Page 109 - Advances in bioenergy (2016)

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Catalytic Pyrolysis of Biomass for Transportation Fuels

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Angelos A. Lappas, Kostas G. Kalogiannis, Eleni F. Iliopoulou, Kostas S. Triantafyllidis
and Stylianos D. Stefanidis
Chemical Process and Energy Resources Institute, Center for Research and Technology
Hellas, Thermi-Thessaloniki, Greece

INTRODUCTION

Catalytic pyrolysis of biomass is a thermochemical conversion process where a heterogeneous
catalyst is used as a heat carrier in the pyrolysis reactor for the in situ upgrading of the quality
of the pyrolysis oil (bio-oil). Bio-oil upgrading refers to minimizing its well-known
undesirable properties [high water (H O) and oxygen content, high viscosity, corrosivity,
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instability, low heating value, etc.). Heterogeneous catalysis is widely used in the
petrochemical industry for the conversion of heavy oil fractions into lighter fuels and
chemicals. This concept is transferred to the biomass pyrolysis process where, ideally, the
heavy oxygenated volatiles from the decomposition of biomass are deoxygenated and
converted to lighter fuels and chemicals by coming in contact with a suitable catalyst. 1
Ultimately, the goal of the process is to produce a liquid with improved properties that could
be either used directly as a liquid fuel or as a feedstock (or co-feedstock) in modern refineries,
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much like crude oil. The downstream upgrading of the conventional (thermal) bio-oil has been
extensively studied in the literature. However, it was proved to be a very complicated issue,
creating many operating problems.

On the contrary, use of a catalytic bio-oil is believed to overcome most of these problems. An
ideal catalyst for the biomass pyrolysis process should produce high quality and yield of bio-
oil with low amounts of oxygen and H O, minimize the undesirable compounds present in the
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bio-oil, and exhibit both resistance to deactivation and thermal stability. The decrease of
oxygenated, bio-oil component species can increase bio-oil's heating value and result in a
product with improved physical and chemical properties. Oxygen is removed from the
pyrolysis vapors in the form of CO, CO , and H O. The removal of oxygen in the form of CO 2
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is more preferable than as CO because only one carbon atom is required for the removal of
two oxygen atoms, whereas in the case of CO formation, one carbon atom is required for each
oxygen atom that is removed. Oxygen removal by CO or CO is in turn more preferable than
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H O formation in order for the hydrogen to be preserved for the hydrocarbon-forming
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reactions. Oxygen removal as CO would effectively enhance the H–C ratio and thus lead to
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reduced coke deposition. Improving the quality of bio-oil using heterogeneous catalysis has
received extreme attention from several research groups. The challenges in developing this
technology involve the processing of lignocellulosic materials and the