Hexane isomers excluding

Despite the fact that both normal and monomethyl-substituted paraffins readily enter the pores of ZSM-5 and ZSM-11, preferential sorption of the normal isomer is observed under thermodynamic equilibrium, non-kinetically controlled conditions. Whereas small-pore zeolites, such as 5A and erionite, totally exclude branched hydrocarbons, and large-pore zeolites exhibit little preference, the intermediate pore-size zeolites ZSM-5 and ZSM-11 show a marked preference for sorption of the linear paraffin, even under equilibrium conditions. Competitive liquid phase sorption studies at room temperature indicated selectivity factors greater than ten in favor of n-hexane relative to... 

The intermediate pore-size ZSM-5 is also effective in selectively sorbing paraffins from cycloparaffins. Certain cycloparaffins such as decalin and cyclooctane appear to be totally excluded from the interior of the zeolite at room temperature. Selectivity factors for n-hexane relative to cyclohexane and for n-heptane relative to cycloheptane, all of which are capable of being sorbed individually, were about 100 in favor of the normal paraffin. Even isoparaffins such as 3-methylpentane were selectively sorbed relative to their cyclic isomers (selectivity factor = 4). 

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