| Multi-element catalysts are gaining more attention than single or double component materials in catalyst preparations. Due to the synergistic effect of co-components, the activity of a multi-component catalyst is significantly improved. Mo-V-Nb-Sb-based mixed oxide catalysts are proven to be active for oxidative dehydrogenation of ethane to ethylene and acetic acid. One of the advantages of the ability to produce ethylene and acetic acid in one process is that the products can subsequently be supplied directly to an integrated process for manufacture of vinyl acetate monomer (VAM). Conventionally, the catalysts can be prepared by aqueous mixing of inorganic forms of starting materials. However, the disadvantage of this method is the difficulty in reproducibility of the catalysts. The alternative way to produce the catalysts proposed here is preferably called “Sol-Gel Method”. Alkoxide forms, instead of other inorganic forms, of some components such as vanadium, niobium and antimony are used as starting materials. This alternative method of preparation can improve the reproducibility of the catalysts in terms of the phases of the catalysts and the activity. In the development, Mo-V-Nb-Sb-based mixed oxide catalysts are prepared by Sol-Gel method and loaded with calcium in four different methods, and are tested on the oxidative dehydrogenation of ethane at 282°C and 304°C, and 200 psig. The activity of the catalysts prepared by different routes was compared. One method was discovered to be the only preparation method yielding the catalyst whose performance was superior to the one containing only four main elements. Furthermore, additional elements were also added to the based mixed oxide catalysts using two selected methods to examine the improvement on the catalyst activity. Roles of calcium contents in the catalysts were also investigated. Catalyst characterization such as XRD, TPD and BET were also performed. Finally, based on the functional forms of rate equations proposed by Thorsteinson et al. (1978), the simulation results are employed to aid in the interpretation of experimental data, and to simulate potential operating methods. |
