Separation of hydrogen from H_2-CO gas mixtures using rare earth hydrogen storage alloy films

研究了非晶态LaNi_5和Ca-Ni合金薄膜对H_2混合气体中有害CO的抵抗性能，并在ni包覆聚合物膜上进行了H_2-CO气体分离。在含CO的H_2气体中，LaNi_5膜的吸氢能力下降了约30%，但其下降程度远小于晶体体样品。分离实验结果表明，50mo1 % h_2 - 50mo1 % co组成气体中的氢气在渗透气体中被浓缩到98 mo1%以上。在373 K以下，Ni/LaNi_5膜的渗透速率大于Ni膜，但在温度以上则相反。Ni/LaNi_5膜的氢渗透活化能在343 K以上约为30 kJ/mo1H_2，在343 K以下约为14 kJ/mo1H_2。与LaNi_5相比，CaNi_5在低压下可以吸收更多的氢。为了提高氢的渗透速率，采用钙镍合金进行了氢分离膜的研制。在注入的H_2-CO混合气体中，50 mo1%的h_2气体在渗透气体中被浓缩到高达99 mo1%。Ni/CaNi_<4.2>薄膜的渗透速率是Ni/LaNi_<5.0>薄膜的4倍。为了阐明LaNi_<5.0>非晶膜和结晶膜中氢原子周围局部环境结构的差异，利用氢压力-组成等温线对热力学数据进行了评价。非晶膜中氢的相对偏摩尔焓和熵与氢浓度的关系与结晶膜中不同。非晶膜似乎有两种类型的氢位点。一种受镧的影响，另一种由更多的镍原子组成。结晶膜中的氢位只是前者。

The resistance of amorphous LaNi_5 and Ca-Ni alloy films to harmful CO in H_2 gas mixtures has been studied and the H_2-CO gas separation has been performed using these films deposited on a Ni-coated polymer membrane. The hydrogen adsorption capacity of the LaNi_5 films decreased about 30% after exposing to the H_2 gas containing CO. The degree of decrement for the films, however, was much smaller than that reported for a crystalline bulk sample.As the results of separation experiments, hydrogen in the applied gas with a composition of 50 mo1%H_2 - 50 mo1%CO was concentrated to more than 98 mo1% in the permeated gas. The permeation rate for Ni/LaNi_5 films was greater then that for Ni films up to ca. 373 K, but the opposite tendency was observed at above the temperature. The activation energy of hydrogen permeation estimated for the Ni/LaNi_5 film was ca. 30 kJ/mo1H_2 or 14 kJ/mo1H_2 above or below ca. 343 K respectively.CaNi_5 can absorb much hydrogen at low pressures in comparison with LaNi_5. In order to increase the hydrogen permeation rate, the development of hydrogen separation film using the Ca-Ni alloy has been performed. A gas of 50 mo1%H_2 in an applied H_2-CO gas mixtures was concentrated to as high as 99 mo1% in the permeated gas. The permeation rate of the Ni/CaNi_<4.2> film was four times as large as that of the Ni/LaNi_<5.0> film.Thermodynamic data have been evaluated from the hydrogen pressurecomposition isotherms in order to clarify the difference of the local environmental structure around hydrogen atoms in LaNi_<5.0> between the amorphous and crystalline films. The dependence of the relative partial molar enthalpies and entropies of hydrogen on hydrogen concentration in the amorphous film was different from that in the crystalline film. The amorphous film appears to have two types of hydrogen sites. One is influenced by lanthanum, and the other is comprised of more nickel atoms. The hydrogen site in crystalline film is only the former.