Pressed graphite crystals as gas separation membrane for steam reforming of ethanol
Pressed graphite crystals as gas separation membrane for steam reforming of ethanol
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DOI：
10.1016/j.memsci.2014.06.047
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发表时间：
2014-11
影响因子：
9.5
通讯作者：
A. Schulz;F. Steinbach;J. Caro
中科院分区：
文献类型：
--
作者：
A. Schulz;F. Steinbach;J. Caro
评价了压石墨作为膜反应器中乙醇蒸汽重整膜的潜力。在乙醇蒸汽重整中，氢气必须从乙醇、二氧化碳和水的混合物中选择性地就地除去。商用石墨薄片（单晶）已被压制成不同厚度的圆盘膜。研究了单一气体渗透和H2/CO2/H2O混合气体渗透。从单一气体渗透率可以预测H2/ co2混合物的理想分离因子为35、…、60。然而，通过气相色谱分析对该混合物的实际分离因子进行研究，得出混合物的实际分离因子在5左右。这一实验发现可以用克努森型机制来解释，该机制具有沿压石墨薄片晶界的渗透路径。在100到250°C之间的温度下，压制石墨膜确实是氢选择性的。氢气从H2/CO2/H2O混合物中分离，相对于CO2的分离系数为5，相对于H2O的分离系数为12，但相对于乙醇的分离系数仅为2.4。压制石墨晶体导致单个石墨晶体的自取向（砖层结构）。平行于排列的片状晶体的氢渗透比垂直于它们的氢渗透快25倍。通过压制石墨膜的氢透性比通过分子筛膜（如负载沸石膜或MOF膜）的氢透性高一到两个数量级。
Pressed graphite was evaluated as a potential membrane for steam reforming of ethanol in membrane reactors. In ethanol steam reforming, hydrogen has to be in situ removed selectively from a mixture with ethanol, CO2, and H2O. Commercial graphite flakes (single crystals) have been pressed into disc membranes of different thicknesses. Both single gas permeation and H2/CO2/H2O mixed gas permeation were studied. From single gas permeation, a relatively high ideal separation factor of 35,…,60 for the H2/CO2mixture could be predicted. However, the study of the real separation factor of this mixture by gas-chromatographic analysis gave real mixture separation factors around 5. This experimental finding is explained by a Knudsen-type mechanism with permeation paths along the grain boundaries of the pressed graphite flakes. At temperatures between 100 and 250 °C, the pressed graphite membrane is indeed hydrogen-selective. Hydrogen is separated from a H2/CO2/H2O mixture with a separation factor of 5 relative to CO2and 12 relative to H2O, but only 2.4 relative to ethanol. Pressing of the graphite crystals results in a self-orientation (brick layer structure) of the individual graphite crystals. Hydrogen permeation parallel to the aligned flake-shaped crystals is by the factor 25 faster than perpendicular to them. The hydrogen permeabilities through the pressed graphite membranes are about one to two orders of magnitude higher than those through molecular sieve membranes such as supported zeolite or MOF membranes.