A variety of processes are licensed for PAN production. Presently in the U. S. all phthalic anhydride is produced by vapor phase oxidation of xylene and naphthalene. The primary naphthalene processes use iluidized bed converters whereas all xylene based plants incorporate tubular fixed bed reactors. Except for the reactors and catalyst handling and recovery facilities reQuired for the fluid units, these vapor phase processes are similar.