Research Article Millisecond Methane Steam Reforming Via Process and Catalyst Intensification The steam reforming of methane on a rhodium/alumina based multifunctional microreactor is simulated using fundamental chemical kinetics in a pseudo-two- dimensional microreactor model. The microreactor consists of parallel catalytic plates, whereby catalytic combustion and reforming take place on opposite sides of a wall. Heat exchange happens through the wall. It is shown that reforming can happen in millisecond or lower contact times and proper balancing of flow rates can give high conversions, reasonably high temperatures, and high yield to syn- gas. It is found that tuning catalyst surface area and internal and external mass and heat transfer through reactor sizing can lead to further process intensifica- tion. Keywords: Catalytic combustion; Hydrogen; Methane; Microreactors; Process intensifica- tion; Pt; Rh; Steam reforming; Syngas Received: May 9, 2008; accepted: May 30, 2008 DOI: 10.1002/ceat.200800237 1 Introduction Hydrogen has received increased attention over the past years as a green power generation fuel. In addition, there has been increased interest in gas-to-liquid (GTL) technology to convert unutilized natural gas at remote locations and coal into liquid fuels. Downsizing the commercial process producing hydrogen or syngas is a pressing research topic because of the associated applications, ranging from portable electronic devices to dis- tributed energy systems, and the process intensification that can be achieved via miniaturization. The latter prospect may have improved economics (operating and capital cost). Steam reforming (SR) of hydrocarbons (usually natural gas) is currently the principal method for hydrogen and/or syngas production in refineries and petrochemical plants. The process is highly endothermic, taking place under high pressure in tu- bular fixed bed catalytic reactors, which are positioned in large gas fired furnaces. Heat is supplied from the flames and the furnace walls primarily through radiation. SR is a relatively slow process, with a typical residence time of a few seconds, and rather bulky, due to the large space required to accommo- date the flames. Over the past decade, a number of theoretical studies have shown that SR is feasible in mesoscale reactors (smallest char- acteristic scale >1 mm) [1–6]. In most of these cases, SR on Ni (the industrial catalyst) is considered and the empirical ki- netics of Xu and Froment [7] are adopted. Experimentally, Venkataraman et al. [8] studied methane SR on Rh in a meso- scale catalytic plate reactor and reported high methane conver- sion (> 95 %) at 70 ms residence time. In addition, in a very recent experimental work, Tonkovich et al. [9] showed that SR on Rh is feasible at microscales (smallest characteristic scale <1 mm) with contact times of ∼1 ms. In the present work, we model the SR process on Rh in a multifunctional microreactor using fundamental chemistry models. We exploit how compact this process can become by process and catalyst intensification. In addition, we study the effect of the characteristic length scale of the microsystem in order to provide guidelines for optimal design. 2 Modeling A schematic of the simulated multifunctional microreactor is shown in Fig. 1. It consists of an exothermic reaction channel, an endothermic reaction channel, and a solid wall acting as a heat exchanger between the two channels. In the exothermic channel, propane combustion on Pt takes place along the wall. In the endothermic channel, methane SR, and water gas shift (WGS) reactions take place on Rh. The use of propane instead of methane for combustion is determined by the higher reac- tivity and stability of propane, as found in our previous work [10]. It has been found that co-current flow configuration at microscales gives better overlap of reaction zones and mini- mizes hot spots [11, 12]. A pseudo-two-dimensional (2D) re- © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.cet-journal.com Georgios D. Stefanidis Dionisios G. Vlachos Department of Chemical Engineering and Center for Catalytic Science and Technology (CCST), University of Delaware, Newark, DE, USA – Correspondence: Dr. D. G. Vlachos (vlachos@udel.edu), Department of Chemical Engineering and Center for Catalytic Science and Technology (CCST), University of Delaware, 150 Academy Street, Newark, DE 19716, USA. Chem. Eng. Technol. 2008, 31, No. 8, 1201–1209 1201