B Cooler 117 B B B B - In Table 1, the letter "A" indicates that the cooler is used for cooling the first crystallization tower while the letter "B" indicates that the cooler is used for cooling the second crystallization tower B. The symbol "-" indicates that the cooler is not used for cooling the tower A or B but is subjected to a cleaning treatment. For instance, in Mode 5, the cooling of the first crystallization tower A is performed with the coolers 113 and 114 while the second crystallization tower B is cooled with the coolers 115 and 116, with the cooler 117 being subjected to cleaning of the heat-exchange surface. After the termination of a predetermined period of time through which the operation in Mode 5 has been continued, the control means are operated so that the process is switched to Mode 1. The cleaning of the cooler is performed for removing deposits of crystalline adduct from the cooling (heat-exchange) surface thereof. This can be suitably effected by introducing a heating medium into the cooler to heat and fuse the deposits on the heat-exchange surface. Since the period of time required for regenerating one cooler is much shorter than the period of time through which a regenerated cooler remains operable, the above cycle shown in Table 1 can work without difficulty. Thus, in the illustrated embodiment, two or more cooling zones connected in parallel with each other are provided for one crystallization zone. A portion of the slurry discharged from the crystallization zone is fed to all of the associated cooling zones except one cooling zone whose cooling surface bears deposits of crystals of the adduct to cool the slurry introduced thereinto with the simultaneous formation of crystals of the adduct part of which deposits on the cooling surfaces thereof. The one cooling zone is treated for removing the deposits from the cooling surface thereof during the cooling of the tower with the all but one cooling zones In the above-described embodiment, the line including the cooler 115 and the pump 125 is commonly used for the cooling of the first or second crystallization towers A and B while the coolers 113 and 114 and coolers 116 and 117 are exclusively used for the first and second crystallization towers A and B, respectively. However, if desired, respective coolers 113-117 may be commonly used for the towers A and B. While the process of this invention can be performed with only one crystallization tower, it is preferred that two crystallization towers be used as illustrated in the drawing, for reasons of obtaining large crystals of the adduct having an improved purity. Namely, by using two towers connected in series, it is possible to make the difference in temperature between the inside of each of the towers and the BPA/phenol feed so that rapid crystallization of the adduct can be avoided, enabling the formation of large adduct crystals with a high purity. Additionally, the use of two towers permits the lowering of the load of the coolers so that the deposition of the adduct on the heat-exchange surfaces of the coolers can be reduced. In each of the coolers, the slurry containing crystals of the adduct is cooled by indirect heat exchange with a cooling medium. Crystals are formed after the liquid phase of the slurry has become in a supersaturated state. Since seed crystals are already present, the growth of the crystals predominantly proceeds in the coolers rather than the formation of new crystal seeds. As the process proceeds, however, scales composed of fine crystals of the adduct and impurities begin depositing on the heat-exchange surfaces. Once the deposits are formed, crystallization proceeds acceleratingly with the deposits serving as seeds of crystals and the heat-exchange efficiency of the cooler is rapidly deteriorated to the extent that cooling failure occurs. Further, part of the deposits is occasionally spontaneously removed from the heat-exchange surface and the resulting scales contaminate the slurry in the crystallization towers to cause a reduction of the purity of the product. Thus, it becomes necessary to clean such a cooler for the removal of scales. Conventionally, the cleaning of the cooler has been performed by removing the cooler from the process line after stopping the process. According to the process of the present invention, the above problems have been satisfactorily solved. When scales begin forming on the heat-exchange surface of a cooler, the feed of the slurry to the cooler is shifted to another, fresh cooler and a heating medium is fed to the fouled cooler to fuse and remove the scale before the growth thereof. Accordingly, it is not necessary to stop the process. Further, the regeneration of the cooler can be easily effected.

