摘要
The similarity in physical and chemical properties between ethylcyclohexane (ECH) and dimethylcyclohexane (DCH) isomers poses significant challenges for the effective separation of ECH from coal-derived C8 naphthenic oil. This study employed a model oil system comprising the three predominant components in C8 naphthenic oil: ECH, Cis-1,3-DCH, and Trans-1,3-DCH. The separation performance of H-beta zeolites with varying silica-aluminum ratios (SAR) was evaluated through static adsorption and dynamic breakthrough experiments. The results indicated that H-beta-55 (SAR = 55) demonstrated superior separation efficiency for ECH, attributable to its hierarchical microporous-mesoporous structure and moderate acidity. Specifically, H-beta-55 achieved an ECH/1,3-DCH selectivity coefficient of 3.7, an ECH adsorption capacity of 7.1 mg/g, and a pseudo-second-order adsorption rate constant of 0.67 g/(mg·min), which was 3.4–4.8 times higher than those observed for the 1,3-DCH isomers. In dynamic breakthrough tests, the ECH breakthrough endpoint (∼350 min) occurred approximately 150 min later than that of Cis-1,3-DCH (∼200 min). Ethylcyclohexane temperature-programmed desorption (ECH-TPD) experiments confirmed that physical interactions predominantly governed adsorption. Grand Canonical Monte Carlo (GCMC) simulations of molecular probability density distributions revealed that ECH (kinetic diameter ∼ 6.37 Å) preferentially accesses secondary pore channels to occupy high-density adsorption sites. In contrast, steric hindrance caused by the methyl groups of DCH isomers restricted them to the primary 12-membered ring main channels. These findings underscore the importance of fine-tuning the SAR of H-beta zeolites to optimize pore size distribution and acidity for efficient C8 naphthene separation. This work provides a molecular-level theoretical basis for designing advanced adsorbents for industrial-grade naphthenic oil separation processes.
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