Patent ID: 7816556
Filing Date: 2010-10-19
Classification: C07C

Abstract:
1. A process for making a polycarboxylic acid composition, said process comprising: (a) feeding an oxidizable aromatic compound to a primary oxidation zone and subjecting a multi-phase reaction medium to oxidation in said a primary oxidation zone under primary oxidation conditions sufficient to produce an initial slurry comprising an initial solid and an initial liquid, wherein said primary oxidation conditions include a primary oxidation temperature in the range of from about 125 to about 200° C., wherein said initial solid comprises a plurality of crude terephthalic acid (CTA) particles in liquid; (b) subjecting at least a portion of said initial slurry to oxidative digestion in a first digestion zone under first digestion conditions sufficient to produce a first digestion product slurry, wherein at least about 30 percent of the initial liquid present in the initial slurry withdrawn from the primary oxidation zone is retained in the initial slurry subjected to the first digestion zone and said first digestion conditions include a first digestion temperature that is within 20° C. of said primary oxidation temperature, and (c) subjecting at least a portion of said first digestion product slurry to oxidative digestion in a second digestion zone under second digestion conditions sufficient to produce a second digestion product slurry, wherein said second digestion conditions include a second digestion temperature that is greater than both said primary oxidation temperature and said first digestion temperature; wherein the ratio of moles of total carbon oxides produced in the process of steps a), b) and c) to moles of oxidizable aromatic compound fed is in the range of from about 0.02:1 to about 0.25:1 and the time averaged concentration of 4-carboxybenzoic acid in the solid polycarboxylic acid composition withdrawn from the second digestion zone is in the range of from 1 to 500 ppmw.