Highly efficient separations of C2H2 from C2H2/CO and C2H2/H2 in metal-organic frameworks with ZnF2 chelation: A molecular simulation study

The separations of fuel gas mixtures are very significant but energy-consuming segments in modern industry. Metal-organic frameworks (MOFs) are promising in saving energy during gas adsorption and separation processes owing to their physical interactions with gas molecules. In our work, the separations of C2H2 from C2H2/CO and C2H2/H-2 in MOFs both non-chelated and chelated by ZnF2 groups were investigated with GCMC method. It was found that the introduction of ZnF2 groups can remarkably improve C2H2 adsorption amount up to 1 similar to 2 magnitudes in MOFs. The selectivities of C2H2/CO and C2H2/H-2 in Zn-2(tmbdc)(2)(ZnF2-bpy) at 1 kPa are nearly 2000 and 10000, much higher than those of the non-chelated MOFs. The influences of pore size, external temperature, electrostatic interaction, adsorption heat difference and gas composition ratio on the separation processes were also analyzed. Smaller pore size and larger adsorption heat difference can benefit the selective adsorption of gas mixtures. Besides, the external temperature and electrostatic interaction can affect the separation of C2H2/CO and C2H2/H-2 mixtures both positively and negatively. This depends on the relative ratio of the effects of external temperature and electrostatic interaction on different gas components. The results also suggest that the ZnF2 chelated MOFs are more suitable for the adsorption of trace amount of C2H2 from C2H2/CO and C2H2/H-2 mixtures.