(600w) Ethane Oxidative Dehydrogenation Over Vox/Al2O3 Catalyst in a Fluidized Bed Reactor Under Oxygen-Free Conditions

Ethane Oxidative
Dehydrogenation over γ-Al₂O₃-Supported Vanadium
Oxide Catalyst in a Fluidized-Bed Reactor

Sameer A. Al-Ghamdi ^(1,2)
, Hugo I. de Lasa⁽¹⁾*, M. M. Hossain ⁽³⁾ and Mara Volpe ⁽⁴⁾

1.     
Chemical
Reactor Engineering Centre,University of Western Ontario, London, Ontario,
(Canada) *hdelasa@uwo.ca

2.    Research &
Development Center, Saudi Aramco Oil Compamy, (Saudi Arabia)

3.   
Department of
Chemical Engineering, King Fahd University of Petroleum & Minerals, Saudi
Arabia

4.    Chemical Engineering
Department, PLAPIQUI-(UNS-CONICET), (Argentina)

Objective

The main objectives of
this study are: to
develop reactivity tests for ethane oxidative dehydrogenation (ODH) on a 7.5 wt. % VO_x/γ-Al₂O₃ catalyst under
oxygen-free conditions,
to elucidate the mechanistic reaction steps involved in the catalytic ODH of
ethane and to establish a heterogeneous kinetic model that describes ethane ODH
on the prepared catalyst.

Materials and Methods

The catalyst was prepared
by wet impregnation method with Gamma form of alumina as support and vanadium
III acetyl-acetonate V (AcAc)₃ as precursor. Reaction experiments
were developed in a novel Chemical Reactor Engineering Center (CREC)
mini-fluidized bed Riser Simulator. Reaction runs were carried out in the CREC fluidized bed
riser reactor at reaction temperatures between 550-600 oC and under atmospheric
pressure and
oxygen free atmosphere.  A number of physicochemical techniques were used to
characterize the prepared catalyst.

Results and Discussion

The prepared catalyst
showed very stable reduction behavior during consecutive TPR cycles with 550 ^oC
as reduction temperature (Figure-1). Given the results obtained from
experiments in oxygen-free environment, it appears that lattice oxygen is
involved in the catalytic ODH reaction where prepared catalyst displayed
promising ethane conversions (6.47-27.64%), ethylene selectivity (57.62-84.51%)
and catalyst stability during ethane ODH at 550-600 0C (Figure-2). A rate
equation is developed based on a lumped model using Langmuir-Hinshelwood kinetics.
The proposed kinetic model satisfactorily predicts the ODH reaction of ethane under the
selected reaction conditions.

Figure (1): Successive TPR
profiles for VOx/γ-Al2O3 catalyst. Pre-treatment: calcination at
773 K.

Figure (2): Temperature dependence of
C₂H₆ conversion and C₂H₄
selectivity (reaction time= 30 sec, C₂H₆ injected= 20 ml,
catalyst loaded = 0.76g).

Conclusion

The development of a very
stable and selective catalyst for ethane ODH is a major challenge that has to be overcome
to have available a viable alternative and less energy demanding ODH process
for olefin production. These new process will likely involve fluidized beds and
as a result a selective fluidizable catalyst is the key for successful
implementation of future ODH processes.