Recent research has shown the potential of membrane-assisted fluidized bed (MAFB) reactors for various applications, and for ultra-pure hydrogen production in particular. For micro MAFBs with gas extraction, the formation of densified zones close to the membrane walls has been recognized to potentially increase the mass transfer resistance from the bed to the membranes. In order to investigate this phenomenon in detail, an classic Euler-Lagrange type model, Discrete Particle Model (DPM) extended with gas-phase component conservation equations has been used to simulate the case with H-2 extraction via perm selective membranes mounted in the confining walls. The simulated membrane walls were set up such that they closely mimic high-flux, thin film, supported palladium-based membranes. It has been found that the formation of densified zones in micro MAFBs has a very small influence on the H-2 mass transfer from the bed to the membranes. The advantages of micro MAFBs have been highlighted through a fundamental comparison with a micro packed bed membrane reactor. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.