Method and apparatus for preparing purified terephthalic acid

An apparatus for producing purified terephthalic acid from crude terephthalic acid comprising:

• means for dissolving crude terephthalic acid in a selective crystallization solvent at an elevated temperature to form a first solution;
• means for crystallizing first stage purified terephthalic acid from said first solution at a reduced temperature;
• means for separating said crystallized first stage purified terephthalic acid from said solution;
• means for redissolving said separated first stage purified terephthalic acid in said selective crystallization solvent at an elevated temperature to form a second solution;
• means for crystallizing second stage purified terephthalic acid from said second solution at a reduced temperature;
• and
• means for separating said crystallized second stage purified terephthalic acid from said second solution.

An apparatus for purifying crude terephthalic acid from a liquid dispersion thereof also containing impurities selected from unreacted starting materials, solvents, products of side reactions and/or other undesired materials, said apparatus comprising:

• means for dissolving crude terephthalic acid in NMP at a temperature of from between about 140.degree. C. and about 190.degree. C. to form a first solution;
• means for crystallizing said dissolved crude terephthalic acid from said first solution at a temperature of from between about 5.degree. C. and about 50.degree. C. to form first stage purified terephthalic acid;
• means for separating said first stage purified terephthalic acid from said first solution by filtration to form a first stage purified terephthalic acid filter cake;
• means for washing said separated first stage purified terephthalic acid filter cake with N-methyl pyrrolidone;
• means for redissolving said first stage purified terephthalic acid filter cake in NMP at a temperature of from between about 140.degree. C. and about 190.degree. C. to form a second solution;
• means for crystallizing said redissolved first stage purified terephthalic acid from said second solution at a temperature of from between about 5.degree. C. and about 50.degree. C. to form second stage purified terephthalic acid;
• means for separating said second stage purified terephthalic acid from said second solution by filtration to form a second stage purified terephthalic acid filter cake;
• means for washing said second stage purified terephthalic acid filter cake with N-methyl pyrrolidone;
• means for washing said N-methyl Pyrrolidone washed filter cake with methanol;
• and
• means for drying said second stage purified terephthalic acid filter cake to provide second stage purified terephthalic acid.