Separation of hexane isomers through nonzeolite pores in ZSM-5 zeolite membranes

Permeation of n-hexane and 2,2-dimethylbutane (DMB) through two tubular ZSM -5 zeolite membranes was studied as a function of temperature and isomer pa rtial pressures. The maximum permeation selectivity is 650, obtained at hig h n-hexane pressures. Though the single-gas isomers permeate at similar rat es, the presence of n-hexane decreases the DMB permeance dramatically, wher eas n-hexane permeation is unaffected by DMB. The nonzeolite pores appear t o be different in size or number in the two membranes, whose pores saturate at different n-hexane pressures. Membranes with smaller nonzeolite pores e xhibit pore saturation. The dependence of permeance on partial pressure and temperature indicates that most of the DMB permeance is through nonzeolite pores, which can be blocked by preferential n-hexane adsorption. These por es are larger than zeolite pores but are apparently in the nanopore size ra nge.