Hysteresis in autothermal methane reforming over Rh catalysts: Bifurcation analysis E. Mancusi a,b,⇑ , L. Acampora a , F.S. Marra c , P. Altimari d,⇑ a Facoltà d’Ingegneria, Università del Sannio, Palazzo ex INPS, Piazza Roma, 21, I 82100 Benevento, Italy b Universidade Federal de Santa Catarina, Departamento de Engenharia Química e de Alimentos, 88040-970 Florianópolis, SC, Brazil c Istituto di Ricerche sulla Combustione – CNR, Napoli, Italy d Dipartimento di Chimica, Università ‘‘Sapienza’’ di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy highlights  Hysteresis characteristics of an autothermal methane reforming reactor are analyzed.  Bifurcation analysis is performed to determine ignition and extinction boundaries.  The mechanisms determining the spatial profiles of oxidation and reforming reaction rates are described.  The addition of water to feed can improve reactor controllability. article info Article history: Received 16 July 2014 Received in revised form 11 October 2014 Accepted 17 October 2014 Available online 24 October 2014 Keywords: Auto-thermal methane reforming Hydrogen production Hysteresis Multiplicity Fixed bed reactor Non-linear analysis abstract Numerical analysis of the hysteresis characteristics of a fixed bed catalytic reactor carrying on autother- mal methane reforming over Rh catalyst is presented. A one-dimensional heterogeneous model describ- ing heat and mass transport and simultaneously accounting for methane combustion, steam reforming and dry reforming is adopted. Parametric continuation is performed to compute steady state solution regimes predicted by the model. Bifurcation analysis is illustrated allowing characterizing the influence of feed temperature, gas flow rate, oxygen to methane and water to methane feed ratio values on ignition and extinction. A thorough description of the physical mechanisms determining the evolution of hydro- gen selectivity, maximum solid temperature and syngas production within the explored region of param- eters space is presented. Particular attention is in this framework devoted to analysing the effect of water addition on reactor bifurcation behavior and performance. The illustrated characterization of hysteretic phenomena provides guidelines for process design, operation and control. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Hydrogen is considered one of the most promising energy car- riers because of its high energy density and capability to burn without producing pollutants [1]. Methane, due to its large abun- dance and high H:C ratio has been traditionally adopted as feed- stock for hydrogen production. Steam reforming (SR) of methane is the process to produce hydrogen from methane on large indus- trial scale (e.g. [2–4]). This process can yield high H 2 /CO ratio val- ues but it is strongly endothermic and requires high reaction temperature (700–900 °C) imposing to supply energy by an exter- nal heat source. The resulting reactor solution is very bulky and heavy, and thus not suitable for a mobile fuel cell system. To over- come the heat transfer problem in steam reformer, catalytic partial oxidation (CPO) of methane has been often adopted as an alterna- tive method to produce hydrogen from methane [5,6]. The CPO is exothermic and is characterized by high temperature and short contact time. Its practical implementation reveals several advanta- ges over the highly endothermic steam reforming since it does not require external heat sources and can be performed in small, sim- ple and compact reactors with low heat capacity and good heat transfer properties. These characteristics enable the application of CPO in fuel cell systems for electric power generation [2,7]. CPO of methane produces on the other hand high carbon monoxide concentrations, which are undesired for polymer electrolyte mem- brane fuel cells (e.g. [5]). http://dx.doi.org/10.1016/j.cej.2014.10.061 1385-8947/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding authors at: Facoltà d’Ingegneria, Università del Sannio, Palazzo ex INPS, Piazza Roma, 21, I 82100 Benevento, Italy (E. Mancusi); Dipartimento di Chimica, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185, Roma, Italy (P. Altimari). E-mail addresses: mancusi@unisannio.it (E. Mancusi), pietro.altimari@uniroma1.it (P. Altimari). Chemical Engineering Journal 262 (2015) 1052–1064 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej