FIELD: chemical industry. SUBSTANCE: improved process comprises oxidizing p-xylene with oxygen or oxygen-saturated gas, in solvent and at pressure, in the presence of catalyst and initiator in stirred reactor in which liquid phase has interphase with gas phase. Said process comprises the following stages (a) main portion of liquid is made to recycle in reaction vessel. Said recycling portion of liquid has no interface between liquid and top gas phase, and said recycling portion of liquid is separated by mechanical means but with possibility to communicate for flowing medium from relatively immovable portion of liquid; said immovable portion of liquid has interphase between liquid and top gas phase; said interface being adapted to variations in liquid level in response to variations in liquid volume between states when liquid contains substantially no gas bubbles, and state when liquid contains desired concentration of gas bubbles; original stream of substantially pure oxygen or oxygen- enriched air containing at least approximately 50% oxygen is introduced directly into recycling portion of said liquid, path of recycling stream and rate of stream of said recycling portion of liquid relative to communication zone of said recycling and immovable portions of liquid are such that oxygen bubbles formed from addition of original stream to recycling portion of liquid are maintained in dispersed form in recycling liquid, thus making it possible to dissolve oxygen and to react it with p-xylene reagent in recycling portion of liquid without any appreciable passage of said oxygen bubbles through communication zone between recycling portion of liquid and its immovable portion, and through its immovable portion, to interface between gas and liquid and thus without loss of oxygen in top gas phase; (c) mixture of liquid and oxygen is maintained in reaction vessel at temperature from about 150 to 200 C and at pressure from about 100 to 100 pounds per square inch (7.0-14.1 kg/sq.cm) for period from about 30 to 90 min; and (d) the resulting desired terephthalic acid is recovered from reaction vessel. As compared with generally known process for preparing air-based terephthalic acid, the claimed process makes it possible to reduce consumption of reagent and solvent and simultaneously formation of undesirable by products. Lower costs are involved for treatment of outgoing gases and less effect on environment. EFFECT: more efficient preparation process. 17 cl, 4 dwg
