Process for purifying phenol-containing bisphenol A

Abstract

The process of the present invention comprises a first step in which crude molten bisphenol A containing phenol is supplied to a flash evaporator and separated into a gaseous phase comprising phenol and a liquid phase comprising bisphenol A and residual phenol, and a second step in which the liquid phase obtained in the first step is heated by a thin film evaporator and separated into a gaseous phase comprising phenol and a liquid phase comprising concentrated bisphenol A and residual phenol, part of the liquid phase obtained in the second step being circulated to the first step and supplied to the flash evaporator along with crude molten bisphenol A. It is possible with this process to obtain high-quality bisphenol A stably from phenol-containing bisphenol A.

1. A process for purifying phenol-containing bisphenol A comprising
 a first step in which crude molten bisphenol A containing phenol is supplied to a flash evaporator and separated into a gaseous phase comprising phenol and a liquid phase comprising bisphenol A and residual phenol, and  
 a second step in which the liquid phase obtained in the first step is heated by a thin film evaporator and separated into a gaseous phase comprising phenol and a liquid phase comprising concentrated bisphenol A and residual phenol,  
 wherein part of the liquid phase obtained in the firstsecond step being circulated to the first step and supplied to the flash evaporator along with crude molten bisphenol A, and further comprising 
   a purification step with water vapor in which the concentrated liquid phase of bisphenol A obtained in the second step is supplied to the top of a packed column to let it flow down in the column while water vapor is blown into the column from its bottom to let it rise in the column so that phenol in the concentrated liquid phase of bisphenol A is removed entrained by water vapor .    
 
     
     
       2. The process according to  claim 1 , wherein phenol-containing crude molten bisphenol A to be supplied to the flash evaporator has been passed through a light ends removing step which comprises melting an adduct of bisphenol A and phenol, and heating it by a thin film evaporator to remove the light ends including phenol. 
     
     
       3. The process according to  claim 2 , wherein removal of light ends including phenol is conducted by melting an adduct of bisphenol A and phenol, heating it by a thin film evaporator, and supplying the product to a gas/liquid separator for separating it into a gaseous phase comprising light ends including phenol and a liquid phase comprising bisphenol A and residual phenol. 
     
     
       4. The process according to  claim 2 , wherein removal of light ends including phenol is conducted under reduced pressure and  at a pressure of more than 60 Torr and not more than  400  Torr. 
     
     
       5. The process according to any one of   claim 2 , wherein the thin film evaporator used in the light ends removing step is a natural falling-thin film evaporator. 
     
     
       6. The process according to any one of   claim 1 , wherein the thin film evaporator used in the second step is a natural falling-thin film evaporator. 
     
     
       7. The process according to any one of   claim 1 , wherein the first step is conducted under a pressure of not higher than 60 Torr. 
     
     
       8. The process according to any one of   claim 1 , wherein the separation into a gaseous phase and a liquid phase in the second step is conducted under a pressure of more than 60 Torr. 
     
     
       9. The process according to any one of  claim 1  further comprising a purification step with water aport in which the concentrated liquid phase of bisphenol A obtained in the second step is supplied to the top of a packed column to let it flow down in the column while water vapor is blown into the column from its bottom to let it rise in the column so that phenol in the concentrated liquid phase of bisphenol A is removed entrained by water vapor. 
     
     
       10. A process for purifying phenol-containing bisphenol A comprising the steps of:
 supplying a melt of an adduct of bisphenol A and phenol to a natural falling-thin film evaporator maintained under reduced pressure and a pressure of not less than 100 Torr,  
 heating said melt to 160° C. to 220° C. to evaporate light ends including phenol to yield crude molten bisphenol A comprising bisphenol A and residual phenol,  
 supplying said melt of adduct of bisphenol A and phenol to a flash evaporator maintained under a pressure of not more than 60 Torr to separate it into a liquid phase and a gaseous phase by flash evaporation,  
 supplying said liquid phase to a natural falling-thin film evaporator maintained under a pressure of not more than 60 Torr,  
 heating said liquid phase to 170° C. to 200° C. and evaporating phenol to obtain a concentrated liquid phase of bisphenol A,  
 mixing part of said concentrated liquid phase of bisphenol A with said crude molten bisphenol A and supplying it to a flash evaporator to be subject to flash evaporation, and supplying the rest of the liquid phase to the top of a packed column to let if flow down in the column into which water vapor is being blown from the bottom so that residual phenol is entrained by water vapor and removed.