Production and uses of naphthoquinone

The oxidation of naphthalene to naphthoquinone is closely related to its oxidation for the production of phthalic anhydride, as naphthoquinone is formed as an undesirable by-product in the latter process. The use for naphthoquinone is almost entirely limited to its reaction with butadiene to produce anthraquinone/ tetrahydroanthraquinone. 

The large-scale production of naphthoquinone by gas-phase oxidation is fundamentally more complex than the production of phthalic anhydride for two main reasons. First, the process conditions and the selected catalyst must assure the minimized formation of co-produced phthalic anhydride and second, as a result, the purification of the crude product is more complex and involves separation of unconverted naphthalene, phthalic anhydride and naphthoquinone, and the purification of the waste gases. 

By analogy with the production of phthalic anhydride, the reaction is performed in a multitubular reactor. The catalyst consists of vanadium pentoxide on a silica support, modified by potassium and ammonium sulfates or potassium hydrogen sulfate. 

The reaction is carried out at a temperature of 400 °C and a concentration of around 40 g naphthalene/Nm air. Based on the naphthalene feed, at 94% conversion about 50% naphthoquinone and about 50% phthalic anhydride are obtained. 

To purify the crude naphthoquinone, the phthalic anhydride is hydrolyzed to phthalic add and extracted by washing with water. The naphthoquinone is then extracted with an aromatic solvent such as toluene, and further purified by an alkali wash to remove residual phthalic add. 

---