Reforming of Liquid Hydrocarbons in a Novel Hydrogen-Selective Membrane-Based Fuel Processor
In this work, asymmetric dense Pd/porous stainless steel composite membranes were fabricated by depositing palladium on the outer surface of the tubular support. The electroless plating method combined with an osmotic pressure field was used to deposit the palladium film. Surface morphology and microstructure of the composite membranes were characterized by SEM and EDX. The SEM and EDX analyses revealed strong adhesion of the plated pure palladium film on the substrate and dense coalescence of the Pd film. Membranes were further characterized by conducting permeability experiments with pure hydrogen, nitrogen, and helium gases at temperatures from 325 to 450 C and transmembrane pressure differences from 5 to 45 psi. The permeation results showed that the fabricated membranes have both high hydrogen permeability and selectivity. For example, the hydrogen permeability for a composite membrane with a 20 {micro}m Pd film was 3.02 x 10{sup -5} moles/m{sup 2}.s.Pa{sup 0.765} at 450 C. Hydrogen/nitrogen selectivity for this composite membrane was 1000 at 450 C with a transmembrane pressure difference of 14.7 psi. Steam reforming of methane is one of the most important chemical processes in hydrogen and syngas production. To investigate the usefulness of palladium-based composite membranes in membrane-reactor configuration for simultaneous production and separation of hydrogen, steam reforming of methane by equilibrium shift was studied. The steam reforming of methane using a packed-bed inert membrane tubular reactor (PBIMTR) was simulated. A two-dimensional pseudo-homogeneous reactor model with parallel flow configuration was developed for steam reforming of methane. The shell volume was taken as the feed and sweep gas was fed to the inside of the membrane tube. Radial diffusion was taken into account for concentration gradient in the radial direction due to hydrogen permeation through the membrane. With appropriate reaction rate expressions, a set of partial differential equations was derived using the continuity equation for the reaction system and then solved by finite difference method with appropriate boundary and initial conditions. An iterative scheme was used to obtain a converged solution. Membrane reactor performance was compared to that in a traditional non-membrane packed-bed reactor (PBR). Their performances were also compared with thermodynamic equilibrium values achievable in a conventional non-membrane reactor. Numerical results of the models show that the methane conversions in the PBIMTR are always higher than that in the PBR, as well as thermodynamic equilibrium conversions. For instance, at a reaction pressure of 6 atm, a temperature of 650 C, a space velocity of 900/16.0 SCCM/gm{sub cat}, a steam to methane molar feed ratio of 3.0, a sweep ratio of 0.15, the conversion in the membrane reactor is about 86.5%, while the conversion in the non-membrane reactor is about 50.8%. The corresponding equilibrium conversion is about 56.4%. The effects on the degree of conversion and hydrogen yield were analyzed for different parameters such as temperature, reactor pressure, feed and sweep flow rate, feed molar ratio, and space time. From the analysis of the model results, it is obvious that the membrane reactor operation can be optimized for conversion or yield through the choice of proper operating and design parameters. Comparisons with available literature data for both membrane and non-membrane reactors showed a good agreement.
- Research Organization:
- North Carolina A & T State Univ., Greensboro, NC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG26-01NT41361
- OSTI ID:
- 882527
- Country of Publication:
- United States
- Language:
- English
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Preparation and characterization of a composite palladium-ceramic membrane
Related Subjects
08 HYDROGEN
36 MATERIALS SCIENCE
COALESCENCE
CONTINUITY EQUATIONS
FINITE DIFFERENCE METHOD
FLOW RATE
HELIUM
HYDROCARBONS
HYDROGEN
MEMBRANES
METHANE
MICROSTRUCTURE
MORPHOLOGY
NITROGEN
PALLADIUM
PARTIAL DIFFERENTIAL EQUATIONS
PERMEABILITY
REACTION KINETICS
REACTOR OPERATION
SPACE-TIME
STAINLESS STEELS
THERMODYNAMICS