Study On The Process For The Synthesis Of Propionic Acid By Oxidation Of Propanol With Hydrogen Peroxide

Propionic acid is an important fine chemical product,which is widely used in food,feed,medicine and other industries.At present,it is mainly produced by ethylene carbonylation and propionaldehyde oxidation.The process of ethylene carbonylation method is complex,and the environmental pollution of propionaldehyde oxidation method is serious.Hydrogen peroxide is a green and safe oxidant for the synthesis of carbonyl compounds from alcohols.The production of propionic acid from propanol by hydrogen peroxide has the characteristics of simple method and environmental protection.In this paper,the catalytic structure and activity of various catalysts were studied,and the method of producing propionic acid by catalyzing the oxidation of propanol by hydrogen peroxide with polyoxometalates catalyst was determined,and the process was studied.The analytical method of the reaction system and the possible substances produced in the oxidation process were established by analyzing the reaction mechanism of the synthesis of carbonyl compounds from alcohols oxidized by hydrogen peroxide.In order to achieve green chemistry,three kinds of catalysts were synthesized:coordination compound catalysts with iron,manganese and copper ions as catalytic centers,peroxide catalysts with planar molecule M?O₂?₂O?M=Mo,W?as the center,and polyoxometalates containing transition metal cations and heteropoly anions.The synthesis of propionic acid by oxidation of propanol with hydrogen peroxide catalyzed by three different catalysts was studied.It was found that the zinc substituted polyoxometalates could efficiently catalyze the oxidation of propanol with hydrogen peroxide to propionic acid.The process route of synthesis of propionic acid by oxidation of propanol with hydrogen peroxide catalyzed by transition metal zinc polyoxometalates was determined.By studying the effects of various conditions such as solvent,reaction time,reaction temperature,catalyst dosage,hydrogen peroxide dosage and propanol concentration on the reaction results,the optimum reaction conditions were obtained:using metal zinc polyoxometalates Na₆[SiW₁₁ZnH₂O₄₀]?12H₂O as catalyst,catalyst dosage 0.15 mol%,molar ratio of hydrogen peroxide to propanol 2.5,propanol concentration 3 mol/L,reaction temperature 80?.The reaction time was 16 hours.The single conversion of propanol reached 81%and the selectivity of propionic acid reached 90%.It was found that the activity of the polyoxometalates catalyst substituted by transition metal zinc did not decrease significantly after 5 cycles.After repeated use,the catalytic activity decreased slightly.After calcination and regeneration,the catalytic activity can reach 90%of the initial catalytic activity.On this basis,the laboratory scale-up experiment was carried out and the technological process was proposed.The reactants in the reactor are separated by simple distillation.The unreacted raw materials and by-products can be further reacted.The selectivity of the whole process can more than 99%,and almost no waste are produced.The synthesis of propionic acid from propanol oxidized by hydrogen peroxide catalyzed by polyoxometalates conforms to the development concept of green chemistry.The whole process is simple,mild,green and safe.It has important application significance for green production of propionic acid.