Production, purification and polymerization of aromatic dicarboxylic acids

A process for purifying naphthalenedicarboxylic acid, comprising the steps of:

• i) mixing crude naphthalenedicarboxylic acid with an aqueous solution of an alcohol;
• ii) heating the mixture produced in step (i) to esterify a part of the naphthalenedicarboxylic acid and thereby give a naphthalenedicarboxylic acid ester, and
• iii) dissolving the naphthalenedicarboxylic acid ester produced in step (ii) in the aqueous alcohol solution;
• iv) then reducing the pressure of the aqueous alcohol solution to remove volatile species;
• and
• v) subsequently crystallizing the naphthalenedicarboxylic acid ester from the aqueous alcohol solution and separating the resultant crystals from the aqueous alcohol solution.

A process for preparing polyethylene naphthalate, comprising the steps of:

• i) oxidizing 2,6-dimethylnaphthalene to produce an oxidation effluent comprising crude naphthalene dicarboxylic acid;
• ii) separating the crude naphthalene dicarboxylic acid from said oxidation effluent;
• iii) optionally washing the crude naphthalene dicarboxylic acid with aqueous acetic acid;
• iv) mixing the separated crude naphthalene dicarboxylic acid with an aqueous solution of ethylene glycol;
• v) heating the resulting mixture to esterify at least part of the naphthalene dicarboxylic acid and thereby produce a naphthalene dicarboxylic acid ester;
• vi) dissolving the naphthalene dicarboxylic acid ester in the aqueous glycol solution;
• vii) then distilling the aqueous glycol solution produced in step (vi) to remove volatile impurities;
• viii) subsequently separating the naphthalene dicarboxylic acid ester from the aqueous glycol solution remaining after step (vii), and
• ix) subjecting the naphthalene dicarboxylic acid ester separated in step (viii) to a polycondensation reaction.