| abstract |
The present invention provides a process whereby by-product isophthalic acid is easily removed from terephthalic acid. The process thus provides a terephthalic acid product of improved purity. The process involves cooling at least a portion of a hot acetic acid production stream from which precipitated terephthalic acid has been removed so as to precipitate at least a portion of the isophthalic acid dissolved therein. The precipitated isophthalic acid is then removed and the production stream is recycled to a reactor from the production of terephthalic acid. The total production stream is thereby rendered unsaturated in isophthalic acid. Following the reaction in the terephthalic acid reactor, pure terephthalic acid in the substantial absence of isophthalic acid is recovered from the production stream as a precipitate. In a preferred embodiment, the cooling step involves cooling about 15 to 75%, and, at times, perhaps up to 100%, of the total hot acetic acid production stream to a temperature below about 50 DEG C. |