| 摘要 |
PURPOSE:To obtain 3,4,3',4'-biphenyltetracarboxylic acid having good filtrating and drying characteristics as well as large size at a specific acid deposition temperature when an aqueous alkali solution containing a salt of said carboxylic acid is subjected to acid deposition treatment to recover a crystal of above- mentioned carboxylic acid. CONSTITUTION:When an aqueous alkali solution containing a salt of 3,4,3',4'- biphenyltetracarboxylic acid (s-BTC) is subjected to acid deposition treatment with a mineral acid and filtered to recover a crystal of the s-BTC, the acid deposition treatment is carried out at 80-140 deg.C, preferably while supplying above-mentioned aqueous alkali solution into an aqueous mineral acid, at the same time using sulfuric acid maintained in a concentration of 50-1wt% as the mineral acid and further maintaining pH on acid deposition to >=3 to provide a crystal of s-BTC having good filtrating properties, short drying time, reduced inclusion of impurity as well as large size. Filtration temperature is preferably >=80 deg.C when a salt of phthalic acid is contained as a by-product.
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