Homogeneous Catalytic System And Technology For Propionaldehyde Oxidation To Propionic Acid

The consumption of propionic acid and its derivatives has been upgraded year by year,but the domestic production of propionic acid is far from satisfying people's needs and requires a large amount of dependence on imports.There are currently three methods of propionic acid synthesis commonly used: by-product oxidation of light hydrocarbons to acetic acid Method,ethylene carbonyl synthesis method,propionaldehyde oxidation method.The process of the light hydrocarbon oxidation method is simple,but the components of the reaction solution are complicated;the raw material cost of the ethylene carbonyl synthesis method is low,and the yield is high,but its high pressure severely corrodes the reactor equipment.The propionaldehyde oxidation method is an effective route for the production of propionic acid,but the complexity of the process flow,rare metals and expensive precious metals as catalysts have limited their use.Therefore,optimizing the production process of propionic acid,preparing high-efficiency catalyst,and constructing a complete system of catalytic oxidation of propionaldehyde are urgent problems to be solved today.In this paper,a method for preparing propionic acid by oxidation of propionaldehyde is used.Two different types of cobalt salts were used to prepare new types of propionic acid catalysts.The crystallinity,thermodynamic properties,element valence,and surface morphology of the catalysts prepared by the two methods were studied,structure-activity relationship between catalyst properties and propionaldehyde oxidation was established.Furthermore,the single-factor experiments and orthogonal experiments were used to optimize the process conditions for the oxidation of propionaldehyde to propionic acid under the new catalyst system and the experimental results were verified.The main research contents are as follows:A new catalyst prepared from cobalt acetate and cobalt sulfate can be identified as a cobalt propionate catalyst by nuclear magnetic resonance analysis.It has good thermal stability,and decomposition at 220 ° C begins in the air.At the same time,the catalyst has a high crystallinity.The crystallinity of cobalt propionate is higher than that of cobalt acetate.No matter which method of cobalt propionate is prepared,the valence of cobalt is divalent,which will greatly promote the oxidation of propionaldehyde.Therefore,cobalt propionate is the catalyst used in the preparation of propionic acid by propionaldehyde oxidation.The reaction law and the range of optimized process conditions were given through single-factor experiments.It was found that as the reaction temperature,reaction time,oxygen flow rate,catalyst amount,etc.increased in a certain range,the selectivity of propionic acid almost increased first and then decreased,the conversion rate of propionaldehyde increases first and then does not change.It is determined that the reaction temperature range is 30-60 ?,and the reaction time range is 3-6 h.The oxygen flow rate range is 20-50 m L/min.The catalyst dosage range is 0.03%-0.09%;The mass fraction of solvent propionic acid is 20%,30%,40%,50%.The major and minor factors affecting the selectivity of propionic acid were obtained through orthogonal experiments,reaction>temperature>oxygen flow rate>amount of catalyst>reaction time>different solvent mass ratio,primary and secondary order of factors affecting propionaldehyde conversion is reaction temperature>oxygen flow rate>amount of catalyst>different solvent mass ratio >reaction time.It is shown that the reaction temperature and air flow rate are the factors that greatly affect the selectivity of propionic acid and the conversion of propionaldehyde.The optimized process conditions were obtained: the reaction temperature was 50 ?,the reaction time was 4 hours,the oxygen flow rate was 40 m L/min,the catalyst amount was 0.05% of the mass of propionaldehyde,and the mass ratio of the cobalt acetate and The amount of solvent propionic acid is 50%.Finally,three parallel verification experiments were performed on the experimental results.The selectivity of propionic acid was 93.18% and the conversion rate of propionaldehyde was 87.21%,which was higher than all the selectivity and conversion values in the orthogonal test.