(98i) Highly Conductive Metal Honeycomb Reactor for Methanol Autothermal Reforming

Hydrogen is economically produced by reforming of fossil fuels. Among the fuels, methanol is easy to reform at low reaction temperatures of 200 ~ 300 ^oC. From methanol, hydrogen can be produced by steam reforming (CH₃OH + H₂O → CO₂ + 3 H₂, ΔH_{298 K} = 49.5 kJ/mol ) or partial oxidation (CH₃OH + ½ O₂ → CO₂ + 2 H₂,  ΔH_{298 K} = -192.3 kJ/mol). Depending on the reaction for hydrogen production, the reaction heat should be either supplied or removed. Instead, the two reactions can be combined to make a reaction having zero enthalphy change (autothermal reforming).

CH₃OH + 0.795 H₂O + 0.102 O₂ → CO₂ + 2.795 H₂ ,  ΔH_{298 K}= 0 J/mol  (1)

In the reactor, however, the exothermic reaction rate and the endothermic reaction rate are not balanced as the stoichiometry of equation (1) suggests. In the front part of the reactor where oxygen is present, the exothermic partial oxidation dominates and after all the input oxygen is consumed, only the steam reforming occurs. With a conventional packed-bed reactor, the unbalance in heat generation and consumption gives rise to a hot spot as high as 570 ^oC due to poor thermal conductivity in the catalyst bed. To make the hot spot disappear, it is essential to quickly transfer the reaction heat of partial oxidation to the latter part of the reactor where steam reforming consumes the heat. For this purpose, we developed in this study a highly conductive metal honeycomb reactor for the autothermal reforming of methanol. The metal structure of the reactor facilitated the heat transfer from the front section to the latter section of the reactor, making the temperature profile smooth and suppressing hot-spot formation. We developed a detailed reactor model for the honeycomb reactor and analyzed the experimental results obtained with an aluminum honeycomb reactor. The design parameters affecting the performance of the honeycomb reactor are identified and the effect of each parameter is described.