Abstract: Substantial proportions of methyl acetate and unreacted polymethylbenzene are recovered from the waste gas produced during the oxidation of a polymethylbenzene to its corresponding polycarboxylic acid by passing the waste gas, after being cooled for removal of water vapor, through at least one bed of activated carbon and subsequently desorbing the methyl acetate and polymethylbenzene from the bed by passing a desorbing medium, such as steam, through the bed. Preferably, the cooled stream is heated to a temperature of at least 21.degree. C. (70.degree. F.) prior to being passed into the bed of activated carbon.There is also disclosed an improved process for the oxidation of a polymethylbenzene to its corresponding aromatic polycarboxylic acid, which process comprises producing the polycarboxylic acid and waste gas comprising methyl acetate, water vapor, and unreacted polymethylbenzene and treating the waste gas according to the above method.