(587a) Catalytic Pyrolysis of Cellulose to Bio-Oil Over Zn/ZSM-5 Catalysts

Catalytic pyrolysis of cellulose
to bio-oil over Zn/ZSM-5 catalysts

             
Haian Xia*, Yuejie Ge, Ranran Xu, Xiucong Wang,Songlin
Zuo

         Jiangsu
Key Lab of Biomass-Based Green Fuels and Chemicals,

        
Nanjing 210037, China

College of Chemical
Engineering, Nanjing Forestry University,

        
Nanjing 210037, China

^* Corresponding author
at: College of Chemical Engineering, Nanjing Forestry

University, Nanjing 210037,
China. Tel.: +86-25-85427635; fax: +86-25-85418873.

E-mail address: haxia@dicp.ac.cn
(Haian Xia, Assistant Professor, PhD).

Abstract

With the increasing
concern on energy shortage and environmental problems, the highly-effective
conversion of renewable biomass resources, such as woody biomass, will play an
important role in the future[1]. Cellulose, a bioploymer which is a bulk
component of woody-biomass, is sustainable raw material in nature. The bio-oil
obtained from fast pyrolysis of biomass has some shortages such as high acid
value, low thermal stability, high oxygen content,  etc., and these
drawbacks limit  its large-scale application. Catalytic pyrolysis of
biomass is an effective thermal conversion method which can improve the thermal
stability of bio-oil by reducing its oxygen content that mainly affect the
thermal value and stability[2-4].  It has been reported that zeolite
catalysts could effectively improve the thermal stability of bio-oil by decreasing its oxygen
content through dehydration, aromatization, decarboxylation, and decarbonylation during
the pyrolysis reaction [5, 6].
More interestingly, after incorporating some transition metal ions such as Ga,
La, and Fe, zeolite catalysts exhibit some special catalytic properties
including olefin aromatization and oxidation-reduction that zeolite catalysts
do not have.

Herein, we use
Zn/ZSM-5 catalyst to catalytic pyrolyze cellulose into the bio-oil in a fix-bed reactor.
The influence of Lewis acid sites and Brönsted acid sites on the pyrolytic behavior of cellulose
was investigated by TG and in situ IR spectroscopy. Physicochemical techniques
including XRD, H₂-TPR, NH₃-TPR, UV-Visible diffuse
reflectance spectroscopy, and IR spectra of pyridine adsorption, were employed
to characterize the properties of Zn ions. The GC-MS, LC-MS, NMR, and FT-IR
spectroscopy were used to analyze the components of bio-oils.

Fig. 1 shows the IR spectra of
pyridine adsorption in the range of 1400-1600 cm^-1adsorbed on HZSM-5
and Zn/ZSM-5 with different Zn contents. Three samples give the band 1450 cm^-1due
to pyridine adsorbed on Lewis acid sites and the band at 1490 cm^-1
assigned to pyridine related with both Lewis and Brönsted acid sites [7]. For
HZSM-5, the band at 1450 cm^-1 could assigned to the Lewis acid
derived from little extra-framework Al species, while Zn/ZSM-5(1.3wt%Zn)
appears a new band at 1460 cm^-1, suggesting that the introduction of
Zn species could form new Lewis acid sites. However, for Zn/ZSM-5(2.7wt%Zn),
the band attributed to the Lewis acid sites shifts from 1450 cm^-1 to
1455 cm^-1 and its band intensity increased compared with HZSM-5. In
comparison with HZSM-5, the total band intensities associated with the Lewis
acid sites of Zn/ZSM-5 samples increase, indicating that the incorporation of
Zn species form new Lewis acid sites.

Fig. 1 IR spectra of
pyridine adsorbed on (a) HZSM-5(Si/Al=25), (b) Zn/ZSM-5(1.3 wt%Zn),  and
(c) Zn/ZSM-5(2.7 wt%Zn) at 200 °C.

