Catalytic partial oxidation of methane in a novel heat-integrated wall reactor Theophilos Ioannides and Xenophon E. Verykios  Department of Chemical Engineering, University of Patras, GR-265 00 Patras, Greece Received 10 April 1997; accepted 7 July 1997 A novel reactor has been developed and applied in the reaction of partial oxidation of methane to synthesis gas. The reactor con- sists of a ceramic tube in the inner and outer surface of which a metal catalyst film is deposited. The CH 4 /O 2 feed enters into the tube and a large fraction of the heat generated on the wall by methane combustion is transported across the tube wall towards the outer catalyst film, where the endothermic reforming reactions take place. In this way, the temperature in the combustion zone is con- trolled and hot spots are significantly reduced in magnitude. Initial results presented in this work demonstrate the feasibility of the concept. Keywords: synthesis gas, methane partial oxidation, wall reactors 1. Introduction Catalytic partial oxidation (CPO) of methane has been the subject of extensive research efforts in recent years, as an alternative process to steam reforming for the production of synthesis gas. Work in this field has been recently reviewed by Pena et al. [1]. The reaction is catalyzed by group VIII metal catalysts, such as Ni, Rh, Ru, Pt, Ir and Pd. In the majority of cases, synthesis gas is produced indirectly, i.e. via the following reaction scheme [1,2]: CH 4  2O 2 ! CO 2  2H 2 O 1 CH 4  CO 2  2CO  2H 2 2 CH 4  H 2 O  CO  3H 2 3 according to which part of methane is initially com- busted by supplied oxygen towards CO 2 and H 2 O and reforming of the remaining methane with CO 2 and H 2 O produced primarily takes place subsequently, leading to formation of synthesis gas. Direct formation of synthesis gas via reaction of CH 4 and O 2 has been reported in the case of Ru/TiO 2 catalysts [3,4] and of Rh- or Pt-loaded monoliths operating at high temperatures (1000  C) and short contact times (10 ms) [5,6]. A major issue in the process of partial oxidation of methane is the heat management of the reactor. Methane combustion (reaction (1)) is strongly exother- mic (H  800 kJ/mol CH 4 ) and the heat produced at the first part of the catalytic bed can result in hot spots of considerable magnitude, considerably exceeding 1000  C. Simulations of an adiabatic fixed-bed reactor containing a Ni/Al 2 O 3 catalyst show that for a CH 4 /O 2 feed with a ratio of 1.67 the hot-spot temperature can be as high as 1500  C [7]. The strongly endothermic reform- ing reactions which take place at downstream sections of the bed lead to cooling of that part of the reactor. This highly uneven temperature profile in a fixed-bed CPO reactor raises serious questions related to catalyst and reactor durability, catalyst stability and to the maximum obtainable methane conversion. Several types of catalytic reactors have been consid- ered for this reaction, in addition to conventional fixed- bed reactors. Fluidized-bed reactors seem promising because of their good heat transfer properties. Studies of CPO of methane in such reactors have been reported by Bharadwaj and Schmidt [8] and Olsbye et al. [9]. Alternative catalyst bed configurations, such as dual- bed or mixed-catalyst bed reactors have been examined by Ma and Trimm [10], while dense oxygen-selective, as well as porous or dense, hydrogen-selective membrane reactors have been also investigated [11^13]. Reactors of the monolithic type have been extensively studied by Schmidt and co-workers [5,6,14]. Rh-loaded monoliths have been found to be the most selective and stable for synthesis gas formation. In the present work, a new reactor concept is pro- posed which can resolve the heat management problem of the CPO reaction in an efficient manner. In addition, the proposed reactor is simple to construct and operate. This is the heat-integrated wall reactor (HIWR), which, in its simplest form, is shown schematically in figure 1. The reactor comprises of a non-porous ceramic tube of high thermal conductivity (i.e. alumina) in the inner and outer surface of which a metal catalyst is deposited in the form of a film. The reactor design offers the flexibility to deposit different catalysts on the inner and outer surface Catalysis Letters 47 (1997) 183^188 183 * To whom correspondence should be addressed. Ä J.C. Baltzer AG, Science Publishers