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

本文研究了非晶态LaNi_5和Ca-Ni合金膜对H_2混合气体中有害CO的抵抗作用，并将其沉积在Ni涂层聚合物膜上进行了H_2-CO气体分离。LaNi_5薄膜暴露于含CO的H_2气体后，其吸氢量下降约30%，但下降程度远小于结晶体样品的报道。分离实验结果表明，在50 mo1%H_2 - 50 mo1%CO的外加气体中，氢在渗透气体中的浓度大于98 mo1%。Ni/LaNi_5膜的渗透速率大于Ni膜，但在一定范围内，其渗透速率大于Ni膜。373 K时，则呈现相反的趋势。估算出Ni/LaNi_5薄膜的氢渗透活化能约为1.5kJ/mol。约30 kJ/mol 1H_2或14 kJ/mol 1H_2以上或以下。与LaNi_5相比，CaNi_5在较低的压力下可以吸收更多的氢。为了提高氢渗透速率，已经进行了使用Ca-Ni合金的氢分离膜的开发。H_2-CO混合气体中H_2浓度为50 mol/ %时，渗透气中H_2浓度可达99 mol/ %。Ni/CaNi_2膜的渗透速率<4.2>是Ni/LaNi_2膜的4倍<5.0>.为了阐明非晶态和晶态LaNi_2膜中氢原子周围局部环境结构的差异，从氢压-成分等温线中估算了热力学数据<5.0>.非晶薄膜中氢的相对偏摩尔比和相对熵与氢浓度的关系不同于晶态薄膜。无定形膜似乎有两种类型的氢网站。一种是受镧的影响，另一种是由更多的镍原子组成。晶体膜中的氢位仅为前者。

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.