BUBBLE COLUMN REACTOR BASED DIGESTER AND METHOD FOR ITS USE

摘要

A method for digestion of a crude terephthalic slurry obtained from oxidation of para-xylene in a bubble column reactor oxidation process is provided. The method is conducted in one or more bubble column reactors having one or more segregrated zones defined by horizontal baffles and particle flow through the digestion system is controlled to maximize conversion of partial oxidation intermediates to terephthalic acid while minimizing formation of other contaminant products. Temperature, oxygen flow and content as well as other process and equipment variables are controlled throughout the process to support formation of terephthalic acid. Also provided are bubble column digestion systems structured to conduct the digestion method.

主权项

1. A method for purification of crude terephthalic acid comprising:
a) obtaining a digester feed slurry of particles of crude terephthalic acid, comprising terephthalic acid, 4-carboxybenzaldehyde and p-toluic acid in a solvent liquid comprising aqueous acetic acid and a catalyst system comprising at least one heavy metal compound; b) feeding the crude terephthalic acid slurry to a first digestion zone of a bubble column system; c) heating the crude terephthalic acid slurry to a temperature of from about 150° C. to about 280° C. either before entry to the first digestion zone or when within the first digestion zone; d) supplying a gas comprising oxygen to the first digestion zone where the superficial velocity of the gas rising near the top of the first digestion zone is in a range of from about 0.1 cm/s to about 8 cm/s; e) at least partially dissolving particles of crude terephthalic acid in the acetic acid thereby releasing at least some 4-carboxybenzaldehyde and p-toluic acid from the particles and exposing the dissolved 4-carboxybenzaldehyde and p-toluic acid to the oxygen to effect oxidation to terephthalic acid, and to obtain a first stage digester slurry; f) passing the first stage digester slurry to a second digestion zone which is optionally located vertically beneath the first digestion zone; g) supplying a gas comprising oxygen to a lower portion of the second digestion zone; wherein a supply rate of the gas to the second digestion zone is less than the rate of supply to the first digestion zone; and h) dissolving and releasing additional 4-carboxybenzaldehyde and p-toluic acid from the particles and exposing the dissolved 4-carboxybenzaldehyde and p-toluic acid to the oxygen to effect additional oxidation to terephthalic acid, and to obtain a second stage digester slurry; i) optionally, moving the second stage digester slurry through one or more further digestion zones structured similar to the second digestion zone and optionally vertically beneath the second digestion zone; j) removing the resulting terephthalic acid crystal slurry from the last digestion zone; and k) isolating the obtained terephthalic acid crystal particles.