173
149], (2) “poisoning” due to S-containing compounds [30], and (3) reduction in
surface area and pore volume. In the third case, Ni/C, ZSM5, 5% Ru/C, and 5% Pt/C
used in upgrading biocrude oil at 350 °C for 10 h with H 2 caused such reduction
(93% surface area, 78% pore volume) because of the development of heavy products unable to adsorb on catalyst surface [115]. The primary issue, therefore, that
must be addressed through research of catalytic upgrading of fuel is catalytic stability. Stability dictates fuel quality which determines it compliance to ASTM D 6751.
9 Perspectives and Direction on the State of Research (SOR)
for Microalgae HTL
Hydrothermal technologies utilize subcritical or supercritical water to process any
form of biomass. It is divided into four regions, depending upon reaction temperature and pressure: carbonization, liquefaction, catalytic gasification, and hightemperature gasification. This chapter focused on hydrothermal liquefaction (HTL).
The state of the art of HTL technology began with terrestrial biomass [17, 18]. Since
the 1940s, the technology has been developed, but it was not until the oil crisis of
1973 that it has expanded to other alternative biomass feedstock which aimed at
reducing foreign petroleum oil dependence. Early challenges associated with HTL
technology were (1) the ability to inject the reactor with high concentration of biomass, (2) the optimum feed rate at which no mechanical problem exists, and (3) the
suitable reactor condition and catalyst type that allow the production of fuel with
consistent and reliable fuel-range hydrocarbons. Several companies have attempted
to develop and commercialize HTL technology. One of them is the “CatLiq Process”
from SCF Technologies, a Danish company. The process converts a continuous
input of organic waste to biocrude oil at subcritical conditions (350 °C and 25 MPa)
using homogeneous (K 2 CO 3 ) and heterogeneous (zirconia) catalysts [150].
Although HTL is a mature technology, no pilot- and demo-scale implementation
has succeeded over the past 50 years. A combination of technological and economic
issues prevented the achievement of a demonstration scale. An advantage for HTL
is its ability to process dilute, high-liquid feedstock, making it suitable for algae
input at 5–10 wt% concentration [7]. Yet, no large-scale HTL implementation using
microalgae as feedstock has been realized thus far. There is no single limiting factor,
but a multitude of challenges prevent the commercialization of microalgae
HTL. These are as follows:
1. Impurities and heterogeneities (e.g., particle size) in the feedstock solution
which can potentially precipitate, plug the reactor, and poison the catalyst’s
active sites.
2. Difficulty in maintaining the minimum microalgae concentration of about
5–10 wt%.
3. Low heat transfer efficiency and recovery efficiency.
4. Low biocrude oil yield.
Catalytic and Non-Catalytic Hydrothermal Liquefaction of Microalgae
149], (2) “poisoning” due to S-containing compounds [30], and (3) reduction in
surface area and pore volume. In the third case, Ni/C, ZSM5, 5% Ru/C, and 5% Pt/C
used in upgrading biocrude oil at 350 °C for 10 h with H 2 caused such reduction
(93% surface area, 78% pore volume) because of the development of heavy products unable to adsorb on catalyst surface [115]. The primary issue, therefore, that
must be addressed through research of catalytic upgrading of fuel is catalytic stability. Stability dictates fuel quality which determines it compliance to ASTM D 6751.
9 Perspectives and Direction on the State of Research (SOR)
for Microalgae HTL
Hydrothermal technologies utilize subcritical or supercritical water to process any
form of biomass. It is divided into four regions, depending upon reaction temperature and pressure: carbonization, liquefaction, catalytic gasification, and hightemperature gasification. This chapter focused on hydrothermal liquefaction (HTL).
The state of the art of HTL technology began with terrestrial biomass [17, 18]. Since
the 1940s, the technology has been developed, but it was not until the oil crisis of
1973 that it has expanded to other alternative biomass feedstock which aimed at
reducing foreign petroleum oil dependence. Early challenges associated with HTL
technology were (1) the ability to inject the reactor with high concentration of biomass, (2) the optimum feed rate at which no mechanical problem exists, and (3) the
suitable reactor condition and catalyst type that allow the production of fuel with
consistent and reliable fuel-range hydrocarbons. Several companies have attempted
to develop and commercialize HTL technology. One of them is the “CatLiq Process”
from SCF Technologies, a Danish company. The process converts a continuous
input of organic waste to biocrude oil at subcritical conditions (350 °C and 25 MPa)
using homogeneous (K 2 CO 3 ) and heterogeneous (zirconia) catalysts [150].
Although HTL is a mature technology, no pilot- and demo-scale implementation
has succeeded over the past 50 years. A combination of technological and economic
issues prevented the achievement of a demonstration scale. An advantage for HTL
is its ability to process dilute, high-liquid feedstock, making it suitable for algae
input at 5–10 wt% concentration [7]. Yet, no large-scale HTL implementation using
microalgae as feedstock has been realized thus far. There is no single limiting factor,
but a multitude of challenges prevent the commercialization of microalgae
HTL. These are as follows:
1. Impurities and heterogeneities (e.g., particle size) in the feedstock solution
which can potentially precipitate, plug the reactor, and poison the catalyst’s
active sites.
2. Difficulty in maintaining the minimum microalgae concentration of about
5–10 wt%.
3. Low heat transfer efficiency and recovery efficiency.
4. Low biocrude oil yield.
Catalytic and Non-Catalytic Hydrothermal Liquefaction of Microalgae