METHOD OF ISOLATING NAPHTHOQUINONE AND PHTHALIC ANHYDRIDE FROM REACTION GAS IN VAPOR RHASE OXIDATION OF NAPHTHALENE

To isolate naphthoquinone and phthalic anhydride from the gas obtained in the gas phase oxidation of naphthalene, the gas product at 250 DEG to 500 DEG C is first quenched with a counter-current liquid stream of naphthalene, naphthoquinone and phthalic anhydride. The liquid is raised to at most 200 DEG C, cooled and partly recycled, the coolant temperature being within 70 DEG C of the temperature of the liquid being cooled. The portion of the quench liquid which is not recycled is the product, viz. a solution of naphthoquinone and phthalic anhydride in naphthalene. The quenched gas is scrubbed with liquid naphthalene and most of the liquid product is cooled and re-cycled, the balance of the liquid product being passed to the quencher. The gas which leaves the scrubber is substantially free from naphthoquinone and phthalic anhydride. The initial gas may have been pre-cooled by evaporative cooling. The surfaces of the quencher, cooler and pipes of the quenching system are preferably of stainless steel or are smoothed either mechanically or by coating with plastic, enamel, ceramic or metal.