(187b) The Effect of Microstructure On the Separation of Xylene Isomers through b-Oriented MFI Silicalite-1 Membranes

Separation of p-xylene
molecules from xylene isomers is very important in the petroleum industry
because p-xylene is a starting material to produce monomers used in the
production of PET plastics and polyester clothing. Conventional method used for
the separation of xylene isomers is a distillation process that separates
molecules based on the difference in their volatilities. However, close boiling
points of xylene isomers make the separation by distillation more costly. Zeolite
membranes have attracted a great deal of research and industrial interest due
to their molecular sieving ability for gas separation. Control of microstructure
such as preferential orientation of pores, size and shape of grain boundary and
membrane thickness are often desirable to improve gas separation performance of
zeolite membranes. For instance, Lai et al.¹ has demonstrated that b-oriented
MFI zeolite membranes show dramatically increased membrane performance as
compared to those oriented randomly or along the other crystallographic
directions. Recently Choi et al.² has improved the performance of c-oriented
MFI membranes by eliminating defects in grain boundaries using rapid thermal
processing. Although control of microstructure provides promising results,
there are still technological challenges for the industrial applications.   

Recently, we have reported a simple
synthesis route for the preparation of b-oriented silcalite-1 membranes
that provided easy ways to control microstructure of membranes such as
orientation, density and structure of grain boundaries.³ In this talk, we will show the
performance of b-oriented silcalite-1 membranes with controlled
microstructure by measuring the permeation of xylene isomers. We will present,
for the first time, the effect of the grain boundary structure on the
separation of xylene isomers by comparing the permeation of xylene isomers
through b-oriented MFI membranes with and without removing TPA from the
grain boundaries. Also, the density of grain and grain boundary are simply
controlled by changing the size of seed crystals and their effects on the
separation of xylene isomers will be discussed.

(1) Lai, Z. P.; Tsapatsis, M.; Nicolich, J. R. Advanced
Functional Materials 2004, 14, 716-729.

(2) Choi, J.; Jeong, H. K.; Snyder, M. A.; Stoeger, J.
A.; Masel, R. I.; Tsapatsis, M. Science 2009, 325,
590-593.

(3) Lee, I.; Buday, J. L.; Jeong, H. K. Microporous
and Mesoporous Materials 2009, 122, 288-293.