Designing the optimal geometry of a membrane reactor for hydrogen production from a pre-reformed gas mixture based on the extent of the reaction boundary layer

• Published in: Chemical engineering and processing 2017-10, Vol.120, p.148-160
• Main Authors: Murmura, M.A., Cerbelli, S., Annesini, M.C.
• Format: Article
• Language: English
• Subjects: Design; Geometry; Membrane reactor; Optimization; Yield
• ISSN: 0255-2701; 1873-3204
• DOI: 10.1016/j.cep.2017.07.011

•Fully coupled mass and momentum transport model for methane steam reforming.•Model highlights the presence of inactive catalyst volume in typical configurations.•Active catalysts zone confined to reaction boundary layer in the near-membrane area.•Yield goes through a maximum when bed thickness is tuned to reaction boundary layer. A typical hydrogen-production system consisting of a pre-reformer catalytic reactor and a membrane reactor is considered: if equilibrium conditions are achieved in the pre-reformer, the reaction in the membrane reactor can only proceed once the hydrogen partial pressure has been reduced by effect of its permeation. An accurate transport-reaction-permeation model of methane steam reforming in catalytic membrane reactors suggests that, in these conditions, only a fraction of the catalyst volume is effectively active towards the advancement of the reaction and hydrogen production is confined to a reaction boundary layer (RBL) located in the near-membrane zone, whose extent is relatively insensitive to the thickness of the catalytic bed. Based on this observation, we developed a detailed study of the structure of the RBL in a wide range of operating parameters for different reactor geometries and showed that, for an assigned value of the total mass flow rate of the process stream, the optimal reactor performance is obtained whenever the thickness of the catalyst bed is comparable to that of the RBL.