Reaction/separation Coupled Equilibrium Modeling Of Steam Methane Reforming In Fluidized Bed Membrane Reactors

With the demand of high purity hydrogen increasing, the fluidized bed membrane reactorattracted general attention for its many advantages. Modeling of membrane reactors presentsinteresting challenges because of the coupling of selective diffusion through the permeablesurface with chemical reactions and mass transfer on the reactor side. However, the hydrogenseparation process by the membrane has not been coupled with the steam methane reformingprocess in most models. Besides, NOx and NHx were not considered with air in put.Based on the Siverts'Lawfor membrane separation and Gibbs minimum energy, CSTRmodel was built for steam methane reforming using MATLAB and EXCEL. The reformingand separation processes were coupled by the mass balance. In addition, the formation ofsolid carbon, NOx and NHx was also deeply studied. The current model was compared withthe model of Ye (International Journal of Hydrogen Energy, 2009, 34: 4755-4762.). The resultshows the CH4 conversion and hydrogen yield predicted by two models are close with themembrane capacity less than 15 Km or greater than 100Km, When Cep ranges from 15Km to100 Km, the CH4conversion and hydrogen yield predicted by CSTR was slightly lower thanthe value byPFR with the greatest difference in 30Km of Cep.To validate the CSTR model, the predictions from the Model was compared withexperimental data in the literature of Adris (Chemical Engineering Science, 1994, 49:5833-5843), Roy (Chemical Engineering Science, 1999, 54: 2095-2102.)AndMahecha-Botero (Chemical Engineering Science, 2008, 64: 2752-2762) comparison. Themodel predictions are seen to be in good agreement with those experimental data.After validating the model, the influences of reactor pressure, temperature, membranethickness, membrane area, steam carbon ratio, oxygen carbon ratio, permeate side hydrogenpartial pressure and the flow rate of sweep gas on reactor performances, carbon deposition,NHXand NOX formation were investigated. The results show that: the removal of hydrogenthrough the palladium membrane can break the original thermodynamic equilibrium, shiftingthe SMR to the direction of the hydrogen produced, reducing the NH3 formation, even beingable to offset the negative effects of pressure on the reaction. However, the formation of solidcarbon increased with the introduction of membrane module, and reducing the reactor'soperating temperature, increasing the reactor pressure, SC and OC can effectively reduce theformation of coke.The platform of fluidized bed membrane reactor for methane steam reforming was built.The experimental results shows that methane conversion and hydrogen yield increased with the temperature and with the incensement of operating pressure, methane conversiondecreased, however, the hydrogen production rate increased. When the water ratio of carbonincreases, the methane conversion rate increased, the hydrogen production firstly increasedand then decreased.