Over the last few decades, the availability of inorganic membranes which can
withstand high temperatures and harsh chemical environments has resulted in a
wide range of opportunities for the application of membranes in chemical reactions.
In particular, the combination of membrane separation and catalytic reaction in a
single operating unit is an attractive way to increase conversions, to achieve better
yields and to make more efficient use of natural resources in many reactions.
In this work, a highly compact multifunctional Pd and Pd-Ag/alumina hollow fibre
membrane reactor (HFMR) have been developed and applied to catalytic chemical
reactions. The developed HFMR consists of a thin and defect free Pd-based
membrane coated onto the outer surface of an alumina hollow fibre substrate with
a unique asymmetric pore structure, i.e. a sponge-like outer layer and a finger-like
inner layer where catalyst is deposited.
In one study, a Pd-Ag layer was coated onto the outer surface of the substrate
followed by deposition of sub-micron sized Pt(0.5wt.%)/γ-alumina catalysts into the
finger-like voids of the substrates. This design achieved propane conversion as
high as 42 % at the initial stage of the reaction at 723 K and space-time yields
(STY) of the HFMR were approximately 60 times higher than that of a fixed bed
reactor (FBR). In order to further increase catalytic surface area in the reaction
zone, a sol-gel method was used to deposit Pt(1 wt.%)/SBA-15 catalysts into the
finger-like voids of a substrate to develop a Pd/alumina HFMR. Benefiting from this
novel design, the functionalized alumina hollow fibre substrates with surface
area/volume values of up to 1918.4 m2/m3 possess a specific surface area of about
31.8 m2/g for catalysts. It was observed that in comparison with a conventional
FBR, greater propene selectivity and propene yield was achieved by using the
HFMR for propane dehydrogenation. The generic advantages of the design of
these compact HFMR systems can be applied to further applications such as the
water-gas shift reaction, which was also carried out in this study.