Table 1 shows the quantitative analysis
of cellulose pyrolytic products over HZSM-5 and Zn/ZSM-5 catalysts. For
catalytic pyrolysis of cellulose over Zn/ZSM-5 catalysts, the main products are
anhydro-sugars such as LGA, LGO and DGP, as well as furan such as furfural and
2.5-dimethyl furan, carboxyl acid and aldehyde. More interestingly, it is found
that the catalytic pyrolysis of cellulose over Zn/ZSM-5(1.3 wt.%Zn) could form
butanoic acid, 2, 3-dimethylbutyl ester, while no-catalytic pryolysis and
catalytic pyrolysis over HZSM-5 did not produce the ester. This could be that
highly dispersed Zn species, i.e. Lewis acid sites evidenced from IR
spectra of pyridine adsorption, catalyzes the reaction. In addition, it is
found that the amounts of furfural and 2,5-dimethyl furan increase compared
with no-catalytic pyrolysis, especially for Zn/ZSM-5(2.7 wt.%Zn) producing
8.86% furfural. It has been reported that ZnCl₂ can catalytically
convert lignocellulosic biomass into furfural [8]. IR spectra of pyridine
adsorption demonstrates that new Lewis acid sites originated from Zn/ZSM-5,
which could be associated with mono-nuclear Zn ions or di-nuclear Zn species
located in the ion-exchange sites of ZSM-5, would play the same role as ZnCl₂
in the formation of furfural. In addition, the new Lewis acid sites could
promote the formation of esters while extra-framework Al species does not have
the function.

Table
1
Quantitative Analysis of Pyrolytic Products Formed from Catalytic Pyrolysis of
Cellulose over HZSM-5 and Zn/ZSM-5 Catalyst. The data in the bracket denotes
that the structural similarity of the component.

In summary, these
results showed that high dispersed Zn ions coordinated with framework Al
species remarkably affects the component content of bio-oil. The Brönsted acid
sites of HZSM-5 effectively lowered the pyrolysis temperature of cellulose and
increased the yields of bio-gas and bio-char.  The Lewis acid sites
originated from Zn ions could promote the formation of esters and furan
compounds.

References

[1]   R.
Luque, L. Herrero-Davila, J.M. Campelo, J.H. Clark, J.M. Hidalgo, D. Luna, J.M.
Marinas, A.A. Romero, Biofuels: a technological perspective, Energy Environ.
Sci., 2008, 1:542-64.

[2]   Q.
Lu, W.-M. Xiong, W.-Z. Li, Q.-X. Guo, X.-F. Zhu, Catalytic pyrolysis of
cellulose with sulfated metal oxides: A promising method for obtaining high
yield of light furan compounds, Bioresour. Technol., 2009, 100:4871-76.

[3]   S.
Yorgun, Y.E. Simsek, Catalytic pyrolysis of Miscanthus x giganteus over
activated alumina, Bioresour. Technol., 2008, 99:8095-100.

[4]   A.
Aho, N. Kumar, K. Eranen, T. Salmi, M. Hupa, D.Y. Murzin, Catalytic pyrolysis
of woody biomass in a fluidized bed reactor: Influence of the zeolite
structure, Fuel, 2008, 87:2493-501.

[5]   T.R.
Carlson, J. Jae, G.W. Huber, Mechanistic Insights from Isotopic Studies of
Glucose Conversion to Aromatics Over ZSM-5, ChemCatChem, 2009, 1:107-10.

[6]   T.R.
Carlson, G.A. Tompsett, W.C. Conner, G.W. Huber, Aromatic Production from
Catalytic Fast Pyrolysis of Biomass-Derived Feedstocks, Top. Catal., 2009,
52:241-52.

[7]   Q.Y.
Ying Li, Jie Yang, Can Li, Mesoporous aluminosilicates synthesized with single
molecular precursor (sec-BuO)₂AlOSi(OEt)₃ as aluminum
source, Microporous and Mesoporous Materials, 2006, 91:85-91.

[8]   P.
Rutkowski, Chemical composition of bio-oil produced by co-pyrolysis of
biopolymer/polypropylene mixtures with K₂CO₃ and ZnCl₂
addition, J. Anal. Appl. Pyrolysis, 95:38-47.