Abstract
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 (
β
p/
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 (
β
p/
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.