Dissertation > Excellent graduate degree dissertation topics show

Study on Surface Reaction of Propylene Ammoxidation Catalyst Based on in Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy and Monte Carlo Simulation

Author: WangYang
Tutor: ChenFengQiu;ZhanXiaoLi
School: Zhejiang University
Course: Chemical Engineering and Technology
Keywords: propylene selective oxidation ammoxidation bismuth molybdate catalyst Monte Carlo simulation site isolation phase cooperation conceptual design
CLC: O643.32
Type: PhD thesis
Year: 2007
Downloads: 256
Quote: 2
Read: Download Dissertation

Abstract


The oxidation and ammoxidation of propylene over bismuth molybdate catalyst was investigated in detail using in situ DRIFTS, molecule probe and dynamic RWMC simulation. Attention was particularly focused on the mechanism of propylene oxidation and ammoxidation, including the complete reaction networks of propylene oxidation, the route of acrylonitrile formation, the formation route of acrylonitrile from acrolein, and the transformation to acetonitrile from acetaldehyde. Conceptual design about propylene ammoxidation catalysts was proposed associated with dynamic simulation of propylene ammoxidation over bismuth molybdate catalyst. Such results were obtained as follows:The in situ DRIFTS equipment was successfully constructed with application to heterogeneous catalytic system, and in situ study on the surface reaction mechanism of propylene oxidation and ammoxidation was carried out. The results of in situ DRIFTS on propylene oxidation show that the allyl species originated from α-H abstraction of propylene were located at the wavenumbers of 1454 cm-1 and 1427 cm-1. The rate-determining step is the abstraction of an α-H abstraction from a lattice oxygen linked to a bismuth ion to form a π-allyl intermediate coordinated to a molybdenum ion. The metal-oxo group then attacks the allyl intermediate forming a σ-bonded oxygen-allyl species, which is in a rapid equilibrium with the π- bonded species. The σ-bonded species then transforms to acrolein by further abstraction of α-H. Such species as formate, carboxylate, carbonate transform to deep oxidation products （COx）. The acetone was derived from propylene by an enolic species at lower temperatures.Based on in situ DRIFTS of propylene ammoxidation, four kinds of ammonia species on catalyst surface include: （i） ammonia dissociate adsorption with the formation of surface NH2 species (1558 cm-1) can take place, （ii） complete proton transfer can occur with the formation of an NH4+ ion (1651 cm-1 and 1435 cm-1) on Bronsted acid sites, （iii） ammonia coordination (1246 cm-1) on Lewis acid sites,which plays a crucial role in the formation of acrylonitrile from acrolein with partial oxidation of propylene, （iv） molybdenum-imido species （Mo=NH） (1029 cm-1) are possibly proposed as the intermediates during the formation of acrylonitrile from the direct ammoxidation of propylene, which provides IR evidences of the presence of Mo=NH. The propylene molecule transforms to formaldehyde and acetaldehyde by degradation, the latter occurs to addition reaction with coordinated ammonia species, and forms acetonitrile by dehydration and oxidation.It is determined that the key active phase exists on the surface of propylene ammoxidation catalyst. The physical model of catalyst surface is built by means of binary digit technique, and the mechanism model of propylene ammoxidation is built. Thereby, the RWMC model applied to simulate the dynamic process of propylene oxidation and ammoxidation is constructed using Matlab. The simulation results show that the proper transfer rate of lattice oxygen is favorable for the reaction process, and the propylene conversion reaches the maximum after the reduction of catalyst to a certain degree. The transfer rate of lattice oxygen to the Mo vacancy differs from that to the OA vacancy, and the latter is more rapid than the former. The probability of oxygen dissociative chemisorption contributes most favorably to the formation of acrylonitrile. Therefore, the improved way of propylene ammoxidation catalyst is proposed above the simulation results. It is inferred that catalytic performance improves greatly if the ratio of capacity for dehydrogenation from adsorbed propylene molecule on catalytically active site of molybdenum metal-imido group （Mo=NH） to that on catalytically active site of molybdenum metal-oxo group （Mo=O） becomes much higher. Another way is to optimize the bulk structure of catalyst to achieve the target of more lattice oxygen originated rapidly from gas oxygen and to speed up the transfer of lattice oxygen to the vacancies of Mo and OA site.The conceptual design of propylene ammoxidation catalyst is proposed associated with the experimental and simulated results of this paper under the guide of site isolation and phase cooperation. Firstly, plenty of molybdenum-oxospecies on catalyst surface is obtained to make gas oxygen transform favorably into lattice oxygen. Secondly, enough molybdenum-imido species is derived from the lattice imido species transformed favorably from ammonia. Finally, it is fitting for the number and proportion of molybdenum-oxo species and molybdenum-imido species to form abundant oxo- molybdenum-imido species on catalyst surface. The actualized means of optimal design about propylene ammoxidation catalyst are suggested on the basis of this conceptual design. The yield of acrylonitrile is improved to optimize catalyst structure using site isolation. Single phase is designed based on phase cooperation, i.e., to integrate such multi-functionalities as hydrogen abstraction, oxygen-insertion （or nitrogen-insertion） into single phase. The acrylonitrile yield is enhanced to reduce the deep oxidation products and by-products originated from degradation reaction by designing catalyst for ammonia activated at low temperature. Finally, corresponding ideas of optimal design on propylene ammoxidation reactor and optimal controlling to reaction process are presented.

Related Dissertations

  1. Aerial Target Anti-interference Recognition and Tracking System,TN215
  2. In the standard model based on VaR Equity Fund Risk Assessment Study,F224
  3. Research on Real Options Models and Applications in China,F832.5
  4. The Application Research to Risk Measurement of Index Futures,F224
  5. Study of Propylene Oxide Wastewater Pretreatment by Five-effect Evaporation Process,X78
  6. Study on the Preparation and Photocatalytic Activity of Titanium Dioxide Nanoparticles,O643.36
  7. Study of High-Efficient Supported Catalysts for Synthesizing Poly-(Propylene-carbonate) and Their Founctional Applications,TQ314
  8. Monte Carlo simulation cC 4 F 8 and CHF 3 mixed gas discharge characteristics,TM213
  9. Complex electromechanical products for multi-domain system design features represents the functional decomposition methods,TH122
  10. Nanoporous materials absorb harmful gases grand canonical Monte Carlo,TB383.1
  11. Testability verification technology and its application in a virtual helicopter heading and attitude System Research,V249.122.2
  12. An Atom-Economic Reaction for Synthesis of 1-Phenoxy 2-Propanol Over Al2 O3 /MgO,O643.32
  13. Analysis of Reliability on Stability of High Slope of Expressway under Seismic Force,U416.14
  14. Light in the steady - state transmission model the layered tablet biological organization,R318.51
  15. Evaluation and selection of our classification method of valuation of the Fund,F224
  16. Application Research of Critical Chain Project Method in Project Schedule Management,F224
  17. Transmission of Polarized Photons in Atmosphere and Interaction between Single Photons and Cavity-quantum Dots,O431.2
  18. Research on Integrated Risk Measurement Model for Defaultable Zero-coupon Bonds,F830.9
  19. The Applied Study of VaR to the Foreign Exchange Risk Management of Commercial Banks in China,F832.2
  20. Numerical Study of Stochastic Supersensitiviy of Generalized Burgers Equation,O241
  21. Pricing Strategy Research of Lng Based on Monte-Carlo Simulation and Genetic Algorithms,F416.22

CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalytic reaction
© 2012 www.DissertationTopic.Net  Mobile