Study On Selective Oxidation Of Two Toluene Compounds

Aromatic aldehydes and aromatic acids are a kind of important chemical products,and can also be used as intermediate products to synthesize fine chemicals in the fields of medicine,pesticides,dyes and so on.The demand is increasing day by day.Among many methods for the synthesis of aromatic aldehydes and aromatic acids,the selective oxidation of methyl aromatic hydrocarbons through oxygen or air to produce specific products has the natural advantages of high atomic economy and environmental protection.Compared with the high temperature and high pressure conditions of gas phase oxidation,which bring strict equipment requirements,liquid phase oxidation is more advantageous because of its mild reaction.The MC（mid-century）catalyst with Co/Mn/Br as the main component has been used early in the oxidation process of methyl aromatics,and the process is mature.The MC catalyst is still the best choice for the selective oxidation process of methyl aromatics considering the price of the catalyst,the difficulty of obtaining the catalyst,the catalytic effect and the recovery efficiency.Therefore,this research takes MC as main catalyst and catalyst on the choice of place of toluene,choose the typical electron-withdrawing groups-Cl and give electronic groups-CH₃,because of its ease para methyl oxidation,will to chlorine toluene and xylene respectively selective oxidation of chlorobenzene formaldehyde and methyl benzoic acid,and study its oxidation process.At the same time,the process flow of specific product is obtained,and it is also valuable for other oxidation process of substituted toluene.The work of this research is summarized as follows:1.Selected acetic acid cobalt,manganese sulfate,potassium bromide as main catalyst and acetic acid as solvent,formed on the selective catalytic oxidation of toluene chloride experiment system,investigates the dosage of solvent,reaction temperature,catalyst,catalyst composition,dosage of initiator system of moisture content on the experiment,the influence of the optimal conditions of various parameters are obtained.Five factors and four levels of orthogonal test were designed based on the five parameters of catalyst dosage,catalyst ratio,reaction temperature,solvent dosage and co-catalyst dosage,and the optimal process conditions were obtained:The reaction temperature is 90℃,the dosage of catalyst is 4wt%,the solvent ratio is 1:2（volume ratio）,the ratio of cobalt and manganese is 3:1（mass ratio）,the co-catalyst dosage is0.625wt%.The conversion of p-chlorotoluene is 31.42%,the selectivity of p-chlorobenzaldehyde is 81.14%,and the yield of p-chlorobenzaldehyde can reach25.49%.2.The concept of tolerance ratio was put forward.The tolerance ratio was defined as the ratio of p-chlorotoluene to p-chlorobenzaldehyde when the selectivity of p-chlorobenzaldehyde was mutated.Calculated kinetic constants before the time of tolerance,reaction conditions are catalyst 3wt%,solvent ratio of 1:2（volume ratio）,cobalt,manganese ratio of 2:1（mass ratio）,don’t add cocatalyst.For oxidation of p-chlorotoluene generated p-chlorobenzaldehyde and oxidation p-chlorobenzaldehyde generated p-chlorobenzoic acid.The k₁and k₂ were obtained at different temperatures.The calculated activation energies Ea₁ and Ea₂ are 24.29 k J/mol and 108.5 k J/mol respectively.3.Using the distillation operation module of Aspen Plus,the separation process of raw materials and products after p-chlorotoluene reaction was designed and simulated.The NRTL physical property equation was selected to perform strict calculation on the distillation column.A two-column continuous distillation model was established and the optimal process parameters were determined.The feeding position is the ninth tray.The theoretical plate number of vacuum distillation tower 2 is 20,the molar reflux ratio is 5,and the feed position is the eighth tray.The solvent and raw material were recovered by continuous distillation in two columns and side extraction in the second column.The purity of p-chlorobenzaldehyde was 99%and the recovery rate was 99%.4.Preparation of p-methylbenzoic acid by selective liquid phase oxidation of p-xylene in solvent free condition was studied.The advantages and disadvantage of three different cobalt salt catalysts were compared,and the effects of catalyst dosage,reaction time,oxygen flow rate and other parameters on reaction effect were investigated.Finally,the optimized reaction conditions were as follows:cobalt naphthenate catalyst,dosage of 0.1%,reaction temperature of 135℃,reaction time of 5 h,oxygen flow of100 m L/min.Under the optimal reaction conditions,the reaction conversion rate was30.5%,and the selectivity of methyl benzoic acid could reach 58.4%.