Xylene isomers, selective sorption

The use of various zeolites for the separation of xylene isomers has received a considerable amount of attention. Numerous patents have been issued for such separations however, equilibrium selectivity factors tend to be relatively low (9). We found virtually no p-xylene selectivity for a dealuminized H-mordenite under equilibrium conditions. H-ZSM-5, however, did exhibit a distinct preference for p-xylene sorption even at equilibrium (Table V). 

The high isomer selectivity observed for ZSM-5 can be further enhanced by imposing kinetic diffusion-al effects upon the thermodynamic selectivity, thereby magnifying the preference for p-xylene sorption (1 ). ... 

Selective Sorption of Xylene Isomers from Solution... 

All the above mentioned high perm-selectivity of zeolite membranes can be attributed to the selective sorption into the membranes. Satisfactory performance can be obtained by defective zeolite membranes. Xylene isomers separation by zeolite membranes compared with polymeric membranes are summarized in Table 15.4. As shown, zeolite membranes showed much higher isomer separation performances than that of polymeric membranes. Specially, Lai et al. [41] prepared b-oriented silicalite-1 zeolite membrane by a secondary growth method with a b-oriented seed layer and use of trimer-TPA as a template in the secondary growth step. The membrane offers p-xylene permeance of 34.3 x 10 kg/m. h with p- to o-xylene separation factor of up to 500. Recently, Yuan et al. [42] prepared siUcalite-1 zeolite membrane by a template-free secondary growth method. The synthesized membrane showed excellent performance for pervaporation separation of xylene isomers at low temperature (50°C). 

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