(729e) Effects of Catalyst Properties on Biomass Conversion By Catalytic Fast Pyrolysis and Hydropyrolysis

Effects of Catalyst Properties on
Biomass Conversion by Catalytic Fast Pyrolysis and Hydropyrolysis

David P.
Gamliel and Julia A. Valla

Department
of Chemical & Biomolecular Engineering, University of Connecticut

191
Auditorium Road, Unit 3222, Storrs, CT 06269-3222, USA,

Phone:
+1-860-486 4602, e-mail: ioulia.valla@.uconn.edu

Biomass is
a clean and renewable carbon source, capable of providing sustainable carbon
for conversion to fuels and platform chemicals. Catalytic fast pyrolysis (CFP)
of biomass is the thermochemical conversion of biomass to liquid bio-oil, gas
and char under inert atmosphere at intermediate temperatures and high heating
rate. Recently, catalytic pyrolysis of biomass under a hydrogen atmosphere at
elevated pressure, termed hydropyrolysis, has been studied as an effective
method for production of deoxygenated high-value bio-oil with plentiful
aromatic and aliphatic hydrocarbons [1]. The objective of this work is to
determine how catalyst properties correlate to CFP and hydropyrolysis product
yields, and propose the ideal catalyst for the production of value-added products
from biomass resources. 

A wide
variety of catalysts were prepared and characterized for this study, such that
the effects of transition metal choice, metal loading, support type and support
acidity could be determined. Each catalyst was completely characterized using a
variety of techniques to find the surface area, morphology, pore structure,
metal oxidation state and crystal structure. Pd, Ru and Ni were chosen as
candidate metals due to their high activity for deoxygenation and hydrogenation
[2]. These metals were deposited via dry impregnation on a variety of
alumino-silicate supports including alumina, silica and ZSM-5 zeolite.
Furthermore, the Si/Al ratio of the ZSM-5 support was varied in order to
determine the effects of acidity on the product distribution.

CFP was
performed in a pyrolysis gas chromatograph (PyGC) unit, at 600 °C, under inert
conditions and at atmospheric pressure. Increasing ZSM-5 catalyst acidity was
found to increase yields of mono-aromatic hydrocarbons (MAHs), naphthalenes and
CO, and decrease char formation. However, once the zeolite Si/Al ratio was
lower than 25, coke formation reactions became dominant. It was found that
significant increase of catalyst acid site density resulted in enhanced
formation of coke and char precursors, such as poly-aromatic hydrocarbons
(PAHs). The results are in agreement with the theory that the primary mechanism
of acid catalyzed deoxygenation of pyrolysis vapors is decarbonylation and
aromatization [3]. Impregnation of 3% of each transition metal slightly favored
permanent gas, primarily in the form of CO, and decreased char yield. CFP with
non-zeolitic support alone was found to have high yields to oxygenates and
char.

Catalytic
hydropyrolysis of biomass was performed in the same unit in pure H¬2
atmosphere, at 600 °C and 450 psig pressure. When hydropyrolysis was performed
in the presence of ZSM-5 zeolite, a similar product distribution to CFP was
observed. When Ni was incorporated on the catalyst, high amounts of CH4 were
produced at the expense of solids, and alkanes were present in the liquid
product, as shown in Figure 1. As the zeolite acidity was increased
naphthalenes, PAHs and carbon oxide yields increased significantly at the
expense of CH4 and liquid alkanes. This demonstrates the competition between
acid-catalyzed decarbonylation, decarboxylation and aromatization and
metal-catalyzed methanation and hydrogenation. As with CFP, hydropyrolysis with
alumina or silica produced few liquids and high char yields. When Ni was
incorporated onto silica, alkanes yield totaled about 6 wt.% carbon, and CH4
yield totaled over 50 wt.% carbon. Alternatively, when Ni was incorporated on
the alumina support, lower CH4 yields and almost no alkanes were observed,
along with higher solid yields, proving that significant Lewis acidity and
large pore structure are detrimental for value-added product formation.

Catalyst
design is essential should the thermochemical conversion of biomass reach
large-scale implementation. Proper catalyst acidity aids in the formation of
MAH compounds, while highly acidic catalysts result in high coke production.
Incorporation of metals in the hydropyrolysis environment aids in the creation
of alkanes and CH4, at the expense of char. In particular, metal-catalyzed
methanation and hydrogenation reactions were found to compete with
acid-catalyzed deoxygenation when both were present. 

 Acknowledgement

The study
was funded by the National Science Foundation Award CBET-1236738 and the
University of Connecticut GK12 program.

References

[1]           V.K.
Venkatakrishnan, W.N. Delgass, F.H. Ribeiro, R. Agrawal, Green Chem. 17 (2015)
178–183.

[2]           T.
Prasomsri, M. Shetty, K. Murugappan, Y. Román-Leshkov, Energy Environ. Sci. 7
(2014) 2660.

[3]           D.P.
Gamliel, S. Du, G.M. Bollas, J.A. Valla, Bioresour. Technol. 191 (2015)
187–196.

 Figure
1.
Bio-oil
product distribution (left) and permanent gas product yields (right) for
hydropyrolysis with ZSM-5 zeolites of various acidity with and without Ni
incorporated.