No abstract

Various models have been tested to describe the influence of carbon number on the kinetics of the selective partial oxidation of R-olefins over iron antimony oxide. Modeling the rate of C 3 -C 6 olefin consumption according to the Mars-van Krevelen redox mechanism showed that the rate constant for the reoxidation was dependent on the carbon number of the used olefin. This and the observed shifts in selectivities cannot be explained in terms of the simplified redox model. The rate of formation of the various product groups was modeled using a power law rate model and mechanistic models on the basis of the single-site Langmuir-Hinshelwood mechanism and on an oxidation mechanism. Using either of the two mechanistic models, one can conclude that the partial oxidation/dehydrogenation products are formed on similar sites, whereas the double-bond isomerization seems to occur on a different site. The kinetic parameters were evaluated as a function of the chain length of the feed molecule.

α-olefins in the range of ethene to 1-nonene were studied over an iron antimony oxide catalyst at temperatures between 350°C and 400°C in a tubular flow reactor. The primary reactions can be classified into five distinct classes, viz. double bond isomerization, partial oxidation, oxidative dehydrogenation, cracking and total oxidation. Ethene was unreactive and only total combustion products were formed. Propene and 1-butene formed conjugative aldehydes while 2-butenal produced 1,3 butadiene. On the basis of these results a mechanism for the partial oxidation and oxidative dehydrogenation of 1-butene is proposed. Increasing carbon number was found to increase the primary rate of total oxidation and the rate of formation of cracking products. Increasing carbon number decreased the rate of oxidative dehydrogenation and partial oxidation, except when going from C 3 to C 4 . The observed carbon number dependencies might be explained in terms of ease of formation and of stability of the π-allyl intermediate.Iron antimony oxide is a well known catalyst for the partial oxidation/ammoxidation of propene (1) and the oxidative dehydrogenation of n-butene (2). Aso et al.(3) studied iron antimony oxide containing various Sb:Fe ratios for the partial oxidation of propene. The activity and selectivity to acrolein increased strongly with increasing Sb contents beyond a ratio of 1:1. In a recent study of the surface properties of FeSb0 4 (4), it was concluded that the surface has a Sb-rich "skin" which is essential to the selective properties of the catalyst. Although iron antimony oxide is a well known catalyst for the selective oxidation of olefins, this catalyst is not selective for the partial oxidation of paraffins (van Steen, E.; Schnobel, M.; O'Connor, C. T., University of Cape Town, unpublished work).The partial oxidation of higher olefins has not been studied to the same extend as the oxidation of ethene, propene and butene. The dependency of the