Biomedical Engineering Reference
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crude oil. The use of microalgal oil over lignocellulosic materials for pyrolysis has
advantages in the form of lower oxygen concentration and a higher heating value
for the former. The heating rate during the thermolysis of microalgae was found to
be an important parameter in the formation of the bioleum, where the slow ther-
molysis did not produce a liquid fuel that could be used as fuel. Maddi et al. (2011)
reported that the pyrolysis products of algal (primarily consisting of Lyngbya sp. and
Cladophora  sp.) and lignocellulosic biomass (corncobs, woodchips, and rice husk)
gave a similar yield of bio-oil. Other compounds that formed along with the bio-oil
were bio-char, gases, and ash. The calorific value of lignocellulosic bio-char (except
rice husk) was higher than that of algae-derived bio-char. This has been attributed to
the higher carbon content in the lignocellulosic biomass. The difference in composi-
tion of the bio-oil in the two feedstocks was the presence of nitrogenous compounds
in the algal bio-oils. This is assumed to have occurred through degradation of the
proteins present in the algae and may decrease its fuel value.
Chakraborty et al. (2012) synthesized bio-oil from Chlorella sorokiniana in a two-
step sequential hydrothermal liquefaction technique to produce bio-oil and valuable
co-products. The bio-oil consisted of 76% carbon, 12% hydrogen, 11% oxygen, 0.78%
nitrogen, and 0.16% sulfur. The low nitrogen content avoids the denitrogenation step
involved in the production of bio-oil. High oxygen content in the bio-oil necessi-
tates further processing viz. hydrogenation to improve its quality. The yield of the
bio-oil obtained by this method consisted of 24% of the dry weight, and optimum
polysaccharide extraction occurred at 160°C. The advantage of the two-step sequen-
tial hydrothermal liquefaction technique over the direct hydrothermal liquefaction
technique was a low formation of bio-char in the former (i.e., 7.6% in comparison
to 20.8% in the latter). Li et  al. (2012) synthesized bio-oil from the marine brown
microalgae, Sargassum patens C. Agardh, via hydrothermal liquefaction within a
modified reactor. A comparatively moderate yield of 32.1 ±  0.2  wt% bio-oil was
obtained in 15 min at 340°C. The feedstock used had a concentration of 15 g biomass
per 150 mL water. The bio-oil obtained had a heating value of 27.1 MJ kg −1 . The
major constituent of the bio-oil was carbon (64.64%), followed by oxygen (22.04%),
hydrogen (7.35%), nitrogen (2.45%), and sulfur (0.67%). The characterization of the
bio-oil by infrared spectroscopy showed a diverse group of compounds consisting of
fats, alkanes, alkenes, alcohols, ketones, aldehydes, carboxylic acids, phenol, esters,
ethers, aromatic compounds, nitrogenous compounds, and water. A high concentra-
tion of water may be the reason for the low calorific value of the bio-oil produced
from the microalgae. Pie et al. (2012) carried out the co-liquefaction of a Spirulina
and high-density polyethylene (HDPE) mixture in sub- and super-critical ethanol at
a reaction temperature of 340°C to obtain bio-oil. The bio-oil thus produced was
similar to that obtained from the pure HDPE derived bio-oil. The benefit of the co-
liquefaction process of Spirulina and HDPE was the synthesis of bio-oil that pos-
sessed a high calorific value (48.35 MJ kg −1 ) due to higher “carbon” and “hydrogen”
contents and a lower oxygen content. The samples analyzed by gas chromatograph-
mass spectroscopy (GC-MS) showed different compositions for bio-oil derived from
Spirulina , HDPE, and Spirulina -HDPE mixture. While the bio-oil derived from
Spirulina consisted of oxygen-containing compounds along with fatty acids, fatty
acid esters, and ketones as prominent compounds, the bio-oil derived from pure
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