Precision pore engineering in coconut shell-derived carbon molecular sieves enables high-efficiency separation of cis/trans-1,3-dimethylcyclohexane isomers

In chemical engineering, biomedical, and reagent applications, cis/ trans -1,3-dimethylcyclohexane (cis/ trans -1,3-DMCH) isomers play critical roles due to their distinct structural configurations. However, their nearly identical boiling points and similar molecular structures make separation particularly challenging. This study developed a coconut shell-derived carbon molecular sieve (CCMS) using a stepwise activation strategy to precisely control pore structure and surface chemistry, creating a series of CCMS-x-y adsorbents. The CCMS-900-0.5 variant demonstrated superior performance in static adsorption tests, achieving maximum cis -1,3-DMCH uptake (62.73 mg/g) and selectivity (14.87). Dynamic breakthrough experiments confirmed exceptional separation efficiency with stable separation intervals of 275 ± 12.5 min, attributed to its optimal pore size distribution (5.37–5.99 Å). Grand canonical Monte Carlo (GCMC) simulations revealed that pure graphene slit models with 6 Å pores achieved maximum cis -isomer selectivity (2.76). Oxygen-containing functional groups were found to reduce separation efficiency by introducing steric hindrance. Advanced disordered mesoporous carbon models demonstrated faster diffusion rates for trans -1,3-DMCH compared to its cis counterpart. Interaction energy analysis indicated that adsorption primarily occurs through van der Waals forces, with stronger combined van der Waals and electrostatic interactions observed between the adsorbent and cis -1,3-DMCH. This work establishes both a practical framework for designing high-performance adsorbents for cyclic alkane isomer separation and a theoretical foundation for developing energy-efficient, low-carbon cis/ trans -1,3-DMCH separation technologies.