| Summary: | 碩士 === 國立中正大學 === 化學工程所 === 96 === Palladium-based composite membranes have been used in hydrogen separation. In general, a dense Pd membrane is prepared on the porous substrate by an electroless plating process. Porous stainless steel (PSS) is suitable for the formation of composite membrane due to its thermal expansion coefficient close to the Pd-based films, ease to assemble with reactors, high mechanical strength and thermal stability. However, it is difficult to prepare thin and defect-free membranes on PSS because of the surface roughness, largest pore size and wide pore-size distribution on its surface. As a consequence, the thickness of the Pd membrane is largely dependent on the surface roughness and largest pores existed in PSS. In this work, the Al2O3 particles were employed to modify the pore size and the surface roughness of PSS to reduce the thickness of Pd membranes and improve hydrogen permeability.
In the first part of the research, aluminum oxide particles with two different size distributions were used to modify the pore size of PSS. The effective number of passage through the porous substrates was kept and the maximum pore size has decreased based on SEM observations after modification with Al2O3 particles. The thicknesses of the Pd membrane supported on 10 μm and 1 μm Al2O3-modified PSS are 22.9 and 18.9 μm, and the hydrogen fluxes at 773K and ΔP=8 bar are 70.2 and 51.6 m3/m2-h, respectively. For comparison, the thickness and hydrogen flux of the membrane without modification is 31.5 μm and 44.8 m3/m2-h. It is evident that suitable substrate pretreatment will reduce the thickness of Pd membranes and improve hydrogen permeability.
In order to decrease the surface pore size distribution as well as the surface roughness, two-step modification strategy was utilized. In the second part of the research, aluminum oxide particles with particle size ~1 micron were employed to modify the surface roughness of 10 μm Al2O3-modified PSS. The pressure difference across the PSS during suction procedure was changed in the second modification. The thicknesses of the Pd membrane supported on ΔP=100 and 200 mmHg Al2O3-modified PSS are 10.5
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