Method for heating a crude carboxylic acid slurry in a post oxidation zone by the addition of steam

Abstract

The present invention relates to a process for heating a secondary oxidizer with steam. More specifically, the present invention relates to a process for heating a secondary oxidizer with steam in a process for the production of a crystallized product. A process to produce a crystallized product comprises the following steps (a) oxidizing in an primary oxidation zone an aromatic feedstock to produce a crude carboxylic acid slurry; (b) oxidizing said crude carboxylic acid slurry in a post oxidation zone in the presence of steam to form a post oxidation product; (c) purifying said post oxidation product to a decolorized post oxidation product; and (d) crystallizing in a crystallization zone said post oxidation product to form a crystallized product.

We claim:  
     
         1 . A process to produce a post oxidation product comprising the following steps: 
 (a) oxidizing in a post oxidation zone a crude carboxylic acid slurry in the presence of steam to form said post oxidation product; wherein said post oxidation zone comprises at least one post oxidation device; wherein said crude carboxylic acid slurry comprises at least one carboxylic acid;    (b) purifying said post oxidation product to form a decolorized post oxidation product having b* color of less than 4.5.    
     
     
         2 . A process according to  claim 1  where said decolorized post oxidation product has a b* color less than 3.5.  
     
     
         3 . A process according to  claim 1  wherein said carboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof.  
     
     
         4 . A process according to  claim 1  wherein said carboxylic acid is terephthalic acid.  
     
     
         5 . A process according to  claim 4  wherein said steam is used to heat said post oxidation zone to a temperature in a range from about 180° C. to about 280° C.  
     
     
         6 . A process according to  claim 5  wherein said post oxidation zone is operated at a pressure of about 10 barg to about 50 barg.  
     
     
         7 . A process to produce a crystallized product said process comprising the following steps: 
 (a) oxidizing in a post oxidation zone said crude carboxylic acid slurry in a post oxidation zone in the presence of steam to form a post oxidation product and an offgas stream; wherein said post oxidation zone comprises at least one post oxidation device;    (b) purifying said post oxidation product before or after a crystallization zone to form a decolorized post oxidation product having b* color of less than 4.5; and    (c) crystallizing in said crystallization zone said post oxidation product; wherein said crystallization zone comprises at least one crystallizer.    
     
     
         8 . A process according to  claim 7  wherein said purified post oxidation product has a b* color of less than 3.  
     
     
         9 . A process according  claim 7  wherein said carboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof.  
     
     
         10 . A process according to  claim 7  wherein said carboxylic acid is terephthalic acid.  
     
     
         11 . A process according to  claim 10  wherein said steam is used to heat the post oxidation zone to a temperature in a range from about 180° C. to about 280° C.  
     
     
         12 . A process according to  claim 11  wherein said post oxidation zone is operated at a pressure of about 10 barg to about 50 barg.  
     
     
         13 . The process according to  claim 10  wherein said crystallizer is operated at a temperature between about 140° C. and 190° C.  
     
     
         14 . A process to produce a post oxidation product comprising oxidizing in a post oxidation zone a crude carboxylic acid slurry in the presence of steam to form said post oxidation product; wherein said crude carboxylic acid slurry comprises terephthalic acid; wherein said post oxidation zone comprises at least one post oxidation device; wherein said post oxidation product has a b* color of less than about 4.5.  
     
     
         15 . A process according to  claim 14  wherein said steam is used to heat the post oxidation zone to a temperature in a range from about 180° C. to about 280° C.  
     
     
         16 . A process according to  claim 15  wherein said post oxidation zone is operated at a pressure of about 10 barg to about 50 barg.  
     
     
         17 . A process to produce crystallized product said process comprising the following steps: 
 (a) oxidizing said crude carboxylic acid slurry in a post oxidation zone in the presence of steam to form a post oxidation product; wherein said post oxidation zone comprises at least one post oxidation device; wherein the pressure of said post oxidation zone is between about 10 barg to about 50 barg; and    (b) crystallizing in a crystallization zone said post oxidation product to form a crystallized product; wherein said crystallization zone comprises at least one crystallizer; wherein said crystallizer is operated at a temperature between about 140° C. and 190° C.; and wherein said crystallized product has a b* color of less than 4.5.    
     
     
         18 . A process according to  claim 17  where said crystallized product has a b* color of less than 3.