370
R. Kumar et al.
6 Hydrogen Separation by Using Membranes
Due to the fact that, the H 2 molecule has the smallest kinetic diameter the selection of
H 2 over other gases is easy. Since H 2 molecule has the biggest diffusion coefficient,
permeability and selectivity of H 2 can be tuned. In this section, we will go through
some of the articles in which the researcher attempted a different type of sample and
method to reach higher H 2 permeability and selectivity.
Because Pd is one of the best absorbent materials for hydrogen, but also expensive
compared to other metals. So researchers are also searching for the alternative to
replace Pd by alloys. Liu et al. (2018) fabricated alloy of Nb 35 Mo 5 Ti 30 Ni 30 as an
alternative of Pd for hydrogen purification/separation application. They presented the
theoretical calculation by DFT for the optimization of the combination of the alloy.
Experimental data indicate that Nb 35 Mo 5 Ti 30 Ni 30 membrane shows remarkable H 2
separation and can be a replacement of palladium metal.
In the same direction of the Pd membrane, Cheng et al. (2002) compared the H 2
permeation from the commercial Towngas (49% H 2 , 28.5% CH 4 , 19.5% CO 2 and 3%
CO) by using alumina, zeolite, Pd, and Pd–Ag alloy membranes. Their results show
that alumina and the zeolite are not suitable options for the H 2 separation from the
Towngas. Whereas Pd and Pd–Ag membranes show great results for H 2 separation
from Towngas to achieve high purity of H 2 , the purification efficiency is further
increased by the addition of silver, due to larger lattice spacing in the resulting alloy
material. Some of the previous review articles for H 2 separation by Pd and Pd alloys
are described significantly (Hatlevik et al. 2010; Cheng et al. 2002).
Beside Pd and its alloys, Chen et al. (2018) used a Pt layer over the surface of
the La 5.5 W 0.45 Nb 0.15 Mo 0.4 O 11.25-δ membrane for the reflection effect on H 2 permeation. With a combination of 50% H 2 —50%, He at 1000 °C achieved permeation
flux of H 2 is 0.483 mL/min cm
2 from both sides. This permeation rate is twice the
uncoated La 5.5 W 0.45 Nb 0.15 Mo 0.4 O 11.25-δ membrane, which indicates that the Pt layer
exhibits a positive effect on the H 2 selectivity. This enhancement is due to H 2 dissociation/combination on the Pt layer. Fasolin et al. (2018) fabricated a vanadium-based
multilayer structure (Pd/V 93 Pd 7 /Pd) having thickness of <7 μm onto porous alumina.
Results show that these membranes have high H 2 selective flux up to 0.26 mol m
−2
s
−1 at 375 °C.
Since the discovery of CNT by Iijima in 1991, CNTs have come to the forefront
of nanostructured materials and research interest has grown exponentially. Extensive
work has been done to characterize CNTs including their exceptional mechanical,
thermal, and electrical characteristics. CNTs are also known to show extremely high
aspect ratios of their length and diameter. Many of the researchers observed some of
the respectable results in the field of H 2 separation/purification. Vijay et al. and his
group are doing a wide-ranging study on the CNT-polymer nanocomposite for the
hydrogen gas separation (Kumar et al. 2011; Sharma et al. 2009, 2010; Sharma and
Vijay 2012). Their results show that the alignment and uniform distribution of the
CNTs is beneficial to enhance the H 2 permeability as well as the selectivity.
R. Kumar et al.
6 Hydrogen Separation by Using Membranes
Due to the fact that, the H 2 molecule has the smallest kinetic diameter the selection of
H 2 over other gases is easy. Since H 2 molecule has the biggest diffusion coefficient,
permeability and selectivity of H 2 can be tuned. In this section, we will go through
some of the articles in which the researcher attempted a different type of sample and
method to reach higher H 2 permeability and selectivity.
Because Pd is one of the best absorbent materials for hydrogen, but also expensive
compared to other metals. So researchers are also searching for the alternative to
replace Pd by alloys. Liu et al. (2018) fabricated alloy of Nb 35 Mo 5 Ti 30 Ni 30 as an
alternative of Pd for hydrogen purification/separation application. They presented the
theoretical calculation by DFT for the optimization of the combination of the alloy.
Experimental data indicate that Nb 35 Mo 5 Ti 30 Ni 30 membrane shows remarkable H 2
separation and can be a replacement of palladium metal.
In the same direction of the Pd membrane, Cheng et al. (2002) compared the H 2
permeation from the commercial Towngas (49% H 2 , 28.5% CH 4 , 19.5% CO 2 and 3%
CO) by using alumina, zeolite, Pd, and Pd–Ag alloy membranes. Their results show
that alumina and the zeolite are not suitable options for the H 2 separation from the
Towngas. Whereas Pd and Pd–Ag membranes show great results for H 2 separation
from Towngas to achieve high purity of H 2 , the purification efficiency is further
increased by the addition of silver, due to larger lattice spacing in the resulting alloy
material. Some of the previous review articles for H 2 separation by Pd and Pd alloys
are described significantly (Hatlevik et al. 2010; Cheng et al. 2002).
Beside Pd and its alloys, Chen et al. (2018) used a Pt layer over the surface of
the La 5.5 W 0.45 Nb 0.15 Mo 0.4 O 11.25-δ membrane for the reflection effect on H 2 permeation. With a combination of 50% H 2 —50%, He at 1000 °C achieved permeation
flux of H 2 is 0.483 mL/min cm
2 from both sides. This permeation rate is twice the
uncoated La 5.5 W 0.45 Nb 0.15 Mo 0.4 O 11.25-δ membrane, which indicates that the Pt layer
exhibits a positive effect on the H 2 selectivity. This enhancement is due to H 2 dissociation/combination on the Pt layer. Fasolin et al. (2018) fabricated a vanadium-based
multilayer structure (Pd/V 93 Pd 7 /Pd) having thickness of <7 μm onto porous alumina.
Results show that these membranes have high H 2 selective flux up to 0.26 mol m
−2
s
−1 at 375 °C.
Since the discovery of CNT by Iijima in 1991, CNTs have come to the forefront
of nanostructured materials and research interest has grown exponentially. Extensive
work has been done to characterize CNTs including their exceptional mechanical,
thermal, and electrical characteristics. CNTs are also known to show extremely high
aspect ratios of their length and diameter. Many of the researchers observed some of
the respectable results in the field of H 2 separation/purification. Vijay et al. and his
group are doing a wide-ranging study on the CNT-polymer nanocomposite for the
hydrogen gas separation (Kumar et al. 2011; Sharma et al. 2009, 2010; Sharma and
Vijay 2012). Their results show that the alignment and uniform distribution of the
CNTs is beneficial to enhance the H 2 permeability as well as the selectivity.