Patent GB-961470-A (GB)
Title: Production of phthalic anhydride by catalytic oxidation of o-xylene
Inventor: NONNENMACHER HELMUT
IPC: B01J23/28
Filed: 1962-04-25
Abstract: A process for the vapour phase oxidation of o-xylene to phthalic anhydride using oxygen or an inert gas containing molecular oxygen comprises contacting the o-xylene and the oxidising gas with bromine or a bromine-containing compound which is gaseous or vaporous under the reaction conditions, in a weight percentage of bromine supplied (based on xylene) of 0.001 to 2%, with a residue time of 5 to 50 seconds and at a temperature of 250 to 380 DEG C., in a fluidised bed of a catalyst comprising a porous carrier containing in the pores thereof a liquid comprising vanadium pentoxide and either potassium pyrosulphate or a mixture of potassium pyrosulphate and sodium pyrosulphate, with or without other additives, the liquid advantageously containing 5 to 30% by wt. of vanadium pentoxide and not less than 60% by wt. of pyrosulphate.  Bromine-containing compounds specified are hydrogen bromide, ammonium bromide, nitrosyl bromide, thionyl bromide, alkyl bromides having 1 to 10 carbon atoms, cycloalkyl bromide having 1 to 12 carbon atoms, aryl bromides having 6 to 10 carbon atoms, aralkyl bromides having 7 to 10 carbon atoms, and carboxylic acid bromides of aliphatic acids having 2 to 10 carbon atoms, of aryl monocarboxylic or dicarboxylic acids having 7 to 10 carbon atoms, or of aralkyl carboxylic acids having 8 to 10 carbon atoms.  The porous carrier of the catalyst may be silicic acid, preferably in the form of silica gel, active carbon, aluminium phosphate, or synthetic or natural zeolites.  In preparation of the catalyst (see Division B1), in place of vanadium pentoxide, vanadium compounds which under oxidising conditions are converted at the reaction temperature to vanadium pentoxide may be used, e.g. ammonium vanadate, vanadium trichloride, vanadium trioxide, vanadium tetroxide, or vanadyl sulphate. Metal activators which accelerate oxidation of hydrogen bromide to bromine may be added, e.g. ceric oxide, manganese dioxide, ferric oxide, cupric oxide, cobaltous oxide and nickelous oxide, preferably in up to 5% by wt. of the liquid. There may also be added (a) phosphoric acid as such or as phosphorus pentoxide or as compounds which yield phosphorus pentoxide, e.g. phosphorus pentasulphide, ammonium phosphate, or sodium and potassium phosphates and hydrogen phosphates, in a maximum of 4% by wt. in the liquid, (b) molybdic acid, molybdenum oxide, molybdenum sulphide, ammonium molybdate, sodium molybdate, potassium molybdate or phosphomolybdic acid, up to 6% by wt. in the liquid, (c) tungstic acid, tungsten oxides, tungsten sulphides, ammonium tungstate or phosphotungstic acid, or mixtures thereof with the above mentioned molybdenum compounds, in up to 6% by wt. of the liquid, and (d) silver oxide in up to 3% by wt. of the liquid; where alkali metal phosphates are used an equivalent amount of sulphuric acid is added and regarded as pyrosulphate, and this is preferably done in the case of alkali metal molybdates.  The catalyst preferably contains 10-60% by wt. of the liquid component.  The oxidation is preferably effected in the presence of small amounts of sulphur trioxide at the catalyst, and accordingly sulphur trioxide, sulphur dioxide, or other sulphur compounds oxidisable to sulphur trioxide, e.g. thiophene, carbon disulphide and thionaphthene, may be added. Specifications 906,311, 908,823 and 941,293 are referred to.ALSO:A catalyst used in the vapour phase oxidation of #s-xylene to phthalic anhydride (see Division C2) in the presence of bromine or a bromine compound consists of a highly porous carrier in the pores of which is a liquid comprising vanadium pentoxide and either potassium pyrosulphate or a mixture of potassium pyrosulphate and sodium pyrosulphate, with, if desired, other additives, the liquid advantageously containing 5-30% by weight of vanadium pentoxide and not less than 60% by weight of pyrosulphate.  The porous carrier may be silicic acid, preferably in the form of silica gel, active carbon, aluminium phosphate or synthetic or natural zeolites.  The liquid may be prepared by heating potassium pyrosulphate or potassium hydrogen sulphate or a mixture of potassium and sodium pyrosulphates or hydrogen sulphates, fusing till all water has evaporated, and adding at 300-450  DEG C. vanadium pentoxide or a compound oxidizable thereto under the reaction conditions, e.g. ammonium vanadate, vanadium trichloride, vanadium trioxide, vanadium tetroxide or vanadyl sulphate.  Metal activators which accelerate the oxidation of hydrogen bromide to bromine may be added, e.g. ceric oxide, manganese dioxide, ferric oxide, cupric oxide, cobaltous oxide p  and nickelous oxide, preferably in up to 5% by weight of the liquid.  There may also be added (a) phosphoric acid as such or as phosphorus pentoxide or compounds which yield phosphorus pentoxide, e.g. phosphorus pentasulphide, ammonium phosphate, and sodium and potassium phosphates and hydrogen phosphates in up to 4% by weight of the liquid, (b) molybdic acid, molybdenum oxide, molybdenum sulphide, amonium molybdate, sodium molybdate, potassium molybdate or phosphomolybdic acid, in up to 6% by weight of the liquid, (c) tungstic acid, tungsten oxides, tungsten sulphides, ammonium tungstate, phosphotungstic acid, or mixtures thereof with the abovementioned molybdenum compounds, in up to 6% by weight of the liquid, and (d) silver oxide in up to 3% by weight of the liquid; where alkali metal phosphates are used an equivalent amount of sulphuric acid is added and regarded as pyrosulphate, and this is preferably done in the case of alkali metal molybdates.  The liquid melt may be applied to the carrier by (a) mixing the carrier and the solidified melt and heating the mixture for several hours above the melting temperature of the liquid, (b) allowing the powdered solidified melt to trickle into a carrier bed fluidized by air or an inert gas, e.g. nitrogen or carbon dioxide, and maintaining the bed for some hours above the solid melting-point, or (c) soaking silica gel in aqueous solutions of the components of the liquid, followed by drying and heating to 200-600  DEG C.; in this case alkali sulphates may be used instead of alkali pyrosulphates, in which case it is necessary to supply during the heating a gas containing sulphur trioxide, sulphur dioxide, or sulphur compounds which give sulphur dioxide at the catalyst, together with an oxygen-containing gas.  The catalyst preferably contains 10-60% by weight of the liquid component.  Specifications 906,311, 908,823 and 941,293 are referred to.