Synthesis of Biodiesel/Bio-Oil from Microalgae - Biotechnological Applications of Microalgae - page 101

for biofuel production) and alkanes. A few algal species may also contain long-chain
hydrocarbons that are formed via the terpenoid pathway (Sivakumar et al., 2012).
Hence, the characterization of the algae is prerequisite to assessing the potential of
the microalgae extract to be converted to biofuel. Once the triglyceride content in
the microalgal species is determined, depending on their feasibility, the microalgae
extract can be utilized for its conversion to either bio-oil or biodiesel. This chapter
deals with the conversion of microalgal lipids into biodiesel or bio-oil, taking into
account the following aspects: esteriication/transesteriication, and chemical method.
8.2 ESTERIFICATION/TRANSESTERIFICATION
Batan et al. (2010) reported that the net energy ratio of biodiesel produced from
microalgae ( Nannochloropsis species) was found to be 0.93 MJ (MJ = megajoule)
of energy needed to produce 1 MJ of energy. The major advantage of using
microalgae-derived biodiesel is the reduction in CO 2 equivalent emissions amounting
to 75 g MJ −1 of energy produced. Liu et al. (2012) also report that biodiesel from
algae has a positive energy impact and estimate 1.4 MJ of energy production per
megajoule consumption of energy. In addition, there will be reduction of 0.19 kg
CO 2 -equivalents per kilometer of travel by transport.
Johnson and Wen (2009) adopted two methods for the production of biodiesel
from a heterotrophic microalga, Schizochytrium limacinum . The first method
adopted was direct transesterification of algal biomass using wet and dry biomass
separately. The second method consisted of two steps involving extraction of oil
from algae, followed by transesterification of wet and dry biomass. When the direct
transesterification method was used, the yield of biodiesel obtained was greater than
66% for wet as well as dry biomass. However, the fatty acid methyl ester (FAME)
content in the wet biomass was found to be very low (7.76%) in comparison with that
from dry biomass (63.47%). A 57% crude biodiesel yield was obtained through the
two-step method with a FAME content of 66.37%. Using the wet biomass, the FAME
content of biodiesel was 52.66%. The one-stage direct transesterification method
used various solvents (e.g., chloroform, hexane, and petroleum ether) to treat the algal
biomass. However, a comparatively higher content of FAME was observed when only
chloroform was used as the solvent. It has been found that direct transesterification
is preferable instead of the conventional steps involved in the production of biodiesel
from microalgae (i.e., extraction of oil from microalgae and transesterification of the
expelled oil) as the production cost of the fuel will be reduced. However, the drying
of algal biomass was found to be a prerequisite in order to obtain a high yield and
conversion of biodiesel when using direct transesterification of the microalgae.
To prevent oxidation of the unsaturated FAME in biodiesel, Johnson and Wen (2009)
added 100 ppm butylated hydroxytoluene to the biodiesel. However, the fuel did not
meet the European standards (EN 14103) specifications, which specify that the ester
content in biodiesel must be at least 96.5% (Sarin et al., 2009).
Vijayaraghavan and Hemanathan (2009) reported on the production of biodiesel
from freshwater algae. A high lipid content of 45 ± 4% was obtained from the micro-
algae and was used for the synthesis of biodiesel by transesterification using metha-
nol as a reactant and KOH as a catalyst. Upon transesterification, the fuel properties