Research On Synthesis Of Benzaldehyde By Ozone Oxidation In High Gravity Field

As a key fine chemistry intermediate,benzaldehyde has been widely used in the synthesis of medicines,pesticides and spices.Currently,metal-catalyzed oxidation is one of the key approaches for benzaldehyde synthesis,while it is limited by high requirement on conditions,high catalyst cost and low recovery.Therefore,it is increasingly significant to develop a kind of benzaldehyde synthesis route with mild conditions,no catalysis and simple process.Based on the outstanding oxidation ability and limited mass transfer in liquid phase for ozone,the idea of synthesizing benzaldehyde by high gravity technique enhancing ozone oxidation was proposed.The mass transfer behavior of gas phase ozone in organic solvents with different polarity was revealed by using ozone as oxidant,organic solvents of different polarities as reaction solvents,high gravity rotating packed bed as reactor and toluene,benzyl alcohol and styrene as research object.The thermodynamics,kinetics and oxidation mechanism of benzaldehyde synthesized by different reactants were explored.The effects of solvent types,high gravity factors and ozone concentration on the synthesis of benzaldehyde were optimized.The main contents and results were as follows:?1?The mass transfer performance of gas phase ozone in organic solvents such as ethanol,methanol,ethyl acetate,acetone,dichloromethane,etc were studied,and the mass transfer behavior of gas phase ozone in rotating packing bed and bubbling reactor was compared.The results showed that the concentration of liquid ozone in different organic solvents firstly increased and then stabilized.The equilibrium concentrations of ozone in ethanol,methanol,ethyl acetate,acetone,dichloromethane,chloroform,1,2-dichloroethane,acetonitrile and n-hexane were 2.31 g/L?1.95 g/L?0.80 g/L?0.81 g/L?0.31 g/L?0.32 g/L?0.31 g/L?0.30g/L and 0.14 g/L,respectively.The equilibrium concentration of ozone in alcohol solvent is higher,which is due to the hydrogen bond formed by ozone molecule and hydroxyl group in alcohol solvent is beneficial to ozone dissolution.The mass transfer coefficient of gas phase ozone in rotating packed bed is 2.07 times that of bubbling reactor by using ethyl acetate as solvent,which provides basic data and theoretical basis for the synthesis of benzaldehyde by high gravity enhancing ozone oxidation.?2?The synthesis of benzaldehyde by ozonation of toluene in the high-gravity field was studied systematically.The group contribution method was used to calculate the thermodynamics of the main and side reactions of benzaldehyde synthesized by ozonation of toluene.It can be concluded that the?35?_rH^q₂₉₈and?35?_rG^q₂₉₈of the main reactions of ozone oxidation toluene are-540.38 k J/mol and-476.23 k J/mol and that of the side reactions are-356.31 k J/mol and-383.77 k J/mol,respectively.The main and side reactions are all strong exothermic reactions and can be carried out spontaneously.The effects of solvent type,high gravity factor,gas phase ozone concentration and liquid flow rate on the synthesis of benzaldehyde by oxidation of toluene were investigated in rotating packed bed.Besides,its reaction mechanism of reaction was explored in this study.According to the results,when the reaction time is 30min,the conversion of toluene is 8%and the yield of benzaldehyde is only 0.8%.The reason for the low yield is that the ozonation of toluene is a series of side reactions and the side reaction rate is much higher than the main reaction rate.In addition,the ethylbenzene,diphenylmethane and fluorene were used as toluene analogues to study the influence of electron substituents on the ozonation reaction.The results show that the optimum yield of target products?acetophenone,benzophenone and 9-fluorenone?is 43%,52%and 59%,respectively,which is significantly higher than that of toluene oxidation to benzaldehyde.It is further proved that the introduction of electron donor substituents at benzyl position of toluene can improve the reactivity.According to the analysis of gas phase-mass spectrometry?GC-MS?and related experiments,the ozone oxidation process of toluene may be the synergistic effect of direct and indirect oxidation.?3?The thermodynamics,kinetics and oxidation mechanism of benzaldehyde synthesized from ozonation of benzyl alcohol in high-gravity field were studied.Thermodynamic study shows that the?35?_rH^q₂₉₈and?35?_rG^q₂₉₈of ozonation of benzyl alcohol are-365.87 k J/mol and-343.20k J/mol respectively.The analysis results of kinetics show the k₁ and k₂ of the reaction rate constants are 0.00073 s^-1 and 0.00162 s^-1,respectively.Besides,activation energy of main and side reaction is 6.35 k J/mol and 15.27 k J/mol,respectively.Under the optimized experimental conditions,the conversion of benzyl alcohol is 94%after 20 min,and the yield of benzaldehyde is 28%.Compared with the ozonation of toluene,the conversion and yield of benzyl alcohol ozonation increase by 86%and 28%,respectively.According to the analysis of Electron Paramagnetic Resonance spectrometer?EPR?,hydroxyl,superoxide and alkyl radicals were detected,which further speculated that the reaction process of benzyl alcohol ozonation included direct and indirect oxidation.?4?Styrene was used as reactant,and the effects law of operating factors,kinetic characteristics and oxidation mechanism of ozonation styrene to benzaldehyde were studied in rotating packed bed.The result shows that the conversion rate of styrene is 100%and yield of benzaldehyde is 96%,30%higher than that of bubbling reactor and 23%higher than that of literature after 15 min.Response surface method showed that there was obvious interaction between high gravity factor and gas phase ozone concentration on the yield of benzaldehyde.Dynamic study showed that the synthesis of benzaldehyde by ozonation of styrene was in accordance with the pseudo-first-order kinetic equation and the activation energy was 3.912k J/mol.In addition,Stilbene was used as the styrene analogue.Compared with ozonation of styrene,the conversion rate and yield of stilbene were similar under the same operating conditions.This was because the formation of formaldehyde was avoided.According to Criegee ozonation reaction mechanism,the ozonation process of styrene is direct oxidation process.Based on the intensification of ozone mass transfer,the reactant type,solvent type,thermodynamics,kinetics and reaction mechanism of benzaldehyde were systematically studied in the paper.A new approach to the synthesis of benzaldehyde by ozonation with mild reaction conditions,high yield,no catalysis and simple process was developed.