OP-II-3

OP-II-7THE ROLE OF CATALYST ACTIVITY ON THE TRANSIENT ANDSTEADY STATE MODELING OF AN INDUSTRIAL PACKED BEDCATALYTIC REACTOR WITH LOW d t /d p : o-XYLENE PARTIALOXIDATION ON A V/Ti CATALYSTCastillo-Araiza C.O. and Lopez-Isunza F.Departamento de Ingeniería de Procesos e Hidráulica, Universidad AutónomaMetropolita Unidad Iztapalapa, México. E-mail: coca@xanum.uam.mxTravelling hot spot and multiple steady states have been observed in nonadiabaticfixed bed catalytic reactors for strongly exothermic reactions whenoperating conditions change drastically, i.e., cooling temperature[1-2]. In particular,for the partial oxidation of o-xylene to phthalic anhydride on an industrialV 2 O 5 /TiO 2 (Anatasa) catalyst, this behavior has been related to reversible andirreversible catalyst deactivation[1-3]: the former being attributed to the combinationof several mechanisms such as an over-reduction of vanadium, deposition ofcarbonaceous materials and strongly absorbed species; and the latter being linked tostructural changes in the catalyst itself such as a TiO 2 anatase-rutile transformation,a decrease in surface area with loss in activity and a decrease in a promotercomposition at the catalyst surface. Although the modeling of this kind ofsystems/phenomena has been performed since 1946 [4], an agreement betweenpredicted and observed temperature and yield profiles has not been satisfactory [1-2,5]. Some studies have shown that these simplified models cannot describe thereactor performance quantitatively, even though independently determined intrinsickinetic and transport parameters are used [3]; besides, several authors have pointedout that the main aspects to be addressed in the modeling of this class of reactorsare related to understand/determine [1-3, 6]: the role of hydrodynamics on heattransport phenomena; and the kinetics of the catalytic and deactivation reactions.The aim in the present work is to develop/propose a modeling approach to predictobservations in steady and transient state for catalytic reaction systems where ahighly exothermic reaction takes place: an adequate consideration of hydrodynamicsand the reversible and irreversible catalyst deactivation into the developed reactormodel is essential on heat and mass transport description.The experimental system is a single-tube industrial scale packed bed catalyticreactor, packed with spheres (d t /d p ∼3) of a non-porous commercial V 2 O 5 /TiO 2(Anatasa) [7]. The cooling system consisted of an air-agitated bath of molten salt attemperatures operating in the range 665-675°K, and the o-xylene feed to air flow rateratio was 44 Ng/m 3 . This system when is operated either at steady or transient state110