| Abstract
| - Adsorption equilibrium and kinetics of four octane isomers: n-octane (nC8), 2-methylheptane (2MC7), 2,5-dimethylhexane (25DMC6), and 2,2,4-trimethylpentane (224TMC4) were studied in a carbon molecular sieve obtained from the pyrolysis of a poly(vinylidene choride-co-vinyl chloride) (PVDC-PVC; Saran, Dow. Co) material. Adsorption capacities calculated at 325, 350, and 400 °C temperatures and partial pressures from 6.9 to 12.8 Pa (via the inverse gas chromatography method), were in the range of 0.5−3.0 g/100 gAds. All isotherms were of type I in Brunauer’s classification. Heats of adsorption (−ΔH0) values were on the order of 76−77 kJ/mol for nC8, 2MC7, and 25DMC6 and 94 kJ/mol for 224TMC5 confirmed selectivity for separation of multibranched compounds with a gem-dimethyl group only. Adsorption kinetic studies at 175, 200, and 250 °C employing the zero length column chromatography (ZLC) technique presented a weak temperature dependence on desorption time (12.3, 10.3, 8.4, and 8.3 kJ/mol for nC8, 2MC7, 25DMC6, and 224TMC5, respectively). Additionally, as the degree of the hydrocarbon branching increases as well as critical size, the uptake was more rapid. Adsorption−desorption variations by temperature changes may be related to specific interactions of the C−H bonding in the hydrocarbon framework with the graphene structures in the carbon molecular sieve (CMS) material which are suggested to be dependent on loading levels and the pore size distribution in the carbonaceous material.
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