Book Description

Propane conversion to propylene has been the subject of intensive researches. This is due to the increasing demand for propylene. Current propylene production processes suffer from several limitations. Oxidative dehydrogenation (ODH) is a promising alternative technology for propylene production overcoming the drawbacks of current processes. However, selectivity control in ODH is still a challenge preventing it from an industrial application. This is due to the formation of undesired carbon oxides. Thus, the development of a selective catalyst is crucial for the commercialization of ODH. Vanadium oxide catalysts have been proposed as the most active and selective catalyst for propane ODH. Moreover, new reactor concepts such as fluidized-bed might also help to make the ODH a feasible alternative for olefins productionas, offering some outstanding advantages in comparison to conventional reactors. This dissertation provides fundamental understanding of structure-reactivity relationship of vanadium oxide catalyst for propane ODH in a fluidized-bed reactor using the lattice oxygen of vanadium oxide catalysts in the absence of gas-phase oxygen. Supported vanadium oxide catalysts with different vanadium loadings (5-10 wt %) supported on?-Al2O3 is used. The prepared catalysts are characterized using several techniques such as BET surface area, H2-TPR, NH3-TPD, O2 Chemisorption, Laser Raman Spectroscopy, Pyridine FTIR and XRD. Characterization of the catalysts reveals that monomeric VOx species are predominant at low vanadium loadings while polymeric VOx species increase with higher loadings until monolayer surface coverage is reached. Moreover, the catalysts display moderated acidity compared to that of the bare alumina due to the relative increase in the number of Brønsted acid sites. Successive-injections propane ODH experiments in the CREC Riser Simulator over partially reduced catalyst show good propane conversions (12%-15%) and promising propylene selectivity (68-86%) at 475-550 0C. Product selectivities are found to augment with the catalyst's degree of reduction suggesting that a certain degree of catalyst reduction is required for better propylene selectivity. Compared to average propylene yields of 5% and 15% obtained in FCC and steam cracking technologies, respectively, promising value of 7% was obtained in the present propane ODH study over vanadium oxide catalyst and under oxygen free conditions. Such result would encourage further investigation of propane ODH in the absence of molecular gas oxygen as promising alternative/supplementary technology for the production of propylene. A kinetic model relating reaction rate to the catalyst's degree of oxidation is proposed. Non- linear regression leads to model parameters with low confidence intervals, suggesting the adequacy of the proposed model in predicting the ODH reaction under the selected reaction conditions.