| 摘要 |
PURPOSE:To obtain crystal of terephthalic acid having large particle diameters and improved filtering properties, by carrying out acid precipitation treatment of waste liquor from process for treatment of reduction in amount of polyester fiber in a specific temperature range. CONSTITUTION:An inorganic acid such as sulfuric acid, hydrochloric acid, phosphoric acid, etc. is added to waste liquor obtained from process for treatment of reduction in amount with an alkali aqueous solution of caustic soda to improve feeling of polyester fiber, an aqueous solution containing 0.5-10wt%, preferably 1-5wt% calculated as terephthalic acid of dialkali phthalate usually at about 10-14pH under pressure (about 1-16 atmospheric pressure) at 100-200 deg.C, preferably at 105-180 deg.C, the aqueous solution is adjusted to <=3.5pH, preferably <=3, to precipitate crystal of terephthalic acid, which is subjected to solid-liquid separation by a centrifugal separator, to recover crystal of terephthalic acid.
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