247
use of phosphates, sulfates, and chlorides is suggested in place of these catalysts
[15]. Use of zeolite-based catalysts such as ZSM-5 and MCM-41 has an advantage
such that selective pyrolysis can be conducted to obtain bio-oil containing
hydrocarbons, much like the gasoline. However, the catalyst activity may decrease
as a result of coke formed on the catalyst surface [16]. The lignocellulose biomass,
along with catalyst and reaction condition, should be selected carefully to get the
desired product.
2.1.5 Catalytic Gasification
Gasification is the process of obtaining gaseous products such as H 2 and syngas
by thermochemical conversion of biomass in an oxygen-deficient environment.
The product syngas is further converted to hydrocarbon fuel through FischerTropsch synthesis. The gasification followed by Fischer-Tropsch is referred to as
indirect liquefaction of lignocellulosic biomass. Another route to make syngas is
partial oxidation of lignocellulosic biomass at elevated temperatures (800–900 °C).
Air is used as a source of oxygen; hence, separation of nitrogen becomes a problem in biomass gasification. The tar formed during gasification contains polyaromatic hydrocarbons, and its conversion to useful products requires multiple
processes. To avoid tar formation, steam gasification is preferred where water at
supercritical conditions is used to improve the solubility of biomass in water,
thereby reducing the mass transfer limitations. Under supercritical conditions
(673 K and 1 MPa), cellulose was converted to methane over Ru/TiO 2 catalyst,
and a 44% yield of methane was obtained [17]. The catalyst can deactivate due to
coke formation. Also, the tar formation can block and foul the downstream process equipment. The best way is to convert tar into syngas using a multifunctional
catalyst and remove bio- char by catalytic combustion. One of the risks associated
with biomass gasification is incomplete combustion leading to the emission of
toxic gases and particulate matter.
2.1.6 Integrated Processing
In integrated processing, two or more processes are combined together to produce
the desired product. For example, in hydroprocessing, hydrogenation follows the
hydrolysis, solvolysis, liquefaction, and pyrolysis. In the integrated approach, the
depolymerization is followed by an in-situ decomposition to yield commodity
chemicals and fuels. On decomposition, the oxygenated molecule is obtained,
which is further deoxygenated/hydrogenated to get new C-C bonds. The commonly
used catalysts for hydrogenation are Pt, Ru, and Pd and for hydrolysis are liquid
acids. When a multifunctional catalyst (Pt/γ-Al 2 O 3 ) is used, the process of
decomposition and hydrogenation occurs simultaneously. For example, a gasolinelike product is obtained (carbon yield, 57%; octane number, 96.5) when maple
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…
use of phosphates, sulfates, and chlorides is suggested in place of these catalysts
[15]. Use of zeolite-based catalysts such as ZSM-5 and MCM-41 has an advantage
such that selective pyrolysis can be conducted to obtain bio-oil containing
hydrocarbons, much like the gasoline. However, the catalyst activity may decrease
as a result of coke formed on the catalyst surface [16]. The lignocellulose biomass,
along with catalyst and reaction condition, should be selected carefully to get the
desired product.
2.1.5 Catalytic Gasification
Gasification is the process of obtaining gaseous products such as H 2 and syngas
by thermochemical conversion of biomass in an oxygen-deficient environment.
The product syngas is further converted to hydrocarbon fuel through FischerTropsch synthesis. The gasification followed by Fischer-Tropsch is referred to as
indirect liquefaction of lignocellulosic biomass. Another route to make syngas is
partial oxidation of lignocellulosic biomass at elevated temperatures (800–900 °C).
Air is used as a source of oxygen; hence, separation of nitrogen becomes a problem in biomass gasification. The tar formed during gasification contains polyaromatic hydrocarbons, and its conversion to useful products requires multiple
processes. To avoid tar formation, steam gasification is preferred where water at
supercritical conditions is used to improve the solubility of biomass in water,
thereby reducing the mass transfer limitations. Under supercritical conditions
(673 K and 1 MPa), cellulose was converted to methane over Ru/TiO 2 catalyst,
and a 44% yield of methane was obtained [17]. The catalyst can deactivate due to
coke formation. Also, the tar formation can block and foul the downstream process equipment. The best way is to convert tar into syngas using a multifunctional
catalyst and remove bio- char by catalytic combustion. One of the risks associated
with biomass gasification is incomplete combustion leading to the emission of
toxic gases and particulate matter.
2.1.6 Integrated Processing
In integrated processing, two or more processes are combined together to produce
the desired product. For example, in hydroprocessing, hydrogenation follows the
hydrolysis, solvolysis, liquefaction, and pyrolysis. In the integrated approach, the
depolymerization is followed by an in-situ decomposition to yield commodity
chemicals and fuels. On decomposition, the oxygenated molecule is obtained,
which is further deoxygenated/hydrogenated to get new C-C bonds. The commonly
used catalysts for hydrogenation are Pt, Ru, and Pd and for hydrolysis are liquid
acids. When a multifunctional catalyst (Pt/γ-Al 2 O 3 ) is used, the process of
decomposition and hydrogenation occurs simultaneously. For example, a gasolinelike product is obtained (carbon yield, 57%; octane number, 96.5) when maple
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…