Study On The Activation Of VPO Catalyst And Kinetics For Oxidation From N-butane To Maleic Anhydride

Maleic anhydride(MA),an important intermediate in the petrochemical industry,is mainly produced by selective oxidation of n-butane in the presence of vanadium-phosphorus-oxide(VPO)catalysts.Studies have shown that the activation of the VPO catalyst has the most important effect on the reaction activity and MA selectivity of the catalyst.Hence,in view of the long induction period and low MA selectivity of domestic VPO catalysts,the influence of ex situ activation conditions on the structure and performance of the VPO catalyst was investigated in this study.In addition,the generation path of acetic acid and acrylic acid was studied,and a kinetic model capable of describing the formation of acetic acid and acrylic acid was established.Furthermore,a two-dimensional model of the single-tube fixed bed reactor was established to provide technical support for the industrial application of domestic VPO catalysts.The main work and research results are as follows:(1)The effect of water content,temperature,duration time and air content on the performance and structure of the catalyst in the ex situ activation was investigated.It is found that the change of activation conditions causes the change of the crystallinity of(VO)2P2O7 and the content of VOPO4 in the VPO catalysts,which leads to the difference in the n-butane conversion and MA selectivity.Research also indicating that water could accelerate the formation of(VO)2P2O7 crystals and the oxidation of V4+to V5+species.The crystal phase transformation process of the VPO catalyst in air/N2/H2O atmosphere was proposed according to the XRD and Raman results.Furthermore,a preferred ex situ activation methodology for obtaining VPO catalysts with high steady-state performance was proposed,and the activation duration was shortened from over 100h for in situ activation to 10h.The long-term test results show that the steady-state n-butane conversion of the catalyst is around 84%,and the steady-state MA selectivity is around 64%,reaching the same level as in situ activation method.(2)Based on the ex situ activated catalysts under preferred conditions,the effects of operating conditions on product distribution of n-butane oxidation reaction,especially acetic acid,acrylic acid and MA selectivity in a fixed bed reactor was investigated.The generation path of acetic acid,acrylic acid and MA was studied.Furthermore,a kinetic model including the often neglected by-products acetic and acrylic acid was established over a wide range of industrially relevant operating conditions,which could precisely describe the n-butane oxidation reaction system.(3)An industrial single-tube pseudo-homogeneous two-dimensional reactor model with salt bath was established according to the kinetic model of n-butane oxidation reaction.The temperature distribution,content distribution of components and the pressure distribution of the reactor under typical operating conditions was calculated.The influence of operating conditions on reactor hot spots was investigated based on the reactor model,which has great significance to the industrial application of domestic VPO catalysts.