Aromatics/Aliphatics Separation by Adsorption:  New Sorbents for Selective Aromatics Adsorption by π-Complexation

• Published in: Industrial & engineering chemistry research 2000-10, Vol.39 (10), p.3856-3867
• Main Authors: Takahashi, Akira, Yang, Frances H, Yang, Ralph T
• Format: Article
• Language: English
• Subjects: Adsorption; Applied sciences; Chemical engineering; Chemistry; Exact sciences and technology; General and physical chemistry; Solid-liquid interface; Surface physical chemistry
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie000376l

New sorbents for benzene/cyclohexane separation based on π-complexation were prepared by dispersion of transition metal salts on a high-surface-area substrate. PdCl2 or AgNO3 dispersed on SiO2 gel exhibited high equilibrium adsorption ratios of benzene over cyclohexane. PdCl2 loading of 0.88 g/g of SiO2 showed the best benzene/cyclohexane ratio of 3.2. The heats of adsorption of benzene on these sorbents were in the range 7−12 kcal/mol and followed the rank order CuCl > PdCl2 > AgNO3 > AuCl3 > PtCl4, compared to 5−7 kcal/mol for cyclohexane. Molecular orbital calculations for the bonding of benzene and chlorides of these metals were performed at the Hartree−Fock (HF) and density functional theory (DFT) levels using effective core potentials. The theoretical bond energies were (in kcal/mol) 12.5 (CuCl), 10.8 (PdCl2), 8.6 (AgCl), 6.5 (AuCl3), and 5.2 (PtCl4), in fair agreement with the experimental results. The M−C interactions followed classical π-complexation in most cases, and differences in the bonds with these metal ions are explained by natural bond orbital results.