The Study Of The Condensation Of Acetic Acid And Formaldehyde On VPO Catalyst To Produce Acrylic Acid

Acrylic acid is the simplest unsaturated carboxylic acid.It has a strong ability of polymerization and esterification,and is widely used in construction materials,automobiles,medical,healthy industries and so on.The mainly industrial method to product the acrylic acid is propene oxidation.At present,petroleum resources are facing depletion,while acetic acid and formaldehyde are in excess of production.As a result,the process of acetic acid and formaldehyde aldol condensation to produce acrylic acid gradually emerged.This non-oil coal chemical synthesis acrylic product line has great potential application value.For the gas-phase aldol condensation of acetic acid and formaldehyde to produce acrylic acid,the choice of catalyst is very important.Combined with the reaction mechanism,it is necessary for the catalyst to have obvious acidity.At the same time,certain alkalinity is also necessary.The VPO oxide catalysts show better catalytic performance in this reaction.To further improve the catalytic performance,it is also necessary to improve the catalysts to some extent.In this paper,in order to improve the catalytic performance,Ti and Nb were added to the VPO catalysts for modification.The preparation conditions of the catalysts and the reaction conditions were investigated.The crystal structure,surface ionic valence,surface acidity and basicity of the catalyst s were characterized by XRD,FT-IR,XPS,TPD,BET and other characteristics.The main conclusions of our work are as follows:1.The influence of the addition of Nb on the catalytic performance of the Nb_x VPO catalysts was examined.With the different amount of Nb,the structure and performance of the catalysts show some regularity.The introduction of a certain amount of Nb helps reduce the average valence of V ions on the catalyst surface,increases the relative content of strong acid sites,and thus increases the selectivity and yield of acrylic acid.2.The preparation conditions for Nb-doped VPO catalysts have been optimized.The optimum preparation conditions were as follows:a mixture of isobutanol and benzyl alcohol was used as the organic solvent,the catalyst was synthesized at 110°C,the P/V atomic ratio was 1.4 and the atomic ratio of Nb/V was 0.06.3.The Nb_x VPO catalyst was used to evaluate the reaction of acetic acid and formaldehyde for the gas-phase aldol condensation to produce acrylic acid.The best reaction conditions were:the reaction temperature was 350°C,the flow of feedstock was 1.0 mL/h,the ratio of the reaction solution was HAc/FA=3.5,and flow of oxygen was 3.0 mL/min.4.When Ti was added to the VPO catalyst,the influence of the preparation method on the catalytic performance was discussed.The catalyst prepared by the grinding method does not effectively improve the catalytic performance,but the catalytic performance of the catalyst prepared by the organic solvent method has been improved to some extent.Among them,the catalyst prepared by the second method(using TBT as the titanium source)has the highest selectivity(78.3%)to acrylic acid,and the stability of the catalyst is also better.