Production of fiber-grade terephthalic acid
AssigneeStandard Oil Company (Indiana)
InventorsChang-Man Park, Donald G. Micklewright
Life of this patent
Estimating the term…
Abstract
Terephthalic acid (TA) or isophthalic acid (IA) of fiber-grade quality is recovered under oxidation temperature and pressure conditions from fluid oxidation effluent from catalytic liquid phase oxidation of the respective xylene isomer in acetic acid with molecular oxygen by crystal size classification and acetic acid mother liquor displacement with hot, fresh acetic acid followed by quenching the new suspension of phthalic acid crystals in said hot solvent with colder fresh acetic acid solvent and separating the product crystals. Such technique eliminates the need for separately purifying crude TA or IA or converting TA or IA to the respective dimethyl ester and purifying the ester.
Claims7
In a process of recovering high purity isophthalic and/or terephthalic acid from the liquid effluent of the oxidation of meta and/or para dialkyl substituted benzene, said alkyl substituents having 1 to 4 carbon atoms, with molecular oxygen in an oxidation zone in the presence of an acetic acid solution of heavy metal oxidation catalyst and a source of bromine at an elevated temperature in the range of from 360.degree. up to 450.degree. F. and a pressure in the reaction zone to maintain said solution in the liquid phase at said temperature, wherein said oxidation produces a liquid oxidation effluent comprising a suspension of said phthalic acid as crystalline product in the liquid acetic acid mother liquor solution of said catalyst components, by-product water, and aromatic impurities and a gaseous effluent comprising a mixture of nitrogen, oxides of carbon, water vapor, vaporized acetic acid, and small amounts of molecular oxygen;
- and wherein said gaseous effluent is cooled to condense water and solvent vapor therefrom and the condensate is returned to the oxidation zone as a means of controlling temperature in said reaction zone, the improvement which comprises:
- (1) adding fresh, hot acetic acid and small phthalic acid crystals to substantially all the orginal acetic acid mother liquor portion of the oxidation effluent at a temperature of from 50.degree. below said oxidation temperature up to said oxidation temperature to form a new suspension of large phthalic acid crystals in hot, fresh acetic acid and (b) the removal of the displaced acetic acid mother liquor and the small crystals suspended therein for recycle to the reaction zone;
- (2) quenching said new suspension of crystalline phthalic acid by the addition thereto of cold, fresh acetic acid in an amount to cool the suspension to a temperature at or below the boiling point of acetic acid at atmospheric pressure;
- (3) depressuring said new suspension of crystalline phthalic acid in fresh acetic acid to atmospheric pressure;
- (4) separating the crystalline phthalic acid from the fresh acetic acid by means for solid-liquid separation at atmospheric pressure;
- (5) recycling the separated fresh acetic acid to the reaction zone;
- and
- (6drying the separated crystalline product.
Dependencies are inferred from the claim text.