초록 ▼

The process for preparing polyethylene naphthalate according to the invention is intended to obtain polyethylene naphthalate having a low impurity content from naphthalenedicarboxylic acid containing impurities. This process comprises the steps of: mixing crude naphthalenedicarboxylic acid and an et

The process for preparing polyethylene naphthalate according to the invention is intended to obtain polyethylene naphthalate having a low impurity content from naphthalenedicarboxylic acid containing impurities. This process comprises the steps of: mixing crude naphthalenedicarboxylic acid and an ethylene glycol aqueous solution, heating the resulting mixture to esterify a part of the naphthalenedicarboxylic acid and thereby give a naphthalenedicarboxylic acid ester and dissolving the naphthalenedicarboxylic acid ester in the ethylene glycol aqueous solution; then contacting impurities, which are contained in the crude naphthalenedicarboxylic acid and capable of being hydrogenated, with hydrogen in the presence of a hydrogenation catalyst to hydrogenate the impurities and dissolving the hydrogenated impurities in the ethylene glycol aqueous solution; and subsequently crystallizing the naphthalenedicarboxylic acid ester, separating the resulting crystals from the ethylene glycol aqueous solution and polycondensing the resulting naphthalenedicarboxylic acid ester. The method of purifying crude naphthalenedicarboxylic acid is intended to obtain naphthalenedicarboxylic acid and a naphthalenedicarboxylic acid ester having a low content of aldehydes from naphthalenedicarboxylic acid containing aldehydes. This method comprises the steps of: mixing crude naphthalenedicarboxylic acid and an alcohol aqueous solution, heating the resulting mixture to esterify a part of the naphthalenedicarboxylic acid and thereby give a naphthalenedicarboxylic acid ester and dissolving the naphthalenedicarboxylic acid ester in the alcohol aqueous solution; then contacting aldehydes, which are contained in the crude naphthalenedicarboxylic acid, with a sulfite to give aldehyde adducts and dissolving the aldehyde adducts in the alcohol aqueous solution; and subsequently crystallizing the naphthalenedicarboxylic acid and the naphthalenedicarboxylic acid ester and separating them from the alcohol aqueous solution.

대표청구항 ▼

[ What is claimed is:] [1.] A process for preparing polyethylene naphthalate, comprising the steps of:mixing crude naphthalenedicarboxylic acid and an ethylene glycol aqueous solution, heating the resulting mixture to esterify a part of the naphthalenedicarboxylic acid and thereby give a naphthalene

[ What is claimed is:] [1.] A process for preparing polyethylene naphthalate, comprising the steps of:mixing crude naphthalenedicarboxylic acid and an ethylene glycol aqueous solution, heating the resulting mixture to esterify a part of the naphthalenedicarboxylic acid and thereby give a naphthalenedicarboxylic acid ester and dissolving the naphthalenedicarboxylic acid ester in the ethylene glycol aqueous solution;then contacting impurities, which are contained in the crude naphthalenedicarboxylic acid and capable of being hydrogenated, with hydrogen in the presence of a hydrogenation catalyst to hydrogenate the impurities and dissolving the hydrogenated impurities in the ethylene glycol aqueous solution; andsubsequently crystallizing the naphthalenedicarboxylic acid ester, separating the resulting crystals from the ethylene glycol aqueous solution and polycondensing the resulting naphthalenedicarboxylic acid ester.