Fine-Tuning the Pore Environment of the Microporous Cu-MOF for High Propylene Storage and Efficient Separation of Light Hydrocarbons

Ethylene
(C2H4) and propylene (C3H6) are important energy sources and raw materials in
the chemical industry. Storage and separation of C2H4 and C3H6 are vital to their practical
application. Metal–organic frameworks (MOFs) having adjustable
structures and pore environments are promising candidates for C3H6/C2H4 separation. Herein,
we obtained a Cu-based MOF synthesized by H3TTCA and pyrazine
ligands. By adding different functional groups on the ligands within
the MOFs, their pore environments are adjusted, and thus, the C3H6 storage capacity and C3H6/C2H4 separation efficiency are improved. Eventually,
the fluoro- and methyl-functionalized iso-MOF-4 exhibits
a better gas storage and C3H6/C2H4 separation performance compared with iso-MOF-1 (nonfunctionalized), iso-MOF-2 (fluoro-functionalized),
and iso-MOF-3 (methyl-functionalized). A record-high
C3H6 uptake of 293.6 ± 2.3 cm3 g–1 (273 K, 1 atm) is achieved using iso-MOF-4. Moreover, iso-MOF-4 shows excellent repeatability,
and only 3.5% of C3H6 storage capacities decrease
after nine cycles. Employing Grand Canonical Monte Carlo (GCMC) simulations,
it is indicated that iso-MOF-4 preferentially adsorbs
C3H6 rather than C2H4 at
low pressure. Single-crystal X-ray diffraction on C3H6-adsorbed iso-MOF-4 crystals precisely demonstrates
the adsorption positions and arrangement of C3H6 molecules in the framework, which is consistent with the theoretical
simulations. Remarkably, gas sorption isotherms, molecular simulations,
and breakthrough experiments comprehensively demonstrate that this
unique MOF material exhibits highly efficient C3H6/C2H4 separation. Additionally, iso-MOF-4 also possesses efficient separation of C3H8/CH4 and C2H6/CH4, indicating
its promising potential in storage/separation of light hydrocarbons
in industry.