Terephthalic acid production using evaporative cooling

An improved process for the production of terephthalic acid by the oxidation of p-xylene present in a body of liquid contained within a reactor vessel, without appreciable loss of oxygen to the overhead gas phase, comprising:

• (a) maintaining said body of liquid containing p-xylene reactant, an organic solvent, catalyst and a bromine initiator in a recirculating flow pattern by impeller means positioned therein, said body of liquid having a gas-liquid interface with an overhead gas phase;
• (b) injecting pure oxygen or an oxygen-rich gas directly into said recirculating portion of the body of liquid at an oxygen injection point or points near said impeller means at a point of high turbulence within the turbulent flow field produced by said impeller means so as to rapidly disperse oxygen in the liquid as small bubbles for rapid consumption of at least about 90% of said oxygen upon injection into the liquid, the heat of reaction due to the oxidation of p-xylene being removed by evaporative cooling upon evaporation of volatile organic material and water present in said body of liquid, with bubbles of said evaporated organic material and water vapor, accompanied by only small quantities of undissolved oxygen, rising upward in said body of liquid through a relatively quiescent, essentially non-turbulent, zone in the upper portion of the reactor vessel to the gas-liquid interface and to said overhead gas phase;
• and
• (c) maintaining the oxygen-p-xylene mixture in the reactor vessel at a temperature of from about 150.degree. C. to about 200.degree. C., and a pressure of between 100 psig and 200 psig, for a residence time of from about 30 to about 90 minutes;
• (d) venting said bubbles of evaporated organic material and water vapor, accompanied by only small quantities of oxygen, from the overhead gas phase;
• (e) recovering terephthalic acid product from the reactor vessel, whereby the oxygen and the p-xylene reactant are mixed under conditions promoting the rapid consumption of oxygen and the evaporation of organic material and water with only small amounts of oxygen bubbles being passed to the overhead gas phase.