Claims: A process for the production of a crystalline adduct of bisphenol A and phenol, comprising the steps of: providing a crystallization zone (A; B) and a plurality of cooling zones (113-115; 115-117) connected in parallel with each other and each having a cooling surface adapted to cool a liquid upon contact therewith; feeding a solution of bisphenol A dissolved in phenol to said crystallization zone (A; B) and cooling same to crystallize an adduct of bisphenol A and phenol and to obtain a slurry containing crystals of the adduct; discharging the slurry from said crystallization zone; introducing a portion of the slurry discharged from said crystallization zone to all of said cooling zones (113-115; 115-117) except one cooling zone whose cooling surface bears deposits of crystals of the adduct to cool the slurry introduced thereinto with the simultaneous formation of crystals of the adduct on the cooling surfaces thereof; recycling the cooled slurry to said crystallization zone (A; B) so that the slurry in said crystallization zone is cooled; recovering the crystals from the slurry discharged from said crystallization zone; and removing the deposits from the cooling surface of said one cooling zone. A process as claimed in Claim 1, wherein said removal of the deposits is performed by heating the cooling surface by contact with a heating medium. A process as claimed in Claim 1 or Claim 2, wherein each of said cooling zones (113-117) is provided with a pump (123-127) operable for feeding the slurry to the corresponding cooling zone and to recycle the cooled slurry to said crystallization zone and wherein the pump of said one cooling zone is also warmed by contact with said heating medium for the removal of deposits of the crystals formed during previous use. An apparatus for carrying out a process for the production of a crystalline adduct of bisphenol A and phenol as defined in Claim 1, comprising: a crystallization tower (A; B) containing a slurry of crystals of an adduct of bisphenol A and phenol dispersed in phenol and having a recycling port and a discharge port; a plurality of coolers (113-115; 115-117) each having an inlet port and an outlet port; first conduit means (102; 105) extending between said discharge port of said crystallization tower and the inlet port of each of said coolers; second conduit means (103; 106) extending between said recycling port of said crystallization tower and the outlet port of each of said coolers; and pump means (123-125; 125-127) operable to continuously discharge part of said slurry from said crystallization tower, to pass the discharged slurry through said plurality of coolers with a selected one of said plurality of coolers being prevented from being fed with the discharged slurry and to return the discharged slurry after passage through said coolers to said recycling port, whereby the slurry within said crystallization tower is cooled with the recycled slurry which has been passed through said coolers to cause the crystals to grow. A crystallization device for use in a process for the production of a crystalline adduct of bisphenol A and phenol as defined in Claim 1, comprising: a first crystallization tower (A) for containing a slurry of crystals of an adduct of bisphenol A and phenol dispersed in phenol and having a recycling port, a discharge port and a feed port; a feed conduit (101) connected to said feed port of said first crystallization tower for feeding a liquid mixture of bisphenol A and phenol; a second crystallization tower (8) containing a slurry of crystals of an adduct of bisphenol A and phenol dispersed in phenol and having a recycling port, a discharge port and a feed port; a first group of two or more coolers (113-114) each having inlet and outlet ports; a second group of two or more coolers (116-117) each having inlet and outlet ports; a common cooler (115) having inlet and outlet ports; feed conduit means (102, 104) extending between said discharge port of said first crystallization tower (A) and the feed port of said second crystallization tower (B) and having feed pump means (120) for feeding a portion of the slurry in said first crystallization tower (A) into said second crystallization tower (B) through said feed conduit means; first introduction conduit means (102) extending between said discharge port of said first crystallization tower (A) and the inlet port of each of said coolers of said first group; first recycling conduit means (103) extending between said recycling port of said first crystallization tower (A) and the outlet port of each of said coolers of said first group; second introduction conduit (105) means extending between said discharge port of said second crystallization tower (B) and the inlet port of each of said coolers of said second group; second recycling conduit means (106) extending between said recycling port of said second crystallization tower (B) and the outlet port of each of said coolers of said second group; a recovery conduit (107) in communication with said discharge port of said second crystallization port for discharging part of the slurry from said second crystallization tower (B) therethrough for recovery; common introduction conduit means for communicating the inlet port of said common cooler (115) with the discharge port of each of said first and second crystallization towers; common recycling conduit means for communicating the outlet port of said common cooler (115) with the recycling port of each of said first and second crystallization towers (A, B); first pump means (123, 124) operable to continuously discharge part of the slurry from said first crystallization tower (A), to pass the discharged slurry through said first group of coolers (113, 114) and to return the discharged slurry after the passage of said coolers to said recycling port of said first crystallization tower (A); second pump means (126, 127) operable to continuously discharge part of the slurry from said second crystallization tower (B), to pass the discharged slurry through said second group of coolers (116, 117) and to return the discharged slurry after the passage of said coolers to said recycling port of said second crystallization tower (B); third pump means (125) operable to continuously discharge part of the slurry from said first or second crystallization tower (A, B), to pass the discharged slurry through said common cooler (115) and to return the discharged slurry after the passage of said common cooler to said recycling port of said first or second crystallization tower (A, B); and controlling means to control the operation of said first, second and third pump means (123, 124; 126, 127; 125) so that selected one of said common cooler (115) and first and second groups of coolers (113, 114; 116, 117) is prevented from being fed with the discharged slurry, whereby the slurry within each of said first and second crystallization towers (A, B) is cooled with the recycled slurry which has been passed through the said coolers (113-117) to cause the crystals in each of said first and second crystallization towers (A, B) to grow.

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