The Study On VPO/γ-Al₂O₃ Catalyst For Methyl Acrylate Fluidized Bed Process

The technical route of methyl acetate and formaldehyde to synthesis methyl acrylate was focused in this theses,VPO/γ-Al₂O₃ catalyst was developed,by studying supports screening,loading mode,loading amount and supports modifying,the best catalyst was obtained,the activity of catalysts was also studied.The main research contents and results are as follows:（1）Six supports γ-Al₂O₃,Nb2O5,Sb2O3,ZrO2 and SiO2,TiO2 were screened and the activites of six catalysts were evaluated,γ-Al₂O₃ as the optimal support was obtained.By the characterization of physical chemical properties,the information about catalyst surface structure,crystallization phases,stability and acid-base properties on different supports was obtained,concluding that the property of VPO phase was effected by supports,the acid-base property was key element to effect the catalyst activity.（2）Two kinds of loading modes were designed,one is in-situ synthesis,the other is deposition-impregnation,the activity of two catalysts was compared.The crystal size of the active phase in-situ synthesized on support was much smaller,VPO phase dispersed well on γ-Al₂O₃ and performed higher reactivity,so the in-situ synthesized preparation method was determined.By changing the loading amount and evaluating the activity,best performance was gained at 15 wt%,the conversion of formaldehyde was 35%,the yield of target products was 33%.By means of BET,XRD,TPD characterizations and so on,the information about catalyst surface structure,crystallization phases,crystal size and acid-base properties was obtained.（3）By studying the effects of support,a modification method of H3PO4 treatment on γ-Al₂O₃ was designed to improve the properties of active phase.By means of characterization,the information about modified catalysts was obtained,the pore diameter of γ-Al₂O₃ was enlarged by H3PO4 and the real loading amount of active phase was increased,the P-OH vibration on catalyst was strengthened and the acidity distribution was also changed due to support modification,medium acid dominated on catalysts.The best performance of modified catalyst was obtained at 2.0 mol/L with the conversion of formaldehyde reaching 42%and the yield of methyl acrylate reaching 39%.（4）The reaction temperature and feed ratio was optimized,the best performance was obtained at 623 K with feed ratio at 5:1.The inactivation reason and regeneration of VPO/γ-Al₂O₃ catalyst were studied,showing that the decrease of activity was due to carbon deposition.The catalyst could be continuously used for 60 h and was able to be fully activated after calcination.The wear-resisting property of catalyst was evaluated,the data support for fluidized bed applications was obtained.