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

研究了非晶态LaNi5和Ca-Ni合金薄膜在H2混合气体中对有害CO的耐受性，并用这些薄膜在镀镍聚合物膜上进行了H2-CO气体分离。在含CO的氢气中，LaNi5薄膜的吸氢量下降了约30%。作为分离实验的结果，外加气体中的氢在50Mo1%H_2-50Mo1%CO的组成下被浓缩到渗透气体中的98Mo1%以上。在约373K时，Ni/LaNi5膜的渗透速率大于Ni膜，但高于373K时的渗透速率则相反。测得Ni/LaNi5薄膜的氢渗透激活能在343K上下分别约为30kJ/mo1H2和14kJ/mo1H2。与LaNi5相比，CaNi5在低压下能吸收更多的氢。为了提高氢渗透速率，用Ca-Ni合金开发了氢分离膜。在外加H_2-CO混合气体中，H_2浓度为50MO1%的气体在渗透气体中的浓度高达99MO1%。Ni/CaNi_lt；4.2&gt；薄膜的渗透速率是Ni/LaNi_lt；5.0&gt；薄膜的四倍，热力学数据由氢压组成等温线估算，以阐明非晶态和晶态薄膜中LaNi_lt；5.0&gt；中氢原子周围的局部环境结构的差异。氢的相对偏摩尔焓和相对偏摩尔熵与非晶膜中氢浓度的关系与晶态膜中的不同。无定形薄膜似乎有两种类型的氢位。一种是受镧的影响，另一种是由更多的镍原子组成。结晶膜中的氢位只有前者。

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.