3 research outputs found

    Mathematical Modeling of High Temperature and High Pressure Dense Membrane for Separation of Hydrogen from Gasification

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    There is an increasing interest in the use of inorganic membranes as a means of separating gas mixtures at high temperatures and pressures. The most important membrane properties are high permeability and selectivity, and good mechanical, thermal and chemical stability. Dense Pd-based composite membranes are suitable for hydrogen separation and use in catalytic membrane reactors because of their high permeability, good surface properties and high selectivity for hydrogen transport. At UTSI, Pd/AlO23 membranes were prepared by a special method of laser based thermal deposition of the thin film Pd on a ceramic substrate by Nd-YAG laser irradiation of PdCl2 coating on a γ-alumina substrate. This work reports a mechanistic model for the hydrogen permeation process in the Pd/Al2O3 composite membrane developed at UTSI. The model takes into account the well known kinetics of hydrogen adsorption/desorption in the palladium surface and hydrogen permeation in the porous alumina layer. Reasonable values for all mass transfer rate parameters were estimated based on the available surface science and membrane permeation literature. One set of experimental data (at 11000F) was used to determine the best values of the necessary rate parameters. These values of rate parameters were then used to predict and compare the experimental hydrogen flux data at two other temperatures (90000F and 1300F). The results demonstrated that the atomic hydrogen diffusion through the palladium layer and pore diffusion in the porous alumina support both played important roles in the permeation of hydrogen through the composite Pd/Al2O3 membrane. A simplified resistance model was also employed to analyze the permeation behavior of hydrogen through the Pd/Al2Omembrane to identify the major resistances to the mass transfer. The results indicated that the mass transfer in the Pd layer contributed about 90% of the total mass transfer resistance. Our model calculations also indicated that by reducing the thickness of the Pd layer to about 18 μm, the DOE goal of \u3e 60 scfh/ft2 for hydrogen gas flux can be achieved. This can also be achieved by reducing the thickness of the Pd layer to about 20 μm and reducing the thickness of the alumina support layer to about 2 mm or by increasing it’s porosity to about 50%.

    Self-assembled photosystem-I biophotovoltaics on nanostructured TiO2 and ZnO

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    The abundant pigment-protein membrane complex photosystem-I (PS-I) is at the heart of the Earth’s energy cycle. It is the central molecule in the “Z-scheme” of photosynthesis, converting sunlight into the chemical energy of life. Commandeering this intricately organized photosynthetic nanocircuitry and re-wiring it to produce electricity carries the promise of inexpensive and environmentally friendly solar power. We here report that dry PS-I stabilized by surfactant peptides functioned as both the light-harvester and charge separator in solar cells self-assembled on nanostructured semiconductors. Contrary to previous attempts at biophotovoltaics requiring elaborate surface chemistries, thin film deposition, and illumination concentrated into narrow wavelength ranges the devices described here are straightforward and inexpensive to fabricate and perform well under standard sunlight yielding open circuit photovoltage of 0.5 V, fill factor of 71%, electrical power density of 81 µW/cm2 and photocurrent density of 362 µA/cm2, over four orders of magnitude higher than any photosystem-based biophotovoltaic to date
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