| 학회 | 한국공업화학회 |
| 학술대회 | 2008년 가을 (11/12 ~ 11/14, ICC 제주) |
| 권호 | 12권 2호 |
| 발표분야 | 초청강연 |
| 제목 | Development of Amorphous Silica Membranes and Membrane Reactors for Hydrogen Production to Prevent Global Warming |
| 초록 | Recently, increasing attention has been directed to use of hydrogen as an energy carrier for sustainable energy consumption with reduced environmental burden. Most hydrogen production occurs by steam reforming of hydrocarbons such as methane. This reaction is endothermic, and the conversion is limited by thermodynamic equilibrium. It is well known that the application of high-temperature membrane reactors to this reaction has a potential to achieve the same conversion as that attained in conventional reactors at significantly lower temperature, and a microporous inorganic membrane is one of the candidates for the development of highly efficient membrane reactors for hydrogen production. We could succeed to prepare stable silica membranes having excellent H2/N2 permeance ratio (over 1,000) by the counter diffusion chemical vapor deposition method using tetramethyl orthosilicate (TMOS) and O2 as reactants at 873 K. H2 permeance at 873K was 1.5ｘ10.7 mol m-2 s-1 Pa-1. H2/N2 permeance ratio was kept for 80 h under the typical steam-reforming conditions of methane for a membrane reactor (76 kPa of steam at 773 K). Organic chemical hydrides such as cyclohexane, methyl-cyclohexane, decaline are promising hydrogen carriers because they have higher hydrogen density, which exceeds the developmental target for fuel cell vehicles according to the estimation made by Department of Energy of USA. Additionally they are liquid under ordinary temperature and pressure, so the present infrastructure such as gas stations can be utilized. However, produced hydrogen has to be separated from the hydride gases and this process exhausts a lot of energy and costs much. Pore-size-controlled amorphous silica membranes were prepared by CVD method with changing the molecular structure of silica precursors; tetramethoxysilane (TMOS), and dimethoxy diphenylsilane (DMDPS). The membrane with DMDPS had larger pores and showed higher H2 permeance at 573 K of the order of 10-6 mol m-2 s-1 Pa-1 and higher H2/SF6 permselectivity of 8,000, compared to the membrane with TMOS. The membrane reactors to produce hydrogen from the dehydrogenation of cyclohexane were constructed with DMDPS membrane or TMOS membrane. Both the membrane reactors showed enhanced conversions compared to the equilibrium conversion, and the enhanced rate was larger in the case of DMDPS membrane than the case of TMOS membrane at from 483 K and 563 K. This trend of the conversion enhancements was due to the difference of hydrogen extraction, as expected in theoretical calculation. Additionally the membrane reactor can be operated with only pressurized cyclohexane as a feed, which means that it does not need some carrier gas, and can supply hydrogen with high purity due to nonuse of some sweep gas. It should be noted that it is a first successful report in the world to operate a membrane reactor under such conditions, except for using a palladium membrane. |
| 저자 | Shin-ichi Nakao |
| 소속 | Dept. of Chem. System Eng. |
| 키워드 | Amorphous silica membranes; membrane reactor |
