Method and device for production of a homogeneous mixture of a vapour-forming aromatic hydrocarbon and an oxygen-containing gas

Abstract

A process and an apparatus for producing a homogeneous mixture of a gaseous aromatic hydrocarbon and an oxygen-containing gas for catalytic gas-phase reactions, in particular a homogeneous mixture of gaseous o-xylene and/or naphthalene and air for preparing phthalic anhydride, are provided. The liquid aromatic hydrocarbon is atomized to form droplets having a diameter of less than 1 mm and injected into an oxygen-containing gas stream ( 12 ) preheated to above the boiling point of the aromatic hydrocarbon. According to the invention, the liquid aromatic hydrocarbon is atomized by means of nozzles ( 15 ) which form a hollow cone ( 16 ), preferably by means of swirl nozzles. The o-xylene/air mixture is advantageously produced in a chamber which is bounded by side walls ( 18 ) heated to above the boiling point of the hydrocarbon.

We claim:  
     
         1 . A process for producing a homogeneous mixture of a gaseous aromatic hydrocarbon and an oxygen-containing gas for catalytic gas-phase reactions, by 
 atomizing the liquid aromatic hydrocarbon to form droplets having a diameter of less than 1 mm and injecting it into an oxygen-containing gas stream preheated to above the boiling point of the aromatic hydrocarbon,    wherein the liquid aromatic hydrocarbon is atomized by means of nozzles which form a hollow cone, preferably swirl nozzles.    
     
     
         2 . A process as claimed in  claim 1 , wherein the hollow atomization cone has an opening angle of from 30° to 70°.  
     
     
         3 . A process as claimed in  claim 1  or  2 , wherein the central axis of the hollow atomization cone is at an angle of from −30° to +30° to the central axis of the preheated gas stream.  
     
     
         4 . A process as claimed in any of  claims 1  to  3 , wherein the mixture is produced in a chamber which is bounded by side walls heated to above the boiling point of the hydrocarbon.  
     
     
         5 . A process as claimed in  claim 4 , wherein the side walls of the chamber are formed by a heated tube, in particular a “Thermoblech” tube.  
     
     
         6 . A process as claimed in  claim 4  or  5 , wherein from 5 to 50% by weight, preferably from 5 to 40% by weight, particularly preferably from 5 to 30% by weight, of the atomized hydrocarbon are vaporized on the heated side walls.  
     
     
         7 . A process as claimed in any of the preceding claims, wherein the mixture after vaporization of the aromatic hydrocarbon is passed through a static mixer.  
     
     
         8 . A process as claimed in any of the preceding claims for use in the synthesis of phthalic anhydride, where the aromatic hydrocarbon is o-xylene and/or naphthalene and the oxygen-containing gas is air.  
     
     
         9 . An apparatus for producing a homogeneous mixture of a gaseous aromatic hydrocarbon and an oxygen-containing gas having gas channels ( 11 ) for a preheated, oxygen-containing gas stream ( 12 ) and an atomization device ( 13 ) for a stream of a liquid aromatic hydrocarbon opening into the gas channels ( 11 ), wherein the atomization device ( 13 ) has swirl nozzles ( 15 ) and the gas channels ( 11 ) have, at least downstream of the swirl nozzles ( 15 ), walls ( 18 ) which can be heated to at least the boiling point of the hydrocarbon.  
     
     
         10 . An apparatus as claimed in  claim 9 , wherein the gas channels ( 11 ) comprise a heatable tube, in particular a double-walled tube or a tube made of “Thermoblech”.  
     
     
         11 . An apparatus as claimed in  claim 9  or  10 , wherein a static mixer is installed in the gas channels downstream of the swirl nozzles.