Production of phthalic anhydride

Claim 1

A METHOD OF OXIDIZING NAPHTHALENE INTO PHTHALIC ANHYDRIDE WHICH COMPRISES PASSING A MIXTURE OF NAPHTHALENE AND AIR THROUGH A SERIES OF OXIDATION REACTIONS; MAINTAINING EACH SUCH REACTION WITHIN A TEMPERATURE RANGE, AT THE START, OF ABOUT 350*C. TO A FINAL TEMPERATURE OF ABOUT 400*C.; COOLING THE MIXTURE AT THE END OF EACH STEP TO THE LOWER VALUE OF SAID RANGE; INJECTING FRESH NAPHTHALENE INTO THE MIXTURE BETWEEN SUCCESSIVE STEPS, THE AMOUNT OF NAPHTHALENE INJECTED AT EACH INJECTION POINT BEING SO ADJUSTED AS TO RAISE THE NAPHTHALENE CONTENT AT SUCH POINT TO A CONCENTRATION BELOW THE EXPLOSION THRESHOLD OF THE REACTING MIXTURE CONTAINING AIR, NAPHTHALENE AND PHTHALIC ANHYDRIDE, AND CIRCULATING SAID REACTING MIXTURE CONTAINING THE PHTHALIC ANHYDRIE PRODUCED THROUGH THE SUCCEEDING OXIDATION STEPS.