(510b) Oxygen-Free Oxidative Dehydrogenation of Ethane Over Vox/γ-Al2O3 ‎Catalyst In Riser Reactor Simulator ‎

The development of a stable and selective catalyst for ethane ODH is the major challenge in developing available alternative ODH process for olefin production. This new process will likely involve fluidized beds and hence a selective fluidizable catalyst is the key for successful implementation of future ODH processes. In the present study reports ethane oxidative dehydrogenation (ODH) under oxygen free atmosphere using 10 wt. % VO_x supported on γ –Al₂O₃ catalyst. A number of  physicochemical techniques such as Brunauer-Emmett-Teller (BET) surface area, temperature-programmed reduction (TPR), temperature programmed oxidation (TPO) ammonia temperature programmed desorption (NH₃-TPD) and X-ray diffraction (XRD), are used to characterize the prepared catalyst. TPR and TPO results show that the prepared γ-alumina supported 10 wt.% VO_x catalyst is stable over repeated reduction and oxidation cycles with reduction temperature around 500 ^oC. The XRD profile for the prepared catalyst indicates the absence of V₂O₅ bulk surface species andhigh dispersion of VO_x on the support surface. The VOx phase is primarily present as vanadate or poly vanadate, which is known to be X-ray amorphous. Moreover, XRD also indicates that no other species is formed due to the interaction between V₂O₅ and Al₂O₃ support. It was shown that the prepared 10 wt. % VO_x/γ-Al₂O₃ catalyst display a low acidity compared to that of the bare alumina support. The addition of V₂O₅ on γ-Al₂O₃ reduces the acidity of bare γ-Al₂O₃, from 532.2 µmole NH₃ /g to 48.7 µmole NH₃ /gram. The reduced catalyst showed even less acidity of 36.1 µmole NH₃ compared to the fresh catalyst sample. This lower acidity of reduced catalyst is more prone to the enhanced activity of the catalyst toward ethane ODH reaction. Reaction experiments are developed using a CREC Riser Simulator unit over successive reaction-oxidation cycles. Given the results obtained from experiments in oxygen-free environment, it appears that lattice oxygen is involved in the catalytic ODH reaction. It is demonstrated with reactivity tests that the prepared catalyst display promising ethane conversions (13.23% - 25.18%), ethylene selectivity (40.68-55.84%) and catalyst stability during multiple reduction cycles at 550-600 ⁰C.  On the basis of the data obtained, a rate equation is developed including both reactant adsorption and reaction on the catalyst surface. This rate equation is based on a Langmuir–Hinshelwood formulation in which the abstraction of ϐ-H from ethane is the rate determining step. This type of rate equation is found to be consistent with the observed rates of reaction and reaction orders of the gathered experimental data. It is shown that the proposed kinetic models are adequate to represent the ethane ODH reactions over the 10 wt. % VOx/γ-alumina and the reaction network accounts for all product gases (C₂H₄, CO, CO2, and CH4).