Patent GB-850594-A (GB)
Title: Improvements in or relating to the oxidation of naphthalene to phthalic anhydride
IPC: B01J8/18
Filed: 1957-01-29
Abstract: <PICT:0850594/IV(b)/1> Phthalic anhydride is prepared by a process comprising passing a mixture of naphthalene vapour and an oxygencontaining gas at a linear velocity of about 0,2 to 2 feet per second through a bed of fluidised particles of vanadium oxide containing catalyst comprising a mixture of V2O4 and V2O5 at a temperature in the range of about 320 DEG  and 420 DEG C and a naphthalene to oxygen ratio of 2,5 to 16,5 mole per cent naphthalene such that upon continued operation the weight ratio of V2O4 to V2O5 in the catalyst would exceed 70 : 30, characterised in that the V2O4 : V2O5 weight ratio is maintained between the limits of 70 : 30 to 20 : 80 by continuously withdrawing catalyst from the bed, continuously partially oxidising it with an oxygen-containing gas to a lower V2O4 : V2O5 ratio within the specified limits and returning it to the catalyst bed.  The naphthalene is preferably oxidised with air or a gas containing less than 21% O2 and the catalyst is preferably oxidised with a gas of higher O2 content.  The catalyst may be supported on, for example, silica or alumina gel or a zeolite and may contain an alkali metal salt of an oxy-acid of sulphur, such as a (initially) V2O5 : silver oxide : potassium pyrosulphate mixture on silica gel as described in Specification 702,616.  The process may be effected with separate reoxidation of the catalyst at about 320 DEG -400 DEG C., by passing a mixture of naphthalene and air up a heated vertical tubular reactor containing the fluidised catalyst, the effluent gases being passed through a catalyst separator at the reactor head and then condensed to recover phthalic anhydride ; catalyst is withdrawn from the base of the reactor and passed in an air stream up a heated tube leading to the reactor separator whereby the re-oxidised catalyst is recycled.  Alternatively, the reoxidation may be effected at the bottom of the tubular reactor as shown in Fig. 4 wherein a convertor 40 provided with baffles 31 and heat exchangers 32 has a zone 37, below the naphthalene feed point 36, wherein a fluidised regeneration bed of catalyst heated by coil 38 is maintained above air-distributing plate 34, the catalyst to be re-oxidised being withdrawn from the reaction zone and fed to zone 37 by one or more down-pipes 40.  Examples are given using the first mentioned apparatus and comparative experiments are described wherein the specified V2O4 : V2O5\t ratio is not maintained or regeneration is omitted. Specifications 583,032 and 665,976 also are referred to.ALSO:<PICT:0850594/III/1> Phthalic anhydride is prepared by a process comprising passing a mixture of naphthalene vapour and an oxygen-containing gas at a linear velocity of about 0.2 to 2 feet per second through a bed of fluidised particles of vanadium oxide-containing catalyst comprising a mixture of V2O4 and V2O5 at a temperatur in the range of about 320 DEG  to 420 DEG C. and a naphthalene to oxygen ratio of 2.5 to 16.5 mole per cent naphthalene such that upon continued operation the weight ratio of V2O4 to V2O5 in the catalyst would exceed 70:30, characterized in that the V2O4:V2O5 weight ratio is maintained between the limits of 70:30 and 20:80 by continuously withdrawing catalyst from the bed, continuously partially oxidising it with an oxygen containing gas to a lower V2O4:V2O5 ratio within the specified limits and returning it to the catalyst bed.  The naphthalene is preferably oxidised with air or a gas containing less than 21% of oxygen and the re-oxidation of the catalyst is preferably effected with a gas having a higher oxygen content.  The catalyst may be supported on a carrier such as silica gel, alumina gel or a zeolite and may contain an alkali-metal salt of an oxy-acid of sulphur such as a (initially) V2O5 : silver oxide : potassium pyrosulphate mixture or silica gel, as described in Specification 702,616.  The catalyst re-oxidation may be effected in a separate bed at about 320 DEG -400 DEG C., a suitable form of apparatus in this event comprising (Fig. 1, not shown) a heated vertical tubular reactor containing the fluidised bed of catalyst up through which the mixture of naphthalene vapour and oxygen-containing gas is passed; the effluent vapours pass out through a separator and are condensed to recover phthalic anhydride.  Catalyst is withdrawn at the base and passed in an air stream up a heated tube leading to the reactor separator whereby the re-oxidised catalyst is recycled. Alternatively, a re-oxidation zone may be provided at the base of the reactor as shown in Fig. 4, wherein a converter 40 having baffles 31 and heat exchanger 32 is provided with a zone 37 below a naphthalene feed point 36, wherein a fluidised regeneration bed of catalyst heated by coil 38 is maintained above an air distributing plate 34, the catalyst to be re-oxidised being withdrawn from the reaction zone and fed to the re-oxidation zone via one or more down-pipes 40. Examples are given wherein the apparatus first described above is used and the results are compared with those obtained in similar experiments wherein the regeneration is omitted or the specified weight ratio of V2O4:V2O5 is not maintained.  Specifications 583,032 and 665,976 also are referred to.