Deshidrogenación oxidativa de alcanos ligeros

Abstract

Venezuelan surplus production of butanes and pentanes is a significant incentive for the development of new technologies that will help transforming them into products of added value. From a literature review presented in Chapter 1, a magnesium and vanadium oxide catalyst was found which showed the possibility for the development of a new way to produce non-saturated hydrocarbons through oxidative dehydrogenation. It was obvious that, in case this new technology was feasible, fluidized bed or mobile bed reactors would be needed to reduce the potential for explosive hydrocarbon-oxygen mix by separating hydrocarbon oxidation zones from those of the catalyst. Such a process has the additional advantage of producing a substantial selectivity increase. This catalyst however, does not offer the required attrition resistance characteristics. We propose to resolve this problem by adding an additional support like silica or alumina, materials commonly used in such reactors. Research efforts were dedicated to investigate the feasibility of such approach since these solids have superficial properties capable of modifying the type of compounds developed in the active phase. The main goal of this work was to bridge knowledge gaps in order to keep such approach alive. In order to assess potential extensions of such technology, some effort was dedicate to improve the active phase behavior by adding promoting components, and to analyze the behavior of the most promising catalysts for the oxidative dehydrogenation of n-pentane. We build a lab setup that would allow us to perform experiments and a set of catalysts were prepared. Catalysts were characterized in order to provide a foundation that would allow us to provide interpretation of observed behavior changes. For each one of these hydrocarbons, we also analyzed the effect of supporting and promoting components. The most extensively studied support material was silica. The main efforts were directed at quantifying the effect of the support on the activity, selectivity and on the optimal Mg/V ratio, as well as the effect of dilution. With increasing silica content we observed a decrease in activity while selectivity changes were mainly related to the products distribution but with global selectivity values similar to those of pure active phase with up to 30% of silica. No meaningful changes were observed with respect to the optimal Mg/V ratio. We determined that the MV4-30 catalyst had characteristics that would allow a new technology to be developed. Other promising supported catalysts that were found in our study were the Gamma30 and the Alfa30. Regarding to promoted catalysts, the following promoting agents were studied: Sb, Bi, Mo and Ga. Encouraging results were found in terms of selectivity. However, with the exception of gallium, these components had a negative impact on activity. Gallium did not affect activity values but improved the selectivity towards butadiene. We also had the opportunity to verify the effect of the vanadium precursor used in our studies and we were able to confirm significant advantages in the use of vanadil-oxalate. For the oxidative dehydrogenation of n-pentane we observed similar results but with lower global selectivity values. Obtained experimental results indicate the need to introduce changes in the catalyst which are outside the scope of this work. Finally, in order to quantify our results and to show that we would be able to translate them into effective values for reactor design, a software program was developed to simulate the experiments. Research efforts were, in our opinion, satisfactory and they resulted in a framework that could be used with other catalysts and in bank scale reactors.