(406h) Paraffin-Olefin Separation By Ag(I)-Doped Nanoporous Carbons: Experiment and Computation

Separation of paraffin and olefins is great of importance in modern world. Two most important paraffin-olefin separations are the separation of ethylene and propylene from ethane and propane, respectively. Owing to very similar physical properties, it is very challenging to separate them; the current state-of-the-art separation involves cryogenic distillation that harnesses the small difference in boiling point of the constituents. However, such separation technique is highly expensive, hazardous and not sustainable. Adsorption could be a benign technique to separate olefins from paraffins, provided a suitable adsorbent is designed and fabricated. In this work, Ag(I) doped microporous and mesoporous carbons were synthesized from different synthetic and natural precursors. It was observed that all the Ag(I)-doped carbons were more selective to olefins (ethylene and propylene) compared to its respective paraffins (ethane and propane) owing to the pi interactions between Ag and pi bond of olefins. All the carbons properly characterized to understand structure-property relationship and it was observed that selectivity is dependent on the Ag(I) content of the carbons. Density Function Theory was employed to further understand the interactions between adsorbates and adsorbents. The DFT calculations indeed revealed that the adsorption energies of olefins are 3.6-6.1 times higher than that of paraffins depending on the width of the functionalized slits or pores. The quantum mechanics calculations highlight the importance of the pores size on the selectivity of the Ag(I) doped adsorbents. Furthermore, overlap between d-orbital of Ag and p orbital of olefins was assessed by Molecular Orbital analysis, thereby confirming the pi complexation process. The overall results suggest that these carbonaceous adsorbents could be suitable for paraffin-olefin separation and the latter can be remarkably increased by choosing size of functionalized slits or pores around 5-6 Å.