On the use of a catalytic H-ZSM-5 membrane for xylene isomerization

An H-ZSM-5 membrane was used in this work for xylene isomerization and for separation of p-xylene from the other isomers. MFI membranes (silicalite-1 and H-ZSM-5) were prepared by seeded growth on porous stainless steel supports. The membranes were tested for separation of the xylene isomers in the temperature range 100–400 °C. The H-ZSM-5 membrane showed higher p-xylene permselectivity (βp/o = 4.3 at 300 °C) and lower permeance to p-xylene (3.55 × 10−8 mol m−2 s−1 Pa−1 at 300 °C) compared to the silicalite-1 membrane (βp/o = 2.1, permeance to p-xylene 7.4 × 10−7 mol m−2 s−1 Pa−1 at 300 °C). However, both were not completely defect-free. The kinetics of xylene isomerization on the catalytically active H-ZSM-5 membrane and, for comparison, on a conventional H-ZSM-5 powder catalyst was studied in a gradient-free recycle reactor (Berty-type). Thereby the membrane showed higher activity than the conventional catalyst. The reaction kinetics was best described by a general triangular scheme. The H-ZSM-5 membrane was then used in a membrane reactor for xylene isomerization and the results were compared to those obtained in a packed-bed reactor using the conventional H-ZSM-5 catalyst. At 400 °C, a relative increase of the conversion of m-xylene by 15% was observed in the membrane reactor combined with higher p-xylene selectivity.