| abstract |
A continuous process for the production of terephthalic acid, isophthalic acid or mixtures thereof by the once-through catalytic liquid phase oxidation of the corresponding xylene or mixtures of xylene with air or enriched air containing up to 50% by volume of oxygen in a single oxidation zone in presence of an acetic acid solution containing bromine ions and a heavy metal as the catalyst system, which comprises charging continuously to the oxidation zone the xylene, the acetic acid solution containing the catalyst system, and the air, the weight ratio of the acetic acid to xylene being in the range 1 : 1 to 10 : 1, the concentrations of total heavy metal and bromine each being 0.01 to 1.0 weight per cent based on the acetic acid, the ratio of air to xylene being 1.0% to 40% in excess over that required to provide the theoretical ratio of 3.0 moles of oxygen per mole of xylene, the reaction temperature of the liquid phase being 390 DEG F. to 475 DEG F. at a pressure of 300 to 500 p.s.i.g., the residence time of the xylene in the oxidation zone being 10 to 60 minutes; continuously withdrawing the resultant liquid phase reaction mixture at a rate regulated to provide the desired residence time and recovering the phthalic acid product. The term "heavy metal" is defined and includes metals of atomic number up to 84, e.g. Mn, Co, Ni, Cr, V, Mo, W, Sn and Ce which may be used in admixture. Sources of bromine are elemental bromine, bromides, bromates, tetrabromoethane, benzyl bromide and "heavy metal" bromides. The bromine to metal atom ratio may vary from 10: 1 to 1: 7. A preferred catalyst comprises 0.03 to 0.5% by weight of bromine and 0.03 to 0.5% by weight of Co and Mn together, based on the weight of acetic acid. |