The production of phthalic anhydride by the oxidation of tar oils

It is known that phthalic anhydride is obtained by vapour-phase oxidation of alkylnaphthalenes and other polycyclic hydrocarbons. Consequently the production of phthalic anhydride from coal-tar naphthalene oils was investigated. When a vanadium pentoxide/potassium sulphate/silica catalyst was used no marked deterioration of catalyst was observed in an experiment with naphthalene oil over a period of 28 hours. Operating variables of liquid- and air-space velocity were studied and naphthalene and naphthalene oils of coke-oven and vertical-retort origin compared. The phthalic anhydride yield can be predicted, and is dependent on the naphthalene content of the oil and the operating variables. The yield of phthalic anhydride from a naphthalene oil is greater than can be obtained from the naphthalene in the oil even if it could be extracted without loss. At the same time the heat evolved in reaction is considerably increased and as a consequence heat removal would present the most important problem in the design of an oxidation plant.