Three-Dimensionally Ordered Silicalite-1 Membrane for Separation of the Xylene Mixture with High Permeance and Separation Factor

The silicalite-1 (SL-1) membranes effectively separate the ortho and para xylene isomers by size. To achieve high para xylene permeances, the channels running along the b axis should be oriented normal to the underlying porous substrates and should not be blocked by mismatched overgrowth between the newly grown layers. The ideal method would be to place a three-dimensionally (3D) ordered array of uniformly sized and shaped SL-1 seed crystals with their three crystal axes oriented uniformly on underlying porous supports with a regular spacing between the seed crystals, and selectively fill up the intercrystalline gaps by secondary growth. We now report that this method is quite doable, and the obtained SL-1 membrane shows very high para xylene permeances despite the fact that the membrane is thick.