Carbon molecular sieves for real industrial feedstock separation of C8 cycloalkanes: A study on pore size distribution and surface functionalization

The separation of ethylcyclohexane (ECH) from coal-based C8 naphthenic oil mixtures poses significant industrial challenges due to their similar physicochemical properties. Herein, we investigate the separation performance of carbon molecular sieves with varying pore sizes and oxygen content through dynamic breakthrough experiments and pulse testing with real industrial feedstocks. The results demonstrate that CMS-100 exhibits superior separation efficiency for ECH with an adsorption selectivity of 1.9 (ECH/ trans -1, 2-dimethylcyclohexane) as well as ECH uptake of 49 mg/g, achieving a separation factor of 0.48, attributed to its optimal microporous structure (0.64–0.86 nm). In contrast, CMS-75, characterized by a larger mesopore volume (2–20 nm), facilitates faster desorption rates, aiding in molecular transport. Grand canonical Monte Carlo (GCMC) simulations confirm that variations in substituent arrangement influence the diffusion rates of C8 cycloalkanes within the pore channels, while oxygen-containing functional groups enhance the interaction energies between C8 cycloalkanes and the adsorbent, particularly for ECH, whose larger ethyl group and electronic effects result in stronger adsorption affinity compared to DCH isomers. However, the presence of oxygen functionalities negatively impacts overall adsorption capacity by introducing steric hindrance. These findings underscore the importance of precisely optimizing both pore size distribution and surface chemistry for efficient hydrocarbon separation. This work provides a solid foundation for developing next-generation adsorbents aimed at industrial-scale separation of naphthenic oils.