III International Conference

PP-III-80MATHEMATICAL MODELING OF TOLUENE INTERRACTION WITHV/Ti-OXIDES IN ANAEROBIC CONDITIONSReshetnikov S.I.Boreskov Institute of Catalysis, Novosibirsk, RussiaE-mail: reshet@catalysis.nsk.suOne of the ways to perform the process of hydrocarbon catalytic oxidation is to divide thereaction space in a few separate zones, for instance, a zone of the catalyst reduction byhydrocarbon and a zone of its oxidation by oxygen and catalyst circulation between zones(see, for example [1, 2]). This operation was industrially used in the DuPont process of butaneoxidation to maleic anhydride over vanadium-phosphorous catalysts [3].Second way is regulation (or periodic operations) when the reagents concentrations, gasflow rates are changed periodically in the fixed bed catalytic reactor input - cyclic reductionand re-oxidation of a catalyst [4, 5]. The possible objectives of the use of periodic operationof catalytic reactors are to provide an increased conversion, improved selectivity, and reduceddeactivation. Aditionally, an important information could be extracted from the transientbehavior of the reaction after the fast change of the composition of reaction mixture over thecatalyst. Modeling of the transient phenomena allows obtaining valuable kinetic constants,which often could not be determined from the steady state experiments.The aim of this work is modeling of toluene interaction with a pre-oxidizedvanadia/titania catalyst under periodic operation.The catalyst was prepared via a well-known grafting technique by the vapor deposition ofVOCl 3 on the surface of TiO 2 (Aldrich). The BET specific surface area was equal to 9 m 2 /g,the amount of vanadium was found to be 0.57 wt. % that corresponds to 0.75 of a monolayer(ML) [7]. It is important that this catalyst contained only about a monolayer of the surfacevanadia species and did not contain any bulk crystalline V 2 O 5 .A typical transient behavior of the toluene, benzaldehyde and CO 2 concentrations as aresult of interaction of toluene with the 0.75 ML V/Ti-oxide catalyst is demonstrated in Fig. 1[8]. The main products of the interaction of toluene with the pre-oxidized vanadia/titaniacatalyst in the temperature range 523-633 К are benzaldehyde (BA), CO 2 , CO and Н 2 О. Thetransient behavior of CO is similar to CO 2 , but the CO concentration is 5–6 times lower.Hence, it was not taken into account. It is seen that the dynamics of the CO 2 andbenzaldehyde formation are different. CO 2 is formed during the initial time of the reaction,declining quickly with time, while BA is formed for a prolonged time.A kinetic scheme with the minimal amount of steps that appropriately describes theresponse curves of toluene and reaction products was chosen. It includes 5 steps [8]:620