Study On Catalytic Oxidation Of Methyl Aromatic Compounds

Both o-chlorobenzaldehyde and o-chlorobenzoic acid are important intermediates in organic synthesis,and are widely used in pharmaceutical,pesticide and dye industries.The two componds can be prepared by liquid-phase oxidation of o-chlorotoluene with oxygen,which has the advantages of mild reaction conditions,low production cost,and less pollutant generation.However,the manufacture of o-chlorobenzaldehyde by the liquid-phase oxidation of o-chlorotoluene with oxygen in a tradional bath suffers from the disadvantages of low selectivity of o-chlorobenzaldehyde and serious potential safety hazard.The microchannel reactor has a large specific surface area,high mass transfer rate,good heat transfer effect,good operability,safety,and small amplification effect,which afford this kind of device with broad prospect of applications in the synthesis of o-chlorobenzaldehyde from the liquid-phase oxidation of o-chlorotoluene with oxygen.First,the synthesis process of o-chlorobenzoic acid by atmospheric liquid-phase oxidation of o-chlorotoluene with oxygen in a bath reactor was investigated.The reaction parmeters including the molar ratios and amounts of Co/Mn/Br,reaction temperature,oxygen flow rate and reaction time were screened by using Co/Mn/Br ternary system as catalyst,oxygen as oxidant,and o-chlorobenzoic acid as co-solvent under atmospheric pressure and solvent-free conditions.The optimal reaction conditions were obtained as fllows:the molar ratios of Co/Mn/Br of 1:1.5:5.3,the total amount of catalyst of 0.94 mol%,the reaction temperature of 145°C,the oxygen flow rate of 60 m L/min,and the reaction time of 17 h.Under these conditions the conversion of toluene reached 100%,and the yield of o-chlorobenzoic acid was up to90.7%.Second,the process for the preparation of o-chlorobenzaldehyde by liquid-phase oxidation of o-chlorotoluene with oxygen catalyzed by Co/Mn/Br system in the microchannel reactor was stydied.It was found that the selectivity of o-chlorobenzaldehyde was higher than 70%when keeping the conversion of o-chlorotoluene about 10%,under the reaction conditions of the Co/Mn/Br molar ratio of0.3:0.3:1,total amount of catalyst of 0.88 mol%,reaction temperature of 423 K,gas-liquid molar ratio of 5.5,reaction pressure of 0.5 MPa,and residence time of 9.4 s.Meanwhile,the kinetics of the oxidation of o-chlorotoluene with oxygen was investigated,and two kinetic equations were obtained as follows:...