Breakthrough separation
Furthermore, we performed actual breakthrough experiments on
Zn2(bpy)(btec) to establish the feasibility of
C2H2/C2H4and C2H2/CO2separations, in which
C2H2/C2H4(v/v, 1/99) and C2H2/CO2(v/v, 50/50) mixtures were used as feeds to mimic the industrial process
conditions (Figure 4 and S6). As shown in Figure 4a, c, only after
several minutes, C2H4 or
CO2 first eluted through the bed to yield a
polymer-grade gas and the purity of C2H4monitored at the outlet was >99.9999%. Then, after a long
period of time (130 min for
C2H2/C2H4,
50 min for C2H2/CO2),
C2H2 broke through from the adsorption
bed. During this process, C2H2 was
clearly captured by Zn2(bpy)(btec), with the
concentration of the impurities decreased to lower than 1 ppm for
C2H4 and 10 ppm for CO2.
Polymer-grade C2H4 and high purity of
CO2 were directly collected at the outlet. From the
desorption curves in Figure 4b, d, it can be found that adsorbates were
fully desorbed from the materials in 20 minutes. Due to the high
C2H2/C2H4and C2H2/CO2 uptake
ratios and selectivities, a high purity of
C2H2 over 98.5 % (b) or 92.5 % (d)
were generated, respectively.
The kinetic ad/desorption rate of C2H2was also investigated in Figure S8 and S9, showing that
Zn2(bpy)(btec) has a high kinetic ad/desorption rate,
and therefore that C2H2 can be saturated
or fully desorbed in about ten minutes. In addition, the desorption and
recycling measurements revealed that this material can maintain its
C2H2 capture ability and high
selectivity in several repeated adsorption and separation cycles (Figure
4b, d, and S7). The breakthrough time remains almost unchanged during
five cyclic breakthrough experiments, confirming the good recyclability
of this material for the
C2H2/C2H4and
C2H2/CO2separation.
Generally, in the real production process, the feed gas also contains
some other components, which is a tremendous challenge in the recovery
of C2H2 from such refinery gas.
Therefore, we investigated the single-component adsorption isotherms of
some main components of refinery gas (CH4,
C2H2,
C2H4,
C2H6,
C3H4,
C3H6 and
C3H8) and common gas components
(CO2, H2, N2 and
O2) as seen in Figure 5 a, b. Based on the well-matched
pore cavity of Zn2(bpy)(btec), this material selectively
adsorbs C2H2 and blocks most other
molecules to achieve an admirable sieving effect (Fig. 4a). The uptakes
of most of the gases were below 10 cm3cm−3 at 1 bar and 298 K. Furthermore, the gas mixtures
separation process was carried out on this molecular sieve material for
the recovery of C2H2 from the simulated
steam cracking mixtures. As can be seen from the breakthrough curves,
most of the mixture gases eluted through the fixed bed quickly and a
trace amount of C2H2 was totally
adsorbed during the long retention time. In the generation process, the
adsorbent was fully desorbed in 20 minutes and obtained high purity
C2H2 (> 98 %). The
multi-component separation and desorption tests show strong evidence of
the efficient C2H2 separation ability of
Zn2(bpy)(btec) materials, which has initiated the
promise of MOF materials for this very important industrial application.