Study On The Synthesis Process Of M-toluic Acid With Heterogeneous Oxidation

As an important organic synthetic raw material and pesticide intermediate,m-toluic acid has important industrial application value and market prospects.It is especially used in the synthesis of methyldiethylamine and m-methyl nitrile,as well as herbicides and expelling production of chemicals and plasticizers.At present,there are many problems in the production process of m-toluic acid,such as high energy consumption,low production efficiency,many by-products and low product yield.The improvement and optimization of the synthesis process of m-toluic acid has always been one of the key issues of industrial production.This research started with the reaction equipment and reaction process,and built a meta-xylene oxidation reactor with reflux.The experiment investigated the material conversion situation of the reaction process under different conditions,the separation,purification and recycling of the product,and the influence of the equipment structure on the gas-liquid mass transfer of the oxidation reactor.In this study,the influence of experimental conditions such as temperature,gas flow rate and pressure catalyst on the reaction process was investigated through a self-made oxidation reactor.Experiments have found that temperature has a greater impact on the conversion rate of the reaction.The higher the reaction temperature is in the experimental temperature range(120～140°C),the greater the conversion rate.As the initiation temperature rises,the time required for initiation gradually becomes faster,and the initiation temperature is 135℃ to meet the needs.There is an optimum value for the gas flow rate,the conversion is best at7L/min,and the oxygen consumption rate is slow at the beginning and the end of the reaction,and the rate is faster after initiation.As the pressure increases,the reaction conversion rate gradually increases,the yield first increases and then decreases slightly,reaching the highest at 0.3MPa.As the reaction time becomes longer,the conversion rate and yield of the reaction show a gradual upward trend.By 6h,the conversion rate reached68.21%,and the yield reached 50.21%.Under the experimental conditions,cobalt naphthenate has the best catalytic effect among the three catalysts used,and the preferred catalyst addition amount is 0.5‰(molar ratio).After adding the co-catalyst,the conversion rate is obviously improved,and the optimal addition amount is 1‰.During the separation and purification of the product by batch vacuum distillation,the purity of the product first increases and then slightly decreases as the temperature of the distillation pot rises.The purity of the product can reach more than 99% in the range of160℃～175℃,and the highest at 170℃,basically no other impurities.The distillation speed has a certain effect on the output of residues.Slow distillation can reduce the entrainment of toluic acid in the rectification and cutting process and improve the separation of the product m-toluic acid,but the amount of residues is larger.In the experiment of recycling the product,using the recovered meta-xylene can promote the forward progress of the reaction process,and adding the mixture of meta-toluic acid and meta-tolualdehyde separated by rectification has obvious promoting effect on the conversion of the reaction.While rectification high-boiler residue has obvious inhibitory effect on the progress of the reaction.Adding a small amount of water can effectively increase the conversion rate and yield of the reaction,and can effectively inhibit the progress of side reactions.In the oxidation tower reactor,the average gas holdup of the liquid phase gradually increases with the increase of the aeration flow.Compared with straight tube aeration,the bubbles generated after using the microporous aerator and the wire mesh aerator are significantly smaller,and the air holdup is increased.Among them,the effect of the wire mesh aerator is better than that of the microporous aerator.As the temperature of the material liquid increases,the viscosity of the material liquid decreases,so that the size of the bubble when it is formed decreases,and the average gas holdup of the whole tower gradually increases.The installation of through-flow sieve plates and wire mesh packing in the reactor can significantly increase the average gas holdup of the entire tower,improve the backmixing phenomenon of the bubble tower,generate smaller and larger microbubbles,and increase the gas-liquid specific surface area.In contact with the phases,the atmospheric liquid is added for mass transfer and mixing.