(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. % VOx 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.% VOx 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 VOx 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. % VOx/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).