Chemical Engineering Science 63 (2008) 5003 – 5009 www.elsevier.com/locate/ces Combustion of toluene–hexane binary mixtures in a reverse flow catalytic reactor Pablo Marín, Salvador Ordóñez ∗ , Fernando V. Díez Department of Chemical Engineering and Environmental Technology, University of Oviedo, Facultad de Química, Julián Clavería 8, Oviedo, 33006, Spain Received 20 April 2007; received in revised form 15 January 2008; accepted 3 March 2008 Available online 6 March 2008 Abstract This work is focused on the application of reverse flow reactors to the combustion of lean mixtures of aliphatic and aromatic hydrocarbons in air. For this purpose, hexane and toluene were chosen as model compounds. The combustion of binary mixtures of these compounds (up to 500 ppmV total hydrocarbon concentration) over a commercial Pt/Al 2 O 3 catalyst in reverse flow reactors has been studied both experimentally, in a bench-scale unit, and by simulations, using a heterogeneous mono-dimensional dynamic model, good correspondence being observed between both approaches. As general trend, it was observed that the behaviour of the reactor is determined mainly by the combustion enthalpies and reactivities of toluene and hexane. Hence, increasing total concentration and increasing fraction of toluene (the most reactive compound) lead to more stable operation. Regarding the kinetic inhibition effects, in the conditions studied no influence on the reactor performance was observed, probably because the hydrocarbons combust in different reactor zones. This behaviour can be extended to the combustion of aromatic and C 5 –C 8 alkanes, characterised by their relatively low concentrations (determined by their vapour pressure) and high reaction rates.  2008 Elsevier Ltd. All rights reserved. Keywords: Reverse flow reactor; Hexane–toluene lean mixtures; Catalytic combustion; Mathematical modelling; Dynamic simulation 1. Introduction Volatile organic compounds (VOC) are among the most im- portant air pollutants, as they contribute to the formation of pho- tochemical smog in urban areas, besides their own toxicity. As a result, extensive environmental regulations have been gener- ally adopted, forcing many installations to implement treatment systems. Catalytic combustion is a destructive VOC treatment technology, widely used because of its high efficiency. Com- pared to thermal combustion, catalytic combustion presents lower ignition temperature and pressure drops, less heat losses, and negligible rates of nitrogen oxides production. Reverse flow catalytic reactors (RFR) consist of a catalytic bed in which the feed flow direction is periodically reversed. The operation with this kind of reactors requires, in the start-up stage, the preheating of the solid up to the ignition temperature of the compound to be burned. After this, the gas mixture can ∗ Corresponding author. Tel.: +34 985 103 437; fax: +34 985 103 434. E-mail address: sordonez@uniovi.es (S. Ordóñez). 0009-2509/$ - see front matter  2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2008.03.001 be fed to the reactor at room temperature, because both bed ex- tremes (usually formed by inert material, instead of catalyst) act as heat regenerators, storing the heat released by the reaction during a cycle and preheating the gas up to the ignition temper- ature in the following cycle. RFR allows the treatment of very lean mixtures of VOC operating in an auto-thermal way, with no need of auxiliary fuel. Extensive investigations on RFR, in- cluding both numerical simulations and experimental analysis, have been performed in the past 30 years and have been re- viewed, for example, by Kolios et al. (2000) and Matros and Bunimovich (1995, 1996). The present work is focused in the experimental study of the behaviour of an RFR for the combustion of very lean VOC mixtures. Most of the studies in this field are carried out for the combustion of single compounds, though industrial VOC emissions consist usually of mixtures of several of these com- pounds. The scope of this work is to fill this lack of studies and elucidate experimentally, whether the RFR behaviour dif- fers strongly in the case of the combustion of VOC mixtures. Moreover, to the best our knowledge, reported works on the