Patent GB-937904-A (GB)
Title: Process for the recovery of organic acid anhydrides
IPC: B01D1/14
Filed: 1960-10-31
Abstract: An organic acid anhydride, such as phthalic or maleic anhydride, is separated by vaporization from the residue of a primary distillation of a product of an air-oxidation of an aromatic hydrocarbon, by contacting the molten residue, in the form of fine particles or a film, with a hot gas, such as combustion gases or the gaseous products from the oxidationreactor.  The anhydride is subsequently separated from the gas by condensation.  Carrier gas containing 90% N2 and 10% CO2 is pumped through heat-exchanger 8, where the carrier <PICT:0937904/III/1> gas is heated to 470 DEG C. by means of the combustion products from a coke-oven gas burner.  The hot carrier gas then flows up a helical path in the cylindrical jacket of evaporator 2, and enters the evaporator through slots directly below the cover. A secondary stream of hot carrier gas is branched off and used to heat the conical lower jacket of the evaporator and also the cyclone separator 3.  Buckets of molten distillation-residue comprising 75% by weight of phthalic anhydride are continuously scooped up by a bucket-elevator in reservoir 1, which is maintained at 200 DEG C., and are discharged via a shoot into a rotating dish in the top of the evaporator where the residue is distributed in the form of fine droplets.  The phthalic anhydride vaporizes from the droplets, and the mixture of vapour and carrier gas enters cyclone 3.  A carbonaceous residue collects in the conical part of the evaporator, where it is flushed with inert gas.  The mixture of anhydride vapour and carrier gas flows from cyclone 3 into condenser 4 in which the mixture is cooled to 137 DEG C. and a large proportion of the anhydride condenses into the liquid state.  The liquid anhydride flows into reservoir 9.  The gas flows on into either separator 4a or 4b where it is cooled to 20 DEG C. so that phthalic anhydride is precipitated in crystalline form.  From time to time the separator containing the solid anhydride is taken off-stream, so that the anhydride can be fused, and the liquid collected in reservoir 9.  A flow of oil is used to cool the separator in use, and the oil is then used as cooling medium in condenser 4.  The last traces of pulverulent anhydride are removed from the carrier gas in cyclone 5, and it is then recirculated via tube-filter 6 to heat-exchanger 8. In an example relating to the separation of maleic anhydride, the gases leaving the condenser are washed with water in order to remove residual anhydride; and the aqueous solution of maleic acid so obtained is fed to the spraying-device in the evaporator.ALSO:An organic acid anhydride, such as phthalic or maleic anhydride, is separated by vaporization from the residue of a primary distillation of a product of an air-oxidation of an aromatic hydrocarbon, by contacting the molten residue, in the form <PICT:0937904/IV(a)/1> of fine particles or a film, with a hot gas such as combustion gases or the gaseous products from the oxidation-reactor.  The anhydride is subsequently separated from the gas by condensation. Carrier gas containing 90% N2 and 10% CO2 is pumped through heat-exchanger 8 where the carrier gas is heated to 470 DEG C. by means of combustion products from a coke-oven gas burner.  The hot carrier gas then flows up a helical path in the cylindrical jacket of evaporator 2, and enters the evaporator through slots directly below the cover.  A secondary stream of hot carrier gas is branched off and used to heat the conical lower jacket of the evaporator and also the cyclone separator 3.  Buckets of molten distillation-residue comprising 75% by weight of phthalic anhydride are continuously scooped up by a bucket-elevator in reservoir 1, which is maintained at 200 DEG C., and are discharged via a chute into a rotating dish in the top of the evaporator where the residue is distributed in the form of fine droplets.  The phthalic anhydride vaporizes from the droplets, and the mixture of vapour and carrier gas enters cyclone 3.  A carbonaceous residue collects in the conical part of the evaporator, where it is flushed with inert gas.  The mixture of anhydride vapour and carrier gas flows from cyclone 3 into condenser 4 in which the mixture is cooled to 137 DEG C. and a large proportion of the anhydride condenses into the liquid state.  The liquid anhydride flows into reservoir 9.  The gas flows on into either separator 4a or 4b where it is cooled to 20 DEG C. so that phthalic anhydride is precipitated in crystalline form.  From time to time the separator containing the solid anhydride is taken offstream, so that the anhydride can be fused, and the liquid collected in reservoir 9.  A flow of oil is used to cool the separator in use, and the oil is then used as cooling medium in condenser 4.  The last traces of pulverulent anhydride are removed from the carrier gas in cyclone 5, and it is then recirculated via tube-filter 6 to heat-exchanger 8. In an example relating to the separation of maleic anhydride, the gases leaving the condenser are washed with water in order to remove residual anhydride; and the aqueous solution of maleic acid so obtained is fed to the spraying-device in the evaporator.