The catalytic conversion of oleic
acid to aromatics (benzene, toluene,
and xylenes, BTX) over a granular H-ZSM-5/Al2O3 catalyst (ϕ 1.2–1.8 mm, 10 g loading) was investigated
in a continuous bench-scale fixed-bed reactor (10 g oleic acid h–1). A peak carbon yield of aromatics of 27.4% was obtained
at a catalyst bed temperature of 550 °C and atmospheric pressure.
BTX was the major aromatics formed (peak carbon yield was 22.7%),
and a total BTX production of 1000 mg g–1 catalyst
was achieved within a catalyst lifetime of 6.5 h for the fresh catalyst.
The catalyst was deactivated due to severe coke deposition (ca. 22.1 wt % on the catalyst). The used catalyst was reactivated
by an ex situ oxidative regeneration at 680 °C
in air for 12 h. The regenerated catalyst was subsequently recycled,
and in total, 7 cycles of reaction-regeneration were performed. A
gradual decrease in the peak carbon yield of BTX was observed with
reaction-regeneration cycles (e.g., to 16.3% for
the catalyst regenerated for 6 times). However, the catalyst lifetime
was remarkably prolonged (e.g., >24 h), leading
to
a significantly enhanced total BTX production (e.g., 3000 mg g–1 catalyst in 24 h). The fresh, used,
and regenerated catalysts were characterized by N2 and
Ar physisorption, XRD, HR-TEM-EDX, 27Al, and 29Si MAS ssNMR, NH3-TPD, TGA, and CHN elemental analysis.
Negligible changes in textural properties, crystalline structure,
and framework occurred after one reaction-regeneration cycle, except
for a slight decrease in acidity. However, dealumination of the H-ZSM-5
framework was observed after 7 cycles of reaction-regeneration, leading
to a decrease in microporosity, crystallinity, and acidity. Apparently,
these changes are not detrimental for catalyst activity, and actually,
the lifetime of the catalyst increases, rationalized by considering
that coke formation rates are retarded when the acidity is reduced.
