OXIDEHYDROGENATION OF PROPANE OVER NI-MO SUPPORTED METAL OXIDES CATALYSTS
M. K. Al-Mesfer, S. M. Al-Zahrani and A. E. Abasaeed Chemical Engineering Department, King Saud University, PO Box 800, Riyadh 11421,
[email protected]
ABSTRACT Oxidative dehydrogenation of lower alkanes to their corresponding alkenes offers many advantages over the dehydrogenation process; such as: lower reaction temperatures and prevention of catalyst’s coking. In this paper, Ni-Mo based metal oxide catalysts (without or with Dopants; zinc and boron are used as dopants) were prepared, characterized and tested. BET experiments showed close average pore diameter for all catalysts (19.59-19.71 Ao ) while their surface areas varied in the range 149.1 - 224.4 m2/g . SEM experiments confirmed the good dispersion of the catalysts ingredients over the support. Higher propene yields were obtained with alumina supported catalysts (10%) compared to silica supported one (0.5%) which showed much higher selectivities when doped with boron (45%). Addition of Zn dopant to γ-Al2O3 supported catalyst decreased both the conversion (28.1% to 16.7%) and the selectivity (34% to 30%.). The propene yield was found to increase with increasing reaction temperatures and/or decreasing propane to oxygen ratios.
KEY WORDS Propane, propylene, oxidative dehydrogenation, catalysts, nickel, molybdenium
INTRODUCTION Propylene is a very important feedstock in the petrochemical industry and is largely used to produce many important intermediate petrochemical products such as polypropylene, propylene oxide, acrylonitrile, acrylic acid and isopropyl alcohol [1]. Worldwide demand for propylene is expected to grow by 5.7% over the next several years [2]. It is currently produced by steam cracking of natural gas or through catalytic dehydrogenation of propane [3,4]. The dehydrogenation reaction is endothermic and equilibrium-limited. Thus, it requires higher reaction temperature that may increase
coking and byproducts [4,5]. To alleviate the problems associated with the dehydrogenation process, oxygen is added to the reaction media. The major challenge for the oxidative dehydrogenation process relates to over-oxidation of reactants and/or products [6]. Different catalytic systems such as vanadium, vanadium-antimony, chromium-based, metal molybdates, phosphates and many others have been used for oxidative dehydrogenation of propane [7-21]. Perhaps, the most studied catalysts are supported and unsupported V-Mg-O and vanadium oxide-based ones [13]. Grasselli et al [14] studied the oxidative dehydrogenation of propane over molybdate-based catalyst. Their study revealed that the reaction of propane to propylene is catalytic and not gas phase radical initiated reaction. Stern and Grasselli [15] further showed the effect of adding metal tungstate and molybdate on CoO4/SiO2 catalysts. They found that the addition of tungstate increases propane conversion with a decrease in propylene selectivity. Opposite results were obtained when molybdate was added. Propylene yields obtained with these catalysts are still relatively low (
