Producing terephthalic acid, comprises dissolving impure terephthalic acid, precipitating acid crystals, separating from solvent liquid, and washing, where degree of contamination is measured before and/or after solid-liquid separation

摘要

Producing terephthalic acid, comprises: dissolving impure terephthalic acid in a liquid solvent; precipitating terephthalic acid crystals; separating terephthalic acid crystals from the solvent liquid, where the terephthalic acid crystals are present as a solid cake; and washing a solid cake with at least one contaminant using a washing liquid, where washing liquid absorbs contaminant and is discharged as wash filtrate. The degree of contamination with the contaminant is measured before and/or after the solid-liquid separation and a quantity of wash filtrate is recycled to the liquid solvent. Producing terephthalic acid, comprises: dissolving impure terephthalic acid in a liquid solvent; precipitating terephthalic acid crystals in at least one crystallization section (16); separating terephthalic acid crystals from the solvent liquid by a solid-liquid separation, where the terephthalic acid crystals are present as a solid cake; and washing a solid cake with at least one contaminant using a washing liquid, to reduce contamination, where the washing liquid absorbs contaminant and is discharged as wash filtrate. The degree of contamination with the contaminant is measured before and/or after the solid-liquid separation and a quantity of wash filtrate is recycled to the liquid solvent depending on the determined measured value of the contaminant, for dissolving the impure terephthalic acid. An independent claim is also included for a plant (10) for performing the above method, comprising at least one crystallization portion in which impure terephthalic acid precipitates as terephthalic acid crystals in a liquid solvent; a washing section for reducing an impurity with at least one contaminant; a measuring device for measuring the degree of contamination; and a recycling device to recycle the wash filtrate to the liquid solvent.