METHOD FOR PURIFYING CRUDE NAPHTHALENEDICARBOXYLIC ACID AND PROCESS FOR PREPARING POLYETHYLENE NAPHTHALATE

摘要

A method for preparing polyethylene naphthalate having a low impurity content from a naphthalenedicarboxylic acid containing impurities, which comprises mixing a crude naphthalenedicarboxylic acid with an aqueous ethylene glycol solution, heating the mixture to esterify a part of the naphthalenedicarboxylic acid to prepare a naphthalenedicarboxylic ester, dissolving the naphthalenedicarboxylic ester in the aqueous ethylene glycol solution, bringing hydrogenatable impurities contained in the crude naphthalenedicarboxylic acid into contact with hydrogen in the presence of a hydrogenation catalyst to hydrogenate the impurities to thereby dissolve the same in the aqueous ethylene glycol solution, crystallizing the naphthalenedicarboxylic ester, separating the crystallized naphthalenedicarboxylic ester from the aqueous ethylene glycol solution, and polycondensating the resultant naphtalenedicarboxylic ester. A method for purifying a crude naphtalenedicarboxylic acid to obtain a naphthalenedicarboxylic acid and a naphthalenedicarboxylic ester each having a low aldehyde content from a naphthalenedicarboxylic acid containing aldehydes, which comprises mixing a crude naphthalenedicarboxylic acid with an aqueous alcohol solution, heating the mixture to esterify a part of the naphthalenedicarboxylic acid to prepare a naphthalenedicarboxylic ester, dissolving the naphthalenedicarboxylic ester in the aqueous alcohol solution, bringing the aldehydes contained in the crude naphthalenedicarboxylic acid into contact with a salt of sulfurous acid to prepare an aldehyde adduct, dissolving the aldehyde adduct in an aqueous alcohol solution, and crystallizing and separating the naphthalenedicarboxylic acid and the naphthalenedicarboxylic ester.