Figure 5 Simulated adsorption density distribution colored by adsorption
potential of (a) CH4, (b)
C2H6 and (c)
C3H8 in
Ni(TMBDC)(DABCO)0.5 at 1 kPa
To further understand the adsorption mechanism of CH4,
C2H6 and
C3H8 in
Ni(TMBDC)(DABCO)0.5, the GCMC was applied to examine the
adsorption density distribution of the three gases in the adsorbent. As
illustrated in Figure 5, the CH4,
C2H6 and
C3H8 were adsorbed on two sites in the
framework of Ni(TMBDC)(DABCO)0.5, which are termed as
Site I and Site II. The gases adsorbed on Site I was mainly influenced
by the methylene group from DABCO pillar, while those adsorbed on Site
II was affected synergistically by the methyl group from TMBDC ligand
and the methylene group from the adjacent DABCO pillar. That is to say,
strong interaction was formed on CH4,
C2H6 and
C3H8 molecule owing to the presence of
methyl and methylene group, and thus these hydrocarbon molecules were
more preferentially adsorbed on the Site II and Site I.
In addition, it shows that the adsorption potentials of these alkanes in
the Ni(TMBDC)(DABCO)0.5 follow the order:
C3H8 >
C2H6 > CH4,
which is consistent with the order of the adsorption capacity at low
pressure region. This phenomenon further confirmed that the framework of
Ni(TMBDC)(DABCO)0.5 showed stronger affinity toward
C3H8 than
C2H6 and CH4, which was
attributed to the existence of both methyl groups and methylene groups
in the channel.
Figure 6 Breakthrough curves of
CH4/C2H6/C3H8(85:10:5, v/v/v) ternary mixtures through
Ni(TMBDC)(DABCO)0.5 packed column
To evaluate the dynamic separation performance of the sample for
CH4/C2H6/C3H8mixture, breakthrough experiments at 298 K were performed, in which the
stimulated industrial gas mixture of
CH4/C2H6/C3H8(85:10:5, v/v/v) was applied. Figure 6 presents the breakthrough curves
of ternary mixtures
CH4/C2H6/C3H8(85:10:5, v/v/v) through the packed column with
Ni(TMBDC)(DABCO)0.5. It demonstrates that these three
gases were completely separated with the breakthrough time of 80 min for
C3H8, 24 min for
C2H6, and 4 min for CH4.
In addition, the recyclability of Ni(TMBDC)(DABCO)0.5was also examined. Figure S7 presents the breakthrough curves of three
adsorption-desorption cycles on Ni(TMBDC)(DABCO)0.5. It
shows that the breakthrough curves of these ternary mixtures almost
overlap, indicating excellent recycling performance of
Ni(TMBDC)(DABCO)0.5. These great separation property and
recyclability of the Ni(TMBDC)(DABCO)0.5 would make it a
great candidate for challenging separation of
CH4/C2H6/C3H8mixture or recovering low content of
C2H6 and
C3H8 from natural gas.