(58b) Selective Production of Aromatics By Catalytic Fast Pyrolysis of Furan with in-Situ Dehydrogenation of Propane

text-align:center;line-height:normal"> font-family:" arial>Selective Production of Aromatics by
Catalytic Fast Pyrolysis of Furan with in-situ Dehydrogenation of Propane

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text-align:center;line-height:normal">Xiaoduo
Qi and Wei Fan

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text-align:center;line-height:normal"> font-family:" times new roman> Department of Chemical Engineering,
University of Massachusetts Amherst, 686 N Pleasant Street, Amherst, 01002

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text-indent:.5in;line-height:normal"> " times new roman>Due to diminishing fossil fuel reserves and
increasing environmental concerns, lignocellulosic biomass has attracted
significant attention as an alternative carbon source for the production of
fuels and chemicals. Catalytic fast pyrolysis (CFP), which directly converts
biomass over solid catalysts in one integrated reactor, is a promising
technique for the production of renewable fuels and chemicals. In this process,
lignocellulosic biomass is converted into pyrolysis gas at an intermediate
temperature. The produced pyrolysis gas then diffuses within the micropores of
zeolite catalysts where it undergoes various reactions to form final products.
One of the major challenges of the current CFP technique is the low yields to aromatic
products, especially to benzene, toluene, and xylenes (BTX). In addition to
developing new catalysts, higher aromatic yield can be achieved by altering the
chemistry involved in CFP. Previous studies have shown that propylene
co-feeding on CFP of furan over ZSM-5 catalyst can increase in the aromatic
yields and lead to higher selectivity to toluene¹.
The enhancement with the co-feeding of propylene might be attributed to the
higher H/C ratio in the feed and the Diels-Alder cycloaddition between furan
and propylene. While the co-feeding of propylene showed promising results, an
inevitable drawback of this method is the use of light alkene, which is also a high-demand
commodity chemical for producing polymers. Hence, it is desired to use alkane
as the co-feeding source and integrate the dehydrogenation of alkane with CFP
process. Recently, shale gas has become an increasingly important source of
natural gas. Great opportunities have appeared for using shale gas as the
co-feeding chemical to produce renewable chemicals from biomass. While shale
gas is mostly made up of methane (~90%) and ethane (~10%), the composition of
propane can be as high as 5%, which guarantees propane availability considering
the total reserve of shale gas³.

In this
presentation, CFP of furan was studied with the co-feeding of propane over a
bifunctional catalyst consisting ZSM-5 and CrO_x/Al₂O₃
in order to combine the dehydrogenation of propane and CFP of furan in
the presence of in-situ generated propylene. With 15 v% propane co-feeding, a
slight increase in aromatic yield was observed over ZSM-5 catalyst. These
enhancements were further improved by using mixed catalysts consisting CrO_x/Al₂O₃
and ZSM-5 with different weight ratios. Over the best mixed catalyst with CrO_x/Al₂O₃
to ZSM-5 weight ratio of 2, a nearly 2-fold increase in the aromatic yield was
obtained. The toluene selectivity was also increased from 37 % to 50 %. The
increase in aromatic yield is directly dependent on the propane to total flow
volume ratio. Moreover, the coke formation within ZSM-5 was also reduced,
leading to a slower catalyst deactivation. From mechanistic studies, a two-step
cascade reaction pathway was observed over the bifunctional mixed catalysts. It
was proposed that propane first dehydrogenate to propylene on CrO_x/Al₂O₃.
The propylene then reacts with furan within ZSM-5 catalyst to selectively form
aromatics. This work demonstrates a simple and economical strategy to further
improve the CFP technique⁴.

text-align:justify;text-justify:inter-ideograph">1.            Cheng, Y. T.; Jae, J.; Shi, J.; Fan, W.; Huber, G. W., Production of Renewable Aromatic Compounds
by Catalytic Fast Pyrolysis of Lignocellulosic Biomass with Bifunctional Ga/ZSM-5
Catalysts. Angew Chem Int Ed 2012, 51, 1387-1390.

text-align:justify;text-justify:inter-ideograph">2.            Cheng, Y.-T.;
Huber, G. W., Production of targeted aromatics by using Diels-Alder classes of
reactions with furans and olefins over ZSM-5. Green Chem 2012, 14,
3114-3125.

text-align:justify;text-justify:inter-ideograph">3.            Bulba, K. A.;
Krouskop, P. E., Compositional variety complicates processing plans for US
shale gas. Oil Gas J  2009, 107 (10), 50-55.

4.            Qi,
X.; Fan, W., Selective Production of Aromatics by Catalytic Fast Pyrolysis of
Furan with In Situ Dehydrogenation of Propane. Acs Catal 2019, 9,
2626-2632.