Phthalic anhydride - Medium-temperature process

Phthalic anhydride is an important raw material in the manufacture of plasticizers (phthalates), polyester and alkyl resins, and pigments.

Phthalic anhydride can be manufactured in a variety of ways: in the liquid phase (ex-orthoxylene), on a fluidized bed (ex-naphthalene) and in the gas phase from both raw materials.

The "high-temperature" process (reaction catches at around 450 ˚C) used a boiling mercury bath to remove the heat released by the reaction. It no longer exists.

The "medium-temperature" process described below (reaction catches at around 330-370 ˚C) uses a molten salt bath as the heat transfer fluid. Yields are better than those of the "high-temperature" process, and the safety-environmental aspects are less delicate.