Method of purifying aromatic polycarboxylic acid

Abstract

Crude polycarboxylic acid is slurried in an aqueous medium and the slurry is brought into contact with a metal catalyst while preventing catalyst components thereof from contaminating crystals. Since hydrogenation or decarbonylation of a polymerization inhibitory substance or a substance causing coloration can efficiently proceed at a low temperature while suppressing side reactions, a product having such a quality as to permit direct use thereof as such for polymerization can be obtained with good productivity. Also, since the contact temperature can be lowered, simplification of apparatus and energy saving may be attained.

1 . A method of purifying aromatic polycarboxylic acid, comprising a step of slurrying a crude aromatic polycarboxylic acid in an aqueous medium and a step of bringing the slurry into contact with a metal catalyst in the absence of oxygen while maintaining the aromatic polycarboxylic acid in a slurried state at such a temperature that aromatic polycarboxylic acid dissolved in the aqueous medium exists together with undissolved aromatic polycarboxylic acid and while preventing catalyst components from contaminating crystals.  
   
   
       2 . The method according to  claim 1 , wherein said contact with the metal catalyst is performed in the presence of hydrogen.  
   
   
       3 . The method according to  claim 1 , wherein the metal catalyst comprises a carrier and a Group  8  metal supported on the carrier.  
   
   
       4 . The method according to  claim 1 , wherein a basket in which the metal catalyst is held is immersed into the slurry, so that catalyst components thereof are prevented from contaminating the crystals of the purified aromatic polycarboxylic acid.  
   
   
       5 . The method according to  claim 1 , wherein the aromatic polycarboxylic acid is terephthalic acid.  
   
   
       6 . The method according to  claim 1 , wherein the aromatic polycarboxylic acid is 2,6-naphthalenedicarboxylic acid.  
   
   
       7 . The method according to  claim 1 , wherein the aromatic polycarboxylic acid is 4,4′-biphenyldicarboxylic acid.  
   
   
       8 . The method according to  claim 2 , wherein the metal catalyst comprises a carrier and a Group 8 metal supported on the carrier.  
   
   
       9 . The method according to  claim 2 , wherein a basket in which the metal catalyst is held is immersed into the slurry, so that catalyst components thereof are prevented from contaminating the crystals of the purified aromatic polycarboxylic acid.  
   
   
       10 . The method according to  claim 3 , wherein a basket in which the metal catalyst is held is immersed into the slurry, so that catalyst components thereof are prevented from contaminating the crystals of the purified aromatic polycarboxylic acid.  
   
   
       11 . The method according to  claim 2 , wherein the aromatic polycarboxylic acid is terephthalic acid.  
   
   
       12 . The method according to  claim 2 , wherein the aromatic polycarboxylic acid is 2,6-naphthalenedicarboxylic acid.  
   
   
       13 . The method according to  claim 2 , wherein the aromatic polycarboxylic acid is 4,4′-biphenyldicarboxylic acid.  
   
   
       14 . The method according to  claim 8 , wherein a basket in which the metal catalyst is held is immersed into the slurry, so that catalyst components thereof are prevented from contaminating the crystals of the purified aromatic polycarboxylic acid.