Chemical Engineering Journal 96 (2003) 125–131 Effect of fluidization conditions on the membrane permeation rate in a membrane assisted fluidized bed S.A.R.K. Deshmukh, M. van Sint Annaland ∗ , J.A.M. Kuipers Department of Science and Technology, Twente University, P.O. Box 217, 7500 AE Enschede, The Netherlands Abstract The effects of fluidization conditions on the membrane permeation rate in a membrane assisted fluidized bed (MAFB) employing micro-porous membranes have been studied experimentally in a square fluidized bed, equipped with vertical ceramic membranes positioned in a staggered arrangement. First, the morphological parameters of the membranes have been determined with separate experiments and the membrane gas permeation rates could be well described with the dusty gas model. Secondly, the effects of the fluidization conditions, such as the particle size, superficial gas velocity and freeboard pressure on the membrane permeate flow rate have been measured. The membrane permeation rates from the fluidized bed could be well described by taking into account the local pressure drop over the membrane, where the local pressure inside the fluidized bed was evaluated as the hydrostatic head using the average bed porosity. © 2003 Elsevier B.V. All rights reserved. Keywords: Membrane assisted fluidized bed; Hydrodynamics; Ceramic membranes; Dusty gas model 1. Introduction A fluid bed membrane reactor (FBMR) is a special type of reactor that combines the advantages of a fluidized bed and a membrane reactor. Despite the excellent heat transfer properties of a fluidized bed axial gas back-mixing can con- siderably decrease the overall reactant conversion and prod- uct selectivity. By insertion of membranes in the fluidized bed, either perm-selective or porous membranes, large im- provements in conversion and selectivity can be achieved. Firstly, the product selectivity can be increased via opti- mization of the axial concentration profiles via distributive feeding of one of the reactants (e.g. controlled dozing of oxy- gen for partial oxidation reactions) or selective withdrawal of one of the products (e.g. selective removal of hydrogen in dehydrogenation reactions). Furthermore, controlled doz- ing of oxygen could be used to achieve high conversions and still avoid the formation of explosive reaction mixtures, rendering the reactor inherently safe. Secondly, the insertion of membranes decreases the ef- fective axial dispersion via compartmentalization of the fluidized bed. Insertion of membrane bundles in a suit- able configuration impedes bubble growth and macroscopic circulation patterns in the fluidized bed, thereby reducing ∗ Corresponding author. Tel.: +31-534894478; fax: +31-534892882. E-mail address: m.vansintannaland@ct.utwente.nl (M. van Sint Annaland). reactant by-pass via rapidly rising large bubbles. Further- more, gas withdrawal through the membranes decreases the superficial gas velocities in the top section of the bed, result- ing in smaller gas bubbles, which increases the inter-phase gas exchange favoring high conversions [1]. Both vertical and horizontal inserts (membranes and heat transfer tubes) can be used to effectively retard the emulsion circulation and increase the bubble breakage. For the controlled dozing of one of the reactants a horizontal arrangement of inserts is usually preferred to directly control the local concentra- tions. For the removal of one of the intermediate products vertical membrane bundles might suffice, which are much easier to be integrated in the reactor. The application of FBMRs to reactions of industrial im- portance has been investigated in the recent past. Adris et al. demonstrated both by experiments [2] and by mod- eling [3] that for the steam reforming of natural gas the in situ separation and removal of hydrogen via perm-selective thin-walled palladium-based membranes shifted the conven- tional thermodynamic equilibrium and increased the syn- thesis gas yields in comparison to the industrial fixed bed steam reformer. Using simulations Abdalla and Elnashaie [4] showed for the catalytic dehydrogenation of ethyl benzene to styrene and Ostrowski et al. [5] for the catalytic partial ox- idation of methane to synthesis gas that with FBMRs higher product selectivities could be realized compared to fixed bed reactors. In these studies the insertion of perm-selective hydrogen membranes in the fluidized bed was investigated. 1385-8947/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2003.08.012