Page 118 - Advances in bioenergy (2016)

compared with acidic zeolites. Specifically, high CO yields were achieved, whereas the
2
liquid products presented high yields of ketones, especially cyclopentanones and
52
cyclopentenones. The mechanisms of the CO production have been presented elsewhere. In
2
short, aldol condensation and ketonization reactions are prevalent, mainly leading to ketones
that are formed from aldehydes and acids condensation and CO as the main by-product. 53,54
2
Moreover, these condensation reactions are essentially carbon–carbon (C-C) coupling
reactions that can condensate smaller aldehyde and acid molecules toward the formation of
larger molecules with molecular weights closer to those of liquid transportation fuels. In this
case, the basic catalysis achieved with MgO presents a very interesting alternative to the
acidic route that has been studied so far.

Chen et al. performed catalytic pyrolysis of pinewood sawdust by microwave heating,
applying inorganic additives with different basicity. All of the eight additives altered yields
and composition of pyrolysis products. However, they caused a significant increase in the
yield of the solid product and a decrease in the yield of gases. Yields of liquid products were
not subjected to dramatic change. All of the eight additives made the gaseous products evolve
earlier. The gases produced from pyrolysis consist mainly of H , CH , CO, and CO , whereas
2
2
4
alkaline sodium compounds NaOH, Na CO , and Na SiO favored H formation in the
2
2
3
3
2
55
56
pyrolytic gases. Babich et al. also used Na CO to catalyze the pyrolysis of chlorella algae.
2 3
In the presence of Na CO , gas yield increased and bio-oil yield decreased, when compared
3
2
with noncatalytic pyrolysis at the same temperatures, but the pyrolysis oil from the catalytic
runs carried higher heating value and had lower acidity. 56
Recently, strongly basic zeolites have been synthesized from reaction of zeolites with ammonia
at elevated temperatures, providing unique activity and selectivity for base-catalyzed
57
reactions. Such basic zeolites, e.g., amine-substituted ZSM-5, are also suggested as
promising candidate catalysts for biomass conversion to hydrocarbons via catalytic
58
pyrolysis. 32,33 Peralta et al. investigated the deoxygenation of benzaldehyde on basic CsNaX
and NaX zeolites. They observed that the direct decarbonylation of benzaldehyde to benzene
could be readily promoted over highly basic catalyst containing Cs in excess. In parallel,
condensation of surface products also occurred, which decomposed and formed toluene. 58

REVIEW ON CATALYTIC BIOMASS PYROLYSIS

PROCESSES

Reactors for Catalytic Biomass Pyrolysis

As biomass pyrolysis reactions are endothermic, a heat carrier should be available to provide
heat to the reacting biomass particles. Different types of heating have been proposed, but the
most effective one is the direct heat transfer using a solid inert material (usually silica sand).
The type of the heat carrier dictates also the type of the reactor and in general the process
scheme of biomass pyrolysis. A review on the various process schemes for biomass pyrolysis