Patent ID: 6580005
Filing Date: 2003-06-17
Classification: C07C,C08J,Y02W

Abstract:
A process for recovering terephthalic acid from pulverized products of spent polyethylene terephthalate, the process comprising the following steps:(1) a decomposition reaction step where the pulverized products of spent polyethylene terephthalate are continuously subjected to a decomposition reaction in ethylene glycol in the presence of sodium carbonate, which is equimolar or excessmolar relative to the polyethylene terephthalate, so that a salt of terephthalic acid and ethylene glycol can be obtained; (2) a solid-liquid separation, dissolution, impurities-removing step where said ethylene glycol is separated from the decomposition reaction slurry of said salt of terephthalic acid and ethylene glycol, and the solid salt of terephthalic acid is dissolved into water, and insoluble impurities are removed; (3) a neutralization, crystallization step, where the solution of said salt of terephthalic acid is neutralized with acid so that terephthalic acid can be crystallized; (4) a solid-liquid separation washing step, where the resulting slurry of terephthalic acid crystals is subjected to solid-liquid separation, so that the terephthalic acid crystals can be obtained and washed; (5) a drying, pulverization step, where the washed terephthalic acid crystals are dried and pulverized; and further comprising a condensation, crystallization, mirabilite-removing step, where water contained in the liquid obtained by said separation step (4) is vaporized, so that alkali sulfate can be crystallized and separated.