| 초록 |
In this study, silica composite membranes were prepared for hydrogen purification from methanol steam reforming. Especially, CO concentration must be under 100ppm to prevent CO gas from poisoning Pt as anode electrocatalyst of PEMFC. Alumina supports which are generally used are brittle, so stainless steel(SUS) supports were used in order to improve mechanical strength of membranes. For material of toplayer of hydrogen-selective membranes, palladium has very high selectivity for hydrogen. But in this study, silica was chosen, because of disadvantages of palladium such as high cost and weakness for sulfur. First, supports were prepared by coating Ni, SiO2(500nm), SiO2(150nm) in turns on SUS. Silica toplayer was coated on the supports with several variations for preparation of toplayer such as calcination temperature, dipping time and number of dipping-drying process. The optimized preparation conditions were calcination temperature of 500℃, dipping time of 60sec and number of dipping-drying process of 4 times. But the membrane still had pinholes, nitrogen or carbon dioxide flowed through there. So, dipping-drying-calcination process was repeated 4 times. As a result, surface of the membrane was much denser than the membrane prepared by repeat of dipping-drying process and even hydrogen was blocked perfectly. So, for material of toplayer, silica sol(5nm) made by base catalyst was replaced with silica sol(1.5nm) by acid catalyst in order to make hydrogen-selective micropores. For single gas permeation test of the membrane, only hydrogen flowed through the membrane and permeance of hydrogen was 2∼5×10-5 cm3*cm-2*cmHg-1*s-1. For mixture gas permeation test using H2(99%)/CO(1%) feed, CO concentration of 10000ppm was reduced to under 81ppm. And permeation mechanism through the membrane was mainly molecular sieving.
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