Page 308 - Advances in Eco-Fuels for a Sustainable Environment

Ecofuel conversion technology of inedible lipid feedstocks to renewable fuel 265

components are pigments, vitamins, and long chain fatty acids [114]. Derivatives of
carbohydrate compounds such as glucose, starch, cellulose, and polysaccharides can
generate valuable chemicals. Derivatives of cellulose resulted in coproducts in biodie-
sel production using wet in situ transesterification [80]. According to Im et al. [80],
ethyl levulinate (EL), ethyl formate (EF), and diethyl ether (DEE) were formed along
with biodiesel using ethanol/chloroform as the solvent and sulfuric acid as the catalyst.
EL can be used as a flavoring agent and also can be used as an additive to improve
biodiesel’s low temperature properties. EF has been known as a fumigant in grain
and fruit stores while DEE addition in biodiesel can improve the fuel property and
reduce emissions [80]. The conversion pathway from cellulose into EL and EF is
hydrolysis of cellulose to glucose, dehydration of glucose to HMF, hydration of
HMF to levulinic acid (LA) and formic acid (FA), and esterification of LA and FA
to EL and EF [80, 115]. Moreover, DEE was formed because of dehydration of the
excess ethanol [80]. Usually, in situ transesterification is conducted under ambient
conditions; however, the operation temperature needed to be increased to produce
coproducts. EL, EF, and DEE cannot be produced at a temperature lower than
100°C. At 125°C, the yields of EF, EL, and DEE were 10.3%, 23.1%, and 52.1%,
respectively, in biomass with 65% moisture content. Coproduct formation is affected
also by the catalyst amount, excess alcohol, and moisture content. Water improves
HMF rehydration and cellulose hydrolysis but excessive water can hinder dehydration
and result in a low yield of EL and EF. Increasing the catalyst amount has a positive
effect on coproduct formation, particularly DEE and EL. Furthermore, excessive alco-
hol increases coproduct yield because alcohol helps the esterification of LA and FA.
However, the alcohol amount needs to be controlled carefully because acidity reduc-
tion due to the catalyst dissolving in alcohol can result in reducing the hydrolyzed
algal cell product and less esterification [80].
Pigments are the other valuable product from microalgae. In general, microalgae
contain pigments such as carotenoids, chlorophylls, and phycobiliproteins. Micro-
algae pigments have gained attention in the pharmaceutical, food, and cosmetics
industries [27]. Carotenoids are lipophilic compounds with a yellow, orange, or red
color. The major carotenoids in microalgae are astaxanthin, β-carotene, lutein, lyco-
pene, and canthaxanthin. Carotenoids have an important role in the photosynthesis of
microalgae. Lutein has a role in absorbing light and diminishing excess energy in the
photosynthetic metabolism while astaxanthin and canthaxanthin are involved in cell
protective mechanisms. Most minor components in the microalgae cell are species and
growth condition dependent. Nutrients, the environment, temperature, and light can
affect the accumulation of minor components of microalgae [116]. Carotenoid content
in microalgae is higher than from other sources. Lutein content in microalgae was
more than 4mg/g while astaxanthin and β-carotene could be more than 50mg/g under
stress cultivation conditions. Fucoxanthin content was 18.23mg/g, which is higher
than seaweed [117]. Carotenoids draw attention in the market due to their antioxidant
activities and health benefits. They can be used as agents for antiinflammatory, anti-
cancer, radiation protection, and cardiovascular health enhancement. Among caroten-
oids, astaxanthin is the strongest antioxidant [117]. Astaxanthin is 10 times more
potent as an antioxidant than β-carotene and 500 times than α-tocopherols [118].