The Phthalic Anhydride is an important product used for the synthesis of resins and coloring agent. Two methods are available for its production: from o-xylene oxidation or from naphthalene oxidation (known as Gibbs Process), both in the presence of catalysts.
However, employing the Gibbs Process to obtain this product generates a serious problem: the reaction is very exothermic and both naphthalene and one of the intermediate products of the reaction (naphthoquinone) are flammable. Explosions might occur in fixed-bed reactors due to the heat that is released by the reaction and the presence of such compounds, since the temperature control in the bed is not totally effective.
On the other hand, a precise control of reaction temperature is found in fluidized beds. The probability of a sudden temperature increase is reduced as the bed-suspended catalyst particles act as a medium for heat dispersion.
The temperature under which the process takes place is 340–380°C, carefully controlled. The heat released from the reaction is removed by steam generation at a 7-28 atm (~ 700000 - 2800000 Pa) pressure in the coil contained in the bed. The catalyst in use is vanadium pentoxide (VO5) and the contact time is 10-20s. The superficial gas velocity is maintained at 0.30-0.60 m/s.