Dynamic behavior of industrial fixed bed reactors for the manufacture of maleic anhydride

by David Lesser

Institution: Technische Universitt Dortmund
Year: 2017
Keywords: ddc:620; n-Butan Oxidation industrieller Festbettreaktor dynamisches Reaktormodell
Posted: 02/01/2018
Record ID: 2186716
Full text PDF: https://dokumente.ub.tu-clausthal.de/receive/clausthal_mods_00000534;https://dokumente.ub.tu-clausthal.de/receive/clausthal_mods_00000534;https://dokumente.ub.tu-clausthal.de/servlets/MCRFileNodeServlet/clausthal_derivate_00000313/Db113383.pdf


Maleic anhydride (MA) is an important intermediate in the chemical industry. It is synthesized by the catalytic oxidation of n-butane with air. Mainly tubular fixed bed reactors are used for this strongly exothermal reaction, where the reaction heat is removed by molten salt. The catalysts consist of vanadium phosphorous oxides (VPO) and are employed as pelletized full body shapes. The main side products of the reaction are CO and CO2.Even after many years of investigation, the reaction mechanism and the nature of the active sites are not fully understood. An important subject of discussion is the assumption that water interacts with the VPO surface forming separated phosphate groups. The slowly progressing loss of these phosphates from the catalyst shifts conversion and MA selectivity to commercially unattractive regions. Therefore, it is industrial practice to add several ppm of an organic phosphorous compound to the reactor feed. The distribution of the phosphorous within the catalyst bed is supported by further addition of steam.For the investigation of these processes the inlet the inlet concentrations of water and trimethyl phosphate (TMP) were dynamically varied in experiments in an industrial-scale pilot reactor filled with full body shaped VPO catalysts. Various, partially opposing effects were observed occurring at different time scales. Variations of these feed components caused e.g. slow changes in shape and height of the forming temperature profiles and in product composition, respectively.As reported so far, kinetic models have been derived primarily from experiments in which significant changes in catalyst activity were not observed. Additionally, there are no studies reported with TMP feed under industrial reaction conditions. Thus, the scope of this work is developing a model which is able to describe all observed effects during complete test periods of several weeks.According to findings in the literature, a novel kinetic model for MA formation was derived which accounts for all observed interactions between TMP and water on the VPO surface. The kinetic model was integrated into a two-dimensional, heterogeneous reactor model (gPROMS) that includes intra particle heat and mass transfer resistances, pressure drop, and radial heat transport from the catalyst bed to the cooling medium. This reactor model could be successfully applied for parameter estimations. Kinetic and heat transport parameters were adapted to the pilot reactor experiments. The model is able to describe well up to 500 h time on stream including many variations of the operating conditions. The dynamically changing activity profiles reflect the evolution of temperature profiles and product compositions in the pilot reactor with only minor deviations. Maleinsureanhydrid (MA) ist ein wichtiges Zwischenprodukt in der chemischen Industrie und wird durch die katalytische Oxidation von n-Butan mit Luft hergestellt. Fr diese stark exotherme Reaktion kommen hauptschlich Festbettreaktoren zum Einsatz. Die Reaktionswrme wirdAdvisors/Committee Members: Turek, Thomas.