Recovery of benzoic acid from residue formed in crude terephthalic acid production process using recrystallization method

In this work we intend to recovery of benzoic acid from residue formed in crude terephthalic acid production process in the Tondgooyan Petrochemical Company. In this process is produced a large amount solid residue in addition to terephthalic acid. Analysis results shows this residue contains of benzoic acid، crude terephthalic acid، p-toluic acid and small amounts of catalysts. Benzoic acid containing residue recycled by recrystallization in water because of benzoic acid have a very high solubility in hot water and a low solubility in cold water. Effective variables on recrystallization process is dilution ratio of water to residue، dissolve and crystallization temperature of benzoic acid in water. The Optimum conditions of recrystallization consist of dilution ratio of water to residue 4 to 1، dissolve and crystallization temperature is 95 and 25 C° respectively. Recovery yield of benzoic acid is 85 percent in optimum conditions of recrystallization. Purity of recovered crystals of benzoic acid is 97. 79 percent. Because of recovered benzoic acid have a high purity، it may applied in different industries.