Single-gas sorption isotherm
Pure component equilibrium adsorption isotherms for
C2H2,
C2H4 and CO2 were
measured at 298 K up to 1 bar, as presented in Figure 3a. The
C2H2 uptake on
Zn2(bpy)(btec) reached 93.5 cm3cm−3 at 298 K and 1 bar, significantly higher than
that of C2H4 and CO2 at
the same conditions. Notably, through size sieving by the appropriate
aperture, Zn2(bpy)(btec) presents the
C2H2 uptake of 93.5
cm3 cm−3, very low
C2H4 uptake of 9.1 cm3cm−3 and low CO2 uptake of 28.9
cm3 cm−3 (298 K and 1 bar), giving
an excellent uptake ratio of C2H2 over
C2H4 (10.31) and CO2(3.23), which are the highest values among the indicated MOFs
(Supporting information, Table S2 and S3).
To compare the separation properties of Zn2(bpy)(btec)
with other top-performing MOFs, its ideal adsorbed solution theory
(IAST) selectivity of C2H2 over
C2H4 and CO2 were
calculated on their single-component isotherms (Figure 3a). The gas
mixtures were selected as
C2H2/C2H4(1:99, v/v) and C2H2/CO2(50:50, v/v) at a total gas pressure of 1 bar and 298 K, to mimic the
composition of the industrial purification process. As seen in Figure
3b, c, Zn2(bpy)(btec) exhibits an extraordinarily high
selectivity of over 107.8 for the
C2H2/C2H4mixture and 33.3 for the
C2H2/CO2 mixture,
notably higher than the previous benchmark SIFSIX-2-Cu-i
(44.54)14, M’MOF-3a (24.03)30, CPL-1
(26.8)31 and ELM-12 (14.8)32 for
C2H2/C2H4separation, and FeNi-M’MOF (24)33 HOF-3a
(21)34, UTSA-74 (9)35, TIFSIX-2-Cu-i
(6.5)36 and for
C2H2/CO2 separation.
In industrial applications, energy cost in the regeneration process is
also an unavoidable problem and should be taken into consideration. The
interactions between the adsorbents and
C2H2 are evaluated by calculating the
isosteric heats of adsorption (Qst), which is measured
from the single component isotherms at different temperatures (Figure
3d). The calculated Qst of
Zn2(bpy)(btec) at zero coverage for
C2H2 is 28.7 kJ/mol (Figure S4), which
is much lower than those values reported in other MOFs with open metal
sites such as MOF-74 series (47 kJ/mol for
Fe-MOF-74).12 Thus, the molecular sieving based
adsorption not only avoided excessive
temperature fluctuations during the adsorption process but also
decreased the cost and energy requirement in the regeneration process,
which indicates advantages of Zn2(bpy)(btec) in real
industrial applications. In addition, comparing with other
top-performing materials (Table S2, S3), Zn2(bpy)(btec)
exhibits the lowest total C2H4 and
CO2 loading in normal conditions (Figure 3e), and less
co-adsorption will lead to a higher C2H2purity in the generation process. Besides, this material exhibits the
highest
C2H2/C2H4uptake ratio (10.31) and
C2H2/CO2 uptake ratio
(3.23), as well as extraordinarily high selectivity (107.8, 33.3)
(Figure 3f), which makes it one of the most promising materials for the
efficient C2H2 separation from
C2H4 or CO2 mixtures.