Selective adsorption of olefin-paraffin on diamond-like frameworks: diamondyne and PAF-302

Olefin-paraffin separation is one of the most significant processes in the petrochemical industry. An energy efficient method such as adsorption is considered to be a promising alternative to the traditional cryogenic distillation for the purification of olefins or paraffins. In this work, the grand canonical Monte Carlo (GCMC) method was used to study the adsorption and separation of light hydrocarbons (including ethylene, ethane, propylene and propane) by two diamond-like frameworks: diamondyne (originally named D-carbon in J. Mater. Chem. A, 2013, 1, 3851) and PAF-302, and further explore the mechanism for the adsorptive separation of olefins and paraffins. It is found that both diamondyne and PAF-302 show high uptake of hydrocarbons under ambient conditions, which greatly exceed those of MOFs and ZIFs. The saturation adsorption amounts of ethylene, ethane, propylene and propane on diamondyne are 14.5, 12.3, 10.3 and 8.9 mmol g(-1), while they are 31.8, 28.0, 32.0, 30.3 mmol g(-1) for PAF-302, which indicates that PAF-302 is an excellent candidate for hydrocarbon adsorption. In addition, it is also found that diamondyne shows preferential adsorption of olefins in the olefin-paraffin mixtures, like most commonly reported MOFs and ZIFs. However, interestingly, PAF-302 exhibits favorable adsorption for paraffins over olefins, which is an entirely different behavior to diamondyne, even though they have similar diamond-like structures.